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LTC-21 manual

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1. Table of Contents Warning Sts aS ads naa io ab o EERE is Es Ad e e Stas a e lo O o E iv Definition of international symbols for warnings and DEZA a DERE PE ie oh ed gs ed ai ee ge ee ae ed vV La TRAE KOOUCE DON 64 6 4 Sie He SRS HE MEER DE SSR a ee eS 1 Pg the POG TE EOS bi on tee Sea ap eben A o eas 1 EAs OPEL Lc ELLOS a A A 4 1 2 1 Input Channel Specifications 4 Zils QUEPUE Speci tea tloOnS mia ada 5 Dalia ACCURACY SpeciFlicatioOnSes ida a 8 2 3 Relay and Alarm Outputs 9 Relay OUEPUESIS ta a act wees da 9 Audible Alarm soc vive ducati Oy 9 Tilda do Remote INTErEac sS 200 eee S86 65 rerin iseks 9 TEBE 43 S Enter Ta CCiire hohe Se aS oe ae he Se 9 RS 232 Interface san gee eee bane ete ee beads 9 aL don Mechanical Form Factors nois e eese oo te Tan 9 lei Ze Os POWE see art 8 eed el oe A eS Seat aed Sy 10 LT BAVEEFORMEN EAL erena argh is alee ew he ee dll 2w Asta MAC ia 13 2 1 Unpacking And Inspectli0ON ooooooooooooooooo 13 Lio ROS Paner avoid ee eds ae ee ede T3 23r Power Regu uirenenbS e a a da ud nee 14 AS FUSE 64 dade NS LS Zaar Ay Grounding And Shielding ts essa dla ad dad TS Zete Heater CONNECE VO Ned ne ras wid Sweeter kilo Be 15 Ze Vie Heater WITI sie io se oS wae eee OE wa aS we Lo Zu Fete Heater Selection eres la goes 16 204 3 Analog Output Connection 24 28 iteris 17 Lada Sensor CONNECELOM sord a oe HS Bee are SS ee Be Se we SS 17 2 6 Relay CONNECCION
2. Display Update Rate Display Configuration Setup Screen Configure Datalog Display Datalog Sensor Configuration PID Mode Table Mode Output Configuration Auto PID Mode Ramp Alarm amp Relay Setup Misc Menu Remote I O Configuration Sensor Calibration Table Figure 4 Menu Tree NEOCERA Instrument and Systems Group Page 21 Model LTC 21 Cryogenic Temperature Controller Page 22 NEOCERA Instrument and Systems Group Chapter 4 Initial Power Up 4 Initial Power Up Sequence And Display When the LTC 21 is first powered up it goes through a series of internal self tests then performs an internal ADC calibration This is indicated by the display of ADC Cal A D Converter Calibration in place of the measured temperature Sensor 1 Sensor 2 ADC Cal ADC Cal Heater Off Push ENTER to Change SET POINT Figure 5 ADC Calibration Screen After the calibration is complete the LTC 21 enters the MONITOR mode and ADC Cal is replaced by the measured sensor value This process requires approximately five seconds First Time Operation As shipped from the factory the LTC 21 is software configured to read and display the resistance in Ohms of a sensor connected to SENSOR 1 input The interface is configured as an IEEE 488 port with ad
3. SSTYPE Format SSTYPE lt 1 Sensor 1 or 2 Sensor 2 gt Controller lt Standard Sensor Type 1 15 or User Sensor Type 16 to 25 gt LTC 21 Response As a precaution the LTC will switch from CONTROL or MONITOR mode to OFF mode Description Assigns the Sensor channel with a specific sensor type o 3 SANN po 4 IsTar o 5 PTOS Cal Res 100 uV Cal Res 32 uV Cal Res 10 uV C o a USER TABLES HERE Table 19 IEEE Sensor Type Selection For a user defined table the index into the user table is added to 10 User table 1 is 1 10 and user table 5 is 15 etc Related Commands QSTYPE SCALT QCALT QTBL Page 88 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller STUNE Format STUNE lt 0 Manual 1 Autotune gt LTC 21 Response None Description Changes the instrument tune state to MANUAL or AUTOTUNE state If AUTOTUNE is selected and when the instrument is in CONTROL mode the instrument will use the existing PID settings to regulate the system and Autotune the system to obtain new PID settings This process of seeking a new PID setting is called TUNING While the system is in AUTOTUNE state the temperature controller will change the heater settings and measure the temperature response in order to determine the thermal characteristics of the system Once the new PID settings are obtained the temperature setting for the system will regulate using the new PID It
4. WARNING TO PREVENT SHOCK AND FIRE HAZARDS ALWAYS CONNECT THE POWER CORD TO A THREE CONDUCTOR GROUNDED RECEPTACLE Grounding and shielding of sensor and output lines are important considerations when using a low noise instrument such as the LTC 21 The sensor inputs the heater output and the analog output are all isolated from earth ground and are connected at one point to circuit ground inside the LTC 21 2 4 Heater Connection 2 4 1 Heater Wiring The Heater output is available on the rear panel at the labeled connector NEOCERA Instrument and Systems Group Page 15 Model LTC 21 Cryogenic Temperature Controller Connect your heater leads to the mating connector supplied Care should be taken not to ground either heater lead If this is not possible ground the lead connected to pin 2 WARNING WITH PROPER VENTILATION THE LTC 21 IS DESIGNED TO OPERATE INDEFINITEL Y WITHOUT DAMAGE TO ITSELF IF ITS HEATER OUTPUT IS SHORT CIRCUITED HOWEVER CARE SHOULD BE TAKEN TO AVOID THIS CONDITION SINCE THE 50 WATT OUTPUT COULD DAMAGE OTHER COMPONENTS OR RESULT IN A FIRE HAZARD The wire size required in your cryostat depends on the maximum power that will be required If 50 Watt power will be required use 24 gauge or heavier stranded copper wires Connect the heater to the positive and negative outputs The earth ground should only be used for shielding Best performance will be achieved if the heater wires are run
5. b Locate the ac input module on the rear panel The ac power configuration can be seen in a small window in the fuse drawer c Push on the small locking tab on the fuse drawer and remove the fuse drawer d To change the ac input configuration remove the switch block from the rear of the fuse drawer Rotate the switch block until the desired ac input appears in the window of the fuse drawer e Install the fuse drawer into the ac input module and connect the ac power cord The LTC 21 will operate properly from either 50 or 60Hz ac power Page 14 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller WARNING Never attempt to operate the LTC 21 at a different input line voltage than is shown on the power input module on the rear panel Serious injury or equipment damage may result 2 3 1 Fuse The instrument fuse is located in the ac power entry module which is mounted on the rear panel of the instrument This module also contains a spare fuse The LTC 21 requires the following fuses depending on the line voltage used 100 120 Va 3 Amp normal blow 220 240 Vac 1 6 Amp time lag Table 2 ac Fusing WARNING Always replace the fuse with the correct value to prevent shock and fire hazards as well as damage to the LTC 21 2 3 2 Grounding And Shielding The LTC 21 is equipped with a three conductor power cord that connects the instrument chassis to earth ground
6. wait loop for setting up long commands j i j 1 if str 0 S Il str 0 amp amp str 4 2 printf Msg Sent s n str return receive_TC rec_string 100 printf Msg Sent s tMsg Received s n str amp rec_string return of putmsg end of test c Page 106 NEOCERA Instrument and Systems Group Appendix C Interface Connector Pinouts Appendix C Interface Connector Pinouts Relays Relay uses an AMP 8 pin receptacle The mating plug is an AMP 206434 1 Connector face view with pin assignments are shown below Relay Normally Common Normally Closed Open Table 26 Relay Connector Pin out Sensors Sensors use a LEMO 4 connector FGG 1B 304 CNAD52 When assembling this connector ensure that the cable shield is firmly connected to the connector metal shell Note also that a sensor and cable assembly is available from NEOCERA Instrument and Systems Group Connector face view with pin assignments are shown below NEOCERA Instrument and Systems Group Page 107 Model LTC 21 Cryogenic Temperature Controller Page 108 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller Signal Name Color Code Table 27 Sensor Connector Pin out Color codes shown are for a Belden 8723 type cable In all cases a shielded twisted pair cable should be used On the instrument end of the sensor cable the shield connection is made via the co
7. Request the number of user calibration tables Returns the number of User calibration tables created e g 2 means two user calibration tables in memory Related Commands SCALT QTBL QDLB Format QDLB lt Buffer number gt LTC 21 Response One character string of datalog consists of the time of day of datalog sensor data heater power If SDLC is set for Both it will show both channels data Description Read one datalog buffer at one time For multiple data buffer read send multiple data buffer commands Related Commands SDLI SDLC SDLS SDLM SDLT Page 92 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller QDLC Format QDLC LTC 21 Response Four ASCII character strings for datalog interval channel selection number of samples and acquisition mode one ASCII number for datalog trigger Description Datalog configuration The first string is an eleven characters datalog interval 1 Second 10 Seconds 1 Minute 5 Minutes 10 Minutes The second string is a four character datalog channel selection 1 Sensor 1 and Heater Power 2 Sensor 2 and Heater Power Both Sensor 1 and Sensor 2 Readings The third string is a five character number of samples for datalog buffer size 4 to 500 4 to 500 The fourth string is an eight character acquisition mode One Shot Cyclical The fifth number is the datalog trigger 0 stop datalog 1
8. e Platinum and RhFe RTDs of any resistance from about 12 K to 500 K Digital control The LTC 21 temperature controller is based on a fast 32 bit microprocessor that uses advanced digital signal processing techniques to implement a completely digital temperature control loop Accurate Use of high resolution Analog to Digital 20 bit converter on all input channels and Digital to Analog 16 bit converter on output channels ensures accuracy and smooth continuous control A high loop sample rate 16 Hz completely prevents instability due to temperature aliasing and allows the use of digital filters to further improve both display and control accuracy Performing all internal arithmetic computations in 32 bit IEEE compatible floating point format ensures that no accuracy is lost due to computational errors Sensor data is interpolated based on sensor calibration tables using a Cubic Spline algorithm NIST Traceable Calibration Factory instrument calibration performed to a NIST traceable standards NEOCERA Instrument and Systems Group Page 1 Model LTC 21 Cryogenic Temperature Controller Variable ac and de Sensor Excitation A wide range of de and ac sensor excitations are possible Diode sensors are biased with 10 Amp dc constant current excitation Linear sensors such as Platinum Pt and Rhodium Iron RhFe sensors can use ac or de with the same range of excitation ac constant voltage excitation may b
9. Model LTC 21 Cryogenic Temperature Controller CONTROL mode by pressing ENTER To enter the SETUP mode and display the INSTRUMENT SETUP SELECTION menu simply press the front panel SETUP button The SETUP mode indicator LED will turn on indicating that the LTC 21 is in the SETUP mode The LTC 21 will continue to regulate temperature if you enter the SETUP mode from the CONTROL mode It will terminate CONTROL only if a setting is changed which makes regulation impossible or which effects one of the operating parameters of the control loop For example you may enter the SETUP mode to change display units without affecting temperature regulation However 1f you change the type of sensor assigned to the input the LTC 21 will turn off the heater The CONTROL mode indicator LED will turn off indicating that you are no longer regulating temperature 5 3 2 Instrument Setup Selection Menu The INSTRUMENT SETUP SELECTION menu is displayed whenever the SETUP button is depressed INSTRUMENT SETUP SELECTION Display Sensors Outputs Misc Press ENTER to select function Press EXIT to return Figure 9 Setup Screen The four selections shown on this menu DISPLAY SENSORS OUTPUTS MISC call up submenus which can be used to change any of the LTC 21 operating parameters Use the right and left cursor keys to highlight the desired choice indicated by a flashing selection on the display and press ENTER When first configuring the LTC 21 it is a g
10. Pwr Limit 35 Gain 1 00 Offset 325 00 Figure 15 PID Mode Screen To change these values move the cursor to the desired field enter the new value from the numeric keypad and press ENTER Exit from this menu using the EXIT key or return directly to the CONTROL mode using the CONTROL key Note that you can change any of the PID coefficients without interrupting temperature regulation Of course if the new PID coefficients entered are not appropriate temperature regulation may quickly deteriorate The P term is an arbitrary gain factor which can be chosen to have any value between 0 1 and 1000 Typical systems will operate with a gain of 10 If the gain is too high the system will oscillate If it is too low it will be slow to respond The I term is given in seconds its reciprocal is the angular frequency at which the integral term has gain equal to the P term The range of allowed values is 0 1 to 10 000 seconds The LTC 21 also recognizes I 0 as a special case which turns the integrator term off completely The purpose of the I term is to provide extremely high gain near dc This allows the temperature controller to regulate at the set point with negligible input error signal Note that to minimize the effect of the integrator the I term should be set to a large value or 0 to completely turn it off A typical cryogenic system will work with I 20 The D term is also given in seconds and its reciprocal is the angular frequenc
11. The LTC 21 provides five PID tables each has 10 PID entries When the Table mode is selected the LTC 21 will use the current temperature setting and obtain the interpolated PID from the selected table for the specified temperature set points The Table mode allows the operator to select the PID coefficients from ten sets of values stored in each of the PID Tables This eliminates the need to remember or reenter coefficient sets that have been stored This is particularly convenient for use with systems that require very different coefficients at different temperatures Once good coefficients have been determined for each temperature range these can be stored in the table The values can then be easily recalled from the table when returning to this temperature range Page 36 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller If the Table mode is selected the screen will change to display the table coefficients currently in use PID Table 4 Set Pt I 350 000K 20 200 000K 25 100 000K 15 20 000K 15 11 000K 60 10 Press EXIT to return Figure 16 Table Mode Screen Example If the current experiment temperature is 150K the PID setting will be 80 20 8 0 00 For 150K the interpolation process takes the PID amp POs from 200K and 100K entries and yield the interpolated 80 20 8 0 00 The heater range will be the 5W range This will change the MAX PWR setting in the output screen if TABLE mode
12. start datalog Related Commands SDLI SDLC SDLS SDLM SDLT NEOCERA Instrument and Systems Group Page 93 Model LTC 21 Cryogenic Temperature Controller QDUR Format QDUR LTC 21 Response An ASCII string of numbers 0 5 for 0 5 seconds 1 2 4 8 16 for respective seconds Description Queries the Input Filter Time Constant or Display Update Rate Related Commands SDUR QHEAT Format QHEAT LTC 21 Response An ASCII string of no more than 5 characters signifying the percentage of heater full scale O indicates the heater is turned off at the time of query and 100 0 indicates full scale Description Determines the HEATER percent of full scale power The Heater Power setting is programmed by the SHMXPWR command While the instrument is in Monitor mode the heater output is turned off Related Commands SHCONT SOCONT SHMXPWR SCONT QISTATE Format QISTATE LTC 21 Response One character byte containing instrument state Description Queries the instrument state A single character which is interpreted as follows 0 Temperature Control is in MONITOR mode 1 Controller is in CONTROL mode 2 Autotune is in progress 3 Controller is in OFF mode No temperature display Related Commands SMON SCONT STUNE Page 94 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller QLLOCK Format QLLOCK LTC 21 Response One byte ASCII number of 0 or 1 0 is no lockout 1
13. 0 25 from 1KQ to 10KQ and 1 between 10KQ and 30KQ The accuracy of diode sensor measurements is 0 05 The accuracy of sensors using the variable ac constant voltage biasing is given in the following table 1 5000 to MO en A 10 500K 10 oeme A 10 150K i o eom Table 1 Sensor Accuracy vs Sensor Excitation All accuracy specifications are valid over the rated environmental temperature range Range of Temperature Measurements The instrument will measure and display temperatures in the range of OK to 800K The actual temperature range for measurement is of course dependent on the type of sensor used Temperature Resolution The temperature resolution of the LTC 21 is 1 part in 512000 Page 8 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller Maximum Frequency of Temperature Variation The maximum frequency component of temperature variation that the LTC 21 can process is 5Hz 1 2 3 Relay and Alarm Outputs Relay Outputs The LTC 21 has two relay outputs one for each input channel Both normally open and normally closed contacts are available on the rear panel The user may set the relays to open or close under specified conditions such as over or under temperature conditions Contacts are rated at 0 5A 30V ss or 60Vpc Audible Alarm The LTC 21 has an audible alarm that may be configured by the user to sound on over and under temperature conditions on either input chan
14. 1KQ and 1000 resistors should be read on the LTC 21 when selected Note that the instrument must perform an autorange function in this mode so it will require several seconds to stabilize to the correct reading To test the 1mV input range 1 e for Carbon Glass Resistors go to the Sensor Configuration menu and select the CAL resistor sensor Page 70 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller 8 Press the Monitor key Values of the 100KQ 10KQ 1KQ and 1000 resistors should be read on the LTC 21 when selected Note that the instrument must perform an autorange function in this mode so it will require several seconds to stabilize to the correct reading This completes instrument calibration check The LTC 21 Calibration fixture is comprised of a set of four precision resistors which can be switched in order to select various sensor current and voltages A schematic of this fixture 1s shown below Note All resistors shown are 0 005 LTC 20 Sensor Cable V black I white Vv red T green Volt Meter Output LTC 20 Sensor Calibration Fixture Figure 28 LTC 21 Sensor Calibration Fixture 10 6 Calibration Procedure Sensor Channels Refer to the Neocera Temperature Controller Calibration Guide for more detailed information on sensor calibration Available from Neocera Please call for more information NEOCERA Instrument and Systems Group Page
15. 2 Tuning Temperature Deviation LTC 21 Response For system response one ASCII character S Slow N Normal F Fast For Tuning Temperature Deviation Setting a number representing the percentage of deviation 0 50 is 50 Description Queries the Autotune parameter settings Related Commands STUNEP STUNE QUERREG Format QUERREG lt 1 Command Error Register 2 Execution Error Register gt LTC 21 Response One byte reply of the register content in ASCII decimal Description Queries the User Error registers This command will also clears the register content COLL LN Not Not Not Not Not Used Bad Parameter Unterminated Unknown Used Used Used Used Command Command Table 24 QUERREG Command Error Register Bit Definition mo poppe CA PT Not Not Not Transmit Buffer Parity Unknown GPIB Receive Buffer Transmit Buffer Used Used Used Overflow Error Error Overflow Under flow Table 25 QUERREG Execution Error Register Bit Definition Related Commands SUERREG QUNIT Format QSUNIT lt 1 Sensor 1 2 Sensor 2 gt LTC 21 Response Single character reply of K or C or F or N or V or O Page 100 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller Description Query the display unit for channel 1 or 2 Related Commands SUNIT NEOCERA Instrument and Systems Group Page 101 Appendix B IEEE 488 2 Example Programs Appendix B IEEE 488 2 Example Programs The
16. 2 9 Changing the SET POINT 6 5 cements sa sera 26 5 2 3 Relays and Alarms in Monitor Mode 27 5 2 3 1 Control Mode Regulating Temperature With The LTC 21 27 5 23 Setup Mode Configuring The LTC 2L its fn nets 28 5 3 1 Introduction To The Setup Mode 28 5 3 2 Instrument Setup Selection Menu 29 5 343 Display Configuration Menu vesrccocrcsses 30 Did SEE Display Units MENU ies sey bo a aches Seeds 30 The Effects of Changing Display Units 30 Input Filter Time Constant Menu 31 iS DataLlod erica daa lia 32 5 3 6 Sensor Configuration Menu 32 Sros Ta OUR DUE Conta guration MENU alada nerona hs 33 Introduction to Configuring the Outputs 33 SENSOR Menu Eleld vistes hE eee 34 MODE Menu Fee Le cisco ce sods e Sie wis We ee Be wes ws 34 MAX PWR Men Freld os ie ale peel a LS Spel oe AE 39 Ramp Menu Field ss a a 39 Ss 1 82 MISE Menu iii E Eaa E ad as 40 5 8 86 Alarm Relay Set FPOintS serrr ask nerti 40 Sess Remte IZO CONE sar ea eke ta e 41 Dias Sensor CAL Tables ia 42 5 3 11 Entering a New Sensor Table 42 5 3 12 Viewing and Editing a Sensor Table 46 prosba Deleting a User Tables nadaa Ss 47 5 3 14 The Instrument Calibration Menu 48 5 3 15 Input Output Tests Menu 48 G PID Theory Ang Tuning TIPS A aL Cals The ETESZ2LAPLD MODE isso 9 3 S906 a a a a 54 biae Selecting COCEELMOTEN ES yiri evk Es lia EEEE
17. 2 Serial MC68332 gt Relays A Front Panel lt gt lt gt RAM 32k x 16 EPROM Non Volitile gt lt gt 64k x 16 RAM 32k x 8 Figure 27 LTC 21 Functional Block Diagram The entire instrument is under control of a very fast embedded microcomputer Analog front ends and outputs are kept to the simplified form possible This allows easy re configuration of the instrument by changing only software that is stored in EPROM Further the minimization of analog circuitry reduces noise and drift problems One primary feature of the MC68332 microprocessor is it s high speed bi directional serial port This port transfers data at One Megabit per second and is used as the primary interface to the Heater DACs the Analog Output Channel DAC and both DACs and ADCs on the NEOCERA Instrument and Systems Group Page 63 Model LTC 21 Cryogenic Temperature Controller sensor channels Using this scheme optical coupling has been provided between all analog devices and the digital circuitry using only a minimum number of coupler devices The Micro Computer Block The central processor unit is a Motorola MC68332 embedded micro controller chip This processor has the following major features e 32 bit instruction execution e 17Mhz clock e Low power CMOS construction e Software compatible with the MC68020 family e Two serial I O ports e Built in failure detection The RAM Memory The controller has 64K by 16 bits of Random Ac
18. 51 6 3 Fine Tuning the Coefficients 22 sce se ee ira 52 G24 Pamp LIT 2 6 3 seal ot amp dos Sed oa cg eee Poe ds Se eet we seed 52 des USHAG AUBORUNGS 44 as tr eee A eh er a Oe a Ee 55 NEOCERA Instrument and Systems Group Page vii Model LTC 21 Cryogenic Temperature Controller Tide ENE CO QUE TON A Be E E ae Soe s 55 Tats AUTOTUNE BASES o A dak be Rad awe eben 55 Tass Advanced Usage Of sAUTOTUNE Mosa ad ta 57 8 Using Data HOG eros occ EER Eee ee eee 59 Oe dls AREF OO UCI TON dotnet Wiebe a Soe esa Seren 59 Gode DATA HOG EURCELO Na a Se Serb ier 59 By Zick DATA LOG SETUD sans do Sy Saeed ee he ey tee Spe 59 Sample Intervalo 2 eee 60 sensor Channel fre Lee dS ie e a dr E 60 Total Samples Channel field 60 Acg isition Mode 7 6 Ces S eave a daa 60 Current Tame 1610 2s cc de eee eee ee a See eee 61 8 3 DISPLAY DAL LALO rona a5 rentas ea 61 9 Model LIC 21 Pu unctional Descrip LON a ASE 63 921 BLOCK DIAL ou imc e a a a 63 Oi FOOSE Gate VOM rks nen arc nda bad id Se ted faja 65 10 Instrument Adjustments Self Test and Calibration PROCCOULES ida a a Se Es 67 101o Display Contrast AdqustmentinVi Dacia nad dota 67 102 Backdoor MOdes tomes beac nea eae Hee wae SEE ee A 67 10 2 1 Clearing Non Volatile RAM 67 10 2 2 Entering Instrument Recalibration Mode
19. 71 Model LTC 21 Cryogenic Temperature Controller Page 72 NEOCERA Instrument and Systems Group Appendix A Remote Interface Commands Appendix A Remote Interface Commands Remote interface commands are used for IEEE 488 GPIB or RS232 interface All commands are applicable for IEEE 488 Some are specific to IEEE 488 use These commands are broken down into 3 major types 1 GPIB common commands XXX These types of commands always have a as the first character and do not have a as the fifth character Not for use with RS232 2 Generic GPIB query commands XXX These types of commands always have as the first character and as the fifth character Not for use with RS232 3 LTC device dependent commands If the command is not a GPIB common or GPIB query command this function assumes it is an LTC command e g SETP QHEAT Some of the LTC commands have more than parameter The separator between the parameters is and the terminator is Spaces CR and LF characters will be stripped out by the parser You may use them when appropriate to make your source code more readable CAUTION There is NO separator between the command and its first parameter Reference Please refer to the IEEE Standard Codes Formats Protocols and Common Commands manual ANSVIEEE Std 488 2 1987 for the definition and intent of IEEE Common Commands and IEEE Common Queries NEOCERA Instrument and Systems Group Page 7
20. End asa Pde Seeded a Baie Sees Bs 85 SMON aci es a ia A A He SS 86 SN o ite ate ety cei oat e e o cos ata a ag he 86 ELIAS sy Oats ass Mahan Soda Sy aetna A A A aay Deb as 86 PLB TS Aaa ata aia 87 BND cate cde ct ices cat cae te cal Sel oe cats sak y os oats 87 ORUP dit weeds eee We be e A a Gad Gr ee ad Sr 87 TOD o Bet Sse ards Sate Gaels Sve tds Saou bares ed Seow tue even end ote 87 SOLD a E EE E A EEE a el 88 SLEUNE tri A RA A RA A cde ler 89 SLUNER a O a 89 SUBRRE Gate ie Sudesh ate Ad e ta artes 90 SUN tata a A A da a a 90 DPT iy re e Sieh SS fey 5 ev ates Souler S5 con 6 sev E SELBY Sey ote ote lt p 91 OAD D Re ais snaa as maaa a Seb il a a ia e a eee ds 91 DAR TB Tee edad a de da ERA 91 ODLB R Sd A DAA A 92 ODER a coeds sts a wo Gots wind Gave ia O a ws avs 93 DURAS A O A Re ERO ORO a ee eae ee Re eae 94 OURA TE y E A Mayan O a Hepes Nope Us 94 ESTATE a sh ey eid wre Se Sher eid eres a ane ee ah 94 OTT OCIS a Sait Sa Ss ote ot a Sy ta Ss Ss 20 se os A his 2 95 DOU TE A AS Ne e ada Nob la a aah Bot bl ae tc 95 LTDA A A shee Gad aye Gags aie ed 5g 96 O LEBNDX tata il ias A ce tai tg 96 DIRE A A Oe Sa oe A 96 DIABLO a todenier as eed 96 CORTE Li a yh RE ide A Riche A i A E 98 AAA 2s oe Sirens era ede 0 ess 0 ahve dish E E Oh eco even Sete et tos 98 OIDO sete cesar as oben or eter 99 OTOD T israel a 99 OTUNEP T e oss ec ii wai ecg Ei tt Bi ote Y 100 QUERRES a a a A enenenien epee a 100 GOUNIT a r
21. GPIB Address should be 15 n putmsg QADDR printf Local Lockout 0 No Lockout 1 Lockout n putmsg QLLOCK putmsg QHEAT putmsg QOUT 1 putmsg QOUT 2 Output Configuration putmsg QSAMP 1 putmsg QSAMP 2 putmsg QSTYPE 1 putmsg QSTYPE 2 putmsg QUNIT 1 putmsg QUNIT 2 putmsg QPID 1 putmsg QPID 2 putmsg QSETP 1 putmsg QSETP 2 putmsg QCALT putmsg QARTBL 0 putmsg QARTBL 1 0 Alarm 1 Relay putmsg QTBL 1 putmsg QTBL 2 putmsg QTBL 3 putmsg QTBL 24 putmsg QTBL 5 putmsg QTBL 6 putmsg QTBL 7 putmsg QTBL 8 putmsg QTBL29 printf nTry some set commands n putmsg SACONT3 putmsg QOUT 2 Set Analog Control to DEFAULT putmsg SARTBL1 0 0 111 11 11 SARTBL2 0 0 222 22 22 Alarm Tbl putmsg QARTBL 0 putmsg SCONT printf Instrument State 0 Monitor Control 2 AUTOTUNE n putmsg QISTATE putmsg SETP1 111 44 putmsg QSETP 1 putmsg SARTBL1 0 1 111 11 11 Alarm Tbl putmsg SARTBL2 0 1 222 22 22 Alarm Tbl putmsg QARTBL 0 putmsg SHMXPWR3 Heater Max Power is now 5w putmsg SOSEN1 1 SOSEN2 2 Output Sensor Heater 1 ANA 2 putmsg SHCONT4 Set HEATER Control to PID putmsg QOUT 1 putmsg QOUT 2 putmsg SOSEN1 1 SOSEN2 3 Output Sensor Heater 1 ANA NONE Page 104 NEOCERA Instrumen
22. P0 1 gt lt TPMAX index 0 to 4 gt lt Set Point 2 gt lt Set Point 10 gt lt P10 gt lt I10 gt lt D10 gt lt P0 10 gt LTC 21 Response None Description Sets the PID Table entries Set points in table must be in descending order or else the table will be rejected Not all entries have to be entered Enter to be the terminator Spaces and new line characters can be used before and after No TAB characters are allowed Related Commands SPTBNDX SACONT SHCONT QPTBNDX SPTBNDX Format SPTBNDX lt Heater 2 Analog gt lt PID Table Index 1 to 5 gt LTC 21 Response None Description Select one of the 5 PID tables for this output channel when utilizing TABLE mode This should be done before the output mode is set to the TABLE mode see SHCONT or SACONT commands If this is not set the last index which is 1 when system is initialized used from the front panel will be used Related Commands QPTBNDX SHCONT SACONT SRMP Format SRMP lt channel gt lt armed gt lt setpoint gt lt degrees minute gt LTC 21 Response None Description Sets ramp parameters Example SRMP1 1 300 0 10 This sets channel 1 to ramp to 300 0K at 10K minute Related Commands QRMP STOD Format STOD lt Hour gt LTC 21 Response None NEOCERA Instrument and Systems Group Page 87 Model LTC 21 Cryogenic Temperature Description Sets the Datalog current Time entry Related Commands QTOD
23. Standard 488 1978 9 IEEE Standard Codes 73 IEEE 488 2 9 13 18 19 23 41 42 65 INC 20 30 31 32 34 42 44 68 69 Input Output Tests Menu 48 Input Filter Time 31 32 84 Installation 13 Instrument Calibration Menu 48 Instrument Fusing 10 Interface Connection 18 interpolation 37 K Keyboard 19 L ED Test 48 L LED tests 68 line voltage 15 LOCAL 19 25 86 M MAX PWR 39 Menu Tree 20 21 MONITOR 19 20 23 25 26 27 28 33 45 46 47 80 96 Monitor Mode 25 27 Mounting 18 N Numeric Keypad 20 O Operating Modes 25 Output Specifications 5 P Packing List 13 PID coefficients 2 3 7 34 35 367 387 39 Dilo 525 DD 56 PID Table 37 75 88 PID Table mode 36 Platinum 33 44 Power Requirements 14 Pwr Limit 36 40 R Rack Mount Use 10 Ramping 40 51 53 Rear Panel 9 13 14 15 17 18 32 Receive Buffer Overflow 91 101 Relay Connection 18 Relay output connector 10 13 relays 3 9 18 23 27 30 41 107 Remote Control 2 9 19 resolution 1 3 5 6 8 RS 232 2 9 13 18 19 41 42 65 S sample rate 1 6 65 Sensor Cable 13 17 Sensor Connection 17 18 Sensor Input 9 13 serial port 63 65 Set point 23 25 26 27 28 31 35 Aly 52 567 714 by 85 88 90 99 SETUP 19 25 27 28 29 30 31 S2ip 337 497 467 Atlee DT 29 Setup Datalog 59 S
24. a percent of full scale and the full scale range i e MAX PWR are shown near the bottom of the display e The SET POINTs are displayed for any output that is currently active If a stored SET POINT value is not shown on the Normal Operating Display the LTC 21 is not correctly configured to regulate temperature at this set point You should check all of the following e The CONTROL indicator LED must be on press CONTROL e A SENSOR must be assigned to the output e MAX PWR range must be a value other than OFF the MAX PWR range is shown after HEATER on the Main Operating Display e A Heater is connected to the HEATER OUTPUT must not be open Changing SET POINT or any other instrument parameter is done as in the MONITOR mode Most parameters can be changed without affecting temperature regulation However the LTC 21 will automatically terminate the CONTROL mode disabling all heaters if a parameter is changed that effects one of the operating parameters of the control loop Changing the sensor assignment or the heater range are examples of such a change If CONTROL mode is terminated the CONTROL indicator LED will turn off 5 3 Setup Mode Configuring The LTC 21 5 3 1 Introduction To The Setup Mode SETUP mode is used to configure all of the LTC 21 s operating parameters with the exception of temperature SET POINT which is selected from either the MONITOR or Page 28 NEOCERA Instrument and Systems Group
25. as twisted pairs which are physically separated from the sensor leads Heater leads should never be connected to the sensor grounds 2 4 2 Heater Selection The Heater output is driven by a current source with maximum capability of 1 Amp This output is calibrated for use with a 50Q heater which also allows the maximum output power of 50 Watts Although the exact heater resistance is not critical the use of a nominal 50Q heater is strongly recommended The LTC 21 will work with other heater resistances but the output will no longer be calibrated If a resistance other than 50Q is used the actual power may be calculated from the power indicated on the front panel using the following equation Actual Power Indicated Power Heater Resistance 50 The voltage compliance of the current source is limited to about 50 volts For this reason full scale linear operation is only possible under the following conditions Range Maximum Heater Resistance 1600 5000 0 05 Watt 1 6KQ Table 3 Conditions for Linear Operation of Heater Use of a heater resistance value less than 50Q provides linear operation under all conditions but the output power is always less than indicated For systems that require heater power substantially less 50 mWatt it is possible to use a current divider having a 500 resistor at room temperature connected in parallel with a higher resistance heater attached to the system Page 16 NEOCERA Instrument and Systems Gro
26. carry electrical current This safety ground becomes the Chassis Ground of the instrument and is used as the ground point for all cable shields Thus it is important to ensure a good quality connection 1 2 7 Environmental Maximum Safe Ambient Temperature Range The Temperature Controller is designed to operate over an ambient temperature range of 0 C to 55 C without damage to the instrument Depending on the sensor type and bias method used accuracy specifications are only guaranteed over a more limited range as described in the following section Accuracy Ambient Temperature Range The accuracy specifications for the LTC 21 are guaranteed over the following temperature range 259 0 459 G Humidity Altitude A normal laboratory environment is expected Proper operation over extremes of altitude or humidity is not guaranteed WARNING To prevent shock and fire hazards as well as damage to the LTC 21 it should not be allowed to get wet or operate in a condensing atmosphere NEOCERA Instrument and Systems Group Page 11 Model LTC 21 Cryogenic Temperature Controller Page 12 NEOCERA Instrument and Systems Group Chapter 2 Installation and Setup 2 Installation 2 1 Unpacking And Inspection Prior to unpacking the LTC 21 you should check the carton for any shipping damage If damage is observed notify the carrier immediately to allow for a possible insurance claim The following items are included with the LTC 21 If
27. following example C language program illustrates how to access and operate the LTC 21 from a remote computer using the IEEE 488 2 interface This program uses a computer to access query and control various LTC 21 functions The NATIONAL INSTRUMENTS AT GPIB controller and NI 488 2 MS DOS Handler were used with the following code DISCLAIMER THIS IN NO WAY CONSTITUTES A REPRESENTATION OR RECOMMENDATION OF NATIONAL INSTRUMENTS PRODUCTS PLEASE CONTACT NATIONAL INSTRUMENTS DIRECTLY REGARDING QUESTIONS ABOUT NATIONAL INSTRUMENTS PRODUCTS TEST C 02 92 Test TC GPIB program l include lt stdio h gt include decl h include lt string h gt include lt time h gt int PC_handle TC_handle TC_handle Temperature Controller device ud PC_handle the PC s gpib board device ud char rec_string 200 char send_string 100 define TRUE 0 define FALSE 1 int send_TC char str int init_TC_GPIB void int receive_TC char str int max_num_char void putmsg char str main int ok i string_length NEOCERA Instrument and Systems Group Page 103 Model LTC 21 Cryogenic Temperature Controller char timebuf 24 datebuf 24 printf Initializing n init_TC_GPIBQ printf Request for Device Identification putmsg IDN printf nGet Current State of Temperature Controller n printf Instrument State 0 Monitor 1 Control 2 AUTOTUNE n putmsg QISTATE printf
28. is local lockout Description Queries the instrument for the local mode setting Related Commands SLLOCK QOUT Format QOUT lt Heater 1 or Analog 2 gt LTC 21 Response Two coded byte for Analog output and Three coded byte for Heater Description Queries the Output Configuration for the Output Channels The first byte is interpreted as 1 Sensor 1 2 Sensor 2 3 No Sensor assigned The second byte is interpreted as 0 AUTO P 1 AUTO PI 2 AUTO PID 3 PID 4 TABLE 5 DEFAULT 6 MONITOR The third byte is only available for the HEATER it is interpreted as 0 Off 1 0 05W 2 0 5W 3 5W 4 50W Related Commands SHCONT SACONT NEOCERA Instrument and Systems Group Page 95 Model LTC 21 Cryogenic Temperature Controller QPID Format QPID lt 1 HEATER 2 ANALOG gt LTC 21 Response Four ASCII character strings each representing a floating point number They are the Proportional gain constant P gain Integration gain constant I gain Derivative gain constant D gain and the percentage of fixed power reset term Fixed power settings For Heater output one additional character string is also provided Power Limit Percentage For Analog output two additional character strings are also provided Gain and Offset Description Queries for the PID Determines the PID for the Heater or Analog output channels Related Commands SPID QPTBNDX Format QPTBNDX LTC 21 Respons
29. refreshed every 0 5 seconds regardless of the Input Filter Time setting Further the input sensors are always sampled 16 times per second The data displayed will be averaged over the period of Input Filter Time Constant e g For an Input Filter Time of 0 5 second the controller will be displaying the average of 8 input samples In effect this process filters out input signal noise by continuously averaging data over the selected time period and updates the display and PID control algorithm with this filtered data The Remote interface uses the SDUR and QDUR commands to set the Input Filter Time Since the Input Filter Time affects the PID control loop correct selection of this value is necessary to ensure optimum PID control Specifically e Selection of a short Input Filter Time may result in noisy control This is especially true in systems that use aggressive Derivative terms since the derivative is most affected by both signal noise and input sample rate The result may be reduced control accuracy near the set point and will be most obvious in systems where there are high noise levels such as a Cryocooler NEOCERA Instrument and Systems Group Page 31 Model LTC 21 Cryogenic Temperature Controller e Selection of a long Input Filter Time will slow the responsiveness of the controller and may result in low level oscillations around the set point This effect is identical to the selection of an Integrator time that is too long for the
30. shielded twisted pairs The shield NEOCERA Instrument and Systems Group Page 17 Model LTC 21 Cryogenic Temperature Controller should not be connected to the low side of the sensor leads The shield ground should be attached to the sensor connector at the rear panel of the instrument Special wire is available for sensor connection from a number of sources In most cases 1t is adequate to run two pair of twisted 0 005 diameter leads inside your cryostat Common choices of metal for these leads include phosphor bronze brass and Manganin Very high resistance leads greater than 100 ohm per wire should be avoided if possible Low resistance copper leads work well so long as they do not conduct so much heat into the sensor as to cause erroneous readings After the sensor is connected it is essential that the LTC 21 software be correctly configured for use with the installed sensor type 2 6 Relay Connection Each relay contact is rated at 0 5A 30Vim or 60Vpc The relay contacts will change state on all relays which are enabled if the temperature exceeds the assigned high or low limits 2 7 Interface Connection Connection to the IEEE 488 is via an industry standard IEEE 488 connector to the IEEE 488 connector on the rear panel Connection to the RS 232 is via a female DB 9 connector to the RS 232 connector on the rear panel 2 8 Mounting The LTC 21 Bench Mounting The LTC 21 is supplied ready for bench use Plastic feet are
31. should be the optimal PID setting for this temperature in this thermal system If a new set point is subsequently given the system will automatically tune to get a new optimal PID setting for the new set point If MANUAL is selected the instrument will regulate the temperature setting using the existing PID setting or as specified by the SPID command SHCONT command must be issued to set the heater control to AUTOPID AUTOPI or AUTOP mode before this command can have any effect Related commands SCONT SMON SPID ISTATE STUNEP Format STUNEP lt 1 System Response 2 Tuning Temperature Deviation gt lt System Response S or 0 Slow N or 1 Normal F or 2 Fast System Response gt or lt Tuning Temperature Deviation 0 1 to 50 Tuning Temperature Deviation percentage gt LTC 21 Response None Description Setting the system response time and deviation temperature for Autotune use System response time denotes the cryogenic system response time A fast system responds rapidly to the heat applied to it A slow system will have a time lag response Please refer to section 8 1 Autotuning for description The system default is set to normal Tuning temperature deviation denotes whether the system should automatically retune to obtain a new set of PID coefficients when the user changes the set point If the new set point deviates from the last autotuning temperature by the tuning temperature deviation percentage the system will g
32. stop flashing and the LEDs will return to their normal state 10 4 Heater Power Output Channel Calibration Note This procedure should only be performed if the heater channel has been repaired or is suspected of being defective It does not affect the control accuracy of the instrument The calibration of the heater output channel involves a dc offset adjustment that is made to ensure that a Zero output from the heater s Digital to Analog converter corresponds to zero output power from the heater stage A DAC output voltage of less than zero volts will cause the heater output stage to output zero current Therefore the offset adjustment is made so that a Zero DAC output corresponds to between 1 and 5 of full scale This will ensure that drift over time will not result in a condition where the heater cannot be completely turned off Tools required are an Oscilloscope and a trimpot adjustment tool To perform this calibration proceed as follows 1 Disconnect ac power from the instrument and remove the top cover plate 2 Remove both sensor boards so the heater board can be easily accessed NEOCERA Instrument and Systems Group Page 69 Model LTC 21 Cryogenic Temperature Controller Connect the oscilloscope probe to TP9 Htr Adj on the heater board Connect the probe ground to TP7 AGnd Apply power to the instrument and turn the front panel switch ON Go the Input Output Tests Menu Cursor to the Heater R
33. supplied on the bottom of the instrument these should not be removed as they allow for an air gap beneath the instrument which aids in cooling The front of the instrument may be elevated for better viewing angle using the built in tilt stand Rack Mounting The LTC 21 may be rack mounted using the optional rack mount kit available from NEOCERA Instrument and Systems Group Simply attach the supplied ears to the sides of the LTC 21 The LTC 21 may then be mounted in any standard 19 rack mount enclosure Page 18 NEOCERA Instrument and Systems Group Chapter 3 Operation 3 Operation 3 1 Use of the Keyboard All keys on the LTC 21 are programmed to provide a consistent result regardless of the menu displayed Response of the LTC 21 to the various keys is summarized in the following sections 3 2 LOCAL Key Pressing the LOCAL key unconditionally terminates remote control of the LTC 21 via either the RS 232 or IEEE 488 port This permits control via the front panel keys The REMOTE indicator LED turns off to indicate this condition All keys other than the LOCAL key are disabled if the REMOTE indicator LED is on 3 3 FUNCTION Keys 3 3 1 CONTROL Regardless of the menu currently displayed pressing CONTROL causes the LTC 21 to enter the CONTROL mode and show the Normal Operating Display Temperature regulation will begin immediately or continue if the LTC 21 is properly configured for temperature control 3 3 2 MONITOR Reg
34. the thermometer before the thermometer can begin to respond AUTOTUNE will usually yield coefficients for this type of system but they may not be well optimized These systems are generally very difficult to regulate using a PID system and the best advice is to try to redesign the system NEOCERA Instrument and Systems Group Chapter 8 Using Data Log 8 Using Data Log 8 1 Introduction LTC 21 provides data log as a feature that is commonly used for data monitor function For most applications this can save the researcher or experimenter a great deal of time for data recording for a particular event LTC 21 saves data in non volatile memory thus the user can turn off the power of the LTC 21 transported to a location and can upload the information to a computer or remote device 8 2 DATA LOG Function From the SETUP screen the user can choose DISPLAY to get to the DISPLA Y CONFIGURATION screen There are two screen dedicated for data log they are the SETUP DATALOG and DISPLAY DATALOG menus 8 2 1 DATA LOG SETUP Choosing SETUP DATALOG from the DISPLAY CONFIGURATION menu calls up the Data Log Configuration menu Data Log Configuration Sample Interval 10 seconds Sensor Channel 1 Total Samples Channel 500 Acquisition Mode One Shot Current Time 00 00 00 Press ENTER to start Data Log Figure 25 Datalog Configuration Screen Enter will start a new session of data log CAUTION The ENTER key in DATALOG configuration
35. 1 parameters with the exception of temperature SET POINT If SETUP mode is selected from CONTROL mode the LTC 21 will continue to regulate temperature unless a parameter is changed which effects one of the operating parameters of the control loop 5 2 Monitor Mode Monitoring Temperature With The LTC 21 5 2 1 Using the Monitor Mode The MONITOR mode is used to monitor the temperature of the sensors The Heater output 1s disabled in this mode so temperature regulation is not possible The Analog output is also disabled if it is configured for controlling temperature if it is configured as a Monitor port it will continue to function normally NEOCERA Instrument and Systems Group Page 25 Model LTC 21 Cryogenic Temperature Controller Sensor 1 Sensor 2 350 00K 263 85C Heater Off Push ENTER to Change SET POINT Figure 6 Monitor Mode Screen Usually the Normal Operating Display will be presented in the MONITOR mode The output of the sensors are displayed in large characters under the assigned SENSOR input number If no sensor type has been assigned to an input the display will be blank under the unassigned SENSOR If there is no sensor attached to the connector on the rear panel of the instrument or if the sensor calibration has not been stored in the LTC 21 that channel may display K or an erroneous reading If no sensor is connected please select No Sensor in the Sensor Configuration Menu refe
36. 21 Response None Description Sets the Alarm table s or Relay table s Low and High limit and their Arm and Disarm functions While the Alarm or the Relay are armed when the measurement for the sensor device exceeds the high limit or falls below the low limit the alarm relay will be set until the measurement falls within the limit or the device is disarmed The units of the High or Low limit are based on the units set by the SUNIT command Related Commands QARTBL SUNIT QUNIT Page 80 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller SCALT Format SCALT lt Sensor Type 0 2V Diode 1 6V Diode 2 R250 3 R2500 4 R1 0M AC gt lt Volt Bias 0 10mV 1 3mV_ additional ranges for Enhanced LTC 21 2 1mV 3 320uV 4 100uV 5 32uV 6 10uV gt lt Calibration table units 0 LogOhms 1 Ohms 2 Volts gt lt Cal table description up to 19 ASCII characters gt lt Cal table multiplier gt lt temperature gt lt voltage or ohms gt lt temperature gt lt voltage or ohms gt up to 149 pairs of temp and voltage or ohms entries lt terminator gt LTC 21 Response None Description Loads a user defined calibration table into the system memory During the downloading of a long user calibration table over 10 entries the LTC needs to process each entry individually Depending on the speed of the host which downloads the table a Transmit overflow error might occur We recommend using a delay func
37. 21 Sensor Parameters SCIe8eN i ccc ooooooooooooooooo 42 Figure 22 Sensor Calibration Edit View Screen o o o o o 45 Figure 23 Sensor Cal Table Menu Screend oo oooooooooooooo 477 Figure 24 Input Output Tests Menu Table o oooooooooo 48 Figure 25 Datalog Configuration Screend ooooooooooooooooo 59 Frg re 20 Data lod Display SCTECM e ita ia iaa a 61 Figure 27 LTC 21 Functional Block DiagIaM oooooooooooooo 63 Figure 28 LTC 21 Sensor Calibration Fixture 71 Figure 29 Platinum Sensor Four wire Connection 109 Figure 30 DT 470 Sensor Four wire Connection 109 Page xii NEOCERA Instrument and Systems Group Chapter 1 Introduction and Specifications 1 Introduction 1 1 Features The LTC 21 is a high performance temperature controller designed for use with most cryogenic temperature sensors It has a wide range of features and capabilities that allow it to outperform competitive models in nearly every application The LTC 21 is designed to accommodate the use of unusual sensors with higher resolution at ultra low temperatures The LTC 21 features include Two Multi Purpose Inputs The standard input modules supplied with the LTC 21 support all common cryogenic sensors including e Silicon and GaAlAs diodes from 1 K to about 400 K e Carbon carbon glass ThermOx Cernox Ruthenium Oxide and germanium resistors from less than 0 3 K to about 300 K
38. 3 Model LTC 21 Cryogenic Temperature Controller Summary of Remote Interface Commands NAME DESCRIPTION Common IEEE Commands Event Status Enable Operation Complete Wait to Continue Status Byte Query Loads a set point for the Heater or Analog output Set the instrument to MONITOR state Page 74 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller NAME DESCRIPTION Table 14 IEEE Remote Interface Commands NEOCERA Instrument and Systems Group Page 75 Model LTC 21 Cryogenic Temperature Controller IEEE Command Reference CLS Format CLS LTC 21 Response None Description The Clear Status command clears the Standard Event Status Register s bit 4 and bit 5 Execution Error bit and Command Error bit and the content of Execution Error Register and Command Error Register For RS232 interface CLS also resets the i o buffer pointers Related Commands ESE ESE ESR SRE SRE STB SUERREG QUERREG ESE ESE Format ESE LTC 21 Response None Description The Event Status Enable command sets the Standard Event Status Enable Register Mask bits as defined by the IEEE 488 2 1987 standard Related Commands CLS ESR ESE ESR SRE SRE STB SUERREG QUERREG ESR Format ESR LTC 21 Response None Description The Event Status Enable command sets the Standard Event Status Register bits as defined by the IEEE 488 2 1987 standard Related Commands CLS E
39. 32 uV and 10 uV peak to peak This allows the user to reduce the power across the sensor increasing the range and utility of the LTC 21 especially for use at lower temperatures Please refer to the table below when choosing a sensor and an excitation voltage for your application Excitation Voltage Resistance Range 1Q to 1 MQ 320 uV 1 Q to 500 KQ CdS weem 1004 V 1 Q to 150 KQ 10 Table 9 Excitation Accuracy Resistance Range The following table can serve as a guide when choosing Sensor Type menu selections for various sensors NEOCERA Instrument and Systems Group Page 43 Model LTC 21 Cryogenic Temperature Controller mV 320 uV 1004V 32 uV and 10 yv Si Diode Usually 2V Diode occasionally 6 V Diode Check the diode nea manufacturer s specification for details GaAlAs Diode 6 V Diode Temp Temp R250 DC or R2500 DC depending on temperature range R250 DC or R2500 DC depending on temperature range Ruthenium Oxide R1 0 M AC if used at low temperatures 10 mV 1 mV 3 mV 320 LV 100uV 32 uV and 10 uV R2500 DC Germanium Resistor R1 0 M AC if used at low temperatures 10 mV 1 mV 3 mV 320 uv ThermOx 1004 V 32 uV and 10 pV R250 DC or R2500 DC depending on temperature range Table 10 Sensor Type Selection Cal Table Units selection Use the down arrow key to select the Cal Table Units choice and then use the INC or DEC key to select Volts Ohms or LogOhms Sensor Type Cal Tabl
40. 68 OB SOLE TOS eer cee eee ee eer 68 1 04 Bede LED TESES tt Meas Sates hoe creas ede 68 10 3 2 Analog Output Channel Tests 68 10 3 3 Heater Output Channel Tests 69 10 4 Heater Power Output Channel Calibration 69 10 5 Checking Sensor Calibration He be bal de eee aes 70 10 6 Calibration Procedure Sensor Channels 71 Appendix A Remote Interface Commands oo oooooooooooo 73 RCV G io Ghee See SA SSE OES OES SG Ee eee es 76 MOP C sid shee aia cs 76 RSL Axa oon a od hee a 77 ESB A a A es oc 77 AMA A EA syed akan wed Ta IEEE Query Command ReferenCe ooooooooooooooooo 78 MES is daa tt ata 78 MES RA A O A A aa ee 78 ZIDN ii A id a ee Ride ee a da 78 OD A ata adds 79 ES O A Wee aid ese ss eae aes 79 SIB a is as 79 LTE 21 Gommanas Reference mm ia da 80 SACONT usa a ew See HS 80 SADDR seata ys e a WG Bee sd sa B S 80 SABIDO Steet the sey tg 5 Te IA Stee et Bh SS as Se EA Soe 80 Page viii NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller SA o a rs Sp Dh Pee o o O o Se a oe 81 GON TE Aita Ea A eee AO DA TR DOLEE AA EA 82 DECIA a O E EISE She 82 A RAR 82 SDEM dewine RO NADA A ay Ne RO A AE 83 SUIS a Sl a ake 4A 83 S D td ia a ot ida aa t 83 TR RO O RO 83 ORLE ara e ds o sn 84 SHCONT lt A Baie SG aig 84 MCP WARS os as A ee ee Re ite E ere etl AS wre ee AA ral 85 TiO C Reg A Gao ce Breda eer A
41. AS DAMAGE TO THE LTC 21 IT SHOULD NOT BE ALLOWED TO GET WET OR OPERATE IN A CONDENSING ATMOSPHERE WARNING Never attempt to operate the LTC 21 at a different input line voltage than is shown on the power input module on the rear panel Serious injury or equipment damage may result WARNING ALWAYS REPLACE THE FUSE WITH THE CORRECT VALUE TO PREVENT SHOCK AND FIRE HAZARDS AS WELL AS DAMAGE TO THE LTC 21 WARNING TO PREVENT SHOCK AND FIRE HAZARDS ALWAYS CONNECT THE POWER CORD TO A THREE CONDUCTOR GROUNDED RECEPTACLE WARNING WITH PROPER VENTILATION THE LTC 21 IS DESIGNED TO OPERATE INDEFINITEL Y WITHOUT DAMAGE TO ITSELF IF ITS HEATER OUTPUT IS SHORT CIRCUITED HOWEVER CARE SHOULD BE TAKEN TO AVOID THIS CONDITION SINCE THE 50 WATT OUTPUT COULD DAMAGE OTHER COMPONENTS OR RESULT IN A FIRE HAZARD WARNING IF THE INSTRUMENT IS USED IN A MANNER NOT SPECIFIED BY THE MANUFACTURER THE PROTECTION PROVIDED BY THE EQUIPMENT MAY BE IMPAIRED Page iv NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller Definition of international symbols for warnings and hazards CAUTI ON ISK OF ELECTR CAL SHOCK REFER TO ACCOMPANYING DOCUMENTS 8 PROTECTIVE EARTH GROUND NEOCERA Instrument and Systems Group Page v Model LTC 21 Cryogenic Temperature Controller
42. ENTER 3 Select Delete a User Table and press ENTER 4 Use the cursor keys to scroll through the listing of tables and select the table you wish to delete 5 Press CLEAR twice to delete the table After you press CLEAR the first time text on the display will flash press CLEAR to delete You must press CLEAR a second time to delete the selected table 5 3 14 The Instrument Calibration Menu The instrument calibration menu is used to view or change sensor channel calibration information This includes Analog to Digital converter offset and gain information and constant current source data This menu is entered via the MISC menu To check or re calibrate your instrument refer to the Temperature Controller Calibration Guide for your model Note that the WARNING field has special significance When the cursor is moved to this field 1t will begin to flash Now 1f the ENTER button is pressed the LTC 21 will move to the Input Output Tests Menu 5 3 15 Input Output Tests Menu The Input Output Tests Menu allows the user to exercise various functions of the instrument as part of a diagnostic or calibration procedure This menu is entered via the Instrument Calibration Menu as described in the previous section Input Output Tests Menu LED Test OFF Heater Ramp OFF AO ut Ramp OFF CCS1 Ramp OFF CCS2 Ramp OFF Heater Range Off RUN NEOCERA Model LTC 21 V5 2 c 1992 1997 Figure 24 Input Output Tes
43. OTUNE 3 7 39 55 56 57 58 TD 87 90 95 101 104 autotuning 55 56 57 90 B BACKSPACI Bail 10 baud rate 9 42 C calibration curve 45 Calibration Curves 2 5 calibration table 42 45 46 74 Sy 92 93 100 Cernox Resistors 4 Chart Recorder 38 39 51 CLEAR 20 48 61 67 68 Contrast Adjustment 67 CONTROL 19 20 25 27 28 29 31 33 34 35 45 46 47 56 65 90 95 Control Mode 27 85 cryogenic systems 51 cryostat 16 17 18 Cubic Spline 1 Cursor Keys 19 NEOCERA Instrument and Systems Group D Data log 59 Datalog Display 59 Datalog Setup 59 DEC 20 30 31 32 34 42 44 Digital to Analog 1 65 69 Diode 33 44 Diode Sensor Connections 108 Display Datalog 59 E Enclosure 10 ENTER 20 26 27 28 29 30 35 37 40 41 46 47 48 56 59 60 68 Environmental 11 Execution Error Register 76 91 LOL EXIT 204 Aly 29 SO Sly 327 334 35 37 40 42 45 46 47 F First Time Operation 23 function keys 19 Fuse 15 G GPIB 73 80 91 92 93 101 103 104 105 Grounding 15 Grounding Requirements 10 H Heater Output 5 9 13 69 109 heater ranges 5 37 Heater Wiring 15 Humidity Altitude 11 Page 119 Model LTC 21 Cryogenic Temperature Controller a IEEE Commands 76 80 IEEE Common Queries 73 IEEE Query Commands 78 IEEE
44. QUE orenen e on e ad 11 Table 31 RS 23 2 SOLEIDOS nda side da e daa a da E e dada 12 NEOCERA Instrument and Systems Group Page xi Model LTC 21 Cryogenic Temperature Controller Table of Figures Figure 1 Four Wire Sensor Connecti0N o oooooooooooooooooo o 5 Fig re 2 Heater Connections iets e ne atone span ia 6 Fig re 3 LTC 21 Rear Panel nina as wi SSeS el Sw Se a 14 EIQuUre Y Meny MP er e A SS eee 21 Figure 5 ADC Calibration SCreeN cccoooooooo oooooooooooooo 23 Fig re 10 Monitor Mode SETE sec e Oe wl iw e a as 26 Frg re T Setpoint GERSON ae aia eran et oe ars 27 Bigure8 Control Mode Serena sue Yee we ake e ane eke aoe ae 28 Figure 9 Setup Sereni s c a ees a ve ooo oS a Se Ewe a as 29 Figure 10 Display Contiguratllon Screen ecchi 30 Figure 11 Display Units SCreens 5 tee sess doe we e ee es 30 Figure 12 Display Update Rate SCreend c c oooooooooooooooooo 31 Figure 13 Sensor Configuration ScreenN c ooooooooooooooo o 32 Figure 14 Output Configuration Screen o oooooooooooooo 33 Frg re 15 PID Mode Sci ad 35 Figure 6c Table Mode Screen eres A a E a A 37 Figure 1 7 Ramp Cont igutatio n Men ir a ir Sie es a a 39 Frg re t8 MESC Men SCT it ja Bea 40 Figure 19 Alarm Relay Setup Sereen sosososesasa sosa 41 Figure 20 Remote Input Output Configuration Screen 42 Figure
45. RA Instrument and Systems Group Page 39 Model LTC 21 Cryogenic Temperature Controller To execute Ramping the Ramp Armed field must be set to ON and the Mode set to PID or Table not Autotune Enter the Control Mode to begin the Temperature Ramp Idle will be replaced by Ramping in the Ramp Configuration Menu Reaching the Target Temperature or entering the Monitor Mode will terminate Ramping 5 4 8 Misc Menu 5 3 7 1 Introduction to the MISC MENU MISC MENU Alarm and Relay Setup Remote I O Config Sensor CAL Tables Instrument Calibration Select and Press ENTER to Change Item EXIT to Quit Figure 18 Misc Menu Screen The MISC MENU is used for the following functions SELECTION FUNCTION Alarm amp Relay Set Points Configures the Alarms amp Relays Remote I O Configuration Configure IEEE 488 and RS 232 ports Sensor CAL Tables Enter Modify Sensor Calibration Tables Instrument Calibration Recalibrates the LTC 21 Table 7 Misc Menu Selections 5 3 8 Alarm amp Relay Set Points To change the configuration of the Alarms or Relays select the Alarm and Relay Set Point menu item from the MISC MENU this will display the Alarm and Relay Configuration menu Page 40 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller Alarm and Relay Configuration Status High Lim Low Lim Alarm 1 Armed 295 000K 235 000K Alarm 2 Disarmed 450 000C 100 000C Relay 1 Armed 290 000K 200 000K Re
46. SE ESR SRE SRE STB SUERREG QUERREG OPC Format OPC LTC 21 Response None Description The Operation Complete command sets the Standard Event Status Register s bit O Operation Complete bit when all the pending operations are completed Related Commands OPC ESE ESE ESR SRE SRE STB Page 76 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller RST Format RST LTC 21 Response None Description The Reset command resets the temperature controller remotely This is equivalent of turning off the temperature controller and turn on again Related Commands None SRE Format SRE lt register enable value gt LTC 21 Response None Description The Service Request Enable command sets the Service Request Enable Register as defined by the IEEE 488 2 1987 document Related Commands SRE WAI Format WAI LTC 21 Response None Description The Wait to Continue command is a synchronization command It prevent the temperature controller from executing any further commands or queries until there is no operation pending Since all temperature controller commands are instantaneous executable commands this command will be acted as an no operation command Related Commands OPC OPC NEOCERA Instrument and Systems Group Page 77 Model LTC 21 Cryogenic Temperature Controller IEEE Query Command Reference ESE Format ESE LTC 21 Response One byte valu
47. Sensor input connectors on the rear panel A mating connector Lemo Inc FGG 1B 304 CNAD52 with attached shielded cable is supplied for use in attaching your sensor The LTC 21 is designed to make accurate readings even in the presence of large interfering signals such as power line pick up Nevertheless it is always best to use properly designed input leads to minimize stray pick up The sensor cable supplied with the LTC 21 has been carefully selected for low noise operation It comprises two twisted pair cables inside a non current carrying shield If it is necessary to replace this cable always use a cable of similar design Additional or replacement connectors with attached cable are available from NEOCERA Instrument and Systems Group Wiring diagrams for various sensor types are shown in Appendix C For best performance all sensors should be connected in a four terminal configuration Polarity is critical with diode sensors but generally unimportant with all other types All four connections should be floating but if it is necessary to ground any part of the sensor circuit it must be the low side The ground connection should only be used for the sensor cable shield The cable shield should be grounded at the connector It is generally best NOT to ground the shield at the cryostat Optimum wire selection for use inside your cryostat depends on many factors In all cases it is best to make a four wire connection using two sets of
48. TDs Alpha types and arbitrary resistance at 300 K ThermOx Resistance Sensors Additionally pre loaded standard calibration curves are supplied for the following Sensors e Pt 100 1000 e Si diode thermometers Lake Shore CryoCal and SI standard curves Other types of sensors may be supported by entry of user Sensor Calibration tables Tables may be loaded via the remote interface or they can be entered from the front panel Excitation Current Sensor excitation is provided by independent current sources ac or de excitation may be selected Diode sensors are dc biased at 10 ma and resistive type sensors Platinum Rhodium Iron Ruthenium Oxide etc can be de biased at 1 ma or 10 ua depending on the resistance range of the sensor Resistive sensors can also be ac biased with a selectable constant peak to peak voltage of 10 mV to 10 uV at a minimum of 100na Input Voltage Ranges Four input voltage ranges are provided on each input channel They are described as follows e 6V Generally used for GaAlAs Diodes e 2V for use with Silicon Diodes e 0 25V for Platinum type resistive sensors e 10 mV 10 uV for other resistive sensors Page 4 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller Sensor Connections Connection to the sensors will be made via L connectors mounted on ES ce the back panel of the H Ze instrument Pins are he a a
49. User s Manual for LTC 21 Temperature Controller E By Aeocera Instrument and Systems Group Beltsville Maryland USA O copyright 1999 Model LTC 21 Cryogenic Temperature Controller NEOCERA Inc Part Number 3000 140 Revision Record May 21 1997 Initial Release October 1 1997 B_ First Neocera Release August 19 1999 Revised QRMP amp SRMP 1999 by NEOCERA Instrument and Systems Group All rights reserved No part of this manual may be reproduced stored in a retrieval system or transmitted in any form or by any means electronic mechanical photocopying recording or otherwise without prior written permission of NEOCERA Inc NEOCERA Inc reserves the right to change the functions features or specifications of its products at any time without notice Any questions or comments in regard to this product and other products from NEOCERA Instrument and Systems Group please contact NEOCERA INC Instrument and Systems Group 10000 Virginia Manor Road Suite 300 Beltsville Maryland 20705 4215 U S A Customer Service and Technical Support 1 800 290 4322 Within U S A 1 301 210 1010 Outside U S A Fax 1 301 210 1042 Cernox ThermOx are registered trademarks of Lakeshore Cryotronics Inc Page ii NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature C
50. WR SHMXPWR STUNE Page 84 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller SHMXPWR Format SHMXPWR lt index 0 to 4 gt LTC 21 Response LTC 21 will exit the CONTROL or MONITOR loop to safeguard against heater range change You can restore the LTC 21 to MONITOR or CONTROL mode after this command by issuing SMON or SCONT respectively Description Sets the Heater output channel Maximum Heater Power selection The heater output percentage is based on the Maximum Heater Power selection Output Index MaxPower Heater 0 of pot oow po O pa2 sw A p3 osw Eo E RNE Table 18 IEEE Maximum Heater Output Selection Related Commands QOUT SLLOCK Format SLLOCK lt O0 no lockout 1 local lockout gt LTC 21 Response Whenever a data transmission occurs on the remote interface ether GPIB or RS232 LTC 21 will set the Local Lockout mode disable the front panel and light the REM LED until the LOCAL key is pressed or SLLOCK 0 command is invoked from the remote I O Description Sets the local lockout mode Local lockout disables the front panel keyboard Pressing the LOCAL key on the front panel will re enable the rest of the front panel keys The Local Lockout function prevents users from inadvertently altering instrument settings while the remote interface is active Related Commands QLLOCK NEOCERA Instrument and Systems Group Page 85 Model LTC 21 Cryogen
51. alibrated sensor is installed and the display units are selected to be Kelvin the Analog Output voltage will be given by V OFFSET Temperature in Kelvin GAIN This feature is commonly used to monitor small changes in temperature on a chart recorder Example for Use with a Chart Recorder For an application with temperature for sensor 1 is in the 230K to 240K range In the Output configuration page set both Heater and Analog Port to Sensor 1 Set Analog Port Mode to Monitor By pressing Enter at Monitor 1t shows the Output Parameters screen Select Offset to 235K and Gain to 1 00 The Chart Recorder connected to the Analog port will show its chart reading for 230K as 5V 235K 230K 1 00 for 235K as OV 235K 235K 1 00 and for 240K as 5V 235K 240K 1 00 The Gain of 1 00 can be changed to 0 5 to get half of the scale Page 38 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller If anything other than Monitor is chosen for the Analog Output PID coefficients will be assigned to it in the same way that they are assigned to the Heater output The Analog output can then be used as a low power temperature regulator with a maximum output capability of 100 mW AUTOTUNE is not available on the Analog output MAX PWR Menu Field The MAX PWR field only applies to the Heater output and is used to set its maximum output power capability Choices are OFF 0 05 Watt 0 5 W
52. amp field and toggle the field to ON Leave all other tests in the OFF state Cursor to the RUN field in order to begin the Heater Ramp test A volt sawtooth wave form should be seen on the oscilloscope at this time The minimum voltage of the wave form should be near zero volts and the maximum near six volts If this is not the case the heater control circuitry is defective Adjust trimpot R9 on the heater card so that the minimum voltage on the output wave form is between 0 5mV and 30mV If the voltage cannot be adjusted to within this range repairs are required This completes the Heater Channel Calibration Procedure 10 5 Checking Sensor Calibration The calibration of the LTC 21 may be tested at any time using the Calibration Fixture Simply set the instrument in the Ohms mode and read the values of high precision resistors Proceed as follows 1 Connect the Calibration Fixture to the channel being tested Turn power to the LTC 21 ON Go to the Setup Display menu and select units of Ohms To test the 6 and 2 volt input ranges Silicon and Germanium diodes go to the Sensor Configuration menu and select the LS Diode 10 sensor Press the Monitor key Values of the 100KQ 10KQ and 1KQ resistors should be read on the LTC 21 when selected To test the 300mV input range Platinum Resistors go to the Sensor Configuration menu and select the Pt 1000 385 sensor Press the Monitor key Values of the
53. any items are missing notify your NEOCERA representative immediately Packing List e LTC 21 Temperature Controller e Fuses installed in the controller Power Entry Module e ac Power Cord e Users Manual e Analog Output Connector Assembly e Sensor Cable with mating connector 5 meters e Heater Connector Assembly e Relay Connector Assembly e CE Declaration of Conformance e CE Kit and Instructions 2 2 Rear Panel Layout The rear panel layout of the LTC 21 provides connections for the following functions e TEEE 488 Interface connector e Heater Output connector Circular AMP 7 pin e Two Sensor Input Connectors Circular Lemo 4 pin e Analog Output Connector AMP 4 pin e RS 232 Connector DB 9 e Relay output connector Circular 8 pin e ac power entry module with fuse and voltage selector NEOCERA Instrument and Systems Group Page 13 Model LTC 21 Cryogenic Temperature Controller SENSOR HEATER MODEL LTC 2 MADE IN USA Figure 3 LTC 21 Rear Panel 2 3 Power Requirements ac power can be provided to the LTC 21 at voltages of 100 120 or 220 240 Volts 50or60Hz These MUST be selected by the voltage selector which is part of the ac power entry module mounted on the rear panel of the instrument To change the power configuration perform the following steps a Disconnect the ac power cord from the instrument
54. ardless of the menu currently displayed pressing MONITOR causes the LTC 21 to enter the MONITOR mode and show the Normal Operating Display Heater outputs are immediately and unconditionally disabled 3 3 3 SETUP Pressing SETUP calls up the MAIN SETUP MENU used to change the LTC 21 operating parameters If the LTC 21 was previously in the CONTROL mode it will continue to regulate temperature until a parameter is changed which effects one of the operating parameters of the control loop 3 4 DATA ENTRY Keys Entering data from the front panel is a straightforward process using the following keys 3 4 1 Cursor Keys The four arrow shaped cursor keys are used to make menu selections by moving the cursor indicated by flashing text around the display 3 4 2 INC Increment and DEC Decrement Keys The two keys labeled INC and DEC are used to scroll through the possible choices for a given item that has been selected using the cursor keys The choices presented are usually NEOCERA Instrument and Systems Group Page 19 Model LTC 21 Cryogenic Temperature Controller limited to those that are valid and the operator is warned of an invalid entry by the internal beeper However in some cases where items on different menus are interrelated invalid choices may be allowed to simplify data entry by not forcing a particular sequence of entries For this reason it is a good idea to verify all instrument settings after a change has been made to any o
55. are rated at 0 5A 30Vims or 60Vpc Control Algorithms A wide range of control algorithms simplify regulation of even the most difficult cryogenic systems The LTC 21 has three AUTOTUNE modes that can regulate the most difficult systems over wide temperature ranges with no operator intervention Full manual control of PID coefficients is possible PID tables are available to store optimized parameters vs setpoint Control Set Points Regulation set points can be entered with 0 001 K resolution over the entire operating range and 0 0001K below 10K for all calibrated sensors For uncalibrated sensors or calibrated sensors that are displayed in ohms or volts the Set Points can be entered with six digit resolution Resolution and Accuracy The temperature resolution and accuracy of the LTC 21 are usually limited by the sensor The limitations imposed by the LTC 21 are discussed in the Instrument Specifications section NEOCERA Instrument and Systems Group Page 3 Model LTC 21 Cryogenic Temperature Controller 1 2 Specifications 1 2 1 Input Channel Specifications There are two temperature sensor input channels each of which can separately be configured to use any of the supported sensor types Types of Sensors Supported Supported Sensors include e Silicon and GaAlAs diodes e GRT s e Carbon Glass and Carbon Composite e Cernox Resistors e Ruthenium Oxide Resistors e Germanium Resistors e Rhodium Iron e Platinum R
56. att 5 Watt and 50 Watt All of these settings assume that a 50Q heater is connected to the output The LTC 21 will work with other heater resistances but the output power will be incorrectly displayed Since the LTC 21 is configured as a current source the actual heater power can be calculated from the following equation Actual Heater Power Indicated Power R 50 This equation is valid for conditions which result in output power less than 50 Watt and output voltage less than 50 Volt For the 50 Watt output there is a built in power limit protection in the output configuration s PID mode setting Please Refer to PID mode on PWR Limit setting Ramp Menu Field This menu field is used to setup the Temperature Ramp parameters and appears as shown below The currently selected field will appear as flashing text Ramp Configuration Set Point 290 000K Target Temperature 400 000K Degrees Per Minute 50 000K Channel Number 1 Ramp Armed OFF Heater 0 of 5W Figure 17 Ramp Configuration Menu In order to change the setup parameters press the cursor keys until the desired selection is shown in flashing text For the Set Point Target Temperature and the Degrees Per Minute fields enter a new value via the numeric keypad and press the ENTER button For the Channel Number and Ramp Armed fields simply press the INC DEC keys The K field displays the current temperature NEOCE
57. ature Controller e Keep the CLEAR button pressed until the ADC CAL message is seen on the LCD display This memory will now be cleared 10 2 2 Entering Instrument Recalibration Mode In order to perform calibration on the LTC 21 the instrument must be in the Instrument Recalibration Mode Refer to the Neocera Temperature Controller Calibration Guide for more detailed information on instrument recalibration 10 3 Self Test In order to enter the Input Output Tests Menu proceed as follows e Go to the Instrument Recalibrate Menu from the Misc Menu e Move the cursor to the WARNING field the word will flash e Press the ENTER key The instrument will now be in the Input Output Tests Menu where three self tests are available The following tests may now be performed e LED tests e Heater Output tests e Analog Output Channel tests 10 3 1 LED Tests To perform a self test of the LED indicators on the LTC 21 front panel proceed as follows 1 Move the cursor to the LED Test field Press the INC key in order to change the field from OFF to ON 2 Move the cursor to the word RUN The word will now flash 3 Observe the LEDs sequentially flashing on and off To terminate the LED test move the cursor away from the word RUN The word will stop flashing and the LEDs will return to their normal state 10 3 2 Analog Output Channel Tests To execute the Analog Output Channel self test proceed as follows 1 Move the
58. cess Memory Contents of this memory is lost when ac power is removed This RAM memory contains data such as the processor stack heap etc The PROM Memory The LTC 21 contains 128K x 8 bits of EPROM in the system This contains e Microcomputer Programs e Factory supplied sensor calibration tables Software can be updated in the field by replacing EPROMs Since virtually everything in the instrument is under computer control significant changes to the controller may be made by simple EPROM changes Note that this memory is socketed and may be changed without affecting the basic calibration of the instrument The Non volatile RAM Memory The LTC 21 contains 32k x 8 bits of non volatile RAM This is battery backed memory that will retain data for a period of 10 years even with ac power to the unit turned OFF Page 64 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller This memory contains All instrument calibration data Setup information User sensor and calibration tables Datalog values If the contents of this memory is cleared as described in Chapter 10 all of the above information is lost and factory supplied defaults are set Interface Ports The LTC 21 has input output ports for the IEEE 488 and RS 232 interfaces on the motherboard The RS 232 port is part of the micro controller chip whereas the IEEE 488 interface is implemented in discrete circuitry using an industry standard cont
59. cursor to the AOut Ramp field and press the INC key to toggle the field from OFF to ON 2 Move the cursor to the word RUN The word will now flash 3 Using an Oscilloscope observe a repetitious ramp on the Analog Output connector The ramp will have peak voltages at 12V and 12V Page 68 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller To terminate the test move the cursor away from the word RUN The word will stop flashing and the LEDs will return to their normal state 10 3 3 Heater Output Channel Tests To execute the Heater Output Channel self test proceed as follows 1 Connect a 500 heater to the Heater Output Connector Connect an Oscilloscope across the heater being careful to connect the probe ground to the LTC 21 ground pin Heater Output Connector Pin 2 2 Move the cursor to the Heater Ramp field and press the INC key to toggle the field from OFF to ON 3 Move the cursor to the Heater Range field and use the INC and DEC keys to select the desired heater range 4 Move the cursor to the word RUN The word will now flash 5 Using the Oscilloscope observe a repetitious ramp on the Heater Output connector The ramp will start at zero volts and go to a positive voltage determined by the range selected If this is not the case perform the Heater Power Output Channel Calibration procedure described below To terminate the test move the cursor away from the word RUN The word will
60. displays For example if SENSOR 1 is displayed in Kelvin the set points for all relays assigned to this sensor will be displayed in Kelvin Changing display units between different temperature units only affects the display it has no effect on the operation of the LTC 21 However if you change from temperature units Kelvin Fahrenheit or Celsius to fundamental sensor units ohms or volts the unit will Page 30 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller leave the CONTROL mode Changing between fundamental units or from fundamental to temperature units has the same effect This happens because the LTC 21 regulates temperature using the displayed units to determine the error signal 1 e If ohms are displayed the regulation is based on the difference in ohms between the measured sensor resistance and the set point If temperature units are displayed the LTC 21 calculates the error signal in Kelvin This is done to provide a much more linear system response when using nonlinear sensors Input Filter Time Constant Menu From the DISPLAY CONFIGURATION Menu the user may enter the SETUP INPUT FILTER TIME CONSTANT menu Use the INC and DEC key to change the input filter time constant of 0 5sec 1 sec 2 sec 4 sec 8 sec and 16 seconds UPDATE INPUT FILTER TIME CONSTANT INPUT FILTER TIME 0 5 Seconds EXIT to Quit Figure 12 Display Update Rate Screen Displayed temperature data is
61. dress 15 SENSOR 2 the heater analog output relays and alarms are all disabled NOTE The LTC 21 performs an internal calibration on each sensor channel on power up To insure highest performance and accurate temperature readings a temperature sensor must be attached to the SENSOR input channel you wish to monitor prior to power up NEOCERA Instrument and Systems Group Page 23 Model LTC 21 Cryogenic Temperature Controller Page 24 NEOCERA Instrument and Systems Group Chapter 5 Operating Modes 5 Operating Modes 5 1 Introduction To The Three Operating Modes The LTC 21 has three distinct operating modes the CONTROL MONITOR and SETUP modes These are accessed using the buttons in the FUNCTION section of the front panel If the LTC 21 is in the LOCAL mode REMOTE indicator LED turned off pressing any of these buttons will immediately put the LTC 21 into the indicated operating mode regardless of its current status MONITOR The monitor mode is used to monitor and display the temperature of calibrated sensors connected to the inputs Uncalibrated sensors and calibrated sensor if desired are displayed in their intrinsic units i e Volts Ohms etc Heaters are unconditionally disabled in this mode CONTROL The control mode is used when temperature regulation is desired Heaters are enabled in this mode which is otherwise identical to MONITOR mode SETUP The setup mode is used to change any of the LTC 2
62. e Two ASCII character numbers indicating the indices of PID Tables set for Heater and Analog channel if TABLE mode is selected Description Two ASCII character number indicating the indices of PID Tables set for Heater and Analog channel if TABLE mode is selected Related Commands SPTBNDX SACONT SHCONT QRMP Format QRMP lt channel gt LTC 21 Response lt armed gt lt Ramp temperature setpoint gt lt degrees minute gt Description Example 1 300 000 10 Related Commands SRMP QSAMP Format QSAMP lt 1 Sensor 1 2 Sensor 2 gt LTC 21 Response String of eleven ASCII characters containing a measurement and unit from a sensor Page 96 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller Description This command requests the temperature measured by sensor 1 or 2 The measurement unit is included as the last character If the measurement is 1 00 this indicates an overrange or underrange condition These conditions can occur if the instrument is in the process of an ADC calibration or the instrument sensor is not assigned or connected Related Commands SETP SOSEN SUNIT QUNIT NEOCERA Instrument and Systems Group Page 97 Model LTC 21 Cryogenic Temperature Controller QSETP Format QSETP lt 1 HEATER or 2 ANALOG gt LTC 21 Response String of eleven ASCII characters containing a setpoint and associated unit Description Queries the Heater or Analog outputs to d
63. e range from 0 through 255 Description The Standard Event Status Enable Query requests the Standard Event Status Register Enable Mask contents in the Temperature controller The content of the mask can be interpreted based on the IEEE 488 2 1987 document Related Commands CLS ESE ESR SRE SRE STB SUERREG QUERREG ESR Format ESR LTC 21 Response One byte value range from 0 through 255 Description The Standard Event Status Enable Query requests the Standard Event Status Register content in the Temperature controller and clears it The content of the register can be interpreted based on the IEEE 488 2 1987 document Related Commands CLS ESE ESE ESR SRE SRE STB SUERREG QUERREG IDN Format IDN LTC 21 Response A string of characters in the form of Neocera Model LTC 21 version Description The Identification Query requests the device identification The intent is for the controlling device to determine the unique identification of devices on the bus Related Commands RST Page 78 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller OPC Format OPC LTC 21 Response An ASCII character of 1 Description The Operation Complete Query returns a 1 when all the pending operations are completed Related Commands OPC ESE ESE ESR SRE SRE STB SRE Format SRE LTC 21 Response One byte value range from 0 through 63 o
64. e System Is Very Slow To Respond To Heat Changes Even if AUTOTUNE is capable of working in principle it may time out before it determines coefficients If you are working in the NORMAL AUTOTUNE mode simply select the SLOW AUTOTUNE mode and try again This should work for any system with a characteristic response time less than a few minutes For extremely slow systems AUTOTUNE may still time out The best remedy is to redesign your system to reduce its thermal time constant If this is not practical you should manually select coefficients see Section 7 1 as follows Ti gt 100 sec Td 0 K 1 NEOCERA Instrument and Systems Group Page 57 Model LTC 21 Cryogenic Temperature Controller Page 58 If the system oscillates turn down the gain by a factor of ten If it seems sluggish and doesn t oscillate increase the gain until the system just begins to oscillate After you get reasonably good results change Td so that Td 0 25 Ti This procedure can be frustrating since the system is so slow that 1t takes many minutes to observe the results of a change The System Has A Long Lag Time This type of system appears similar one with a long time constant but it is different in the following way A long lag system will have essentially no response to a change in heater power for some period of time It may then begin to respond rather quickly Such systems usually are the result of mass flow e g warmed gas must flow from the heater to
65. e Units Carbon Glass or other resistive sensors with Log Ohms logarithmic temperature characteristics Table 11 Cal Table Units Edit Cal Table selection Refer to the Optional Entry of Calibration Table paragraph later in this section Multiplier selection Use the down arrow cursor key to select Multiplier and enter the desired value using the numeric keypad The multiplier is used to scale the calibration table s Volts or Page 44 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller Ohms column by a constant factor i e if the calibration table has an entry pair of 100K and 100 with a multiplier of 2 000 the LTC 21 would interpret the entry pair as 200 K and 200 The multiplier is almost always set to 1 000 Enter a multiplier other than 1 0000 only under the following two conditions e Enter a minus sign in front of the multiplier if your sensor has a negative temperature coefficient sensor reading decreases with increasing temperature AND you do not enter a temperature calibration table Diodes normally have negative temperature coefficients e Use a different value than 1 0000 so that you can scale an existing table This 1s most commonly done with platinum sensors For example a standard calibration curve can be entered for a 2130 platinum sensor 2130 at 0 C by entering the calibration curve for a standard 1000 sensor and a multiplier of 2 130 Description selection Use th
66. e down arrow cursor key to select Description and enter any desired identifier from the numeric keypad Alpha numeric descriptions are allowed but must be entered from a computer using either interface port see Appendix A The LTC 21 does not check to see if the selected identifier is unique Existing tables are not overwritten even if they have the same identifier This can result in multiple tables having the same identifier Optional Entry Of Calibration Table If you do not wish to enter a calibration table Press SETUP CONTROL MONITOR or EXIT to leave this display and save the sensor configuration IF you wish to enter a calibration table position the cursor key to the Edit Cal Table and push ENTER You will be in the Calibration Table View Edit Menu Calibration Table View Edit Menu Description user Entry Kelvin Volts 0 999 9902 0 0000V 1 0 0000 1 Figure 22 Sensor Calibration Edit View Screen Use the cursor keys and numeric keypad to enter the calibration table You must observe the following conventions e All sensor entries must be in the units shown at the top of the columns All temperatures must be in Kelvin You must convert your data to Kelvin and NEOCERA Instrument and Systems Group Page 45 Model LTC 21 Cryogenic Temperature Controller the displayed sensor units before proceeding to enter the data in the calibration table You may enter the table with sensor units in any order Upon exiting the
67. e used with Carbon Germanium and other resistive sensors Using this constant voltage excitation the power dissipated in the sensor is kept at very low levels minimizing any self heating at low temperatures high resistances There are 7 constant voltage excitation outputs in the LTC 21 10 0mV 3 0mV 1 0mV 320uUV 100UV 32uV and 10u4V peak to peak This feature enables the instrument to measure resistances from 1Q to 1 MQ with very low power dissipation Calibration Curves Standard calibration curves are stored for several sensor types supplied by the major cryogenic sensor manufacturers including LakeShore Cryotronics Scientific Instruments and CryoCal Up to 16 additional user defined curves may also be entered into non volatile memory There may be up to 149 points per table and they are easily entered from the front panel or downloaded over one of the two remote interfaces The standard tables supplied can be easily modified to adjust for one or two or three point calibrations of your actual sensor Dual Heater Outputs The LTC 21 has two standard outputs A 50 Watt heater and an Analog Output Each of the two input channels may be configured to control either heater output The 50 Watt heater is a Constant Current Source type that can output up to 1 0A at up to 50V Constant current is used to ensure that the port is short circuit protected When used with a 50W heater element the corresponding maximum output power wi
68. eay o rt as inte s 6 Ss a e BO 100 Appendix B EEE 488 2 Example Programs o ooooooooo o L03 NEOCERA Instrument and Systems Group Page ix Model LTC 21 Cryogenic Temperature Controller Appendix C Interface Connector PinoutS ooooooo o 107 ROA MS 2 A A A AS A PORE DEE 107 SENSO rS Hs A A a A aren ae 107 Analog OUTPUT SD oases a di a a EAR ee dd la a 110 HOGS LL ta A A ARS A RA ype aR 110 Appendix Ds Application Notes se lt 5 tees ni She ir aa 111 Procedure to interface with LTC 21 using Windows 3 1 TELMO A 111 Procedure to Transfer Datalogged data to PC using PROCOMM LEO DO Sissi ca sa dr a wares a a is as LY NDEX da a ek Bere eee A A A A A a e 119 Page x NEOCERA Instrument and Systems Group Model L TC 21 Cryogenic Temperature Controller Table of Tables Table 1 Sensor Accuracy vs Sensor Excitation 8 Table 2 Ac FUSING arsed rake a eee ME Dae eae o Ee Dam 15 Table 3 Conditions for Linear Operation of Heater 16 Table 4 ETC 2L S upported Sensors asar bide ae ETRY eae aS oak 33 Table 5 Output CONETOUFAtTOM OPELONS woi eh ee eee ek eee es wks 34 Pablie 6 PTD MOdES sles eid are tad spe eda eed aye Sed aha eee a 36 Table 7 Misc Menu Selections ooo
69. ed dangerous high voltages are present near the power entry module the ac power transformers and in the heater section of the motherboard Use extreme caution to avoid these areas 10 1 Display Contrast Adjustment The contrast of the front panel LCD display is adjusted by the POT R14 which is located on the controller circuit board near the display connector Adjust R14 for maximum readability on the display There is no brightness adjustment 10 2 Backdoor Modes 10 2 1 Clearing Non V olatile RAM Clearing the non volatile RAM in the LTC 21 will erase all user entered data and re set the instrument to factory supplied default values After the Clear operation is executed the state of the instrument will be e Sensor Calibration data ADC offset and gain for the instrument will NOT be affected This is only changed by recalibration of the LTC 21 e All user calibration tables will be erased Only ROM based calibration tables will be available until user tables are entered e PID tables Alarm limits Relay limits etc will all be set to factory defaults e Sensor units for both channels will be set to Kelvin Sensor type will be set to LakeShore 10 diodes Remote interface will be set to IEEE To clear the non volatile RAM follow this procedure e Turn power to the LTC 21 OFF e Press and hold the CLEAR button of the LTC 21 while turning power ON NEOCERA Instrument and Systems Group Page 67 Model LTC 21 Cryogenic Temper
70. emperature on a chart recorder or computer select your best estimate for the PID coefficients and watch the output as the system comes to equilibrium at the setpoint If you are fortunate the output will be stable at the desired temperature If not observe the period and amplitude of any oscillations that occur Then change the setpoint and observe the temperature as it tries to reach the new setpoint It should quickly come to the new setpoint with no more than a few overshoots on either side If not observe the amplitude of each overshoot and the rate that they decay if at all All the information you need to set the PID coefficients can be obtained from simple measurements exactly like these The following sections give hints as to how to use this data to select PID coefficients The P term is an arbitrary gain factor which can be chosen to have any value between 0 1 and 1000 Typical systems will operate with a gain of 10 If the gain you used was too high the system will oscillate If it is too low it will be slow to respond Since incorrect values of the I and D terms can cause oscillations that appear similar to too high gain it is best to first select values for the I and D terms see below and then adjust the gain To select your first guess for the P term and to gather information needed to select the I term you should turn up the P gain slowly until the system begins to oscillate To do this use the PID mode with I and D both s
71. er specifies everything needed to bias the sensor and correctly read its value in fundamental sensor units Ohms Volts or LogOhms The optional calibration table is used to convert the fundamental units into temperature Each calibration table accommodates up to 149 calibration points 5 3 11 Entering a New Sensor Table Entering a new sensor is a simple straightforward process that can be done entirely from the front panel It can also be done via either interface port as described in Appendix A Sensor Parameters Sensor Type R1 0M ac Voltage Bias 3 mv Cal Table Units LogOhms Multiplier 1 000 Description CGR 2 5 300K Edit Cal Table Figure 21 Sensor Parameters Screen Sensor Type selection The Sensor Type field allows the user to select the bias technique and algorithm used to measure and calculate temperature Use the INC or DEC key to select the Sensor type that most closely resembles the characteristics of the sensor you desire to use Sensor type selections are Diode 2V Diode 6V R250 DC R2500 DC R1 0 Page 42 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller AC Menu selections Diode 2V Diode 6V R250 DC R2500 DC bias the sensors with constant de current R1 0M AC biases the sensors at a constant voltage which can be selected by the user AC bias voltage choices are 10mV 3mV 1mV 320 uV 100 uV
72. es an AMP 9 pin connector The mating plug is AMP 211400 1 Connector face view with pin assignments are shown below pins 3 7 are unused Signal Name Color Code ee a IRAI Page 110 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller Table 30 Heater Connector Pin out Appendix D Application Notes Procedure to interface with LTC 21 using Windows 3 1 Terminal LTC 21 Setup 1 Turn on LTC 21 2 Select SETUP MISC REMOTE INTERFACE 3 Toggle Remote VO Selection to RS232 4 Select Baud rate 9600 is the default Baud rates greater than 9600 may not work with Windows 3 xx 5 EXIT EXIT Make sure the RS232 cable is connected between the PC and the LTC On your PC run Windows 3 xx and then select the Terminal program Terminal exe From the Terminal menu make the following selections Settings Communications to AUS NEOCERA Instrument and Systems Group Page 111 Model LTC 21 Cryogenic Temperature Controller Data Bits Parity None Flow Control Xon Xoff Connections Com1 Com2 Table 31 RS 232 Settings Terminal Preferences to Terminal Modes Local Echo Terminal Emulation select DEC VT 100 ANSI Text Transfers select either One Line at a time or One Character at a time When you finish you may save your settings to a file by selecting File Save As and a file name the next time you run Terminal from Windows just open this file to have all your settings r
73. estored If the LTC is powered on and the RS232 cable is connected to LTC from the proper COM port your PC should be ready to communicate with the LTC Start by typing in OPC Do not use any backspaces or tabs or the parser will interpret them as characters and flag an error if the LTC emits a beep it has encountered an error The Terminal program should display the response Page 112 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller 1 followed by a carriage return If this doesn t happen try a few more times Remember back spaces and tabs should not be used You may need to enter CES to clear the system buffers If you are not receiving any characters from the LTC check the cable connections and COM port settings Once you have established a connection try the following query commands to see how the LTC responds IDN QPID 1 QSAMP 1 QUNIT 1 QISTATE QOUT 1 You can use the terminal program to download calibration tables to the LTC Create a txt file with the calibration table in the SCALT command format see appendix A or example below From the Terminal program menu select Transfers Send Text File and select the calibration text file Click OK to send the contents of your text file to the LTC NEOCERA Instrument and Systems Group Page 113 Model LTC 21 Cryogenic Temperature Controller If you create your text file in another program a spread
74. et a constant output power use PID with P I D 0 and 10 lt PO lt 90 2 SELECT AUTOTUNE OUTPUT CONFIGURATION After the system has OUTPUT SENSOR MODE MAX PWR stabilized simply select AUTOTUNE by selecting HEATER al 2CTOBID an one of the three Autotune ANALOG NONE Monitor Ramp choices AUTO_PID AUTO PI or AUTO P from the output configuration page HEATER P 150 I 25 D 6 PO0 0 0 This puts the system in the ANALOG GAIN 1 00 OFFSET 375 000K NEOCERA Instrument and Systems Group Page 55 Model LTC 21 Cryogenic Temperature Controller selected AUTOTUNE mode and displays this choice in the upper left hand corner of the main display page In most cases you will use the AUTO PID mode The LTC 21 will stay in this mode until another mode is selected 3 SELECT TUNING PARAMETERS After the Autotune selection the LTC 21 also provides two tuning parameters The first one is called system response time This 1s a thermal property of the system The sections are NORMAL SLOW and FAST The default is set to NORMAL If the system temperature response is extremely sensitive you may select FAST On the other hand if the system response to the heater is very slow you should select SLOW The second parameter is the Retune Interval It is set to 10 initially This parameter defines the interval measured by the setpoint deviation from the last Autotune temperature in Kelvin from which the system should update and do another Au
75. et to zero Then slowly select increasing values of P until the system oscillates Observe the oscillation period and then turn the gain back down until the oscillations are very small or disappear completely The I term is given in seconds its reciprocal is the angular frequency at which the integral term has gain equal to the P term The range of allowed values in the LTC 21 is 0 1 to NEOCERA Instrument and Systems Group Page 51 Model LTC 21 Cryogenic Temperature Controller 10 000 seconds The LTC 21 also recognizes I 0 as a special case which turns the integrator term off completely The purpose of the I term is to provide extremely high gain near dc This allows the temperature controller to regulate at the set point with negligible input error signal Note that to minimize the effect of the integrator the I term should be set to a large value or 0 to completely turn it off A typical cryogenic system will work with I 20 You can get a good estimate of the best value for the I term by observing the natural period of oscillation that occurs when the gain is too high Simply use the oscillation period TN observed with the P gain set too high see above and then select I 0 5 TN The D term is entered in seconds and its reciprocal is the angular frequency at which the D gain is equal to the P term The range of allowed values in the LTC 21 is from 0 to 1000 seconds Most systems work best with D I 4 To minimize the effect of the D
76. etermine the set point Related Commands SETP QHEAT QSTYPE Format OSTYPE lt 1 Sensor 1 or 2 Sensor 2 gt LTC 21 Response String of characters as the description of the sensor as given in the standard or user defined calibration tables Sensors Type Standard Cal Table po 2 Coapa O po 3 SHIN PS TG 20 E O 6 PT1000385 po 8 Prisa O pO _CalResi mwy ___ O Table 22 IEEE Standard Cal Table Sensor Type Indices Description Inquire the type of sensor for the specific sensor channel Related Commands SSTYPE Page 98 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller QTBL Format QTBL lt index 1 to 10 or 10 number of user Calibration table entries gt LTC 21 Response A string of 5 entries separated by Description Query the contents of the standard and user calibration tables pod EII RLOM AC Multiplier farne TT Sensor Description 110 19 bytes Mo Bees Voltage Bios string omv fv f iv TV UTN ee a A Table 23 IEEE Standard and User Tables Contents Related Commands SCALT QTOD Format QTOD LTC 21 Response One ASCII string of HH MM SS where HH is the Hour of day MM is the Minutes SS is the Seconds Description Queries the current time Related Commands STOD NEOCERA Instrument and Systems Group Page 99 Model LTC 21 Cryogenic Temperature Controller QTUNEP Format QTUNEP lt 1 System Response
77. etimes a small buffer will not confuse the issue Acquisition Mode field The two choices here are Oneshot and Cyclical Oneshot provides the data logging of the said total samples ONE time Cyclical provides continuous data collecting in a ring buffer You may setup the DATALOG to be collecting 100 data samples or you may set 1t up to Page 60 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller collect the last 100 data samples If the experiment need to run overnight Oneshot will save one buffer full of data Cyclical will save the last one buffer full of data The choice is yours Current Time field The system does not have a separate clock Each time after the system is powered up user needs to reset this field If this field is not set it will just use 00 00 00 as the starting time In entering Hour Minute Second you may use the two side arrow key to move from one field The Enter key will have the side effect of starting a NEW data log 8 3 Display Datalog Choosing DISPLAY DATALOG from the DISPLAY CONFIGURATION menu calls up the Data Log Display menu Data Logging Display 09 06 00 200 Samples 10 sec interval One Shot Time Sensor 1 Heater Power 09 05 30 27 987K 35 09 05 40 27 995K 35 09 05 50 27 987K 35 09 06 00 27 995K 34 UP DOWN cursor to scroll entries Figure 26 Datalog Display Screen For One Shot data log it collects the number of samples as specified and stop
78. etup Mode 28 NEOCERA Instrument and Systems Group Page 120 Model LTC 21 Cryogenic Temperature Controller Size 10 Software Revision number 49 Standard Event Status Register 76 91 T Table mode PID Table 36 Technical Support ii Transmit Buffer Overflow 91 101 U Unpacking 13 User Error Register 91 W WARRANTY iii Weight 10 NEOCERA Instrument and Systems Group Page 121
79. f the sensor e Integrator wind up correction is implemented so that rapid convergence is attained even with large changes in setpoint e To ensure accuracy all computations are performed in IEEE 751 32 bit floating point Output to the heater is done using a 16 bit DAC for 1 part in 65 000 Page 6 NEOCERA Instrument and Systems Group re Model LTC 21 Cryogenic Temperature Controller solution All loop variables including the set point are also in 32 bit floating point e High frequency damping is performed on the differentiator term so that effective use of this term can be allowed without instabilities caused by high frequency noise e Safety monitoring is implemented so that an open or shorted connection to the input sensor will be detected and will cause the control loop to be terminated and the heater to be turned off Heater Autotune Function The heater control has an Autotune function wherein the instrument will learn the thermal characteristics of the system under control then generate appropriate PID coefficients required to efficiently control it Analog Output A low orasa power analog output channel provided This output can be used as a linear output second heater for temperature control of low power systems Output voltage is 12 V with a maximum current of 100mA This is a voltage output and over current protection is NOT provided Therefore this output can be destroyed if connected to a low res
80. ffective technique that usually obtains excellent results even with difficult to regulate systems It is very unusual for the operator to be able to find better coefficients than are selected automatically Many systems can be regulated using the AUTOTUNE function that are nearly impossible to adjust manually even after hours of trial and error searching The autotuning algorithm used is a complex multi step process that checks for a wide variety of conditions which could cause problems in determining optimized PID coefficients The fundamental principles however are quite simple It begins with the system in a steady state condition constant power and temperature and applies a sequence of controlled changes in power Optimized coefficients are calculated based on the system s response to these changes Although the AUTOTUNE algorithm is extremely robust there are some systems for which it will work poorly or not at all These are almost always systems that have a large temperature dependent time delay before the thermometer responds to a change in heater power 7 2 AUTOTUNE Basics In order to begin using AUTOTUNE you must 1 STABILIZE THE SYSTEM The AUTOTUNE function must begin with the system in a steady state condition The output power and temperature must both be steady You can achieve this any way you want Usually the DEFAULT PID coefficients will stabilize the system if you wait long enough If this doesn t work you can s
81. hrenheit No sensor Volts or Ohms The units can also use lt 0 or 1 or 2 or 3 or 4 or 5 gt Related Commands QSUNIT Page 90 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller DCALT Format DCALT lt index gt LTC 21 Response None Description Deletes the user calibration table entry by index The index will be checked to be within the valid number of user calibration table entries created Related Commands SCALT QCALT QTBL QADDR Format QADDR LTC 21 Response One byte containing the GPIB address of the instrument The content will be between 0 and 31 inclusive Description Inquire about the current IEEE GPIB address setting for the instrument This number must be of the value between 0 to 31 decimal Related Commands SADDR QARTBL Format QARTBL lt 0 for Alarm Tables 1 for Relay Tables gt LTC 21 Response Two sets of three parts First byte is 0 if Armed 1 if disarmed Second character string is the High limit in 10 characters of number with unit for Volts or Ohms and third character string 1s the Low limit setting in 10 characters of number with unit for Volts or Ohms Description Request the Alarm or the Relay table settings Related Commands SARTBL NEOCERA Instrument and Systems Group Page 91 Model LTC 21 Cryogenic Temperature Controller QCALT Format QCALT LTC 21 Response One to two characters of the value of O to 16 Description
82. ic Temperature Controller SMON Format SMON LTC 21 Response None Description Monitor command This command places the instrument into the Monitor mode Temperature is continuously monitored but no heater control is applied This command will terminate the temperature control and Autotune functions if in progress Related Commands QISTATE SCONT STUNE SOSEN Format SOSEN lt 1 Heater 2 Analog gt lt 1 Sensor 1 2 Sensor 2 3 NONE gt LTC 21 Response None Description Assigns a sensor to source the HEATER or ANALOG output Related Commands QOUT SPID Format SPID lt 1 Heater 2 Analog gt and lt P Gain 1 1000 gt lt I Gain 1 10000 gt lt D Gain 1 1000 but not greater than I 2 gt lt PO Manual Percent term gt lt Power Limit Percentage gt for Heater or lt P Gain1 1000 gt lt I Gain1 10000 gt lt D Gain 1 1000 but not greater than 1 2 gt lt PO Manual Percent term gt lt Analog Out Gain gt lt Analog Out Offset gt for Analog Output LTC 21 Response None Description Loads a PID and Power Limit for the HEATER or PID and Gain amp Offset for ANALOG output when the Output control mode is set to PID mode Related Commands QPID SHCONT SACONT QOUT Page 86 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller SPTBL Format SPTBL lt PID Table Index 1 to 5 gt lt Set Point 1 gt lt P1 gt lt I1 gt lt D1 gt lt
83. iew Edit a Sensor Table Enter a New User Table Delete a User Table Select and Press ENTER to Change Item EXIT to Quit Figure 23 Sensor Cal Table Menu Screen 3 Select View Edit Sensor Table and press ENTER 4 Use the up and down cursor keys to select the desired sensor table Press ENTER 5 Use the up and down cursor keys to scroll the sensor data If this is a standard table you will only be able to view the data CAUTION If You Are Viewing A User Table Be Careful Not To Accidentally Change Any Entries You Should Read And Be Thoroughly Familiar With Section 5 4 12 Of This Manual Entering A New Sensor Table Before Changing Any Entries In The Sensor Table 6 Edit any selected entry by overwriting it with a new value entered from the numeric keyboard Delete each entry by entering 1 in the sensor unit column 7 Enter new values by adding the new entry at the end of the table Upon exiting the table the table will be sorted automatically 8 When you are done press EXIT SETUP CONTROL or MONITOR to exit and save this table 5 3 13 Deleting a User Table You may delete an entire user entered Sensor Data Table but it is not possible to delete a factory entered standard table To delete a user entered Sensor Data Table 1 Press SETUP select MISC and press ENTER NEOCERA Instrument and Systems Group Page 47 Model LTC 21 Cryogenic Temperature Controller 2 2 Select Sensor CAL Tables and press
84. imum Output Power 50 Watt Table 5 Output Configuration Options SENSOR Menu Field This field assigns the outputs to a particular SENSOR input The possible choices are 1 2 and NONE Either output may be assigned to either sensor Note that both outputs may be assigned to the same input This may be used for example to regulate temperature using the HEATER output while monitoring small fluctuations using the ANALOG output It is not possible or reasonable to assign both inputs to the same output MODE Menu Field This field determines the method used to calculate the output power current There are five basic methods MODEs used Auto PID PID Table Default and Monitor The MODE assigned to the heater is always displayed in the upper left hand corner of the Main Operating Display while the instrument is in CONTROL MODE PID Mode The PID mode provides direct operator control of all PID coefficients Correct selection of these terms is often difficult for cryogenic systems and may require substantial trial and error adjustment by the operator Chapter 6 provides useful information which may help in selecting these values Page 34 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller If the PID mode is selected the screen will display the currently used values for P L D and P OUTPUT PARAMETERS HEATER ANALOG P 150 P 50 wees Sec I bOSec D 6Sec DZ OSec PO 0 00 PO 0 00
85. is selected To select a new Table entry for the Heater output move the cursor to the Index field the number after the PID Table heading and use the numeric keypad to enter the new Index Press ENTER and then EXIT the menu in the usual way CAUTION The last Index selected before exiting the PID Table screen will be the PID Table selected Be sure to enter the proper index upon exiting the table To change the entries in the Table move the cursor to the desired field and enter the desired value from the numeric keypad Press ENTER and then EXIT the menu in the usual way NEOCERA Instrument and Systems Group Page 37 Model LTC 21 Cryogenic Temperature Controller Default If the Default mode is selected the LTC 21 displays and uses the following factory default values for PID coefficients Most systems can be regulated using these values but the response will be far from optimum The values were chosen to err on the side of stability rather than speed Monitor The Monitor mode is only applicable to the ANALOG Output The LTC 21 allows you to use the ANALOG output either as a low power heater output or as a temperature monitor port If Monitor is selected OUTPUT PARAMETERS of Analog Gain and Offset are assigned to this output rather than PID coefficients Gain determines the change in output voltage for a given temperature change Offset given in sensor units is used to Adjust the zero output point For example if a c
86. istance load that will require an excess of 100mA Connection to the analog output channel is made via a 4 pin connector on the back panel The connector housing provides a shield ground CAUTION When using the analog output as a heater output it is important to remember that at 0 power setting the output is not at 0 volts Dut can be as much as 100mV The anal external log output may also be used to drive a user provided power supply resulting in a heater output ranging from 30W to kWs Control Channel Configuration Each output Heater or Analog may be assigned to either input channel independently Therefore all combinations of monitoring one channel and controlling another are allowed If the Heater output and the Analog output are configured for temperature control the LTC 21 will maintain two completely separate control loops NEOCERA Instrument and Systems Group Page 7 Model LTC 21 Cryogenic Temperature Controller 1 2 2 Accuracy Specifications Display Sensor data may be displayed in units of Kelvin Fahrenheit Celsius Volts or Ohms e All displays are six digits plus sign a floating decimal point and a units indicator e Time averaging may be performed by operator selection of intervals between 0 5 and 16 Seconds Accuracy of Sensor Measurements The accuracy of linear resistance sensor measurements including Platinum Carbon Glass etc is 0 1 within the resistance range of 1000 to 1KQ
87. l take effect when the CONTROL mode button is pressed 5 2 3 Relays and Alarms in Monitor Mode Relays and Alarms remain active in the MONITOR mode To enable disable them or to change their high low limits press the SET UP key and follow the directions given in Section 5 4 9 When this is done the SETUP mode indicator LED will turn on Note that the MONITOR mode indicator LED remains lit while you do this indicating that the LTC 21 is still in the MONITOR mode with Relays Alarms and the Monitor function of the Analog output still active The LTC 21 will leave the MONITOR mode if some critical configuration parameters such as sensor type are changed In this case the MONITOR indicator LED will turn off relays alarms and analog output will be disabled 5 2 3 1 Control Mode Regulating Temperature With The LTC 21 The CONTROL mode regulates temperature and is identical to the MONITOR mode with the following exceptions e Heater output is enabled e Analog output is enabled regardless of its configuration NEOCERA Instrument and Systems Group Page 27 Model LTC 21 Cryogenic Temperature Controller Sensor 1 Sensor 2 348 782K 263 854C Set Point 350 000K Heater 23 of SW Push ENTER to Change SET POINT Figure 8 Control Mode Screen The Normal Operating Display shows the following additional information in the CONTROL mode e The Heater MODE is displayed in the upper left hand corner e The Heater power as
88. lay 2 Disarmed 271 000C 100 000C Figure 19 Alarm amp Relay Setup Screen Use the cursor keys in the usual way to select the item you want to change Alarm 1 and Relay 1 displayed in the first column of the Alarm and Relay Configuration Menu are always assigned to Sensor 1 Alarm 2 and Relay 2 are always assigned to Sensor 2 The Status of the alarms and relays is displayed in the second column Each alarm and relay may be separately armed enabled or disarmed disabled The High Lim and Low Lim columns of this display are used to change the set points Move the cursor to the limit you want to change enter the new value with the numeric keypad and press ENTER If the temperature exceeds High Lim or drops below Low Lim the internal audible alarm will sound continuously Likewise the relays will change state i e the normally open contacts will close if the temperature goes outside the selected limits The relays will remain in this state until the temperature returns inside the limits Each relay contact is rated at 0 5A 30V sms or 6OVpc with a non inductive load Pin assignments for the relay connector are given below Normally Closed Normally Open Table 8 Relay Connector Pin Assignment 5 3 9 Remote I O Config Select Remote I O Config from the MISC MENU to change the remote I O setups e g TEEE 488 bus address Detail on remote I O commands are described in Appendix A amp B Remote Input Output Configuration Remo
89. ll be 50W This output also has four user selectable ranges so that 50W 5W 0 5W or 0 05W may be selected as the maximum output power The second output is the Analog Output channel This is a voltage type output that can be configured as a monitor or as a low power heater In either case it will output a maximum of 12V at up to 100mA When used as a monitor the Analog Output can be connected to recording devices including chart recorders In this mode user specified offset and gain parameters are applied to input temperature data in order to generate an analog output voltage If the Analog Output is configured as a control heater PID coefficients are applied to generate the output voltage level Remote Control IEEE 488 and RS 232 Interface Ports The LTC 21 is designed for incorporation in automated systems using either IEEE 488 or RS 232 interface ports Both ports are supplied as standard features Full computer control of all front panel functions is possible Sensors readings and instrument status can be read remotely using either or both ports Page 2 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller Alarms Both channels have audible alarms with user programmable high and low limits Relay Outputs Relays are supplied on both channels with separately programmable high and low temperature set points They may be used to control external equipment based on temperature range Relay contacts
90. nd select new coefficients Page 56 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller Each Autotuning process will take a different amount of time depending on the thermal characteristic of each system The averaged time for each Autotune process is as below System Response Fast Normal Slow Time Selected Averaged Time for 1 5 minutes 5 minutes 12 minutes each AUTOTUNE Time out Exit Table 12 Autotune Process Time If an Autotune is unsuccessful 1t will time out and return to CONTROL mode with its PID values restored 7 3 Advanced Usage of AUTOTUNE Correcting Common Problems In most cases your system temperature will regulate tighter and faster using AUTOTUNE than with manually selected coefficients If it doesn t regulate well the following are the most likely causes of problems 1 The System Was Not At Equilibrium With Constant Temperature And Power Before Starting Autotune You can often get reasonably good coefficients even if the system is not stable when you start but failure to begin with the system stable is the most common cause of AUTOTUNE failure With difficult to tune systems it is sometimes helpful to try autotuning even if the system is not stable Even if the results are less than perfect you can use these coefficients to achieve a stable starting point for AUTOTUNE Simply exit AUTOTUNE go to MANUAL PID from the SETUP OUTPUTS menu and reenter AUTOTUNE again Th
91. ndard full width 19 inch rack mountable type that may be used either stand alone or incorporated in an instrument rack Bail An instrument bail is provided standard Size Enclosure size is 432mm wide x 89 mm high x 337mm deep 17 x3 5 x13 25 Rack Mount Use The Rack mounting accessory package contains two front panel angle brackets that can be used to attach the instrument into a rack Weight The LTC 21 weighs 7 1Kg 1 2 6 Power ac Power Requirements The instrument will require single phase ac power of 50 to 60 Hz Voltages are selectable at the power entry module for 100 120 or 220 240 Va tolerance 10 Power requirement is 126VA A low power cordset meeting the following minimum specifications is required for system operation North America Low power 10A max single phase NEMA terminations UL CSA approvals EC countries Low power 10A max single phase IEC 320 terminations VDE approval Instrument Fusing A user replaceable 5x20mm fuse is mounted in the power entry module This module also includes a spare Page 10 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller A 5 x 20 mm 4 Amp normal blow fuse is required for 100 and 120 Va configurations and a 5 x 20 mm IEC 127 1 6 Amp time lag fuse is required for 220 and 240 Va configurations Power Grounding Requirements The Ground wire on the ac line cord must be connected to a safety ground that does not normally
92. ne of them 3 4 3 Numeric Keypad The 12 keys on the numeric keypad are only used when a numeric entry is required Ifa numeric entry is not appropriate these keys are automatically disabled 3 4 4 BACKSPACE The BACKSPACE key erases the last character entered from the numeric keypad 3 4 5 CLEAR The CLEAR key erases the entire entry from the numeric keypad and allows you to start over 3 4 6 ENTER The ENTER key is used to terminate the entry of data from the keypad If you EXIT a menu without pressing ENTER the previous data is restored and the new entry is lost 3 4 7 EXIT The EXIT key will unconditionally move you back up one menu see Section 3 6 The Menu Tree Pressing EXIT does not cause an implied ENTER i e if data has been input but ENTER has not been pressed it may be lost when EXIT is pressed 3 5 Special Key Assignments Occasionally a key will be assigned a special usage other than that described above If this is done the display will always prompt the user and describe this special usage For example the ENTER key is used in the CONTROL and MONITOR modes to allow entry of a new temperature setpoint Page 20 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller 3 6 Menu Tree LTC 21 functions are represented by the following menus Monitor Mode Screen Power Up Screen Setpoint Screen Control Mode Screen Display Units
93. nel 1 2 4 Remote Interfaces IEEE 488 and RS 232 interfaces are both standard All functions and read outs available from the instrument may be completely controlled by either of the interfaces TEEE 488 Interface The IEEE 488 interface allows complete remote control of the instrument as well as the ability to read all temperature information to full internal accuracy The interface is compliant with IEEE Standard 488 1978 RS 232 Interface The RS 232 interface allows full operation of the instrument as does the IEEE 488 interface The baud rate is selected by the front panel 1 2 5 Mechanical Form Factors Front Panel The front panel including the display area is sealed membrane type panel with the following characteristics e Large Vulcanized silicon rubber tactile keypad e Super Twist LCD display with LED type dc backlight e Power Switch Rocker Switch NEOCERA Instrument and Systems Group Page 9 Model LTC 21 Cryogenic Temperature Controller Back Panel The back panel interfaces are listed below e TEEE 488 Interface connector e Heater Output connector Circular AMP 7 pin e 500 25Q Heater Selector Switch e Two Sensor Input Connectors Circular Lemo 4 pin e Analog Output Connector AMP 4 pin e RS 232 Connector DB 9 e Relay output connector Circular 8 pin e ac power entry module with fuse and voltage selector Enclosure The LTC 21 enclosure is a sta
94. nnector body On the sensor end of the cable the shield should be connected to a non current carrying earth ground whenever possible If no such ground is available the shield should be left disconnected Never connect a shield to a current carrying conductor While using a Platinum sensor th e polarity of the connection y IA Black A Ms terminals is not important White e I4 O o However when a Diode type ag I Green oo sensor is used the Anode must be Hed E connected to the positive terminal y Y Am and the Cathode must be A Shield connected to the negative terminal Figure 29 Platinum Sensor Four wire Example Diode Sensor Connection Connections The proper connection for a LakeShore DT 470 diode is shown to the right This connection may be used for the DT 470 DT 471 or DT 450 type diodes DT 470 Top View Figure 30 DT 470 Sensor Four wire Connection NEOCERA Instrument and Systems Group Page 109 Model LTC 21 Cryogenic Temperature Controller Many of the CryoCal Silicon Diodes have four color coded leads They are connected as follows Table 28 CryoCal Silicon Diodes Wire Color Codes Analog Output The Analog Output uses a AMP 4 pin connector The mating plug is AMP 206429 1 Connector face view with pin assignments are shown below Table 29 Analog Output Pin out Heater The Heater Output us
95. o enter CLS NEOCERA Instrument and Systems Group Page 117 Model LTC 21 Cryogenic Temperature Controller to clear the system buffers If you are not receiving any characters from the LTC check the cable connections and COM port settings You can use PROCOMM to upload information from the LTC If you use datalogging on the LTC you can save the LTC s stored data to disk Create a txt file containing the LTC datalog queries that will retrieve the data you need For example QDLB 1 QDLB 2 QDLB 3 QDLB299 Set up Log to file in PROCOMM ALT F10 will give you all the PROCOMM choices Select the Log Toggle ALT F1 Enter a filename where you would like to keep the datalog from the LTC Send file s over to LTC from PROCOMM ALT F10 again and select Receive Files by pressing Page Up key Select 7 for ASCII Then type in the file name of the txt file containing the Data Log Query commands Watch the data coming back from the LTC it should be in the format of XX xx xx datal data2 where xx xx xx is the time of date associated with each logged data Exit Procomm by pressing ALT X and Y Page 118 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller INDEX A AC Power 10 alarm 9y 20y 414 07y 75 gt 81y I2 104 Ambient Temperature Range 11 Analog Output 2 7 9 13 17 38 39 037 69 168 69 109 Analog to Digital 1 48 65 ANSI IEEE Std 488 2 1987 73 AUT
96. o into retune to obtain a new set of PID coefficients Any value less than 0 1 will always retune when a new setpoint is entered Related commands QTUNEP NEOCERA Instrument and Systems Group Page 89 Model LTC 21 Cryogenic Temperature Controller SUERREG Format SUERREG lt 1 Command Error Register 2 Execution Error Register gt lt Register setting gt LTC 21 Response None Description Sets the User Error Register enable bits The register value will be evaluated as a decimal number User Error registers are internal to the LTC The enable bits are normally set to zero When a particular error condition occurs if the enable bit for that condition is enabled the specific GPIB Standard Event Status Register bits will be set accordingly bit 5 of ESR for command bit 4 of ESR for Execution moppe pape LN LN Not Not Not Not Not Bad Parameter Unterminated Unknown Used Used Used Used Used Command Command Table 20 IEEE SUERREG Command Error Register Bit Definition mope pepe pepe a LS Not Not Not Transmit Buffer Parity Unknown GPIB Receive Buffer Transmit Buffer Used Used Used Overflow Error Error Overflow Under flow Table 21 IEEE SUERREG Execution Error Register Bit Definition Related Commands QUERREG ESE ESE ESR SUNIT Format SUNIT lt 1 Sensor 1 or 2 Sensor 2 gt lt K or C or F or N or V or O gt LTC 21 Response None Description Sets the sensor channel display unit to Kelvin Celsius Fa
97. ontroller WARRANTY NEOCERA Limited Warranty NEOCERA Inc warrants this product for a period of twelve 12 months from date of original shipment to the customer Any part found to be defective in material or workmanship during the warranty period will be repaired or replaced without charge to the owner Prior to returning the instrument for repair authorization must be obtained from NEOCERA Inc or an authorized NEOCERA service agent All repairs will be warranted for only the remaining portion of the original warranty plus the time between receipt of the instrument at NEOCERA and its return to the owner This warranty is limited to NEOCERA S products that are purchased directly from NEOCERA its OEM suppliers or its authorized sales representatives It does not apply to damage caused by accident misuse fire flood or acts of God or from failure to properly install operate or maintain the product in accordance with the printed instructions provided This Warranty Is In Lieu Of Any Other Warranties Expressed Or Implied Including Merchantability Or Fitness For Purpose Which Are Expressly Excluded The Owner Agrees That NEOCERA S Liability With Respect To This Product Shall Be As Set Forth In This Warranty And Incidental Or Consequential Damages Are Expressly Excluded NEOCERA Instrument and Systems Group Page iii Model LTC 21 Cryogenic Temperature Controller Warnings WARNING TO PREVENT SHOCK AND FIRE HAZARDS AS WELL
98. ood idea to go through all selections from left to right on this menu to display select and verify all the possible choices NEOCERA Instrument and Systems Group Page 29 Model LTC 21 Cryogenic Temperature Controller 5 3 3 Display Configuration Menu Choosing DISPLAY from the INSTRUMENT SETUP SELECTION Menu calls up the DISPLAY CONFIGURATION menu DISPLAY CONFIGURATION SETUP DISPLAY UNITS SETUP INPUT FILTER SETUP DATA LOG DISPLAY DATA LOG Select and Press ENTER to Change Item EXIT to Quit Figure 10 Display Configuration Screen 5 3 4 Set Display Units Menu Choosing SETUP DISPLAY UNITS from the DISPLAY CONFIGURATION Menu calls up the SETUP DISPLAY UNITS menu Use the cursor keys to choose the desired SENSOR and then select the desired units using the INC and DEC keys Return to any operating mode by pressing the appropriate front panel button or return to the INSTRUMENT SETUP SELECTION menu using EXIT SET DISPLAY UNITS SENSOR 1 2 UNITS Kelvin Celsius Figure 11 Display Units Screen Note that it is possible to select units that are not appropriate for the currently assigned sensor e g Ohms can be selected for diode sensors and Kelvin can be selected for uncalibrated sensors This is done to simplify entry of data for new sensors It is left to the operator to assure that the selected units are appropriate for the sensor The Effects of Changing Display Units Changing display units has a global effect on all
99. oooooooooooooooooooooo 40 Table 8 Relay Connector Pin Assignment oo oooooooooo o 41 Table 9 Excitation Accuracy Resistance Range 46 43 Table 10 Sensor Type Selection ws tense psi bene See be we eS 44 Babe Ti Cal Table WIS atada a ao ee et Wise case Bean eee OA 44 Table 12 Autotune Process TAME sus weoses we sie as Be ee Matera be we aes FF Table 13 Datalog Configuration Selections 60 Table 14 IEEE Remote Interface Commands o oooooooooooo 75 Table 15 IEEE Analog Output Channel Control Information 80 Table 16 IEEE Sensor Calibration Selections 81 Table 17 IEEE Heater Output Channel Control Mode Selection 84 Table 18 IEEE Maximum Heater Output Selection 85 Table 19 TEEE Sensor Type Selection smuisomidnana e 88 Table 20 IEEE SUERREG Command Error Register Bit Definition 90 Table 21 IEEE SUERREG Execution Error Register Bit Definition90 Table 22 IEEE Standard Cal Table Sensor Type Indices 98 Table 23 IEEE Standard and User Tables Contents 99 Table 24 QUERREG Command Error Register Bit Definition 100 Table 25 QUERREG Execution Error Register Bit Definition 100 Table 26 Relay Connector Pin 0Ut oooooooooooooooooooo o 107 Table 27 Sensor Connector PIRN SOUE Leitte weet nh a ete 109 Table 28 CryoCal M Silicon Diodes Wire Color Codes 110 Tabhe A9 Analog Out PU PIRSOUE 2100 A A AA 110 Pable 30 Heater Connector BIN
100. ored data to disk Create a txt file containing the LTC datalog queries that will retrieve the data you need For example QDLB 1 QDLB 2 QDLB 3 QDLB 148 From the Terminal program menu select Transfers Send Text File and select the text file you just created Click OK to send the contents of your text file to the LTC Terminal will receive the responses from the LTC which can then be copied and pasted to the NEOCERA Instrument and Systems Group Page 115 Model LTC 21 Cryogenic Temperature Controller Windows Clipboard Once copied to the clipboard your data can be read into another application like Excel or another spreadsheet program Page 116 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller Procedure to Transfer Datalogged data to PC using PROCOMM for DOS LTC 21 Setup 1 Turn on LTC 21 2 Select SETUP MISC REMOTE INTERFACE 3 Toggle Remote VO Selection to RS232 4 Select Baud rate 9600 is the default 5 EXIT EXIT Make sure the RS232 cable is connected between the PC and the LTC On your PC run PROCOMM from the DOS prompt Set up PROCOMM ALT P setup the line settings 20 is for COM1 21 is for COM2 11 is for 9600 N 8 1 ESC will come back to PROCOMM Test the communication by entering OPC The response should be the character 1 followed by a carriage return If this doesn t happen try a few more times Remember back spaces and tabs should not be used You may need t
101. ormat SDLM lt 0 Oneshot gt lt 1 Cyclical gt LTC 21 Response None Description Sets the Datalog Acquisition mode selection Related Commands QDLC SDLC SDLS SDLI SDLT SDLS Format SDLS lt 4 to 500 gt LTC 21 Response None Description Sets the Datalog buffer size Related Commands QDLC SDLC SDLI SDLM SDLT SDLT Format SDLI lt 0 stop datalog 1 start datalog gt LTC 21 Response None Description Sets the Datalog Interval selection Related Commands QDLC SDLC SDLS SDLM SDLT SDUR Format SDUR lt 0 0 5 sec 1 1 sec 2 2 sec 3 4 sec 4 8 sec 5 16 sec gt LTC 21 Response None Description Sets the Input Filter Time Constant or Display Update Rate index Related Commands QDUR NEOCERA Instrument and Systems Group Page 83 Model LTC 21 Cryogenic Temperature Controller SETP Format SETP lt 1 HEATER 2 ANALOG gt lt setpoint in specified unit gt LTC 21 Response None Description Loads a set point for the Heater or Analog output Related Commands QSETP SHCONT Format SHCONT lt 0 AUTO P 1 AUTOPI 2 AUTOPID 3 MAN 4 TABLE 5 DEFAULT gt LTC 21 Response None Description Sets the Heater output channel Control Mode selection Output Index Control Heater 0 AUTOP po po AUTOPID o 3 PD maa po TABLE lo S DEFAULT Table 17 IEEE Heater Output Channel Control Mode Selection Related Commands QOUT QHMXP
102. r 128 through 191 Description The Service Request Enable query requests for the Service Request Enable Register content The content are defined by the IEEE 488 2 1987 document Related Commands SRE STB Format STB LTC 21 Response One byte value range from 0 through 63 or 128 through 191 Description The Read Status Byte query requests for the Status Byte Register content The content are defined by the IEEE 488 2 1987 document Related Commands CLS ESE ESR SRE SRE NEOCERA Instrument and Systems Group Page 79 Model LTC 21 Cryogenic Temperature Controller LTC 21 Commands Reference SACONT Format SACONT lt 3 PID 4 TABLE 5 DEFAULT 6 MONITOR gt LTC 21 Response None Description Sets the Analog output channel s control information Output Index Control po ps TABLE o 5 DEFAULT 6 MONTOR Table 15 IEEE Analog Output Channel Control Information Related Commands QOUT SADDR Format SADDR lt 0 31 or 232 gt LTC 21 Response None Description Set the IEEE GPIB address for the instrument This number must be a value from 0 to 31 The system default is 15 To set the instrument to RS232 SADDR 232 will do the initial switch from IEEE to RS232 Baud rate is assumed to be 9600 Related Commands QADDR SARTBL Format SARTBL lt 1 Sensor 1 2 Sensor 2 gt lt 0 Alarm 1 Relay gt lt 0 Armed 1 Disarmed gt lt Hi limit gt lt Lo Limit gt LTC
103. r to Section 5 4 6 5 2 2 Changing the SET POINT The temperature SET POINT row of the Normal Operating Display will not be shown in the MONITOR mode since the heaters are disabled Nevertheless it is possible to change the stored SET POINT for both sensors by pressing ENTER to bring up the HEATER SETPOINT SELECTION display The Heater Set Point Display is a multi functional display showing most of the information regarding temperature control The Heater and Analog set points are displayed in the center column of the screen The actual temperature of the sensor assigned to the particular heater is displayed just to the right of the setpoints Below the heater information the heater mode selection PID Auto PID etc and actual heater power of range is displayed The bottom of the screen displays the P I D and PO values in effect for the Heater and Analog set points Page 26 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller Heater Set Point Selection Heater Set Point 325 00K 305 000K Analog Set Point 315 00K 300 000K AUTO PID 46 of 0 5 W Heater P 50 I 235 1D 76 PO 0 0 Analog GAIN 1 00 OFFSET 1 00 Press EXIT to return Figure 7 Setpoint Screen To change to SETPOINT move the cursor to the desired SETPOINT and use the numeric keypad to enter new values Press ENTER to confirm the new entries Press EXIT to return to the Main Operating Display The new SET POINT wil
104. roller chip set 9 2 Operation During normal operation the interrupt timer within the LTC 21 s micro controller is set to a period of 62 5ms Upon each interrupt the following sequence occurs The Analog to Digital converter ports from all sensor channels are read via the high speed serial port Conversion to temperature is performed based on the units selected for each channel as required If the instrument is in CONTROL mode an enhanced PID algorithm is applied to the temperature data in order to generate both the Heater and Analog Output values Control voltages are output to both output port Digital to Analog converters Note that the display averaging function averages temperature for display purposes only It does not affect the sample rate of the loop itself NEOCERA Instrument and Systems Group Page 65 Model LTC 21 Cryogenic Temperature Controller Page 66 NEOCERA Instrument and Systems Group Chapter 10 Adjustments and Calibration 10 Instrument Adjustments Self Test and Calibration Procedures The following sections describe calibration procedures for the LTC 21 These procedures require the adjustment of trimpots on the controller s motherboard More detailed calibration notes included in the Neocera Temperature Controller Calibration Guide outline the installation of calibration values in the software using the INSTRUMENT RECALIBRATE menu Please note that when the top cover of the LTC 21 has been remov
105. s The data presented is in the logged data order It will enter the Data Logging Display to show the last four samples of data Users may use the UP DOWN cursor to see other data It will not pass the last logged data For Cyclical data log it continuously collects data into the buffer The data is presented in the same logged data order with the exception of also allowing the user to traverse through the who data buffer Each time when entering into the Data Log Display menu it will always position to see the latest logged data Users may traverse forward and backward using the UP DOWN cursor While in the Data Log Display menu user may use the CLEAR key to abort any data logging session The data in the buffer are not cleared The time of data field and new data log entries are not automatically updated User should use the UP DOWN cursor to see the update This enables the user to copy down the data values NEOCERA Instrument and Systems Group Page 61 Model LTC 21 Cryogenic Temperature Controller Page 62 NEOCERA Instrument and Systems Group Chapter 9 LTC 21 Functional Description 9 Model LTC 21 Functional Description 9 1 Block Diagram A block diagram of the LTC 21 is shown below Analog Output A Heater 4 Crystal a Sensor 1 Micro gt RS 232 Interface e High Speed gt Controller Sensor
106. sheet for instance be sure to strip out any tab characters the program may use If your calibration table has more than a few temperature voltage pairs you may need to send the table in smaller sections to avoid overflowing the LTC s input buffer A user defined calibration table might appear as follows SCALT0 0 0 Custom Diode 1 0 475 0 09062 470 0 10191 460 0 12547 440 0 17464 380 0 32416 340 0 42221 290 0 54294 240 0 66208 210 0 73238 180 0 80138 150 0 86873 131 38 0 912 106 56 0 95487 86 058 0 99565 75 876 1 01525 61 26628 1 04353 48 475 1 07053 31 46527 1 0949 27 70204 1 10263 26 16111 1 10945 Page 114 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller 25 684 1 11517 25 47 1 11896 25 03143 1 12463 24 165 1 13598 20 08429 1 2144 14 72065 1 31403 11 72 1 38021 9 236535 1 45048 3 4 1 65134 1 8 1 69177 After downloading the table type in the command QCALT This will return the number of user tables currently stored in the LTC You can use this command before and after your download to ensure your table downloaded properly Any modifications to the header information in the user loaded calibration table can easily be made from the LTC front panel under Misc View amp Edit Calibration Table selection You can also use the Terminal program to upload information from the LTC If you use datalogging on the LTC you can save the LTC s st
107. sis oe 5S ok oe ES ae we eee ae 18 2 Ps Interface CONNECELON ssas 6 8 ets dee ewes de ee es 18 2 28 Mounting The DTCZ Desne syed eee A os 18 Su OD Cele OM ats o a Ss ts ae A oo Or GO aaa 19 Seda USE OF ENE MOKREY DOA drid Dd ii BS hee 19 2 AHO Allis KEY Gass eva ea Bed GARE OE EON ENCE OO 19 323 FUNCTION K YS on 44 004468 da Sa we Dae ee ee la a 19 33 li CONTROL a de ia 19 Sedaaa MONTTOR Lo Se A eee BH a 19 SB SETUP aa bea 6 rs da ac de Oe 19 3d DATA ENTER KEV Sa A A A da 19 SSA VOUS GO KO a Se ae 19 3 4 2 INC Increment and DEC Decrement Keys 19 Subs Numerio Key PAG ss e406 8 dal a ae ii ta ta 20 Page vi NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller Sis BAGCKSPAGCEH un Su Siete hee ee et eS eee ees 20 SiGe Sie IGMBAR ds si etd a ee doers aod e Reda ere ds 20 A ENTER O URRE DE 20 SN da A BA he a RAL A ia ee 20 Sede Special Key ASSUONMENES sirtyi wh de ii 20 3z Ge Menu TRECY oi Saige oe cote ae atid Be a aie A 21 4 Initial Power Up Sequence And Display 23 De Operating MODES uss duster Sack oe a See eee Seles eee ee ele wee 25 5 1 Introduction To The Thr Operating Modes 25 5 2 Monitor Mode Monitoring Temperature With The LLC gale Ne pea sh ee ot oats are ae ence Ge Sree EE alent y ati oe 25 5 2 1 Using the Monitor Mode 25 5 2
108. sor the LTC 21 will always leave the Control mode to prevent dangerous operating conditions After selecting the desired sensor press EXIT MONITOR or CONTROL to enter the sensor and exit the display 5 3 7 Output Configuration Menu Introduction to Configuring the Outputs Choosing OUTPUTS from the INSTRUMENT SETUP SELECTION menu displays the OUTPUT CONFIGURATION menu used to assign and configure the HEATER and ANALOG outputs OUTPUT CONFIGURATION OUTPUT SENSOR MODE MAX PWR HEATER 1 PID SW ANALOG NONE Monitor Ramp HEATER P 150 I 25 D 6 PO 0 0 ANALOG GAIN 1 000 OFFSET 375 000K Figure 14 Output Configuration Screen NEOCERA Instrument and Systems Group Page 33 Model LTC 21 Cryogenic Temperature Controller As usual use the cursor keys to select the menu field you want to change and the INC and DEC keys to scroll through the choices for that field The options available are summarized below ooo pe Assigns the selected OUTPUT to SENSOR 2 NONE Disablestheselected OUTPUT pC AUTOPI ___AutoTuned Proportional and integral gain o AUTOPID AutoTuned Full PID settings o O o ppm oo Tabe PIDcoefficientsselected from stored data Default FactorydefaultPID coefficients Monitor Analogoutputused for temperature monitor Turns off the Heater 005 W Sets Maximum Output Power 0 05 Watt po Osw Sets Maximum Output Power 0 5 Watt o SW Sets Maximum Output Power 5Watt po SOW Sets Max
109. switch is provided on the rear panel of the instrument to select between 50Q and 250 heater resistors When the 250 heater is selected the power range can be determined by dividing the displayed range by 2 The following ranges are available in the 25Q mode 0 025W 0 25W 2 5W 25W Heater Element aay Guard Figure 2 Heater Connection Connection to the heater channel is provided by a 9 pin high power connector mounted on the back panel of the instrument Pins provide power power return and a shield ground Set Point Resolution Setpoints in the LTC 21 are maintained as 32 bit floating point numbers ensuring at least six digit resolution Heater Feedback Type The heater control algorithm is an enhanced digital PID type The sample rate of the loop is 16 Hz so that sample rate aliasing is prevented Enhancements to the standard PID control are e Loop output is converted into units of power unlike most PID loops which output in volts or amperes Therefore the loop is linear with respect to the process variable ensuring faster settling and better regulation This is very important in cryogenic systems where the thermal load varies significantly with changes in temperature e Sensor inputs are converted to temperature first then used to update the control loop Therefore the gain of the loop is a constant and is independent from any non linear characteristics o
110. system being controlled For optimum PID control the best value for the Input Filter Time is about one tenth of the Integrator time This will provide the maximum noise rejection while still ensuring responsiveness and control stability Smaller values may be used with relatively quiet systems or systems where the Derivative term is not used Larger values of Input Filter Time are not recommended 5 3 5 Datalog Refer to Chapter 8 for a discussion of the Datalog feature 5 3 6 Sensor Configuration Menu Choosing SENSORS from the INSTRUMENT SETUP SELECTION menu calls up the SENSOR CONFIGURATION menu used to specify the sensors connected to the inputs SENSOR CONFIGURATION DESCRIPTION SENSOR 1 LS DIODE 10 SENSOR 2 PT 100 392 Press EXIT to quit Figure 13 Sensor Configuration Screen Use the cursor keys to move to the desired SENSOR which refers to the SENSOR INPUT labeled on the rear panel Select the sensor type connected to this input using the INC increment and DEC decrement keys The types of sensors presented may vary from instrument to instrument depending on configuration Page 32 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller The Model LTC 21 will present the following choices for sensors in the Sensors Menu 1000 Platinum European Std 3852 at 100 C de 10042 Platinum American Std 3924 at 100 C de Table 4 LTC 21 Supported Sensors When you select a new sen
111. system will sort the table into sensor units Ascending order If you have chosen LogOhms sensor units you must enter the log base 10 of the resistance in ohms i e 100 ohm is entered as 2 0000 All values must be in the following ranges 0 to 800 Kelvin for temperature 1Q to 9 999 MO for resistance 0 to 5 8 volt The last point in the table must be 1 in the sensor units column Note that the LTC 21 automatically enters this point for you The temperature value entered next to 1 is the value that will be displayed if your sensor reading exceeds the calibration table limit the value located above the 1 in the table If your sensor reading exceeds the table at the other end the display will show the temperature in Entry 0 in the table Enter no more than 149 data pairs in the table Edit the table by overwriting any entry Delete the entry by entering 1 in the sensor unit column When you are done press EXIT SETUP CONTROL or MONITOR to terminate table entry and store the values 5 3 12 Viewing and Editing a Sensor Table The procedure for viewing any Sensor Table is the same whether it is a user entered table or standard table However it is not possible to edit a standard table To View Edit a Table 1 Press SETUP select MISC and press ENTER 2 Select Sensor CAL Tables and press ENTER Page 46 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller Sensor Data Table Menu V
112. t and Systems Group Model LTC 21 Cryogenic putmsg QOUT 1 putmsg QOUT 2 putmsg SPID1 150 25 6 0 putmsg QPID 1 putmsg QSTYPE 1 putmsg SSTYPE1 4 putmsg QSTYPE 1 putmsg QSTYPE 2 putmsg SSTYPE2 2 putmsg QSTYPE 2 putmsg QUNIT 1 putmsg SUNIT2 F putmsg QUNIT 2 putmsg SMON printf n End of Test n Display DOS style date and time _strtime timebuf _strdate datebuf printf This GPIB test for LTC 20 is done on s s n n timebuf datebuf end main int init_TC_GPIB void initializes the TC box PC_handle ibfind GPIBO TC_handle ibfind DEV15 ibtmo TC_handle 11 int receive_TC char str int max_num_char int i ibrd TC_handle str max_num_char read string from TC put terminator on end of string str ibent MO end function receive_TC int send_TC char str int i j j 0 ibwrt TC_handle str strlen str write string to TC for i 1 i lt 15000 i NEOCERA Instrument and Systems Group Temperature Controller Page 105 Model LTC 21 Cryogenic Temperature Controller wait loop for Setting up Cal Tables j i j 1 3 counting fingers 1 2 3 end function send_TC void putmsg char str inti j j 9 ibwrt TC_handle str strlen str write string to TC for i 1 i lt 9000 i
113. te I O Selection TEEE 488 IEEE 488 Bus Address 15 RS232 Baud Rate 9600 RS232 Parity None RS232 Bits Per Word 8 Press EXIT to return NEOCERA Instrument and Systems Group Page 41 Model LTC 21 Cryogenic Temperature Controller Figure 20 Remote Input Output Configuration Screen The system is configured with IEEE 488 as default settings User can change to RS232 Only one of the two can be activated at one time Enter any desired IEEE 488 bus address between and 31 inclusive using the numeric keypad The LTC 21 supports RS 232 baud rates between 300 and 19 200 These are selected using the INC and DEC keys in the usual way RS232 is set to Parity None and Bits per word as 8 and cannot be changed The display is for informational use only Once an selection is made press EXIT to activate the change 5 3 10 Sensor CAL Tables All the information required to utilize any specific sensor is stored in non volatile memory in a Sensor CAL Table Two types of Tables are used One type has been loaded at the factory and can not be changed by the user These tables store standard calibration curves for 8 different resistive and diode sensors The other type of table is loaded by the user and can accommodate nearly any type of cryogenic sensor manufactured Up to 16 user entered calibration tables may be entered Each Sensor CAL Table includes a mandatory header followed by an optional calibration table The mandatory head
114. term you should select a small value Never select values where D gt I 2 For your first guess select D 1 4 The PO term provides a fixed output power independent of sensor value Itis given as a percent of full scale power with 0 lt PO lt 100 and should usually be set to zero It is most commonly used by itself i e with P I D 0 in order to fix the output power at a selected level Unless you have a specific reason not to select PO 0 6 3 Fine Tuning the Coefficients The techniques described above should give you a reasonable estimate of the PID coefficients needed You can improve on these by making small changes to each coefficient separately and observing the systems response to a change in setpoint You need to be careful when interpreting these results since changing the P term will also change the effect of the I and D terms Vary all three terms individually and systematically by a small amount in both directions You should be very suspect of your combination of choices if you have either a an I term where 2 TN lt I or TN gt 8 I b a D term where D gt 0 4 I 6 4 Ramping The power generated by the LTC 21 s control loop can be expressed as C dT Power po estra E foo a p Page 52 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller where k is a constant having units of W K P is the proportional or gain coefficient dimensionless T and T are the c
115. tion between some of the entries Be sure not to use TAB characters in the SCALT command otherwise an error may occur Entry Name Sensor Type 0 2V Diode 1 6V Diode 2 R250 3 R2500 4 R1 0 mV Voltage Bias 0 10mV 3 320uV 4 100uV l Po ES 6 10V Cal Table 0 LogOhms 1 Ohms 2 Volts Units Sensor 1 to 19 Spaces will Description characters be eliminated Multiplier Anon zero 2 to 149 T K Volts Ohms Entries pairs terminator Table 16 IEEE Sensor Calibration Selections Related Commands QCALT QTBL NEOCERA Instrument and Systems Group Page 81 Model LTC 21 Cryogenic Temperature Controller SCONT Format SCONT LTC 21 Response None Description Control command This command sets the instrument to control mode Temperature monitor and heater control are both continuously applied in this mode Related Commands QISTATE SMON STUNE SDLC Format SDLC lt 1 Sensor 1 2 Sensor 2 3 Sensor 1 and Sensor 2 gt LTC 21 Response None Description Sets the Datalog channel selection Related Commands QDLC SDLI SDLS SDLM SDLLT SDLI Format SDLI lt 1 1 second 10 10 seconds 60 1 minute 300 5 minutes 600 10 minutes gt LTC 21 Response None Description Sets the Datalog Interval selection Related Commands QDLC SDLC SDLS SDLM SDLT Page 82 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller SDLM F
116. totune For example if the Autotune is done at 100K and a new setpoint of 105K is entered since it is less than 10 deviation from 100K the LTC 21 will not retune It will use the last set of PIDs from the autotuning process If a new setpoint of 112K is entered the system will however go into Autotune to obtain a new set of PIDs The range for this parameter is from 0 1 to 50 Any value entered less than 0 1 will be taken as 0 1 e always do another Autotune when the user entered a new setpoint This is handy when the user is experimenting with the Autotune process 4 SELECT A NEW 348 782K 263 854C TEMPERATURE csi Enter a new setpoint in Point 350 000K the usual way press ENTER while in the CONTROL mode By selecting a new temperature it will put the instrument into the Autotune motion The upper left corner of the display will blink TUNING to indicate the LTC 21 is in the process of determining PID coefficients TUNING Sensor 1 Sensor 2 Heater 23 of SW push ENTER to change SET POINT The LTC 21 will begin the Autotune algorithm and then proceed to regulate the system at the new set point using optimized coefficients It will continue to use these coefficients for small changes in the set point less than the Retune Interval percentage from the temperature in Kelvin where it originally selected these coefficients If a larger change in setpoint is made the system will go through the Autotune algorithm again a
117. ts Menu Table Tests of the front panel LEDs the Heater output and the Analog output may be performed using this menu Details of these testing procedures are given in Section 10 3 Self Tests Page 48 NEOCERA Instrument and Systems Group Model LTC 21 Cryogenic Temperature Controller The last line on the display shows the following information e The Model Number e The Software Revision number V5 2 shown NEOCERA Instrument and Systems Group Page 49 Model LTC 21 Cryogenic Temperature Controller Page 50 NEOCERA Instrument and Systems Group Chapter 6 PID Theory Tuning and Ramping Tips 6 PID Theory And Tuning Tips 6 1 The LTC 21 PID Mode The PID mode provides direct operator control of all PID coefficients Correct selection of these terms is often difficult for cryogenic systems and may require substantial trial and error adjustment by the operator If the PID mode is selected the screen will display the currently used values for P I D and PO The LTC 21 allows you to change any of the PID coefficients without interrupting temperature regulation Before trying to optimize your choice of PID coefficients it may be necessary to configure the Analog output as a Monitor port and connect a chart recorder to it or perform some type of data collection using a computer It is nearly impossible to get good results by simply observing the front panel display 6 2 Selecting Coefficients After you are prepared to monitor the t
118. up Model LTC 21 Cryogenic Temperature Controller Some users may want to use a 25Q heater and therefore a heater voltage switch is provided on the rear panel of the instrument to select between 5002 and 250 heater resistors When the 250 heater is selected the power range can be determined by dividing the displayed range by 2 The following ranges are avallable in the 25Q mode 0 025W 0 25W 2 5W 25W 2 4 3 Analog Output Comnection The Analog output port can be software configured as either a 1 W max output for temperature regulation or as a calibrated analog output for monitoring temperature The hardware connection is the same in either case The ground connection should only be used for shielded leads The low side of this output may be grounded when using it to monitor temperature but a differential measurement is usually preferred to avoid adding noise to the measurement The low side should not be grounded when using the Analog output for temperature regulation If this can not be avoided it is essential that the low side be grounded at one point only and that it not be connected in common with the sensors The type of wire used to connect to the Analog output is usually not critical Shielded twisted 24 gauge copper wire is commonly used inside the cryostat but the exact choice depends on thermal requirements and electrical noise in your cryostat 2 5 Sensor Connection Sensors can be attached to the two labeled
119. urrent and target temperatures in K set p t is the power output of the controller from over the last I seconds C is a constant units of watt I is the integral coefficient units of seconds D is the differential coefficient units of seconds The ramp rate is defined by R AT At where AT Tatia T a The integration time I in seconds corresponds to the system response time Because of this there will be an inherent thermal lag on the order of I Obviously it is unrealistic to set a ramp rate faster than the system can respond e g setting R 1 million K min For a ramp of rate R you can expect a temperature deviation both at the start and completion of the ramp on the order of T I R A good rule of thumb is to have AT I R gt gt 1 If you are ramping over a wide temperature range it may be worthwhile to use the TABLE rather than PID mode in the output configuration menu Obviously to get the best ramping performance it is best to predetermine the optimum PID coefficients using the AUTOTUNE mode NEOCERA Instrument and Systems Group Page 53 Model LTC 21 Cryogenic Temperature Controller Page 54 NEOCERA Instrument and Systems Group Chapter 7 Using Autotune 7 Using Autotune 7 1 Introduction The AUTOTUNE mode of the LTC 21 will select optimized PID coefficients to regulate the temperature of most cryogenic systems It is a highly e
120. vailable for Four wire V V Lae Guard connections to each sensor and the metal shell must be connected to the Figure 1 Four Wire Sensor Connection cable shield It is recommended that all sensors be connected using shielded dual twisted pair cable as shown Calibration Curves Eight calibration curves for various types of sensors are built into the LTC 21 Additionally 16 user curves with up to 149 points each may be input via the front panel or remote interface User calibration curves are stored in non volatile RAM and will be retained for a period of 10 years 1 2 1 Output Specifications Heater Output The heater output provides up to 1 Ampere at 50 Volts When using a 500 heater this corresponds to 50 Watts The heater output is a Constant Current Source drive and is short circuit protected Output current has a resolution of 0 1 There are four heater ranges to allow selection of a control range which closely matches system heat capacity They are e Zero to 50W e Zero to5W e Zero to 0 5W e Zero to 0 05W The LTC 21 heater is designed to have a load of 50Q and it is strongly recommended that this value of heater resistor be used The instrument assumes this load when displaying the heater power range on the front panel NEOCERA Instrument and Systems Group Page 5 Model LTC 21 Cryogenic Temperature Controller However some users may want to use a 25Q heater and therefore a heater voltage
121. will start a new session of DATALOG It will clear the buffer and start to log data Be sure to Save or analyze the previously logged data before pressing ENTER NEOCERA Instrument and Systems Group Page 59 Model LTC 21 Cryogenic Temperature Controller CAUTION The ENTER key in DATALOG configuration will start a new session of DATALOG It will clear the buffer and start to log data Be sure to save or analyze the previously logged data before pressing ENTER i seconds _ Collect data every 10 seconds pt minute Collectdataevery minute pT Sminutes Collect data every 5 minutes 10 minutes Collect data every 10 minutes Collect Sensor 1 data and heater power output ee power output Total 4 to 500 Buffer Size Samples Channel Acquisition Mode Acquire One buffer full of data Po Cyclical Continuous data collection Table 13 Datalog Configuration Selections Sample Interval field This field sets the sampling interval for each data log Every 1 10 60 300 600 seconds the system will save the data into the data memory Sensor Channel field User may choose to select sensor 1 2 or Both sensors For 1 or 2 the data collected will include current time of date data collected with the Display Units assigned and the Heater Power in percentage form Total Samples Channel field The internal buffer set aside is 500 data samples User may choose to set it to any value that 1s between 4 to 500 Som
122. y at which the D gain is equal to the P term The range of allowed values is from 0 to 1000 seconds Most systems work best with D 1 4 To minimize the effect of the D term you should select a small value NEOCERA Instrument and Systems Group Page 35 Model LTC 21 Cryogenic Temperature Controller The P term provides a fixed output power independent of sensor value It is given as a percent of full scale power with 0 lt P lt 100 and should usually be set to zero It is most commonly used by itself i e with P I D 0 in order to fix the output power at a selected level e7 Pwr Limit this is a safety setting for the SOW power range only The default setting from the factory 35 This is equivalent to 10W for the 50W Max Power range If user desires to have more than 10W for the 50W range simply increase the P term If the PO term is set to lt 100 and the heater is outputting at this limit the heater output percentage sign will blink to signal that it has reached the preset limit Auto PID Modes The Auto PID modes are used if you want the LTC 21 to automatically select PID coefficients Three such modes are available Auto PID Auto PI and Auto P Auto PID selects a complete set of proportional P integral I and derivative D coefficients Auto PI sets the derivative term to zero uses only proportional gain Table 6 PID Modes The use of these modes is described in detail in Chapter 7 TABLE mode

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