Model DTC-500 - Lake Shore Cryotronics, Inc.
Contents
1. 1 volt per step 100 mV per step and 10 turn interpolating potentiometer with 0 2 mV graduations 0 1 linearity 100 microvolts For a DT 500 at 4 2 K this represents 0 001 K 3 to 100 second variable time constant or off Manual Output Control Range 10 turn potentiometer control 0 to full current Full Scale Heater Current Ranges 10 mA 30 mA 100 mA 300 mA 1A Heater Resistance for Max Power 10 Ohms Controller Proportional Gain 1 Amp mV in automatic mode nominal Temperature Readout 2 Sensor connections front panel selectable between control sensor and temperature sensing only sensor Accuracy 150 microvolts 100 microvolts calibration error of sensor Excitation Current 10 microamperes 5 Excitation Current Regulation 0 05 Sensor Calibration Chart Must be supplied by manufacturer of sensor in use 1 4 Major Assemblies Supplied The Model DTC 500 Cryogenic Temperature Controller includes as standard equipment in addition to the controller proper the following additional components 1 1 Operating and Service Manual 2 2 Five pin plugs for temperature sensor cables 3 1 Seven pin plug for remote set point cable Temperature sensitive diodes are not supplied as part of the DTC 500 Controller 1 5 Accessory Equipment and Custom Options Available The following accessory equipment and custom options are available from the factory Items marked with an asterisk are of a cus2. 031108102 duflVHddWil 005 010 WVNOVIG 390T18 RUND I 17 81 yeqpesy 32000 5 3205905 1201220101011 001 4 pue 1 IO A 3ueiin 19289 0095 30 _ A Ne 989310A JUTOd 5 3 04 V uour I 123891 oanos 8 IS 2118 251105 14 programmed set point temp sample holder temp new set pi 5 temp E A initial set pt instantaneous temp error temp l time time of abrupt change in set pt temp programmed set point temp initial set p VG sample holder temp temp instantaneous temp error set pt temp time time of abrupt reduction in set pt temp FIGURE 3 4 TEMPERATURE VERSUS TIME CHARACTERISTICS OF CONTROLLER 15 After determining the set point voltage refer to the diode calibration chart to ascertain the diode temperature 3 5 Constant Temperature Control Mode Assume that a calibrated diode is in use as described in paragraph 3 4 To maintain a constant temperature determine the corresponding set point voltage from the diode calibration chart Set this voltage on the SET POINT switch and vernier Position controls as indicated below 1 Temperature set point switch Key No 19 to INTERNAL 2 Mode switch Key No 6 to AUTO A 3 MAN RESET Key No 7 to zero 4 MAX HEATER AMP Key No 8 to 1 0 AMP 5 GAIN Key No 4 to minimum setting 6 AUTO RESET Key No 5 to
3. FIGURE 4 1 SIMPLIFIED EQUIVALENT CIRCUIT OF AUTOMATIC RESET AMPLIFER 23 4 3 Detailed Description Regulated Power Supplies There are four regulated supply voltages in the instrument They are designated as P S 1 through P S 4 in Figure 5 1 a Reference Current Referring to Fig 5 1 power supply P S 1 and 11 provides 15 Volts DC to the operational amplifier constant current source as well as its current reference for 10 microamperes bias current b Diode Constant Current Supply Power supply P S 1 and operational amplifier Al constitute the main components in the diode constant current supply Due to the high input impedance of the operational amplifier Al the diode current is forced to flow through resistor R5 developing 4 99V at 10 microamperes The voltage across R5 is therefore equal to the voltage at the inverting input terminal of Al with a voltage of 4 99V applied to the non inverting input of Al by the reference circuit of R1 R2 R3 R4 and CRS The current through R5 4 99 K will maintain the regulated current through sensor to 10 microamperes The entire constant current supply system was designed to be fully floating so that the cathode of the sensor diode might be returned to common c Set Point Voltage Supply and Divider Floating power supply P S 2 preregulates the voltage used to supply reference diode CR 12 The doubly regulated voltage appearing between tie point TP 5 and the cathode of 08 12 is
4. OFF MIN MAX of integrator See Fig 3 3 Effectively determines time constant of integrator between 100 and 3 seconds MIN and MAX respectively 6 AUTO A MAN A Mode selector switch AUTO A uses MAN B sensor A to automatically control temperature MAN A disengages automatic control feature but permits readout of sensor A voltage MAN B permits readout of sensor B voltage NO KEY 7 10 11 12 13 14 15 16 17 18 19 Table 3 1 cont NAME MAN RESET MAX HEATER AMP POWER NO LABEL HEATER CURRENT NULL 115 230V 50 60 Hz LA S B NO LABEL 1 0A S B SENSOR A SENSOR B TEMP SET POINT INTERNAL REMOTE FUNCTION When mode selector switch 5 is in either MAN A or MAN B position the MAN RESET ten turn potentiometer permits the user to manually adjust the current to the heater element Caution High settings will quickly boil away cryogenic fluids Switch selected current limiter Use of a low setting will avoid inadvertent boil off in setting up system and or system oscillations A C line switch ON OFF A C line pilot light Meters heater element current Full scale deflection corresponds to MAX HEATER AMP switch 8 setting Indicates the difference between the set point voltage and the sensor output voltage Meter is non linear for large errors of either sign A C line voltage selector slide switch A C line fuse FUl
5. See para 2 3 A C line cord Heater element line fuse 1 AMP Slow Blow Sensor A cable receptacle Five pin Amphenol type 126 217 Plug Sensor B cable receptacle Five pin Amphenol type 126 217 Plug Selects between internal set point voltage divider and external divider for comparison with sensor voltage Front panel set point controls in operative when switch is in the REMOTE position Be sure this control is set on INTERNAL since its location on the rear panel may cause one to overlook its setting when initially checking out the instrument 10 SY en VE TT T3NVd LNOUA ZAJ A RZA E PRIV S NO Id EIS ea 2 SNS T 11 12 T3NVd 1 6 4 ZEE 0 4 TEST at New CE A Da Der Bran E 7 RZY 7 CZA 72717 A WHEE 1 CERY nat a RR lt S IA NN RI L SZ 2 a Eu PEE EU ER RENE ROH de AT we OF Nate PORA ante D POE AA q NST Dd EY PRE MAN a whe Cun amp L sa POE Pee aban v e T I 1 cz Table 3 1 cont NO KEY NAME FUNCTION 20 NO LABEL Remote set point voltage divider cable receptacle Amphenol 126 195 plug 21 HEATER Heater element lead terminals Grey is the high side and Black is the low side 22 GROUND Chassis ground terminal 3 3 Initial Checks Initial check
6. The amplified error signal causes a current to flow in the heating element which raises the diode temperature and reduces its voltage As the diode temperature approaches the set point temperature the error signal is reduced and less power is supplied to the heater element At some small temperature error or offset the power supplied to the heater element is just sufficient to heat the sample holder and diode to maintain a steady but slightly lower temperature The AUTOMATIC RESET feature of the controller is used to reduce this error to zero The automatic reset circuit integrates the error and this accumulated signal drives the output power amplifier The integrator signal continues to grow as long as an error exists The heater current continues to increase in response to the integrator signal Eventually the error is driven to zero and the integrator signal assumes a constant value This signal is precisely the value of heater current required to maintain the error at zero The integrator capacitor stores or remembers this signal as the appropriate heater current level to maintain temperature coincidence between the diode and the set point temperature In control theory terminology the AUTO RESET circuit raises the system type number from zero to one tReedback Control System Analysis and Synthesis by John J D Azzo and Constantine H Houpis McGraw Hill Book Co New York 1966 Pg 397 22 R gt 1 2 ES
7. at approximately 70 of full scale from center f Automatic Reset Circuit Bounding Circuit The bound circuit variable gain integrator and the constant gain amplifier shown in Fig 3 3 are realized by operational amplifier A3 bipolar transistor 01 and field effect transistor 02 in Fig 5 1 A simplified equivalent circuit of the stage is given in Fig 4 1 Application of the principle that the summing junction currents must add to zero yields the overall transfer function of the stage The constant gain amplifier in Fig 3 3 is represented by the term R32 R23 while the variable gain amplifier following the ideal integrator is represented by the term 1 R32 Re R23Cj6 in the equation in Fig 4 1 The bounding circuit disables the integrating function for large errors when rapid corrective action is desired The memory action of integrating capacitor C16 causes the controller to be sluggish in such transient operations The method of disabling the capacitor depends upon the sign of the error and the polarity of the voltage across C16 If the voltage across capacitor C5 is of such a polarity as to make TP19 positive with respect to TP17 diode CR 25 conducts reducing the effective gain of the stage and discharging the capacitor The second mode of bounding occurs if the error signal at the base of 1 becomes excessively negative Ql is normally biased by 08 19 so that field effect transistor Q2 is cut off approximately 9V at the gate As
8. 1974 Section I Gen 1 1 1 2 1 3 1 4 1 5 II III IV VI 5 1 2 4 5 6 0 3 3 3 de 3 3 3 3 3 ON U1 4 Ww e Table of Contents eneral Information Introduction Description General Specifications Major Assemblies Supplied Accessory Equipment and Custom Options nstallation Introduction Initial Inspection Power Requirements Grounding Requirements Installation Repackaging for Shipment peration Instructions Introduction Controls Indicators and Connectors Initial Checks Temperature Readout Mode Constant Temperature Control Mode Manual Reset Heating Mode Temperature Readout Mode Sensor B Remote Temperature Programming Grounding Theory of Operation 4 1 452 4 3 Introduction General Description Detailed Description Regulated Power Supplies a Reference Current b Diode Constant Current Supply c Set Point Voltage Supply and Divider d Amplifier Supply Voltages e Variable Gain Amplifier f Automatic Reset Circuit Bounding Circuit g Output Power Amplifier h Manual Heater Current Control i Heater Current Metering and Limiting Maintenance and Trouble Shooting UTUTYTUTUTUTOT UT UT Oo JJ ON W Introduction Test Equipment and Accessories General Remarks Servicing Printed Circuit Boards Operational Checks Normal Operating Voltages and Gains Calibration of Set Point Voltage Calibr
9. R101 104 R105 106 R107 117 R118 R119 R200 R201 R202 R203 R204 R205 R206 R207 R208 R209 LAKE SHORE DESCRIPTION PART NO OPTIONAL 51K 1 4W 5 12K 1 4W 5 56K 1 4W 5 200 1 8W 054 TRIMMING RESISTORS SET POINT 48 7 1 8W 054 VOLTAGE DIVIDER TRIMMING RESISTORS ASSEMBLY 100 ohm 475 1 8W 6 54 9 1 4W 1 HEATER CURRENT 16 9 1 8W 1 RANGE AND 4 99 1 8W 1 METER SWITCH 1 64 1 2W 1 ASSEMBLY 0 4925 1W 1 1000 1 4W 1 324 1 2W 1 90 2W 1 25 33 SW 1 100 MFD 50 VDC Electrolytic 100 MFD 50 V Electrolytic 10 MFD 25 V Tantalum 10 MFD 25 V Tantalum 0 25 MFD 50 V Mylar 0 68 MFD 50 V Mylar 0 16 MFD 50 V Mylar 10 MFD 25 V Tantalum 100 MFD 50 400 MFD 50 400 MFD 50 0 0015 MFD 0 0015 MFD 2 7 MFD 25 2 7 MFD 25 100 MFD 15 0 0056 MFD VDC Electrolytic VDC Electrolytic V Electrolytic 50 V Mylar 50 V Mylar V Tantalum V Tantalum V Tantalum 25 V Ceramic 2500 MFD 25 V Electrolytic 0 027 MFD 50 V Mylar 32 REF DESG CR1 4 CR6 7 CR8 11 CR12 CR13 CR14 CR15 CR16 CR17 CR18 CR19 CR20 23 CR24 CR25 CR26 CR27 CR28 CR29 Al A2 A3 4 01 02 05 Q1 Q2 Q3 S1 52 S3 54 S5 S6 57 LAKE SHORE DESCRIPTION PART NO SILICON RECTIFIER IN4004 REFERENCE DIODE IN4571A SILICON PROTECTIVE DIODE 411 RECTIFIER IN4004 REFERENCE DIODE IN4571A SILICON PROTECTION DIODE 411 SILICON PROTECTION DIODE 411 ZENER DIODE 10 V ZENER DIODE 10 V G
10. a test plug made up according to Fig 2 1 c Substitute a precision resistor for the sensor diode in the test plug Remove the heater element leads and place a ten watt ten ohm resistor across the heater output terminals Ten microamperes flowing through the test resistor should develop a potential of 1 00 volts across a 100 K ohm resistor With the gain set at maximum position and the mode selector switch in position MAN A assuming the test plug is in SENSOR A receptacle attempt to null the error with a set point voltage in the vicinity of 1 0 volts The null meter should swing smoothly as the set point voltage vernier is varied in the vicinity of the null 28 While still in the MAN A position set the MAXIMUM HEATER AMP switch at 1 amp Vary the MAN RESET potentiometer from zero towards its maximum The current meter should increase linearly along with the advance of the MAN RESET control With the MAN RESET control set to give mid scale heater current meter deflection rotate the MAX HEATER AMP switch through all of its positions The heater current meter indication should remain approximately at mid scale in all of the positions Zero the null meter with the set point voltage controls Turn the AUTO RESET and GAIN controls to mid scale position Set the MAX HEATER CUR switch to 1 amp Position the mode control switch to AUTO A Abruptly rotate the set point voltage vernier counter clockwise sufficiently to cause a 10 unit deflection
11. above is given in Figure 3 4 Observe that there is no temperature overshoot or oscillation when the GAIN and AUTO RESET controls are properly adjusted This statement presupposes that the sample holder heater and sensor may be accurately modeled as a simple R C type time constant thermal circuit If oscillation or overshoot are observed when changing the set point voltage in small increments reduce the GAIN and increase the AUTO RESET time constant rotate CCW settings until oscillations are no longer observed and or adjust the MAX HEATER AMP Key No 8 to a lower setting 3 6 Manual Reset Heating Mode By placing the mode selector switch Key No 6 in either position MAN A or MAN B a manually settable constant current may be supplied to the heater element The magnitude of the current is determined by the setting of the MAN RESET potentiometer Key No 7 and the MAX HEATER AMP switch Key No 8 The current supplied to the heater is indicated on the HEATER CURRENT meter The full scale reading of the meter corresponds to the MAX HEATER AMP switch setting 3 7 Temperature Readout Mode Sensor B In some applications the temperature is controlled or regulated at one physical location while it is desired to measure the temperature at a second location This requires two sensors Sensor A located at the temperature control point and Sensor B at the second point where only the temperature is to be measured Sensor B
12. applied to a 3 stage Kelvin Varley voltage divider consisting of R101 R119 R12 12 R16 and R17 The set point voltage proper consists of the potential developed between tie point 5 and the wiper of potentiometer R119 The floating set point voltage power supply and Kelvin Varley voltage divider constitute a potentiometer loop When the set point voltage proper equals the sensor diode voltage no error signal appears at the input terminals of preamplifier A2 d Amplifier Supply Voltages Referring to Fig 5 1 power supply P S 3 provides 15 Volts DC to the circuitry including operational amplifiers A2 A3 and A4 etc e Variable Gain Amplifier The variable gain amplifier shown in Fig 3 3 with a gain range of 5 to 509 is realized by chopper stabilized operational amplifier A2 The input resistor is R8 and the feedback element consists of R10 R11 R13 and R15 or R10 R11 R14 and R15 24 Diodes CR 13 14 15 16 and Ro comprise limiter circuitry Large signals cause forward biased diodes to conduct which in turn reduces the effective feedback resistance and amplifier gain and prevents the amplifier from saturating The output of amplifier A2 drives the null meter and subsequent stage A3 For small errors the meter reading is proportional to the error As the error amplitude increases either diode CR 17 or CR 18 conducts causing the meter reading to be logarithmic Cross over from linear to non linear deflection occurs
13. at the rear of the case with all normal operating controls on the front panel The instrument is line operated from either 115 volt or 230 volt mains 50 or 60 Hertz The controller is designed to accept a voltage signal from a temperature sensitive transducer generally a DT 500 or TG 100 Diode which is not supplied compare this signal with an internal set point voltage amplify and process their difference error signal and drive an external heating element An internal precision 10 microampere constant current source is provided to excite the temperature transducer The error processing section of the controller is of the proportional plus integral mode design Generous amplifier gain ranges have been provided to affect rapid closed loop response times low steady state temperature offsets and to insure system stability over a wide range of thermal system parameters The output power amplifier is capable of supplying up to 10 Watts of heater power In view of the high cost of some cryogenic fluids such as heliun cost consciousness suggests that cryostat design and operating strategies be planned to limit heater power requirements to substantially less than ten watts Power boosters are available from the company as accessory equipment if required for special applications The principal intended application of the DTC 500 Controller is as a constant temperature regulator for laboratory size cryostats Its basic design however enables it
14. front panel switched to the appropriate sensor input A or B The TEMPERATURE SET POINT switch on the rear panel should be switched to REMOTE and remote plug 20 be disconnected A high quality potentiometric voltmeter connected to the precision resistor should measure a voltage equal to 10 microamperes times the value of the resistor Typically a 100 K 01 resistor should read 1 0000 within 100 microvolts If recalibration is indicated the voltage across the precision resistors can be recalibrated after removing the case cover and adjusting trimmer Rz on the circuit board 30 5 9 Parts List Component Location Diagram and Schematic REF DESG Table 5 1 PARTS LIST LAKE SHORE DESCRIPTION PART NO 7 87K 1 8W 1 10 3K 1 8W 1 1K Helitrim 78 PR 1K Current Adjust 40 1K 1 499K 1 8W 1 470 1 4W 5 100K 1 4W 5 100K 1 4W 5 511 1 4W 5 2K 1 4W 5 2 2M 1 4W 5 10 ohm Helitrim 78 PR 10 Gain Control 10 1 8W 1 25K POTENTIOMETER Gain Control 25K 1 4W 5 300 1 8W 1 TRIM NOMINAL 698 NOMINAL 1 8W 1 1 47K 1 8W 1 10 1 4W 5 10 1 4W 5 464 1 8W 1 8 68K 1 8W 1 332K 1 8W 1 TRIM NOMINAL 470 1 4W 555 TRIM NOMINAL 100K 1 4W 5 18K 1 4W 5 680K 1 4W 5 2 7M 1 4W 5 2 4K 1 4W 5 1M 1 4W 5 1 Meg POTENTIOMETER AUTO RESET 1K 1 4W 5 1 21 1 5 1 2K 1 4W 5 15K 1 8W 1 1K 10 TURN POT MANUAL RESET 3 92K 1 8W 1 33K 1 4W 5 12K 1 4W 5 1 5K 1 4W 5 31 REF DESG R43 R44 R45 R46
15. of the NULL meter to the left The heater current meter deflection will consist of two components The first is a rapid step rise due to the steady null error and a second gradually rising component due to the AUTO RESET circuit integrating the steady error The heater current meter will gradually rise towards full scale deflection The rate at which the heater current rises is determined by the AUTO RESET time constant setting The rate is a minimum in the counterclockwise position and a maximum in the fully clockwise position Abruptly rotate the set point voltage vernier clockwise to cause 10 units deflection of the NULL meter to the right The HEATER CURRENT meter should gradually decrease from full scale deflection to zero The rate at which the current meter goes to zero is in part determined by the bounding circuit Its non linear behavior accounts for the asymetry in the temperature versus time characteristics as shown in Fig 3 4 If the instrument responds to the tests outlined above as indicated either the trouble lies elsewhere in the system or the malfunction in the controller is of a subtle nature As an aid in trouble shooting in the latter case typical voltages and gains under specified conditions are given in Section 5 6 5 6 Nominal Operating Voltages and Gains The following voltage measurements were made with an RCA Senior Voltohmist meter A 1 75 K ohm resistor was used to simulate the diode and a 10 ohn 10 watt resist
16. off 7 SET POINT VOLTS switch and potentiometer to voltage corresponding to desired temperature 8 POWER switch Key No 9 to on If the block or sample holder whose temperature is to be controlled is colder than the set point temperature the sensor diode voltage will be high and the null meter will deflect to the left Slowly increase the GAIN setting Key No 4 in a clockwise direction The HEATER CURRENT meter should show an immediate up scale deflection proportional to the GAIN setting The NULL meter should start to come off its full left deflection position as the gain is increased As the sample holder temperature approaches the set point temperature the NULL meter will approach center scale and the HEATER CURRENT meter will assume a steady value even with a further increase in the gain setting Continue to increase the gain until an incremental change in gain produces a negligible reduction in the null error but not so high as to produce oscillations To further reduce the null error rotate the AUTO RESET gain control Key No 5 out of the detent off position in the clockwise direction As the control is advanced the null meter should approach the center position with unobservable error Leave the AUTO RESET vernier in the position required to reduce the null error to zero but below any level which induces oscillations After achieving a stable operating point reduce the MAX HEATER AMP Key No 8
17. to be used as a general purpose controller for sensors whose raw outputs range between 0 and 3 0 volts and whose incremental sensitivities are in the range of tenths of millivolts In addition to its use as a closed loop automatic temperature controller the Model DTC 500 Controller may be used as a precision thermometer By adjusting the set point voltage so that the error signal as indicated by the null meter is zero the output voltage of the temperature sensor is accurately obtained Reference to a voltage versus temperature calibration curve for the transducer in use will then give its temperature 1 3 General Specifications The following specifications for the DTC 500 Controller are applicable when used with the TG 100 or DT 500 full range temperature sensitive diode General Controller Range Heater Output Sensor Sensor Input Sensor Current Input Line Voltage Power Consumption Circuit design Weight Dimensions Sensitivity Temperature Control Set Points Repeatability Automatic Reset 19K to 400 K nominal 3 10 to 10 watts 0 1 Amp 0 10 Volts Models TG 100 or DT 500 temperature sensitive diodes single ended or floating model Four terminal connection constant current potentiometric 10 microamperes 115V or 230V 50 60 Hz 30VA Solid State 15 pounds 5 high 19 wide 115 deep rack mounting Amp millivolt into 10 ohm resistor at maximum setting 0 to 3 0 volts Switch
18. 2607 10 TURN DIAL FOR R119 HELIPOT 2607 34 6224 009 460 5 o 5 w 73 T 7 o el JVA 00 001 vcy Sl ECH ctt Nh WVADVIG OLLVWSHOS LINDUID 1 S 9 cel 03 12 149 Icy 9 gt T28 T38 Tae G 7429 A CR28 CR29 FIGURE 5 2 PARTS LAYOUT FOR PRINTED CIRCUIT BOARD 36
19. ABLE Do not ground shield C ALTERNATE SENSOR CABLE FIGURE 2 1 SENSOR AND HEATER CABLES 2 5 Installation The DTC 500 Controller is all solid state and does not generate significant heat It may therefore be rack mounted in close proximity to other equipment in dead air spaces However the heat from such adjacent equipment should not subject the DTC 500 Controller to an ambient temperature in excess of 50 C 1229F As with any precision instrument it should not be subjected to the shock and vibrations which usually accompany high vacuum pumping systems The recommended cable diagrams for the sensor diode and heater element are given in Figure 2 1 a and b The use of a four wire diode connection is highly recommended to avoid introducing lead IR drops in the voltage sensing pair The indicated shielding connections are the recommended standard practice to avoid ground loops The alternate wiring scheme shown in Fig 2 1 c may be used for the diode in less critical applications The heating element should be floated to preclude the possibility of any of the heater current being conducted into the diode sensor leads Electrical feedback in addition to the desired thermal feedback may cause oscillations and certainly erroneous temperature readings Inspect the heater element fuse FU2 Key No 16 Pg 12 for proper value 3 AG 1 0A Slow Blow or smaller current rating if desired This fuse protects the output amplifier f
20. AGILE warnings SECTION III Operating Instructions 3 1 Introduction This section contains a description of the operating controls their adjustment under normal operating conditions typical controller applications and suggested cryostat adjustment techniques These instructions are predicated upon the instrument having been installed as outlined in Section II The diode polarity as shown in Fig 2 1 a in particular must be correct A calibrated diode is assumed to be connected as shown in Fig 2 1 a to the Sensor A receptacle and a 10 ohm heating element is assumed to be connected to the Heater terminals as shown in Fig 2 1 b 3 2 Controls Indicators and Connectors The operating controls indicators and connectors on the instrument s front and rear panels are shown in Figures 3 1 and 3 2 The numbers with leaders to various controls in the figures are keyed to the entries in Table 3 1 Table 3 1 Entry Number Correlation NO KEY NAME FUNCTION 1 SET POINT VOLTS Ten turn vernier interpolator 0 0 1 potentiometer to continously adjust set point voltage between switch setting and next higher setting 2 SET POINT VOLTS Selector switch of Kelvin Varley 0 1 and 2 VOLTS divider 1 0 volt steps 3 SET POINT VOLTS Selector switch of Kelvin Varley 0 to 9 VOLTS divider 0 1 volt per step 4 GAIN 1 100 Adjusts overall controller gain between 100 and 10 000 Figure 3 3 5 AUTO RESET Adjusts auto reset time constant
21. ERMANIUM PROTECTION DIODE IN358 GERMANIUM PROTECTION DIODE IN358 SILICON DIODE IN645 RECTIFIER IN4004 ZENER DIODE 4 V SILICON DIODE IN814 SILICON DIODE 411 SILICON DIODE IN645 SILICON RECTIFIER IN1612 SILICON RECTIFIER IN1612 OPERATIONAL AMPLIFIER 5825 OPERATIONAL AMPLIFIER 5823 OPERATIONAL AMPLIFIER 5825 OPERATIONAL AMPLIFIER 5824 VOLT REG RC 4195 ON VOLT REG 78 M15 HC VOLT REG MC 1468 R 2N4249 2N5459 2N42 34 2N4901 MODE SELECTOR SWITCH SET POINT SWITCH ASSEMBLY PART OF POTENTIOMETER R55 HEATER CURRENT METERING SW ASSEMBLY POWER SW A H amp H 81024 GB LINE VOLTAGE SELECTOR SWITCH SWITCHCRAFT 46256LF TEMP SET POINT INTERNAL REMOTE SELECTOR SWITCH SWITCHCRAFT 46206L 33 REF DESG FUI FU2 HS1 HS2 HS 3 NE M M2 DL1 DL2 LAKE SHORE DESCRIPTION PART NO FUSE HOLDER LITTLEFUSE 342004 FUSE HOLDER LITTLEFUSE 342004 HEATSINK WAKEFIELD ENG MODEL 690 3 BA HEATSINK CR28 WAKEFIELD ENG MODEL 695 B HEATSINK CR29 WAKEFIELD ENG MODEL 695 B 5 PIN SENSOR SOCKET AMPHENOL 126 218 5 PIN SENSOR SOCKET AMPHENOL 126 218 7 PIN REMOTE SET POINT AMPHENOL 126 198 HEATER BINDING POST E F JOHNSON 111 0113 001 HEATER BINDING POST E F JOHNSON 111 0103 001 CHASSIS GROUND POST E F JOHNSON 111 0103 001 POWER TRANSFORMER T 25 29 PILOT LIGHT INDUSTRIAL DEVICES 1040A87 NULL METER 100 0 100 MicroAmp CURRENT METER 0 1 MilliAm 10 TURN DIAL FOR R38 HELIPOT
22. User s Manual Model DTC 500 Cryogenic Temperature Indicator Controller Obsolete Notice This manual describes an obsolete Lake Shore product This manual is a copy from our archives and may not exactly match your instrument Lake Shore assumes no responsibility for this manual matching your exact hardware revision or operational procedures Lake Shore is not responsible for any repairs made to the instrument based on information from this manual Lakeshore Lake Shore Cryotronics Inc 575 McCorkle Bivd Westerville Ohio 43082 8888 USA Internet Addresses sales lakeshore com service lakeshore com Visit Our Website www lakeshore com Fax 614 891 1392 Telephone 614 891 2243 Methods and apparatus disclosed and described herein have been developed solely on company funds of Lake Shore Cryotronics Inc No government or other contractual support or relationship whatsoever has existed which in any way affects or mitigates proprietary rights of Lake Shore Cryotronics Inc in these developments Methods and apparatus disclosed herein may be subject to U S Patents existing or applied for Lake Shore Cryotronics Inc reserves the right to add improve modify or withdraw functions design modifications or products at any time without notice Lake Shore shail not be liable for errors contained herein or for incidental or consequential damages in connection with furnishing performance or use of this material Obsolete Manual
23. alibration as described above is sufficient it may be desirable to check several points In that case a precision rheostat may be used for R at the sensor input connector however the leads as well as the divider resistor should be shielded 20 and the shields connected to pin H of the sensor input connector J Similarly the leads and box housing the externally programmable temperature resistance network should be shielded through pin H of external set point plug Jz 3 9 Grounding The chassis is grounded by the 3 lead power cable to the electrical supply common ground The common lead of the controller circuitry Lo terminal of the heater output Key 21 Fig 3 2 is externally connected to the chassis ground terminal Although the grounding of the controller common is normal operation practice the common Lo terminal may be disconnected from chassis ground if doing so helps to eliminate accidental ground loops within the system 21 SECTION IV Theory of Operation 4 1 Introduction This section contains the theory of operation of the DTC 500 Controller and a functional characterization of the controller in Laplace transform notation to aid the thermal system designer in system stability analysis 4 2 General Description Refer to Figure 3 3 and Figure 5 2 as an aid in the following discussion With reference to Figure 3 3 a precision constant current source causes 10 microamperes of DC current to flow throug
24. ary to replace a component To remove the printed circuit board unscrew the bolts from the bottom of the case which attach the board to the stand off studs Swing the rear of the board up using the front edge as a pivot Be sure to clear the line cord retainer and fuse holders Be sure to support the board in the raised position If the board is stressed it may break or develop hairline cracks in the printed wiring Use a low heat 25 to 50 watts small tip freshly tinned soldering iron Use small diameter rosin core solder Remove a component lead by applying heat to the lead observing the solder melt and then pulling the lead through the board from the top side Never apply tension to printed wiring from the bottom side Thoroughly clean all of the old solder from the mounting hole before in serting a new component with the use of a wick or desoldering suction device Shape the new component and insert in mounting hole Do not use heat or force to insert the new component If the leads will not go through the hole file the lead or clean the hole more thoroughly Once mounted properly apply heat to lead and wiring pad simultaneously and resolder Clean excess flux from the connection and adjoining area with warm water and weak detergent if need be Contamination in some areas of the board can seriously degrade the high input impedance of the operational amplifiers 5 5 Operational Checks Replace the sensor diode connector plug with
25. ation of Sensor Current Parts List Printed Circuit Board Component Locator and Schematic Appendixes Page W AN SUT U1 ui UT Table of Illustrations Reference Description Figure 1 1 Figure 2 1 Table 3 1 Figure 3 1 Figure 3 2 Figure 3 3 Figure 3 4 Figure 3 5 Figure 3 6 Figure 3 7 Figure 4 1 Table 5 1 Figure 5 1 Figure 5 2 Model DTC 500 Cryogenic Temperature Indicator Controller Sensor and Heater Cables Entry Number Correlation Front Panel Rear Panel Block Diagram DTC 500 Temperature Controller Temperature versus Time Characteristics of Controller Remote Temperature Programming Programming Networks Programmer Voltage Simplified Equivalent Circuit of Automatic Reset Amplifier Parts List Circuit Schematic Diagram Printed Circuit Board Component Diagram Page iv 14 15 18 19 20 23 31 34 35 36 ii UHTIOWLNOD HOLVOIGNI FUNIVYUYdNAL 3 005 03 1 61 ORM Se adr ede Pr ATA 4 DZE Figs c x a SECTION I General Information 1 1 Introduction This section contains a description of the Model DTC 500 Cryogenic Temperature Controller its applications general specifications major assemblies supplied and accessory equipment available 1 2 Description and Applications The Model DTC 500 Cryogenic Temperature Controller is housed in an aluminum case with standard 19 relay panel front for rack mounting 1 connections are
26. e corresponding incremental NULL meter error change will yield the gain The nominal cascade gain of the last two stages is 60 Gain checks should be performed by first zeroing the NULL meter with the SET POINT VOLTAGE VERNIER A small voltage change is made in the vernier dial setting and the resulting changes in the NULL meter and CURRENT meters observed 5 7 Calibration of Set Point Voltage The instrument has been carefully calibrated to within 100 microvolts plus a residual base line resistance of the 10 turn potentiometer R119 Should it be desirable to check or recalibrate the set point reference voltage the sensor should be disconnected and the TEMPERATURE SET POINT switch on the back panel be in the INTERNAL position The reference voltage may be measured between pin E of Jl and pin D of J3 without opening the case cover Voltage measurements should be taken with a high precision potentiometric instrument If recalibration is indicated after allowing a minimum of 20 minutes warm up time adjust trimmer R1 SO the voltage between terminal pins 5 and 3 is 3 0000 100 uv 5 8 Calibration of Sensor Current The sensor current has been factory calibrated to 10 microamperes 10 nanoamperes To check the sensor current without removing the case cover a conveniently available precision resistance of not less than 01 tolerance should be connected to pins A B of the sensor connector socket Jj or Jo and the sensor selector switch on the
27. fier stage to the wiper of potentiometer R38 Varying the wiper position from zero to its maximum will vary the voltage at TP20 from zero to approximately 10 5 volts The heater element current is thus varied proportionately to the setting of R38 and the maximum heater current switch S4 position i Heater Current Metering and Limiting The heater element current is measured by the heater current ammeter shunted by resistor R20I through R205 as appropriate for the current range selected The full scale output current is determined by the series combination of the heater element resistance and one of the group of resistors R206 through R209 This series combination is connected across the nominal 10 5 volt output of the power amplifier Approximately 5 volts appears across the Heater Current Meter M1 and R200 and its appropriate shunt resistor Under no circumstances shall the rating of fuse FU2 be increased above one ampere in an attempt to achieve a power dissipation of ten watts in a heater element whose resistance is less than ten ohms Such a substitution invalidates the instrument warranty and is likely to damage the output power amplifier circuit 26 SECTION V Maintenance and Troubleshooting 5 1 Introduction This section contains instructions for maintaining and calibrating the controller nominal voltage values and gains circuit schematic diagram printed circuit board component diagram and parts list 5 2 Test Equip
28. h the sensor diode The set point voltage source or bucking voltage is subtracted from the diode voltage and the difference or error signal is amplified in a variable gain amplifier stage operational amplifier A2 in Fig 5 1 The amplified error is displayed on the NULL meter and also applied to 1 a gain of 20 amplifier 2 an integrator circuit and 3 a bound or clamping circuit The bounding circuit disables the integrator for large errors The output of the integrator is amplified by a variable gain amplifier whose gain is set by the AUTO RESET potentiometer The gain range is from 1 to 100 The integrator bounding circuit post integrator variable gain amplifier and constant gain of 20 amplifier are associated with operational amplifier A3 transistor Q1 and field effect transistor Q2 in Figure 5 1 The processed error signal drives the output power amplifier circuit whose voltage gain is 4 Operational amplifier A4 and transistors Q3 and Q4 in Fig 5 1 comprise the power amplifier The output of the power amplifier is metered by the HEATER CURRENT indicator and passed to the heater element Closed looped control action is achieved through the thermal path between the heater element and the temperature sensing diode To illustrate the automatic temperature control action suppose the sensing diode is colder than the programmed temperature setting The diode voltage will be greater than the set point voltage which results in an error voltage
29. ic fluid due to thermal shorts in dewar ice blocks in lines sample holder immersed in cryogen sample holder in vapor whose temperature is above the controller set point temperature etc 4 Excessive thermal path phase lags will cause the control loop to be unstable at high gain settings Physical separation between the diode and heater particularly by paths of small thermal cross section should be avoided S Examine heater element fuse FU2 If it is indicated that the controller is malfunctioning after performing the tests to be described below it is recommended that the instrument be returned to the factory for repair The components used in the instrument are 27 costly and may be permanently damaged if subjected to inappropriate test voltages or excessive soldering iron heat Although premium materials and techniques have been used to fabricate the instrument circuit board there is always the risk of lifting a connection pad or cracking the board when unsoldering a component 5 4 Servicing Printed Circuit Boards It is suggested that components be unsoldered for trouble shooting only as a last resort since ample information is available at the numbered terminal pins Attempt to infer component currents by voltage tests rather than removing a lead and seriesing it with an ammeter All voltages are available for measurement from the top side of the printed circuit board Therefore the board need only be removed when it is necess
30. ment and Accessories An RCA Senior Voltohmist vacuum tube voltmeter or an equivalent high input impedance digital voltmeter a ten ohm ten watt resistor to simulate the heater element and a precision resistor connected to simulate the diode in a connector assembly wired according to Fig 2 1 c are normally sufficient for testing and calibrating the DTC 500 Controller 5 3 General Remarks Upon initial installation the single most probable cause of system mal function is an improperly connected temperature sensing diode If it is impossible to zero the null meter at any setting of the set point voltage controls carefully examine the cable diode assembly to insure that the diode polarity is correct that the sensor is plugged into the SENSOR A receptacle and that the TEMPERATURE SET POINT INTERNAL REMOTE slide switch at the rear of the case is in the INTERNAL position Because of the highly reliable solid state design of the controller it is most unlikely that the controller will be a source of difficulty For this reason it is advisable to examine other portions of the cryogenic system before testing the controller proper Some suggested checks are 1 Open or shorted sensor and heater leads particularly in the vicinity of the sample holder if it is subject to frequent dis assembly 2 Leakage paths between heater and sensor leads giving rise to electrical feedback in addition to thermal feedback 3 Premature loss of cryogen
31. must be calibrated 17 Assume that the temperature at Sensor has been stabilized by operating the controller in the constant temperature control mode as described in Section 3 5 By observing the steady HEATER CURRENT reading one may switch to the MAN mode as described in Section 3 6 and establish this same current by adjusting the MAN RESET potentiometer By alternating between the AUTO A and MAN modes the MAN RESET potentiometer may be trimmed sufficiently accurately to hold the temperature steady over a brief period in the MAN position Then switch to the MAN B position and quickly adjust the SET POINT VOLT switch and potentiometer to zero the NULL meter This reading is used to determine the temperature of Sensor B After taking the Sensor B voltage reading reset the SET POINT VOLT switch and potentiometer to the desired temperature control point and then return to AUTO A control mode If there is appreciable null error upon returning to the AUTO A mode of control the adjustment of the MAN RESET control should be refined and the measurement of the Sensor B voltage repeated Since the system is operating open loop or is coasting in both the MAN A and MAN B mode of control positions no adjustments or changes should be made in the cryostat system which would introduce transients during this period of time 3 8 Remote Temperature Programming Remote temperature control can be achieved by replacing the internal Kelvi
32. n Varley voltage divider with an external resistive divider connected to and switching the TEMPERATURE SET POINT to the REMOTE position To insure maximum accuracy the total resistance between pins E D of Jz should be equal to 615 ohms The remote set point connection diagram is shown in Figure 3 5 m nil PEM Pin E E Pin B Pin D 8 gt Pin H Equivalent Set Point Network Shield Figure 3 5 Remote Temperature Programming 18 A number of external temperature programming networks are shown in Figure 3 6 D D D Rp Trim Resistor A B C D Figure 3 6 Programming Networks The following is a suggested procedure for designing external temperature set point control circuitry 1 Determine the range of desired temperature control voltage 2 Choose the most suitable control circuit for your application a Temperature control range 100 b Limited temperature control range C Fixed temperature set points selected in steps d Most flexible arrangement allowing for selected steps and continuously variable temperature set points 19 Additional variations of the above may be tailored to fit the intended application 3 To insure that the total resistance between pins F amp D of the external programming voltage divider be of the correct value to develop a drop of 3 volts it is suggested that the divider calculation be based on more than 210 ohms per 1 volt and a shunting resist
33. or Rr in Fig 3 6 used for precision trimming to 3 volts between pins E D The 3 0 volts between pins E D can be measured with a precision floating voltmeter with the sensor circuit open i e sensor plugs disconnected or calibrated with the DTC 500 internal set point volts switch and 10 turn dial as follows a Connect a precision known resistor R any value between 50K 250K to the pins AE and BD of the sensor A input plug Jl amphenol type 126 217 or equivalent in place of the sensor as shown in Fig 3 7 and turn the sensor selector switch on the front panel to Manual A position A E R Shield B D Figure 3 7 Programming Voltage The voltage drop across resistor R is equal to 10 x 1070 amperes X R ohms volts thus a 100 K ohm resistance would result in a 1 volt drop With the TEMPERATURE SET POINT switch on the rear of the instrument in INTERNAL position the null meter will indicate zero error when the internal temperature set point switch on the front panel is at 1 000 volts Increase the gain to maximum and adjust the 10 turn dial of the internal set point control if necessary for the null meter to indicate zero Move the reference set point switch on the rear panel to external position and adjust trim resistor RrT on the external set point programming instrument so that the null meter reads zero The external programming network is now matched to the internal reference source Although one point c
34. or was used in place of a heater element The voltage across the input filter capacitors Cl C2 C9 C10 and 1 in power supplies P S 1 through P S 3 are nominally 24 volts with the output voltages appearing across capacitors C14 C15 C8 C14 and C15 being 15 volts 15 volts and 15 volts respectively Reference diodes CR 5 and CR 12 are reverse biased at 6 4 volts The voltage appearing across capacitor C18 and P S 4 varies between approximately 14 and 20 volts depending upon the heater element current At no load the voltage is 20 volts decreasing to 14 volts at 1 ampere output 29 The emitter of 01 is biased to 0 5V to compensate for the turn on voltage of Ql The output power amplifier stage may be checked by placing the mode selector switch in the MAN A position The potential across R38 terminals 6 to 7 is 3 2 volts The voltage at terminal 20 should be approximately 3 5 times the voltage selected between the slider of R38 and ground The voltage at the output of amplifier A4 is about one volt more negative than the voltage at terminal 20 because of the base emitter drops of Q3 and Q4 With the AUTO RESET control in the off position in the switch detent and the MAX HEATER CUR switch in the 1 amp position the total voltage gain of amplifiers A3 and A4 may be inferred The CURRENT METER corresponds to a 10 volt full scale voltmeter if a 10 ohm heater element is used Comparison of the incremental output voltage change to th
35. rder upon receipt To confirm this the instrument should be inspected visually for obvious damage upon receipt and tested electrically by use to detect any concealed damage Be sure to inventory all components supplied before discarding any shipping materials If there is damage to the instrument in transit be sure to file appropriate claims with the carrier and or insurance company Please advise the company of such filings In case of parts shortages please advise the company The standard Lake Shore Cryotronics warranty is given on page ii 2 3 Power Requirements Before connecting the power cable to the line ascertain that the line voltage selector switch 115V or 230V is in the appropriate position for the line voltage to be used Examine the power line fuse FUl Key No 14 Page 12 to insure that it is appropriate for the line voltage 115V 0 25 Amp 230V 0 15 Amp Nominal permissible line voltage fluctuation is 10 at 50 to 60 Hz Caution Disconnect line cord before inspecting or changing line fuse 2 4 Grounding Requirements To protect operating personnel the National Electrical Manufacturers Association NEMA recommends and some local codes require instrument panels and cabinets to be grounded This instrument is equipped with a three conductor power cable which when plugged into an appropriate receptacle grounds the instrument Do not ground shield GREY J 5 BLACK B RECOMMENDED HEATER C
36. rom damage in case of heater element shorting Use of a larger fuse may cause damage to the instrument and invalidates the instrument warranty 2 6 Repackaging for Shipment Before returning an instrument to the factory for repair please discuss the malfunction with a factory representative He may be able to suggest several field tests which will preclude returning a satisfactory instrument to the factory when the malfunction is elsewhere If it is indicated that the fault is in the instrument after these tests the representative will send shipping instructions and labels for returning it When returning an instrument please attach a tag securely to the instrument itself not on the shipping carton clearly stating 1 Owner and address 2 Instrument Model and Serial Number 3 Malfunction symptoms 4 Description of external connections and cryostats If the original carton is available repack the instrument in plastic bag place in carton using original spacers to protect protruding controls and close carton Seal lid with paper or nylon tape Affix mailing labels and FRAGILE warnings If the original carton is not available wrap the instrument in protective plastic wrapping material before placing in an inner container Place shock absorbing material around all sides of the instrument to prevent damage to protruding controls Place the inner container in a second heavy carton and seal with tape Affix mailing labels and FR
37. s calibration checks and servicing procedures are described in Section V MAINTENANCE 3 4 Temperature Readout Mode To use the DTC 500 as a cryogenic thermometer to measure the temperature of a calibrated diode connected to SENSOR A terminals initially position switches and controls as follows 1 Temperature set point switch Key No 19 to INTERNAL 2 Mode switch Key No 6 to MAN A 3 MAN RESET Key No 7 to zero 4 MAX HEATER AMP Key No 8 to 0 01 5 GAIN Key No 4 to minimum setting 6 AUTO RESET Key No 5 to off 7 POWER switch Key No 9 to on The null meter will probably deflect off scale either left or right when the power switch is turned on If the deflection is to the left the set point voltage is less than the sensor voltage If the deflection is to the right the set point voltage is greater than the sensor voltage Adjust the set point voltage until the NULL meter is centered while increasing the GAIN towards maximum Increasing the voltage will move the meter pointer to the right decreasing the set point voltage will deflect the meter pointer to the left After centering the meter read the set point voltage by adding the vernier potentiometer reading approximately scaled to the SET POINT switch setting value The ten turn dial s 500 divisions correspond to 100 milli volts so that each dial division corresponds to 0 2 millivolts readable to 0 1 millivolt 13
38. the base of Q1 becomes more negative 01 conducts current increasing the collector voltage toward zero The reduced bias on FET Q2 causes its source drain impedance to act as a shunt resistor across capacitor Cl6 This shunting effect discharges the capacitor and converts the ideal integrator action to a type zero action The switch S3 is closed when the AUTO RESET control is in the off position g Output Power Amplifier The processed error signal appearing at TP18 is greatly amplified in power by op amp A4 Q3 and Q4 before being applied to the heater element Transistors Q3 and Q4 constitute a Darlington series pass element in a current amplifier circuit They are inside the feedback loop associated with op amp A4 R46 being the feedback resistor The input resistor for the op amp is R37 so that the voltage gain of the power amplifier circuit 1s R46 R37 or approximately 3 5 At rated output current of one ampere the voltage appearing at TP20 is 10 5 volts Use of a heater resistance in excess of ten ohms will reduce the available heater current below the rated maximum value of 1 ampere See application notes in Section VI 25 Winding 5 6 7 on transformer P S 4 diodes CR 28 and CR 29 and capacitor C18 constitutes the power supply for the series pass elements Q3 and Q4 h Manual Heater Current Control When the mode selector switch is set to either MAN A or MAN B position switch section 51 8 connects the input of the power ampli
39. to a lower setting As lower settings are dialed in the percent of maximum heater current being used should increase The optimum area for control can be obtained by keeping the meter pointer between 0 2 and 0 7 on the meter face 16 Abruptly increase the set point vernier control by ten units the sensor voltage now represents a temperature warmer than that represented by the set point voltage The NULL meter should deflect to the right and the HEATER CURRENT should go to zero immediately As the sample holder cools the NULL METER pointer should return towards zero As the NULL METER pointer approaches zero the HEATER CURRENT will increase from zero to the new steady state value required to maintain the sample at the lower temperature requested The NULL METER should read zero as the HEATER CURRENT stabilizes at its new value Now abruptly decrease the set point vernier control by ten units the sensor voltage now represents a temperature colder than that represented by the set point voltage The NULL meter should deflect to the left and the HEATER CURRENT meter should deflect toward full scale As the sample holder heats the NULL meter pointer will tend to zero and the HEATER CURRENT meter reading will decrease toward its new steady state value As the NULL meter centers the HEATER CURRENT should stabilize at the new constant value required to maintain the desired temperature A sketch of the temperature versus time pattern described
40. tom nature The customer should discuss these items with a factory representative before ordering 1 Estra 5 and 7 pin connectors 2 3 4 5 6 7 Multisensor selector panel Special low thermal offset switch and cabling for selecting among multiple sensors Remote set point voltage control and programming module Custom modification of sensor current supply value TG 100 Gallium Arsenide or DT 500 Silicon Temperature Sensitive Diode Uncalibrated See data sheets at end of this manual for nominal operating characteristics and case styles available TG 100 Gallium Arsenide or DT 500 Silicon Temperature Sensitive Diode Calibrated Standards laboratory calibration service for correlating diode output voltage with diode temperature See sensor data sheet for additional information Power Boosters for heater power requirements in excess of ten watts or other than ten ohm heater resistances SECTION II Installation 2 1 Introduction This section contains information and instructions necessary for the installation and shipping of the Model DTC 500 Cryogenic Temperature Controller Included are initial inspection instructions power and grounding requirements installation information and instructions for repackaging for shipment 2 2 Initial Inspection This instrument was electrically and mechanically inspected prior to shipment It should be free from mechanical damages and in perfect working o
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