Omega Engineering DP251 User's Manual
Contents
1. 4 2 7 Callendar van Dusen using data pairs If you choose method 4 for data entry the Callendar van Dusen equations are utilized by entering data pairs of resistance versus temperature The data pairs are used to calculate the coefficients for the CvD equations which are then used to create the temperature vs resistance look up table The prompts are as follows i r Lo Minimum resistance value for the conversion table ii rhi Maximum resistance value for the conversion table iii t0 Temperature nearest to 0 C iv r t0 Resistance at temperature nearest 0 C v t 100 Temperature nearest 100 C vi r t100 Resistance at temperature nearest 100 C vii eP Another positive temperature viii rteP Resistance at positive temperature ix tn A negative temperature x rtn Resistance at negative temperature Example isplay Pro Value Key Input r Lo 80 ENTER S OJ ENTER rhi 198 5 ENTER 1 9 8 J S5 ENTER to 2 0 051 ENTER 0 f 0 5 1 ENTER r t0 100 020 ENTER 1 0 0 J O 2 ENTER t 100 99 993 ENTER 9 9 9 9 B ENTER r t100 138 498 ENTER 1 31181 J 4 9 S ENTER and so on for tP rtP tn and rtn When all data has been entered the display initially goes blank As the DP251 starts to generate the resistance temperature look up table the actual number of points to be generated will appear on the display and will count down to 0 at which point the process will be compl2. 8 and DP250 16 multiplexers are a specially designed option for the DP251 When calibrated thermometers are used with the DP251 either with or without multiplexers the calibration data can be entered via the keypad on the front panel from where it is stored in internal memory A fuller description of the data entry options available to the user can be found in Chapter 4 Security is important for data entry and a key operated switch on the front panel helps to ensure that only authorized personnel can access the calibration mode Finally the front panel also incorporates a Zero button to allow A B or A B displays to be set to zerc to enable single channel or differential mode to be displayed relative to a set point Optional accessories for the DP251 include RS232C and or IEEE488 computer interfaces a scaleable analog output for recording to chart or other types of recorders and the 8 or 16 channel input multiplexers models DP250 8 and DP250 16 as described above 1 2 1 3 Definitions and Terminology used in this Manual v vi Note vii 1 C 1K mK milli Kelvin is commonly used to describe 0 007 C All push button actions shown by square brackets for example pressing the ENTER button is shown ENTER Alpha or a represents the fundamental slope or temperature sensitivity of the Platinum wire used in resistance thermometers Generally speaking the higher the alpha value the better the thermometer As th
3. 005 C year 12 4 General Features Measurement 4 wire auto balance ac resistance ratio bridge Carrier Frequency 375Hz Display 6 digit filtered vacuum fluorescent display indicating in C F K and Q ohms Display update 0 5 3 seconds in low high resolution respectively Probe current 1mA constant current source Probe cables 4 core screen 2 meters standard Alternative cable lengths to special order See Chapter 7 for more prt probe information input Connectors Front Panel 5 pin DIN professional sockets connected in parallel to rear panel inputs Rear Panel 5 pin screw Terminal sockets connected in parallel to front panel connectors 37 38 Digital Output if installed RS232C serial and or IEEE488 parallel interface available as options see more detail in Chapter 9 Analog Output if installed 10v dc output is available as an option resolution 1mK or 10 mK depending on front panel resolution setting Linearity 0 05 full scale 125 Range Dependent primarily on the probe used typically within 200 C to 800 C OMEGA can advise on suitable probes See Chapter 7 on suitable sensors 12 6 Environment Operating Temperature 15 C to 25 C for full accuracy 0 C to 50 C maximum Power Requirements 240 Vac 8 220 Vac 8 120 Vac 8 or 100 VAC 8 Supply Voltage range is user selectable on rear panel Dimensions Metal case with adjustable rest handle 240mm Deep x 260mm Wide x 80mm Hi
4. IEEE RS232 Output Socket IEEE Address Switch 10 Fan Output RH versions only 11 Channel B Input Connector 12 Channel A Input Connector OOANODAAWDHD Note The IEEE Address Switch number 9 will only be accessable when the IEEE option is installed 2 2 1 ac Power Input Socket Accepts an IEC type power connector The ac Power input unit incorporates a voltage selection tumbler to enable the user to match the DP251 to the local ac voltage supply and two fuse holders The correct 20mm fuses to install are as follows Voltage Fuse 220 240V T250mA 250 Vac 100 120V T500mA 250 Vac 2 2 2 Power ON OFF switch The switch itself will be illuminated green when the DP251 is turned ON 2 2 3 Digital Analog Output Options If installed this is at the top of the rear panel Depending on which options are installed and which way the Output Options board is installed the following will be accessible Analog Output only RS232C Interface only IEEE488 Interface only Analog Output and RS232C Interface Analog Output and IEEE488 Interface Where the IEEE488 Interface is installed an IEEE address select switch for setting the DP251 in the range 1 to 7 is provided Address 0 enables the RS232C interface if installed 2 24 Expansion Port Below the Output Options panel A 25 pin D type socket female for power and data highway connection to the DP250 8 or DP250 16 multiplexers 2 2 5 Probe Input Connectors A a
5. Select the digital output required and hold the board over the DP251 such that this output is at the rear of the instrument Figure 9 1 Removing Screws The interface board is held into the DP251 between two metal spacers at the front end and two screws into captive nuts on the back panel Connect the appropriate ribbon cable on the board to it s connector on the DP251 mother board and then lower the interface and secure in place Replace the instrument top case and secure with the 4 screws 9 2 RS232C Interface With the RS232C option installed communication happens via the 25 pin male D type connector on the back panel as shown in Figure 9 2 22 Figure 9 2 RS232 Connector 9 2 1 Pin Connections A a OP Function 25 Pin 9 Pin Function 25 Pin Connections Connector Connector Connector Tx 2 De RO E a OE TEA ERA A AA as RI joa or 6 6 oR 2 Tma e OND tn ND a E oR JOR 6 ms 9 2 2 RS232C Settings As supplied by the factory unless requested otherwise the RS232C interface is configured as follows 19 200 Baud 8 Character bits No Parity 2 Stop Bit These parameters can be changed using the following procedure 1 Remove the 4 screws holding the top half of the instrument case after first turning off and removing the power cord 2 Lift off the top half of the case and ing that the in rd is installed such th RS232C connection is to the rear locate the DIP switch at the rear of th
6. flashing digit will clear the whole number which can then be re typed To move the decimal point position the flashing digit on it using lt or gt and press CLEAR The decimal point is removed and can be inserted elsewhere using the lt or gt keys Starting the Data Entry Routine For all 5 Conversion Methods Insert the key and turn the RUN CAL switch to the CAL position and the display will indicate CAL for nominally 2 seconds before changing to ChAn This question asks the operator which Channel Input A or B is data entry required At the same time the LEDs below the A and B switches alternate on off Select the Input required by pressing the appropriate button for example if data entry is required for Input A then press A once Switch actions CAL A iil If a multiplexer is connected in this case to Input A the next display will ask the question Ch and after a few seconds the display will change to which is the prompt for you to enter the multiplexer channel number which requires probe data entry At this prompt enter the channel number via the keypad as follows a as a two digit number for example 01 09 or 13 b a single digit may be entered followed by ENTER For example if channel number 7 is required use the following key sequence 0 7 or 7 ENTER Switch actions 0 7 Please note 7 is example only iv If no multiplexer is connected or after the multi
7. switches to select Zero and Hi Res Zero This function is used to display temperature relative to a set point To activate Zero press Zero once only When this button is pressed the value displayed is subtracted from all subsequent readings until i Zero button is pressed again ii The Input or Channel number is changed iii Units are changed When Zero is used with the Input A or B display selected the status LED above the Zero button flashes If the Zero facility is activated when A B is selected the LED lights continuously Figure 4 2 Zero Hi Resolution Switches Hi Res When initially turned on the DP251 displays to 2 decimal places in all Units To increase resolution to 3 decimal places press Hi Res once Press Hi Res again to reduce resolution back to 2 decimals In addition to changing the display resolution the Hi Res button also changes the update time for the display see Specifications Note that when temperatures of lower than 99 999 are to displayed Hi Res will not be able to select 3 decimal places as the only 6 digits are available including the ve sign This can be overcome by switching either to C or K depending on the displayed temperature For example 100 000 C 173 15K or 100 000 F 73 333 C 4 2 4 1 3 Figure 4 3 shows the switches on the keypad to select dim or bright display Press to change the display from bright to dim Press gt to change the display from dim
8. 10 B 5 802 x 10 C 4 2735 x 10 and R 100 ohms then the DIN standard as in 4 2 6 has been entered 4 2 6 DIN Standard Entering 3 from the data entry menu selects the DIN Standard data entry is required only for Rmn r Lo and Rmax r hi as the coefficients which are a special case within the Callendar van Dusen equation are stored in memory As usual Rmin and Rmax determine the temperature range over which the look up table wilt be created 13 14 Example Display Prompt Value Key Input rLo 65 5 ENTER 6IS I JS ENTER rhi 196 8 ENTER 1 9 6 8 ENTER When all data has been entered the display initially goes blank As the DP251 starts to generate the resistance temperature look up table the actual number of points to be generated will appear on the display and will count down to 0 at which point the process will be complete The message stored confirms that the look up table has been created and safely stored in memory but in case you require to enter data for another channel the message ChAn appears along with Inputs A and B turning alternately on off If more channels require data entry follow the procedure as described under the appropriate method If no additional data entry is required turn the RUN CAL switch to RUN when the screen will display the message Abort This message indicates that you have left Data Entry CAL mode and is accompanied by an audible beep
9. 2 2 4 Expansion Port cccccccccscsccscscsssssesssssscsssscsessavevscsaceeeessscestsesaescaecaeass 2 2 5 Probe Input Connectors A amp B BaP an ada cd dois Installati n isise si 3 1 Power Supply Connection cccccccccccceccccscscsssesvscsesstscsesevscsecevscatsvecasseaeaeaseaes 3 1 1 Checking Voltage and Fuse RatinQ o ocoooncionnniininicnninicicccconononanos 3 1 2 Setting the Voltage and Fuse Rating ooocococcncicnnininiconinincnincnon 3 1 3 Turn On and Start Up Display ooocooccnioinonnininconnnononiniciccccnnccnnncncns Operating the DP251 Thermometet ccssssssssscssscssssscesscsesssscsecserecessssenssssseseseraraceree 41 Normal RUN Operation oooooooccconoococcocccccocicononononcconannonacononnnancnncnocnnannccnncnconns 4 1 1 Probe Input Selection oo ccccecsseccescescssesssesssssssecesneseesetssaceees 4 1 2 Zero Hi Res Functions Selection oooooocooniononononcnocccoconinninccncnncnncnos 4 13 Dim Bright Display Selection 0 ccc ccceecseesecnecsseesessceecescesseecseeas 4 2 Data Entry CAL Operation cceeesesseseseeseescecscescsessesssesessescsasensseesssceecaees 4 2 1 Data Entry Options o oo cecceesesseesceseceecsscesessseeesscescevssesseesecess 4 2 2 General Rules for Data Enty o oooococionooniononnoninonnnccccnnonanincnnononoracnins 42 3 Starting the Data Entry Routine For all 5 Conversion Methods 4 2 4 ITS90 Data Entry 2 cece cesccsee
10. 5 149K Note that the string is always 9 characters long plus CR LF except in ohms in high resolutio mode when it is 10 characters long CR LF TorD None Not applicable U Sets the units on the DP251 to C F K or Q ohms Un where n 0 1 2 or 3 n 0 selects C n 1 selects K n 2 selects F n 3 selects Q ohms n 0 C Z Sets present reading to zero nuli or clears a zero if already set Z None No zero COMMAND M Service Request Mask A Service Request Function is set up using the M command The M command is issued with a single byte parameter see the list below which specifies the output required from the DP251 Once selected the DP251 will continuously output information until a cancel command is received The Display on the DP251 will flash as data is sent BIT 2 1 0 BIT 3 BIT 4 BITS BIT6 BIT 7 000 Cancel Service Request 001 set to channel A and set service request when data available 010 set to channel B and set service request when data available 011 set to channel A B and set service request when data available 100 set alternately to channel A then B and set service request when data available Add multiplexer channel number to the data output from the DP251 Not used Not used RSV Service Request Bit Sets DP251 to give an output when an error occurs 31 9 5 32 When using the Service Request Mask the bits are sent to the DP251 in order of signific
11. AT OF TITLE AND ALL IMPLIED WAR RANTIES INCLUDING ANY WARRANTY OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE HEREBY DISCLAIMED LIMITATION OF LIABILITY The remedies of purchaser set forth herein are exclusive and the total liability of OMEGA with respect to this order whether based on contract war ranty negligence indemnification strict liability or otherwise shall not exceed the purchase price of the component upon which liability is based In no event shall OMEGA be liable for consequential incidental or special damages Every precaution for accuracy has been taken in the preparation of this manual however OMEGA ENGINEERING INC neither assumes responsibility for any omissions or errors that may appear nor assumes liability for any damages that result from the use of the products in accordance with the information contained in the manual SPECIAL CONDITION Should this equipment be used in or with any nuclear installation or activity purchaser will indemnify OMEGA and hold OMEGA harmless from any liability or damage whatso ever arising out of the use of the equipment in such a manner RETURN REQUESTS INQUIRIES Direct all warranty and repair requests inquiries to the OMEGA ENGINEERING Customer Service Department BEFORE RETURNING ANY PRODUCT S TO OMEGA PURCHASER MUST OBTAIN AN AUTHORIZED RETURN AR NUMBER FROM OMEGA S CUSTOMER SERVICE DEPARTMENT IN ORDER TO AVOID PROCESSING DELAYS The assigned AR number shoul
12. Control Probe connection may be via the front panel or the back panel for a easier installation Each channel has high isolation low resistance 5 pin relays giving full 4 terminal measurement plus ground Visual indication of the Input and Channel selected is provided One or two DP250 8 or DP250 16 multiplexers can be operated from the keypad or remotely using the DP251 communications board When operated via RS232 or IEEE the channel can be selected and the temperature read in any of the usual formats available to the DP251 5 1 1 Multiplexer Address Before a multiplexer can be used on channel A or B the address must be set The address switch is hidden behind a plastic rivet on the right hand side of the front panel of the multiplexer close to the A and B LEDs When in use the appropriate LED is illuminated to confirm to which Input it is connected When two multiplexers are in use one must be set for A and the other to B or there will be an address conflict To adjust the multiplexer address connect as described below and after removing the plastic rivet use a small screw driver to set the switch to the required Input 5 1 2 Connections Connectors 0 15 or 0 7 for 8 channel units allow the thermometer probes to be connected at the front of the multiplexer or to the rear if the screw terminals are used on the back panel Each paralleled connector pair shown in Figure 2 2 for the DP251 represents one channel with the LEDs o
13. DP251 Precision RTD Benchtop Thermometer Operator s Manual OMEGA An OMEGA Technologies Company m OE OMEGA Am OMEGA Technologies Company Servicing USA and Canada Call OMEGA Toll Free USA Canada One Omega Drive Box 4047 976 Bergar Stamford CT 06907 0047 Laval Quebec H7L 5A1 Telephone 203 359 1660 Telephone 514 856 6928 FAX 203 359 7700 FAX 514 856 6886 Sales Service 1 800 826 6342 1 800 TC OMEGA Customer Service 1 800 622 2378 1 800 622 BEST Engineering Service 1 800 872 9436 1 800 USA WHEN TELEX 996404 EASYLINK 62968934 CABLE OMEGA Servicing Europe United Kingdom Sales and Distribution Center 25 Swannington Road Broughton Astley Leicestershire LE9 6TU England Telephone 44 1455 285520 FAX 44 1455 283912 The OMEGA Complete Measurement and Control Handbooks amp Encyclopedias Temperature Data Acquisition Systems Pressure Strain amp Force Mm Electric Heaters Flow and Level Environmental Monitoring pH and Conductivity and Control Call for Your FREE Handbook Request Form Today 203 359 RUSH CJISO495APC2BA Unpacking Instructions Remove the Packing List and verify that you have received all the equipment including the following quantities in parentheses DP251 1 ac Power Cord 1 Calibration Report 1 Operators Manual 1 If you have any questions about the shipment please call the OMEGA Customer Service Department f When you receiv
14. DP251 takes a little longer to display a first reading and to subsequently update the reading see Specifications If any error messages other than E 1 are displayed then refer to Error Codes in Chapter 10 to find their meaning and probable cause If no suitable explanation can be found for any fault contact OMEGA Chapter 4 Operating the DP251 Thermometer Note Make sure that calibration data for your probes has been entered before carrying out temperature measurement 4 1 Normal RUN Operation The DP251 must be set to RUN on the key operated switch for all functions in the sections below All measurements are made in RUN mode me 4 1 1 Probe Input Selection Figure 4 1 shows the selection switches to display Inputs A and B plus the differential value A B To select the required display simply press the appropriate button once For example if you want to display the temperature measured by the probe connected to Input B press B If a DP250 8 or DP250 16 multiplexer is connected to Input B then the temperatures displayed will also depend on which Channel is selected on the multiplexer See Chapter 5 for operation with multiplexers A To display the differential temperature A B press A B however KALE probes must be connected to both Inputs directly or via a multiplexer otherwise an error message will be displayed Figure 4 1 Channel Selection Switches 4 12 Zero Hi Res Functions Selection Figure 4 2 shows the
15. Environmental Chamber Probe ocooccoonicnnonoinincnococconocnocononconononacnos International Temperature Scale ccc eeraa ea aana Communications Output Options ccscssscsscccsecccecesesserscrstacecesecenecsssecsecrsesaccesees 9 1 Retro Fitting or Changing an Interface Board cecccccccccscscsescsssceesvecscecaceees 9 1 1 Retro fitting ooocococononcnncnnnccconcoconcnconcnccononacncons CIA 9 2 RS232C Interface ee eccecssscssssescsessescesessseseseeeuacscseecaesesssacassesescavseieasacseaeacs 9 2 1 MA O ALE SOUINGS NA 9 2 3 Interpretation ccc cccccccsesssssscssescsscssssccesecssesssesacserssaceaterersaesesseesaes 9 2 4 Commands and Syntax oo ccccccccescscscececsescesetseseseststerststsseseeeavaes 9 3 IE E488 NSIC 2 adds 9 3 1 PI CONOCIO id 9 39 2 1EEE488 S tting citan tals 9 3 3 Specification nanan n A 9 3 4 Commands and Syntax oo cccccescscssecscecseecscseeestsseststeestaveveneevs 9 4 Command M Service Request Mask 0 c cccccccsccescscsssscscsesescecssssersersceneneees 9 5 Analog QUIPUL srein antinen a n e e iuinil aa a eoa 9 5 1 A ira earen aa i A ET 9 5 2 Analog Output Connection ccccccesccsscescscescucsesseseessveveseavevars 9 5 3 Analog Output Operation eee A E EMO Ooo l ii ad s Options and AccesSori8S oconmommmmmmmmnsommmes 11 1 Communications Output Options oooocooinncncnnocnnoncnoononncncnccncoroconornnnncccnnos 11 2 SACCOSSONES A a Besta AAA aapac
16. FF is then converted to a floating point integer scaled and converted to complementary offset binary ready to be output to the 16 bit D to A converter The complementary offset binary 16 bit data is sent in two bytes to an 8 bit parallel to 16 bit parallel converter ICI to IC5 The high order byte is set on the data bus first and latched through and held on the output of an 8 bit data latch IC3 by addressing the appropriate latch through the address decoding IC1 and C2 3 to 8 decoder and inverter respectively 33 The low order byte is then set on the 8 bit data bus latched through and held on the output of IC5 8 bit data latch also the input of the 16 bit digital to analog converter At the same time the high order byte is latched through and held on the output of IC 4 8 bit latch also the input of the 16 bit digital to analog converter completing the 8 bit parallel to 16 bit parallel conversion The 16 bit complementary offset binary is then converted to a linear output current in the range of 2mA by IC6 digital to analog converter The analog current is converted to a corresponding output voltage by IC7 Slope and zero presets are factory set to correct but may be adjusted if necessary Specification Resolution 16 bit Analog Output range 10vdc Scrutiny front panel selectable 1 10 100 1000 Linearity 0 0015 FS typical 0 3mV Linearity 0 003 FS max 0 6mV Monotonicity 14 bit ion Per Scal Scale Analog Ou
17. ance Example To set the DP251 to send channel A data when it is available send M01001001 To cancel output from the DP251 send M01000000 Analog Output Figure 9 6 Analog Output The DP251 analog output provides a dc output voltage in the range of 10 volts that is directly proportional to the displayed reading and selected scale factor The analog output is updated on completion of every balance cycle and is obtained by digital to analog conversion from the digital measurement Defaul in On power up of the DP251 the instrument will revert to the following default settings Measurement units deg C Measurement channel A Resolution low resolution Analog output scale factor 1000 9 5 1 Scale Factor The analog output full scale voltage can be scaled to represent a change in displayed units of 1 10 100 or 1000 displayed units may be C F or ohms To view or alter the scale factor of the analog output enter the scale factor menu by pressing the switch of the data entry keypad The display will flash A OP to indicate that you have entered the analog output menu it will then continue to cycle through displaying the available scale factor options with the associated data entry key for each scale factor selection To indicate the current set scale factor when it appears on the display it will repeatedly flash To select the required scale factor press the appropriate data entry keypad number associated with th
18. ar or general reset resets the DP251 to it s switch on state Syntax C Parameters None Initial State Not applicable COMMAND F Function Sets the sensitivity of the analog output if installed Syntax Fn where n 0 1 20r3 Parameters n 0 selects 10v degree or ohm n 1 selects 1v degree or ohm n 2 selects 0 1v degree or ohm n 3 selects 0 01v degree or ohm Initial State n 3 0 01v degree or ohm 29 30 COMMAND Function Syntax Parameters Initial State COMMAND See Section 9 4 Syntax Parameters COMMAND Function Syntax Parameters Initial State COMMAND Function Syntax Parameters Initial State COMMAND Function Syntax Parameters Initial State COMMAND Function Syntax Parameters Initial State L Local lockout enables or disables the DP251 front panel controls Ln where n 0 or 1 n 0 enables front panel lockout off n 1 disables front panel lockout on n 0 lockout off Mn where n A B C or D n cancels Service Request n A sets probe to A and Service Request on when reading available n B sets probe to B and Service Request on when reading available n C sets probes to A B and Service Request on when reading available n D sets probes to alternate A then B and Service Request on when reading available P Set probe input for display Pn wheren 0 10r2 n 0 selects the A input for display n 1 selects the B input for dis
19. d temperatures The prt s supplied by OMEGA have been optimized for their stated ranges and where calibrated temperature cycled to enhance stability in use Probes which are used outside their design and or calibration range especially higher temperatures risk alteration to their calibration either by induced thermal stresses or by contamination caused by materials being used beyond their recommended ranges 7 2 1 Uncalibrated 1 3rd DIN PRT Ro 100 0 a lt 0 00390 typically 0 00385 Range 50 C to 250 C Sheath Stainless Steel Sheath Size 350mm x 6mm diameter Cable Length 2 Meters Calibration UNCALIBRATED 1 3rd DIN 7 2 2 PRP 2 PRP 3 PRTs Ro 100 Q a lt 0 00390 typically 0 00385 Range 50 C to 250 C Sheath Stainless Steel Sheath Size 350mm x 6mm diameter Cable Length 2 Meters Calibration 4 point 50 0 100 and 250 C Cal Uncertainty 0 01 C NIST traceable 19 7 2 3 PRP 4 PRP 5 PRT s Ro 100 Q a lt 0 00390 typically 0 00385 Range 70 C to 450 C Sheath Stainless Steel Sheath Size 350mm x 6mm diameter Cable Length 2 Meters Calibration 4 point 70 0 100 and 420 C Cal Uncertainty 0 04 C 70 to 50 C 0 01 C gt 50 to 250 C 0 1 C gt 250 to 450 C NIST traceable 7 2 4 Environmental Chamber Probe Contact OMEGA Ro 100 Q a lt 0 00390 typically 0 00385 Range 70 C to 200 C Sheath Stainless Steel Sheath Size 30mm x 3mm diameter Cable Length 2 Me
20. d then be marked on the outside of the return package and on any correspondence FOR WARRANTY RETURNS please have the FOR NON WARRANTY REPAIRS OR CALIBRA following information available BEFORE con TION consult OMEGA for current repair tacting OMEGA calibration charges Have the following infor 1 PO number under which the product was mation available BEFORE contacting OMEGA PURCHASED 1 P O number to cover the COST of the 2 Model and serial number of the product repair calibration under warranty and 2 Model and serial number of product and 3 Repair instructions and or specific prob 3 Repair instructions and or specific problems lems relative to the product relative to the product OMEGA s policy is to make running changes not model changes whenever an improvement is possible This affords our customers the latest in technology and engineering OMEGA is a registered trademark of OMEGA ENGINEERING INC Copyright 1995 OMEGA ENGINEERING INC All rights reserved This documentation may not be copied photocopied reproduced translated or reduced to any electronic medium or machine readable form in whole or in part without prior written consent of OMEGA ENGINEERING INC Where Do Find Everything I Need for Process Measurement and Control OMEGA Of Course TEMPERATURE Thermocouple RTD amp Thermistor Probes Connectors Panels amp Assemblies 4 Wire Thermocouple RTD amp Thermistor A Calibra
21. ded that a value of nominally 2 ohms higher than the maximum calibration value is entered this will avoid an out of range error message 15 tit The maximum difference between r Lo and r hi must be no greater than 396Q or an error will occur See error codes in Chapter 10 Almost certainly this range is greater than many probes and most applications The calculation time for a smaller range is also shorter iv Where values for coefficients are not provided in ITS90 or CvD coefficient entry for example if no calibration is carried out below 0 C and no An or bn values given the value 0 or a no entry should be made followed by ENTER v Once the look up table number countdown has started you can turn the RUN CAL switch back to RUN If you do this DP251 will start to measure temperature immediately at the end of the entry process and will not prompt you for further data Vi if you are entering data for more than one Input or Channel then any combination of the 5 conversion methods may be used Chapter 5 Working with the DP250 8 or DP250 16 Multiplexer 5 1 16 DP250 8 8 channel and DP250 16 16 channel multiplexers have been specially designed to allow thermometer Inputs A and B on the DP251 to be expanded to measure up to 16 channels each with no degradation in instrument performance Both direct absolute and differential measurements can be made when using the DP250 8 or DP250 16 multiplexer Connection and
22. digital communications interface 1 E488 parallel digital communications interface dc Analog Output The board itself is normally factory installed but can be retrofitted by the user The interface board has 3 separate areas each devoted to one of the options as indicated below and may be installed in the DP251 in one of two orientations depending on which digital interface is used If an analog output is included an outpu socket is installed at both ends of the board to enable access no matter which digital interface is being used When the DP251 is turned on the display will show rS232 even if no board or RS232C is installed If IEEE488 is installed the start up display will show IEEEn where n is the number from 1 to 7 for the IEEE controller address in the DP251 Retro fitting or Changing an Interface Board The interface board will normally be factory installed but can be installed by a competent technician As the interface board can be dual purpose for example both RS232C and IEEE 488 may be installed it may from time to time be necessary to reverse the board to access one or other interface WARNING Turn off the instrument and remove the power supply cord before removing the instrument case 21 9 1 1 Retro fitting 3 4 Remove the 4 screws holding the top half of the instrument case and lift off vertically The interface board may be installed with any combination of RS232C IEEE488 or Analog outputs
23. dsanesusasdhysencchcgsivessauavetiainccdicsdasasiesusansbionets 42 40 ACCUTANE titi 12 2 Resol iii a rd iS bebo 12 5 Slade daa te tadeds 12 4 General AI 12 5 ARM ui ed eee 126 Environment 2203 ie tata lr E 17 17 17 18 This page is intentionally left blank Chapter 1 Introduction 1 1 Description The DP251 Precision Digital Thermometer is based on ac bridge technology the performance and multi channel capabilities of which make it ideal for a wide range of applications The DP251 operates with any 4 wire Pt100 100 ohm Platinum Resistance Thermometers prt to provide temperature measurement in C F K Kelvin plus resistance in ohms The ac Resistance Ratio Bridge technology provides a basic accuracy for the instrument alone of 0 01 C 10mK see temperature equivalents below or up to 20mK with calibrated prts A more detailed specification can be found in the specifications however the overall system accuracy will always depend on the quality of probe used Temperature Equivalents 1 milli degree C 0 001 C 1m C 1mK 1 8m F 1 milli degree F 0 001 F 1m F 0 56mK 0 56m C The DP251 Precision Thermometer has a useful range of features Two measurement inputs A amp B are provided enabling A B or their difference A B to be displayed Both A and B inputs will operate with 8 or 1 channel models DP250 8 and DP250 16 multiplexers enabling up to 32 prts to be measured The DP250
24. e DP251 uses probe calibration data to overcome this problem and creates a look up table stored in EPROM non volatile memory within the instrument The look up table enables the DP251 to convert resistance accurately to temperature uniquely for each probe used up to 32 when DP250 8 or DP250 16 multiplexers are connected It is very important therefore that thermometers are used on their correct Input or Channel for accurate measurement The SYSTEM accuracy is a combination of the DP251 accuracy at measuring resistance and the calibration uncertainty placed on the thermometers by the calibrating laboratory Typically this sum for OMEGA probes type PRP 2 PRP 3 and PRP 4 PRP 5 is 0 025 C depending on the temperature range Non volatile memory retains information stored in it even when all power is removed from the instrument Chapter 2 Parts Of The Thermometer 2 1 Front Panel Figure 2 1 shows the DP251 front panel the functional parts of which are described below EOMEGA DP251 PRECISION THERMOMETER A B A B Zero HiRes Figure 2 1 Front Panel umber Description Channel A Input Socket Channel B Input Socket Numeric Keypad Digital Display Channel A Selector Switch Channel B Selector Switch Channel A Channel B Selector Switch Zero Switch Hi Resolution Switch Units Selector Switch Run Calibrate Switch RSCMONOMAWN 2 1 1 Probe Input Connectors A and B 5 pin DIN sockets to allow the connection o
25. e DP251 has thermometer inputs which are also used for connection to multi channel multiplexers also with thermometer inputs it useful to differentiate between them In this manual inputs on the DP251 are referred to as Inputs and those on the multiplexers are referred to as Channels Platinum resistance thermometers are regularly referred to with several alternative abbreviations as follows PRT PT100 PRT with 100Q resistance at 0 C RTD In this manual Platinum Resistance Thermometers are also referred to as probes or sensors System accuracy refers to the overal combined accuracy of the DP251 and the prt in use plus a small amount to allow for additional margin Basic Principles Of Operation DP251 operates with 100 ohm Platinum resistance thermometers prts by first measuring the ratio n of their resistance Rt to that of a very stable internal reference resistor Rs The instrument is calibrated with its reference resistor so that it is able to determine very precisely using n Rt Rs the actual resistance of the thermometers connected to an input from R n x R For resistance thermometers the relationship between resistance and temperature varies slightly from one prt to another Therefore no matter how accurately the DP251 measures the probe resistance if we do not know the relationship between resistance and temperature for a particular probe we will not be able to accurately measure temperature Mod
26. e board on the left when looking at the DP251 from the front The DIP switch has a row of small lever switches down one side the one nearest the rear is number 1 so the front lever is number 8 aN pu Switch imernal S23 Figure 9 3 Board Layout 3 When a lever is in the down position this is ON or 1 so you can adjust the switches according to the following tables Baud Rate Baud rates Switches Parity ee eee Pemeaw oe f osea fo o x eithera 1ora0 Data Bits Switch Stop Bits 1 Stop Bit 2 Stop Bits 1 NOTE Switch 8 is not used 24 142 Examples To set 4800 Baud no parity 8 data bits and 1 stop bit select the following Note x either a 1 or a0 To set 9600 Baud even parity 8 data bits and 2 stop bits select the following Note x either a 1 or a0 When set to your requirements replace the instrument top lid and secure with the 4 screws 9 2 3 Interpretation Commands sent are executed after a line feed or carriage return line feed combination If the input buffer within the DP251 becomes full 64 bytes including carriage return CR line feed LF the commands are also executed as far as the end of the buffer The DP251 returns data almost immediately after receiving the command Q T or D The controlling device must therefore be ready to receive as soon as the command is sent All data returned is terminated with a CR LF sequence No lead
27. e required scaling factor Data Entry Scaling Factor Sensitivity Keypad No o i a 10v degree or ohm q 10 1v degree or ohm 2 100 0 1v degree or ohm 3 1000 0 01v degree of ohm On pressing the appropriate data entry keypad number the display will flash your choice store it and return the instrument to run mode On completion of the next balance cycle the analog output will be updated Alternatively to the keypad the scaling factor can be set via the RS232 or IEEE interfaces if installed by sending the common Fn where n 0 1 2 or 3 as for the keypad 9 5 2 Analog Output Connection Connection to the analog output is via an insulated BNC output socket on the rear panel of the DP251 instrument Connection to peripheral equipment should be made via a suitable twin core twisted pair screened cable see Figure 9 7 to the instrumentation input amplifier of the peripheral equipment BNC INNER INSTRUMENTATION BNC INPUT AMP OUTER Figure 9 7 Twin Core Twisted Pair Screen Cable 9 5 3 Analog Output Operation A more detailed explanation of the analog output operation follows The DP251 analog output provides a dc output voltage in the range of 10 volts that is directly proportional to the displayed reading and selected full scale reading The analog output is updated on completion of every balance cycle the measurement value is held in a variable called DAC BUFF in BCD format The contents of DAC BU
28. e the shipment inspect the container and the equipment for signs of damage Note any evidence of rough handling in transit Immediately report any damage to the shipping agent NOTE The carrier will not honor damage claims unless all shipping material is saved for inspection After examining and removing contents save packing materia and carton in the event reshipment is necessary Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 TABLE OF CONTENTS Introduction Wii ida 1 1 DESCUIDO aii lA ita bine 1 2 Definitions and Terminology used in this Manual coccion 1 3 Basic Principals of Operation 0 0 0 snene rasne nrinn Parts Of The Thermometer csscscsssecscsssccerssssssecrosscssssesceceseaseceessseneasscecesserceseavecesersers 2 1 Front a EE E EAE A EN E E Oe E oa 2 1 1 Probe Input Connectors A amp Bu cccccesccecssccseseecsesseeseetanesens 2 1 2 Data Entry Keypad o00 ccc cscescsecsseeccescesesstscsessetseesseescsesees 213 DISPLAY ii A ads 2 1 4 Main Selection Switches ccccccccescssesssessesesesestsseceessacseeceeeeneecacacs 215 AN 21 6 RUN Cal ia Led shave ata i 2 2 Rear Panel aio ei ces ve corti hen oi cesses Mat vie ce lle aa A eee natn eo 2 2 1 ac Power Input Socket ccc cccscesccecescecseseceeesecsececsesaeseeereaeeavaes 2 2 2 Power ON OFF SWitCh a0 ccc ccc ccccecesceececeeesseeessscenasensecsaesuaenaeesnes 2 2 3 Digital Analog Output Options 0 0 cecesceseecescecescecseeeacssesesecaes
29. ecsscescesceeecescausascsassstssvesensonsevaceuee 425 Callendar van Dusen method using coefficients 4 26 DIN Standard tucan 4 2 7 Callendar van Dusen method using data pairs oocoocinnin 4 2 8 DIN using proposed new coefficients to align temperatures with ITS90 4 2 9 General Comments 00 0 ccc ceccecceccseeesseseecvesevseceeeascesvasseasseenaeeseeseates Working With DP250 8 or DP250 16 Multiplexer cccscccesscscsessscssessscrsssaceescareres 5 1 Connection and Control co ooooooooiciocococcccocococannnnonnnoconnancnnocncononan cacon cnonocncnccanoncnannans 5 1 1 Multiplexer AdUFesS oocooccoocoonccononccionoccnonoconononicinononononcnnnccnccncnncononenoo 5 12 Connections ota Lt is S 3s T MS oss IS Oe 5 2 Probe Data Entry c cs ie ctziee pits ast ae ted dh a iii o MAOMOOaAnAnMAAA A A WwW DW w NNOO f Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 11 Chapter 12 AMIE EARL o e 6 1 DP25 i titeres acetal aad ee afd es ena etn 6 2 Resistance Thermometers Sueccoevsaseuseccoecseucoaseseevessosssnssnsassasssoosoessoscenonsouuaaosesssssasnpensesopososesasosaoressss 7 1 High Alpha PRE a A n aa 7 1 1 183 C to 560 C PRT renina a aan a a A TAZ OO S O O PRY a A a aiii 7 2 Low Alpha A ee ARR 7 2 1 Uncalibrated 1 3rd DIN PRT nreno 122 PRP 2 PRP 3 PRIS oia adds oa cdas 1 23 PRP PROS PRTS uc a 7 2 4
30. ed thermometers In particular th calibration of a platinum resistance thermometer can no longer be extrapolated beyond the freezin point of zinc 419 527 C but requires a measurement at the freezing point of aluminum 660 323 C iti Alternative definitions are permitted in certain sub ranges so that the calibration of a thermomete can be terminated at almost any fixed point This provision allows primary calibrations to be carrie out with suitable thermometers over reduced ranges and will be of especial importance t metrologies who need to make precise measurements at ambient temperatures iv The scale extends to 0 65 K by specifying the use of an interpolating gas thermometer and heliur vapor equations By virtue of these and other changes ITS 90 has much improved continuity precision and reproducibility compared with IPTS68 The implementation of the scale according to it s definition calls for significant changes in equipment and procedure but lower uncertainties of calibration will be achievable in all parts of the range On the other hand the instruments and equipment needed for it s dissemination to and from secondary calibration laboratories will be substantially the same if you would like more detailed information regarding ITS90 contact OMEGA Chapter 9 Communications Output Options 9 1 An optional output board may be installed in the DP251 and can be supplied with any combination of 3 interfaces RS232C serial
31. eld in non volatile memory EPROM within the multiplexer itself although data entry is performed in the same way as when using the DP251 alone and as described in Section 4 2 The 5 alternative methods of data entry ITS90 Callendar van Dusen coefficients DIN Callendar van Dusen data pairs and DINQO are available as with the DP251 alone Follow the data entry procedure in Section 4 2 taking particular note of the requirements when a multiplexer is connected Once data entry has started the appropriate DP250 8 or DP250 16 channel will be selected to enable the data to be stored in the section of the EPROM reserved for that channel Chapter 6 Calibration 6 1 6 2 DP251 The ac bridge technology of the DP251 is inherently very linear however this is improved further by calibration during final test After soak testing each DP251 is measured against four 4 precision resistors which are traceable to International Standards This calibration information is then stored in non volatile memory within the instrument providing a corrected linearity to better than 10mK The long term stability of ac bridge technology makes this method of linearization valid over long periods of time and it will not normally be necessary to re linearize the DP251 on a regular basis Experience has shown that other instruments using this method have very little correction necessary after several years of use Unlike calibration data entry for prts instrument
32. ete The message stored confirms that the look up table has been created and safely stored in memory but in case you require to enter data for another channel the message ChAn appears along with Inputs A and B turning alternately on off If more channels require data entry follow the procedure as described under the appropriate method If no additional data entry is required turn the RUN CAL switch to RUN when the screen will display the message Abort This message indicates that you have left Data Entry CAL mode and is accompanied by an audible beep 4 2 8 DIN using proposed new coefficients to align temperatures with ITS90 When 5 is selected from the menu an alternative method for generating a DIN look up table is available Until this new equation set is approved by the IEC it is stressed that this route is not Officially recognized The advantage is that it removes the errors associated with the current DIN which is based on the earlier and obsolete International Practical Temperature Scale IPTS68 Example ispl m Value Key Input r Lo 65 5 ENTER 6 5 5 ENTER rhi 196 8 ENTER 11 91 61 J S ENTER When all data has been entered the display initially goes blank As the DP251 starts to generate the resistance temperature look up table the actual number of points to be generated will appear on the display and will count down to 0 at which point the process will be complete The message stored confir
33. except in ohms in high resolution mode when it is 10 characters long CR LF TorD None Not applicable U Sets the units on the DP250 to C F K or Q ohms Un where n 0 1 2 or 3 n 0 selects C n 1 selects K n 2 selects F n 3 selects Q ohms n 0 C Z Sets present reading to zero null or clears a zero if already set None No zero 9 3 28 IEEE488 Interface The optional IEEE488 interface allows the DP251 to be controlled by an external computer and apart from some additional features it uses the same device dependent commands as described under the RS232C interface All the primary functions on the front panel can be controlled If the IEEE option is installed then the DP251 will display it s device address during the start up display routine as follows EEE n where n is the device number 1 to 7 pano sma mac bav poi oos 9 3 1 Pin Connections Pin connections for EEE488 are shown in Figure 9 4 Figure 9 4 IEEE Connector 9 3 2 lEEE488 Setting Address Selection To set the device address the rotary switch on the interface panel at the instrument rear is used The switch has positions 0 to F though only addresses 1 to 7 should be used Positions 9 to F simply repeat the sequence Address 0 is used for the RS232C controller so is not available for IEEE When delivered the switch is set to 3 The address switch is only interrogated at turn on or after a clear command so if the addre
34. f suitable resistance thermometers to the DP251 Connection details are shown in Figure 2 2 Note Each front panel input is connected in parallel to a 5 pin terminal socket on the rear panel for use with 4 wire probes without DIN plugs therefore Input A must only have a probe connected to the front socket OR the back socket NOT to both Similarly for Input B However it is permissible to have a thermometer connected to the front socket of Input A and a thermometer connected to the rear socket of input B and vice versa FRONT PANEL REAR PANEL DIN SOCKET SCREW TERMINAI Figure 2 2 Probe Input Connectors ca 2 1 2 Data Entry Keypad The 16 key Keypad permits entry of data into the DP251 memory It operates in conjunction with visual instructions displayed on the instrument readout and is primarily for storing thermometer calibration data As data entry can be corrupted by unauthorized entry access to this function on the keypad is limited to those personnel with a key to fit the Run Cal lock see Section 2 1 6 Other functions include bright dim control of the display using the right left arrows respectively gt lt 2 13 Display A 6 digit numeric vacuum fluorescent display Since the 6 digits include the minus sign for negative temperatures those lower than 99 999 C F will be limited to 2 decimals resolution for example 100 00 C F To obtain 3 decimal resolution in these cases switch to K Kelvin as this re
35. gh 9 45 Deep x 10 24 Wide x 3 15 High Weight 2 6kg 5 72Ibs NOTES 39 40 NOTES WARRANTY o be free of defects in materials a tory service for a period of 13 months from date of purchase OMEGA Warranty adds an addition al one 1 month grace period to the normal one 1 year product warranty to cover handling and shipping time This ensures that OMEGA s customers receive maximum coverage on each product If the unit should malfunction it must be returned to the factory for evaluation OMEGA s Customer Service Department will issue an Authorized Return AR number immediately upon phone or written request Upon examination by OMEGA if the unit is found to be defective it will be repaired or replaced at no charge However this WARRANTY is VOID if the unit shows evidence of having been tampered with or shows evidence of being damaged as a result of excessive corro sion or current heat moisture or vibration improper specification misapplication misuse or other operating conditions outside of OMEGA s control Components which wear or which are damaged by misuse are not warranted These include contact points fuses and triacs OMEGA is glad to offer suggestions on the use of its various products Nevertheless OMEGA only warrants that the parts manufactured by it will be as specified and free of defects OMEGA MAKES NO OTHER WARRANTIES OR REPRESENTATIONS OF ANY KIND WHAT SOEVER EXPRESSED OR IMPLIED EXCEPT TH
36. ied coefficients from a draft proposal referred to the IEC fo adoption This brings the coefficients for DIN in line with ITS90 temperatures Uncalibrated probes conforming to EC751 DIN 43760 BS1904 would normally use method 3 which provides a conversion identical to readily available DIN or BS1904 tables However these tables were created using temperatures as defined by the obsolete Temperature Scale IPTS68 and as such have errors OMEGA has included the new version as adoption is likely in the near future 10 4 2 2 General Rules for Data Entry When the question prompt is displayed such as r LO first press ENTER to confirm that you understand what data is required The display then changes to the cursor when the numerical data can be entered and then press ENTER again to confirm and to move to the next entry Mistakes in data entry can be corrected easily provided the number has not been Entered in other words the final ENTER has not been pressed i ii iil 4 2 3 If the data has been entered i e ENTER pressed the next prompt will be displayed and no correction is possible Turn the key to RUN to exit the CAL mode then back to CAL to start again So always double check data entered before pressing ENTER if the data has not been entered it can be edited Use lt or gt keys to move the flashing digit and re type over the incorrect data Alternatively pressing CLEAR while on a
37. ing or trailing spaces are sent When command A is used the DP251 sends data after every measurement update Section 9 2 4 gives full details of the command set 9 2 4 Commands and Syntax All of the primary functions available from the DP251 front panel can be accessed via the serial interface typically from an external computer or terminal Following is a list of the commands that can be sent to the DP251 all are single letters followed by up to 2 single digit parameters with the exception of the multiplexer commands which have 2 alphabetical characters followed by 2 digits 26 COMMAND Function Examples Syntax Parameters Initial State COMMAND Function Syntax Parameters initial State COMMAND Function Syntax Parameters Initial State COMMAND Function Syntax Parameters Initial State COMMAND See Section 9 4 Syntax Parameters COMMAND Function Syntax Parameters A Requests the DP251 to send back the probe setting the temperature or resistance and the units every time the display is updated The probe may be A B or D differential and units may be C F Kor A 0 00C or B273 150K Note that the return string is always 9 characters long plus CR LF except in ohms in high resolution mode when it is 10 characters long CR LF An where n 0 1 2 3 or 4 n 0 selects probe A n 1 selects probe B n 2 selects probe A B differential n 3 selects alternate m
38. ix CP diG Coefficient C digits enter in the same way as for A Example Display Prompt Value Key Input 10 100 005 ENTER 1 O O f O O S ENTER r Lo 79 ENTER 7 9 ENTER rhi 198 ENTER 1 9 S ENTER AP EE 3 ENTER IS ENTER AP diG 5 3 ENTERJISIJISIENTER and so on with B EE B diG C EE and C diG Where values for coefficients are not provided in CvD coefficient entry for example if no calibration is carried out below 0 C and no value for C is given the value 0 or no entry should be made followed by ENTER When all data has been entered the display initially goes blank As the DP251 starts to generate the resistance temperature look up table the actual number of points to be generated will appear on the display and will count down to 0 at which point the process will be complete The message stored confirms that the look up table has been created and safely stored in memory but in case you require to enter data for another channel the message ChAn appears along with Inputs A and B turning alternately on off If more channels require data entry follow the procedure as described under the appropriate method If no additional data entry is required turn the RUN CAL switch to RUN when the screen will display the message Abort This message indicates that you have left Data Entry CAL mode and is accompanied by an audible beep If the coefficients entered are as below A 3 90802 x
39. l appear on the display and will count down to 0 at which point the process will be complete The message stored confirms that the look up table has been created and safely stored in memory but in case you require to enter data for another channel the message ChAn appears along with Inputs A and B turning alternately on off if more channels require data entry follow the procedure as described under the appropriate method If no additional data entry is required turn the RUN CAL switch to RUN when the screen will display the message Abort This message indicates that you have left Data Entry CAL mode and is accompanied by an audible beep 4 2 5 Callendar van Dusen using coefficients On selecting 2 the Callendar van Dusen equations data entry is required for the following information which apart from i and ii should be available from the thermometer calibration certificate see general comments Section 4 2 9 i 10 Probe resistance at 0 C ii rlo Minimum resistance value for the conversion table iii rhi Maximum resistance value for the conversion table iv AP EE Coefficient A exponent e g if A 5 3 x 10 enter 3 v AP diG Coefficient A digits e g if A 5 3 x 10 enter 5 3 if 5 3 then enter as 5 3 vi bP EE Coefficient B exponent enter in the same way as for A vii bP diG Coefficient B digits enter in the same way as for A viii CP EE Coefficient C exponent enter in the same way as for A
40. linearization is not a user entry option Resistance Thermometers For accurate temperature measurement the DP251 uses stored data for each prt that it operates although for less accurate work this data can be the general industrial specification for resistance thermometers IEC751 which encompasses more familiar specs such as DIN43760 Additionally 100 Ohm prts are available in low and high Alpha wire although the former is the norm for industrial applications See Chapters 7 and 8 on Sensors and on the International Temperature Scales respectively Calibrated Platinum resistance thermometers supplied with the DP251 will be traceable to the National Institute of Science and Technology and therefore to International Standards 17 As described in Sections 7 and 8 in more detail the relationship between temperature and resistance varies depending on several factors including their Alpha value Consequently more than one equation is required for resistance to temperature conversion Calibration data for the thermometers can also take the form of either data pairs or coefficients The DP251 therefore gives the user 5 alternative data entry formats Section 7 provides more detailed instruction on data entry methods Chapter 7 Sensor Information 7 1 18 The DP251 will operate with any 4 wire 100 Ohm prt often referred to as Pt100 however the best performance will only be extracted if good quality probes are used from reputable p
41. ms that the look up table has been created and safely stored in memory but in case you require to enter data for another channel the message ChAn appears along with Inputs A and B turning alternately on off If more channels require data entry follow the procedure as described under the appropriate method If no additional data entry is required turn the RUN CAL switch to RUN when the screen will display the message Abort This message indicates that you have left Data Entry CAL mode and is accompanied by an audible beep 4 2 9 General Comments i rLo This is the minimum resistance for DP251 to generate a temperature resistance look up table This resistance should in general not be lower than the range over which the probe has been calibrated and for which coefficients have been provided The DP251 will generate a conversion table over a wider range but temperatures derived from extrapolation beyond the calibration minimum point will not be traceable to International Standards It is recommended that a value of nominally 2 ohms lower than the minimum calibration value is entered this will avoid an out of range error message ii rhi The maximum resistance for DP251 to generate a temperature resistance look up table This resistance should in general not be higher than the range over which the probe has been calibrated and for which coefficients have been provided The extrapolation rule above applies It is recommen
42. n the front panel indicating which channel is selected The same LEDs are also used to indicate the selected channel when probe calibration data is being entered Power calibration table data and channel select information is all carried on a ribbon cable between the DP251 and the DP250 8 or DP250 16 The ribbon cable is connected between the Control Input port on the DP250 8 or DP250 16 and the Expansion Port on the DP251 The 4 wire measurement signals plus ground are carried separately from the Output screw terminal on the DP250 8 or DP250 16 to the appropriate A or B Input on the DP251 5 2 5 13 Turn On After connecting the DP250 8 or DP250 16 to the required Input on the DP251 as described above turn on and the display test will proceed as in Section 3 1 3 If necessary reset the address switch to the required Input Connect a thermometer to channel 0 either via the front panel connector or the back panel connector but not both With no calibration data installed the DP251 will be able to display resistance only so set units to Q ohms Using the A or B push buttons on the DP251 select the Input with the multiplexer attached upon which the prompt for channel number will appear Ch Enter the channel number 0 and press ENTER Note when the channel number is two digits it is accepted automatically and pressing ENTER is not required Probe Data Entry When DP250 8 or DP250 16 multiplexers are used probe data is h
43. nd B 5 pin Terminal connectors This rear panel connection is for use where 5 pin DIN plugs are not installed to thermometer cables Note the warning regarding front and back panel probe connectors in Section 2 1 1 Chapter 3 Installation 3 1 Power Supply Connection 3 1 1 Checking Voltage and Fuse Rating WARNING DO NOT CONNECT THE POWER CORD OR SWITCH THE UNIT ON UNTIL THE VOLTAGE AND FUSE RATING OF THE INSTRUMENT HAS BEEN CHECKED AND CHANGED IF NECESSARY The supply voltage setting of the DP251 is shown on the power inlet socket on the rear panel Check that this corresponds to the local voltage and that the fuse installed is as specified Voltage select Figure 3 1 Power Input Unit and Fuse Rating Block 3 1 2 Setting the Voltage and Fuse Rating Selection is achieved by levering open the power inlet filter from the top with a flat bladed screwdriver Insidi is a plastic cam remove this and then replace it so that the voltage to be set is displayed through the window See Figure 3 1 Where fused power plugs are installed to the supply cable provided the correct fuse rating is 3 Amp The supply cable provided with the DP251 is color coded as follows Ground Green Yellow Live Brown Neutral Biue 3 1 3 Turn On and Start Up Display Once you are certain that all is correct connect the DP251 to a single phase 50 60 Hz grounded power outlet and with the RUN CAL switch in the RUN position switch ON Initially do n
44. ode n 4 cancels continuous output Not applicable Note Sets service request mask when used with IEEE interface see Section 9 3 4 Cc Clear or general reset resets the DP251 to it s switch on state C None Not applicable F Sets the sensitivity of the analog output if installed Fn where n 0 1 2 or 3 n 0 selects 10v degree or ohm n 1 selects 1v degree or ohm n 2 selects 0 1v degree or ohm n 3 selects 0 01v degree or ohm n 3 0 01v degree or ohm L Local lockout enables or disables the DP251 front panel controls Ln where n 0 or 1 n 0 enables front panel lockout off n 1 disables front panel lockout on n 0 lockout off Mn where n A B C or D n cancels Service Request n A sets probe to A and Service Request on when reading available n B sets probe to B and Service Request on when reading available n C sets probes to A B and Service Request on when reading available n D sets probes to alternate A then B and Service Request on when reading available P Set probe input for display Pn where n 0 1 or 2 n 0 selects the A input for display n 1 selects the B input for display n 2 selects A B differential for display Initial State COMMAND Function Syntax Parameters Initial State COMMAND Function Syntax Parameters Initial State COMMAND Function Syntax Parameters Initial State COMMAND Function Examples Synta
45. ot connect a temperature probe to either input channel After switch on all the switch lights LEDs or light emitting diodes should be on and the digital display will proceed through a short self test with all digits showing the number 8 Also all the decimal points will illuminate one at a time This is to check the integrity of the display and it s drivers After this initial procedure the display will change to show the IEEE address if this option is installed and oi RS232 whether or not this is installed When the display test has finished the DP251 will set to the default Start up condition that is Channel A C and low resolution The display will indicate the error code E 1 which indicates no probe is connected or open circuit exists on input A See Error Codes in Chapter 10 for lt full list and description of error codes Tum off the DP251 connect a thermometer to Input A and now tum on the instrument again After the initial display test the display should now indicate a temperature in C and low resolution Check that you can change units to F K and Q ohms and then back to C by repeatedly pressing the Units switch Check alsc that you can select high resolution with Hi Res and that the display can be set to zero with the Zero buttor Unless you have a second thermometer connected to Input B then selecting it will cause the E 1 message t be displayed as will selecting A B Note that in high resolution mode
46. play n 2 selects A B differential for display n 0 probe A being measured and displayed orQ Query the DP251 will return the status of the function a or Qa where ais P R U Zor _ a P queries the probe setting 0 1 or 2 a R queries the resolution setting 0 or 1 a U queries the units setting 0 1 2 or 3 a Z queries the zero function setting 0 no zero set 1 zero set a _ queries all settings plus reading Not applicable R Sets the DP251 resolution as 2 or 3 decimal places Rn where n O or 1 n 0 selects 2 decimal places 3 decimals for ohms n 1 selects 3 decimal places 4 decimals for ohms n 0 2 decimal places S Remote control of the optional DP250 8 and DP250 16 multiplexers if used Smn where m A or B and n is a number 00 to 15 m A directs control to the multiplexer on channel A m B directs control to the multiplexer on channe B n the number of the channel on the selected multiplexer SA00 SB00 Note 4 characters must be sent to form a valid command for example SA02 SB13 9 4 COMMAND Function Examples Syntax Parameters Initial State COMMAND Function Syntax Parameters Initial State COMMAND Function Syntax Parameters Initial State TorD Asks the DP251 to send the probe setting the reading to the present resolution and the units The probe may be A B or D differential and the units may be C K F or Q ohms A 0 003C or B 7
47. plexer channel is selected the IEP indicates the 5 data entry options sequentially as shown in Figure 4 5 To select the option you require for your probe 1 2 3 4 or 5 press the appropriate number on the keypad For example if data entry is required in Callendar van Dusen coefficients press 2 On selecting the data conversion method the display will momentarily flash confirmation of the operator s choice Switch action 2 Conversion equation type 2 is example only Total switch actions with multiplexer CALJ A O 71 2 Total switch actions without multiplexer CALJ A 2 Figure 4 5 Temperature Selection Scrolling Menu v The DP251 will now request data from the probe calibration certificate This will vary according to thu choice of resistance to temperature conversion made but before moving to the appropriate sectio please note the general rules above on entering and correcting data vi Now go to the following section for ITS90 Section 4 2 4 CvD coeff Section 4 2 5 DIN Section 4 2 6 CvD d p Section 4 2 7 DIN 90 draft Section 4 2 8 4 2 4 ITS90 Data Entry On selecting 1 the ITS90 equations data entry is required for the following information which apart from ii and iii see general comments Section 4 2 9 should be available from the thermometer calibration certificate i 10 01 Resistance R at 0 01 C Triple point of Water ii rLo Minimum resistance value for the conver
48. quires no minus sign 2 1 4 Main Selection Switches A Selects the probe connected to Input socket A front or back panels for display B Selects the probe connected to Input socket B front or back panels for display A B Selects display to read the difference between A and B thermometers Zero Nulis the present DP251 reading and the display then indicates any subsequent changes relative to this value Hi Res Sets the DP251 to high resolution mode for example normally 0 001 C F or K or 0 001 ohm when set to Q ohms 2 1 5 Units Selects display units C F K or Q ohms Continuous operation of the Units switch cycles the selection top to bottom 2 16 Run Cal This key operated switch allows the operator to enter calibration data pairs or coefficients for Inputs A and B and for up to 16 thermometers connected to each Input via the DP250 8 or DP250 16 multiplexers A data pair is a value for temperature and the resistance value for a probe at that temperature The data so entered is used to produce an internal look up table unique to that probe enabling the best accuracy conversion from resistance to temperature 2 2 Rear Pane Figure 2 3 shows the DP251 rear panel the functional parts of which are described below Figure 2 3 Rear Panel Number Description Grounded Power Outlet Power ON OFF Switch Fuse Rating Label Address Label Serial Number Label Multiplexer Expansion Port Analog Output
49. roven sources As with any measured parameter the performance of a measurement system is dictated by stability and repeatability and low quality Pt100 s will most likely reduce the system performance For this reason OMEGA provides a range of proven prt s specially for use with the DP251 as well as offering a service of customized probes to meet individual requirements High Alpha PRTs The best possible system accuracy is achieved using high Alpha 1 probes or more correctly probes using high a wire This is because the way that they are constructed usually permits a better calibration uncertainty on the thermometer and therefore the system 7 1 1 183 C to 500 C PRT Contact OMEGA Ro 100 2 a 20 00390 Range 183 C to 550 C Sheath Fused Silica Sheath Size 480mm x 8mm diameter Cable Length 2 meters 7 1 2 0 to 550 C PRT Contact OMEGA Ro 100 Q a gt 0 00390 Range 0 C to 550 C Sheath Fused Silica Sheath Size 450mm x 6 35mm diameter Cable Length 2 meters 7 2 Low Alpha PRTs Low a probes contain a higher level of impurities in their platinum wire which affects the resistance value at any given temperature As impurities already exist additional contamination has a reduced affect and so these thermometers are best in industrial applications where for purposes of robustness the detector itself within the probe is constrained within other materials which can also be the source of contamination at elevate
50. rter 5 pin screw terminal to DIN plug converter Package of 5 additional DIN plugs Package of 16 additional 5 pin screw terminal plugs Rugged carrying case for DP251 and probes System performance is the combined total of the DP251 accuracy plus the calibration uncertainty of the probe The instrument and system accuracy s with a variety of probes are shown below DP251 Only 0 01 C 10mK DP251 PRP 2 or PRP 3 probe 50 C to 250 C 50 C 25mK 0 C 25mK 100 C 250 C 25mK 25mK DP251 PRP 4 or PRPS probe 70 C to 450 C 70 C 45mK 100 C 25mK 40 C 25mK 250 C 25mK 0 C 25mK 450 C 100mK DP251 200 C to 550 C probe contact OMEGA for quote on 200 C to 550 C probe 189 C 20mK 420 C 20mK 0 C 20mK 50 C 35mK 100 C 20mK DP251 uncalibrated 100 Ohm DIN probe see Chapter 7 for Internationally recognized probe categories Typical figures only 1 3rd DIN 0 C 100 C 250 C 150mK 300mK 600mK 12 2 Resolution User selectable via front panel or under interface control if installed 0 01 C F or K and 0 001 C F or K In ohms resolution is 0 01 or 0 0012 on display but 0 001 or 0 00012 via the interface Display update rate is every nominally 2 5 seconds in high resolution and every 0 5 second in low 12 3 Stability Temperature Coefficient 0 0005 C C 0 5mK C Term Stability Typically better than 5mK year 0
51. sion table iii rhi Maximum resistance value for the conversion table iv AP EE Positive temperature Coefficient A exponential for example if A 5 3 x 10 enter 3 v AP diG Positive temperature Coefficient A digits for example if A 5 3x 10 enter 5 3 if 5 3 then enter as 5 3 vi bP EE Positive temperature Coefficient B exponential enter the same way as for AP EE vii bP diG Positive temperature Coefficient B digits enter the same way as for AP diG viii CP EE Positive temperature Coefficient C exponential enter the same way as for AP EE ix CP diG Positive temperature Coefficient C digits enter the same way as for AP diG x An EE Negative temperature Coefficient A exponential enter the same way as for AP EE xi An diG Negative temperature Coefficient A digits enter the same way as for AP diG xii bn EE Negative temperature Coefficient B exponential enter the same way as for AP EE xiii bn diG Negative temperature Coefficient B digits enter the same way as for AP diG 11 12 Example Display Prompt Value Key Input 10 01 2 100 05 ENTER 1 0 101 J OJ S ENTER Lo 79 ENTER 7 9 ENTER rhi 198 ENTER 1 9 8 ENTER AP EE 4 ENTER EJAJENTER AP diG 2 458 ENTERJ 2 1 114115 8 ENTER and so on with bP CP An and bn When all data has been entered the display initially goes blank As the DP251 starts to generate the resistance temperature look up table the actual number of points to be generated wil
52. ss is changed the DP251 will continue to respond to the old address unless turned off on or sent a clear The interface has no remote local switching facility so the DP251 does not have to be turned on line before commands are sent To return the DP251 to it s turn on state the IEEE488 device clear command can be used having the same effect as the device dependent command C Figure 9 5 shows the address selection switch Figure 9 5 Address Selection Switch 933 Specification For people with a knowledge of the IEEE488 1987 standard the DP251 IEEE interface has the following specification i SH1 Full source handshake ii AH1 Fuill acceptor handshake iii T8 Basic talker unaddress on MLA iv L4 Basic listener unaddress on MLA v LEO No extended addressing vi TEO No extended addressing vii SR1 Service request available viii RLO No remote local function ix LLO No local lockout function x PPO No parallel poll xi DC1 Device clear reverts to power on state 9 3 4 Commands and Syntax All of the primary functions available from the DP251 front panel can be accessed via the parallel interface typically from an external computer or terminal Following is a list of the commands that can be sent to the DP251 all are single letters followed by up to 2 Single digit parameters with the exception of the multiplexer commands which have two letters followed bya two digit parameter COMMAND Cc Function Cle
53. ters alternatives to order Calibration 4 point 50 0 100 and 200 C Cal Uncertainty 0 05 C NIST traceable Chapter 8 International Temperature Scale The purpose of the International Temperature Scale is to define procedures by which certain specified practical thermometers of the required quality can be calibrated in such a way that the values of temperature obtained from them can be precise and reproducible while at the same time approximating the corresponding thermodynamic values as closely as current technology permits Since 1968 when the IPTS68 was adopted there have been significant advances in the techniques employed in establishing temperature standards and in the measurement of thermodynamic temperature The ITS 90 gives practical effect to these improvements Particular features are i ITS 90 specifies the use of the platinum resistance thermometer up to the freezing point of silver 961 78 C Above this temperature radiation thermometry based on the Planck law of radiation is specified The platinum 10 rhodium platinum thermocouple is no longer specified for use in the scale though it and other noble metal thermocouples will continue to be used as secondary standards 20 il Several new more precise fixed points have been introduced and the mathematical procedure have been revised so as to reduce the non uniqueness of the scale that is to reduce th differences which occur between different identically calibrat
54. to bright Dim Bright Display Selection Figure 4 3 Dim Bright Display Switches Data Entry CAL Operation The key operated switch on the DP251 must be set to CAL for all functions in the sections below Note To enter any numerical values via the keypad in the Data Entry routines first press ENTER the required number and then press ENTER again For example the value 9 635 must be entered as ENTER 9 635 ENTER All data entry is performed on the 16 key keypad as shown in Figure 4 4 See General Comments at the end of this section for additional notes 4 2 1 Figure 4 4 Data Entry Keypac Data Entry Options The DP251 allows you 5 alternative mathematical methods of converting resistance to temperature and therefore 5 choices for entering probe calibration data This will depend on the type of thermometer and its calibration see Chapter 7 on Sensor Information for more detail i ii iii iv v ITS90 coefficients intended for probes with high Alphas of 0 00390 to 0 00392 generalh laboratory type thermometers Callendar van Dusen coefficients for industrial or low Alpha thermometers of 0 00385 DIN used with uncalibrated industrial probes with 0 00385 Alpha value to provide a genera conversion of resistance to temperature Callendar van Dusen data pairs as ii except where data is provided in data pairs of resistance anc temperature DIN9O As iii except using modif
55. tors amp Ice Point References 4 Recorders Controllers amp Process Monitors 4 Infrared Pyrometers PRESSURE STRAIN FORCE Y Transducers amp Strain Gages F Load Cells amp Pressure Gauges 4 Displacement Transducers 4 Instrumentation amp Accessories FLOW LEVEL Y Rotameters Gas Mass Flowmeters amp Flow Computers 4 Air Velocity Indicators 4 Turbine Paddlewheel Systems 4 Totalizers amp Batch Controllers H CONDUCTIVITY pH Electrodes Testers amp Accessories F Benchtop Laboratory Meters Controllers Calibrators Simulators amp Pumps F Industrial pH amp Conductivity Equipment DATA ACQUISITION F Data Acquisition and Engineering Software 4 Communications Based Acquisition Systems 4 Plug in Cards for Apple IBM amp Compatibles 4 Datalogging Systems LF Recorders Printers amp Plotters HEATERS 4 Heating Cable 4 Cartridge amp Strip Heaters F Immersion amp Band Heaters 4 Flexible Heaters UY Laboratory Heaters ENVIRONMENTAL MONITORING AND CONTROL EF Metering amp Control Instrumentation 4 Refractometers Y Pumps amp Tubing LF Air Soil amp Water Monitors 4 Industrial Water amp Wastewater Treatment EF pH Conductivity amp Dissolved Oxygen Instruments M2011 0495
56. tput DP251 1000k 0 3mV 30mK 100k 0 3mV 3mK 10K 1mV 1mK 1k 10mV 1mK Temperature Coefficient Gain drift 10ppnv C typical 25ppm C max Zero drift 5ppm FS C typical 12ppm FS C max Chapter 10 Error Codes Error codes can be generated by the DP251 for a variety of reasons as follows Code El E2 E3 E4 ES EG E7 E8 E9 E10 E11 Meaning Cause Balance error No probe probe open circuit or ratio over range Temperature over range Probe at temperature outside limits of look up table CAL ROM A error No A ROM IEEE or RS232 error Unrecognized instruction sent IEEE or RS232 error illegal argument sent RAM failure Not used Unable to track temperature change temperature change too large Look up table too big Table larger than 396 points Singular matrix Unable to create look up table Singular matrix Unable to create look up table Chapter 11 Options and Accessories 11 1 Communications Output Options Communications Output options can generally be retrofitted to an existing DP251 Order Suffix Description RS2 RS232C Communications IEEE IEEE 488 Communications A Analog Output 35 11 2 Chapter 12 36 Accessories Part Number DP250 RACK DP251 SOFT DP250 DT DP250 TD DP250 DINS DP250 STP5 DP250 CASE 12 1 Accuracy SPECIFICATIONS Description 19 rack mount kit for DP251 Lab Windows software for DP251 DIN plug to 5 pin screw terminal plug conve
57. x Parameters Initial State COMMAND Function Syntax Parameters Initial State COMMAND Function Syntax Parameters Initial State n 0 probe A being measured and displayed orQ Query the DP251 will return the status of the function a or Qa where ais P R U Zor _ a P queries the probe setting return setting 0 1 or 2 a R queries the resolution return setting 0 or 1 a U queries the units return setting O 1 2 or 3 a Z queries the zero function return setting 0 or 1 a _ queries all settings plus reading 25 characters CR LF Not applicable R Sets the DP251 resolution as 2 or 3 decimal places Rn where n 0 or 1 n 0 selects 2 decimal places 3 decimals for ohms n 1 selects 3 decimal places 4 decimals for ohms n 0 2 decimal places S Remote control of the optional DP250 8 DP250 16 multiplexers if used Smn where m A or B and n is a number 00 to 15 m A directs control to the multiplexer on channel A m B directs control to the multiplexer on channel B n the number of the channel on the selected multiplexer SA00 SBOO Note 4 characters must be sent to form a valid command for example SA02 SB13 TorD Asks the DP251 to send the probe setting the reading to the present resolution and the units The probe may be A B or D differential and the units may be C K F or Q A 0 003C or B 75 149K Note that the String is always 9 characters long plus CR LF
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