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Lake Shore Cryotronics, Inc.

Application Notes

FIGURE 1. Four-Wire Configuration for DT-470 Installation

SENSOR OPERATION

Temperature controllers and thermometer instrumentation manufactured by Lake Shore Cryotronics are designed to be

directly compatible with the DT-470 sensor to give optimum performance and accuracy together with direct temperature

readouts. Simply follow the instructions provided with the instrument concerning sensor connection and instrument

operation. If a user-supplied current source, voltmeter, or other instrumentation are going to used with the DT-470

sensor, special attention should be given to the following details.

The DT-470 is designed to operate at a constant current of 10 microamperes while the voltage variation with temperature

is monitored. Therefore, the accuracy of the temperature measurement depends directly onf the specifications of the

current source and the voltmeter. A current source operating at the level of 10 ±0.01 microamperes (±0.1%) gives a

nominal temperature uncertainty of 10 millikelvin (0.01 K) which is probably suitable for most applications The voltmeter

resolution required can be estimated from the sensitivity (dV/Dt) of the DT-470:

Temperature (K)

Sensitivity (mV/K)

305

2.4

1.9

4.2

Multiplying the above sensitivity by the desired temperature resolution in kelvin will give the required voltage resolution in

millivolts.

The static impedance of the DT-470 sensor operating at a 10 microampere current is on the order of 100,000ohms.

Therefore, the input impedance of the voltmeter must be significantly larger than this to avoid measurement errors.

Voltmeters with input impedances of greater than 109 or 1010 ohms should be used.

Good quality instrumentation must be used and all instrumentation and wiring should be properly grounded and shielded.

Temperature measurement errors will result if there is excessive AC noise or ripple in the circuitry. Further details can be

found in the article by Krause and Dodrill given in the references.

NOTE:

All materials mentioned which are used in sensor installation are available from Lake Shore Cryotronics, Inc.

References

Krause, J. K. and Swinehart, P. R. (1985). Demystifying Cryogenic Temperature Sensors.

Photonics Spectra

. August, 61-

68. (Available on request from Lake Shore Cryotronics, Inc.

Krause, J. K. and Dodrill, B. C. (1986). Measurement System Induced Errors in Diode Thermometry. Review of Scientific

Instruments 57 (4), 661-665. (Available on request from Lake Shore Cryotronics, Inc.)

Sparks, L. L. (1983). Temperature, Strain, and Magnetic Field Measurements. In Materials at Low Temperatures, Ed. By

R. P. Reed and A. F. Clark. American Society of Metals, Metals Park, 515-571.

White G. K. (1979). Experimental Techniques in Low Temperature Physics. Clarendon Press, Oxford.

Содержание DRC-91 C

Страница 1: ... Fax 614 891 1392 Telephone 614 891 2243 Methodsand apparatusdisclosedand describedherein have been developedsolely on company fundsof Lake Shore Cryotronlcs Inc No governmentor other contractualsupport Or relationshipwhatsoeverhas existedwhich in any way affectsor mitigatesproprietaryrights of Lake Shore Cryotronlcs Inc in these developments Methods andapparatusdisclosed hereinmay be subjectto U ...

Страница 2: ... ohm Rh Fe conversion module 100 ohm platinum conversion modul 1000 o h m platinum conversion modu 9305 Thermocouple Input Card 9317C Ultra low 0 3K Germanium input Card 9318C Germanium Carbon Glass I No Input Card Precision Option s 8223 RS 232C Interface 8001 8002 8225 Analog Output Interface 0 Output Power 8229 Scanner Input Option W50 W60 High Resolution Set Point This manual applies directly ...

Страница 3: ...ryotronics Inc at a reasonable cost LIMITATION OF WARRANTY This warranty does not apply to defects resulting from improper or inadequate maintenance unauthorized modification or misuse operation outside of the environmental specifications for any product or part or buyer supplied software or interfacing THIS WARRANTY IS IN LIEU OF ANY OTHER WARRANTIES EXPRESSED OR IMPLIED INCLUDING MERCHANTABILITY...

Страница 4: ... 2 6 1 The RS 232C O p t i o n 2 6 2 6 2 T h e 8 2 2 9 Scanner O p t i o n 2 6 2 6 3 T h e 8 2 2 5 Linear Analog O p t i o n 2 6 2 6 4 H i g h R e s o l u t i o n Set Point 2 6 2 6 5 The 8001 and 8002 Precision O p t i o n s 2 6 2 6 6 The W50 and W 6 0 Power O u t p u t Options 2 6 2 7 ENVIRONMENTAL REQUIREMENTS 2 6 2 7 1 O p e r a t i n g Temperature 2 6 2 7 2 H u m i d i t y A l t i t u d e 2 6 ...

Страница 5: ...Precision Option Table 3 7 3 10 SENSOR CURVE SELECTION 3 8 3 10 1 SENSOR I D Switch 4 Open 0 3 8 3 10 1 1 Display of Accessed curve 3 8 3 10 2 SENSOR I D Switch 4 Closed 1 No REMOTE SENSOR ID Present 3 9 3 10 3 SENSOR ID Switch 4 Closed 1 REMOTE SENSOR I D Present 3 9 3 10 4 Addition of 8229 Scanner Option 3 10 3 10 5 Display of Accessed Position and Assigned Curve 3 10 3 10 6 Sensor Curve assignm...

Страница 6: ...8 1 Units for Set point The FOC1 Command 4 10 4 8 2 Units for A and B Inputs The F1AC1 and F1BC1 Commands 4 11 4 8 3 Display Sensor Selection The F2C1N1 Command 4 11 4 8 4 Resolution for A and B Inputs The F3AN1 and F3BN1 Comands 4 11 4 8 5 The A and B SENSOR ID Information 4 8 6 The Sensor ID on Return to Local 4 11 4 8 7 The W1 Data String 4 13 4 9 THE CONTROL COMMANDS 4 13 4 9 1 The Set Point V...

Страница 7: ...i s t e r Mask a t Power up 4 21 4 11 4 The WQ Data String 4 23 4 12 Command Operations 4 23 4 12 1 O u t p u t Data Statemants 4 23 4 12 2 The WO Data String 4 23 4 13 1 HP860 Keyboard Interactive Program 4 24 4 13 2 National Instruments IBM Example 4 25 4 13 3 National Instruments QUICK BASIC IBM Example 4 25 4 13 4 HP86B Bus C o m a n d s Program 4 26 4 14 SENSOR CURVE PROGRAMMING INSTRUCTIONS ...

Страница 8: ... of GAIN RATE and RESET 5 3 5 6 4 Calibration of Power Output 5 3 5 7 TROUBLESHOOTING 5 4 SECTION VI ACCESSORIES INPUT CARDS AND OPTIONS APPENDIX A Standard Curve Data APPENDIX B Sensor Curve C h a r a c t e r Information APPENDIX C E r r o r C o d e Summary ...

Страница 9: ...C o n n e c t o r 3 11 SECTION I V REMOTE OPERATION T a b l e 4 1 Interface Functions 4 2 Figure 4 1 ZEEE 488 A d d r e s s Switch for the DRC 91C 4 3 T a b l e 4 2 A l l o w a b l e A d d r e s s Codes for the DRC 9lC 4 4 Table 4 3 IEEE 488 BUS Commands 4 6 T a b l e 4 4 DRC 91C Program Code Summary Instrument Setup 4 7 T a b l e 4 5 DRC 9lC Summary of O u t p u t R e q u e s t s 4 8 T a b l e 4 ...

Страница 10: ...d accessory information The DRC 91C gives a direct reading 1 2 DESCRIPTION in temperature when used with any DT 470 Series Temperature Sensor The DRC 91C Temperature Controller All MI 470 Sensors follow the same is a microprocessor based instru temperature response curve Four ment which provides true analog bands of tracking accuracy are control It is capable of scanning available Refer to DT 470 ...

Страница 11: ... for additional discussion curves to be stored in the instru of calibration accuracy ment Depending on the complexity of the curves up to 25 can be The Model DRC 91C can also be used programmed into the unit A rear with the 9220 input card which panel DIP switch Sensor ID is handles both diodes and positive used to select the particular temperature coefficient metallic sensor response curve for ea...

Страница 12: ...input cards are used data from units may be selected independently both inputs is available via the from the display sensor units The standard set point temperature 1 3 SPECIFICATIONS can be set to 0 1 degree This temperature is converted to an Instrument specifications are equivalent voltage with a resolu listed in Table 1 1 These tion of 100 microvolts out of 3 specifications are the performance...

Страница 13: ...interface istics are a function of Sensor Input Option Installed The DRC Temperature Accuracy Dependent on 91C can accommodate two input Sensor Input Card and Sensor See options which allows the A input Input Options available and the B input to each be assigned their own input card This allows Temperature Range Dependent of concurrent use of different sensors dependent on the application Sensors ...

Страница 14: ...ge to reach rated panel knobs or with interface Heater output Up to 25 watts IEEE 488 Interface Allows remote 1A 25V standard Four output control of set point gain rate ranges can be selected either from reset units and heater power front panel or interface and range Provides output of display provide approximate decade step in units chosen units and all reductions of maximum power output front pa...

Страница 15: ...00 120 220 or 240 VAC mechanically and functionally in 5 10 50 to 60 Hz single spected prior to shipment It phase should be free from mechanical damage and in perfect working CAUTION order upon receipt To confirm this the instrument should be visually inspected for damage and tested electrically to detect any concealed damage upon receipt Be sure to inventory all components supplied before discard...

Страница 16: ...A recommends and some local codes require instru ment panels and cabinets be ground ed This instrument is equipped with a three conductor power cable which when plugged into an appro priate receptacle grounds the instrument 2 3 4 Bench U s e The DRC 91C is shipped with plastic feet and a tilt stand installed and is ready for use as a bench instrument The front of the in strument may be elevated fo...

Страница 17: ...applica tions where lead resistance is small and small readout errors can be tolerated c Measurement er rors due to lead resistance for a two lead hook up can be calculated using T IR dV dT where I is 10 microamperes R is the total lead resistance dV dT is the diode sensitivity and T is the measure ment error For example R 2 5 0 with dV dT 2 5 mV K results in a 2 3 8 SENSOR ID Switches temperature...

Страница 18: ...d s t o preclude the possibility of any of the heater current affecting the sensor input signal The heater leads should not run coincident w i t h the sensor leads due t o the possibility of capacitive pick up between the two sets of leads If they are i n close proximity they should be wound so a s t o cross the sensor leads a t ninety degrees i f a t a l l possible The heater output is a current ...

Страница 19: ...put up to three 8084 or 8085 Sensor Display Scanners with the 8082 Position Data Adapter Remote position 1F The HEATER meter can be set to 31 is reserved to indicate that read either of output power or more than one scanner is active to of output current The internal the 8082 When this condition is DIP switch setting main board S7 present the DRC 91C displays ERR09 switch 1 controls whether the un...

Страница 20: ...ment to our service depart 2 6 5 8001 precision option Cus ment tom programing of specific Sensor calibration curve s at factory W h e n returning an instrument for Provides highest degree of readout service the following information accuracy must be provided before Lake Shore 2 6 6 The W50 and W60 Output Op tions will deliver 50 or 60 watts 1 Instrument Model and Serial s respectively The W50 is ...

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Страница 34: ... contained AND OPERATION on the bus The following discussion covers the 1 8 Data Lines general operation of the IEEE 488 2 3 Transfer Control Lines interface For a more detailed 3 5 General Interface Management description of signal level and Lines interaction refer to the IEEE Standard 488 1978 publication IEEE The data lines consist of 8 signal Standard Digital Interface for lines that carry dat...

Страница 35: ...Remote Enable management have received the DATA line is pulled low by the BUS CONTROLLER to enable a device the 4 3 INTERFACE CAPABILITIES DRC 91C to perform the functions of TALKER or LISTENER The IEEE 488 Interface capabilities of the Model DRC 91C are listed The E01 End or Identify management in Table 4 1 as well as in mnemonic line is pulled low by the BUS format on the instrument s rear CONTR...

Страница 36: ...nating characters instrument s terminating characters are changed by the user these are delimiters The OPEN 0 position only i n effect until the instrument selects the ASCII characters CR and is turned off LF Carriage Return and Line Feed as the terminating characters for 4 4 2 TALKER and or LISTENER input and output data For the Configuration output data from the DRC 91C back to the computer over...

Страница 37: ...s Codes for the DRC 91C Only the first five bits of the binary code are listed and LISTEN address The sixth and seventh bits BUSCONTROLLER originated determine instrument is being addressed to TALK or LISTEN These bits are the same for the TALK whetherthe 4 4 COPYRIGHT 3 88 LSCI ...

Страница 38: ...ER Addressed commands SDC Selective REN and IFC See Table 4 3 When Device Clear GTL Go To Local the B U S CONTROLLER executes the ap propriate software code the effect is to pull the corresponding Inter SDC Selective Device Clear The face Management line low For SDC command performs essentially example when the software command the same function as the DCL command REMOTE712 is executed by the HP86...

Страница 39: ...vice dependent command or GTL addressed command as desired For T a b l e 4 3 summarizes the IEEE 488 Bus most but not a l l computers the Commands acknowledged by the DRC 91C DRC 91C as a TALKER does not have to be placed i n REMOTE operation 4 5 5 Device Dependent Commands but can remain under LOCAL control This allows the user t o collect The DRC 91C supports a variety of data while maintaining ...

Страница 40: ...and its LISTENER ment since the DRC 91C updates the ASCII Code is comma The IEEE address on power up only controller referred to in the Confirm that the address selected following discussion is the BUS is correct by holding in the REMOTE CONTROLLER and is normally a digital button for longer than one second computer It should not be confused and observe the IEEE address on the with the temperature...

Страница 41: ...e l i s t i n g Command and explanation of the 91C commands are summarized i n Table 4 4 There 4 7 2 1 Iocal This message M0 are commands for Interface Setup Table 4 61 clears the remote opera Instrument Setup Control Setup tion of the DRC 91C and enables Scanner Setup and Status R e g i s t e r front panel operation Pressing the front panel LOCAL button also The Output Statement Requests are sets...

Страница 42: ...nterface Setup commands and Request Status a Ni corresponds to a numeric value 0 9 b T h e AND symbol is used to indicate messages sent concurrently c END EOI d DAB l a s t data byte e Ci corresponds to an alphanumeric 0 F COPYRIGHT 3 88 LSCI 4 9 ...

Страница 43: ... i n Input A Many IEEE 488 cards for IBM PC s and B whether the analog option is automatically place addressed presentand the interface option instruments into Local Lockout To is present A typical data string be able t o place the DRC 91C into would be Remotewithout Local Lockouttheuser may need t o reconfigure h i s IEEE A 9220 P2 B 9318C 1 8225 2 8223 488 card 3 8229 4 7 3 TerminatingCharacters...

Страница 44: ...amples below which are given as F1BS Temperature units are SENSOR A ID S they pertain to selected with the same command with K C or F substituted for S for either input A20 Select Sensor Curve02 to be 4 8 3 Display Sensor selection The sensor to be selected for display can be changed by the F2C1N1 command This command is important with a A28 Enables the REMOTE SENSOR scanner card because it choose...

Страница 45: ...section IV Model DRC 91C Table 4 7 DRC 91C Command Summary for Instrument Setup 4 12 COPYRIGHT 3 88 LSCI ...

Страница 46: ... the various sen Display Sensor is A0 the Control sors the set point is limited by Sensor is BO set point is i n the input card present as shown i n kelvin units the remote position the table Note that the temper is off the SENSOR A I D indicates ature l i m i t can be different for that the Digital Filtering for this the DT 470 depending on whether channel is ON and the curve assigned curve numbe...

Страница 47: ...t point range of the set point are set within the software when i n temper 4 9 2 The WP Request Data S t r i n g ature units these limits are not possible for sensor units due to This request is a subset of the the different characteristics for WO command the WP command each sensor giving the set point value by itself Table 4 9 DRC 91C Command Request Summary for Setpoint Setup 4 14 COPYRIGHT 3 88...

Страница 48: ...ained A P transmitted by 99 0 1 990 A gain of 0 0 is not itself is equivalent to PO or P0 0 allowed T h e format is free field and sets the gain to 0 1 When with examples of the command being returning to LOCAL the gain setting P 1 P0 1 P9 p9 P9 0 P99 if changed over the IEEE 488 Bus is P99 etc no longer valid since the 91c w i l l now read the front panel gain potentiometer setting Table 4 10 DRC...

Страница 49: ...he Return to Local This channel w i l l be read over the IEEE 488 Bus only i f the channel is Although the Gain Rate R e s e t and designated as the Display Sensor or Sensor ID s can be changed over the Control Sensor N o r m a l operation IEEE Bus w i t h the 91C in REMOTE would be for the B input t o be when the 91C returns t o LOCAL Control Sensor input w i t h the these settings are read and u...

Страница 50: ...he Y H command T h e scanner SRQ Service Request management should be i n hold when any of the line low The BUS CONTROLLER uses other scanner commands are sent t o the serial poll SPOLL t o obtain the scanner the contents of the register i n the DRC 91C called the Status Register 4 1 0 6 The WY Data S t r i n g The DRC 91C Status Register is a This command gives the scan informa single byte of dat...

Страница 51: ...rument on the Bus has the capability to send this message Bit 0 of the Status Register is set the BUS CONTROLLER must decide when a valid Display data reading is which instrument is sending the available Bit 1 of the Status request Register is set when a valid Control a Serial Poll of the instruments data reading is available If the on the Bus The instrument polled Service Request is enabled eithe...

Страница 52: ... 91C t o pull the SRQ T h e Status Reports listed above may management low t o signal the BUS not be desired o r perhaps only a CONTROLLER This Status R e g i s t e r few are of interest T h e Status b i t is reset to zero upon reading Register Mask is provided t o allow the Status Register the user t o select whether he wants a given Status Report or not The This function can be inhibited by vari...

Страница 53: ...gister to all zeros or error was detected by sending Executing the Q command also resets the Output Data Statement WO See the Status Register to all zeros Section 4 12 2 and T a b l e 4 15 The Status Register Mask connnand is the ASCII letter Q followed by two For example in Figure 4 2 Q2l will alphanumerics representing the most allow the setting of the Overload significant four bits and the leas...

Страница 54: ...ed The BUS CONTROLLER can Control Data Ready and Control read the Status Registertodetermine Channel L i m i t W i t h a band of 0 1 appropriate instrument conditions about the control point In this case bit 1 is continuously updatedtoreflectcurrentinstnnnent 4 1 1 3 6 Status Register Mask at status of the Sample Data Ready PowerUp Example 2 Q2F All Status The Status R e g i s t e r Mask a t power...

Страница 55: ...Section IV Model DRC 91C Figure 4 2 DRC 91C S t a t u s Register Mask ard Status Register Format Table 4 14 Commands to Fix the Status Register Mask 4 22 COPYRIGHT 3 88 LSCI ...

Страница 56: ...output data from the DRC 91C The addition of the MO U S123 4P45130D25R4W1 CR LF command returns the instrument to front panel control where it stays T h e Universal Unlisten Cormnand even when data is requested from is sent so that no other instru the 91C by the HP computer ments on the Bus will eavesdrop on the Bus and assume that the data 10 DIM A 19 being sent is for their attention 20 OUTPUT 7...

Страница 57: ... a valid DRC 91C command such as WO the program will result in the display of the DRC 91C response on the screen 10 REM Set IEEE Address to 12 20 REM Address switch 1 OPEN 0 to get CR LF 30 REM This program allows the user to communicate with the 91C interactively 40 DIM A 100 Must be increased for curve information 50 INPUT B INPUTKEYBOARDCOMMAND 60 OUTPUT 712 B SEND COMMAND To 91C from the compu...

Страница 58: ...E BELOW 140 PRINT A Display received information on screen 150 A SPACE 255 Clear A 160 GOT0 110 170 END 180 REM The 91C w i l l return the data requested but i f the command input 190 REM does not request new information the 91C w i l l give the information 200 REM last requested 4 13 3 IEEE 488 TEST PROGRAM Quick Basic 3 0 Example This program w i l l allow the user t o communicate w i t h Lake S...

Страница 59: ...e setting 240 DISP Reset A 9 11 250 DISP hEATER Range A 13 Heater Range 260 DISP Power A 15 173 270 DISP Space a Line 280 OUTPUT 712 WS Set for WS 290 ENTER 712 A Ask for string WS 300 DISP WS A Display Sensor Reading 310 DISP Space a Line 320 OUTPUT 712 WC Set for WC 330 ENTER 712 A Ask for string WC 340 DISP WWC A 350 DISP Space a Line 360 OUTPUT 712 WP Set for WP 370 ENTER 712 A Ask for set poi...

Страница 60: ...SCIT As can be 04 31 2OOO cRV 10 seen from the output shown on this 05 31 20BO RESVRD page the instrument is shipped 02 02 02 02 02 02 02 02 w i t h a l l remote positions calling 02 02 02 02 02 02 02 02 up Standard Curve 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 The information lines for Sensor 02 02 02 02 02 02 02 02 Curves 05 through 31 w i l l only be 02 02 02 02 02 02 02 02 present i...

Страница 61: ...e Properly Due to the length of some of the data strings appropriate computer time outs must be allowed when performing these functions If a hardware problem is detected in modifying one of the NOVRAM locations an Err01 error will be displayed and instrument operation is halted An Err02 error is displayed if the u n i t detects a NOVRAM hardware problem 4 28 COPYRIGHT 3 88 LSCI ...

Страница 62: ...Model DRc 91C Section IV Table 4 17 Sensor Curve Information Table OutputFormat XDT Table 4 18 XDN1N2 S e n s o r Curve Output Format xDn1N2 COPYRIGHT 3 88 LSCI 4 29 ...

Страница 63: ...C D N 31 are the Standard Curves with Curve 0 00000 499 9 0 19083 365 0 05 reserved The format for the 0 24739 345 0 0 36397 305 0 XC command is given in Table 4 16 0 42019 285 0 0 47403 265 0 The format for the XC command must 0 53960 240 0 0 59455 220 0 be followed for the curve entry to 0 73582 170 0 0 84606 130 0 be successful Following the 0 95327 090 0 1 00460 070 0 XCN1N2 where N1N2 is betw...

Страница 64: ...herefore the minimum number of data points T h e command XKN1N2 erases a l l the which the user can input for a data associated w i t h curve number curve is 1 which would result i n a N1N2 and repacks the remaining 3 data point curve and the maximum curves stored within the NOVRAM number of data points is 97 which Standard Curves 00 thru 05 are would result i n a 99 point curve stored i n a Prom ...

Страница 65: ...Section IV Model DRC 91c Table 4 19 Conversion o f Raw Units Data for the XC command Input Card 9210 20 3 9210 20 6 9215 9317C 9318C 9220 P2 9220 P3 9220 R1 4 32 COPYRIGHT 3 88 LSCI ...

Страница 66: ...selection and performance testing is contai For continued protection against fire hazard replace only with the same type and rating of fuse as specified for the line for the line voltage selected To prevent shock hazard turn off instrument and disconnect it from AC line power and all test equipment before replacing the fuse ...

Страница 67: ... A or J2 INPUT B connector should read as follows to simulate a diode sensor input is required for operational checks of 9210 20 3 1 0000V 100µV the DRC 91C The test connector 9210 20 6 1 0000V 100 µV can be made by taking one of the 9220 P2 0 10000v 10µv plugs supplied with the DRC 91C and 9220 P3 0 10000v 10µV the temperature sensor in the two 9317C N A wire configuration as described in 9318C N...

Страница 68: ... sequence K C by verifying the current source and F V K etc Note the unit goes the A D settings for this input as to V for a diode configuration well as the units change 9210 3 6 or 9220 3 6 or for a resistance card configuration 5 5 6 H e a t e r Output Test 9220 P2 P3 R1 or 9317C 9318C Input card 5 5 6 1 Heater output conditions The heater should output power when 5 5 5 3 Check sensor u n i t s ...

Страница 69: ...rom power to read approximately 1volt Setting current by switching internal dip the GAIN to 99 will result in a switch 57 1 reading of approximately 7 2 volts 5 5 7 checking Gain R e s e t and Rate 5 5 7 2 Reset Set up the con troller as instructed in step Check the operation of the Gain 5 5 6 1 Enter a gain and setpoint Rate and Reset as follows value that results in less than If a Reset 1 Place ...

Страница 70: ...et nominal values If they are slight point the amount of gain the ly off it should not effect opera speed at which you change the volt tion since the heater circuit is age as well as when the reading is part of a feedback loop read by the DVM For the change from 80 to 1 0 0 the reading will be negative in value 5 6 CALIBRATION The GAIN RATE and RESET values are The adjustments and test points summ...

Страница 71: ...ale 3 To calibrate the Set Point volt the DVM reads 1 0000 volts DVM reads 1 0000 volts 5 Repeat 3 and 4 until they do not Note TP 24 CNT V is the control 5 Enter a set point of 2 7000V and voltage For the 9210 20 3 it is adjust the potentiometer labeled the voltage across the sensor for SP SPAN ADJ until the DVM reads the 9210 20 6 it is 0 458 times the 2 7000 volts voltage across the sensor TP 2...

Страница 72: ...proxi volts as the gain setpoint or mately a factor of ten lower reset values are changed then the The same three IC s are circuit i s probably operating cor involved rectly Now measure the voltage across from TP19 to TP21 The If the monitor voltage is incor voltage should vary from 0 to 1 rect the input card may control at volt as the analog out signal var an offset or not at all ies f r o m 0 to...

Страница 73: ...y bad and both should be replaced Before it is decided that U47 and U48 are bad be sure the relays K4 K8 are working If they can be heard clicking as they are turned off and on then they are probably operating properly They are turned off and on by se lecting different heater ranges 5 8 COPYRIGHT 3 88 LSCI ...

Страница 74: ...Table 5 1 Input Card Characteristics COPYRIGHT 3 88 5 9 ...

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Страница 78: ...Figure 91C lb Schematic DRC 91C Main Board 1 Input Power Supply ...

Страница 79: ...Figure 91C 1c Schematic DRC 91C Main Board 2 Output Power Supply ...

Страница 80: ...Figure 91C 1d Schematic DRC 9 1C Main Board 3 Digital Section ...

Страница 81: ...Figure 91C 1e Schematic DRC 9 1C Main Board 4 Interconnections ...

Страница 82: ...igure 91C 1f Schema Setpoint and Summation ...

Страница 83: ...Figure 91C 1g Schematic DRC 91C Main Board 6 PID Control ...

Страница 84: ...Figure 91C 1h Main Board 7 Output Stage ...

Страница 85: ...Figure 91C 1i Schematic DRC 9 oard 8 Rear Panel Interconnections ...

Страница 86: ...REPLACEABLE P A R T S L I S T D R C 9 1 C D I S P L A Y BOARD Figure 91C 2a Component Layout DRC 9 1C Display Board ...

Страница 87: ...splay Board 1 ...

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Страница 91: ...REPLACEABL R T S LIST A 9 CROPROCESSOR CARD ...

Страница 92: ...essor Card ...

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Страница 96: ...racy See Table 9210 1 9210 3 SPECIFICATIONS Specifications for the Model 9210 Diode Input C a r d are given in Table 9210 1 The card can be configured by the user as either a 3 volt 9210 3 or a 6 volt 9210 6 card COPYRIGHT 12 87 LSCI 9210 1 Sensor ordered separately DT 470 series DT 500 series and TG 120 series from LSCI as well as any other diode sensor See Lake Shore Diode Sensor brochures Tempe...

Страница 97: ...tion The digitized value is converted to a serial data string and transferred 2 Remove the four screws that to the main microprocessor using secure the calibration cover to optical isolation The sensor its clips and remove the cover voltage is also buffered and transferred to the rear panel 3 If an Input Card m u s t be MONITORS connector for external removed disconnect the wiring monitoring as we...

Страница 98: ...e Input Card must be put Connect the DVM plus lead to the in table form consisting of voltage I pin and the minus lead to the and temperature points w i t h the I pin Adjust the trimpot voltage in ascending voltage order marked 10µA on the Refer to Section 4 of this manual calibration cover for the for a discussion of how the data appropriate Input Card until must be formatted for entry into the v...

Страница 99: ...R E P L A C E A B L E P A R T S L I S T 9210 ANALOG I N P U T C A R D ...

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Страница 102: ... with a maximum of 30 nanofarads for example Lake Shore CS 401 Series Sensors The 9215 150 configuration will accommodate Capacitance sensors of up to 150 nanofarads for example Lake Shore CS 501 Series The card can be configured by the user as either a 15 nanofard 9215 15 or a 150 nanofarad 9215 150 card by switches on the card Specifications for the Model 9215 COPYRIGHT 2 88 LSCI 9215 1 Display ...

Страница 103: ...capacitance Input Card DRC 91C 93C Table 9215 2 Typical Temperature Ranges and sensitivities Notes 1 9215 15 configuration 2 9215 150 configuration 3 No Calibration Data Available 9215 2 COPYRIGHT 2 88 LSCI ...

Страница 104: ...a DRC ture will decrease with t h e and 91C 93C Temperature Controller or for temperatures above 290K will can be field installed at a later increase with time date If field installation is required use the following 9215 3 2 Thermal Cycling and procedure Reproducibility 1 Set the POWER switch to OFT and Thermal cycling of capacitance disconnect the power cord from sensors can produce variations i...

Страница 105: ...ess locking tab is seated current connections and the other over the extended edge of the pair or the voltage connections wiring harness mating connector The pin contact of the connector is Verify that the wiring harness and the socket is in place correctly by noting that the A or B on the harness mating connector is 9215 6 SELECTION OF THE SIGN OF THE the harness installation again Thread the wir...

Страница 106: ...e ap The 9215 15 configuration provides propriate channel either 15 15 or a charging current switched at a 15 50 the 15 for the 9215 15 frequency of 5 kilohertz The configuration or 50 for the 9215 frequency i s precisely controlled 150 configuration The sign by a crystal oscillator The indicates whether the Temperature operation of the 9215 150 is Coefficient is positive or nega identical except ...

Страница 107: ... on the card This Section provides information 1 Locate DIP switch package Slh to permit recalibration if needed Switch 2 Under normal opera tion this switch is CLOSED 1 Change this switch to the NOTE Calibration f o r zero OPEN 0 position capacitance may be required to meet accuracy specifications if your 2 connect the DVM plus lead to the sensor lead capacitance or stray V Buffered sensor Output...

Страница 108: ... reads 0 000 on the 9215 15 or 0 00 on the 9215 150 9215 8 3 Span calibration 1 Be sure that the leads are in the configuration which will be used in your system Attach the standard capacitor in place of the capacitance sensor 2 Verify that the Display indi cates the Capacitance Input Card 3 Adjust the trimpot marked SPAN so that the display reads the value of the standard capacitor 9215 9 REPLACE...

Страница 109: ...R E P L A C E A B L E P A R T S LIST 9215 C A P A C I T A N C E I N P U T CARD ...

Страница 110: ...Figure 9215 1 Model 9215 Capacitance Input Card ...

Страница 111: ...ONS Specifications for the Model 9220 User Configurable Input Card are given in Table 9220 1 of this manual The card can be configured Equivalent temperature accuracy as a 9220 3 or 9220 6 diode card a is a function of sensor type 9220 P2 or 9220 P3 platinum card or sensitivity and Precision option a 9220 R1 rhodium iron input card COPYRIGHT 12 87 LSCI 9220 1 9220 3 See 9210 3 specifications 9220 ...

Страница 112: ...ove the four screws that resulting sensor voltage is secure the calibration cover to amplified by a factor of 10 its clips and remove the cover negative 10 and digitized by a 16 bit A D converter with a resolution 3 If an Input Card must be of better than 100 microvolts out removed disconnect the wiring of 3 0000 volts full scale The harness mating connector by digitized value i s converted to a l...

Страница 113: ... screws and slide the panel off volts and verify that the unit displays 200 00 and 100 00 ohms 2 set 100 µa 1mA 3mA Current within 0 01 ohms or Connect the appropriate equivalent for the 9220 P3 and precision resistor across the A 9220 Rl I and B 1 pins of the five pin input connector for the 5 Install the top panel input J1 or J2 the 9220 occupies Connect the DVM plus lead to the I pin and the mi...

Страница 114: ...220 8 REPLACEABLE PARTS Included in this section is Figure 9220 1 It includes the Model 9220 input schematics replaceable parts list and illustrated component layout Refer to the manual for ordering information 9220 4 COPYRIGHT 9 87 LSCI ...

Страница 115: ...REPLACEABLE PARTS LIST 9 2 2 0 A N A L O G INPUT CARD ...

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Страница 117: ...REPLACEABLE P A R T S LIST 9 2 2 0 ANALOG I N P U T CARD ...

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Страница 119: ...red for field installation Gold 0 03 at Fe Chromel vs the Input Card Configuration Table Gold 0 07 at Fe E K and T located on the first page of the thermocouples are supported with Instruction Manual should be internal curves that enable the updated to keep documentation controllers to operate in current temperature units C F and K as well as voltage in millivolts Use the following procedure for t...

Страница 120: ...rence Junction Temperature disabled Offset Adjustment Terminal Block Electroni cResolution 1 microvolt Electronic Accuracy 3 µV for 10 to 10 millivolts 5 µV up to One point hardware adjustment built into the the 15 and 15 millivolt full scales Overall Accuracy Controllability Typically 0 2K in a properly designed system Display Resolution 5 digits Compensated and uncompensated voltage in millivolt...

Страница 121: ...Terminal Block i n t o t h e Plug t h e 9305 i n t o t h e Alternate Connector Slot J9 i f appropriate Input C a r d Slot the Card is Input A or i n with the component side facing Alternate connector Slot J11 i f to the left of the unit as the Card is Input E with the viewed from the front Make w i r e s facing the input card sure the card is thoroughly Slots are shown i n Figure seated Verify tha...

Страница 122: ...oelement KP and a Cu A1 correspond with the positive alloy Alumel as the negative thermoelement listed for each type thermoelement KN It should not of thermocouple in Section 9305 5 be used in sulphurous or reducing atmospheres or in environments that promote corrosion 9305 5 3 Type K Thermocouples 9305 5 NOTES ON THERMOCOUPLES Lake Shore s 9305 Thermocouple Input C a r d supports the Chromel vs T...

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Страница 124: ...ed in the Instruction Manual The SENSOR ID Switches on the rear panel of the DRC 91C are used to select curves as described in Instruction Manual Section 2 3 8 Curve selection can also be made 9305 7 3 Selection of Reference over Computer Interface as Junction Compensation on the described in Section 4 8 5 DRc 93c On the DRC 93C the Thermccouple When a 9305 Thermocouple Input Table is selected by ...

Страница 125: ...ould interface use the AC1C2 and BC1C2 show 9305 when the SENSOR key commands described in the DRC 91C is pressed See Section 4 8 9 Instruction Manual The Reference Junction Compensation bit 4 Adjust the Offset Adjustment may be listed as Switch 3 or the trimpot so that the Display Thermal Correction bit used on the r e a d s t h e R e f e r e n c e 9318C card Turning on 1 that Temperature positio...

Страница 126: ... Instruction manual it positive and multiplied by one The only additional instructions hundred to shift resolution required when calibrating the setpoint D A converter with the VTABLE V 100 9305 card is to make sure that the THERMOCOUPLE mv 15 mv Reference Junction Compensation is turned off Section 9305 7 3 A 15 0000 millivolt thermocouple voltage will result in a 0 00000 volt table value and 15 ...

Страница 127: ...ent lead wires with the TPl GND 2s found on the terminal screws calibration card of the 5 Locate the Rear Panel Offset Section 9305 7 2 7 Avoid using clip on leads Section 9305 7 3 controller The calibration procedure is divided into three parts 4 Apply a zero signal to the V and V Thermocouple Input 1 Calibration of the Secondary terminals by shorting across Sensor Current Source the Terminal Blo...

Страница 128: ...pleA D Span so that shorting the two halves of the the voltage read on the Display is 10 000 millivolts 3 verify that thermal correction This test is to verify that the A D converter i s symmetrical Apply a 10 millivolt signal to 4 Slide the top cover onto the the V and V Thermocouple instrument and replace the Input terminals The DVM three screws should read 2 0000 0 0006 volt The Display should ...

Страница 129: ...ple sensors 9305 ThermocoupleInput Card 9305 11 REPLACEABLE PARTS Included in this section is Figure 9305 1 sharing the Model 9305 Thermocouple Input Card Schematic Replaceable Parts List and illustrated Component Layout Also included is Figure 9305 2 showing the 9305 Terminal Block Schematic Replaceable Parts List and Component layout COPYRIGHT 6 88 LSCI 9305 11 ...

Страница 130: ...9305 Thermocouple Input Card Model DRC 91C 93C Table 9305 4 9305 Thermocouple Curves 9305 12 COPYRIGHT 6 88 I S C I ...

Страница 131: ...Model DRC 91C 93C 9305 Thermocouple Input Card Table 9305 4 cont 9305 Thermocouple Curves COPYRIGHT 6 88 LSCI 9305 13 ...

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Страница 137: ...9318C WARNING can be used with germanium carbon glass or carbon resistors or any other negative temperature coeffi cient resistors Both cards read in ohms from a full scale reading of 10 ohms with 1 milliohm resolu tion to a full scale reading of 10 000 ohms with 0 1 ohm resolution 1 Set the POWER switch to OFF and for the 9317C and 100 000 ohms with disconnect the power cord from 1 ohm resolution...

Страница 138: ...fications 9317C 9318C Resistance Input Cards Input Range sensor Excitation Temperature Ranger sensors orderedSeparately Sensor Response Curve Input Resistance Maxi Sensor Power Dissipation Display Resolution Temperature Control signal 9317C 9318C 2 COPYRIGHT 12 87 LSCI ...

Страница 139: ...icroprocessor controlled controlled 15 bit A D converter Input Card It s resistance The microprocessor also has measuring technique is distinctly calibration constants stored for different from the way a DMM would the gain and offset of the input measure resistance Most DMMs amplifier As a result of the A D force a large enough signal across resolution and calibration constant the device being mea...

Страница 140: ...ut card is control thermal correction is asked for an update approximately disabled once a second and a new thermal value is determined If the Enable or disable the control voltage changes more than 0 5 of thermal correction from the front reading the card stops reversing panel by using a combination of the the current and uses the thermal SENSOR SCAN and keys value previously determined until as ...

Страница 141: ...sts and the heater power should be o f f 9317C 9318C 6 CALIBRATION SCHEDULE The 9317C 9318C changes the current it applies to the sensor in order to maintain between 0 8 and 1 0 The design of the 9317C 9318C 9317C or 8 and 10 9318c Resistance Input Card is such that millivolts across it until the set re calibration should not be point current range and value have required more often than every six...

Страница 142: ...itions of CAL 8 through a 1 9317C or 10 9318C CAL 1 References are made to test millivolt signal to the V and points adjustments and calibration V Sensor Input terminals switches that are labeled on the Enable CAL 6 on the card CAL 8 calibration cover Use the is still enabled The DVM following procedure to calibrate should read about 1 volt and the 9317C 9318C Resistance Input the display of the u...

Страница 143: ...d position of the Internal ID Current Range 3 Value 6 switches before proceeding Substitute a 100 ohm 9317C or Attach the plus and minus leads 1K 9318CO resistor for the of the DVM to TP25 SP V and previous resistor and enable TPl GND 2s respectively of CAL 3 The display will the Calibration and Service indicate 260 for approximately card Make switch 7 CLOSED 30 seconds then 306 for ON This forces...

Страница 144: ...curve except the resistance is converted to a LOG value where 1000 ohms would look like 4 0000 R e f e r to APPENDIX B for a definition of the curve requirements The curve data The is in resistance order resistance and temperatures for t h e 9317C 9318C are in ohms up to 100 000 ohms and in kelvin up to 399 9 9317C 9318C09 REAPLACEABLE PARTS Included in this section is Figure 9317C 9318C 1 It incl...

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Страница 149: ...p bits that separate and synchronize the transmission and receipt of data The baud rate i s switch selectable at 300 or 1200 baud and the interface maintains E I A voltage levels f o r data transmission Figure 8223 2 gives a transmission format which shows the data bits framed by the start and stop synchronization bits The data is transmitted using two voltage levels which represent the two binary...

Страница 150: ...e when left disconnected the 300 and 1200 baud rates have been tested and are fully Data Set Ready CC indicates to supported the Interface that the host computer or terminal is not in a Table 8223 3 Baud Rate Switch S1 test mode and that power is ON Signal Ground AB this line is the common signal connection for the Interface Received Line Signal Detector CF this line is held positive ON when the I...

Страница 151: ...INSTALLATION Note on the calibration cover the position of Option Slot 2 which the The 8223 Rs 232C Interface is 8223 will occupy factory installed if ordered with a DRC 91C Temperature Controller or 3 Remove the four screws that can be field installed at a later secure the calibration cover to its date If field installation is clips and remove the cover Remove required use the following the two b...

Страница 152: ...s t a l l the calibration cover by The Output Statement commands given reversing procedure 3 in T a b l e s 4 9 and 4 10 w i l l result in the requested data being output 8 Install t h e top panel immediately following the reception of the EOL sequence I f more than one Output Statement command is 8223 6 OPERATION given the last one received w i l l be acknowledged Programming Codes The 8223 RS 23...

Страница 153: ...ry locations an ERR01 error w i l l be displayed i n the Display Table 8223 6 Interface Error Codes and instrument operation w i l l be halted Consult a factory r e p r e s e n t a t i v e i f t h i s e r r o r occurs There are three errors that could be detected by the 8223 interface as defined i n Table 8223 6 Detection of an error does not effect t h e operation of t h e interface The software ...

Страница 154: ... Duplex with Handshake character length parity and stop b i t configuration are the same as Figure 8223 4 shows the adapter those of t h e 8223 Interface when c a b l e f o r Half Duplex with shipped none of t h e switches on handshake communications with an the 8223 board need t o be changed HP 86B Serial Interface The arrows indicate t h e source and When connecting t h e HP 86B Serial direction...

Страница 155: ...guration jumper pins 5 6 8 and 20 to already takes care of some of the disable the handshake functions of interface interconnection problems the Host This is not required for to route signals to their proper the 8223 Interface pins Figures 8223 5 and 8223 6 give more general interconnection 8223 8 REPLACEABLE PARTS configurations for Half Duplex with and without Handshake Included in this section ...

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Страница 158: ... on the 91C 93C back panel with pin C being the V output and pin D being the v output 8225 3 SPECIFICATIONS Specifications for the Model 8225 Analog Output are given in Table 8225 1 8225 4 INSTALLATION The 8225 can be installed in the DRC 91C 93C Option Slot 1 or Option Slot 2 if a Model 8223 Rs 232C Interface is not present The 8225 Analog Output is factory Note a The resistance of the installed ...

Страница 159: ...onnector pin C and and white wires from the 8225 the minus lead to pin D along the inside edge of the rear panel and solder the white 3 With the load resistors or the wire to MONITOR connector J3 voltage standard to simulate Pin C and black wire to Pin D the input sensor go to a low temperature and adjust the 5 Install the calibration cover by trimpot labeled Z for Zero on reversing procedure in 3...

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Страница 162: ...v e a The 8229 A1 through A4 channels can make before break switching action be selected directly using the and the voltage leads are SENSOR A key or included i n the break before make The BO through SCAN sequence An independent B2 outputs on J9 are a BCD Dwell time 0 to 99 seconds can be representation of the channel assigned to each of the additional selected with BO being the least inputs signi...

Страница 163: ...k hazard turn off instrumentanddisconnect it from AC line power and all test equip lent before removing cover 1 Set the POWER switch t o OFF and disconnect the power cord from the unit Remove the three top panel screws and slide the panel off N o t e on the calibration cover the position of option Slot 2 which the 8229 w i l l O C C U P Y 2 Remove the four screws that secure the calibration cover ...

Страница 164: ...ermined either locally from the front from Table 3 4 the Curve Number to panel or remotely through the Position Number Correlation Table remote interfaces A complete discussion of curve selection is given in Section 3 9 8229 5 1 Local 8229 operation and in particular Section 3 9 2 1 The 8229 A1 through A4 channels are accessed locally using the SENSOR A key The Display Sensor is incremented each t...

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Страница 167: ...APPENDIX A Standard Diode Voltage Temperature Characteristics ...

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Страница 170: ...APPENDIX A DIN Standard Curve for 100 ohm Platinum Sensors ...

Страница 171: ...ve 18 Character Information Line Reserved character Definitions Each Sensor Curve has an 18 character information line Some of the characters are reserved for specific operations T h e definitions are as follows COPYRIGHT 5 88 B 1 ...

Страница 172: ...B 2 COPYRIGHT 5 88 ...

Страница 173: ...rame error conditions the Err1x codes are for Input Card error conditions If an Err0x or an OL or Err2x error occurs for an input selected as the control input the heater range is taken to OFF and must be reset following correction of the fault condition The following is a summary of the error codes ERR01 ERR02 Err09 ERR10 COPYRIGHT 5 88 c 1 ...

Страница 174: ...c 2 COPYRIGHT 5 88 ...

Страница 175: ...Err25 Err26 Err27 Err28 COPYRIGHT 5 88 c 3 ...

Страница 176: ...he values of heat capacity lower Cp and thermal conductivity often higher κ are such that much shorter thermal time constants τ α Cp κ are the rule at low temperatures 2 The temperature sensor used in a furnace is almost always one of a variety of thermocouples with sensitivities in the 10 100uV C range In the cryogenic regime resistance thermometers both metallic and semi conductive diode and cap...

Страница 177: ...r but is related to the maximum amount of error signal allowed before the controller is directed to produce full output power The DRC 82C requires a 0 to 8 volt signal from the deviation amplifier to drive the power output stage from zero to maximum In Figure 2 For Av 1000 there is a narrow band of error signals 0 to 8 mV within which the proportional action occurs This proportional band expands t...

Страница 178: ...that to control at 20 kelvin the heating power required is 0 2 watts Assume also that 50 watts of heater power is available reducible in five steps of one decade each Figure 5 shows the control offset for an amplifier gain of 100 and three output power settings which will deliver enough power to the system to balance the cooling power The temperature offsets for a power level of 0 2 watts at 20 ke...

Страница 179: ...PORTIONAL GAIN PLUS INTEGRAL RESET TEMPERATURE CONTROL The manual reset adjustment described above varies markedly with the temperature set point and with the often changing heater power demands of the system Thus it is normally neither convenient nor desirable to have to resort to such a means of eliminating temperature droop offset Instead suppose a circuit could be added to the loop that would ...

Страница 180: ...n be 10 30 minutes In cryogenic systems it is usually less than a minute even near room temperature Consequently placement of the control sensor with respect to the heater is extremely important in the design of a cryogenic system as is the placement of both the heater and sensor with respect to the cooling power Rate action can be achieved by means of a differentiator circuit which provides a sig...

Страница 181: ...sampling times in the half second range In the world of ovens furnaces and other large industrial processes which operate above room temperature stable control can be maintained by digital systems updating temperature only once or twice a second This is for the same reason that ON OFF controllers are successful in these cases the large thermal time constants of the controlled environments However ...

Страница 182: ... 136 Some of this material has appeared in Principles of Temperature Control available from Gulton Industries West Division Unlike reference 1 the discussion is not related to cryogenics but temperature control system principles are briefly and clearly explained 3 C L Pomernacki Micro Computer Based Controller for Temperature Programming the Direct Inlet Probe of a High Resolution Mass Spectromete...

Страница 183: ...98 1 12463 1 11896 1 11517 1 11212 1 10945 1 10702 1 10263 1 09864 1 09490 1 09131 1 08781 1 08436 1 08093 1 07748 1 07402 1 07053 1 06700 1 06346 1 05988 1 05629 1 05267 1 04353 1 03425 1 02482 1 01525 1 00552 0 99565 18 6 18 2 18 0 17 7 17 6 17 4 17 4 17 4 17 6 18 5 20 6 21 7 15 9 7 72 4 34 3 34 2 82 2 53 2 34 2 08 1 92 1 83 1 77 1 74 1 72 1 72 1 73 1 74 1 75 1 77 1 78 1 79 1 80 1 81 1 84 1 87 1...

Страница 184: ...omial given in Equation 4 No term in Equation 1 will be greater than the absolute value of the coefficient This property makes it easy to determine the contribution of each term to the temperature calculation and where to truncate the series if full accuracy is not required FUNCTION Chebychev Z as double as double REM Evaluation of Chebychev series X Z ZL ZU Z ZU ZL Tc 0 1 Tc 1 X T A 0 A 1 X FOR I...

Страница 185: ...ryogenic temperatures to guarantee that heat is not being conducted through the leads to the sensor A final thermal anchor at the sample itself is a good practice to assure thermal equilibrium between the sample and temperature sensor Note that the CU CY BO and DI mounting adapters serve as their own sample thermal anchor If the connecting leads have only a thin insulation such as Formvar or other...

Страница 186: ...sor and mounting surface of any residual flux Next re heat the mounting surface to the melting point of the solder press the device into position and allow the sensor to warm to the melting point of the solder After both tinned surfaces have flowed together remove the heat source and let the sample and sensor cool Under no circumstance should the sensor be heated above 200 C and the solder must be...

Страница 187: ...pter is a spring loaded clamp to attach the DT 470 SD package to a flat surface It maintains pressure on the SD package as the temperature varies First remove the hold down cap which holds the three piece CO assembly together The CO assembly should appear as shown in the accompanying drawings Bolt the assembly into a 4 40 threaded hole The stop on the brass screw should rest against the mounting s...

Страница 188: ...nsitivity by the desired temperature resolution in kelvin will give the required voltage resolution in millivolts The static impedance of the DT 470 sensor operating at a 10 microampere current is on the order of 100 000ohms Therefore the input impedance of the voltmeter must be significantly larger than this to avoid measurement errors Voltmeters with input impedances of greater than 109 or 1010 ...

Страница 189: ...better than 50 mK Figure 1 shows the voltage variation with temperature for a typical silicon diode temperature sensor An error arises in diode thermometry if the excitation current is not a true dc current but has an ac component superimposed on the dc Although the ac component can be due to a poorly designed current supply a more common source of the ac is noise induced in the measurement circui...

Страница 190: ...ristic of the diode was measured at each temperature from 0 1 to 150 µA Although detailed measurements were taken on only one diode other diodes were randomly selected and spot checked at all three temperatures and frequencies to verify consistency with the measured data The diodes tested were of the DT 500 series of Lake Shore Cryotronics Inc and have been in production long enough to have a subs...

Страница 191: ...de can be calculated from V T V I I t dt dc ac T z 1 0 cos ω 3 where T the period of integration of the voltmeter or approximately 2π ω Implied in this derivation is the assumption that ω is sufficiently small so that effects from diode capacitance on the order of picofarads can be ignored On carrying out the integration of Eq 3 and subtracting V Idc the dc offset voltage is V V V I nkT e eV nkT d...

Страница 192: ... of the extended calculation have not been given as the mathematics is somewhat tedious and the slight discrepancies between the small signal model and the extended model do not justify the added complexity For all practical purposes Eq 6 can be reliably used above 40 K The physics of a p n junction at 4 2 K is not clearly understood and attempts to correlate the present data by modeling low tempe...

Страница 193: ...A operating current A capacitor in the range of 10 to 20 µF should reduce most noise effects to an acceptable level However because the capacitor increases the time constant in the circuit a sluggish response should be expected In switching operations 30 seconds or more may be required for the circuit to stabilize This quick fix is not meant as a substitute for proper measurement techniques but in...

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