Lakeshore 330 User Manual page 99

Lake Shore Model 330 Autotuning Temperature Controller User's Manual
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 ±.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
77
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.
Application Notes
FIGURE 1 Four-Wire Configuration for DT-470 Installation
2.4
1.9
33
B-13