Measuring Temperatures - Geokon 4200 Series Instruction Manual

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5.5 Measuring Temperatures

All vibrating wire strain gages are equipped with a thermistor for reading temperature. The
thermistor gives a varying resistance output as the temperature changes. The white and green
leads of the instrument cable are normally connected to the internal thermistor.
The GK-403, GK-404, and GK-405 readout boxes will read the thermistor and display the
temperature in degrees C. (Except when using the 4200HT strain gage, which must be read using
an ohmmeter.)
To read temperatures using an ohmmeter:
1) Connect an ohmmeter to the green and white thermistor leads coming from the strain gage.
(Since the resistance changes with temperature are large, the effect of cable resistance is
usually insignificant. For long cables a correction can be applied, equal to 14.7 ohms per
one thousand feet. Multiply this factor by two to account for both directions.)
2) Look up the temperature for the measured resistance in Appendix C, Table 9. For the
4200HT use Appendix D, Table 10.