Measuring Temperatures - Geokon 4100 Series Instruction Manual

22 | TAKING READINGS | GEOKON
For more information, consult the GK-405 Instruction Manual.

6.4 MEASURING TEMPERATURES

All vibrating wire instruments are equipped with a thermistor for
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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-404 and GK-405 readouts will read the thermistor and display the
temperature in degrees Celsius.
TO READ TEMPERATURES USING AN OHMMETER:
1. Connect an ohmmeter to the green and white thermistor leads coming from
the instrument. 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 approximately 48.5Ω per km (14.7Ω per
1000') at 20 °C. Multiply these factors by two to account for both directions.
2. Look up the temperature for the measured resistance in Appendix C.