Measuring Temperatures - Geokon 4820 Instruction Manual

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3.4 Measuring Temperatures

Each Vibrating Wire Pressure Cell is equipped with a thermistor for reading temperature. The

thermistor gives a varying resistance output as the temperature changes. Usually the white and

green leads are connected to the internal thermistor.

1) Connect the ohmmeter to the two thermistor leads coming from the stress cell. (Since the

resistance changes with temperature are large, the effect of cable resistance is usually

insignificant.)

2) Look up the temperature for the measured resistance in Table 6 in Appendix B. (For 4800HT

models use Table 7 in Appendix C.) Alternately, the temperature could be calculated using

Equation 5 in Appendix B. For example, a resistance of 3400 ohms is equivalent to 22° C.

When long cables are used, the cable resistance may need to be taken into account. Standard

22 AWG stranded copper lead cable is approximately 14.7Ω/1000' or 48.5Ω/km, multiply by

two for both directions.

Note: Geokon readout boxes will read the thermistor and display temperature in °C

automatically.

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4830 4815 4800 series