Campbell Scientific AVW200 AVW200-series Vibrating Wire Interfaces - Page 67
Appendix B. Thermistor Information, B.1 Converting Resistance to Temperature
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Appendix B. Thermistor Information B.1 Converting Resistance to Temperature The AVW200 outputs a resistance value for sensors that contain a thermistor. Temperature is calculated by applying the resistance to a known equation (e.g., Steinhart-Hart equation) which converts resistance to temperature. The Steinhart-Hart equation for converting resistance to degree Celsius is as follows: Temperature = 1/(A + B*LN(resistance) + C*(LN(resistance))^3) - 273.15 Where A, B, and C are coefficients for the Steinhart-Hart equation. The coefficients for the Steinhart-Hart equation are specific to the thermistor contained in your sensor and are obtained from the sensor manufacturer. NOTE Please see your manufacturer to get the coefficients for their thermistor. B.1.1 Resistance Conversion Example - Geokon Sensor If the coefficients for Steinhart-Hart equation are as follows A=0.0014051 B=0.0002369 C=0.0000001019 The equation for converting the resistance measurement to degrees Celsius is: Temperature = 1/(0.0014051 + 0.0002369*LN(resistance) + 0.0000001019*(LN(resistance))^3) - 273.15 If the measured resistance is 2221 ohms, the calculated temperature in degree Celsius is: Temperature = 1/(0.0014051 + 0.0002369*LN(2221) + 0.0000001019*(LN(2221))^3) - 273.15 Temperature = 31.98°C B.2 Accuracy and Resolution The accuracy of the temperature measurement is a function of the following factors: 1. Thermistor's interchangeability 2. Resistance of the wire 3. Steinhart-Hart Equation error B-1