Campbell CDM-VW300 Series Manuál stáhnout pdf (Strana 89)

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Appendix F. Thermistor Information

F.1 Converting Resistance to Temperature

The CDM-VW300 outputs a resistance value for sensors that contain a

thermistor. Temperature is normally calculated by applying the resistance to

the 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.

Please contact the sensor manufacturer to get coefficients for a

specific thermistor.

NOTE

F.1.1 Resistance Conversion Example – Geokon Sensor

If the coefficients for the Steinhart-Hart equation are as follows

A = 1.4051E–03

B = 2.369E–04

C = 1.019E–07

The equation for converting the resistance measurement to degrees Celsius is:

Temperature = 1/(1.4051E–03 + 2.369E–04 • LN(resistance) +

1.019E–07 • (LN(resistance))^3) – 273.15

If the measured resistance is 2221 , the calculated temperature in degree

Celsius is:

Temperature = 1/(1.4051E–03 + 2.369E–04 • LN(2221) +

1.019E–07 • (LN(2221))^3) – 273.15

Temperature = 31.98°C

F.2 Accuracy and Resolution

The accuracy of the temperature measurement is a function of the following

factors:

1. Thermistor interchangeability

2. Resistance of the wire

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Campbell CDM-VW300 Series Manuál Strana 89