FIGURE 4-19: RTD 4-WIRE CONNECTION VIA THE EX1200 DMM BUS
Programming Interface
The VTEX DMM and VTEX Scanner drivers provide the access to the features of EX1200 DMM.
Refer to the below functions of the driver in its documentation.
IVTEXDmmTemperature Interface
IIviDmmTemperature..::.RTD Property
Using a Thermistor
While RTDs can be used over a wide temperature range, thermistors offer a higher sensitivity to
temperature change, although they must operate in a more restricted temperature range.
Thermistors are resistance-based passive transducers whose output resistance varies with
temperature changes. By measuring the resistance of the thermistor, the temperature can be
derived. The following thermistors are predefined on the EX1200 DMM and use built-in software
conversions: 2.252 kΩ (default), 5 kΩ, and 10 kΩ.
Custom thermistors can be defined by providing the appropriate variables in the Steinhart-Hart
equation: A, B, and C (refer to the thermistor manufacturer’s data sheet for more information). The
equation is as follows:
Where: T
K
= calculated temperature in Kelvin
ln(R) = natural log of measured resistance value of thermistor
T = temperature in °C
A, B, C = curve-fitting constants
Curve fitting constants used by the DMM for supported thermistor types:
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