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Example 4-20mA thermistor transmitter wiring diagram

The 4-20mA transmitter can be looked at as a temperature controlled variable load, in series with the power supply and current measurement shunt resistance. The effect is similar to the transmitter acting like a potentiometer, that will vary total load resistance (according to change in temperature), varying total current in circuit; to be measured as a voltage change across the current shunt resistance.

When the ROI-XMA Thermistor transmitter is wired, with the correct DC power supply and current measurement device, the transmitter is wired as a 4-20mA loop circuit; as shown in the following diagram. 

When the ROI-XMA Thermistor transmitter is used with the ROI-USB current measurement A-D, the PC can be used to measure a Thermistor with higher precision than a direct measurement system. 

The 4-20mA transmitter gain can be adjusted to minimize the span of the temperature sensor range. The result is a PC temperature recorder, with precision greater than a tenth of a degree. 

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