Design, Manufacture and Supply of Process Instrumentation

Simple temperature measurement using a PT100 loop powered temperature transmitter.

The following Status transmitters can be used in this way

SEM203P SEM310(X) SEM1801

SEM206P SEM315 SEM1802

SEM210(X) SEM1603P TTR200(X)

SEM213P SEM1610


Pt100 Probes

A Pt100 probe or sensor is a type of resistive temperature detector (RTD) that will change its resistance as a function of temperature.

Pt100 probe resistance most commonly measures 100 ohms at 0°C and 138.51 ohms at 100°C, the temperature range for a Pt100 probe is normally within (-200 to 850) °C. However, in practice we tend to switch to thermocouples over 600 Deg C.


A change in temperature on the Pt100 creates a change in its resistance. The resistance of the probe can be measured and its temperature can be attained.

Pt100 Transmitter Connections

A three wire Pt100 probe normally has two red wires and one white wire. One end of the internal Pt100 sensor is connected to the red wires and the other end of the sensor to the white wire.

The resistance of the sensor is measured across the red wires and the white wire.

The two red wires are joined where they connect to the internal Pt100 sensor, this method is used to compensate for the length of the wires so the resistance in the leads will not cause an offset in the temperature reading.

2 Wire Connection

Two wire PT100 probe connected to a loop powered temperature transmitter

A two wire probe can be connected to a three wire input temperature transmitter by shorting two of the input terminals on the temperature transmitter. However, there will be no lead resistance compensation. In this case lead resistance will be added to sensor resistance. (0.38ohms = 1 DegC)


3 Wire Connection