Pt-100 temperature sensor – working principle and test procedure

Pt-100 or pt100 is one of the most used temperature sensor. It is one of the most used temperature sensor. Cheap but robust for use and capable to directly interface with PLC. The use of pt-100 is limited to below 150°c. Moreover, it is not suitable for internal use, with its hard plastic body as it has own limitation.

Pt-100 temperature naming and working principle

Pt-100 is named as such because platinum is used as the sensing material and at with perfect calibration it has 100-ohm resistance at 0°c. For increment or decrement of temperature, the resistance value of platinum changes linearly. Thus it can be used to identify the temperature by comparing the resistance value and temperature-resistance variation log value (provide by manufacturer).

The zero scale for pt-100 is 100 ohm at 0°c. Thus, the measuring value of pt-100 is resistance and for thermocouple temperature sensor, measuring parameter is voltage. With the measuring value, matching by chart the perspective temperature can be found.

In PLC programming for a certain pt-100, the temperature log chart with resistance is programmed, thus it can be used in automation system.

                                          Fig: pt-100 temperature sensor principle

How to test Pt-100 temperature sensor

The checking of pt-100 temperature sensor is a matter of sense. In my power plant, we checked pt-100 temperature, used to find 114ohm to 120ohm for functioning pt-100 (subject to ambient temperature being 30°c – 40°c) and for faulty Pt-100, it used to be 0 ohm or infinite (open).

Pt-100 temperature sensors can be tested or checked to see if it’s working properly. The testing of Pt-100 requires a resistance meter or ohmmeter.

Open Pt-100 sensor cover to check

                                 Fig: Test Pt-100 temperature sensor with resistance meter.

Open the cap.

Use multimeter (resistance measurement). Take out one wire from PT-100 connection box.
Check Pt-100 sensor resistance:

                                     Fig: Check the resistance value of Pt-100 to check / test if it’s okay

Connect the multimeter between two-connection pins. Measure the resistance. Compare measured resistance to the values in engine manual, If the value is not zero or infinite, the sensor is working ok.

                                               Fig: Industrial grade Pt-100 temperature sensor