What is the difference between 2 wires RTD's and 3 wires
RTD's.Kindly explain the wiring diagram.

Answer Posted / dale bergemann

RTD is Resistance Temperature Detector. It will change resistance at its leads when the sensor is exposed to changing temperature. They are commonly found in windings of motors or surfaces of bearings or immersed in liquid to produce a resistance when converted by a monitoring device can indicate degrees in the medium it is placed.
A lead wire is place on each side of the sensor and the resistance can be measured across those two leads, commonly Red and White in color. Because it measures ohms, the value will be affected by the length of the leads, which will 'bias' the reading and convert incorrectly. To address this, a third wire can be added in parallel with the white wire. Now the monitor measures the resistance between and R & W and compensates it with the resistance measured between the two white wires. Now we have the true resistance change of the sensor, without the error caused by lead length.
They also make 4 wire RTDs which have two Red and two White leads to further enhance capability and increase accuracy by analyzing in a bridge fashion.

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