what is difference between 3 wire and 4 wire RTD sensor?

Answer Posted / vikas dubey

3-wire construction is most commonly used in industrial applications where the third wire provides a method for removing the average lead wire resistance from the
sensor measurement. When long distances exist between the sensor and measurement/control instrument, significant savings can be made in using a three wire
cable instead of a four-wire cable.The 3 wire circuit works by measuring the resistance between #1 & #2 (R 1+2) and subtracting the resistance between #2 & #3 (R 2+3) which leaves just the resistance of the RTD bulb (R b). This method assumes that wires 1,2 & 3 are all the same
resistance..

4-wire construction is used primarily in the laboratory where close accuracy is required. In a 4 wire RTD the actual resistance of the lead wires can be determined
and removed from the sensor measurement.
The 4-wire circuit is a true 4-wire bridge, which works by using wires 1 & 4 to power the circuit and wires 2 & 3 to read. This true bridge method will compensate for any
differences in lead wire resistances.

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