Wiring RTDs

This is not specifically a PLC question but is related. I am very familiar with wiring transmitters and sensors to PLCs using 2-wire shielded cable. I have an application for temperature control where I will be using a 3-wire RTD connected to a stand-alone controller. My question is this, do I need any special wire for this application or can I just use a 3-wire cable? Also does it need to be shielded? I know I can use a locally mounted temperature transmitter but the controller I am using has a PT100 RTD input.

The third lead is for compensation of the length of wire you use to connect the sensor to the temp controller or transmitter. The type of wire typically is plain copper. Special wire is reserved for the thermocouple and in that case they are chosen to match the type of junction used. The need for shielding is an application question and should be considered if there is allot of electrical or Radio Frequency noise.

Hope this helps...

3 conductor 18 to 22 guage shielded wire will work just fine.

i do it many many times. most projects have more than 200 of them.

just have a three wire shielded cable.
maximum resistance in cable is 10 ohms.
shield should be connected at controller or cabinet side and not on sensor side.
all wires should be same type and same length. check is possible by swapping two wires and you should have same reading.

I would always use shielded wire. As it is generally easier to pull wire then it isto re-pull wire if a problem occurs. Also be careful as there are four types of 100 ohm platinum RTD's. I've run across two types, 1.3850 and 1.3926. The kicker was they were both on the same machine. There was a 4 deg F error at 285 deg if the wrong curve was used to calibrate the transmitter, which was too much for us. Be sure that the RTD and the transmitter calibrations match.

Andy