We have 4 wire RTD, it is connected to 3 wire+shield cable. Can we use the shield as the fourth conductor ?

 

I notice that several of the vendors are providing 4 wires now.
Unless you require super accuracy e.g. 2 decimal places you can just ignore one wire. (make sure it can't short to ground) If your measuring device has terminals for the 4th wire you can jumper that.

Having said that you need to study the input device wiring and figure out which two wires are required for lead length compensation.

Regards,
Roy

 

Just configure the receiving instrument for three wire, and snip off one of the four at the RTD end. Ground the shield at the instrument end only. 3-wire is a very common configuration and just as accurate as four wire as long as all the leads are the same length.

 

Definitely not. Three and Four wires connection is for compensate the resistance added by the wires that connect to the RTD element. The shield have different resistance and will carry the noise current induced to your cable.