RTD Measurements

4-wire can be used in a 3- or 2-wire compatible transmitter simply by leaving the unused cores disconnected. 2-wire can be used in 3- and 4-wire transmitters, though the transmitter terminals will need to be linked-across to make it operate.

4- and 3-wire RTDs offer accuracy advantages compared to 2-wire RTDs, as the third and fourth wires are intended to be used to cancel-out any effects of series resistance in the cable conductors. For short runs between RTD and transmitters it matters diddly squat. For longer runs, the inaccuracies caused by series cable conductor resistance can be significant. Using 3- or 4-wire systems overcomes this difficulty.