Can we use 4 wire RTD(PT-100) At 3 wire RTD I/O point at PLC
Yes, we can use it, but it will not do accurate temperature compensation. Because the 4th wire is used for more than 100Mtr temperature compensation. 3wire is used for less than 100mtr
Yes, a 4-wire RTD can be used with a 3-wire AI card. One of the four wires is not connected, but the accuracy is as good accuracy as the 3-wire AI card can provide.
There are VERY few true 4 wire RTD AI cards for PLCs, and those are expensive, high end cards.
One PLC RTD input card claims to be 2, 3, or 4 wire but when you read the fine print, they are 3-wire inputs, where they use a jumper to ‘fake’ the 3rd wire compensation for a 2-wire RTD, and do not use the 4th wire for a 4-wire RTD.