Why is 4-wire connection recommended with Pt100 Class A (acc. to IEC 60751)?
Only 4-wire connection is completely compensating the wire resistance effect of the whole cable circuit. With 2- or 3-wire connections there might be possibility to manually program the measured cable resistance as a transmitter parameter to correct the final readout. But even in these cases the parameter is correct only at the ambient temperature of the moment of measuring the cable. The measurement circuit loses its accuracy if the ambient temperature changes. The 4-wire connection compensates also ambient temperature variations. The Class A Pt100 RTDs are meant for accurate temperature measurement, that’s why the wire connection should always be implemented with 4 wires. More details on page How does a Pt100 sensor work?