Rockwell Automation 1771-IR , D17716.5.76 RTD INPUT MODULE - Manual (Page 60)

Appendix
E
EĆ1
2 and 4-Wire RTD Sensors
You can connect 2–wire and 4–wire sensors to the RTD module. Before we
show you how to do this, let’s examine the differences between 2, 3 and 4–wire
sensors.
A 2–wire sensor is composed of just that; a sensor and 2 lead wires. Its
schematic representation is shown in Figure E.1.
Figure E.1
Connections for a 2-Wire Sensor
C
B
A
12950-I
A sensor requires at least three leads to compensate for lead resistance error,
that is, an error caused by resistance mismatch between the lead wires.
Therefore, a 2–wire sensor cannot provide compensation for error caused by
lead wire resistance. We do not recommend that you use 2–wire sensors.
Three–wire and 4–wire sensors compensate for lead resistance error. Their
schematic representation is shown in Figure E.2. The amount of error
elimination depends upon the difference between the resistance values of the
lead wires. The closer the resistance values are to each other, the greater the
amount of error that is eliminated.
About 2 and 4-Wire Sensors