Rockwell Automation 1771-IR Series D RTD Input Module User Manual - Manual (Page 66)

2 and 4–Wire RTD Sensors E–2
Publication 1771Ć6.5.129 - March 2000
Three–wire and 4–wire sensors compensate for lead resistance error.
Their schematic representation is shown below. 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.
Connections for 3 and 4–Wire Sensors
C
B
A
3-Wire Sensor
C
B
A
Leave Open
4-Wire Sensor
There are several ways to insure that the lead resistance values match
as closely as possible. They are:
•
use heavy gauge wire (16–18 gauge)
•
keep lead distances less than 1000 feet
•
use quality cable that has a small tolerance impedance rating.