Rockwell Automation 1762-IR4 RTD/Resistance Input Module - Manual (Page 9)

MicroLogix 1200 RTD/Resistance Input Module 9
Publication 1762-IN014B-EN-P - July 2013
RTD Wiring Configurations
For a 3-wire configuration, the module can compensate for a maximum cable length associated
with an overall cable impedance of 25 ohms.
Three configurations of RTDs can be connected to the 1762-IR4 module:
• 2-wire RTD, which is composed of an RTD EXC (excitation) lead wire and a RTN
(return) lead wire
• 3-wire RTD, which is composed of a Sense and 2 RTD lead wires
(RTD EXC and RTN)
• 4-wire RTD, which is composed of a Sense and 2 RTD lead wires
(RTD EXC and RTN). The second sense wire of a 4-wire RTD is left open.
2-Wire RTD Configuration
IMPORTANT
Using 2-wire configurations does not permit the module to compensate for
resistance error to do lead wire length. The resulting analog data includes
the effect of this uncompensated lead wire resistance. The module
continues to place the uncompensated analog data in the input data file, but
the open-circuit status bit (OCx) is set in word 4 of the input data file for
any enabled channel using a 2-wire configuration. These status bits may be
used in the control program to indicate that the analog data includes error
due to uncompensated lead wires. See page 16 for a detailed discussion of
the open-circuit status bits.
EXC 2
SENSE 2
RTN 2
NC
Belden 9501 Shielded Cable
Cable Shield (to Ground)
RTD EXC
Return
RTD EXC
Return