Rockwell Automation 1746-NR8 SLC 500 RTD/Resistance Input Module/ Instructions - Manual (Page 11)

SLC 500™ RTD/Resistance Input Module 11
Publication 1746-IN007C-EN-P - December 2002
Terminal Block Removal
If the terminal block is removed, use the write-on label located on the side of the
terminal block to identify the module location and type.
To remove the terminal block:
1. Loosen the two terminal block release screws.
2. Grasp the terminal block at the top and bottom and pull outward and down.
Wiring Considerations
Follow the guidelines below when planning your system wiring.
Since the operating principle of the RTD module is based on the measurement of
resistance, take special care in selecting your input cable. For 2-wire or 3-wire
configuration, select a cable that has a consistent impedance throughout its entire
length.
For a 3-wire configuration, the module can compensate for a maximum cable
length associated with an overall cable impedance of 25 ohms.
As shown in the figure on the next page, three configurations of RTDs can be
connected to the RTD module:
•
2-wire RTD, which is composed of 2 RTD lead wires (RTD and Return)
•
3-wire RTD, which is composed of a Sense and 2 RTD lead wires (RTD and
Return)
•
4-wire RTD, which is composed of 2 Sense and 2 RTD lead wires (RTD and
Return). The second sense wire of a 4-wire RTD is left open.
Configuration Recommended Cable
2-wire Belden™ #9501 or equivalent
3-wire
less than 30.48 m (100 ft.) Belden #9533 or equivalent
3-wire
greater than 30.48 m (100 ft.) or high humidity conditions Belden #83503 or equivalent