Rockwell Automation 1746-NT4 SLC 500 Thermocouple/mV Input Module Installation Instructions - Manual (Page 13)

SLC™ 500 4-Channel Thermocouple/mV Input Module 13
Publication 1746-IN010D-EN-P - June 2004
Wiring Considerations
Follow the guidelines below when planning your system wiring.
• To limit noise, keep thermocouple and millivolt signal wires as far away as
possible from power and load lines.
• To ensure proper operation and high immunity to electrical noise, always
use Belden™ 8761 (shielded, twisted-pair) or equivalent wire for millivolt
sensors or shielded, twisted-pair thermocouple extension lead wire specified
by the thermocouple manufacturer for the thermocouple type you are using.
Using the incorrect thermocouple extension wire type or not following the
correct polarity convention will cause invalid readings.
• Special considerations for using the analog common (ANALOG COM)
terminal based on thermocouple type:
(See page 12 for an explanation of thermocouple junctions.)
– When using grounded thermocouple(s), jumper the ANALOG COM
terminal to any single active grounded channel’s plus (+) or minus (-)
terminal.
– When using exposed thermocouple(s) that have the thermocouple
junction touching an electrically conductive material, jumper the
ANALOG COM terminal to any single active exposed channel’s plus (+)
or minus (-) terminal.
– When using ungrounded (shielded) or exposed thermocouples that are
not touching an electrically conductive material, do not use the
ANALOG COM terminal.
– When using a mix of grounded, ungrounded, and exposed
thermocouples, jumper the ANALOG COM terminal to any single active
grounded channel’s plus (+) or minus (-) terminal.
ATTENTION
The possibility exists that grounded or exposed thermocouples
can become shorted to a potential greater than that of the
thermocouple itself. Due to possible shock hazard, care should
be taken when wiring these types of thermocouples. See
page 12 for definitions of thermocouple junctions.