Rockwell Automation 1746-NT4 Series B,D17466.6.1 SLC 500 4-Channel Thermocouple/mV Input Module User Manual - Manual (Page 37)

Publication 1746-UM007C-EN-P - July 2004
Installation and Wiring 3-9
•
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 Appendix D for definitions of thermocouple types.)
– 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.
– I f millivolt inputs are used, the terminal should be handled as
discussed on page 1-7.
The Series A 1746-NT4 does not have an ANALOG COM
terminal and cannot be used with multiple grounded and/or
exposed thermocouples that touch electrically conductive
material. The Series A can be used with a single grounded
and/or exposed thermocouple that touches electrically
conductive material, or multiple grounded thermocouples that
have the protective sheath made of an electrically
non-conductive material such as ceramic.
•
Ground the shield drain wire at one end only. The preferred
location is to the same point as the sensor ground reference.
– For grounded thermocouples or mV sensors, this is at the
sensor.
– For insulated/ungrounded thermocouples, this is at the
module.
– (Refer to IEEE Std. 518, Section 6.4.2.7 or contact your sensor
manufacturer for additional details.)