Rockwell Automation 1746-NT4 Series B,D17466.6.1 SLC 500 4-Channel Thermocouple/mV Input Module User Manual - Manual (Page 19)

Publication 1746-UM007C-EN-P - July 2004
Overview 1-7
Linear Millivolt Device Compatibility
A large number of millivolt devices may be used with the 1746-NT4
module. For this reason we do not specify compatibility with any
particular device.
However, millivolt applications often use bridges of strain gages. To
allow the NT4 Series B (or higher) to operate correctly, the analog
common (
ANALOG COM
) terminal of the module needs to be biased to a
level within 2V of the signal of interest. A resistive voltage divider
using 10k
Ω
resistors is recommended to accomplish this. The circuit
diagram below shows how this connection is made.
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. Refer to
Appendix D for more details.
+
-
ANALOG COM
fixed
fixed
variable
fixed
INPUT
(CHL0, CHL1,
CHL2, CHL3)
Vcc
+
10k Ω
10k Ω
NT4
Strain
Gage
Bridge