Rockwell Automation 1746-NT4 Series B,D17466.6.1 SLC 500 4-Channel Thermocouple/mV Input Module User Manual - Manual (Page 62)

Publication 1746-UM007C-EN-P - July 2004
5-10 Channel Configuration, Data, and Status
Select Open Circuit State (Bits 6 and 7)
The open-circuit bit field lets you define the state of the channel data
word when an open-circuit condition is detected for that channel.
This feature is active for thermocouple input types, millivolt input
types, and CJC device input.
An open-circuit condition occurs when the thermocouple itself or its
extension wire is physically separated or open. This can happen if the
wire gets cut or disconnected from the terminal block.
If either of the two CJC devices (thermistors) are removed from the
module wiring terminal, any input channel configured for either a
thermocouple or CJC temperature input will be placed in an open
circuit condition. An input channel configured for millivolt input is not
affected.
If zero is selected, the channel data word is forced to 0 during an
open-circuit condition.
Selecting upscale forces the channel data word value to its full scale
value during an open-circuit condition. The full scale value is
determined by the selected input type and data format.
Selecting downscale forces the channel data word value to its low
scale value during an open-circuit condition. The low scale value is
determined by the selected input type and data format.
IMPORTANT
You may receive up-ramping data values from the
time the open circuit condition occurs until the
condition is flagged. The NT4 requires 500 msec or
one module update time, whichever is longer, to
indicate the error. Depending on your program scan
rate, ramping data may be written for several
program scans after the open circuit occurs.