Rockwell Automation 1746-NT8 SLC 500 Thermocouple/mV Analog Input Module User Manual - Manual (Page 64)

Publication 1746-UM022B-EN-P - January 2005
5-8 Programming Examples
Monitoring Channel Status
Bits The following example shows how to monitor the open-circuit error
bits of each channel and set an alarm in the processor if one of the
thermocouples opens. An open-circuit error can occur if the
thermocouple breaks, one of the thermocouple wires gets cut or
disconnected from the terminal block, or if the CJC sensors are not
installed or are damaged.
The example shows how to automatically switch between reading the
channel status words and channel sensor data words. Specifically, this
example shows a simple method of utilizing a timer to periodically
switch between reading the channel status and data words.
The program utilizes a timer accumulator value to determine when to
set up the configuration words and when to read in the channel status
and channel data information. The channel status information is
copied from the I:2.0 to I:2.7 registers into registers N7:10 to N7:17.
The channel data information is copied from I:2.0 to I:2.7 into registers
N7:0 to N7:7. This allows sensor data and channel status information
to be accessed at any time from these registers. However, when the
module channels are configured to read sensor data, the channel
status words (as reflected in N7:10 to N7:17) are not being
dynamically updated, and vice-versa.
IMPORTANT
If a CJC input is not installed or is damaged, all
enabled thermocouple alarms are set, and all
enabled thermocouple