Rockwell Automation T3431-CA ICS Regent Thermo Couple Input Assembly - Manual (Page 5)

Thermocouple Input Assembly (T3431)
P D - 6 0 2 4 M a r - 0 6
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Each type of module has a unique identification code that is
read by the controller. This code lets the controller know
which type of module is installed in each I/O chassis slot and
how to address that module and its points specifically. If a
module is removed, or is replaced with a module of a different
type, the processor modules will indicate an I/O module error.
Loopback logic tests periodically write data to the module and
then read it back to determine whether the module’s I/O bus
interface logic is functioning correctly.
Multiplexer Testing
The serial communications link to the thermocouple Mux is
continuously monitored. Additionally the data received from
the Mux is checked for proper data format, parity and numeric
range reasonableness. The cold junction sensor values are
monitored and compared to detect a failed cold junction
sensor. The precision voltage references on the multiplexer
are also checked to verify that the power to the Mux is present
and that the voltage references are within tolerance.
Input Module Front Panel Indicators
Figure 3 shows the physical features of the thermocouple
input module. The front panel of each module contains status
indicators to display the operational status of the input
module, multiplexer and cold junction sensors.
Active and Fault Status Indicators
These green and red LEDs indicate the overall health of the
module. During normal operation the green ACTIVE
indicator flashes at the controller's scan rate. If a module
fault occurs the red FAULT indicator turns on and the green
ACTIVE indicator turns off.
MUX Fault Indicator
The red MUX FAULT indicator turns on when any of the
following fault conditions are detected:
· No data received from the Mux.
· Corrupted data from the Mux.
· Unreasonable data values from the Mux.