Rockwell Automation T3411 ICS Regent Monitored Digital Input Modules - Manual (Page 4)

Monitored Digital Input Modules (T3411)
4
Industrial Control Services
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
address that module and its points specifically. The processor
modules periodically check each module’s identification code
to determine whether the type of module installed matches
type of module indicated in the I/O configuration that was
loaded when the system was started. If a module is removed,
or is replaced with a module of a different type, the processor
modules will indicate I/O module errors.
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.
Input Circuit Testing
The field interface circuits of the monitored input module are
completely tested to detect stuck-on or stuck-off input circuit
faults and optionally identify input wiring open and short
circuits. The automatic execution and evaluation of the input
testing is controlled by the triplicated Regent processor
modules.
During normal operations, the internal reference voltage is
set to three levels and the comparator output is read. These
three reference voltage levels represent thresholds that
determine whether the input signal is on or off and if the field
wiring is open circuit or short circuit. The logic-side FPGA
determines input status and line fault status based on the
comparator data for the three voltage levels. The FPGA data
is provided to the I/O processors for application processing.
On a background basis, the I/O processors test the input
circuit comparators and logic circuits for stuck-on and stuck-
off failure modes. During testing the D/A converter generates
two reference voltages outside the normal operating range of
the field input voltages to test that the comparator output can
turn-off and turn-on. The I/O processors read the resulting
input status, line fault status, and reference voltage readings
for the test cycle to determine if there are faults in the input
circuits or the common data paths.