Rockwell Automation T7488/T7488A ICS Regent+Plus Monitored Guarded Output Modules - Manual (Page 5)

Monitored Guarded Output Modules (T7481/81A, 84 and 88/88A)
P D - 6 0 3 3 M a r - 0 6 (Issue 2)
5
During testing, the output state is changed; outputs that are
on are turned off and outputs that are off are turned on.
When two monitored guarded output modules are wired in
parallel for fault tolerance, the output circuit testing of the
dual modules is coordinated. The test coordination is
automatically performed by the system when the modules are
properly configured for dual mode (see Configuration, starting
on page 17). When dual modules are tested, the second
module’s outputs are turned off momentarily while the first
module’s outputs are tested. Subsequently, the first module’s
outputs are turned off while second module’s outputs are
tested.
When an output switch is tested, the test pulse duration is
nominally 250 msec, and is insufficient to affect the state of
most field loads. With modules configured in dual mode, the
maximum test pulse may be 425 msec if one module has a
switch failure. The output circuit test interval will range from
1 to 60 seconds, depending on the quantity of I/O configured
in the system.
If an output switch doesn’t change state when tested, an
output switch fault is detected. An output switch failure is
annunciated as a module fault. An I/O module fault is
indicated by the module FAULT LED on the module, the red
I/O fault LEDs on the processor modules and the system
control relay fault bit for the module assembly and slot.
Load and Fuse Monitoring and Testing
During output switch testing, the module also monitors the
change in current flow in the field power for the outputs. The
sensed state changes of the output switches and the field
power current are reported back to the processor modules.
The triplicated processor modules use this information to
identify if an open load, shorted load or blown fuse condition
exists.
Any of these load/fuse fault conditions are annunciated via
the LOAD/FUSE fault LEDs on the face of the module and the
Fault Name variables configured for each point. Load/Fuse
faults are not reported as module faults and so do not turn on
the red Module FAULT LED or associated system variable
control relay fault bit. The Fault Name variables should be