Rockwell Automation T3468A ICS Regent DC Guarded Digital Output Modules - Manual (Page 4)

DC Guarded Digital Output Modules (T3461A, 62A, 68A)
4
Industrial Control Services
majority-voted result to the processors produces an I/O
module error indication at the processor modules and a
module fault indication at the I/O module.
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.
Fuses are checked for continuity. Blown fuse detection is
independent of load connection or the output circuit’s on/off
state.
To detect a failure in the redundant logic drive circuits, each
pair of output switches is checked for state discrepancies. If a
discrepancy is detected, a module fault is indicated. These
state comparison tests allow for normal variances in FET
switching times.
Approximately once every second each FET on the module is
tested for its ability to change its current state. During
testing, the output state is changed; outputs that are on are
turned off and outputs that are off are turned on. The testing
time is nominally 0.75 milliseconds, and is insufficient to
affect the state of most field loads.
Testing of the output switches is non-overlapping, i.e. no turn
on pulse is applied to the load unless one of the switches is
shorted. Also, in a dual module configuration, no turn-off
pulse is applied to the load unless the asynchronous test
pulses between the dual modules overlap, a output switch is
open, or a module is removed. In any case, the nominal test
pulse duration of 0.75 milliseconds is insufficient to disturb
field outputs.
Output circuit test results are not affected by the presence or
absence of a load. Output FET current leakage greater than 2
mA is detected as a shorted FET.