Rockwell Automation T3464 ICS Regent AC Guarded Digital Output Module - Manual (Page 3)

(T3464) AC Guarded Digital Output Module
P D - 6 0 2 1 M a r - 0 6
3
the TRIAC will be de-energized. If the TRIAC itself fails
shorted when commanded off, either microcomputer section
can trigger an internal crowbar switch that disables the
output by blowing the fuse for that circuit.
The combination of dual independent drive signals, a TRIAC,
and a crowbar circuit provides fail-safe activation of the load
devices. No single failure can prevent the output from being
turned off when commanded. Single failures result in either
continued correct control or a fail-safe output as shown in
Table 1.
To achieve fault tolerance, two Guarded output modules are
used with their outputs connected in parallel. This
configuration provides for continued correct control even
when an output TRIAC fails open (class 2 and 5 in Table 1).
The module failure is automatically detected and the failed
module can be removed and replaced without interrupting
output control.