Rockwell Automation T3464 ICS Regent AC Guarded Digital Output Module - Manual (Page 5)

(T3464) AC Guarded Digital Output Module
P D - 6 0 2 1 M a r - 0 6
5
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 periodically checked for continuity. Blown fuse
detection is independent of load connection or output circuit’s
on/off state.
Incoming AC field power is checked for proper frequency,
stability, and phase. Tests that depend on AC power timing
information, such as turn-on testing, will not execute if the AC
power is unacceptable. However, crowbar switch activation is
not dependent on these power conditions.
Approximately every 2 seconds, output circuits commanded to
be off are tested for their ability to turn on. Three test pulses
are applied on successive AC voltage phase zero crossings to
verify the output switch's ability to conduct bi-directional
current flow. The pulses are limited to 50 volts with a
maximum duration of 1 millisecond. This energy is
insufficient to drive most field loads.
Output TRIACs commanded to be on (output switch closed)
are not tested for their ability to turn off. Instead, the crowbar
circuit is periodically tested for its ability to turn on. If a
TRIAC fails to tuns off when commanded, either
microcomputer can energize the crowbar switch and remove
power from the load by blowing the fuse for that circuit. In
this way, an output’s inability to turn off is not discovered
until the switch is commanded to turn off. The result is a
maximum time to switch off a shorted output (blow the fuse) of
200 milliseconds.
Outputs commanded to be on are occasionally tested for open
load and open circuit (faulty output switch) conditions. If load
current is below the minimum requirements, the module tests