Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 227 of 265
3
3
3
3
H
H
A
A
R
R
D
D
W
W
A
A
R
R
E
E
C
C
H
H
E
E
C
C
K
K
S
S
33.1 Monitoring the Signals
The correspondence check (also known as an equivalence check) is available on all
three colours, not just greens. A correspondence error on a monitored green will
always cause the controller to shut down. For Non-UK Controllers, correspondence
errors on reds and ambers can be configured to report the failure but allow the
controller to continue normally, shown by the options (a) to (d) in the table.
Switched signs are treated separately. Their monitoring option is set regardless of
which colour output they are assigned to; i.e. a switched sign assigned to a spare
green output can be monitored differently from all the other ‘normal’ green outputs.
See section 14.4 ‘‘Fail to Part-Time’ State’ for details of how faults on one stream
can be configured to just ‘switch off’ that stream, while the other streams continue to
operate normally.
The following table summarises the hardware checks performed by the firmware,
identifying which processor (Main Processor or Signal Monitor) performs the check
and what the action will be when the fault is confirmed.
Table 24 – Hardware Checks and Fault Actions
Condition CPU Fault Action
Red Correspondence Failure
Compares “required” states against actual
states or the dual voltage monitors disagree.
Measured by voltage on drive. Functions with
no external load. Monitoring can be disabled.
See section 33.2 for details of the options a)
to d) available for Fault Actions.
Main
CPU
a) Controller Shutdown
b) Stream direct to part-time state
c) Stream direct to part-time state
d) Fault report only
Sig
Mon
a) Controller Shutdown
b) Controller Shutdown
c) Check Disabled
d) Check Disabled
Amber Correspondence Failure
Compares “required” states against actual
states or the dual voltage monitors disagree.
Measured by voltage on drive. Functions with
no external load. Monitoring can be disabled.
See section 33.3 for details of the options a)
to d) available for Fault Actions.
Main
CPU
a) Controller Shutdown
b) Stream direct to part-time state
c) Stream direct to part-time state
d) Fault report only
Sig
Mon
a) Controller Shutdown
b) Controller Shutdown
c) Check Disabled
d) Check Disabled