Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 231 of 265
33.2 Correspondence Monitoring – Greens
Option a) Fail to Part-Time State is not selected. Both processors will
independently detect a green correspondence failure. If the actual states of the
greens do not match the requested states and the fault will be confirmed if the
situation persists. When the fault is confirmed, the processor will shut down the
whole controller.
Option b) Fail to Part-Time State is selected (Non-UK Only). Correspondence
monitoring of greens is performed independently by both processors. The Main
Processor moves the stream to its part-time state. If the fault persists, or a green
fault occurs while already in the part-time state, the Signal Monitor will shutdown the
controller.
Options c) and d) cannot be selected (because this would disable checking).
33.3 Correspondence Monitoring – Reds / Ambers
Option a) Correspondence monitoring is enabled and Fail to Part-Time State is not
selected. Correspondence monitoring of that colour is performed independently by
both processors and either processor can shut down the controller when a fault is
confirmed.
Options b) and c) are available if Fail to Part-Time State is selected (Non-UK Only).
Option b) Correspondence monitoring is enabled and ‘Ignore during Fail to Part-
Time’ not selected. Correspondence monitoring of that colour is performed
independently by both processors. The Main Processor moves the stream to its part-
time state. If the fault persists, or this fault occurs while already in this state, the
Signal Monitor will shut down the controller.
Option c) Correspondence monitoring is enabled and ‘Ignore during Fail to Part-
Time’ is selected. Correspondence monitoring of that colour is disabled in the
Signal Monitor and monitoring is only performed by the Main Processor. The Main
Processor moves the stream to its part-time state. If this fault occurs while already in
this state, the Main Processor will just record the fault.
Option d) Correspondence monitoring is disabled (Non-UK Only). Correspondence
monitoring of that colour is disabled in the Signal Monitor. Monitoring is still enabled
in the Main Processor, but no action (other than recording of the fault) is performed
when a fault is detected.
33.4 Monitor Validation (ST900 and ST900 ELV)
The Main Processor periodically (approximately once every second) checks that the
Lamp Switch Card Processors are correctly reading aspect output states by
activating a signal for one mains cycle which causes pre-defined states to be
produced by the monitors. It then checks that this modification is correctly passed
back to it.
If a particular test is not successful, several further attempts are made. If the failure
persists, the Main Processor will shut down the controller.