Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 242 of 265
38.1.2 Lamp Monitor Operation
For each sensor, a configurable threshold (in watts at the nominal lamp supply) can
be defined, or is implied by the selection of the Load Type (detailed in section
38.1.4).
When a change in the current is detected, if the size of the change is larger than
this threshold, the lamp monitor will start to confirm the lamp fault or replacement.
The time period over which the lamp monitor confirms a lamp fault is defaulted to 10
seconds but can be altered using the KLC handset command. Note that vehicle red
lamps monitored by the red lamp monitor, see section 38.2, use shorter fixed
confirm times to meet the UK requirements of that facility.
If the change is smaller than this threshold and no lamp fault or replacement is
being confirmed, the change is simply tracked and used to adjust the ‘learnt load’.
When a lamp fault has been confirmed, the lamp monitor will log the current drop in
watts (at the nominal lamp supply). For example, if a 50W lamp fails, the fault log
will show ‘KLD 1 0:50W A/Red’, or some other value of about 50, even if the lamp
fault was confirmed while the signals were dimmed.
This allows the lamp monitor to monitor many different types of lamps. It simplifies
the monitoring of 40W waits with 50/60W reds since the threshold can be set low
enough to detect a 40W wait lamp failing without causing a 60W pedestrian red
lamp failure to be counted as two lamps.
Given that the fault log records the load drop, any unexpected rise in load will be
tracked but not logged as a fault. If an increase is confirmed, an event is recorded in
the rolling log but no fault is recorded in the fault log. This allows the replacements
of lamps to be learnt without generating a fault if the lamp monitor did not confirm
the lamp failure in the first place because, for example, the lamp had already failed
when the lamp monitor was reset and asked to relearn. If no lamps were working
when the lamp monitor was reset, e.g. due to a feeder failure or powering the
controller in a depot with no signals attached, a lamp monitor reset must
be issued
after all the lamps are reconnected to allow the controller to learn the dim/bright
profile of the lamps.
Other faults can also cause an unexpected rise in current, e.g. a short-circuit
between the red and amber drives so that when the controller drives one colour, the
lamps of both colours illuminate, or by a faulty drive that the controller is unable to
switch off. However, since voltage monitors are provided on all three colours of each
phase on all controller types and the ELV Controllers also include over-current
detection (see FLF 33), these faults will be confirmed (within 300ms) and can
optionally extinguish all the signals by removing the lamp supply (see section 33).