Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 214 of 265
Clearing DFM Faults: If the RFL=1 or the RDF=1 handset command is entered, or
the DFM Reset push-button on the Manual panel (if configured) is operated, the
DFM fault will be cleared assuming the controller has seen the input change state.
The cabinet alarm lamp will be extinguished, the input will no longer be forced active
or inactive, and the fault log entries will be cleared from the controller’s fault log.
Each controller input can be assigned to one of eight DFM groups. Each DFM group
can be configured with up to four DFM ‘timesets’ that are switched by the timetable,
see section 26.3.7. Each ‘timeset’ includes one ‘stuck active’ (measured in minutes)
and ‘stuck inactive’ (measured in hours) threshold time.
For example: DFM Timeset 0 DFM Timeset 1 DFM Timeset 2 DFM Timeset 3
Active Inactive Active Inactive Active Inactive Active Inactive
DFM Group 0 60 2 30 4 30 4 30 4
DFM Group 1 30 9 30 18 15 9 15 255
etc…
In this example, the DFM thresholds used during DFM timeset 0 for all the inputs
assigned to DFM Group 0 are 60 minutes for the ‘stuck active’ threshold and 2 hours
for the ‘stuck inactive’ threshold. Thus if any of those inputs remain permanently
active for longer than 60 minutes or permanently inactive for longer than 2 hours a
DFM fault will be reported.
The range for the ‘stuck active’ thresholds is 1 to 254 minutes, in 1-minute steps.
The range for the ‘stuck inactive’ thresholds is 1 to 254 hours, in 1-hour steps.
(A value of 255 disables DFM monitoring of that state during that timeset)
Note that the ‘stuck inactive’ threshold for DFM group 1 during DFM timeset 3 is set
to ‘255’. This disables detector fault monitoring of the input(s) in their inactive state.
Thus the input(s) may remain inactive during the whole of timeset 3 without a DFM
fault being logged. For example, it may be required that pedestrian push buttons are
not monitored over the weekend when there may not be many pedestrians present.
Note that the timer for each input resets when the input changes state, but it is not
reset when the timetable switches between the different DFM timesets. Therefore, if
the timer value is greater than the new threshold when a new DFM timeset is
introduced by the timetable, a DFM fault is reported straight away.
Therefore, short DFM thresholds should not be introduced at the beginning of a
period where demand is expected to increase, but some time later to allow for the
fact that timer may already exceed the new threshold.