Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 152 of 265
Time’ time range is 0 to 255 seconds in 1-second steps, and is sometimes referred
to as the ‘Detection Interrupt Period’.
If the input is inactive for less than the configured Gap Time, the timer for the
Monitor Time continues to time, and the unit will be disabled if it expires.
Only when the input has been inactive for longer than the Gap Time, is the timer for
the Monitor Time reset and the Emergency Vehicle Unit no longer disabled.
16.2.16 Priority Vehicle DFM (PMT & PVG)
The operation of Priority DFM differs between Priority Units and Emergency Vehicle
Units. See section 16.2.15 for Emergency Vehicle Units.
The Priority Units may not operate for long periods due to their normal use and so
are not considered for the Detector Fault Monitor (DFM), see section 29.6. In order
to monitor the input to a Priority Unit, a Priority Monitor Time (PMT) is used. The
‘Priority Monitor Time’ range is 0 to 2550 seconds in 10-second steps.
If the Priority Input is active for longer than the configured Monitor Time (PMT), the
input has been active for an abnormal amount of time. When this occurs:
 The Priority Unit is disabled.
 A Priority DFM fault is logged.
 The Cabinet Alarm (if fitted) is illuminated.
 The count of ‘good’ activations is reset (see PDR below).
For the purposes of Priority Vehicle DFM, the input is not ‘confirmed’ as inactive
until it has been inactive for longer than the configured Priority Vehicle Gap Time
(PVG). The ‘Gap Time’ time range is 0 to 255 seconds in 1-second steps, and is
sometimes referred to as the ‘Detection Interrupt Period’.
If the input is inactive for less than the configured Gap Time, the timer for the
Monitor Time continues to time, and the unit will be disabled if it expires. Only when
the input has been inactive for longer than the Gap Time, is the timer for the Monitor
Time reset.
The Priority Unit remains disabled until the fault is manually reset (by fault log reset
or DFM reset) or automatically reset by the ‘Priority DFM Reset’ (PDR) feature, see
section 16.2.17.
16.2.17 Priority Vehicle DFM Automatic Reset (PDR)
The ‘Priority DFM Reset’ (PDR) value specifies whether the priority DFM fault can
only be reset manually, or whether it can be reset automatically by the controller.
Automatic reset can be configured to occur when the input goes inactive (1 or 255)
or after a number of good activations.