Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 151 of 265
A priority demand stored during the ‘inhibit period’ will be cancelled if the demanded
phase is served at the normal VA level during the ‘inhibit period’ (this will also
cancel the ‘inhibit period’).
The ‘Inhibit Period’ may be in the range 0 to 255 seconds in 1 second steps.
16.2.14 Compensation Period (PCA, PCB, …)
The compensation period is an extension to the normal maximum green time of the
phase that will be introduced (next time the phase gains right of way) when the
associated bus priority unit causes a priority change that curtails or skips the phase.
This gives the phase more green time after the priority change omitted or curtailed
the phase. Note that a compensation period will only be introduced on a particular
running phase if there is an outstanding vehicle extension present when the phase
is curtailed.
MAXIMUM GREEN
MINIMUM
GREEN
PHASE COMPENSATION
TIME
THE CONTROLLER WILL
STILL GAP CHANGE
DURING THIS PERIOD IF
EXTENSIONS CEASE
IF VALID EXTENSIONS STILL EXIST
AT THIS POINT, THEN THE PHASE
COMPENSATION TIME IS STARTED.
Figure 28 – Phase Compensation
The timing range is 0 to 255 seconds in 1-second steps.
For every priority unit, up to four values can be specified for each phase, one for
each priority timeset.
16.2.15 Emergency Vehicle DFM (PMT & PVG)
The operation of Priority DFM differs between Priority Units and Emergency Vehicle
Units. See section 16.2.16 for Priority Vehicle Units.
The Emergency Vehicle 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 an Emergency Vehicle Unit, a Monitor Time
(PMT) is used. The ‘Monitor Time’ time range is 0 to 2550 seconds in 10-second
steps.
If the input is active for longer than the configured Monitor Time (PMT), the input
has been active for an abnormal amount of time and the unit is disabled, but no fault
is logged.
For the purposes of Emergency Vehicle DFM, the input is not ‘confirmed’ as inactive
until it has been inactive for longer than the configured Gap Time (PVG). The ‘Gap