Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 150 of 265
16.2.8 Enforce VA Demands (PSE)
This facility works on the same basis as ‘Allowed VA Demands’ except that VA
demands for the specified phases are inserted to ensure that the specified phases
will run.
Note: This facility is not compatible with priority phases of type 2 appearance, i.e. if
the stage in which the priority phase appears is active when a priority demand is
received, the priority phase appears immediately. At the same time unwanted
“allowed” and “enforced VA demands” are entered, which may cause unnecessary
timing of priority maximum and unnecessary stage changes when the priority phase
terminates.
16.2.9 Priority Extension (PVE)
Outputs from the SVD while the Priority Phase is at right of way generate Priority
Extensions. The Priority Extensions will hold the Priority Phase at right of way.
The timing range is 0 to 31.8 seconds in 0.2-second steps.
16.2.10 Priority Maximum Running Period (PVM)
A further maximum running period which commences at the expiry of the normal
maximum running period if a priority extension period is running or if a priority
vehicle detector output is present.
The timing range is 0 to 255 seconds in 1-second steps.
16.2.11 Priority Units Inhibited (Priority Mode Only) (PUI)
When a Priority Phase gains right of way, it is possible to inhibit specified Priority
Units (including the one at right of way) for a specified time.
16.2.12 Revertive Demands to Inhibit (Priority Mode Only) (PRI)
This facility allows the Priority Units inhibited facility to be activated when a Priority
Phase gains right of way due to a Revertive Priority Demand being present.
16.2.13 Inhibit Period (PVI)
A period following a priority change, during which priority changes originating from
the same priority unit shall not occur, but priority extensions will still be serviced if
the phase gains right of way through normal operation.
The Inhibit timer starts as soon as a priority phase gains right of way if it was a
priority demand that requested right of way and if phases were curtailed or demands
skipped in order for the priority phase to gain right of way.