Issue
How fast are supervised inputs scanned?
Environment
ACX5720
ACX5740
Netcontroller
Netcontroller II
CX9702
AC1, AC1A, AC1-plus
Cause
Want to know how quick a TROUBLE condition is measured on a supervised input.
Resolution
The Supervised inputs behave a bit differently to the other inputs. The input value is scanned every 100ms to determine its current state and this is compared to a matrix to determine if a trouble event is being generated.
To determine that there has been a cut or short, the input needs to see a TROUBLE value 3 times, meaning it needs to be in trouble at least 300ms.
There is a caveat to this though. When going from On-TROUBLE-ON or OFF-TROUBLE-OFF, the input just needs to see 1 TROUBLE condition before a trouble alarm is generated. This can be a problem when the input hardware is very fast (such as a Mortise lock or plunger style REX button pressed quickly) and the input goes through the OFF-TROUBLE-ON-TROUBLE-OFF scenario within less than 500ms (100ms for each sample), the samples actually measured (seen by the controller) could be OFF-TROUBLE-OFF...which will raise a trouble condition.
You can mitigate the problem by using a more tolerant supervised circuit such as series or parallel. The SeriesParallel circuit is the most secure but is the least tolerant due to the smaller voltage range between each distinct value.
