Hi,
I would like to understand a bit more about how scan classes affect tag alarms and events. If I set the scan class of a tag to leased with a slow rate of 60.000 and a fast rate of 500, what about its Alarming and Tag events properties? Do they run at their own time, indipendently on the set scan class? I mean: if the alarm condition gets true and then false during the slow rate 60.000 msec period, does the alarm gets recorded anyway? Same question about tag events: if the event condition gets true during the 60.000 msec period, does the event function get eveluated anyway?
In general, no. The lease scan class is intended to reduce communication traffic between Ignition and your PLC for values you don’t need when not displayed. There’s no magic wand that will let Ignition know that your tag source cycled to another value and back again while it wasn’t looking.
If you need a tag to be read often to not miss short events, you must use a scan class that is always faster than the shortest possible event. If that’s not practical, you must use PLC logic and a timer to extend short events (pulses) into longer-duration signals that won’t be missed.
