RedBarn (Customer) asked a question.
I am using a CMORE EA9 HMI. A significant thing I use it for is for the stripchart logging. I am struggling to find how long a tag needs to persist for it to act as a trigger for an event log. Also, how long do the other tags need to persist?
The C-more has to "see" an Off-to-On transition of the trigger tag (if set for an "On" bit state). (Or an On-to-Off transition if set for an "Off" bit state) If the PLC changes the trigger tag from Off to On and then to Off before this state change is received by the HMI, the event will not be logged. The exact time the trigger bit must stay on before turning off again depends on the communication. When not catching the trigger was even a remote possibility, we would set the trigger tag on, and then reset it after a time delay.
This is similar to other tags, in that the data must "persist" long enough for the HMI to receive the data during its communication cycle.
It would be interesting to start a timer in the PLC and turn on a bit, then in the HMI, this bit turning on would trigger a Tag Action in an Event, and this tag change would stop the timer. And the elapsed time would indicate the time it took for this communication. But this would be academic, in that you could not depend on this time being consistent.
------ Original Message ------
From "Community Admin" <communitymod@automationdirect.com>
To "rdrane@draneengineering.com" <rdrane@draneengineering.com>
Date 9/29/2026 3:53:39 PM
Subject K Price answered you: I am using a CMORE EA9 HMI. A significant thing I use it for is for the stripchart logging. I am struggling to find how long a tag needs to persist for it to act as a trigger for an event log. Also, how long do the other tags...?
Just ran some tests to measure the time it takes for the C-more to log an event and then for a C-more Tag Action to reset the event latch. A Do-more PLC and EA9 HMI. Only a few rungs of PLC code and a few indicator lights on (1) HMI screen, and the Alarm Log. (so not a real PLC/HMI application) The "Event" was a rising-edge contact of an "X" input, (so on for one scan). This rising edge latched on a "C" contact, started a PLC timer, and triggered an alarm in the HMI Alarm Log. A HMI Tag Action turned on a "C" bit, which stopped the timer. Time for this communication varied from 67ms to 120ms with Avg PLC scan 185us.
This latching and resetting with a "handshake" will assure that your alarm is logged to the HMI Event Log, even if trigger is on for (1) PLC scan. Times would be longer for a real PLC/HMI application.
------ Original Message ------
From "Community Admin" <communitymod@automationdirect.com>
To "rdrane@draneengineering.com" <rdrane@draneengineering.com>
Date 9/30/2026 10:28:24 AM
Subject K Price answered you: I am using a CMORE EA9 HMI. A significant thing I use it for is for the stripchart logging. I am struggling to find how long a tag needs to persist for it to act as a trigger for an event log. Also, how long do the other tags...?