PLC5 Alarm and Acknowledge

I am having the issue with creating an HMI alarm station. I have to find a way to hit an alarm and this alarm is then acknowledged and will do 1 of 2 things go away or stay up but no longer flash.

Sitution:

Want to trigger an alarm for high water. When the high water limit switch is hit have it set a bit that is sent to the HMI alarm handling software. This software can process the alarm after this point. Basically if the alarm is recieved it blinks and then an acknowledge button is pressed. If the alarm is still there after acknowledge it goes solid and not flash. If the water goes low before the acknowledge or anytime after the acknowledge it goes away. If the alarm triggers and goes away before acknowledge then have it blink until acknowledge and then disappear after.

Dilema:

If for example the trigger hits so instantaneously that it does not trigger to the HMI. This would be a missed alarm and would be a problem no matter how instantaneous this alarm is. So I have thought of trying to latch the alarm using:

--------[a]------------------(x)---
|---[x]----[\c]---|

The problem that this creates is a double acknowledge situation which we don't want.

-----[a]---------------(x)------ works if it would garauntee that the HMI would pick up and instantaneous trigger.


Now i know the best solution is to use a TOF and apply a 1 second delay for sure long enough to trigger the HMI but there has to be a better way of doing this.

!excuse the crude ladder diagram hard to make it on this.

Jordan546 said:

If the water goes low before the acknowledge or anytime after the acknowledge it goes away. If the alarm triggers and goes away before acknowledge then have it blink until acknowledge and then disappear after.

Click to expand...

I guess that should be if the alarm is triggered and goes away before the acknowledge bit is hit it will continue to flash until acknowledge is hit then go away. This is all controlled in the HMI software. The biggest problem is the instantaneous alarm situtaion. If the HMI see the bit set at anytime for any amount of time it will do as it should but if it never sees the trigger because it was so fast I would miss the alarm.

Jordan546 said:

Now i know the best solution is to use a TOF and apply a 1 second delay for sure long enough to trigger the HMI but there has to be a better way of doing this.

Click to expand...

What's wrong with doing it that way? Seems like a perfect solution to me if you merely want to avoid having your HMI miss a transient alarm state.

The Only thing I can think of using code would require the PLC to have access to the Acknowledge button. That way you could parallel the Normally closed acknowledge button with the Normally Closed clear condition in your holding circuit which would require both to be true before alarm is reset. But even that causes more issues of acknowledge all conditions and not a specific alarm. If you can have multiple alarms.

i have several hundred alarms that was the problem with the TOF. We currently use a 2 bit alarm stratedgy but they want to move away from this