Digital events/event messages/alarms

Hi -

I’m trying to use a digital event to turn off digital points (TPO) running as the outputs for some PID loops if an analog input value gets too high. I have this currently set up with a digital point state reaction and my points in the off mask. Because the TPO function is stopped once you send an on or off state to the point, this requires me to reset the TPO function once the input value normalizes. This all works fine, but I would like a way to monitor the state of this “emergency off” function from my HMI hopefully with just a boolean value.

Is there maybe a way to do this using digital latches instead? I think this should have the same desired result - I would just need to change my alarm reaction event to set the off-latch and change my normalization event to clear the latch (and maybe still reset the TPO function?). I could then just add the OPC item for the off-latch state to my HMI to monitor it looks like.

Is there a special memory map address I can use to set a digital off-latch using an event message? I haven’t seen a way to do this in the default list of commands for an expanded digital event.

This is all on an EB2 with 9.3b firmware. If this all looks eerily familiar, it’s the same project Tricia was working on with some related questions from a couple months ago.


Hi SeanT,

Welcome to the OptoForums! Ah, yes, “eerily familiar” indeed. Thanks for the clue that it’s related to Tricia’s earlier questions–I need all the clues I can get!

You ask about doing some kind of “set the off-latch.” Unfortunately, there’s no magic mem map address to let you write to an INPUT (or related value).

Since you’re looking for something to map to an OPC tag, maybe you could create a “fake” output and have your digital events turn that on/off when appropriate? For example, I have and 8-position rack here, but if I put a “fake” output in the 15th slot, I can turn that on/off w/PAC Manager (or a digital event), and perhaps have an OPC item which looks at it… could something like that work for you?


Hi Mary -

For the first part, I’m a little confused? I (think) I was talking about using the off-latch for the outputs instead of the method we are currently using (just setting the output state off). Or I misunderstand what you mean by input?

For the second part, I will have to take a closer look at our rack layout (16-module), but I think it’s almost all filled up!


The “on-latch” and “off-latch” features apply only to inputs. They’re intended to let you keep track if someone, for example, has pressed a button (and optionally let go) since you last looked at the latch–it’ll stay latched until you clear it. The “on-latch” and “off-latch” features don’t apply to outputs, ditto for the related “counter” feature.

Perhaps you meant “on-[I]mask[/I]” vs. “on-[I]latch[/I]”?

Okay - for some reason I was thinking you could also latch an output to keep it in a certain state until the latch was cleared.

I’ll play around with the dummy output idea to see if we’ll be able to use that.


Just solved the issue (this is going to be silly) - I just added tags linked to ALARM_LO_STATE and ALARM_HI_STATE.

Not sure how I didn’t see that right away, but thanks for the help and cool idea Mary.