I am trying to conditionally disable alarm so it is only enabled while a certain piece of equipment is operating. I have the built in low alarm configured as such

When I right-click on the displayed analog tag it shows Disable Low Alarm as checked, but the alarm is still active in my alarm history. How do I keep this disabled while not operational?

Thanks.

Click on the window icon to edit the expression and check/uncheck the option box so the expression evaluates on change and not only on start condition.

In your case, you likely have a race condition when the app is initializing.

There is nothing to check/uncheck..

Cool, I didn't realize we have that option fixed in this menu but it makes sense here. I would suggest that you still have a race condition here where you are likely having the alarm trigger, as well as the, disable set at about the same time (let me know if this isn't the case but I did some testing on my own installation as things worked as I'd expect.)

I suspect you can avoid the race condition by adding a slight delay to your alarm. Try adding a three-second alarm delay to ensure that your disable function has time to set the disable property before the alarm condition becomes true.

To update the expression click on the window icon and check/uncheck the choice box such that the expression can determine the adjustment and not only the start state.

In your scenario, as the device is initializing you would definitely have a racial problem.

Thanks,
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Feeling the need to clarify this thread a bit for the sake of anyone else who finds it.
Dave's first comment would apply if you were configuring an I/O tag, where the expression would have been created as a tag parameter expression. That has the optimize checkbox, and I strongly encourage anyone who is thinking of deselecting that option to read the relevant help topics first.

In this example, we're working with an Analog Status tag, where there's a Constant / Expression / Tag selection below the Enable / Disable parameter.

The expression is nearly fineyou'd want to wrap the tag name in a PickValid so that you don't get errors on startup or communications loss. The expression would then become:
PickValid([SDC2_RUN], 0) == 0
Because Invalid isn't True and Invalid isn't False.
Now, you're only going to turn Disabled off when the tag has a valid value of 1

And going back to the original, original question... Your expression was imperfect, but it would work and the alarm is disabled when SDC2_RUN is running. But that won't erase it from the History list. What you'd see there is the alarm activating, then another line for the alarm being disabled.