'Persitent' Expression tags

Ignition
1

Hi,
i have a little question regarding expression tags. Currently i’m using expressions like this in an UDT:

if(someCondition, newValue, coalesce({[.]value}, initialValue))

where value is the expression tag itself. The idea is to use the current value of the tag until a condition is met (Imagine a simple maximum value storage for example). This works good while the gateway is running, but i loose the current value if the gateway restarts. That’s the reason for the coalesce, that sets an initial value in this case.
Is there any other way to do this (without having to access an external database)? I’m trying to maintain a core functionality, even if the DB server fails.

2

Not really since initially the tag is NULL. You have to wait until the first scan cycle usually.

3

As Travis said, not now. However, I will look into how difficult it would be to have the expression store its value, when it references itself. It already detects a self-referencing expression, so it’s possible that it may not take much work.

Regards,