Help with scripting for tags in ignition

Ignition
1

Hey all, this is my first ignition project so excuse me if this question is rather obvious, but I have this tag (called ProcessIndex) whose value maxes out at 60 when a process is completed, and I want that when the value reaches 60 it increases the value of another tag (called Compelted_Processes) by one. To do this I wrote a script under ProcessIndex that is as follows:

if previousValue.value != current.value and current.value == 60:
value = system.tag.read("[.]…/Data History/Completed Processes")
value += 1
system.tag.write("[.]…/Data History/Completed Processes", value)

However, this does not seem to work and I tried using previous posts and the ignition manual to figure out why, but I still cannot find out why this is not working. Any help would be appreciated!

2

This might need to be currentValue.value, rather than current.value.

3

Plug for - Browse the Lesson Library at Inductive University

If you haven’t gone through these videos yet, it will explain a lot about Ignition.

4

That would make sense but unfortunately upon changing it and applying the change my Completed_Processes tag is still 0 and not increasing.

5

I have watched some videos from the lesson library but not many videos over the scripting so I will probably do that, and see if I can find my solution from the videos.

6

Keep in mind that system.tag.read() is going to return a QualifiedValue object. I’d adjust your script to be something like the following:

if previousValue.value != currentValue.value and currentValue.value == 60:
	# Are you needing to move two folders up in the hierarchy?
	# If so, use `../../`
	qualifiedValue = system.tag.read("[.]../../Data History/Completed Processes")
	# Notice that we must use the `.value` off of `qualifiedValue` to get our new primitive value
	newValue = qualifiedValue.value + 1
	system.tag.write("[.]../../Data History/Completed Processes", newValue)
7

You shouldn’t ever use previousValue.value if you haven’t checked initialChange. previousValue is None when initialChange is True, breaking your script.

2 Likes
8

Thank you for that, I will be sure to always check the initalChange now. I wrote this line of text to see if initalChange was true and if that was breaking my script:

if initalChange == true:
	system.tag.write("[.]../../Data History/Completed_Processes", 1)

However, the Completed_Processes tag is still reading 0 so I assume the initalChange is false and is not breaking my script but please correct me if this line of reasoning is inccorect.

9

This is not valid python. Python True is case sensitive. But even better is simply

if initialChange:

You should look in your gateway log for error reports from your scripts. (Mostly the error will only appear once.)

10

Though I think actually you want to insure it isn’t the initial change, so

if not initialChange:

otherwise previousValue is None

1 Like
11

I apologize, I am used to writing code in c++ and not python so that is a mistake from my c++ background. I will be sure to go back and check my syntax for the rest of my code to see if I made a similar mistake.