Auto Engineering Unit

Ignition
,
1

Hello,

I am trying to figure out a way to automatically determine my engineering unit based off the tag name that I enter in. For example, if my tag starts with a ‘T’ then I want my unit to be F*, or if my tag starts with a ‘P’ then I want my unit to be ‘PSI’ etc. I’m using an expression tag with the data type set to String inside my UDT that has the following script/code, but I can’t seem to get it to work write. Any thoughts or best practices?

If({TagPrefix} like 'P%', 'PSI', 'Null')||
If({TagPrefix} like 'F%', 'MCFD', 'Null') ||
If({TagPrefix} like 'T%', 'F', 'Null') ||
If({TagPrefix} like 'L%', '%', 'Null')||
IF({TagPrefix} like 'D%', 'INH2O', 'Null')

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2

use a case

case( left({TagPrefix},1),
    'P', 'PSI',
    'F', 'MCFD', 
    'T', 'F',
    'L', '%',
    'D', 'INH2O',
    null
)
1 Like
3

That did the trick. Thank you for the quick reply!

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4

Ewww! This may work, but it is a terrible idea. Tags have an engUnit property for a reason!

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5

Add them here!

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Use them like this. You can drill down to the EngUnit using the Browse Tags selector.

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1 Like
6

That gives me Bingo! :joy:

I was so anxious to fix his expression, I skimmed over the actual application of it.

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7

Mini rant but it annoys me to no end the fact that there is no way to make labels respect the formatting set in the tag and/or display the units without additional bindings. Like the data is already in the tag and it can correctly format it in the tag browser. Why isn't there a way to bind that. Having to throw 3 bindings for the pv, format, and units and then an expression to combine it all just seems like something that could be made more efficient.

I really wish we had a PV.value and a PV.valueFormatted option or something

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As others have said for OP's question though, I'd ditch the case statement and just write your values into the EngUnits field and then use that. You can even run a script to set them all if you're concerned with trying to avoid manual effort

8

True, but you should be able to create a view taking a tag path as a parameter and have the view retrieve the value, formatString and EngUnit and render them all appropriately. Then you can quickly embed that view anywhere.

9

You can just create a UDT param for EngUnit and then use this in all the tags’ eng unit props values needing these units

1 Like
10

Absolutely true but then the reality of Ignition struggling with embedding objects too many layers deep often comes into play unfortunately.

2 Likes