Write to UDT property with tag change script

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#1

I am developing a UDT for a weigh scale that reports its units as an integer. So there is an OPC tag called ReportedUnits which is an integer, interpreted as follows:

0 = g
1 = kg
2 = t

I have an expression tag simply called Units that converts this integer into the relevant string:

switch({[.]ReportedUnits, 0, 1, 2, "g","kg","t","")

I would then like to bind this “Units” tag to the EngUnit parameter of all other weight-related values within my UDT, so that any time I see a weight, it’s shown with the units that the weigh scale is actually using. However, as I understand it, I can’t directly bind a UDT member parameter to another UDT tag value (please correct me if this is possible as it will solve my problem in a far easier way).

I know that I can bind a UDT member parameter to a UDT parent parameter, so if I had a UDT parameter “Units”, I can easily bind all my weight value EngUnit to that. But then, I just need to make sure that the UDT parameter updates if my weigh scale units change.

I found another thread that mentioned I can write to a UDT parameter, but did not specify how. I assume I need to use system.tag.writeBlocking but I can’t work out what my path would be. Can anyone help me out with the path (or an easier way to achieve my end goal)?

#2

Easiest way to get the parameter path is to drill into the UDT with the tag browser, right click the parameter and select copy path.
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#3

Thanks, but this is within a UDT definition so it needs to be dynamic - I need to work out how to extrapolate the path to the parent UDT parameter from a UDT element tag change script.

#4

You would need to build the string then, If you have good organization and naming conventions that shouldnt be too bad.

#5

Yes, that’s what I’m seeking some assistance with

#6

We create expression tags in all of our UDTs to expose meta information.
Just add an expression tag called MetaTagPath and set its Expression to {PathToParentFolder}

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#7

Thanks, that’s a great starting point. I wasn’t aware of the {PathToParentFolder} property!