I am studying how to convert an RTAP system with 65K datapoints to an Ignition System.
As starting point I took the PAX tree, these are all Passenger bridges.
In total there are 130 bridges, 45 different types of bridges, the 45 types use a different number of datapoints to get info from the PLC, this number can vary from 92 to 25 datapoints.
Some of these datapoints (types) are used in multiple types so I can capture them in about 10 UDT types some derive from each other and extend with extra points.
My idea was to create a folder structure and reference between tags in the same folder:
You can't use expressions in the OPC Item Path. You can only use parameters. So what I've done on my UDTs is create a parameter on the UDT of whatever name you want to use (could just be opcPath) and use a tag change script on your OPC_Path tag to write to that parameter, then use that parameter in your OPC item path everywhere else.
Your OPC path though will need to be in this format if you're using the Ignition OPC Server:
To clarify: expression tags can use the full panoply of expression features. Property bindings within tag definitions cannot. They can only use a subset, and that subset does not include references to other tags.
Be aware that the workaround, to write to UDT parameters, or perhaps to write directly to specific properties (like OPC Item Path), causes the tag to restart. Because changes to tag properties is reconfiguration, and it is not free.
I strongly recommend using startup scripts to perform OPC reads as needed, to obtain such configuration information, and conditionally write just changes to runtime tags/udts.
