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.
This is the one thing I kinda wish existed in the lifecycle of a tag that did exist in Wonderware System Platform. In WW it was the OnScan event script, but essentially it was executed when the tag came online and it's where I would always trigger a separate execute script to do my dynamic tagging to the OPC server (that would make it more asynchronous and allow values in the object to populate before running my "Set References" script). It always worked really well, and it's one of the few things I miss about WWSP. If there was a section of the scripts that were like Tag Events with a Startup and Shutdown or something similar, that would be really neat especially if it let you dynamically set parameters of the tag before it came online without causing a restart of the tag itself. I wouldn't have a use for the shutdown of the tag, but I can think of some cases where it might be useful. Then even if you moved a tag, it could trigger those scripts.
