I'm not thrilled with any approach so far, but I'm looking for the least painful solution.
I have a UDT containing several OPC tags, each with an associated expression tag that modifies its quality. The status and value of these expression tags are used in the application.
Now, I need to add a new tag pair to the UDT, but I want to force its value until real data is available from the field device.
My current idea is to initially set the new OPC or expression tag as a memory tag when updating the UDT, then switch it back once real data becomes available. Ideally, each instance would have a unique initial value.
Another option could be adding an if condition to the expression tag that checks a memory tag. If true, it would use a predefined value instead of live data.
KEPServerEX is the OPC server, and has a simulation driver that I'd have to path to or simulated mode for the device, but I only need to force a single tag, not the entire device.