Demand Polling?

I feel like I’m missing something major here.

Can a tag be a scan class for scheduled polling but also exist within a scan class for demand polling?

If I want to demand poll the OPC server, whats the best method to place a button on a screen and demand poll the indirect tag bindings that are there.

A tag can’t belong to more than one scanclass, so there’s not really an easy way to accomplish what you’re trying to do…

If you’re just trying to get more recent values while the tags are being used on a screen you could use a leased scanclass.

Otherwise there’s a trickier solution where you use a driven, read-mode, scan class that looks a boolean expression tag whose value is a combination of the current time mod the rate you want the tags to refresh at normally ORed with another boolean memory tag that is basically true when you want to short circuit the expression and cause a scan to happen.

kevin, why dont you guys add a demand poll for a device in the ignition drivers? the opc servers that we normally use all have this feature and this was recently added into kepware after requests from many of the customers from the oil and gas sector. It would be nice if you guys would add this in the ignition drivers also.