OPC Unsolicited does not update with same value


Thread Starter

Peter Mellemans

We have build an OPC server using an Advosol SDK. The client is Cimplcity.

A script needs to be run on Cimplicity when a specific value is updated, even with an identical value. For performance we want to config the point as unsolicited, but the script doesn not fire when the point is updated with the same value.

I have the following question. Does an OPC point that is set to unsolicited get updated when the server sets it with the same value?

We need it to trigger a script even when the value does not change.


Fred Loveless

That is because the Change event is only triggered when the point value or quality changes from the previously scannd value.

This is the way that OPC is designed and if you change it then you are no longer compliant. Your only option is going to be to forca a poll of the point, i.e. do a sync or async read.

Fred Loveless
Senior Application Engineer
Kepware Technologies