What is the timeout to cancel the subscriptions from 800xA ( both OPC DA & OPC HDA )
When we open a PG2 Graphic Display, it will show all the live values for the properties configured. If we switch to another graphic display, will it cancel all the subscriptions ? or hold for sometime ?
What about OPC HDA i.e., related to Trend Displays. Howmuch time it will hold the subscriptions ?
There are two aspects to answer your question
the update rate between the OPC Server and the controller (MMS) and the Update Rate (SubscriptionRate) between the Client (800xA) and the OPC server.
The update beteen the Client and OPC server depends on the subscription group.If a PG2 Graphic Display is called up then the Subscription group will increase by 1 and if the same display is closed the subscription is stopped for it and the subscription group will be decreased by 1.
The second part on how the data is logged in trend. It is done by the basic history service.Based on the default log configuration(I guess its 3 months) It will store the data for this period even if the trend is not subscribed by the client for a long time.But when you do subscribe then it will display the value that is stored by the basic history service in the trend display