With One OPC service in a Project (say PPA-800xaBase 5.1), how many controllers(AC800M) can be connected to the maximum?
All controllers can communicate with single service provider? or service providers has to be defined individually for each controller?
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This is listed in the System Guide - Capacity and Performance document.
In practice; the maximum is limited by the number of MMS telegrams per second a controller can handle. This depends on type of CPU (PM851 up to PM891) and Cyclic Load.
At some stage 12 controllers were a maximum; I think this figure is a bit higher now.
Bottom line; a project with a lot of communication (eg a rolling mill with lots of computations, cross communications and very fast control loops down to just a few milliseconds) can sustain less controllers per OPC server than a project where application load is lower and cross communication is less (eg district heating with some rather slow flow and temperature control loops).
I think some version of the System Guide tried to address this hard-to-predict limit.
Not more than 50 controllers shall share the same RNRP Area (for a pure PM891 based control net the figure is 100), however I assume you would have to split it over at least two OPC server pairs).