OPC DA Slower after Update 6.0.3 to 6.1
Since 6.1 we have slower UpdateRates ond OPC DA
DAUpdateRates 500 2000 5000 10000 30000 10000
But in OPC Statistics, there is 1000 as the fastest update rate for a few Groups. In the old test system OPC Statistics says: 500 as expected!
I double checked it in IBA-Tool, also only update 1s since new 800xA Version
Voted best answer
Where the old accepted "any" update rate asked for, the new puts a minimum accepted rate at 2 x the fastest MMS group. This is in line with the idea to always run MMS twice as fast as OPC. As per the OPC specification, a server may reject and supply a revised update rate in case it does not support what was asked for.
It is possible to have OPC at 500ms even with 6.1, but you must adjust the MMS rates so that the fastest group run at 250ms or faster. With some effort you can rearrange additional rates so that the bulk of the 1000ms subscriptions seen from 800xA graphics, etc. stlll land in a MMS group of 500ms. Merely adjusting the fastest group from 500ms down to 250ms will likely affect a large number of OPC items and result in more MMS transactions per second and a lesser margin before receiving data having uncertain quality (which is set roughly 2.5 seconds after the most recent successful MMS transaction). If the outage last longer, the MMS TCP connection will be teared down and bad quality set (until communication is successful again).
MMS transactions drive CPU load and require "open spots" in the AC 800M's "calendar". Those spots are to be manually created by the programmer during Task Tuning (insertion of a voluntary Task Offset value, typically 20ms or more). With no manually set offset, all tasks run may end up running consecutively as requested, potentially up until the 700ms maximum allowed cyclic execution limit, after which the remaining 300ms is designated communication and other housekeeping duties.
Having the OPC server to run MMS transactions at 250ms will push the controller's Total CPU Load value upwards and increase the need for Task Tuning and use of Task Offset.