Recomendation for OPC DA or HDA for 800xa
Hi Rob, im writing to you directly as your anwers to other questions have been of interest and you seem to have a lot of exerience with this system. My question is, today, do you still recomend HDA over DA interface for logging 800xa OPC data. We currently use informIT and barely use it, we already have plenty of log configurations setup using basic history and IM server. Our Pi system is using a DA interface but with a 3rd party OPC client/Server (Cogent Datahub) that connects to our 800xa OPC server as a client, polls manaully added tags and then acts as a server which the pi OPC DA connects to. No idea wothout talking to the original installers why we have this middle man OPC server. We are looking to completely update our PI system and starting from scratch but would like to recover history data. I believe the Pi OPC HDA connected to our basic history server would be the way forward but i would like your advice please.
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> "today do you still recomend HDA over DA"
For collecting History into a third party historian like PI - Yes.
> "Our Pi system is using a DA interface but with a 3rd party OPC client/Server (Cogent Datahub)"
I cannot think of any logical or sensible reason for doing this. Perhaps there was some discussion about performance or loading issues or protection of the ABB OPC server - I dont know.
> " I believe the Pi OPC HDA connected to our basic history server would be the way forward"
I assume you've already seen my previous answers about this topic on the website. I wont repeat them.
Remember, regardless of method to collect data to third party...
... always study the source OPC server's performance guideline or recommendation.
E.g. 800xA for Advant Master performs best when *subscribing* at 9 seconds (not to be mixed up with a client *scanning* at 9 second interval). Moving a large set of logs from 9 seconds to 15 seconds can turn things upside down (as Advant 400 controllers cannot pump data on anything but 1, 3 or 9 second interval - and anything else forces the OPC server into "Single Query/Answer mode" which has more than 10x overhead than using 1, 3 or 9 seconds.
If OSI PI is to present 800xA for Advant Master data, the above performance hint comes in to play *regardless* if data is temporarily stored in e.g. Basic History and collected by OSI PI OPC HDA collector or collected directly by OSI PI OPC DA collector.
Interpositioning a historian like Basic History to perform the primary logging and deferring third party to read via OPC HDA removes one possibility for "improper" OPC DA subscription reaching a sensitive OPC DA server, however, if the staff configuring the logs in Basic History does not know about the "AC400 Controller's 9 second interval rule of thumb", the same mistake can be made in Basic History.
With applog (and some basic skill set) it is very very very easy to call the hand of any OPC DA client connecting System 800xA. Are you subscribing? What rate? Are you scanning? How often?
Ergo: get to know your source OPC server and how to use it efficiently and without risk of jeopardizing plant operations, e.g. by introducing overload.
I have lost count of how many support cases I have handled that boiled down to "overloaded OPC server due to 3rd party requirement"