Hello,
We noticed a generally slow and rather unpredictable update of SCADA variables in our application via UniOPC and now we are making some tests in our lab to determine cause.
We configure UniOPC for 3 PLC on a single com port (RS422 style with *R4 converter modules), and define a large number of variables for each of them on our SCADA. Some 50 to 100 variables for each PLC. That is more or less what our production application is.
Our goal is to achieve very high com port utilisation and in doing so - as fast refresh on variables as possible - something we are definitely not seeing in our production application. Since our RS232/422 modem has TX/RX LEDS we can observe activity visually. Polling sessions for each PLC and that number of variables are quite long and visual. And inconsistent.
We try to set various refresh rate (for example 1 or 3 seconds) and the speed to 9600 or 38400 and retries 1 or 3 - does not seem to affect result in a significant way.
First of all UniOPC refresh period SEEMS to affect the PAUSE or idle time between polling session and not the frequency of such sessions as is written in manual. Polling sessions last at least one second for each PLC and we safely can set the refresh interval to 0.1 seconds and the UniOPC does not seem to get any worse performance - such as overlapping of reading sessions as might be expected - just the pause between sessions increase or decrease accordingly.
The stange thing and the problem is that behaviour of UniOPC is not consistent. It would seem that the number of variables defined have a very strong effect on UniOPC polling behaviour. For example we define 300 (3x100) variables - we get "normal" polling session - all 3 PLC are cyclically polled, process repeats after refresh period. The variables seem to be correctly updated on SCADA every few seconds as is expected. .
If we try to delete (!) some SCADA variables very often we get "sporadic" sessions - like 2 PLCs polling, then some 10 seconds pause, then polling of third PLC and the like. Obviously we also get plenty of problems with SCADA variable display this way - they timeout and update more or less randomly every 20 to 100 seconds - that is probably the problem with our production application. The definition of PLC in UniOPC does not change when we try one or another SCADA applications, just the different number of variables are created by UniOPC (as expected)
We are quite new to Unitronic and OPC so maybe we are missing something obvious?
Any ideas somebody?