I am testing out the new Siemens Enhanced Driver to communicate with a S7-1500 PLC. I have the communications working, but they are very slow. It seems to take 4 to 5 seconds for the tag values from the PLC to update. I am using the symbolic addressing mode.
Prior to this I was using the third party Tanni OPC driver to communicate with the PLC using symbolic tags and didn't notice any issues with slow update rate.
Has anyone else experienced this?
When I first started testing with the new driver and only had it connected to a few tags I didn't notice the slow update rate. It was only when I switched all of the tags in the project over to using the new driver that I noticed the slow update rate. I am monitoring the seconds value of the time clock in the PLC so that I can see how often it is updating. It’ll jump 4 to 6 seconds on every update.
I’m pretty sure its not a bottleneck at the PLC because I am monitoring the same “seconds” tag using the tanni driver and its updating like clockwork every second.
There's one known issue that slows the polling that I think will get fixed in 8.3.2 or 8.3.3. Basically, the polling is happening using a fixed delay rather than a fixed rate.
This means the next poll isn't scheduled until after the subsequent poll finishes, e.g. if you are subscribed at 1000ms, it takes 500ms for the PLC to respond with all the items, then +1000ms from the response the next request is schedule. It makes the update rate more like ~1500ms.
Other than that... not sure. You might want to work with support so they can get a better idea of your tags and setup.
Thanks for the reply Kevin. I think I have it fixed now. Pretty sure it was network hardware related. The comms eventually stopped working altogether, so I bypassed the switch and cabled straight to the PLC and everything came back and the update rate greatly improved. Seems to be updating very reliably at around 1.5 to 2 seconds like you mentioned it would. Just a strange issue because the tanni OPC server never stopped working.