Hi all, I have been testing Ignition’s Siemens Enhanced driver for symbolic access to optimized DBs in an S7-1500 PLC via S7 communication and have found it to work quite well. My only question is I cannot seem to find any documentation on what the maximum tag / subscription count is when using this driver and am wondering where I can find this information. I already reached out to my Siemens sales rep and they said it would depend on exactly how Ignition is communicating to the PLC, hence I am asking here.
There is no hard limit for tag/subscription count on the Ignition driver side. As far as I know, there's not a hard set limit on the PLC either. You can theoretically subscribe to every tag on the PLC. That being said, the driver may not be able to read those tags as quickly as you would like. How many tags you can read at a one second scan rate can vary drastically based on your environment. For example, you may be able to read ~15,000 tags per second when the gateway sits very close (<1ms ping) to the PLC. That number may drop to ~3,000 tags per second when introducing 30-60ms of latency.
We're working on being able to provide some test results from our in house testing environment so that users will have some idea of performance. However, as I mentioned before, this performance can vary drastically based on your environment (network latency, tag types, PLC resource, PLC load, etc.). So, we are also working on providing some metrics to help users understand how the driver is performing in their specific environment.
Would you be willing to share more about your use case? Number of tags, desired rate, etc.
I see, thank you for the detailed response! I will do my own internal testing but am very curious to see your results.
This project has ~50,000 tags split between 3 PLCs, hoping for 1s refresh rate on the bulk of them but probably 10,000 of them can be 5s+ for less critical monitoring. The plan is for a fiber ring network connecting the PLCs to each other and to the Gateway host, all within the same 0.5 sq. mile. I’m primarily hoping that I don’t need to buy more PLCs solely to communicate more tags.