What is the advantage of the Ignition S7 driver

Ignition
1

Hi Everyone,

I am currently testing a project on a Siemens S7 1516 PLC. The PLC is communicating to ignition using the internal OPC/UA server function of the PLC without the ignition S7 driver.

The problem is that I have just surpassed the 4000 item limit and am frequently losing connection with the PLC.

I am considering switching all the tags to use the ignition S7 driver but I cannot find any information on the tag limits of the S7 driver.

Will using the S7 driver improve the recommended amount of tags?

Best,

2

It might, but there's a lot of downside too. It's absolute addressing only, no browsing, no access to optimized DBs.

3

The HMI is unusable right now because of the resource limit so any increase in tag count would be beneficial.

Is there a quantitative measure of how much the S7 driver would help?

4

No, sorry, there's nothing like this available. It will depend on things like whether you already have other PLCs, HMIs, or systems communicating with this PLC via S7 protocol and probably things like your program scan time affecting how much time can be dedicated to servicing comms, though to be honest I don't know exactly how this works on Siemens PLCs.

5

In regards to reaching the 4000 item limit - are you subscribing to every tag individually or are you taking advantage of structures on the S7 side and documents/UDTs on the Ignition side?

I've also seen people side step this limit by using a Tag Group in OPC Polled/Read mode, at least for a subset of tags that can be updated slower, because this uses the OPC UA Read service instead of creating MonitoredItems.

6

Currently, I am using all leased and polled tag connections. I also have different tag groups for setpoints, status, and push buttons.

Each device uses a UDT that follows that contains these groups.

Is there anything else that could be done to increase the tag limit? On the Siemens side, I have already limited the available tags to what needs to be used.

7

The tag limit is entirely on the Siemens side. If you're not on the latest firmware version that could be something to look into, I think they increased the limits once in the past.

8

Thanks,

I will try updating the PLC's firmware.

9

I know this thread is a bit older, I’m just catching up, being the “new kid on the block” :wink:

I think things will have improved over time, but we once competed against an integrator trying to push new OPC-UA plcs in a project, where they wanted to read 2600 tags every 2 seconds. The OPC-UA server in the S7 devices gave up at 300 every 2 seconds. The PLC shut down due to excessive IO load (I expect this number to have improved), however we used the S7 protocol for reading the same tags and were able to read the 2600 datapoints within 200ms with only an increase of CPU load of something round 5%.

While I expect the OPC-UA implementation to have improved, so did our driver. This now automatically optimizes reads and writes so I’d still say: If you want to read a LOT of tags, using OPC-UA will most probably kill your PLC and using the native protocol of your PLC is the thing I’d do.

Chris

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