Slow read/write requests when the connection to siemens PLC is via an external ethernet card

Hello everyone,

I have a strange performance issue when I connect Ignition to Siemens PLC
The PLC has not an enbedded ethernet port on the CPU , but has a ethernet card ( the CPU is S7 300 315-2AG10-0AB0 )

I definited only a tag , and I connected the PC with ignition directly to the PLC with a ethernet cable ( without swicth, router firewall et etc…) the time to read only a tag are more o less 42ms, of course the PLC has not a program so the time cycles are very fast

If I use the PLC with the ethernet port ebedded to Cpu the time for read one tag is more or less 2ms.
These times are really because I have seen them via wireshark logs, so I can tell that the problem is the ethernet card of the PLC. ( obviously I tried witha new PLC and a new ethernet card but I had the same behaviour)

This behaviour imply if I have only few hundred tags ( 160 with a scanclass of 1000ms) the load factor of communication is very very high and the time for read the tags are very very slow.

The thing is very strange, maybe, are there some setting to make to the ethernet card ?

Do you have any suggestions?

Thank you very much
Andrea

IIRC, the backplane on those older processors has nowhere near the bandwidth of a network connection. Meaning, you’ll never be able to push much to/from that non-ethernet processor. You will probably have to replace the PLC with a model with an onboard ethernet port.

While what @pturmel said is true (about backplane speed), the performance from your post is really to (s)low.
There must be something else in play.
I’ve done a lot of Siemens PLC’s (in fact we work ONLY with Siemens PLC’s) and Ignition connection over CP (Communication processor for Ethernet, CP343-1) and over embedded ethernet port on the PLC and I never had such a poor performance. And I’m talking about thousands of tags…
Can you share your step7 or TIA portal project so that I can look into it?
And also how did you set the device connection for the Siemens PLC on the Ignition device configuration page…

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Today I made some tests…
and this is what I got no mater what I tried in the plc (cp) configuration…


on the PLC port:

on the CP port:

With almost 10000 tags I’ve got around 60% load factor on the CP (communication processor - external ethernet card)…

Based on the (remarkably consistent) response times, the CP is almost precisely 8 times slower than direct connection. I would have expected the CP to be even worse. Can you test with andrea’s processor model and a CP?

The delay seems to be quite consistent, i see about 26ms with a CPU318 over a CP.

No I can’t… this two is what I have in my office for testing purposes…
But I checked some Ignition gateways in production (and two of them are connected also to the same type of PLC like Andrea have) and it’s like @chi said: the response times are pretty consistent, all around 25-35 ms, where we have CP.
Only the load factor varies quite a lot, but that’s because of the size and complexity of the PLC programs…
So, the only thing it comes to my mind is firmware on the Andreas CP. Siemens is quite ‘famous’ about theirs FW’s not performing as they should from time to time, especially when they release a new major version…

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Hi

zxcslo you gave me a good advise telling me to check the CP firmware.
I 'm using the CPU 315 and not 318 so I start with a slower CPU

I can’t do some other tests for the moment , but I 'll try asap.

I 'll keep you informed

Thank you very much