Odd Siemens communications problem.

This one has been proven to be a real stumper, any help would be appreciated.

CPU 316-2 DP

When adding a Wincc Flex connection to the existing PLC, very odd communication stuff starts happening.

Right now the PLC is talking over ethernet to another PLC, and two WinCC stations. It also is talking to a small OP over profibus.

When I enable comm to the PLC from the new WinCC Flexible station (50 bytes or so), we start getting intermittent comm to the WinCC stations over ethernet, and the OP station over profibus. This new WinCC Flex is also talking to 5 or so other PLCs without problem.

Even more perplexing is that on two occasions, after a powercycle, the analog inputs froze. Had to turn off the WinCC flexible and cycle power to get the analogs reading again. no fault on PLC while this was happening.

I know that the PLC will give out connections as they are requested, not sure why this would affect IO (analogs on an IM365 remote rack). Anyways, this PLC should have more than enough connections.

I tried to change the connection settings to dedicate more OP connections and such, but saw no difference. Tech support didn't think that would make a difference, nor would changing the CPU comm processing from 20% (I tried 50%). I tried anyways, and they were correct, no difference.


Any ideas?

Post a screenshot showing the connection status of the CPU while online.
What is the cycle time ?

JesperMP said:

Post a screenshot showing the connection status of the CPU while online.
What is the cycle time ?

Click to expand...

Hi Jesper,

I will try to get that tomorrow if the remote connection works. Unfortunately this site is a few hours away and I don't plan on being there for at least a few days.

When you say connection status, where do you mean? CPU properties, or somewhere else?

Thanks

Yes, the communications tab of the online CPU properties.

JesperMP said:

Yes, the communications tab of the online CPU properties.

Click to expand...

Hmmm... I don't remember it being any different online then offline, but I can't say for sure.

Offline it's set:

PG 1
OP 4
S7 Basic 7
S7 Comm (non configurable) 0

Maximum connections 12

I tried upping the OP connections previously.

What are the S7 Basic connections for ?
The way that you have used all connections it does seem plausible to have to do with not enough connections. That even if you have configured 4 OP connections.

JesperMP said:

What are the S7 Basic connections for ?
The way that you have used all connections it does seem plausible to have to do with not enough connections. That even if you have configured 4 OP connections.

Click to expand...

I am not sure what the S7 Basic connections are for, I did not set up this PLC.

A few weeks back I tried increasing OP connections to 7 (intent is for 3 new WinCC Flexible stations) and decreasing S7 Basic connections to 4, it made no difference.

Seems no matter what, as soon as I add one more communicating to the PLC things go flakey. If I turn off one of the old WinCC stations, I can connect with the new WinCC Flexible, and it seems happy. Just not all together.

At one point the person developing one of the WinCC programs noticed that he had his string tags with the wrong length (too long). If helped quite a bit when he corrected this, just not completely.

Tech support was saying it may be noise introduced on the comm lines, which I don't buy. All ethernet connections are getting to the local switch over fibre so the new WinnCC Flex station is totally isolated electrically.

I still can't wrap my head around the fact that adding more comm on ethernet will make the profibus OP have intermittent errors. Let alone the analogs freezing.

repeat:

JesperMP said:

Post a screenshot showing the connection status of the CPU while online.
What is the cycle time ?

Click to expand...

JesperMP said:

repeat:

Click to expand...

As soon as I can!

Thanks

Sooooo, what's the configuration of the system like?
Your CPU supports a max of 12 connections.
From the information you supplied, all 12 are being used.
Now is this with or without the extra WinCC flex?

PG takes one.
OP's take one each. Check config of HMI's, make sure you haven't accidentally configured 2 connections to same PLC. Copy/paste of anything linked to tags in WinCC Flex will usually result in creating additional connections. Silly software.
The IM365 takes at least one connection.
Communication with other PLC's take one each.

How's the communication between the PLC's configured?
Use NetPro, switch to online view and check the current active/configured connections for said PLC. Might have a few configured but not used. (PLC > Activate connection status, or the connector icon with the blue/white 'i' )
If you are using GET/PUT from another PLC to retrieve/transfer data, it becomes quite hard to quickly see the connections. Especially if the PLC's are not in the same project.

When you are using more connections than the PLC can handle, it will drop another random connection.
This might be OP's, PLC comms and yes, also the connection with the IM365, which will result in seemingly frozen Analogs.

Another route you can, and should, investigate is to replace the CPU.
The 316 2DP has been discontinued for several years now and support for it will stop in 2013.
Replacing it with a 315 2DP would not only secure support for the next couple of years, but in choosing the correct one, it'll also solve your current problem. Most of the 315's these days have 16 connections available.

Had a rather similar problem once, where we tried to use more connections than the CPU could handle.

Jeebs said:

Another route you can, and should, investigate is to replace the CPU.
The 316 2DP has been discontinued for several years now and support for it will stop in 2013.
Replacing it with a 315 2DP would not only secure support for the next couple of years, but in choosing the correct one, it'll also solve your current problem. Most of the 315's these days have 16 connections available.

Had a rather similar problem once, where we tried to use more connections than the CPU could handle.

Click to expand...

Hi Jeebs,

Thanks.

I am looking into a new CPU right now. The CPU 315-2 DP would have been my first choice, but I need 2 profibus ports, so I will likely go with CPU 317-2 DP.

I was told by local Siemens supplier that IO does not take a connection, so not to count that stuff. Are they wrong?


Ethernet:

2 x WinCC
1 x WinCC Flex
1 x PLC

Profibus:

1 x OP
1 x PLC
2 x VFD
1 x Festo valve block
1 x P&F safety barrier

Other:

1 x IM365
1 x programming laptop


Even if all that counts, it still only adds up to 12. I guess I could still be missing something. If DP_SEND and DP_RECV each take up one connection, that would put us over the limit.

That is not the way connections are counted.
I am worried about the S7 basic connections. These are for normally MPI connections. But there is no MPI in the project as you describe it.

Post a screenshot from Netpro with the list of connections open.

JesperMP said:

Post a screenshot from Netpro with the list of connections open.

Click to expand...

Thanks

In the pictures shown, do you at the same time have the problems with the OPs ?

Is the WinCC Flexible station you mention connected when you took the screenshots ?

Why is the WinCC Flexible station you mention not in the NetPro view ?

What about the WinCC Stations ?

Is the WinCC Flexible station connected over MPI, Profibus or Ethernet ?

Are there MPI partners connected to the MPI port on the 316-2DP ?

What is the ISO-on-TCP connection used for ?

Are the any XPUT or XGET blocks in the program in the 316-2DP CPU ?

In the pictures shown, do you at the same time have the problems with the OPs ?

- I see intermittent comm errors on the profibus OP as is. They become even more frequent if I add the WinCC Flexible. The WinCC tags get data but show many errors.

Is the WinCC Flexible station you mention connected when you took the screenshots ?

- No, if I leave it connected and the power gets cycled to the PLC, there is a chance (happened twice) that analogs will freeze.

Why is the WinCC Flexible station you mention not in the NetPro view ?

- At this plant, most of the PLCs are setup this way (by others). I brought it up with local supplier before and they recommended not including HMI/SCADA in netpro (can't remember reasoning).

What about the WinCC Stations ?

- same answer as above. This new WinCC Flex is also talking to multiple other newer S7 PLCs with no problem.

Is the WinCC Flexible station connected over MPI, Profibus or Ethernet ?

- Ethernet

Are there MPI partners connected to the MPI port on the 316-2DP ?
- No, both ports are configured as DP.

What is the ISO-on-TCP connection used for ?

- Communications to a remote PLC.

Are the any XPUT or XGET blocks in the program in the 316-2DP CPU ?

- No, just DP_SEND, DP_RECV and AG_SEND, AG_REC