S7 315 DP & Profibus problems

[Oxidation]

We have an installation using Profibus DP connecting the master (315-DP) to a PC running S7 with CP5611 card & a remote i/o station (Stahl).
Comms speed is 187kbps. It was 1,5Mbps.
Problem is I continuaaly get regular coomunications hang ups. I have laid new Profibus cables & installed a new 315-DP. Now I am no wizard on PLC's, but can find my around fairly easily. I have attached a copy of the PLC file (hardware set up will show you my scheme), what I'm not sure about is whether S7 has any "tools" within it to allow me to monitor the comms & see why I'm getting problems.
mainly it is OB82 or OB86 that are reporting problems.....but I am not sure why.
On the PC we are running WinCC as a HMI
This installation is 4 years old & has only started to give problems over the last 9 months.......

 

[controlsdude]

check the following
If your going to a lower baud rate that is usually says that your not terminated correctly at your connectors or the shield is losing its connection, is the cable pinched, do you have at least 2 meters of cable between nodes, is all your connectors screwed in tight, did you check to see if you have a pushed or bent pin on the connector, do you need a profibus repeater?

did you use siemens style connetors, these are very idiot proof, most other manufactures suck or of poor quality.

check your dip sw settings on your profibus connectors
at each end dip sw setting = ON
at each inbetween dip sw setting = off


Usually when your online with the system it will tell you want the issues are by being online. What did you see when you saw problems?

What did your PLC online diagnostics say, was there a missing rack or did it point you to a one of the devices on the network?

see if you can get a profibus test unit from your area rep or do you have one?

With system powered down, at one end turn the dip sw off, but leave the other end with the dip sw on. Measure at the one end where you turned the dip sw off.

Do you have 220 ohms between pins 3 and 8 on the connector?
Is the shield at same potential as the case ground?

My biggest problems with profibus is connectors and the need for repeaters. In the past couple of years I think the we had to use more repeaters with newer equipment for no reason.

 

[controlsdude]

forgot
when your connected to your plc network
to view online diagnostics

have your mouse highlight your blocks under S7 program directory
right click, go to PLC, go to Module Information

This should bring up your plc online diagnostics

What does it say? Might not have a problem now with your profibus at 187baud.

When your at 1.5mbaud what does it say?

 

[Oxidation]

New connectors were installed, switches have been checked.
Earthing has also been checked....in fact at one poit we isolated earth on the Profibus cable at the connector at the slave ends.

PLC diganostics says, when the error occurs:
Module fault present in the event window
Details
Module type: DP standard slave
Input adress 1022
User information available
Diagnostic interrupt from substitute
External module error

The slave is a Stahl IS system (remote i/o +Stahl CPM), when the problem occurs, the Stahl CPM is not indicating any fault? At least by the time I inspect the remote i/o there is no fault shown

 

[controlsdude]

since you said this

Comms speed is 187kbps. It was 1,5Mbps.

sounds like you downloaded the hardware configuration before. When you save and compile your hardware it creates a "System Data" file in the blocks menu.

This would be the the "System Data" file in the Blocks directory.

Can you go back to an earlier archive retrive this System Data file and download it? The reason I am saying this is maybe you did not have the correct GSD files on your laptop when you made this hardware change. This might be the reason your network is choking. The address 1022 is the hardware address of the rack in the config. I can see your GSD in the hardware. Does the GSD file match the one from the archive? I see when I open the Stahl config I see missing data in the config, only because I do not have the GSD in my hardware catalog pull down on the right.

So check your GSD file for the correct version
See if you can download the System data file from the old archive, as a check that it is not your hardware config.

Maybe when you did all this work on the network that you fixed the problem and now you have a hardware config issue.


If these are not the case then you still have some comm issue as stated above.

 

[controlsdude]

oh yea, here is another idea

I had this system I installed everything was working when I left site. A year later they had this profibus problem. The end result of all the troubleshooting that I did when I had to go back to that site was that I had to put a repeater in the system due to losing nodes. Just a thought.

 

[Oxidation]

After consulting with quite a few people what we have done is turned off the harware error reporting at the remote I/O station (Stahl harware) & put a trend in the WinCC system to see which error number the profibus/S7 reports from OB1.
we will then use this error number to go to the next step of solving the problem.
Thanks for your input

 

[jraef]

The most common mistake I see is that people who are used to cable shielding in instrumentation systems are not used to the fact that Profibus cables MUST have the shield grounded at BOTH ends, not one end as we are used to. It may have worked OK for a while if you didn't ground one end, but eventually the noise issues would get worse. The common symptom is that you must continuously lower the baud rate over time to keep it working. Sound familiar?

Siemens offers a great little portable tester called a BT-200 that will diagnose all kinds of common network problems.

If you have a repeater in the system now, you can also replace it with a "Diagnosing Repeater, which does most of the functions of the BT-200.


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