Profibus Network

NickMiller

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Join Date
May 2002
Location
Lancashire
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I am looking for any advice with a profibus network.

The system copmprise the following:-

Siemens S7 315 DP2 PLC, 4 Siemens TP270 screens,6 Lenze servo drives, various Murr remote IO nodes and 6 linear encoders.

The system was working fine until 2 days ago when all the TP screens stopped displaying data from the PLC and could not write back to the PLC.

Using the diagnostics on the S7 software the nodes appeared in a complete random pattern and other time the software would just not talk to the PLC over the profibus.

I disconnected all the screens and tried the system again but still no luck. Slowed the network down to 187.5kps without the screens attached and managed to see all the nodes at there correct address.

Re-connected the first screen the network would then work for a couple of seconds then the screen would disconnect, then a couple of seconds later re-connect, this then repeated.

Talked to tech support at Siemens tried all they offered still no luck.

Checked all the obvious like duplicate node addresses, bad connections, damaged cables, everthing looks OK.

The customer is now demanding an explanation of the problem as they condsider 30 minutes a major breakdown, this has been down 2 days.

Any advice or that may resolve this problem would be greatfully recieved. :confused:
 
Have TP-screens in Profibus ? Other (better) choice is MPI.
What version 315 DP2 you have ? Older models don't support many TPs in MPI.
 
Its probably something simple-
Are you sure the termination resistors are ON at the ends?
Did anyone move the cables or put them near motor leads?
 
The TP screens are on the profibus. The processor is configured for multiple TP screens.

The system has been running for about 4 weeks without any problems.

The processor is the lastest version from Siemens (ver2), can't remember the exact part number.

I have checked the resistors and even tried new one to check the havn't failed.

The cabling has been moved but not near the drives. It looked OK visually, it will be worth replacing to see if it is damaged.
 
Last edited:
Divide and Conquer

I don't know of any magic bullet.

First you need to know what might have changed? You need to know of ANY little thing that changed or happened. Even moving a cable. Spilling something on a cable. Running another cable by the Profibus cable. Moving equipment by the cable. Would it surprise anyone if I said that we often ask what changed and the reply is "nothing". Yeah sure.

Are all the Profibus DP devices certified? If not I would look at them first.

Disconnect all the devices and then connect each device one at a time so it is the only device on the network. This will tell you if a particular unit is bad. Sometimes this requires carting a spare PLC to each station and connecting each device to the spare PLC. Remember that cables must have the termination on at the ends.

If all units test out OK we then add devices back one at a time until the system fails. If it does fail then start again adding units in a different order and see if it fails with the same device.
Profibus DP is an isolated network. Sometime the optical isolators just get weak or slow and no longer meet specifications. This weak unit may work by itself but may not be able to drive more than a few loads.

We also use a SST card in diagnostic mode. This lets us know what and when data is being sent ahd who sent it. We are getting to serious finger pointing now.

In the end it is important to methodically divde the problem down to smaller problems. This may require getting out some spares. As often as not the Profibus DP works again because the connectors get cleaned and securely fastened again.

I have also had customers divide the network into two networks using another master card such as a CP342-5.
 
Have you tried reloading the program to the PLC?
I assume its the Master?
Looks like a long night ahead, may have to connect each device one at a time to determine if one device is causing the problem.
If not using redundant cabling then may have to check all cable.

Follow Peter close, he has much experience with Profibus.

Definitely verfiy the profibus certification, the Lenze drives probably are but I am not familiar with the Murr RIO.
 
Hello Nick;
It seems to me that what you are experiencing ia a limitation on the number of OP connections on a CPU315-2DP. The older versions (6ES7 315-2AF0x-....) are limited to 3 Op connections. The newer ones can go up to 16 connections, of which 8 can be OP type, if I remember well. So you can not set-up more than 3 operator interfaces at the same time on an older cPU 315-2.
Check out Siemens' website or your Siemens rep. for more details,
Hope this helps,
Daniel Chartier
 
Could you elaborate?

I know that Profibus DP master have a limited number of I/O points that can be mapped into I/O. I also know the S7-315 DP has a limited number of bytes that can be sent with data consistency. I don't know why a OP would be different from any other Profibus DP device.

Is it just that the OP uses a lot of mapped I/O space so the old S7 could only support 3?

Do the newer S7-315 DP support a larger I/O space?

The S7-315 DP that I have is very old. It is limited to about 512 Profibus DP bytes that can be mapped into I/O.

How much I/O space does an OP require?

I am really interested in why there is a limit to the number of OPs or any device on Profibus DP.
 
Hello!
Have you checked that the panel is online ??
Sometimes it can goto offline mode!
We had that problem in one project --> you just choose online from the panel. (startup or you have a standard screen to change modes)
 
If the profibus cable is connected the wrong way, A or B channel mixed then the panel will start, almost start showing and then re-start the panel..again
 
Hello Nick;
The reason an OP is not treated as any other Profibus slave is that it is not a Profibus slave; it is a Profibus master Class 2 (look it up on Profibus.com, Technology).
This type of master connects to any master and slave on the network, when it has the Profibus token in hand, and requests any number of data that it needs at that moment (to show up on your display, for example). A Master Class 1 (your CPU 315-2 is a good example) exchanges cyclically with configured slaves and exchanges only strictly configured data with each one; it also accepts acyclic requests for any available data from a Master class 2. Implementing more than one master class 2 on a network tends to stretch the Profibus cycle time (the master class 2 will poll an indeterminate number of bytes each time it connects); this could build up to the point where the Profibus netwoork could crash; therefore the limitation on the maximum number of connections, especially with older CPUs.
You do not configure I/O adresses for an OP on the CPU 315-2 (except for area pointers for specific jobs). Instead you create a "connection" (in Protool, and the Netpro editor of Step 7).
If all available connections are occupied in your project, you cannot setup a new one. Frustrating, but it is the price to pay for ease of setup and flexibilty of configuring an OP (so goes the Siemens mindset).
Hope this helps,
Daniel Chartier
 

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