Profibus Cable Error

[Avatar_41]

Hello everyone, friends. We have a machine where our main CPU is a Siemens S7-300, but with different makes and models of drivers, and modules like ET-200 and IM-151. Today, the Baumuller brand driver worked for a few seconds and caused the CPU to experience BF and SF errors. In case of a malfunction, we turned to the driver, which caused us some loss of time, and the malfunction arose from the profibus cable of the ET-200 modules, which were connected to each other via profibus at two different points.
What I want to ask you is this; How should I act in such cable faults? And what is the method to detect cable faults? Since the distance between the cables is long, it is quite difficult to re-wire. Can we detect this via plc or another way?

 

[JesperMP]

You can detect the loss and return of DP slaves with OB86.
But you cannot know exactly why a DP slave disappears from the master or where if the problem is caused by cabling issues.

There are Profibus analyzers which can provide very detailed error information including cable or connector issues..
One is Profitrace.

 

[Lare]

Siemens additional FB126 block and example project can also used instead of OB86.


https://www.plctalk.net/qanda/showthread.php?t=101535

 

[Avatar_41]

Hello, I think the link you gave is for Profinet (FB126) . How can I use OB86 with simatic manager and is there an example or explanation of how to use it exactly?

 

[Lare]

Hello, I think the link you gave is for Profinet (FB126) . How can I use OB86 with simatic manager and is there an example or explanation of how to use it exactly?

FB126 should work for both profinet and profibus.

 

[AlfredoQuintero]

What cable length over all, not only the length between those two nodes is?
What is the baud rate the master has been set to?
What is the overall logic execution cycle an IO payload?
You must check that termination is correct and that cabling does not have issues.
If cabling is OK but you are using a high baud rate you can consider lowering the transmission speed if that would not affect the process. Or you can use a repeater in the middle of the bus and that should improve the signal’s quality

 

[Ken Moore]

Almost every Profibus problem I have encountered was a cabling issue, usually the ends are not connected well, or the resistors are not set correctly. The Siemens 'vampire' cable ends are horrendous. Sometimes just loosening and re-tightening works. If you do not have a testing device. Try moving the resistor from the end to the next to last node, then the next, etc.. until BF clears. When it clears you know the last node you set the resistor at is faulty.

 

[AlfredoQuintero]

Ken, what is the meaning of "Siemens 'vampire' cable".
I kind of think I know the meaning. I do a lot of Profibus troubleshooting and am interested in the Profibus ingo used elsewhere. BR

 

[jdbrandt]

ProfiTrace is the right tool

 

[Ken Moore]

Siemens 'vampire' cable ends, have metal, triangular "teeth", that look like a vampire's teeth. You do not have to strip the cable ends, just insert, and the teeth "bite" down into the cable for a connection. Sold as faster and simpler.
https://external-content.duckduckgo...59d392f743d9460e18dbecae17f844ff21&ipo=images

 

[Rob...]

No affiliation with them, but I've stuck to using these profibus connectors when I can.

https://www.helmholz.de/en/products...th-diagnostics-led?number=700-972-7BB12&c=125

Their built in diagnostic LEDs are extremely useful for troubleshooting. The plugs are also a far better build quality to Siemens own offering.

 

[AlfredoQuintero]

Siemens 'vampire' cable ends, have metal, triangular "teeth", that look like a vampire's teeth. You do not have to strip the cable ends, just insert, and the teeth "bite" down into the cable for a connection. Sold as faster and simpler.
https://external-content.duckduckgo...59d392f743d9460e18dbecae17f844ff21&ipo=images

Thanks. I take it that you would not recommend this type of Profibus connector, am I right?

 

[AlfredoQuintero]

No affiliation with them, but I've stuck to using these profibus connectors when I can.

https://www.helmholz.de/en/products...th-diagnostics-led?number=700-972-7BB12&c=125

Their built in diagnostic LEDs are extremely useful for troubleshooting. The plugs are also a far better build quality to Siemens own offering.

Thanks for sharing this information. Very interesting product.

 

[JesperMP]

FB126 will tell you quickly that a DP node has Problems. So if you are frequently experiencing Profibus problems then that could be worth the effort.
FB126 wont tell you exactly what is wrong, only that the DP master has a problem with one of its DP slaves.

As to your question,

How should I act in such cable faults? And what is the method to detect cable faults?

Without a diagnostics tool for Profibus, then you are down to checking cables and connectors and replacing parts.

 

[Ken Moore]

Thanks. I take it that you would not recommend this type of Profibus connector, am I right?

Correct. However, many folks have them installed, because they have Siemens on the product.