I have a problem with connecting 1 slave and 1 master between each other on PROFIBUS. Can anybody explain me what kind of faults/damages could happen with PROFIBUS cable ? I have already checked the integrity of wire and it is OK. Terminators and plugs ale probably also ok (ON on each side) , project in TIA also seems to be OK.

Hello Jacplacu;

Do you have screenshots of the network view or a copy of the diagnostic buffer we could examine, to help sort out the problems you seem to have?

The connection of a standard Profibus cable to a standard Profibus connector is very simple and described in many locations in Siemens documentation. For example, look at section 4,2,2 in this manual:

PROFIBUS Networks - Siemens Support

Many things can happen to cables in a plant, from lightning strikes to the famous forklift accident... Those are generally easy to catch.

What can happen with Profibus cables and connectors on installation or after operating a while?

- wires  A (Green) and B (red) on the Profibus cable could be crossed (reversed)from one connector to another.

- the shield connection (on the Profibus cable) could be loose in the Profibus connector (it must be pressured by the connector body when you screw the connector shut); if the ground connection is not maintained over the length of the network cable tranmssion will be impeded. Sometimes vibrations will cause the shield to become loose in the connectors; continuity tests will reveal that.

- the terminating resistance must be ON (and powered) for the 2 end stations of the bus: the first and the last node (physically) must be be powered and the terminator at ON. Loss of the termination will cause the whole network to crash, because the terminators eliminate reflexions on the bus; reflexions will disrupt transmissions. Always check that the end nodes are powered; if you need to take one down for maintenance, place the terminator on the closest station to ON (or use an externally-powered termination module.

For more information. these documents could be of interest to you; they are produced by Profibus.com (Profibus International -PI), the governing body of all thisng Profibus and Profinet:

http://www.profibus.com/nc/download/installation-guide/downloads/profibus-installation-guideline/display/

Hope this helps,

Daniel Chartier

Thank You for comprehensive answer

in my case I suppose the problem is shield.

I have 15m profibus cable. There is no tightly fixed shield to the plug. Could the lack of correct installation of shield in the plug affect the connection to the point of indicating by PLC CPU error ?

I perform the test in office, not in plant.

Hello Jacplacu;

The loss of contact between the cable shield and the connector body will impact the transmission of Profibus messages. One way to check this is to lower the speed of the bus (by increments) and see if transmission resumes correctly at lower speeds: the network is much more forgiving of ground errors at 9600 Baud than at 1,5 MB. 

Also, I suggest you look at the link proposed for the Profibus.com documents, if you are planning to test your network in lab: it points to 3 manuals (3 in English and 3 in German); the ones on planning and installation are very instructive, but for your tests you really should open the one on Commissioning Profibus networks: it shows you how to use a multimeter to test shorts to ground and between data lines, and resistance tests to look for open circuits, amongst other checks.

Note: the commissioning manual also shows how to check for MBP networks (Profibus-PA), these will not be useful fortests on a Profibus-DP (RS-485) bus.

Hope this helps,

Daniel Chartier