Discuss Profibus faults in the Commercial Electrical Advice area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

T

TF and the wire

More and more machines where I work are being wired using Profibus. So that the PLC CPU is connected to remote I/O units by this type of 2 wire shielded cable.

Occasionally a machine will go into fault and a Bus fault (BF) LED will be lit on the CPU. This usually means that we have to physically check the wiring which may run into long distances, removing trunking lids or access covers looking for damage. The last couple of faults were caused by damage from a fork lift truck, and a turntable that had gone round and round twisting the cable until it broke. Both took a lot of finding.

I have been trying to think of an easier way of finding which length of cable is faulty. I know that the cable starts off at the CPU then runs in and out of each Profibus connector with the end one having its "end of line resistor" turned ON and in circuit. The remainder being turned OFF.

If I turn all power off and connect my meter on ohms to the two outgoing cores, in effect looking into the bus. Should I be able to read the end of line resisitor in an intact circuit, or will the I/O units affect the reading? If so, could I disconnect the plug and connect a dummy made up connector to simply connect the ingoing and outgoing cables together so it makes a continuous cable?

Assuming a broken bus, I could then start at nearby connectors switching their resistors ON, seeing if I have a reading and gradually moving out until i have no response. The fault being in between that one and the previous.
 
Profibus can be a nightmare when finding cable faults, i hate them!!
What you say makes sence. What i would do, is disconnect all the profibus plugs from each unit from CPU to EOL, split the cable at half way point and work from there........easier said than done maybe?
 
Have you got access to the PLC?

In the PLC software, such as Siemens S7 you will be able to faultfind to a degree, within the hardware setup ie NetPro, to see what the last station is that is healthy.

As with Profibus connectors, terminating resistors are typically switched ON on connectors with only one cable into it ;-)

Termination resistors:

WBT PROFIBUS Installation Guide - 2 Assembling PROFIBUS cables
 
weve got the easy life, the profibus system we are working with at the moment shows you the address of the node with problem on the scada screen, so you can check the unit in the panel its self or follow the cable back down the daisy chain to the next unit.

Have any joy finding your fault?
 
bit of topic but can a belden cable for allen bradley be used instead of a profibus for Siemens and where is the best place to learn about plc i am a contractor how builds panels and install the network cabling for the io heads and would like to learn more about it
 
Have any joy finding your fault?

We always manage to find the fault but it can take hours sometimes.

I've tried the PLC option by trying to see where the fault lies on the laptop using S& but because the PLC has a bus fault error, I struggle to get on line. Is there a way around it?
 
Have any joy finding your fault?

We always manage to find the fault but it can take hours sometimes.

I've tried the PLC option by trying to see where the fault lies on the laptop using S& but because the PLC has a bus fault error, I struggle to get on line. Is there a way around it?

If you plug your programming cable into the PLC either via a spare port or on a "piggy back" connector, you should be able to go online same as when there's no bus fault.

I have found that the easiest way is to draw a simple schematic of the system as you are tracing the cables then you can just go panel to panel switching on the EOL's to see which clears the fault. Bear in mind that the PB network is not always wired the same as the PB adress structure. i.e. address no 5 on the network could actually be the 9th piece of hardware on the net.

We have started to migrate to Proifinet wherever possible now as it seems to be much more bullet proof than PB.
Also we're using a lot of control techniques drives which uses its own network called CTnet and does away with the need for the PLC altogether!!
 

Reply to Profibus faults in the Commercial Electrical Advice area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock