do any of you guys know about profibus communication problem, especially REFLECTION faults in the communication system. 

im facing such problems in the quay crane and i have only partial knowledge regarding this issue and i tried with that but still i cannot sort it out.

the issue is as follows,

there is frequent control trip with fault showing spreader communication is missing.

all the drives, modules, display units and spreader canbus module were interconnected with probifus communication and for longer distance ( i.e. from operator cabin to plc room ) optical fibre cable is used.

everything is ok with the spreader and to confirm further i have replaced the module and moreover i changed the spreader too. the resistor between the hi and low can is ok (120 ohms).  but still the fault existed.

so i switched my views on other modules. i isolated the cabin display unit from the communication link (as the analog values in the display unit are not displayed sometimes) and i found that the crane was working fine but  tripping once in 9 or 10 hours of continuous operation showing communication fault in operator cabin I/O module and sometimes gantry I/O or EROOM I/O module. the fault is rapidly switching every time.

i have checked all the profibus connectors (shielding, voltages both +ve & -ve) and also the optic fibre cable, can bus module and all ET200M  modules. i didnt find anything odd and there is no fault led glowing in any of the modules during this fault. 

it is very difficult for me to sort it out, need your help guys.

Hello ganivz;

If your intuition is correct, and the cause of your problem is really reflections on the Profibus-DP network, these can be caused by termination problems on the different segments.

The issue is then: how to use the diagnostics of the Profibus master to locate the faulty terminator. Or any other type of problem that you are facing.

As a short basic theoretical guide, have a look at the PPT presentation (there are many more diagnostic guides, more detailed and more advanced, that you can find in the Downloads section of Profibus.com):

http://www.profibus.com/uploads/media/pxddamkey%5B9099%5D_PROFIBUS%20health%20checking-Andy%20Verwer.pdf

Is your Profibus master a Siemens PLC? In that case open the Diagnostic Buffer of the CPU (go to the online help to find out how to access the diagnostic buffer of your particular CPU). Look for messages related to OB 86 (rack fault) or loss of Profibus connection (or remote rack). If this is difficult for you, save the messages of the diagnostic buffer and post them here so we can help identify the problem stations.

If your master is a 3rd-party CPU, then you will have specific diagnostic tools monitoring the Profibus slaves, you will have to study the information provided to catch sporadic error signals. Try to give us an idea of the results of the diagnostics from your master.

If you are lucky enough to have access to an electronic diagnostic tool for Profibus-DP, such as Siemens' BT200 or Procentec's Profitrace, this is the perfect time to use it  They are particularly useful for detection of problems of this nature, unpredictable and sporadic.

In any case, we would need a sketch of the Profibus network, identifying the master, the slaves, and the fiber-optic converters (with their Profibus address), with a special attention to the location of the terminating resistors (please mark the ones that are ON). That way we can follow the information from your Profibus diagnostics.

Hope this helps,

Daniel Chartier

siemens step7 - CPU 417F

LOOK FOR THE ATTACHMENT

thanks for your help Mr. Daniel

the above attached file shows the communication path of probifus and OFC. the end connectors are in ON position and others are in OFF position.

i faced similar problems like this before, where the analog display unit was malfunctioning which was included in the profibus communication network, when i isolated the display unit, the issue was solved. then i replaced a new display unit. (troubleshooted with the help of andy verwer's presentations.)

but the scenario what im facing now is totally different, the fault is sparodic as i explained above in my first comment.

i will try to get the details of the diagnostic buffer and post them soon.

the messages that were displayed in the diagnostic buffer.,

*i/o access error when updating the process image

*i/o access error when transferring the process image

*distributed i/o station return

*distributed i/o station failure

and the dialogue box shows.,

distributed i/os station return

address of the affected dp slave station number:15

dp master system id: 1 

log base address of dp slave i/p address:16332

log base address of dp master:16382

requested OB: rack failure OB (OB86)

priority class:25

external error, outgoing event

Hello ganivz;

Two things in the messages you show:

- Requested OB: OB 86--> do you have an OB 86 in your program blocks? If not, I suggest you create and download one to the CPU (no program necessary inside at this point).  The presence of this OB in the CPU program will allow the CPU's OS to collect more information on the fault when it appears again.

- Is the faulty slave always identified by address 15? Or are there others involved? Which station is at address 15 (your drawing does not show this)? Check in the HWConfig editor.

Once you have identified it, please:

• check the wiring and connectors attached to this station, change them if you have the possibility.
• make sure the termination switches are in their position (either ON or OFF, depending on their location on the network, and check that the switch is not  able to toggle due to vibration or shock.
• Verify that there are no motor leads or powerlines that are too close to the Profibus RS-485 cables.
• If this station is on a part of the machine that is subject to constant or important vibrations, try mounting the station rack on vibration absorbing mounts.

Most of these faults have a physical cause.

Hope this helps,

Daniel Chartier

hello dc,

OB86 is present in the program,

the mentioned station address 15 is gantry station ET200M and the fault keeps on shifting between 3 or 4 ET200M stations everytime. 

Hello ganivz,

I am Also facing the same issue with ET 200S IM 151-1 Standards , two IM's with address 31 & 41 are keep showing Bus Fault , communication error randomly on one another simulatneously , did you get your issue resolved , if yes what solution you tried to get it resolved?

first you can settle this problem by 

change of profibus properties to USER defined , then change the retry time to  up of 5 then press calculate and save compile and download 

you will see the fault repetition will decreased and may be disappear as you increase the retry time and the the other parameter that will found in siemens profibus diagnostic and commissioning PDF