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Old December 20th, 2017, 09:19 AM   #1
lanester
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PROFIBUS ProfiTrace Diagnostics Assistance

Hi All,

Looking for some advice in interpreting ProfiTrace Scope images.

The PROFIBUS network topology of the machine was as follows;

PLC(2) <-> ET200(3) <-> SEW_GW(50) <-> SEW_SERVO(55) <-> SEW_SERVO(56) <-> SEW_GW(51) <-> SEW_GW(52) <-> SEW_GW(53) <-> SEW_VFD(57) <-> SEW_VFD(58) <-> SEW_VFD(59) <-> ET200(7) <-> ET200(10) <-> TR Elec Encoder(70) <-> TR Elec Encoder(71) <-> TR Elec Encoder(72) <-> TR Elec Encoder(73) <-> TR Elec Encoder(74) <-> TR Elec Encoder(75) <-> TR Elec Encoder(76) <-> TR Elec Encoder(77) <-> TR Elec Encoder(78) <-> ET200(11) <-> TR Elec Encoder(79) <-> TR Elec Encoder(80) <-> ET200(12) <-> ET200(13) <-> ET200(16) <-> ET200(18) <-> TR Elec Encoder(81) <-> TR Elec Encoder(82) <-> TR Elec Encoder(83) <-> TR Elec Encoder(84) <-> ET200(14) <-> ET200(15)

Baud is 3Mbps. We were having constant bus failures all from station 12 onwards. All the interface modules and connectors for the ET200's were replaced as we chased bus fault lights around. All the wiring from station 13 on has been replaced.

We noted that the length of the run was probably greater than 100m and also that there were more than 32 stations on the the network. We then decided to split the network using a repeater from Station 13 on inclusive. The repeater was installed immediately after station 7. Terminator resistors for station 12, Repeater side 2 turned on.

This allowed the machine to run but still on the odd occasion would fault out with a bus fault. Generally the bus fault was from the new segment that had been created (Stn13-Stn15).

We purchased a ProfiTrace tool. Connecting to the PLC DB9 I get the following (see PDF or ProfiTrace file https://www.dropbox.com/sh/sjson41m2...YhCtXr3ia?dl=0 as fle too big) I therefore assume I am dealing with a wire break. Unless all I am looking at is the reflection from the stub connection.

What is also odd is that between station 71 and 72 there is a large drop in quality. We have replaced both the encoder back plates and cable between the two but this has not improved the quality between the two devices. station 72 and on the amplitude and quality of the signal is very degraded.

Now I am looking for some advice as to what the ProfiTrace tool data is telling me and wether my conclusion is correct?

All help appreciated.
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Old December 20th, 2017, 01:12 PM   #2
jacoffey85
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I had a similar issue with a ProfiBus network before where I had an encoder fault out and cause some issues. Every node after the encoder would be totally faulted out, and the 4 or 5 nodes before it would have random faults that came and went. I imagine the reflection from not having a terminating resister caused the issues with the nodes in front of the encoder.

The way I troubleshot this (I didn't have a trace tool) was I went to the first node that was faulted out and unhooked the outgoing ProfiBus cable. If the comm fault cleared out, I would hook it back up and move to the next node. This was how I was able to narrow it down to a specific device. What I ended up doing was adding an external ground to the the encoder and have not had any issues since.

I don't know if this helps, but your diagnostic results seem similar to what I was have happening.
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Old December 21st, 2017, 02:29 AM   #3
lanester
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Thanks Jacoffey85. I was thinking of doing this looking at the tracetool to see if the waveform improved. My issue is downtime on the machine is minimal so getting the time to do this is an issue. Hence why i was asking if anyone could take a look at the waveforms to assist me in narrowing down the issue until I can get to the machine.
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Old December 21st, 2017, 02:41 PM   #4
Mad_Poet
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Any chance there is a bad terminator switch?

The Profibus connectors I work around have little switches on them which are supposed to disconnect the bus and switch in the terminator . . . I flipped the switch one day to test and evaluate - got the expected trouble symptoms, then switched it back and had more problems. Till I pushed the switch back on then hard back off. Cleared that problem.
Poet.
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