# Profibus problems



## dronai (Apr 11, 2011)

mikey383 said:


> I have 7 flowmeters installed on the same Profibus scanner. There used to be 8, but one was removed and an EOL resistor installed in it's place.
> 
> Last week, all the flowmeters lost communication. I went device by device and got the first 4 working. But when I hook up the wire going to the 5th flowmeter (even if the 5th flowmeter isn't hooked up on it's end) I lose communication again.
> 
> ...


I also had only a one time problem, when a motor stopped working on a conveyor. Turned out to be the Profibus connection located at one of the VFDs ! Was just loose.


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## mikey383 (May 21, 2012)

dronai said:


> I also had only a one time problem, when a motor stopped working on a conveyor. Turned out to be the Profibus connection located at one of the VFDs ! Was just loose.


I checked all the connections and they were all tight. The first 4 flowmeters are in a washdown safe area, so they have watertight Turck connectors on them, and the 4th flowmeter cable goes into a 4x4 Hoffman enclosure with a terminal strip installed in it. From there, the rest of the flowmeters are all hardwired. 

I also checked resistance on the cable, and found that it's around 3.5Ω in roughly 100 feet. 

I even took the wires off the terminal strip and wire nutted them to eliminate the possibility of a corroded terminal strip. But no matter what, once that cable is hooked up, the 4 flowmeters lose communication...whether the 5th meter is hooked up or unhooked. :icon_confused:


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## Big John (May 23, 2010)

Do you have a scope or a good DMM that can read mV? I'd hook it up at your outputs with the 5th flowmeter loop disconnected. Have someone connect the loop, if your peak-to-peak voltage drops way out you've got a low impedance connection somewhere in the cable.

Can you temporarily move the the EOL resistor to the output and then see if you can get all the flowmeters working except number 5? That would reduce the possibility to that you're seeing the result of cumulative losses due to multiple bad connections, i.e., if that's the problem you'll also see a signal loss when you connect #6 or #7.

-John


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## mikey383 (May 21, 2012)

Big John said:


> Do you have a scope or a good DMM that can read mV? I'd hook it up at your outputs with the 5th flowmeter loop disconnected. Have someone connect the loop, if your peak-to-peak voltage drops way out you've got a low impedance connection somewhere in the cable.
> 
> Can you temporarily move the the EOL resistor to the output and then see if you can get all the flowmeters working except number 5? That would reduce the possibility to that you're seeing the result of cumulative losses due to multiple bad connections, i.e., if that's the problem you'll also see a signal loss when you connect #6 or #7.
> 
> -John


I checked voltages with my Extech meter, and with the first 4 meters working, I got 1.105 volts from + to - on meter #4. When I unhooked meter #3, I got 1.005 volts. Once I hook up the cable going to #5 (regardless if #3 is in the loop or not in the loop, and regardless of #5 being in the loop or not), it drops to .89 volts and all communication is lost. I moved the EOL resistor to meter 7, 6, and 5, and same outcome. 

At this point, I'm led to believe that the cable from 4 to 5 is bad. Especially considering there was standing water in the bottom of the Hoffman enclosure in the washdown area, and the cable sheathing being below the Meyer's hub when I opened the enclosure. My thought is that water got down in the cable, corroded it, and it causing an issue with that particular cable. 

I plan to megger the cable and check it with a scope in the morning.

But like I said, I have zero experience with Profibus, or Fieldbus.


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## dronai (Apr 11, 2011)

Is this what your connectors look like ? 

They all looked good on our problem too. But when we moved the connector around on the VFD that controlled this motor, it established a connection, and the I/O registered it working again.


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## mikey383 (May 21, 2012)

dronai said:


> Is this what your connectors look like ?
> 
> They all looked good on our problem too. But when we moved the connector around on the VFD that controlled this motor, it established a connection, and the I/O registered it working again.


They're more like this:










Only with an orange cable instead of individual conductors. I can't recall the exact part that we used to interconnect them, but it still has the brown/blue/green-yellow conductors. 

I've already troubleshooted the connectors, and replaced Ts, replaced connectors.


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## dronai (Apr 11, 2011)

I bet your right with water corrosion.


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## dronai (Apr 11, 2011)

Found this. May not work if your on your phone

http://us.profibus.com/docs/A%20Guide%20to%20Troubleshooting%20PROFIBUS%20PA%20Networks.pdf


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## mikey383 (May 21, 2012)

dronai said:


> Found this. May not work if your on your phone
> 
> http://us.profibus.com/docs/A%20Guide%20to%20Troubleshooting%20PROFIBUS%20PA%20Networks.pdf


I have that same info...but that's for Profibus PA, I have DP...not sure what the difference is. I used it to troubleshoot what I have. 

The thing is, I need to be 100% sure the cable is the problem. This facility is going to replace all wiring to the washdown safe area within the next year, and doesn't want to spend the money on something that will be replaced in several months. 

My suggestion to them was to leave the 4 working flowmeters on their own Profibus network, and install a new Profibus scanner for the other 3, but a new Profibus scanner is $2800, plus new cable to FM 5, plus labor. I'm trying to give them the best option.


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## dronai (Apr 11, 2011)

_Bad connections_: This is one of the hardest he rst step. The connectors made by Siemens rocess that the design engineers used when ad device from a device that is simply aving trouble communicating on a bad ou can connect the bus monitor on e PROFIBUS DP side and watch the traffic the etwork and compare on the ion d a program look for SAP (destination service access point) of '3C'. This is ems. _Too many terminations_: This will require going over the network from one end to the other and trying to find where the extra termination is. 
*problems to find since it could either be caused by a faulty part or by not tightening the connector enough. Testing the tightness is tproblems t*
fifi
(Figure 5) require a fair bit of tightening to make the connection (use a screwdriver 

This what I saw.


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## mikey383 (May 21, 2012)

Megged the wire today. Found that conductor to conductor, I got 52MΩ, conductor to shield I got around 60MΩ at 269V. 

So I megged the wire to meter 6...about 35 feet. Got roughly 10GΩ from conductor to conductor, and conductor to shield. 

With those readings, we collectively decided to order new cable.


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## Big John (May 23, 2010)

Thanks for the follow up, glad you got it sorted.

-John


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## mikey383 (May 21, 2012)

Update: 

I haven't got around to pulling the new cable yet (there are higher priorities right now), but I had a letter in my work mailbox this morning. The boss, myself, and 2 other guys are taking a Profibus class at the end of the month. :thumbsup:


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## Del (Feb 10, 2011)

Sorry Mikey383 I've been of the site for a little while- I could of helped you more.

If you are going on the certified engineer course at the PTO in Johnson city, get infoed up on your Binary, and Hexedecimal.
As these are critical to an understanding of Profibus.
There are free online training materials at Profibus.com
It comes in 2 flavours Profibus DP, which is a general purpose, multiple baud rate flavour, and Profibus PA, which is low speed, and can power instruments, and be intrinsically safe.

One thing to remember is there is a terminator switch on every device, which does 2 things- adds in the teminating resistor, and opens the wiring downstream so you can fault find.
The certified Profibus engineer course is the toughest one I ever took, on a 4&1/2 day course had 4hrs practical exam, and 4hrs written(open book).
If you have a lot of Profibus equipment, you should also consider purchase of Procentec Profitrace (there are others aswell), and consider installing Procentec Profihub B5's in your panel to split up the network, add diagnostic ports, and give you a place to add to a hot profibus network.
If you cannot get profitrace, you should look at a high speed USB oscilloscope, as one of the diagnostic methods.
Also if you have vampire tap (sub D) connectors replace them with screwed units.
The Voltage differential between A &B should be greater than 6V.
Profibus DP cable is Purple sheathed(hence nickname of Barney) with red and green insulated wires.
If you have orange cable it sounds like you have foundation fieldbus wiring- which is different.
Note the standard speed on Profibus DP is 1.5megbaud- I would suggest slowing it down abit to get a more reliable network if you are having problems. 
Regards

Derrick


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## mikey383 (May 21, 2012)

Hi Derrick, 

Thanks for the info!

This class is only a one day deal. I don't recall what they go over, but I believe it's just a simple basic 8 hour class. 

You're right, the wiring is Fieldbus and not Profibus. I spoke with my boss this morning, and another contractor pulled in the wrong wire when the building was under construction. Although, it's worked fine until recently. 

I'm fairly new to the automation part of the electrical trade (I did a lot of installation, not so much on the PLC/technical end), so some of this stuff is like trying to read Chinese for me. But, I'll do what I can and soak up every bit of knowledge I can.


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## Del (Feb 10, 2011)

No problem mate.

I started as an electrician myself, and my intro was rewiring over 100 PLCs for a major food manufacturer.

Look for the resources, covert thy PDF's- most essential.

Look for the PLC book 5 as a good intro to control.

There are over 365 different networks out there, but only a few common one.

DeviceNet. This is similar to CanBus which controls your car engine management system and heavy plant controls.
ControlNet. An early ethernet derivitave.
Modbus - one of the most common. used every where.
RS232 point to point comms to the device.
Profibus- Probably the largest installed base, after Modbus. over 30 million nodes.
+ many many others.

Comms is the most difficult area of automation, and the one most likely to fail.

Regards

Derrick


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## wane (Aug 27, 2012)

change the terminal strip in the hoffman box,I`ve come across problems like this not just with profibus, humidity, heat, vibration will affect the connections over time


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## mikey383 (May 21, 2012)

wane said:


> change the terminal strip in the hoffman box,I`ve come across problems like this not just with profibus, humidity, heat, vibration will affect the connections over time



I already tried removing the terminal strip from the equation and wire nutting the leads together. Simply connecting the wire from meter 4 to meter 5 makes all meters stop communication. 

I'm 99% sure the cable is bad, considering this system worked flawlessly for almost 10 years, up until the last few months. Right now I'm just waiting on the cable and the time to install it.


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## wise119 (Mar 10, 2016)

mikey383 said:


> I already tried removing the terminal strip from the equation and wire nutting the leads together. Simply connecting the wire from meter 4 to meter 5 makes all meters stop communication.
> 
> I'm 99% sure the cable is bad, considering this system worked flawlessly for almost 10 years, up until the last few months. Right now I'm just waiting on the cable and the time to install it.


Is that one a Profibus DP cable or PA cable, they are slightly different and speed is also different? I usually convert Profibus to Modbus RTU using GW-7552 gateway from ICP DAS to communicate with SCADA. Another way to test for communication would be using their converter I-7550. If you don't see anything on the RS-485 side(voltage), you probably have a bad cable. Just a suggestion, it's hard to troubleshoot in Profibus.
http://www.icpdas-usa.com/gw_7552.html
http://www.icpdas-usa.com/i_7550.html


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