Static on the line, ethernet edition

[tmoulder]

Hello All,

I have a robotic welding application, using a Unitronics V570 with ethernet communications to a motion controller, 2 robots and a camera system, all Modbus TCP.  About a year ago, we switched the plasma welder on the line to TIG welders.  This was an enormous cost savings over the old ones, which were obsolete anyhow.

Buuuuttt... (You knew there was a "but" coming somewhere, didn't you?)  Since the conversion we have had an intermittent-but-persistent problem where when one of the welders strikes, it knocks out the ethernet communications.  The TIG torch uses a burst of RF to establish the arc, and this is the moment the drop takes place, if it happens at all, which it can go weeks without happening, and then it comes raging back.

I've taken a plethora of steps to try and correct this issue:

1. The machine is more heavily grounded than my smart-alec teenage daughters.  I've checked the paths to ground for everything on the system, and I cannot find anything I've missed in terms of grounding.
2. Shielded Cat5e cables throughout, then took the additional step of replacing those with fiber optics.  The longest single conventional cable is now 2 meters in length, and isolated from the rest of the system.
3. Replaced the V570 and the ethernet card.

In terms of troubleshooting, I added some counters to the PLC program, and it appears the the link is being lost.  It reconnects automatically, but by then, it's burned a hole in the part.  For mitigation, I switched some of the responsiblity for the welding movement from the PLC to the motion controller, so even if communication is lost for 1 second, the welding process continues unabated, and comms are restored before the weld move finishes.

The nature of the drop (link lost) makes me think the issue is somewhere with the PLC itself.  The fiber optic convertor for it is located in the same operator panel, connected by a 1 meter shielded cable, all contained within a fully grounded enclosure.

I'm thinking a different ethernet card may be in order.  I've pack-ratted several of these over the years, but can someone explain to me the difference between the V200-19-ET1, the V200-19-ET2, and the V200-ET-E?  And is there some version that offers more robust performance for electrically noisy environments?

 

Thanks!

 

TM

 

[kratmel]

Based on what you said - the cause of all the problems was the replacement of standard welding on TIG with high-frequency ignition.

In my experience, the main problem with this improvement is the lack of complete filtering of the interference signal from the TIG torch to the rest of the system equipment. I have repeatedly encountered various methods of combating radio frequency interference, which did not work because insufficient or no filtering on one of the wires of the system - turned this wire into an antenna, creating radio frequency chaos.

The main idea you need to implement is described in the figure.

None of the wires installed in the welding system should pass without measures that implement filtration and high-voltage galvanic isolation.

The figure describes the equipment mounted on the Panasonic robot to switch its operation to TIG mode. You can see how the control signals to the manipulator are implemented. No other measures to protect against interference from the robot itself and network cables to the computer that sends it the task is not applied.

In short, you are trying to eliminate the effects of interference - instead of reducing and limiting them in the welding circuit.

You must find ready to use standard TIG filtering system used in automatic TIG welding. Or use it diagram for build self made filering station for all TIG tourch.

Than you can return to first not optical variant of your system without any problem.

 

 

[tmoulder]

Hi Kratmel,

Thank you for the information.  Do you have an example or source for a "standard TIG filtering system"?  I've searched google and can't seem to find anything.

Is this something that can be added to an existing welding system?  It can't be as simple as throwing some ferrite chokes on the wires... can it?

Thanks,

TM

[kratmel]

Hi on foto you can see standard upgrade kit for Panasonic robot

43 minutes ago, tmoulder said:

ferrite chokes on the wires... can it

It is present in this box, but also some RLC chain and snabbers used. I have only some  foto inside this box. Try to find it ... it takes some time.

 

[Ausman]

Taking everything from Kratmel as great, some thoughts.

Is the PLC itself totally within  the enclosure?  Or is it being used the way it's meant.....user interaction via the screen being on the outside of the panel? 

If so, that's a great RF entry point in itself, so perhaps a hinged shield of sorts might help.

Was also intrigued by "it comes raging back".  Does this timeline match some MTBF on the TIG componentry?  In that the TIG is making far more interference after a certain amount of use on new tips etc?

Also loved the daughter reference.  So, so true! 

cheers, Aus

[kratmel]

Sorry i can't find foto of board inside TIG box. Maybe i can make new one on next week.

This manual maybe useful. Also please see correct grounding on p.21-22

https://www.millerwelds.com/files/owners-manuals/O611L_MIL.pdf

 

If it possible please post your TIG connection setup. I have some diagram from different TIG welders maybe we can find solution.

 

P.S  

I have some trouble with Ethernet connection to the V700 panel installed near properly grounded VFD in metal control box. If VFD start - connection is lost.

Issue is solved by connection -24V (GND) of V700 Power supply to the control box common ground point. Ethernet run stable after this.

Many machines provide this connection (-24VDC to ground) by default.     

[tmoulder]

14 hours ago, Ausman said:

Is the PLC itself totally within  the enclosure?  Or is it being used the way it's meant.....user interaction via the screen being on the outside of the panel? 

Was also intrigued by "it comes raging back".  Does this timeline match some MTBF on the TIG componentry?  In that the TIG is making far more interference after a certain amount of use on new tips etc?

Hi Ausman,

It is being used as it was meant - operator interface, and I did consider that.  There is something there however that also references your second question.  There are two weld stations on this machine, let's call them WS1 and WS2.   The V570 is positioned in an operator box that is mounted slightly to the right of the entire machine.

WS1's welder is only 3-4 feet from the V570, but it never produces this problem.  WS2 is about 10 feet from the V570, and it's the one that causes the issue.  Granted, that not a lot of range difference, but if the design of the V570 were the suspect, I would think it would error out with either or both welders.  But no, it's only the furthest one.

That's the reason I've been focusing on mitigating the RF noise.  It's frustrating because I feel like the answer is staring me in the face, (the difference between the welders), and somehow I'm missing it.

[kratmel]

Checklist:

- swap welder power supply;

- use two separate control V570 system (you can make the same distance condition to the WS);

- check - is it possible that separate welding only WS1 or only WS2 work without lost communication.  I have issue on two TIG welders working simultaneously on the one big machine part    - one of welder - sometimes lost settings parameter.   

- all system powered from the same power line, Than you can temporary power V570 from the isolated UPS or battery. Than RF spike can't go to the V570 power line.

- I do not know how to test it.... - is it possible that motion conroller lost communication and it is  not V570 problem?

- is it some addon wire used near or in weldind gun ( home sensor, collision detector, arc voltage supervision, ect) - what circuit used for filtering or isolating  for this cirquit?

TIG torch uses a burst of RF to establish the arc - generate above 8000V - then standard isolation -like stadard transformer or optical isolator is not enough.