Welding & Analog Modules

joaco1993

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Hi all,

I would like to know if there are some precautions to take when doing a welding nearby instruments.

Im asking this because today we weld a pipe, and although there was no instrument near that pipe, that pipe on the other side is welded to a tank which does have instruments.

After the welding we figure out 2 analog modules where showing OK status in the plc, but no channel was working, having the field power off bit set to 1.

We had to replace both of them, and when we took them out , in the chip in the corner, both of them had black area like they were blown (dont know how to post pictures)

Could this welding had something to do ?

PLC Contrologix, remote IO adapter AENTR, 1794-IE12 module used

Thanks!
 
Many years ago I was working on a startup of some textile machinery. The line included a needle loom and an external carriage to maintain tension in the product. Something had to be welded to the carriage. A welder was already working on the needle loom so he was asked to weld the piece to the carriage. As soon as he started a cloud of smoke issued from the cable festoon between the needle loom and the carriage. It turned out that the welder was grounded to the frame of the needle loom and the only connection between that and the carriage was the shields in the analog cables in the festoon.
In short, indirectly, welding could have had something to do with it. Not necessarily the welding itself, but the way it was being done.
 
Many years ago I was working on a startup of some textile machinery. The line included a needle loom and an external carriage to maintain tension in the product. Something had to be welded to the carriage. A welder was already working on the needle loom so he was asked to weld the piece to the carriage. As soon as he started a cloud of smoke issued from the cable festoon between the needle loom and the carriage. It turned out that the welder was grounded to the frame of the needle loom and the only connection between that and the carriage was the shields in the analog cables in the festoon.
In short, indirectly, welding could have had something to do with it. Not necessarily the welding itself, but the way it was being done.

I see,
In my case i have 2 AENTR in the first one i have 10 modules connected, one of them is an analog and the rest are digital input and output. Why only the analog blow ? shouldnt have all of them happen the same ??
 
Its been my experience if the person that is doing the welding, that they put that ground cable next to where they are welding. Otherwise the return ground path for the welder will find its way thru equipment that you do not want that ground path to go thru like your instruments and PLC equipment that is in the area. Like above the ground path is critical to not effect your equipment in area.

I had this experience recently with a profibus network. Welder was welding in area and the equipment was running in area. I thought the welding was causing the network to glitch and shut down.

All I can say is that the ground has to be on the area that the person is welding locally, not 100 feet away from where that welder is welding.
 
I have done many commissioning jobs where the mechanical installation is running behind so there have often been engineers welding on the plant. I have two instances where analogue cards have suffered with welding spikes. However, in most cases this is because the engineer did not clamp the earth close enough to the weld. There is no doubt that a poor weld earth will destroy or damage analogue or even digital cards. The best solution if at all possible is to power down the whole system & isolate any analogues, this I suggest not only disconnect the signal cables from the cards but also isolate the instruments themselves.
 
Meh, electrical issues from welding; you guys are so wimpy ;).

My brother was on a job in Croatia, and a fellow on a scissors lift welding something the roof was generating blebs falling like rain on the equipment. The interesting part was, there was a bucket of some kind of volatile solvent on the lift deck (why? I sure dunno!), and when a bleb ignited it, that welder, 25 feet in the air on a platform maybe 2mx1m with a bucket and a column of flame and no quick exit strategy, had a bit of a situation. He eventually snuffed it out by covering the bucket with a two-by that was handy.
 
I worked in a stamping plant that had occasional, weird failures/devices explode in control panels all over the shop.

After a year of this the maintenance welder was pushing his portable MIG welder out onto the shop floor and said "I wonder what is going to blow up this time?"

I asked him what he meant and he said every time he went out and welded something in the shop some machine near him blew something up.

Took his welder out of service and had it checked - it was returning ground cable weld current through the ground lead to the power plug, which then routed through the power going to the machine and through whatever component in the panel had the least resistance until it blew up.
 
There is no end to the tales of problems with welders burning up electrical panels.
I know of one when the welder was repairing a pump casing in a sump put connected the ground to the discharge pipe. but current flowed through the control panel and quickly burned up the panel containing the controls for multiple pumps in addition to the down time it cost the major buck to replace the panel.
But this all falls to the welder if they are not going to do the job right then you should get another welder there are many of them out there.
PLC's and welder can play nice together if you do it right
i have built several machines using welders controlled by PLC's they also have VFD's they have ben working great for many years without any problems
you just need to be careful
 
Gary is right, I was involved in a project with a 1.5mw welder on a continuous pipe welding line, although it used to make the Scada screen wobble a bit it never destroyed anything. Some companies I have worked with included a training scheme on welding on sensitive equipment as part of the contractor induction scheme where the above precautions in this thread are drilled home.
 
Bad grounding can be a big issue.
Make sure ground is firm and NOT going through any bearings.


Also... is it an induction welder? I have seen these make a lot of field generated emf.

I was work on a job where the disk kept getting corrupted.
Measuring the read head voltage, it went from mV to >10 volts when the induction welder (about 3 feet from it) started welding.
 
Thanks for all the answers but now i have more questions !

By bad grounding you mean the return clamp of the welding machine ? actually why do you call it earth or ground ?? its just the return path of the welding machine.. its not actually connected to earth at some point in the welding machine, is it ?

If the pipe or structure you are welding is connected to earth (like all metal structure should be) how do you guarantee that the return path for the welding machine will be with the return clamp and current wont go to the "safety earth of the structure" ??

Another scenario, if I have an instrument in that structure or pipe and that instrument its not properly grounded, and lets say the 0vdc of the instrument power is touching the pipe, and the impedance of the that wire is lower than the return path of the welding machine.. the current will go through the instrument and then into the panel and blow the module right ?

i dont know much of welding machines. its the simple one with an electrode and a clamp.

I have more questions now as you keep answering,

thanks!!
 
Joaco993
I will try to answer your questions
Yes the ground is the return lead that can be AC, DC- or DC+ depending on your settings
It is connected to work while the power lead holds the electrode
Normally the ground lead of the welder is at the earth / ground potential but that is not always true.
And when you are welding it should be attached to the work as close to the point of the weld as possible to keep the ground resistance as low as possible
Most welders use an isolation step down transformer the open loop arc voltage is usually about 48v
I say usually because there are many different types of welder in use today.
You can even weld with a 12VDC car battery if the job is not too big.
It is my understanding that underwater welders are generators to prevent ground loop from charging the water the divers are working in and electrocuting the divers they may have some new technology.
As we all know if we work in this industry that ground in not at the electrical potential over a large area.
Since to weld you need a large current. Most welds are done at well over 100 amps depending the metal. Most industrial welders run at about 200-400 amps but I have both worked on and used welders with output up to 1200 amps. The one company I did work for it was common to run welder in parallel.
The one job I remember they setup 2 800amp welders to one weld electrode ( they were using Submerged ARC ) I think it was around 1400 amps to one weld puddle
The reason grounding is critical it that electrons will find the least resistive path back to the source if path cannot handle the current it will burn up the wires. Sometimes that path will be the equipment ground other times may be the system wiring

Just for reference welding is kind of a hobby of mine, I can do stick weld, Tig weld (Steel, SS, Aluminum)
and torch welding
 
Just as a reference. Even if you have field-bus based devices and not just Analog, you might have some issues for Ethernet communication, and might want something like an ethernet isolator.
 

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