Effect of welding work near PCs and PLCs.

In my lifetime, I've had one pressure transmitter and a dozen or so load cells that were damaged by welding works. The damage occurs when welding current passes through the device.

For other devices, it's possible for the welding current to pass through the cables into the PLC inputs.

Then there's the strong magnetic field present in the welding cables. This can induce stray currents into signal cables, damaging equipment or confusing the signals.

It is best practice to electrically isolate and/or mechanically remove all small-current equipment from the neighbourhood of all forms of electric arc welding, including though not restricted to:

• computers
• plant instruments
• anything else containing semiconductors
• electromagnetic relays
• anything containing plastics
• anything containing timber, paper, cloth or other easily combustible solids
• anything containing oils, paraffins, or combustible liquids and gases.

simply because the risk of damage to these items from stray currents induced by the arc-welding process is high.

Electronic items are not affected by flame welding, forge welding or Thermit welding in the same way, as these processes do not involve electric current.

All metal welding and casting processes may give undesirable effects of concentrated heat paths. Many plastic casings and semiconductors do not respond well to high heat inputs.

Is that enough theory, perhaps?

I would just like to add to your excellent post that the back EMF when using a welding transformer can cause large spikes back on the mains that some (possibly badly designed) electronics simply do not like.....these spikes should be snubbed inside the welder, but are not always done well......anything digital on or near the same supply, may do really unfunny things when the spikes get onto the supposedly filtered supplies....

There are a number of problems related to welding next to Computers. The most important are:

The Electro-Magnetic Field or EMF. Any time there is high current, as in arc welding, a strong EMF field is created. Computer chips have no protection from EMF unless it is completely shielded such as tempest computers. This is the one disadvantage they have over the old vacuum tubes, which were immune to EMF.

The next is the power surges. The welder can significantly affect the power lines on both the hot, and the ground. Although most power supplies have some built in protection, surges will definitely shorten the life of the electronics.

Although it's already been covered, I'll throw in my bit to confirm the statements about EMF and computers. We work with HV on a regular basis and even at very low currents nearby computers can be affected.

I've seen lots of weird symptoms like ghost keystrokes, mysterious speaker bleeps, etc. I've even seen one PC permanently disabled from arcs being generated yards away.

One particularly nasty problem can occur when the item being welded is earthed.

What happens is that the person doing the welder can forget to attach the welder's earth lead to the work.

When an arc is struck, the current returns to the welder via the mains earth electrode and the earth wiring to the socket that the welder is plugged into.

This has a fairly predictable effect on the wiring....

Dear friend,

when welding is done, the arc of welding generates emi( electro magnetic

interference) which will induce voltages in the drives and PLCs. These devices may got damaged or malfunction due to induced voltages . So It is advisable to switch off the sofisticated equipment while carryingout welding.

Bhushan

Thanks a lot to all my friends for posting valuable comments. Now I am cleared what happen during the welding work.

Dear All

what i can do to protect my devices like (PLC, PCs,...........) from this problem.

I cannot switch off the equipment.

Can i found any modern welding machine which will not make this problem?

More comment than anything. Although the EMF's and EMI's have been known to cause mishaps, a lot of this depends on what type of welding procedure is taking place and what voltage /amp is being used for welding on this machine. (SMAC,FCAW,GMAW,GTAW) If using a larger voltage machine (440vac-575vac) I would probably recommend shutting them down, if your welding is in very close proximity to this equipment. The farther the distance between the arc and the CPU the better. As long as the machine has a solid ground to the material being welded, you should not see any spikes in voltage through your computer hardware, or at least no more than you get from power fluctuations through the electrical lines in any given city. I do frequent fabrication changes using a 110v. MIG welder on automated machines in the auto industry where these lines can not be shut down due to on time production, and I've personally never had a problem.

I can add this: a few months ago, I was the recipient of a state-of-the-art cardiac pacemaker. I was warned to stay well away from electric welding equipment because it could be negatively impacted by such equipment. I presume a computer would fare no better.

Most of the time, damage is caused by bad ground on the welding ground, then the return voltage will try o find a way and it may be through the instrumentation.

It is not real rare however it does happen, just not every time.

Go ahead, you might stay lucky?

I agree with jmart23 Bad work lead connections [ rather than ground] causes most of the problems.

Work lead connections should be placed as close to the weld as is practical.

The item being welded should never be grounded this will avoid stray paths for the welding current to take.

Never use the metal structure of the building as a common connection for work leads.I have seen this many times in factorys.

Keep welding leads away from sensitive electronic sensors etc.