Hi Everyone,

I am working on an arc welding machine. I would like to measure the arc voltage between the metal part I do weld and the welding machine. There ,sparks a high voltage around 300V or more when the welding machine is first ignited. Then, it settles down to 10-15 volts which is the most I interest in. I tried voltage divider method. But, it doesn't work simply as I expected. My op amps burnt. I would really appreciate your ideas and help.

 

Hi Everyone,

I am working on an arc welding machine. I would like to measure the arc voltage between the metal part I do weld and the welding machine. There ,sparks a high voltage around 300V or more when the welding machine is first ignited. Then, it settles down to 10-15 volts which is the most I interest in. I tried voltage divider method. But, it doesn't work simply as I expected. My op amps burnt. I would really appreciate your ideas and help.

This would be a TIG welder correct? The only one I know of that has a high voltage start. Instead of trying to measure the part your not interested in, why not use the controls built into the welder that control the start voltage? By not measuring until the start is off should make things easier.

But I have to ask why you're interested in arc voltage? It is the current that does the work of welding.

 

It's power that does the work of welding. I * V. There is a built in assumption of arc working voltage with plasma welding using arc gap control.

https://static.lorch.eu/Wissen/Y00.0120.1-02_EN.pdf

 

My guess is that the HF used for starting is going across surfaces and frying your components. Assuming it is TIG, when you take your argon (or other gas) tank in for exchange, they always inspect it for arc damage. Similar process, and if detected, it will cost you the core. At least, that is what I have been told. Hasn't happened to me yet.

As shortbus asked, why are you interested in that voltage? Is your arc not starting? Do you get any "hiss" from the HF as it tries to start?

 

Correct, TIG welder. A start-up company produces a cnc based automated welding machines. I am in a project with them where arc voltage is needed to be measured. The arc voltage is proportional to distance of z axis. Therefore, Longer the distance higher the voltage. One knows the arc voltage can adjust the z-axis and get a better welding job.

 

The arc voltage is proportional to distance of z axis. Therefore, Longer the distance higher the voltage. One knows the arc voltage can adjust the z-axis and get a better welding job.

That's what I thought you were doing. The one automatic TIg I was around the gap was set by experimenting, since they are usually only used for one certain job. The Z axis never changes, in that case. When the electrode needed changed a gauge was used to reset the gap.

 

Are you trying to tap into HV supply?

 

It's necessary for stepper motor to adjust z axis while it's operating. I really need that voltage to be measured. The pipe surfaces aren't always smooth and perfect round. It affects the welding job. When voltage settles down to10-15 volts, it's not problem to measure. But, the high voltage at start kills the op amps. If I use TVS diode instead of zener diode, could it make any difference?

 

Are you trying to tap into HV supply?

No

 

It's necessary for stepper motor to adjust z axis while it's operating. I really need that voltage to be measured. The pipe surfaces aren't always smooth and perfect round. It affects the welding job. When voltage settles down to10-15 volts, it's not problem to measure. But, the high voltage at start kills the op amps. If I use TVS diode instead of zener diode, could it make any difference?

As you can tell by the link I sent you it's not that simple to utilize the measurements even it you could measure the arc voltage exactly and reliably with clamping and RF filtering.
https://forum.allaboutcircuits.com/threads/arc-voltage-measurement.170308/post-1518845

 

It's necessary for stepper motor to adjust z axis while it's operating. I really need that voltage to be measured. The pipe surfaces aren't always smooth and perfect round. It affects the welding job. When voltage settles down to10-15 volts, it's not problem to measure. But, the high voltage at start kills the op amps. If I use TVS diode instead of zener diode, could it make any difference?

You are trying to do something new. Most automatic welders for things like that are MIG not TIG. Automatic TIG welding is usually done by simple fusion welding on a linear surface. TIG also needs a way to feed the filler rod, for joints that aren't very close fitting, no gaps. Like two machined parts, with no corners or projections.

Most automatic welders for other things, things that are saw cut or have corners or projections are done by MIG. MIG uses the filler metal for the electrode and is far more forgiving to both fit and distance.

I'm not trying to insult you by asking this question, but, have you ever TIG welded? Have you ever done a hands on weld, not just looking at someone doing it? It takes a lot of coordination of torch distance and filler metal feed to do. If I was trying to automate it measuring arc voltage would be low on my list of things to measure. And yes I have and do TIG weld, have used all types of welding in my years.

 

You are trying to do something new. Most automatic welders for things like that are MIG not TIG. Automatic TIG welding is usually done by simple fusion welding on a linear surface. TIG also needs a way to feed the filler rod, for joints that aren't very close fitting, no gaps. Like two machined parts, with no corners or projections.

Most automatic welders for other things, things that are saw cut or have corners or projections are done by MIG. MIG uses the filler metal for the electrode and is far more forgiving to both fit and distance.

I'm not trying to insult you by asking this question, but, have you ever TIG welded? Have you ever done a hands on weld, not just looking at someone doing it? It takes a lot of coordination of torch distance and filler metal feed to do. If I was trying to automate it measuring arc voltage would be low on my list of things to measure. And yes I have and do TIG weld, have used all types of welding in my years.

While it's possible I don't think there is a simple DIY solution to translate arc voltage directly into a gap offset. As for TIG welding? Yes, I've worked in several Naval shipyards building custom parts for computerized weapons systems for ships up and down the west coast in the 80's.

 

You are trying to do something new. Most automatic welders for things like that are MIG not TIG. Automatic TIG welding is usually done by simple fusion welding on a linear surface. TIG also needs a way to feed the filler rod, for joints that aren't very close fitting, no gaps. Like two machined parts, with no corners or projections.

Most automatic welders for other things, things that are saw cut or have corners or projections are done by MIG. MIG uses the filler metal for the electrode and is far more forgiving to both fit and distance.

I'm not trying to insult you by asking this question, but, have you ever TIG welded? Have you ever done a hands on weld, not just looking at someone doing it? It takes a lot of coordination of torch distance and filler metal feed to do. If I was trying to automate it measuring arc voltage would be low on my list of things to measure. And yes I have and do TIG weld, have used all types of welding in my years.

No problem. You are right I have never TIG welded. I only focused on what company asked for.

 

Are you trying to invent an orbital welder. https://www.swagelok.com/en/product/welding-system# "We" used one of these for welding a bunch of VCR fittings. That thing was so cool.

We had a leaky fitting and the TIG/ARC welder we had was HUGE. It really wasn't "portable". One guy called my wiring a "Kill-me-quick" and I earned that reputation a few times.

#1. I opened up a low current 240V outlet and pulled the wires out and connected it to the very large diameter wires of the welder with wirenuts.

#2. Another time, I had to fix a valve controller, so I had to take it out of service for a little while. It was for a vacuum system. I "stuffed" the valve wires into 120V outlets. The outlets were on a outlet strip with individually switched outlets. I actually think I did this 2x on 2 different systems.

 

As for TIG welding? Yes, I've worked in several Naval shipyards building custom parts for computerized weapons systems for ships up and down the west coast in the 80's.

Wow! From all of the "jobs" you say you've had over the years you must not be able to hold one very long.

 

No problem. You are right I have never TIG welded. I only focused on what company asked for.

To get a better idea of what your up against in doing this you need to have someone show you how to TIG. Not necessary to be an expert but to just get the feel of how the process works. Are the parts to be welded machined joints? How thich is the metal?

 

Wow! From all of the "jobs" you say you've had over the years you must not be able to hold one very long.

Are you saying I'm lying because you can't conceive of a person learning a simple skill (it's not rocket surgery ) like welding over a lifetime?

Welding was a valuable skill in the 80's that I was interested in, had the equipment and means to work with in addition to other things in my line of work that involved working on ships being overhauled during the 600 ship Navy push. Being able to make a small jig or fixture was a time saver for me to compete a job on time instead of asking some union shop that took days. Some of us don't have physical or mental limitations on what we can do over a lifetime of work.

 

Years ago I was involved with measuring arc voltage to some extent. Prior to the arc starting there was the open circuit voltage which as I recall was about 100 volts give or take, The arc was started by an RF burst. One big problem was that RF would destroy the meters people were trying to use. The machines were older before real nice new stuff came along. So here is what was done. A choke was placed at the weld head and that eliminated any RF start problems. Next there was a voltage divider circuit to reduce the open circuit voltage. Then the open circuit voltage was fed into a comparator circuit and when it dropped to a preset level the arc voltage was measured and actually recorded. I have forgotten what choke value we settled on. Also I understand in the TIG welding world they have moved from a scratch or RF start to something called a lift start but not being a welder I haven't a clue. Anyway the way I would look at measuring arc voltage would be start measuring once there is an arc and the way to know that I would look at a comparator circuit.

Ron

 

Hi Everyone,

I am working on an arc welding machine. I would like to measure the arc voltage between the metal part I do weld and the welding machine. There ,sparks a high voltage around 300V or more when the welding machine is first ignited. Then, it settles down to 10-15 volts which is the most I interest in. I tried voltage divider method. But, it doesn't work simply as I expected. My op amps burnt. I would really appreciate your ideas and help.

High voltage spike usually made by output inductance.your output filter that common in welders make very high transient response (because current is so high in welders).its always hard to see transient response because this happened in a short time you need to have a digital oscilloscope or a peak detector.

 

Also I understand in the TIG welding world they have moved from a scratch or RF start to something called a lift start

All of the TIG welders I'm familiar with , or at least the ones worth ahving, use a RF or high frequency start today. Lift and scratch start are two names for the same thing.