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Up Topic Welding Industry / Technical Discussions / Welding Machine Calibration Procedure Dialog
- - By eekpod (****) Date 07-09-2008 16:54
Does anyone know if AWS has a code/ specification on how to calibrate welding machines??

It seems like with all the other requirements that are placed on fabricators that there would be a document that would specify how/ when, and what to check on welding machines.

It seems somewhat lax to have a statement" machines shall be calibrated annually at a minimum".  That leave's a lot of options for different ways to do it.  Is there anything out there other than what the manufacturer says.

For instance some people use an Amp Probe while a welder runs a bead.  But when you get into it and talk with the service centers and machine manufacturs they say that's not the way to do it because of the variables with arc length, stickout, and such.  They say to use a load cell that puts a measurable and repeatable load at differnt settings on a machine, thats the true way to check it. 
I would think that this would be considered something that AWS would be concerned with and want to nail down to make sure that at least a minimum amount of consistancy is achieved.
Open to thoughts and suggestions
Chris
Parent - - By bmaas1 (***) Date 07-09-2008 16:58
I have done it both ways.  The problem you may have with a load bank is that they will run your machine thru the full range of it's output which could cause failures in the machine.

Brian
Parent - By js55 (*****) Date 07-09-2008 17:24
There are some good threads on this subject. A search would help. And there is representative disagreement as well.
Just my opinion but I think its difficult for AWS (and I'm not speaking for them of course-just expressing my thoughts-and they certianly aren't alone here if I'm right) to get motivated to jump into the calibration homogenization business (their eagerness to increase income notwithstanding  :) ), though I do believe they have a guideline available, when its difficult, if not impossible, to relate a few amps here and a couple volts there to any failures (a lesson to be learned from ASME here), the AWS restrictions on parameters notwithstanding. Especially considering that actual calibration is rapidly disappearing with solid state digital technology. You don't calibrate a circuit board, you replace it. And so what big difference is there between load banking it or a simple tong meter. Of course the service centers won't be anxious to agree with this I would think. Maybe I'm wrong.
It was after all a service center guy who first asked me what I really needed him for, and suggested how I might simplify things. 
Though I could also be wrong here, there just doesn't seem to be alot of motivation anywhere to rein in calibration except amongst QA hardliners. Those born and bred in the exciting world of audits, files, typos, verification, and reports.
Parent - - By jwright650 (*****) Date 07-09-2008 17:07
Chris,

I think this is partially the reason for the generous tolerances in the Table 4.5 for electrical parameters. If you check the amperage close to the business end of the lead with a amp clamp while welding, and check the voltage....you will be close enough to stay with your WPS.
Parent - - By OBEWAN (***) Date 07-09-2008 17:18
This is a real thorny issue with some of our orbital tube welding equipment.  As little as 1-2% change in amps can make or break some of our weld procedures.  With different manufacturers having different calibration methods, the machines are not always calibrated apples to apples.  If we move procedures between machines we often have to requalify. In fact, some of our procedures require customer approval if we change machines - just like an ECN.  I prefer welding on a load resistor and measuring voltage using an NBS traceable DVM.  That is the method one of our suppliers uses and they supply an NBS cert sheet when they calibrate their power supplies.
Parent - - By eekpod (****) Date 09-18-2009 13:40
I needed to ask for a clarification and didn't want to start a new post so I highjacked this one.

Using the clamp Amprobe to verify/ calibrate a welding machine in the field; when the power unit is 4 stories below and there is about 400' of lead going to the suitcase welder; if the dial on the power unit is set on let's say 300 amps, but the amprobe is checked at the actual gun nozzle and I get lets say 250amps, then I'm good right?

Just because the dial is set high, becasue of all that lead and loss/ attenuation the proper amperage is coming out at the gun.  I want to confirm the actual welder (person) has the machine set right to stay in the variables of the WPS.

Thanks in Anvance for input
Chris
Parent - - By OBEWAN (***) Date 09-18-2009 14:10
I am not sure how much tolerance you can have on your acceptance limits.

I was always taught in my theory classes that voltage drops in a welding circuit, but current stays the same.  So, you should have 300 amps at the arc too.  No?
Parent - By cwi49cwe (*) Date 09-20-2009 15:26
All those theory are fine to use as a basis of understanding an I've used them for many years teaching in trade classes, which very few care about any more today. Most students today ONLY want to be taught HOW to weld and little to nothing ABOUT welding. Back then the " E ; I ; R " formula was a great teaching aid for understanding,  [  E (volts) divided by I ( amps ) times R ( resistance ) ]  , But remember there is a different constant value with the conventional process of C.C. (stick-TIG) or C.V.(MIG, FCAW, SAW). But after many sessions with very knowledgable people at Lincoln and Miller, all those theory ideas with welding are going right out the window with the introduction and advancements of all this highly advanced electronics of todays power supplies. Example: Lincoln's SST and Miller's "adaptive and accu-pulse". These machines read different at the meter than what is actually happening at the arc. It is possible to change one variable ( parameter ) with out effecting another. But in actual practice remember , if absolute arc parameters are absolutely critical and mandatoy, the whole welding circuit MUST be considered.  i.e. ,with those advanced units, 200 ft.plus of lead, work voltage leads not properly attached, loose connection in the WHOLE electrically circuit (leads to contact tips) arc length and wire stick out ( electrical stick out ). Any time I have an AI ( authorized inspector ) question this I immediately get into this discussion about all these variable and it doesn't take long for him or her to take the power supply meter reading as his accepted value. In my opinion, IF you want an accurate and honest calibration that will stand up all by itself , the manufacture has to come in and do there thing. MEGGA BUCKS ..... FOOD FOR THOUGHT ........ 
Parent - - By CHGuilford (****) Date 09-18-2009 16:19
My advice is not to make more of it than is actually needed.
Obviously, some situations require more precision than others - I am assuming run-of-the-mill job site welding here but these principals still apply.

If you have a calibrated volt/amp meter and check the parameteres near the "arc end" of the circuit.

It is OK if your machine meter says 300 amps but the clamp meter says 250.  You now know that a 300 setting will give you 250 amps. Is that reliable/ does that always give 250 amps? Check it several times, even daily if you want.

What if you need an actual 300 amps?  Set the machine to 350, check it with your calibrated meter, and if you have 300 then you're good.  If not, what setting gives you 300 amps?

If you want to check a range, because you need that amount of adjustment, by all means do that.  But do you need to calibrate every 1 amp, 5 amps, 10 amps or will a high/low check suffice?

If your work site conditions are such that you have a lot of day to day variation more/less cable, different power supplies, etc. then check after the change.  Still get 250 amps on the 300 setting?  You're good to go.  If not, then you need to stay on it.

The key to remember is that you may be required to prove your amps, volts, and travel speed and in those cases you need some reliable way to know what those are.  Use what works best for your situation.  If your situation changes then you change with it.
Parent - - By 803056 (*****) Date 09-20-2009 03:48
My personal opinion on the subject is that the intent is to check the meters on the equipment to verify they are operating properly and providing reasonably accurate readings. Amperage and voltage fluctuate while the machine in operation so does it really matter? My response is that it does matter if consistency is expected from one weld to the next, from one welder to the next. The amount of variation is dependent on the welding process and the type of equipment being used. Variation of the welding parameters must be closely controlled when using automatic processes such as orbital welding, but not as necessary with a manual process such as SMAW.

Calibration is typically performed using a load bank so the load is "constant" and the meter on the machine can be easily compared with reading obtained with a meter that is "calibrated" to a "standard". If the meter on the machine is not within a reasonable range it can be adjusted. If the meter is damaged so that it can't be corrected, it should be replaced. 

Meters are a necessity with semi-automatic, mechanized, or automatic welding, but nearly meaningless with a manual process (from the welder’s standpoint) except for QC surveillance. A meter that isn’t functioning properly can lead to unacceptable welding conditions when setting up any machine where arc voltage, wire feed speed, or amperage are essential to producing acceptable welds in cases such as SA, ME, or AU welding systems.

If there is a need to calibrate a meter on a welder, a load bank is easy enough to build. All it takes is a five gallon bucket of water, a one pound bag of sodium chloride, and a couple of plates.

Best regards – Al
Parent - - By tom cooper (**) Date 09-20-2009 21:50
Uhhhm.......say AL-

".....All it takes is a five gallon bucket of water, a one pound bag of sodium chloride, and a couple of plates...."

Can't let you off easy on this. You will have to explain. In disgusting detail please. Thanks.
Parent - - By 803056 (*****) Date 09-20-2009 23:12
I figured someone would ask.

Use a 5 gallon plastic bucket or garbage container; nonconductive, bigger is better.

Fill with water to within several inches of the top edge of the container.

Mix in salt, 1 pound for every 5 to 10 gallons of water. Make sure the salt dissolves completely. It is what makes the water conductive.

Find two plates; steel, aluminum, copper, it doesn't really matter. The bigger the better as long as they fit into the container and can be moved several inches apart. 6 inches wide X 10 or 20 inches in length, as long as they don't hit the bottom of the container.

Punch holes in the plates or make a loops from rod stock so you can suspend the plates from a broom handle or other nonconductive material. Keep in mind that the water is going to boil and get the wooden handle wet if it is too close to the water. That isn't good! This is where the garbage container is better than a 5 gallon bucket, but the bucket is better than a sharp stick in the eye.

Construct a Make/Break switch and place it in the circuit. I use a piece of scrap plate and a large diameter welding rod or carriage bolt. This is so you can break the circuit and prevent the welding machine from cooking and going up in a puff of fire and smoke.

Place the plates as far from each other as possible in the salt water. Set the machine at its lowest setting and make contact with the Make/Break switch. Check the voltage and amperage. As you move the plates closer together, the resistance will decrease and allow the voltage to drop and the current to rise. Set the machine to the next higher range and repeat the process starting with the plates as far apart as possible. You can also lift the plates out of the water as a means of controling the current. Lift them out: low current, drop them in: higher current.

Compare the meters on the machine to your calibrated standard (multimeter and clamp-on tongs for most of us). If they are within 10% of the full range, that is usually considered "good enough".

This process creates oxygen and hydrogen gas. It is an explosive combination, so do this outside, not in your shop, garage, kitchen, or bedroom (unless you are looking for a new spouse). The water will bubble and roil and it will generate plenty of heat, so keep your hands out of the water.  There will be a pop or a bang or an explosion when you allow the plates to strike each other depending on the amount of gas generated. The amount of gas generated is dependent on the power, i.e., volts x amps.

It is exciting, it's fun, the kids will love it, the dogs will howl, the wife will scream; "Are you crazy? Are you trying to kill us all?"

She has a valid point.

Good luck.

Best regards - Al
Parent - - By tom cooper (**) Date 09-21-2009 00:43
Thanks for that. The detail was certainly disgusting.     :-)
Parent - - By eekpod (****) Date 09-21-2009 10:43
oh I'd love to explain that to my next AISC auditor how I comfimed  my calibration results with my homemade load cell. 
I wonder how upset the guys in the field would get as we splashed salt water all around the 35 story building trying to calibrate their machines.  Thanks for the tip though, it is interesting. Chris
Didn't they do something like this on Gilligan's Island??
Parent - - By 803056 (*****) Date 09-21-2009 23:30
Yes, but I think it was a radio or was it a high fidelity stereo?

Best regards - Al
Parent - By 803056 (*****) Date 09-21-2009 23:41
I used to use the load cell to burn out the carbon in my diesel welder if it idled for too long a period. If I didn't work it hard enough it would "wet stack". That's when I would put it on the load cell and make that engine get down and growl. Just keep an eye on the voltage and amperage so you don't overheat the generator/alternator.

Best regards - Al
Parent - - By CHGuilford (****) Date 09-22-2009 13:06
Just make sure there is plenty of ventilation to dissipate the hydrogen and oxygen gases that will be generated.
Parent - - By eekpod (****) Date 09-22-2009 17:19
or capture it and run a hydrogen fueled cell car!!
Parent - - By CHGuilford (****) Date 09-23-2009 16:14
Great idea!  I'm just not sure if that is an effiecient way to generate hydrogen - probably not.  But if you're gonna make it anyway it......

Actually I now recall learning about the saltwater load cell some years ago.  I had completley forgotten about it until Al posted it.  Quick, cheap, and it works.
Parent - - By DaveBoyer (*****) Date 10-01-2009 03:12
There is no "efficient" way to generate hydrogen. Electrolysis is the way the environmentalists expect Us to do it, using wind & solar electricity.

The salt water load cell on a smaller scale was used to dim theater lights [as a variable resister] years back, before electronic dimmers.
Parent - By 803056 (*****) Date 10-01-2009 03:33
Cool!

Al
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