How long do your calibrations take?

[Shox Dr]

Unfortunately lots of people don't seem too worried and all too often I hear "I just need a piece of paper that says my kits ok, and that's all I'm interested in thanks."

There's a massive difference between half a days inconvenience and downtime and 40hours and £1800 more on top, for the same bit of paper when some people are just interested in Covering their own **** and ticking boxes.
It's called covering ones **** while ticking all the b

 

[Jim Davey]

I get that, I really do, but why not make up the certificates yourself if you're really that unconcerned with the accuracy?

 

[Welderpaul]

Companies probably don't make it easy for you, i know i don't.....'Calibrate it, need it doing now, make sure it's done correctly, and the paperwork is right, but god forbid we have any down time on the sets'...how quickly can you do it??

 

[Shox Dr]

I get that, I really do, but why not make up the certificates yourself if you're really that unconcerned with the accuracy?

As I said, butt saving/covering exercise. Nothings cheap, but £1200 is better than £3k all day long. Besides the person tasked with "obtaining" the certs will (I guess) have little knowledge of what is involved,and will be interested in just the bottom line.

example for you, firm I sub to got a Forklift tester in, free (something to do with Gov) but as it was taking too long.

So they kicked them off site: bottomline wins everytime.

 

[Robotstar5]

Will the roll out of EN1090 help?, as in "welding plant must be calibrated to BS/EN xxxx in order to comply with certification". That would rule out the "cowboys" as traceability would would require the correct calibrated test equipment which a bloke with a voltmeter & ammeter in a tatty box would be unable to comply.

 

[Hitch]

We had ours done a few months ago, two guys, a full day. 8 sets. Whip the covers off, blow out, check connections are tight and plug it into a box.. one was taken away to be worked on as it was out of calibration apparently.

I wasn't paying much attention. Box was about the size of a small CRT Tele on a trolley. With some big red buttons on the front IIRC.

 

[Jim Davey]

Will the roll out of EN1090 help?, as in "welding plant must be calibrated to BS/EN xxxx in order to comply with certification". That would rule out the "cowboys" as traceability would would require the correct calibrated test equipment which a bloke with a voltmeter & ammeter in a tatty box would be unable to comply.

No, that's just it. As long as they have the relevant documentation and test kit they are covered. The issue is their clients don't low they are being ripped off. Half of the places I calibrate for the buyer has no clue what I actually do on site and I'm sure I could send out all the same certs from last year but just change the dates and no one would be any the wiser. I wouldn't of course but the fact is the process is very open to manipulation and some cannot resist the lure of a fast buck.

 

[Robotstar5]

....but the fact is the process is very open to manipulation and some cannot resist the lure of a fast buck.

You can get the same thing with disreputable sparkies with whats known as "drive by" testing, most of the forms are already filled in before they start testing.

 

[Jim Davey]

Companies probably don't make it easy for you, i know i don't.....'Calibrate it, need it doing now, make sure it's done correctly, and the paperwork is right, but god forbid we have any down time on the sets'...how quickly can you do it??

It's not really that bad on downtime, just because it might take all day to get through 10 machines doesn't mean all 10 sets are out of action for a day. I can only calibrate one at a time after all and many of the places I go not all the sets are in use anyway so the impact on production is usually minor.

 

[AndyStobbs]

On the subject of calibrations, I've just been playing with the SAF - still making the manifolds on quiet days.
Thought I would stick the current clamp on it for the sake of it, and discovered its miles out. There is no current display on the welder, rather a table which translates each of 10 positions on a POT to an expected welding current.
Have attached two images which speak volumes... So how do I go about dialling it back in - any ideas?

Ah sugar, they've lost the notes with me saving them as JPEG, anyway, top image was set for 50A, bottom image for 75A.

Andy

 

[Jim Davey]

How were you achieving those readings? Arc length and torch/earth length and condition are all major factors.
If you're not working to a procedure Andy I'd just not worry about it, just keep adding amps until things are hot enough.

 

[AndyStobbs]

How does length of lead affect anything? Current in a circuit is conserved.
That's in TIG mode with me welding while the scope did its stuff. Would be nice to adjust it if its just a case of twiddling a trimmer pot.

 

[Jim Davey]

The longer the leads the greater the voltage drop. Sounds a bit over simple for a techy guy like yourself, but it's sometimes as simple as removing the knob and refitting it in a position that more accurately matches the stated output.

 

[AndyStobbs]

The longer the leads the greater the voltage drop. Sounds a bit over simple for a techy guy like yourself, but it's sometimes as simple as removing the knob and refitting it in a position that more accurately matches the stated output.

Surely though, the welding set will aim to achieve the set current, so compensating for any voltage drop?
Need to switch to rods to test the higher current settings, may well find that moving the knob is the easiest option.

 

[Jim Davey]

Only sophisticated machines do that. As far as I'm aware your SAF is a pretty simple machine with no sampling of the returning volts/amps and subsequent correction.
I think your time would be better spent just welding at all settings and making a note of approximate amps.
There's a lot more to it than there might at first seem but if the set works I'd learn to live with it.
Take appropriate precautions to ensure HF doesn't damage your expensive test equipment.

 

[AndyStobbs]

Hf is the red trace in the pictures, taken with secondary ignition pick up clamp. The scope is well screened as its designed to operate near an engine bay, which in the case of petrol vehicles can be pretty noisey anyway.
Current monitorng on SAF is achieved through a module on one side of the rectifier, ie. The weld current passes through this module and it outputs a voltage proportional to the current going through the wire. Think its described as an LMxxxxx something, will have to re-read it. Does that sound plausible for a means of current monitoring?

 

[Wedg1e]

Andy, would it be anything to do with the output being half-wave rectifed DC? When we do MPI machines we get strange readings that are usually about half of the expected output as the measuring kit is only catching the positive-going halves of an AC waveform.

 

[AndyStobbs]

Welding current should be pretty good DC, from the secondaries the AC is rectified then smoothed. Scope would pick up the whole AC waveform anyway, current would just appear as negative.
I can try to hook up a voltage probe at some point, though it'll only be a rudimentary few turns of wire around the leads, as I can't risk direct connection of the scope to the HF, nor am I tempted to try it on rods - scope is just too valuable (and it is an automotive scope after all, not a lab scope)
Will set it up one evening and weld away on as many settings as I have time for and observe the outcome.

 

[Wedg1e]

I thought you were using one of those Pico dataloggers, not sure how it was sampling the output current.
I'm pretty sure my MIGs are all HWDC rather than full-wave. Most clamp-type ammeters get a bit flustered on HWDC.

 

[AndyStobbs]

Its a 600A ac/dc current clamp. Will be interesting to set it up again and deliberately vary the arc length to see how current changes.