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Recommend UK calibration service please?

terryn

Oct 27, 2017
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I'm looking to get a couple of DMMs calibrated (HP34401a and Fluke8842a).

Can anyone recommend a good service please? Not too expensive as I'm a home engineer (hobbyist!).

Thanks
 

kellys_eye

Jun 25, 2010
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I don't know of anyone that's cheap.... but I'd ask the question why?

It is possible to purchase some pretty accurate voltage reference units that would offer accuracy better than 0.1% which would, for a hobbyist, be more than sufficient. These are based on now very common industrial calibration devices that can be relied upon. IIRC Practical Electronics had a project offering such - I built one for the sum total of around £10!

If you then purchase a 0.1% (or better) stable resistor you can derive a 'standard' current and resistance !!

Unless, of course, you have a particular requirement for accuracy exceeding 0.1%?

Here's the datasheet for the active device it's built around

http://pdf1.alldatasheet.com/datasheet-pdf/view/48068/AD/AD584.html
 

dorke

Jun 20, 2015
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The HP34401A has no "mechanical calibration" inside it .
The manual does recommend calibration at least once every 2 years.
This is mandatory if your meter has been repaired!
If not,in practice you can do it yourself through the extensive "self test".
Read about it in chapter 4 of the 34401A service guide .

Once you have one trusted meter ,you can compere the readings to any other one you have and verify calibration of all your other meters.http://www.keysight.com/upload/cmc_upload/All/34401-90013-mla2.pdf
i.e. if you do decide to send your DMMs out for calibration(I agree with the folks here who say you don't as a hobbyist ),you need to send just one,the most accurate one!

BTW,
these 2 DMMs aren't exactly the 4$ hobbyist type;)
 

terryn

Oct 27, 2017
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Kellys_eye and dorke. Thank you for your quick replies and helpful suggestions. You've certainly made me think. Perhaps I should have given more information in my original post.

My main interest is repairing and restoring equipment from the 60's - 90's, mainly test equipment and audio. So calibrating against a reasonably accurate reference is quite important for me. While I have lots of kit, I'm frustrated by finding that none of it ever seems to agree! So my thinking is that I should splash out on a good piece of kit e.g. the 34401A and use that as the reference for everything else (as dorke's suggestion). I can justify getting such a DMM by buying a tired / broken one and calibrating it.

Kellys_eye: I have in fact already done exactly as you suggested, and attached is a pic of my 5V standard based on a design by Skullcom on YouTube.
. It has out of the box accuracy quoted at 0.01% and can be further tuned externally. I have a set of resistors rated at 0.05% (cost me £3-4 each), so can produce a range of DC voltages and currents., Pic attached of the unit built into a business card box. I need to fit stouter wiring when I get a moment.

This works well to confirm calibrations for low voltage DC but to follow the calibration procedure properly you need a range of voltages and resistances. For example, my Keithley 177 requires 19mV, 190mV, 1.9V, 19V, 190V and 1000V and that's just for DC voltage!

dorke: Understood that calibration is performed from the front panel, but I believe you still need an external calibrator to provide the reference. The Agilent manual suggest the Fluke 5700a or the Agilent 3458a, both of which are of course rather expensive. The self tests only confirm performance, not allow a recalibration if the unit has been repaired for example.

Thanks again, and do shout at me if I'm still missing anything :).


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dorke

Jun 20, 2015
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Well,
If you are into test equipment repair you definitely do need to have a calibrated and very accurate DMM.

You didn't specify which kind of equipment...
There are so many types, which may require calibrators for R,L,C,ACV,RF power,distortion etc...
you may end up having a full Calibration LAB.:)

BTW,
I was once told that HP(now Keysight) had relatively reasonable prices for calibration
,worth checking about the DMM.
 

kellys_eye

Jun 25, 2010
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I was going to suggest scullcom for a reference voltage! Nice to know we're on similar thought lines.

Clearly you have more than is required for a amateur setup and I can now understand your reasoning for accurate references. Sadly I have no further assistance to offer re a cal lab - when I was required to have test equipment calibrated it went off courtesy of the company expense sheet and all I knew of it was when it came back 'calibrated'!!!

Regardless, I would always be suspicious of calibrated equipment anyway - unless I had two or three sets to compare with I would never know if I was progressing with 'out-of-cal' setting up procedures! Didn't bare thinking about too intently..... fortunately there wasn't much need beyond a fraction of 1% for most cases so the problem rarely arose.

Maybe it's time someone came up with a universal 'calibrate-everything-from-one-box' solution. It can't be far off happening given the state of accuracy of some cheap devices nowadays!
 
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