EEVblog #422 - How To Calibrate A Calibrator

Les Thomaidis shows and explains the calibration rack at the Agilent Melbourne Standards Lab that is used to "calibrate the calibrators". This is where other calibration labs send their multimeter and oscilloscope calibrators to get calibrated.

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[ghffrsfygdhfjkjiysdz]

For those who care: The central calibration agencies (National Institute of Standards and Technology in US or JIST Japanese Institute of Standards and Technology in Japan or similar in other nations) of different nations each have their "golden" standard. For Example the mass unit of Kilogram has 8 cylinders of platinum-iridium metal in different labs across the world. Every so often those cylinders are brought together and have their masses compared with differences recorded. The cylinder in France is the only one that is exactly 1 kilogram; all other ones are very very close but not exactly. For example the cylinder from US NIST may be of a kilogram. Then each national lab will have a set of secondary standards which are regularly calibrated by comparison to the NIST primary standard. Other cal labs would send their standard weights to be calibrated at NIST either against NIST primary standard (Crazy expansive) or against their secondary standards (very expensive). And then you send your scales or set of weights to these cal labs and they cal your part against their primary or their secondary standards. Each step removes the calibration further from the "world" standards increasing the uncertainty of the measurement. This is where the math comes in; to calculate the statistical, combined uncertainty of your part.

[EEVblog]

At this level in the traceability chain all the standards labs send their references around to each other to keep them in periodic check. Note that this is a standards lab and not just a calibration lab, it has a higher level of certification.

[wrlgmail]

Amazing- I used to work for Datron Instruments- and it is a surprise to see HP still using our calibrators to calibrate calibrators. Here in Stuart FL, we made the standards to calibrate- the calibrators, which calibrate the calibrators... decades ago. It was too uninteresting for the crew at Norwich to bother. So the place where this *was once* done is Stuart, Florida. The old Datron facility is now a self-storage building. Very cool.

[PaulTurner_Haizo]

Back in the mid-70's I was the chief digital instrument repairer at S.E. Labs Ltd, later Thorn EMI Datatech. Our fanciest instrument was the SM215 MkII Transfer Standard Voltmeter that cal' labs used for cell measurements. It only had a resolution of 1 uV, like the multimeter in your thermocouple video (that made me grin) but probably much lower uncertainty.

[xm]

I love the way how he doesn't want to tell Dave that they use qualified guess for uncertainty "calculation". I like this method - it save reaaaaly lot of boring calculations. :-)

[EEVblog]

Yep, it's just a bonus. It was going to be part of a larger one about the standards lab.

[tomjones]

Dave is like the Gad Fly of the tech sector...he's always buzzing around nosing into things asking questions and such.

[xm]

HP3458 - that's the most annoying meter I've been forced to work with! There are loads of versions with different fw, so it's miracle if your software works with another one you used for development. :-) But it has unique features - there's no common meter that can sample as fast with such accuracy.

[sbreheny]

Not only do they have to all agree to within some uncertainty level but also ultimately the national labs derive their standards from either experiments which employ a fundamental physical principle (like some atomic resonance) or (less preferred) in a few cases a single international physical standard (like the kilogram mass standard, which is a physical object).

[DMStern]

From the title I was expecting a bunch of engineers getting plastered in the pub.

[EEVblog]

Yes, +/-1degC as opposed to the usual calibration lab across the hall that has a range of 5degC

[IIGrayfoxII]

How do you calibrate the calibrator?
Then how do you calibrate the calibrators calibrator?

[rogertopful]

How do you calibrate the calibrating equipment? Then how do you calibrate that?

[jan.tichavsky]

When you get down to this kind of accuracy, you need to control the humidity as well as temperature.

[PaulTurner_Haizo]

Anyway, our chief engineer left to found his own company and while browsing the junk warehouses of Cambridge, I came across a bank of Weston Standard Cells fresh from a deceased cal' lab, but better by far than just the cells, they had the logs so we had traceability (after a bit of settling down due to moving) That was what made them worth many times what we paid for them.

[Pwaak]

DEEP!...But it cleared up some mystery! Thanks for this video!

[Dreamer]

Felt like on a excursion, but thank you, great video.

[ExplosiveAnyThing]

Thats a video i 've always wanted to see!!!

[TheSurvivalSecrets]

6:15 Dave playing with a light saber behind the camera?

[Gameboygenius]

You should start these videos with something like "Les is a metrologist, not a meteorologist, from Australia, not Austria!"