Electronics > Metrology

Null Detectors/Voltmeters - how useful for a turbo-hobby metrology lab?

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Rax:
I may have the ability to acquire a null detector/voltmeter and would love to hear some thoughts on exactly how useful such an instrument is in today's "extreme hobbyist" home metrology lab.

To note, I have a Kelvin-Varley divider about to reach me soon (an ESI RV 722). I also have a Data Precision 8200, a set of ESI SR1 resistors, and a hoard of other pieces of instrumentation (these not being standards). I am thinking to pair with the KVD I rather need a voltage standard, though the null meter, from my understanding, is critical for applications where it can help avoiding any current draw through the KVD. Exactly how that works in practice I'm still studying.

It'd be great to hear some thoughts on how all these instruments can be put to work. I've read Conrad Hoffman's excellent synopsis and also (not thoroughly) Fluke old edition "Calibration - Philosophy in Practice."

alm:
A null detector has some advantages over a DMM for adjusting dividers, like adjusting a KVD so the output voltage is equal to that from another source (like a differential voltmeter), or when nulling a bridge (like matching resistors in Conrad's article, but also when for example adjusting a Fluke 752A or 720A). You could use a null meter, KVD and a voltage standard to form an old-school differential voltmeter (something no doubt discussed in the Fluke book). You might also be able to use it to compare the ratio of the KVD to the DP 8200 voltage standard for linearity verification / adjustment. It wouldn't be the first on my list, because you can do an okay job with a DMM. But if you an get a good deal, then I think you'll find uses for it.

The Soulman:
It depends on what null-meter you're looking at and what dmm you already may have (that could also be used as a null-meter) and more importantly,
what problem are you trying to solve?

Rax:

--- Quote from: alm on February 23, 2023, 12:54:04 am ---You might also be able to use it to compare the ratio of the KVD to the DP 8200 voltage standard for linearity verification / adjustment. It wouldn't be the first on my list, because you can do an okay job with a DMM. But if you an get a good deal, then I think you'll find uses for it.

--- End quote ---

I think this is something that seems pretty useful. The KVD provides a .1ppm resolution and I think that's why these seem to still be used for primary calibration purposes - Fluke still seems to sell the 720A for both arms and both legs in this day and age, which is pretty similar with the ESI I got - and probably also where it far exceeds what a DMM can do (right?).

Rax:

--- Quote from: The Soulman on February 23, 2023, 01:06:56 am ---It depends on what null-meter you're looking at and what dmm you already may have (that could also be used as a null-meter) and more importantly,
what problem are you trying to solve?

--- End quote ---

Starting with the problem I am trying to solve... a metrology itch? ;)

But seriously, it's repairing and calibrating DMMs and other instrumentation up to whatever level I can possibly get (currently, I'm dissecting a 7.5 digit DMM, as it pertains to its 10V scale...).

The null meters I'm looking at are an HP 419A and a Fluke 845AR.

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