Electronics > Metrology

How do old (25+ year) digital multimeters measure RMS voltages?

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Dr. Frank:

--- Quote from: acbern on July 07, 2016, 09:31:31 am ---Dr Frank:
You mentioned somewhere you use the Swerleins algorithm. Is there a simple way to do this (I do not want to reinvent the wheel and do programming or so on this one but rather buy old computer gear if need be if there is a readily available code somwehere). Any hints appreciated.
And what about the CREST factor / THD acceptable to the algorithm?
Thanks

--- End quote ---

Correct, I forgot, that the original Swerlein Algorithm is based on a pure sine wave only; higher harmonics will give errors, specified in the description of the algorithm, for up to 1% distortion.
In fact, I use this in conjunction with my Fluke 5200A, which has very low distortion (max. 0.041%).

I also found some other publications, which were extensions to Swerlein, where harmonics were included, but you have to program this on your own.

The source of the Swerlein Algorithm for the 3458A is available on Keysight site, and there's also an executable which runs directly on modern  PCs (even on W10), with N.I. compatible GPIB cards.
That's currently not visible on Keysight.com, but if you are interested, I can send it to you.

Frank

TiN:
I can see related page on Keysight site.
If you have no access to the page and linked files by some reason, I mirrored it here.

Dr. Frank:

--- Quote from: TiN on July 07, 2016, 11:30:53 am ---I can see related page on Keysight site.
If you have no access to the page and linked files by some reason, I mirrored it here.

--- End quote ---

Nope, there's an additional zip, which consists of an installation file. This sets up the Swerlein program as an executable VB program (.exe)

Frank

branadic:

--- Quote ---After my military service, in 1982, I visited the PTB department in Braunschweig, where my Airforce calibration unit had close connections to.

This guy at PTB was designing by hand (the first ever) multi junction thermo couples. These looked relatively simple, and it seemed not so difficult to build.

So, having the right equipment, it should be possible to copy that DIY.
--- End quote ---

Are you refering to something like this? http://www.nist.gov/pml/div684/grp06/acdc.cfm

There are other converter beside LT available like: http://www.nikkohm.com/resistor_thermopile.htm

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