Electronics > Metrology

Prema 8017 (sick ?) vs. Tektronix DM5120 vs. HP 34401A

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I have tried to compare the stability of some of my bench DMMs:
HP34401A (6 1/2 digits),
Prema 8017(7 1/2 digits),
Tektronix DM5120 (6 1/2 digits) (see https://www.eevblog.com/forum/repair/tektronix-dm5120-6-12-digit-multimeter-(need-repair)/msg3076415/)

All of them are connected to the same (cheap) Plexiglas boxed AD584-M reference (AD584KH).
They are configured to perform measurements with the best resolution, with some filtering.
Log covers about 6 hours. Raw data plot (obviously, there is a slight calibration difference between them):

It seems that the reference stability is not bad. Temperature must have rise during the day.
The HP 34401A is very stable, the Tektronix is not bad, but the Prema does not behave as I would expect with "large" jumps at some points.
On this graph, the difference in ppm, centered around 0, vs. the HP that I considered the reference:

I don't know what could explain that, I have already changed the electrolytic filtering caps.
Any thoughts ?


The Soulman:
A bad connection from a connector, relay or switch? do you have the schematic?

The jumps look a little like popcorn noise or a bad connector. Jumps of some 6 ppm look really bad, like a defect or error of some kind. Some smaller jumps, like 0.5 ppm would be normal for a LM399 or similar reference. So this could explain the curve for the TEK5120.

One could do a similar check with a short to see if the noise is more additive (e.g. amplifier) or more multiplicative (e.g. reference).


are the jumps also there if the Premo is connected alone?
There could also be some charge injection from one of the other DMMs.

with best regards


I'd check your 8017 analog board supply voltages and capacitors. That kind of movement is pretty excessive even at 2s integration. What was the integration time by the way, average or auto filter, 10/20/40?


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