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Best Budget 6.5 Digit multimeter
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maxwell3e10:
As a point of reference, here is a comparison of Allan variance for HP3457 and Keysight 34465 and 34470. Even 34465,  a top-brand 6.5 digit meter, drifts too much, in my opinion. Well, it does give 6 digits stability at 10^4 seconds, but not any more than that. In general, I would say modern equipment, even from A-brands, just barely meets the specs these days. Older equipment usually was significantly better than specs.

And unlike say oscilloscopes, which are more WYSIWYG, multimeters have many ranges and obscure effects, it takes a highly experienced and dedicated team of engineers (with few project managers and accountants) to properly design one. So for measurements that really need 6 digits, I would definitely choose an old used meter. Newer budget meters only have an advantage of a graphical display for real time monitoring of short-term changes. But  there are several ways to easily read and plot data over GPIB developed by members of this forum.
Kleinstein:
The grapf for the Allan variance is not that relevant for the meters accuracy. 1 µV of standard deviation in the 10 V range would already be the limit where one would consider it 7 digit resolution. The noise noise part is one where even the relatively cheap one can be OK and easily meat there specs. This part is easy to check and also easy to come up with reliable specs. 

The more tricky part is the stability with changing temperatur and especially the long term drift. Here it is even hard to come up with good specs for a new meter.  It is only a good guess how much it may drift in the next years to come.

The old HP3457 is one meter that may not be the best when it come to long term drift, because of the somewhat odd internal design with a 3 V prime range.
The general tendency with the more modern meters is that the noise noise got better, but the long term stability not so much or not at all.
The low cost 6 digit meter are based on SD ADC chips and there good long term stability is a bit more tricky.
maxwell3e10:

--- Quote from: Kleinstein on October 13, 2022, 09:01:30 am ---The old HP3457 is one meter that may not be the best when it come to long term drift, because of the somewhat odd internal design with a 3 V prime range.

--- End quote ---
And yet this data clearly show that 3457 drifts less than 34465. As for long term drift in calibration, I find that  A-brand meters are somewhat comparable, i.e. older meters drift similar amount in 30 years as newer meters drift in a few years.
https://www.eevblog.com/forum/metrology/usa-cal-club-round-2/msg3552046/#msg3552046


bdunham7:

--- Quote from: maxwell3e10 on October 13, 2022, 02:09:17 am ---As a point of reference, here is a comparison of Allan variance for HP3457 and Keysight 34465 and 34470. Even 34465,  a top-brand 6.5 digit meter, drifts too much, in my opinion. Well, it does give 6 digits stability at 10^4 seconds, but not any more than that. In general, I would say modern equipment, even from A-brands, just barely meets the specs these days. Older equipment usually was significantly better than specs.

--- End quote ---

I'm not sure what we're looking at there.  What is the initial condition of these meters at the start of the graph (are they fully warmed up), what are the thermal conditions of the room, etc?  And what specifications are the newer meters 'just barely meeting'?

coromonadalix:
Thats why sometime getting an old model  can or could be the best  ... they have aged

You have some good software here to do logging

An 3457, 34401a,  8845, 8846 could be useful etc ...   many meters are supported in the software


For 10-20 amps current measurements, simply use a  dedicated shunt or a clamp meter,  more practical and you wont blowup  10-13 $ fuses in case of a problem
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