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Best Budget 6.5 Digit multimeter
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H.O:
One datapoint on one of the "b-brand" meters - for what its worth.
I have a DM3068 that I got brand new in August 2013. According to its paperwork it was calibrated in May 2013. It has never been calibrated or adjusted since. Unfortunately no data was provided, just a certificate.
I also have a 34410A that I bought second hand a couple of years back. It was last calibrated August 18 2022, so less than 60 days ago. The calibration report provided says that at 10.0V nominal it measures 10.00001V.

After a 45min warmup period, with both meters set to 100PLC:
34410A: 2.49900V
DM3068: 2.49903

34410A: 10.00012V
DM3068: 10.00032V

Lets say that the 34410A is spot on. Then the DM3068 is 200uV out which, I admit, might feel like "a lot". But even the 24h specification for the DM3068 says 0.002% of reading + 0.0004% of range which, if I'm not making a fool of myself equals 280uV. It might have drifted, I don't really know that, but its still within its 24h specification, 9 years down the road. Or did I indeed goof the math?

nctnico:

--- Quote from: ali_asadzadeh on October 10, 2022, 12:25:17 pm ---Hi
This is the first time that I want to buy a 6.5 Digit multimeter, so any feedback is welcome,
My budget is limited so I have these models that are with in my budget.
From Chinese brands we have these models
HDM3065B from hantek that's very similar to keysight 34461A
GDM-9061 from GWinstek
SDM3065X from siglent it's almost a copy of lecroy T3DMM6-5
DM3068 from Rigol

Which model do you choose? why?

--- End quote ---
When on a budget I'd go for the GW Instek. They have been in the DMM business longer and they are a company targeting the professional market.

But it is likely worth it to spend more and go for a Tektronix / Keithley DMM6500 or Keysight 34661A. Nowadays I'd probably prefer the DMM6500 because it is more versatile.
bdunham7:

--- Quote from: ali_asadzadeh on October 11, 2022, 08:53:18 am ---I have found that almost all of the 6.5 Digit meters have horrible tolerances in the order of  0.15%+0.04 for AC current in 10A range, The DC current has it around 0.150+0.010, SO the question is why they have this kind of big tolerance?

--- End quote ---

You have to look at what is feasible to make a judgment like that--and those specs are not 'horrible', they're typical for a good instrument.  If your plans depend on getting significantly better results than that on any reasonable budget, you are in for a shock.  The two issues are that the shunt can only be so large in a bench meter, so the design has to allow for some self heating and rely on a low-tempco shunt--and then there is a practical limit to how accurately you can measure TRMS AC without specific conditions on the measured signal.  The first just depends on how much space and money you want to allot to the 10A current shunt.  The second comes down to how accurately you can measure an AC signal without any guarantee that it is perfectly repetitive.  The answer for most practical technologies is about 600ppm or 0.06% in the 50/60Hz region that you are interested in.  Even if you got a $5K Keysight 34470A with TrueVolt or a $13K 3458A, you wouldn't do much better than that.  To do better than this typically involves some more advanced (expensive) technology like Fluke's thermal converters or the HPAK synchronous subsampling mode--and then you still have the current shunt issue.


--- Quote ---I agree with you, I’m mostly toward HDM3065B from hantek, since it has the most options and the specs are copy paste of  keysight 34461A , it has 30K readings per second too, also I have found an 850$ deal on it. It has front and back plugs, and has USB and Ethernet too. Surprisingly in it’s catalog they have used keysight software for PC side connection!

--- End quote ---

Its physical similarity to the Keysight and the 'copy-paste' of the specs is no guarantee of actual performance.  I have no personal experience with it and I haven't seen any reviews that would address how accurate or stable it is, but I wouldn't be terribly optimistic TBH. 
Kleinstein:
The video on the Hantek 6 digit meter shows a MAX6325 reference, which is a bit more drifty than the LM399 used in more classic 6 digit DMMs (and the HP3468/3478). This reference alone makes the accuracy specs questionable. I very much doubt they would do an extensive (e.g. 500 hours) burn in to at last reduce the long term drift. In addition to the reference the 10 V range would also need some divider, as the ADC (though I don't know the type) very likely only does some 2.5 or maybe 5 V range.  So I would not really count on the accuracy specs - maybe add a k factor of 2 ?  >:D.

From the internals the protection against high voltage spikes also looks not that good. So the cheaper design comes at a price.

I would consider the HDM3065 more like a cheaper "copy" of the SDM3065, not so much to original, though it only offers 10 V and not 20 V with high impedance.

strawberry:
they push hardware to the limits to get 6 digit
even 34401A is basically useful 5 digit
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