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DMMCheck Plus Multimeter Reference(and other References) - Experiences..

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jchw4:

--- Quote from: jchw4 on July 08, 2023, 04:43:13 am ---
--- Quote from: J-R on July 08, 2023, 04:24:07 am ---I have the original calibration cert from the DMMCheck Plus I purchased from Doug in 2018 and it only has the DCV listed to the 100uV, no further.  I would make the guess that by that point he decided the extra digits can provide a false impression to the customer, so he reduced the resolution to make it clear what can be reasonably trusted and what can't, especially in between calibrations.

--- End quote ---

My original cert is from 2018 too. And it lists DCV to the 100uV too. But later recalibration certificates are more precise. So I would guess the opposite.


--- Quote ---But I don't see the point in idolizing Doug either.

--- End quote ---

Sure. I just demonstrated the two certificates that present attention to details.


--- End quote ---

I feel that I look too aggressive here, but this story just blew me away.


But let me explain which details I had in mind here.

As you can see from my certificate from Doug, these references are often more stable than stated.  I.e. both "before" and "after" DCV values start with "5.0000".
To see the behavior of the reference you need to get into the unstable area, this is why (at least) the next digit is important.

But it is also only important if stated before and after the adjustments too. This way I could estimate how precise my measurements were just before sending it for recalibration.
If it was "5.5000" before the adjustments I would need to double-check what I did just before sending it for recalibration. If it was "5.00001" - probably not.

I have only one DMMCheckplus, so I don't have the total statistics, but looking at the annual stability of all the values, losing the "before adjustments" part and a significant digit is a major loss.
I believe they should know that stability of the values are often better than what they measured.

So I am not saying it is not useful or suitable for this or another purpose. I am just saying that it's a different product now.
Before I could predict the actual value, now I am not sure. There is no information on where the uncertainty area of this particular reference starts.

It used to be a reference (not extremely precise, but with known behavior), now it's just "Check your DMM pass/fail".

The device price is still good, so I would recommend the hardware itself (but I don't have a new version, so I just hope they did not "improve" the hardware part). Hopefully it's just the measurements setup that is now different.


--- Quote ---Not sure about your comment regarding my comment to the issue being out in the open.

--- End quote ---

If you noticed the issue with the L/C board too, then it's fair to assume that we are not alone and many other people have also noticed it.
Do you mean that the issue has to go public to be addressed?


--- Quote ---You said you e-mailed them but they blew you off or whatever, but now you've pointed it out in the forums for everyone to see and we agree with you.  So we should expect them to have to deal with it at some point.

--- End quote ---

No, they did not. We had a very polite discussion. I just learned that they could not provide the data that I needed and stopped.
I don't see any point arguing with them because the lost data won't magically come back, and my knowledge is definitely less than theirs. They want their product to look like this for some reason, whatever.

My point is just that the prior Doug-era experience may not be relevant to the current device. So when comparing it to cheap Chinese references we should not take prior experience into account.

Martin72:
Today my Brymen BM869s..

tomud:

--- Quote from: Martin72 on July 08, 2023, 05:55:11 pm ---Today my Brymen BM869s..

--- End quote ---

Chinese reference voltage for a few dollars, on a relatively poor AD584  :popcorn:

Martin72:
Looks good.  8)

bdunham7:

--- Quote from: J-R on July 08, 2023, 04:24:07 am ---When I received my L/C board I did notice the fact they were using the BK 891 and wasn't super-impressed.  But on the flip side DMMs and LCR meters are known to use different test methods so it's already going to be a tricky situation to get useful numbers.

--- End quote ---

IMO the 891 is more than adequate for this type of low-cost standard given it's objectives and the fact that it is on a small PCB and not some sort of fixture.  The only problem is the 0.05% claim--that's not an easy spec to meet even at much higher cost.  They need to get real about that, although there will be howling if they revise it downwards.

The issue of DMMs and LCR meters giving different results due to the differences in their test methods is a result of the type of capacitor used.  A very high quality, low-D, low-ESL/ESR and low leakage unit--polypropylene, polystyrene, wet tantalum or silver mica--will give similar results on different instruments and to an extent, with different test frequencies. 

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