Brymen BM869 - measurement of DCV linearity

[Dr. Frank]

Hello,

following the very positive review of Dave about that instrument, I finally bought one, arriving right to-day.
After a quick check against my calibration instruments, it really turns out to be very accurate and robust.

Then I determined the linearity of the extended resolution DCV range, 5 4/5 digits.
That mode promises 530,000 counts, and I wondered, if the last digit of that long scale would be useful.

I used my Fluke 5442A, which has a proven non-linearity of  < 0.1ppm.
I measured the linearity on the 500mV and the 1V range and determined the max. deviation from a best fit line.
All output values were averaged over 10-20 stable data from the BM869.

Results from the tables reveal, that the A/D converter is linear to 2-3 counts or 4-6 ppm.
That means, that all measurements using the normal 4 4/5 digits resolution are accurate to < 1 count  on the last digit, if an exact F.S. calibration has been performed.

Using the DCV extended resolution, the accuracy will approach 0.001% , if the instrument has been properly calibrated.
Certainly, this may be only a short-term accuracy.

Therefore I will monitor the stability of this instrument, to qualify the overall uncertainty, i.e. mid- and long-term accuracy, and thereby questioning the 0.02% specified uncertainty.

Frank

[retiredcaps]

Looking forward to seeing the results over a long period of time.  Thanks for doing this even though I don't have a Brymen BM869.

[Lightages]

Thanks Dr. Frank. I have found mine to be very stable over the long term.

[Wytnucls]

Then I determined the linearity of the extended resolution DCV range, 5 4/5 digits.
That mode promises 5,300,000 counts, and I wondered, if the last digit of that long scale would be useful

Don't you mean 530,000 counts?

[Wytnucls]

Could you expand a little on the non-linearity of less than 0.1ppm of the Fluke 5442A.
I have some trouble deriving that figure from the datasheet:
http://www.testequipmentconnection.com/specs/FLUKE_5442A.PDF

[Dr. Frank]

Could you expand a little on the non-linearity of less than 0.1ppm of the Fluke 5442A.
I have some trouble deriving that figure from the datasheet:
http://www.testequipmentconnection.com/specs/FLUKE_5442A.PDF

See here instead:
https://www.eevblog.com/forum/testgear/hp34401-measurement-of-linearity/msg356304/#msg356304

Yep, I meant 530,000 counts, sorry.

Frank

[Dr. Frank]

Here's a quick update.

I measured the stability over 10 min. and 24h on the 5V range.
Temperature was very stable, 21.1°C over 24h.

The 10min standard deviation (600-1200sec), a parameter for the noise, gives 2,36ppm, about +/- 1digit.
After a warm-up phase, the reading stabilized very well, better than +/- 10ppm.
That would also be the DCV  transfer accuracy of the instrument.

The 24h stability gives 3,2 ppm noise, same order of magnitude, i.e. 1.5 digits.

The 24h stability is better than 20ppm = 0.002%, if you include the drift at the beginning.

Very well for an instrument, without an ovenized reference.

Frank

[Fsck]

did you notice any fluctuations due to voltage source? (I'm guessing you're using a battery and not hooking the thing up to a precision PSU)

I'd personally be curious to see if there are any differences from max input voltage allowed and min voltage before it cuts out.

[Dr. Frank]

10min stability was done on battery, 24h on a stable PSU.

I have checked the supply compliance.

The instrument delivers rock stable F.S. readings , i.e. no measurable change down to 6.4V supply voltage. Battery low warning starts earlier, around 7V already, afaik.

Frank

[Dr. Frank]

After one year, I checked and recalibrated my BM869 (vs. 3458A and 5442A, 5200A, resistance box).

First, here are some "as found" values:

DCV:              deviation     specification
500.074mV     +0.015%    (0.02%/yr.)
5.00051V        +0.010%    (0.02%/yr.)
50.0059V        +0.011%    (0.03%/yr.)
500.073V        +0.015%    (0.04%/yr.)
1000.17V        +0.017%    (0.15%/yr.)

Ohm, 3458A    BM869    deviation    specification
500.066          499.92    -0.03%      (0.07%/yr.)
4k99999         4k9987    -0.026%    (0.07%/yr.)
49k9988         49k989    -0.02%      (0.1%/yr.)
500k017         499k92    -0.02%      (0.1%/yr.)
999k997         1M0002   +0.02%     (0.3%/yr.)

DCI                deviation        specification
500.06µA        +0.012%       (0.15%/yr.)
5000.6µA        +0.012%       (0.1%/yr.)
50.008mA       +0.016%       (0.15%/yr.)
99.99mA         -0.01%          (0.15%/yr.)

ACV, 1.1kHz     deviation        specification
500,03mV        +0.006%        (0.3%/yr.)
5.0003V           +0.006%        (0.4%/yr.)
50.009V           +0.018%        (0.4%/yr.)
110,16V           +0.15%          (0.5%/yr.)


Therefore, these ranges are well inside specification.

Then I recalibrated DCV and OHM and again rechecked the ranges.
All DCV ranges were spot-on afterwards, to the last digit.

Ohm has to be calibrated on 1/2 of full scale, i.e. at 250 Ohm, 2k5, 25k, and so forth.. that's a little bit strange, indeed.
When I afterwards rechecked the Ohm ranges  on full scale, i.e. 500, 5k, 50k,.. I encountered a strange phenomenom:

500Ohm was also spot on, but all other, higher ranges were all a little bit low, nearly exactly to the as-found values before!
But the midscale values all were spot-on!

I recalibrated and rechecked all Ohm ranges several times, coming to the same conclusion:

The higher ranges all suffer from a slight non-linearity for values above mid-scale. That's also the reason, why it has to be calibrated on midscale.

I conclude, that the input protection circuitry causes this non-linearity, and that the Ohm ranges before the recalibration did not drift over the year as much, as I originally determined.

That's a slight disadvantage of this instrument, as it could perform better in Ohm mode.

In summary, the BM869 is quite reliable and stable, but needs calibration every year.

Frank

[dadler]

DCV:              deviation     specification
1000.17V        +0.017%    (0.15%/yr.)

Therefore, these ranges are well inside specification, only 1000V DC was a little bit outside.

I am confused - how is the 1000V outside of the spec?

[wraper]

1000.17V        +0.017%    (0.15%/yr.)

Therefore, these ranges are well inside specification, only 1000V DC was a little bit outside.

I don't see figures matching with what you wrote.

[Dr. Frank]

Sorry, 1000V was also well inside spec, like the other DCV ranges.
I corrected my statement already.

Anyhow, the annual drift in DC mode is quite close to the specified limits, therefore an annual calibration really is necessary.

Other brands may have better stability margin.

Frank

[Lightages]

I wonder if the new new revision, BM869s, would have a different drift or at least less error on the ohms range. Brymen revised the input protection and so maybe there is a difference. Staying within spec for a year is pretty good, but not as good as I had expected.

[miro123]

I have pretty much the same experiance with Brymen BM869s
I've bought  BM869s two years ago.
The multimeter has tendency to shows more in DC voltage ranges since the begining but it was acceptable.
The situation got worse since the device started to deviate further away from my 3 Fluke 187 /189s
It triggers me to do calibration + adjustment. AT the moment I did it only at few DC ranges. My two HP3456 ,one HP34970A and ARRAY 3500 are spot on. T=23.2C Rh=45% for at least 24h. Here are the result

DCV:              deviation     specification
500.126mV     +0.025%    (0.02%/yr.)
5.00124V       +0.025%    (0.02%/yr.)
50.0011V        +0.022%    (0.03%/yr.)
500.118V        +0.024%    (0.04%/yr.)

The number itself does not say a lot. I don't have any tracking history.  I will try to be more more accurate and repeat the measurements 1 year later.
What do I mean with tracking history

1. I ve ordered via local Dutch shop www.eleshop.nl. I don't know how long it stayed at shop shelf.
2. I don't know how big was the deviation when I bought it 2 years ago.

I have one question - can I find back the production date of my BM869s - any sticker or serial number?
==============
I've checked my two fluke 187/189 out of curiosity. They they deviate +-50...+90ppm in DC range +-500mV,5v,50V,500V. It is really impressive numbers for 20+ years multimeter. Flukes have  never seen any calibration/ajdustments.

Another question :Does somebody/except Mr.Frank and me/ did an long term stability check of those brymen meters?

[J-R]

My BM869s was similarly a bit out when I received it a couple years ago from Welectron.  I ran through a DC calibration/adjustment and it's still pretty much spot on, assuming I reproduce the calibration/adjustment conditions exactly.

Because of that, I find the BM869s to be slightly annoying sometimes.  Temperature and time from power-on can cause it to swing high and low, I would say typically about 5 counts at the top of the range in 50,000 count mode (post calibration/adjustment).

Probably we are unreasonable and asking too much of this handheld...