Brymen BM869 Resistance Quirk

[cluca1969]

No matter what tests were or will be done by us, Brymen had to be aware of these fields and interferences.
I personally am still waiting for an official response from Brymen.

[bdunham7]

The meter passed the 3 A/m EM field strength compatibility already.

What does that mean?  As in--does the test involve just the meter or the test leads too, and what required for it to pass the test?

[Martin72]

Here it is...

Read the norms, then you´ll find it.

[bdunham7]

Here it is...

Read the norms, then you´ll find it.

Gee thanks.  For only $375 per standard I can read them.  Maybe there's a summary somewhere so I can whittle it down to 3 or 4 to keep it affordable?

EDIT: OK, it looks like of the ones it lists, EN61000-4-8 is the relevant one. https://www.iecee.org/dyn/www/f?p=106:49:0::::FSP_STD_ID:4229

Anyone have a copy?  Does the test require the instrument to remain accurate to specs even with external leads and devices, or just not fail or quit working?

[Wytnucls]

The meter passed the 3 A/m EM field strength compatibility already.

What does that mean?  As in--does the test involve just the meter or the test leads too, and what required for it to pass the test?

Severity Level 2   3 A/m
Performance criterion required: A
Criterion A: The multimeter shall continue to operate as intended without operator intervention

Multimeter modes: Voltage, Frequency, Resistance, Current, PC connect
Multimeter placed inside induction coil (1mx1m)
Coil orientation XYZ in turn
Test duration 5 minutes in each direction

[_Wim_]

Anyone have a copy?  Does the test require the instrument to remain accurate to specs even with external leads and devices, or just not fail or quit working?

Indian standards are a good read...

https://www.eevblog.com/forum/metrology/emi-measurements-of-a-volt-nut/msg3308348/#msg3308348

[dcac]

Down-ranging always occurs at a fixed / digital count of about < 5000 counts.
Up-ranging occurs at random counts. In DCV mode, that's about > 53125 counts, in Ohm modes it's about > 53300 counts.
In the first place,  I tripped about other contributions here, which reported >56000 counts, or so.

Up-ranging is therefore initiated by an over range condition, not by a fixed upper digital A/D value, like in other DMMs (e.g. 1 200 000 ... counts for all HPAK bench DMMs).
Obviously that over-range detection inside the BM869 is realized analogously by a window comparator (OpAmp) which probably monitors directly the input signal over an additional input resistor.

I think what we’re seeing actually is digital switching points for the Up-ranging after all.

What gives the impression of somewhat diffuse switching points that doesn’t seem to occur at the same value each time - is caused by noise and/or low (lower) resolution from the ADC.

What I meant earlier by “dynamic filtering” should rather be called “two stage filtering”. 121GW uses this too - the first stage is the HY3131 Sinc2 filter which is set to give 40 SPS output rate and is used for the Bargraph. The same value is then filtered by the STM32 MCU but with a simple Sinc1 stage and this gives the display output rate of 5 SPS. And 121GW uses this 5 SPS rate + some delays for the auto range which makes it rather slow.

I believe BM869 is configured in a similar manner - but here the first stage filter gives 80 SPS for the Bargraph but this value is then also used for the auto range and will fluctuate just like the Bargraph does when subjected to interference. Then for the second stage filter BM869 likely uses a Sinc4 (or higher) as it has quite noticeably better noise rejection than i.e. 121GW.

It’s also possible the auto range has its own filter settings but one that’s still not nearly as effective as for the final value shown on the display - all to make the auto range faster. But doing it this way the display will never show the exact value that actually caused the range to change.

If BM869 is in fact configured like this it should also be fixable in firmware. It quite strange though that current FW allow auto range to act this fast and hunt back and forth between two ranges without some kind of damping routine i.e. stopping the hunt if it changed back and forth several times within a couple of seconds.

[bdunham7]

Severity Level 2   3 A/m
Performance criterion required: A
Criterion A: The multimeter shall continue to operate as intended without operator intervention

Multimeter modes: Voltage, Frequency, Resistance, Current, PC connect
Multimeter placed inside induction coil (1mx1m)
Coil orientation XYZ in turn
Test duration 5 minutes in each direction

OK, I guess that is just based on the verbiage of the standard.  I found this:  http://www.compliance-club.com/pdf/EMCTestingPart6.pdf
which indicates that 'industrial' meters may be tested to 30A/m, if not more.  Out of curiousity, I got one of those hand-held trifield EF/EMC/RF Power meters and checked around my bench and office.  There are areas that exceed 3A/m (4.75uT) and when I checked on my bench, I just tested near 2 DMMs where they happened to be sitting at the moment, hooked up and testing something.  The highest one read 24A/m (30uT) and 99% of that was caused by the transformer in my Hakko FX888, which was about a foot away.

So, compliance with a nominal standard doesn't imply that it just barely met that standard--it could be a lot better.  But apparently being immune to 3A/m wouldn't keep you out of trouble, at least on my bench.

[Wytnucls]

The point is that manufacturers can't be held responsible if their meters are used in an environment that exceeds the IEC standards.
The onus is on the operator to comply with safety requirements.

[bdunham7]

The point is that manufacturers can't be held responsible if their meters are used in an environment that exceeds the IEC standards.
The onus is on the operator to comply with safety requirements.

I'm more interested in the technical issues and determining what the actual performance issues are here, not assigning blame or denigrating or promoting products..  As far as standards, they are just minimums.  You don't have to live down to them.  And the onus is not on the operator to use the meter within its standard, but rather to select a meter that meets their particular requirements even if those requirements exceed some common standard.

[Wytnucls]

The standards are minimum published safety requirements that manufacturers have to comply with.
While meters may well exceed those requirements, measurement accuracy and operator safety is not documented.

Electromagnetic Compatibility: In an RF field of 3 V/m total accuracy = specified accuracy + 20 counts (Fluke)
What is the accuracy at 30V/m?

[bdunham7]

The standards are minimum published safety requirements that manufacturers have to comply with.
While meters may well exceed those requirements, measurement accuracy and operator safety is not documented.

Electromagnetic Compatibility: In an RF field of 3 V/m total accuracy = specified accuracy + 20 counts (Fluke)
What is the accuracy at 30V/m?

Well, I don't know and I would like to.  'Not documented' can happen for a variety of reasons, not the least of which is the legal department discouraging the publication of any more information than is necessary.  Every claim you make becomes a potential liability.

The link I had was for power line EM fields at 50/60Hz and A/m.  However, my trifield gizmo measures V/m as well and if that is an actual spec from Fluke, then the question is certainly germane because I also see EF readings well over 3 V/m all over the place.  One point in my office had 981V/m, but that is an extreme example and I'm not likely to be making a measurement right in front of my air purifier.

[2N3055]

The standards are minimum published safety requirements that manufacturers have to comply with.
While meters may well exceed those requirements, measurement accuracy and operator safety is not documented.

Electromagnetic Compatibility: In an RF field of 3 V/m total accuracy = specified accuracy + 20 counts (Fluke)
What is the accuracy at 30V/m?

Well, I don't know and I would like to.  'Not documented' can happen for a variety of reasons, not the least of which is the legal department discouraging the publication of any more information than is necessary.  Every claim you make becomes a potential liability.

The link I had was for power line EM fields at 50/60Hz and A/m.  However, my trifield gizmo measures V/m as well and if that is an actual spec from Fluke, then the question is certainly germane because I also see EF readings well over 3 V/m all over the place.  One point in my office had 981V/m, but that is an extreme example and I'm not likely to be making a measurement right in front of my air purifier.

 981V/m would for sure be dangerous to humans..

[joeqsmith]

... because I also see EF readings well over 3 V/m all over the place.  One point in my office had 981V/m, but that is an extreme example and I'm not likely to be making a measurement right in front of my air purifier.

There is a major story here that you need to tell!

Many years ago, I was working on a design for 100V/m.  Something was going on and I had to use an outside lab.  Ended up at Cincinnati Electronics's in Mason.  In the main entryway there was a full size model of a missile.  Their lab at that time could support up to 1000V/m.   You don't want the radar knocking out your missiles electronics.   I went on about my humble 100V/m.     

[bdunham7]

[2N3055]

(Attachment Link)

I have no doubt you can read...

BUT....

Maybe that instrument is reading static electricity field from that IONIZER in the purifier....... ??

[bdunham7]

(Attachment Link)

I have no doubt you can read...

BUT....

Maybe that instrument is reading static electricity field from that IONIZER in the purifier....... ??

Yes, hopefully and obviously, it is a static field.  If it were RF you wouldn't need a radio, or at least you wouldn't need to turn it on! V/m doesn't actually tell you the whole story--frequency counts.  You can see pretty high V/m just from power line effects.  Also, just the great outdoors on a sunny day will give you a vertical field of over 100V/m.  None of those things would matter much to most DMMs, but the air purifier and my Keithley 414a are best friends--the Keithley can tell if the ionizer is on from quite a distance.  The air purifier just sits in the corner quietly until it gets dirty and usually doesn't bother anything, but I have to shut it off a good while before I do anything with the picoammeter or the 1G range on my DMM.

I've no idea how accurate the instrument is, but it seems to identify things correctly and at least sort of matches up with my preconceived notions of what familiar things should emit.  It does tell me that where I sit at my desk I'm exposed to 57V/m of 'mixed' EF and 13mW/m² of RF.  I'm not sure what to think about that.

[2N3055]

(Attachment Link)

I have no doubt you can read...

BUT....

Maybe that instrument is reading static electricity field from that IONIZER in the purifier....... ??

Yes, hopefully and obviously, it is a static field.  If it were RF you wouldn't need a radio, or at least you wouldn't need to turn it on! V/m doesn't actually tell you the whole story--frequency counts.  You can see pretty high V/m just from power line effects.  Also, just the great outdoors on a sunny day will give you a vertical field of over 100V/m.  None of those things would matter much to most DMMs, but the air purifier and my Keithley 414a are best friends--the Keithley can tell if the ionizer is on from quite a distance.  The air purifier just sits in the corner quietly until it gets dirty and usually doesn't bother anything, but I have to shut it off a good while before I do anything with the picoammeter or the 1G range on my DMM.

I've no idea how accurate the instrument is, but it seems to identify things correctly and at least sort of matches up with my preconceived notions of what familiar things should emit.  It does tell me that where I sit at my desk I'm exposed to 57V/m of 'mixed' EF and 13mW/m² of RF.  I'm not sure what to think about that.

I'm just saying ...

That static field would not impact BM869S much, unless in nS mode....

The only thing that would have major impact would be induction in wires from magnetic field..
And that only if it is not common mode..

[Martin72]

Today I did a normal resistance measure in practice, without any disturbances - No wonder, that this "quirk" wasn´t detect in the first time.
Also today, I´ve finally wrote to welectron what´s about this quirk from brymen´s official side, because I want to order a second one.
Apart from this, I got another 100Khz multimeter for free
A fluke 187 was sorted out last week because of fading LCD segments (I know what to do with this) and I raised my hand and shout, here! to me ! 

[2N3055]

F 187 ? Nice!!!
It is same as 189 except logging, which wasn't much anyway, only 100 points..
Congratulations, St. Nicholas was good to you this year.. You must have been good  .

[joeqsmith]

(Attachment Link)

Ok, not too much of a story.   meter = distance.   More it a meter away from the source and you read??

[bdunham7]

Ok, not too much of a story.   meter = distance.   More it a meter away from the source and you read??

Well, V/m doesn't imply an actual whole meter.  981mV/mm would be the same field.  But yes, the field drops rapidly as you move away.  The real field is inside the unit between the plates and what I'm reading is just a bit of leakage loops.  And I don't actually know that it is a static field--when the unit gets dirty it snaps and hums, so maybe rectified but not filtered DC? 

[joeqsmith]

Ok, not too much of a story.   meter = distance.   More it a meter away from the source and you read??

Well, V/m doesn't imply an actual whole meter.  981mV/mm would be the same field.  But yes, the field drops rapidly as you move away.  The real field is inside the unit between the plates and what I'm reading is just a bit of leakage loops.  And I don't actually know that it is a static field--when the unit gets dirty it snaps and hums, so maybe rectified but not filtered DC?

I thought the standards call for a meter minimum to setup the UFA, 3 meters preferred?

[bdunham7]

I thought the standards call for a meter minimum to setup the UFA, 3 meters preferred?

I wouldn't know, but sure, maybe.  If you want a uniform field for some standard test, you'd need a big area.  Same for the EM test, big coils to get a uniform area in the center.  But that's just a standard, and standards are designed to be, well, standard--accurate, repeatable tests, not to necessarily a reflection of any real-world situation.  I'm sure most real-world EMC issue don't involve huge, uniform fields. 

[kwinz]

So no firmware/software update for this?
But I can solder an SMD capacitor in parallel to fix it without messing up the multimeter calibration?