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Brymen BM037 clamp meter bug: false readings in Crest mode?
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shapirus:
I was going to post this a long time ago, and shot a demonstration video, but never posted.

My Brymen BM037 has a strange bug: in Crest mode, which is made to measure momentary max and min values (within a few ms window IIRC), it shows readings ~4-5 times higher than the actual value is. Normal continuous measurements work fine. It's not a user error: there's no unaccounted for inrush current, it can be seen with plain DC constant current.

Now, the meter shown in the video has this bug in both the 60 A and 600 A ranges. I did communicate with the distributor and they did their best to resolve this. They even contacted Brymen I believe, but it resulted in pretty much nothing. They proposed me to return the meter and refund the money, but I didn't want the money, I wanted a nice clamp meter with good peak current registration.

I don't remember precisely what happened then, but I believe they exchanged the original unit (shown in the video) with another, and the one that I currently own has this bug only in the 60 A range. The 600 A range works fine, and Crest measurements aren't different from normal ones when measuring a stable DC current. I think that was where I considered the issue settled: resolution in the 600 A range is sufficient, as I don't usually need precise measurements of inrush current, and for anything precise and/or low-current I'd need to use a dedicated shunt or Hall sensor connected to an oscilloscope anyway.

Does anyone else have this bug? If not, what's your firmware version (hold the Hold button during power-on)? Mine shows "030d".

Any idea if it can be fixed?

Here's the video showing the issue with the old unit that had it in both ranges. Unfortunately I didn't record what its firmware version was.

electr_peter:
How do you know which meter shows correct reading? What are the specs?
Why would you expect that a cheap DC load supports ideally constant DC current?

It could be a bug, but there is not enough evidence to support it.
shapirus:

--- Quote from: electr_peter on March 26, 2024, 08:23:50 pm ---How do you know which meter shows correct reading? What are the specs?

--- End quote ---
BM869s:


--- Code: ---Crest mode (Instantaneous Peak Hold)
Resolution: 5000 counts
Accuracy: Specified accuracy ± 100 digits
for changes > 0.8ms in duration

--- End code ---

DC current base accuracy is 0.5%+20d in the 10A range.

BM037:


--- Code: ---CREST (Peak-Hold)
Applicability: Voltage and Non-invasion Current functions
Accuracy: Add +/- 250 digits to specified accuracy for changes > 5ms in duration

--- End code ---

DC current clamp base accuracy in 60A range is 1.0% + 5d.



--- Quote from: electr_peter on March 26, 2024, 08:23:50 pm ---Why would you expect that a cheap DC load supports ideally constant DC current?

--- End quote ---
Because it does, it can be verified with an oscilloscope. Of course I did verify this. Not ideal (nothing is), but quite sufficient.
Besides, this bug can be reproduced with any other load, including a plain resistive load (and I did that as well, of course). Take a wire with a dead constant DC current flowing in it, take a measurement with the BM037 in normal mode, and it's well within spec, then, without changing anything, enter Crest mode, and voila, it shows several times (it's not like 30% off) the actual value of the current. Besides, as I mentioned, the 600 A range in my current meter works fine, this issue is only present in the 60 A range. So I assume they maybe forgot to calibrate it at the factory or something like that. Or maybe there's a hardware or firmware bug -- that's why I'm interested to hear if others have seen this behavior too.
electr_peter:
Thanks for clarification. I was thinking about BW limitations and momentary spikes with DC load, etc.
From you description this really does sound like a bug in BM037.
AdAstra:
Did Bryman ever get back to you on this? Wanting to buy one of these but now hesitating. What distributor did you work with?
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