Brymen BM037 clamp meter bug: false readings in Crest mode?

[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]

How do you know which meter shows correct reading? What are the specs?

BM869s:

Code: [Select]

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

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

BM037:

Code: [Select]

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

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

Why would you expect that a cheap DC load supports ideally constant DC current?

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?

[shapirus]

Did Bryman ever get back to you on this?

No, but I have never contacted them directly.

Wanting to buy one of these but now hesitating. What distributor did you work with?

It was one of our local distributors based in Kyiv, so knowing it isn't likely to be of any use to you. They were nice and willing to help, but, alas, they couldn't do much without cooperation on the Brymen side.

Brymen may have fixed this in a later firmware, who knows. This is a nice meter in every other respect besides the mentioned issue, but I surely don't like the manufacturer's overall attitude. I have no direct reason to say one thing or the other about their customer support, it's just my impression. Lack of firmware update support, lack of (non-NDA'ed) calibration procedure info, no schematics, no sign of any involvement with general public on the internet -- nothing. If it works, it works. If it doesn't, you can get a refund -- I was offered one, but I didn't want a refund, I wanted to keep the meter and have this specific issue fixed (or at least paid attention to!), since other meters, at least several of the same batch, had this bug too. But apparently Brymen had no interest in investigating and troubleshooting this bug, so in the end I kept it as it was. I'm still using it from time to time and I still have not seen another clamp meter that I would want to buy to replace the BM037.

Either way, you could get one from a distributor that has an easy return procedure and see if the meter you receive has this bug (and then, if it does, make a hard decision on keeping it or returning it, lol). It would be interesting to know. Or, find a distributor who will agree to test the meter for this particular issue before shipping.

[AdAstra]

Thanks, I emailed them directly with a link to this post, will report if I hear back.

[AdAstra]

They replied with:

“After inquiring, I was told this problem was caused by improper calibration. To re-calibrate BM037 current functions is able to fix it. I was also advised that every BM037 production unit from Year 2003 needs to pass an additional production test point to check if its CREST mode was calibrated properly. Thus the unit with the S/N (manufactured number) from 231xxxxxx does not have this problem.”     

(I assume the 2003 is a typo and they mean 2023.)

[shapirus]

That's nice.

Now I wonder if there's any way of obtaining a calibration procedure for my BM037... I'm even ready to honestly promise not to share the instructions if I receive them :)

[AdAstra]

Try them at info@brymen.com, especially since they apparently know it was an issue.