New Brymen BM2257 Multimeter

[EEVblog]

but is the 257 not based on the 235? or is the 235 based on the 257? or is there some other intermediate model that we have not seen yet that links them all together?   

The BM235 came after the BM257.
I wanted to sell the orignal BM257 but they said no, and to wait for the BM235 they were working on, which took about a year BTW.

[J-R]

A thought on the jack placement:

If you line up all of the Brymen DMMs you can see that they really only have to keep track of a handful of building blocks: enclosures, PCBs, jacks, LCDs, etc.  And I'm confident the final assembly is done by hand.  So it's trivial to add another product to their lineup because they just need to spray the top cover a little differently, apply different stickers and have the pick/place machine add or remove components as the PCB goes by.  Then it's all brought together for assembly/calibration/etc.  They don't have to place an order for a million units and hope they sell over the next 5 years; they can make just enough for that quarter's demands.

To bring that paragraph together, I think they are always going to be adding new products on a regular basis to cover even the furthest corners of the market.  There are probably just as many people who insist on having the A jack next to common as there are people who want mAuA next to common.

Looking back through DMM design, it seems a lot of them don't have a mA jack at all, only A - COM - V, in that order.  So when a designer was initially adding mAuA they probably placed to the side to avoid offending existing users.  Eventually, designs came out with the order changed to what is maybe a more common arrangement of A -mAuA - COM - V, of which Fluke and Brymen's high-end DMMs currently follow.

Ultimately, test equipment is SO different, it's never going to be realistic to standardize on this or even things like selector switch order.  You always need to think before you leap...

[EEVblog]

They don't have to place an order for a million units and hope they sell over the next 5 years; they can make just enough for that quarter's demands.

Brymen don't even do that, they never carry excess stock. They literally make to order, and there is at least a two month lead time on all orders. Dealers like myself have to plan ahead and work around this.
Many times I have forgotten this and been left without stock for months.

[EEVblog]

Teardown photos:
https://www.flickr.com/photos/eevblog/albums/72177720320285816

[Fungus]

What's with all the wires?

[EEVblog]

What's with all the wires?

PCB routing constraints I would presume. Probably compliance reasons forcing a certain layout and they have to work around that.

[Furna]

What's with all the wires?

PCB routing constraints I would presume. Probably compliance reasons forcing a certain layout and they have to work around that.

Compliance with?
I have the idea that the more cables you put in a DMM the less compliant with anything.

From the functionality perspective I do not really care; if it measures within specs I am fine.

[EEVblog]

What's with all the wires?

PCB routing constraints I would presume. Probably compliance reasons forcing a certain layout and they have to work around that.

Compliance with?

The various CAT requirements and the Low Voltage Directive (LVD) 2006/95/EC etc

For example, my new 1980s pocket meter from Sanwa has just had to have some PCB changes in terms of creepage distances due to the LVD requirements.

[floobydust]

Teardown photos:
https://www.flickr.com/photos/eevblog/albums/72177720320285816

From the pic, confirm the ferrite bead L4 is actually soldered, it looks bad. Likely for current measurement function.
No offense Dave but Brymen still has poor PCB design. El crapola footprints the wrong size, as always. I think they are better with this board but there is a limit as to how oversized a footprint can be. No idea why a bunch of traces have removed soldermask on them. Hint: not a guard-band lol.

[EEVblog]

From the pic, confirm the ferrite bead L4 is actually soldered, it looks bad. Likely for current measurement function.

Joint looks fine from that photo, the pad likley extends under the component.

[blue_lateral]

Do I offer yet another meter, (with the new pocket one coming, that would be 5 meters), or do I <snip>

Sure BM2869s ... I am not good at understanding how companies name their products series over the years.

My new pocket meter is the 1980s 

<snip> For example, my new 1980s pocket meter from Sanwa has just had to have some PCB changes in terms of creepage distances due to the LVD requirements.

I've googled the crap out of this and got nowhere. I gather there is a new EEVblog pocket meter in the works? The only references I can find are to a Sanwa pocket meter from about 6 years ago that is no longer in the store. I'm just curious. Is there a thread somewhere?

[EEVblog]

I've googled the crap out of this and got nowhere. I gather there is a new EEVblog pocket meter in the works? The only references I can find are to a Sanwa pocket meter from about 6 years ago that is no longer in the store. I'm just curious. Is there a thread somewhere?

No thread. It's my own branded updated version of the PM3

[J-R]

I've googled the crap out of this and got nowhere. I gather there is a new EEVblog pocket meter in the works? The only references I can find are to a Sanwa pocket meter from about 6 years ago that is no longer in the store. I'm just curious. Is there a thread somewhere?

No thread. It's my own branded updated version of the PM3

Have you considered branding these Sanwa kits:
https://overseas.sanwa-meter.co.jp/products/teaching_materials/kit-8d.html
https://overseas.sanwa-meter.co.jp/products/teaching_materials/pc20tk.html

[EEVblog]

I've googled the crap out of this and got nowhere. I gather there is a new EEVblog pocket meter in the works? The only references I can find are to a Sanwa pocket meter from about 6 years ago that is no longer in the store. I'm just curious. Is there a thread somewhere?

No thread. It's my own branded updated version of the PM3

Have you considered branding these Sanwa kits:
https://overseas.sanwa-meter.co.jp/products/teaching_materials/kit-8d.html
https://overseas.sanwa-meter.co.jp/products/teaching_materials/pc20tk.html

Interesting. Didn't know they had kits.
Don't know why they have the DCV adjust pot, that seems kinda dumb from a practicality point of view.
The one problem with Sanwa is that their FOB prices are not cheap.

[Fungus]

Don't know why they have the DCV adjust pot, that seems kinda dumb from a practicality point of view.

I assume they aren't calibrated. 

[Kleinstein]

The PCB for the BM2257 looks a bit simpler (less chips) than the BM257. In the data sheet the AC frequency range is quite limited. I wonder if the meter uses some digital RMS internal to the DMM chip - still not mentioning the fast response typical for digital RMS.

The input jack-PCB looks rather similar to the 257 version where I have found pictures.  An update for additional slots and likely possible to fit the new version also to the 257 (or already used in later versions of the 257).

[Fungus]

TRMS bandwidth isn't something I'd go out of my way for in a DMM these days.

I'm sure a $25 FNIRSI oscilloscope can run rings around any DMM when it comes to measuring AC over a couple of kHz, and 12-bit oscilloscopes are under $400.

It's not the 1980s. 

[floobydust]

I won't use a low bit scope to measure ACmV when I'm looking for small dB losses. Love the 80's and multimeters good for over 1.5kHz when needed. The Sanwa kit and pocket meters are not true-RMS, 400Hz spec. as well.
It's OK I'm not expecting the world in something low cost and compact. I'm more worried about them (Sanwa) passing the BBQ lighter test lol

[EEVblog]

The PCB for the BM2257 looks a bit simpler (less chips) than the BM257. In the data sheet the AC frequency range is quite limited. I wonder if the meter uses some digital RMS internal to the DMM chip - still not mentioning the fast response typical for digital RMS.

Yes, all the low end meters from every brand have on-chip true RMS conversion these days.

[floobydust]

I find the low-end multimeters are usually running 8-bit clunker MCU's with the true-RMS done as a H/W DSP section AC-coupled and good to around 1.5kHz
Not sure what silicon-base Brymen is running in this BM2257 but AC freq. response seems to be 40-1,000Hz.

Sanwa pocket multimeters using e.g. Fortune Semiconductor FS9721-LP3 is just a basic rectifier 40-400Hz rated.

[EEVblog]

I find the low-end multimeters are usually running 8-bit clunker MCU's with the true-RMS done as a H/W DSP section AC-coupled and good to around 1.5kHz
Not sure what silicon-base Brymen is running in this BM2257 but AC freq. response seems to be 40-1,000Hz.

Actually, a 32bit clunker, probably the same as in the 78x series, as they seemed to have switched from ROM based devices to flash now, so makes sense to standardise.

[Kleinstein]

For a modern DMM chip including digital RMS makes absolute sense. SD ADCs can work up to the audio range and the extra math to calculate the RMS result is not that much (e.g. can be done even with a 8 bit µC).
The simple digital RMS is also not that bad. On the positive side They could also work ok close to zero, with correct subtraction of it's own noise. They can be fast responding and no issue with lower frequencies.
The analog RMS chips have have to compromise between low frequency accuracy and response speed. Already the need to work well at mains frequency makes them a bit sluggish to respond. So accuracy usually drops, not much below 40 Hz.
So both ways have there pros and cons and a good digital implementation can outperform the old style analog in most aspects. Fast sampling could still add a bit to the power consumption.

Good higher frequency response would however also need compensation at the divider / input amplifier.
Somwhere in the kHz range is a cross over from the resistive to capacitive divider part. With several taps the compensation may not be easy.
So no need for the cheap RMS to work to much higher frequencies and limiting the frequency can reduce the noise.

[EEVblog]

For a modern DMM chip including digital RMS makes absolute sense. SD ADCs can work up to the audio range and the extra math to calculate the RMS result is not that much (e.g. can be done even with a 8 bit µC).

The interesting thing is the modern design Brymens don't even have a DMM chipset, it's just a micro with some analog functionality.

[Fungus]

The interesting thing is the modern design Brymens don't even have a DMM chipset, it's just a micro with some analog functionality.

It's the logical next step.

[mihaip]

Dave, thanks for all your work.

Are you planning a review of this multimeter ?
I'm quite interested in buying this instead of BM257s, but I want an expert opinion first.

Regards