Products > Test Equipment
Brymen BM789
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Fungus:

--- Quote from: bdunham7 on September 14, 2021, 02:03:30 pm ---This meter is atypical, although documented in the specs, and would be unable to read power supply ripple in the mVAC range without an external blocking capacitor.

--- End quote ---

Yes, but it's a 50,000 count meter so you should be able to read power supply ripple perfectly well on the normal ACV range.

The only problem is that you have to read the fine manual.


--- Quote from: bdunham7 on September 14, 2021, 02:03:30 pm ---
--- Quote from: Fungus on September 14, 2021, 12:49:45 pm ---You've done several similar tests on bigger scale, adding hundreds of volts of offset on the ACV scale. Many meters fail to handle it gracefully.

--- End quote ---
That was simply a ranging issue.
--- End quote ---

I wasn't referring to that specific case of the 87V giving incorrect readings.


--- Quote from: bdunham7 on September 14, 2021, 02:03:30 pm ---The vast majority of meters will not be able to handle over-range normal mode AC rejection, it's just an inherent limitation that can't be easily solved with one component.

--- End quote ---

Yep. Joe gave the 87V a pass on the incorrect reading because it's quite atypical.

bdunham7:

--- Quote from: AndrewBCN on September 14, 2021, 02:16:53 pm ---Except in this case it's not exactly a "limitation" of the BM789.
An operator error that leads to a DMM incorrect display is anecdotal information of next to zero value.

--- End quote ---

The meter is unable to read AC ripple on a DC bias in the mVAC range, such as a very common PSU ripple measurement.  How is that not a limitation?

As for the value of the information, I don't know why you think it has zero value.  It certainly is instructive about how to avoid a particular issue in using the meter.  Of course, as I posted, it's in the manual too, but who reads those?
Fungus:

--- Quote from: bdunham7 on September 14, 2021, 02:28:35 pm ---To be clear, since you are implying what 'others' agree on and I'm an other, I don't agree and think the meter should show an overload indication.  Whether that's a design issue or a one-off defect with your unit, I don't know.

--- End quote ---

That assume the meter can detect the condition, which is an unknown.

The way to find out would be to have Joe do a video on it. If Brymen fixes it and sends him another meter for his collection then we know it's a firmware issue.   :D


--- Quote from: bdunham7 on September 14, 2021, 02:28:35 pm ---And no, this doesn't happen with most meter designs AFAIK, at least not the ones I have with an explicit mVAC function.  I think it is a result of 'bangforbuckitis' or the manufacturer trying to add as many features as possible at a price point.  Something has to give.

--- End quote ---

Yep. This is a massive bangperbuck meter. Maybe that capacitor plus a few other components was just a bit too much.

Neutrion:

--- Quote from: AndrewBCN on September 14, 2021, 02:16:53 pm ---
--- Quote from: Fungus on September 14, 2021, 12:49:45 pm ---...
Which is fine! It's good to know the limitations of the tools we own, playing is a good way to find them.

--- End quote ---

Except in this case it's not exactly a "limitation" of the BM789. The OP stumbled upon an edge case which is very similar to a operator error, where the BM789's autorange algorithm doesn't compute an appropriate response. The obvious "fix" for this issue is not to reprogram the MCU inside the multimeter (because there is an almost unlimited number of similar edge cases), but to operate the Brymen BM789 following standard good practices, which even a beginner can learn is less than 15 minutes.

Also note that the edge case / wrong operation of the BM789 that the OP stumbled upon is completely different from the methodical stress testing that joeqsmith performs on his DMMs. Joe simulates real-life accidents and situations that the meters are supposed to be able to cope with, within and sometimes beyond their specifications.

Joe stresses the hardware and points to flaws in the design and safety of DMMs, the OP just found an operator error that the programmers at Brymen didn't account for in their autorange algorithm.

I very much enjoy Joe's videos where he goes through various steps to test his DMMs, because what I see is a talented engineer making sure his tools are fit for the job, and this information is very valuable. An operator error that leads to a DMM incorrect display is anecdotal information of next to zero value.

--- End quote ---

Sudden unforeseen  levels of voltages are also real life issues, which you don't want, but it just happens.

Now with this meter if you are measuring 300 mV AC, and the value goes over 500mV, you have to doublecheck it on an other scale.

But we are arguing here about whether it is the intended use of the meter: No it is not (except if one wanted to buy the meter for the mentioned ripple measurement.)
But the real question in the whole topic is whether the missing "OL" indication is solveable in FW.
According to Dave possibly not, 2N3055 provided a possible technical description why not, Joe seems to agree?.


--- Quote from: Fungus on September 14, 2021, 02:19:30 pm ---
--- Quote from: Neutrion on September 14, 2021, 02:00:12 pm ---I also really like the warm white backlight, which is uniqe.

--- End quote ---

OT, but... Brymen do some orange backlights, too, eg. my BM857.  :)



--- End quote ---

 I also like the orange more than the cool colors. Especially during the winter season it is more confy. But still the warm white is my favourite.
Just waiting to see a user configurable rgb backlight  Deep purple would be also nice before going to bed and taking a final look at the meter before sleeping. :)
joeqsmith:

--- Quote from: Neutrion on September 14, 2021, 02:00:12 pm ---
--- Quote from: joeqsmith on September 14, 2021, 01:36:36 pm ---
I certainly have and in cases where the meter doesn't want to switch to the next range,  it makes for a less than impressive review.   I was glad Brymen's engineers were able to sort it out before the meters release.   

The BM789 is not a bad little meter.  Add a few changes like split display and I think I would have a new favorite.    Considering the abuse that both BM869s have seen and their continued trouble free service,  its proving to be more difficult to find something I would take over them.

--- End quote ---

This missing split display was for me the only major point why I could not decide for a while between the 789 and the 869. Is there any major technical reason they decided not to go that way?
Or is it that in some industrial application maybe the big numbers are the number one priority?
I also really like the warm white backlight, which is uniqe.

--- End quote ---

Outside of any influence my small YT channel and posts on DMMs may have had on peoples purchasing decisions, I am not involved with marketing or sales.    I don't work for Brymen and really have no understanding of the hows and whys they or any other DMM company make the choices they do. 

Again,  I find meters that can display more than one parameter at a time allow me to work more efficient.   That's my personal choice.   As a consumer, it's good to have such choices to make! 
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