Products > Test Equipment

Brymen BM789

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joeqsmith:
I think the OPs concern is that meters may read what appears to be a normal level.   They just want to know that they are out of range without using the ACV or any other mode.  Again, just my understanding as I boil these few pages down. 

I can believe we could find meters that would show 0.000 mVAC with volts applied.  :scared: 

joeqsmith:

--- Quote from: bdunham7 on September 14, 2021, 04:14:03 pm ---
--- Quote ---So perhaps people who are trying to find a fault in a multimeter should read the manual first :-DMM?

--- End quote ---

A documented limitation is still a limitation.

--- End quote ---
It seems like its an undocumented limitation we are after.   

bdunham7:

--- Quote from: joeqsmith on September 14, 2021, 04:00:11 pm ---The problem I see when looking for these fringe cases is the OP has not provided any constraints. 

--- End quote ---

I agree, and didn't realize until he posted it that he doesn't have an actual AWG. That makes his test hard to replicate reliably.  I'm sure either you or I can make any meter display a "wrong" reading fairly easily.  A good challenge might be to come up with a signal that 'good' meters get wrong but the Harbor Freight free one reads correctly.

bdunham7:

--- Quote from: joeqsmith on September 14, 2021, 04:21:09 pm ---It seems like its an undocumented limitation we are after.

--- End quote ---

Yes, the lack of an overload indication even at higher voltages seems odd, which is why I had speculated that perhaps the clamping circuit was breaking down too early.  But that's just rampant speculation that needs to be tested.

Caliaxy:

--- Quote from: AndrewBCN on September 14, 2021, 04:12:36 pm ---I have one suggestion for the firmware engineers at Brymen: please program the BM789's MCU to display the following characters when the ACmV or AC+DCmV ranges are selected and an input peak voltage including DC offset > 1000mV is detected:

RTFM

Honestly, why didn't they think of that?  :-DMM

--- End quote ---

If I understand correctly, the chief complain here is not that the meter cannot measure outside its published specs (DC offset > 1V in AC mV mode), but that it displays erroneous values when this happens (as opposed to "OL"), tricking the unsuspecting user (other people, of course, not us, because now we know it).

BTW, the AC+DC mV mode (a press of a button away from AC mV) displays OL correctly under these conditions. Then you need to press the yellow button 5 more times to return to the AC mV mode (which is why I'm not in love with Brymen...)

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