Brymen BM789

[EEVblog]

2. Low battery indicator - as per the video, the threshold for this is different for the different functions.
   For example, I did some measurements and, when in ACV measurement mode, the threshold for displaying low battery is approx. 3.76V.
   At the same time, the threshold for displaying low battery when in DCV mode is 3.58V.
   Is this intended, I wonder (i.e. Brymen feel confident the meter will display accurate DCV readings even with lower battery levels?)?

Very likely intentional, as the True RMS converter might require extra voltage headroom.
You should treat all multimeters the same when it comes ot the low baterry indictor. i.e if the low battery light is on then take any measurements with a grain of salt.

[mwb1100]

There are several in depth reviews of Brymen meters (among many other brands) on https://lygte-info.dk/info/DMMReviews.html

The reviews include measurements of when the battery low indicator came on and at what point readings became unstable.  The list of Brymen meters reviewed doesn't include the BM78x series, but for the five reviewed two (BM27s and BM869s) remained stable until shutdown or an error message is given.  The others (BM235, BM525s and BM829s) gave what seems to be quite a bit of buffer between the voltage where the battery low indicator comes on and the reading become unreliable.

As I said there is no data for the BM78x series in the reviews, but in general it looks like Brymen takes care to show the battery low indicator well before the meter starts giving questionable readings.


BM235: Meter works down to 1.7V where meter turns off, battery symbol show at 2.5V
       Reading is stable until about 1.8V where it increase significantly (5.000V -> 5.206V)
       
BM27s: Meter works down to 2.3V where meter turns off, battery symbol show at 2.5V.
       Reading is stable until meter turns off.
       
BM525s: Meter works down to 4.0V where it says "InErr", battery symbol show at 6.8V
        The meter reading is stable down to 5.7V on battery.

BM829s: Meter works down to 4.0V where it says "InEr", battery symbol show at 6.7V.
        The meter reading is stable down to 5.6V, then it will show too high value (It was 36% to high at 4V)

BM869s: Meter works down to 5.6V where it says "InErr", battery symbol show at 6.3V.
        The meter reading is stable until it reports "InErr".

[ru_tash]

what is the voltage reference chip inside BM789?

[NoMoreMagicSmoke]

what is the voltage reference chip inside BM789?

The chipset has the same package and pinout as a Hycon technologies HY3131. If that is indeed the chipset used it contains an internal voltage reference.

[ru_tash]

what is the voltage reference chip inside BM789?

The chipset has the same package and pinout as a Hycon technologies HY3131. If that is indeed the chipset used it contains an internal voltage reference.

thank you for reply, if HY3131 then chip's internal reference has 70ppm/С drift.
BM869s has stand alone reference REF43G with 25ppm/С