Author Topic: Brymen BM235 Calibration Procedure (Read 6485 times)

hgg · « **on:** March 15, 2019, 10:39:20 am »

Hi,

Does anybody know what is the voltage calibration procedure for the BM235?
(assuming there is one..) I've searched the forum and couldn't find anything.

My Uni-T 136C has been spot on for years!

Thanks.

cs.dk · « **Reply #1 on:** March 15, 2019, 11:34:41 am »

How do you know which meter is the more precise?

hgg · « **Reply #2 on:** March 15, 2019, 11:56:51 am »

So, do you know the answer?

hgg · « **Reply #3 on:** March 16, 2019, 04:24:36 am »

??

So many people have the BM235 and nobody knows anything about its calibration procedure?

cs.dk · « **Reply #4 on:** March 16, 2019, 05:20:08 am »

Since brymen uses their own chipset in their meters, I would believe the procedures are the same for most of their meters; https://www.jackenhack.com/calibrating-brymen-bm-series-multimeter/

Martin Lorton has posted a youtube video on the topic also.

hgg · « **Reply #5 on:** March 16, 2019, 05:24:40 am »

But have you tried it?

When I press the button combination and power up the meter I get the symbol 'C' and when
I let go the buttons, it just returns to normal. Does the 'C' stands for Calibration? It seems
that the procedure is different from the BM869.

coromonadalix · « **Reply #6 on:** March 16, 2019, 12:05:03 pm »

I did receive calibrations procedures for brymen meters but they asked me to not disclose them.... ask Brymen ... you never know ?

Some of the cals procedures are now know with trials and errors and a few hints loll

hgg · « **Reply #7 on:** March 16, 2019, 12:45:01 pm »

Are you kidding me ?!?
Calibration procedure for the BM869 is public while the one for the 235 is a secret?

Are you sure?

EEVblog · « **Reply #8 on:** March 16, 2019, 01:13:21 pm »

You need 50mV and 500mV sources, the dividers take care of the rest. So if your 50mV and 500mV are spot on then it's not possible to calibration tweak the 5V range.
Yes Brymen keep the cal procedure secret. It involves shorting an internal jumper.

EEVblog · « **Reply #9 on:** March 16, 2019, 01:17:11 pm »

Quote from: hgg on March 16, 2019, 05:24:40 am

But have you tried it?
When I press the button combination and power up the meter I get the symbol 'C' and when
I let go the buttons, it just returns to normal. Does the 'C' stands for Calibration? It seems
that the procedure is different from the BM869.

It's slightly different but close enough to figure out.

hgg · « **Reply #10 on:** March 16, 2019, 01:20:36 pm »

David thank you for the reply.
I do not have a 50 and 500mV references but I am willing to take it to the local metrology lab for
calibration. Will they be able to calibrate it, or is this a secret for everybody? I hate to see my
Uni-T being more accurate that the BM235..

If I am close to finding it as you say, I guess I will keep trying until I do!

EEVblog · « **Reply #11 on:** March 16, 2019, 01:32:56 pm »

Quote from: hgg on March 16, 2019, 01:20:36 pm

David thank you for the reply.
I do not have a 50 and 500mV references but I am willing to take it to the local metrology lab for
calibration. Will they be able to calibrate it, or is this a secret for everybody?

A calibration house could request the info I'm sure.
But a calibration "adjustment" will likely cost you more than the meter is worth.
You can use a trimpot for a 50mV and 500mV, you have the other meters for reference.

hgg · « **Reply #12 on:** March 16, 2019, 01:36:16 pm »

You are right I suppose.
Only thing now is to find how to enter the calibration mode.
Maybe I need to open the meter and look for that jumper location.

2N3055 · « **Reply #13 on:** March 16, 2019, 02:46:23 pm »

So to be clear, you have perfectly good working instrument, that has 0.3% + 2d specification for that measurement, that shows 0,12% (3x better than spec) error and you want to mess with it?
Just leave it alone, in few days with different temperature they will all show something different.
My 2c off course, you do with your stuff whatever you like.
Regards,

joeqsmith · « **Reply #14 on:** March 16, 2019, 05:00:03 pm »

Quote from: 2N3055 on March 16, 2019, 02:46:23 pm

So to be clear, you have perfectly good working instrument, that has 0.3% + 2d specification for that measurement, that shows 0,12% (3x better than spec) error and you want to mess with it?
Just leave it alone, in few days with different temperature they will all show something different.
My 2c off course, you do with your stuff whatever you like.
Regards,

Those three counts will drive them nuts.

hgg · « **Reply #15 on:** March 16, 2019, 05:03:29 pm »

With 3mV you can go to the moon!

IanB · « **Reply #16 on:** March 16, 2019, 06:23:23 pm »

My BM235 also reads 3 counts low on voltages in the 1 to 5 V range. It might be a systemic problem with the meter and maybe it can't be adjusted out without upsetting something else.

hgg · « **Reply #17 on:** March 16, 2019, 06:42:35 pm »

Interesting to know so I do not waste a lot of time trying.
I have just contacted Brymen as well asking for the calibration procedure.
I don't expect an answer though..

EEVblog · « **Reply #18 on:** March 16, 2019, 11:59:33 pm »

Quote from: IanB on March 16, 2019, 06:23:23 pm

My BM235 also reads 3 counts low on voltages in the 1 to 5 V range. It might be a systemic problem with the meter and maybe it can't be adjusted out without upsetting something else.

I have not tried the cal procedure myself, but it specifically states that only the 50mV and 500mV ranges are set and the meter relies on the voltage divider for the other ranges. This is different to the BM869

hgg · « **Reply #19 on:** March 17, 2019, 10:12:26 am »

I've checked with a 50mV & 500mV reference voltage.
(that was the closest I could go with a el cheapo 2k chinonsiometer divider..)
Can this error account for the 3mV inaccuracy on the 2.5V reference?
Maybe it needs calibration after all.

What about the new 121GW calibration procedure?
Will you be able to calibrate it?

Gyro · « **Reply #20 on:** March 17, 2019, 10:52:23 am »

If you only have calibration points at 50 and 500mV and if, as Dave says, the other ranges are taken care of by the internal dividers, then the calibration lab isn't going to be able to do anything about the tolerance of those dividers. It sounds as if they are within the manufacturer's spec anyway.

Not quite sure why you are so fussed with a couple of counts on LSD of a handheld DMM when you clearly have something with higher resolution and accuracy?

beanflying · « **Reply #21 on:** March 17, 2019, 11:01:55 am »

Quote from: hgg on March 17, 2019, 10:12:26 am

I've checked with a 50mV & 500mV reference voltage.
(that was the closest I could go with a el cheapo 2k chinonsiometer divider..)
Can this error account for the 3mV inaccuracy on the 2.5V reference?
Maybe it needs calibration after all.

What about the new 121GW calibration procedure?
Will you be able to calibrate it?

The 121GW Cal procedure is in the manual. It is far from trivial to recal however.

hgg · « **Reply #22 on:** March 17, 2019, 11:08:21 am »

Perfect.

Fungus · « **Reply #23 on:** March 17, 2019, 11:28:25 am »

Quote from: Gyro on March 17, 2019, 10:52:23 am

Not quite sure why you are so fussed with a couple of counts on LSD of a handheld DMM when you clearly have something with higher resolution and accuracy?

Gyro · « **Reply #24 on:** March 17, 2019, 11:31:07 am »

Just a bit surprised to see such, err 'dedication' in the Test Equipment section rather than Metrology.


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Author Topic: Brymen BM235 Calibration Procedure (Read 6485 times)

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