Brymen BM235 Calibration Procedure - Page 1
Forum section: electronics / testgear

author: hgg
author_rank: Frequent Contributor
timestamp: March 15, 2019, 10:39:20 am
content: 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.

author: cs.dk
author_rank: Unknown
timestamp: March 15, 2019, 11:34:41 am
content: How do you know which meter is the more precise?

author: hgg
author_rank: Frequent Contributor
timestamp: March 15, 2019, 11:56:51 am
content: So, do you know the answer?

author: hgg
author_rank: Frequent Contributor
timestamp: March 16, 2019, 04:24:36 am
content: ??So many people have the BM235 and nobody knows anything about its calibration procedure?

author: cs.dk
author_rank: Unknown
timestamp: March 16, 2019, 05:20:08 am
content: 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.

author: hgg
author_rank: Frequent Contributor
timestamp: March 16, 2019, 05:24:40 am
content: But have you tried it?When I press the button combination and power up the meter I get the symbol 'C' and whenI let go the buttons, it just returns to normal. Does the 'C' stands for Calibration? It seemsthat the procedure is different from the BM869.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 16, 2019, 12:05:03 pm
content: 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

author: hgg
author_rank: Frequent Contributor
timestamp: March 16, 2019, 12:45:01 pm
content: Are you kidding me ?!?Calibration procedure for the BM869 is public while the one for the 235 is a secret?Are you sure?

author: EEVblog
author_rank: Unknown
timestamp: March 16, 2019, 01:13:21 pm
content: 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.

author: EEVblog
author_rank: Unknown
timestamp: March 16, 2019, 01:17:11 pm
content: Quote from: hgg on March 16, 2019, 05:24:40 amIt's slightly different but close enough to figure out.

author: hgg
author_rank: Frequent Contributor
timestamp: March 16, 2019, 01:20:36 pm
content: 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 forcalibration. Will they be able to calibrate it, or is this a secret for everybody? I hate to see myUni-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!

author: EEVblog
author_rank: Unknown
timestamp: March 16, 2019, 01:32:56 pm
content: Quote from: hgg on March 16, 2019, 01:20:36 pmA 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.

author: hgg
author_rank: Frequent Contributor
timestamp: March 16, 2019, 01:36:16 pm
content: 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.

author: 2N3055
author_rank: Super Contributor
timestamp: March 16, 2019, 02:46:23 pm
content: 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,

author: joeqsmith
author_rank: Super Contributor
timestamp: March 16, 2019, 05:00:03 pm
content: Quote from: 2N3055 on March 16, 2019, 02:46:23 pmThose three counts will drive them nuts.

author: hgg
author_rank: Frequent Contributor
timestamp: March 16, 2019, 05:03:29 pm
content: With 3mV you can go to the moon!

author: IanB
author_rank: Super Contributor
timestamp: March 16, 2019, 06:23:23 pm
content: 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.

author: hgg
author_rank: Frequent Contributor
timestamp: March 16, 2019, 06:42:35 pm
content: 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..

author: EEVblog
author_rank: Unknown
timestamp: March 16, 2019, 11:59:33 pm
content: Quote from: IanB on March 16, 2019, 06:23:23 pmI 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

author: hgg
author_rank: Frequent Contributor
timestamp: March 17, 2019, 10:12:26 am
content: 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?

author: Gyro
author_rank: Super Contributor
timestamp: March 17, 2019, 10:52:23 am
content: 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?

author: beanflying
author_rank: Super Contributor
timestamp: March 17, 2019, 11:01:55 am
content: Quote from: hgg on March 17, 2019, 10:12:26 amThe 121GW Cal procedure is in the manual. It is far from trivial to recal however.

author: hgg
author_rank: Frequent Contributor
timestamp: March 17, 2019, 11:08:21 am
content: Perfect.

author: Fungus
author_rank: Super Contributor
timestamp: March 17, 2019, 11:28:25 am
content: Quote from: Gyro on March 17, 2019, 10:52:23 am

author: Gyro
author_rank: Super Contributor
timestamp: March 17, 2019, 11:31:07 am
content: Just a bit surprised to see such, err 'dedication' in the Test Equipment section rather than Metrology.

author: beanflying
author_rank: Super Contributor
timestamp: March 17, 2019, 11:45:51 am
content: Everyone starts their journey by just taking a peek into the Rabbit Hole

author: Fungus
author_rank: Super Contributor
timestamp: March 17, 2019, 11:54:22 am
content: Quote from: Gyro on March 17, 2019, 11:31:07 amThe problemonlyexistsbecausehe has "something with higher resolution and accuracy".If he didn't have that fancy HP meter he'd be perfectly happy with the handheld.Moral: Ignorance is bliss.Me? I'm sticking with my $20 ANENGs.

author: beanflying
author_rank: Super Contributor
timestamp: March 17, 2019, 11:59:39 am
content: Quote from: Fungus on March 17, 2019, 11:54:22 amBut is it 'actually' more accurate and to what references. A better resolved inaccurate reading is uselessEDIT: Massive image removedBOO Where is the Fun in that

author: Fungus
author_rank: Super Contributor
timestamp: March 17, 2019, 12:09:57 pm
content: Quote from: beanflying on March 17, 2019, 11:59:39 amJoy comes from creating a closed system where everything reads the same value.

author: hgg
author_rank: Frequent Contributor
timestamp: March 17, 2019, 12:30:20 pm
content: ...

author: beanflying
author_rank: Super Contributor
timestamp: March 17, 2019, 12:33:17 pm
content: Quote from: Fungus on March 17, 2019, 12:09:57 pmSuggesting anyone should re calibrate Meters for the sake of having them agree with each other is pointless and for all the user knows may be worse than they were before they twiddled their knob.

author: Gyro
author_rank: Super Contributor
timestamp: March 17, 2019, 12:42:18 pm
content: ... Followed by 'twiddler's remorse' and a fresh purchase.

author: Fungus
author_rank: Super Contributor
timestamp: March 17, 2019, 01:18:44 pm
content: Quote from: beanflying on March 17, 2019, 12:33:17 pmWhat's the alternative? Having them disagree?How would you know which meter to use if they don't agree?

author: EEVblog
author_rank: Unknown
timestamp: March 17, 2019, 01:30:47 pm
content: Quote from: Gyro on March 17, 2019, 10:52:23 amCorrect. Although I have not actually tried it myself, you could tweak the 500mV range to get the 5V range correct, but then your 500mV would be out. It's just a limitation of this meter.You could be sneaky and tweak the hardware divider if you were desperate enough

author: hgg
author_rank: Frequent Contributor
timestamp: March 17, 2019, 01:55:48 pm
content: Ok, I am not that desperate.The 121GW looks nice, but recently here in Greece the customs are going crazy taxing everything.It would cost me AU$436 ... !Are there any authorized resellers in Europe?

author: Fungus
author_rank: Super Contributor
timestamp: March 17, 2019, 02:00:23 pm
content: Quote from: hgg on March 17, 2019, 01:55:48 pmSimon (board moderator) sells them from the UK but I don't think it's much cheaper:https://simonselectronics.co.uk/product/121gw-multimeter-eevblog-with-probes/(get in quick before Brexit!)

author: hgg
author_rank: Frequent Contributor
timestamp: March 17, 2019, 02:02:31 pm
content: Thank you!

author: Apochrom
author_rank: Contributor
timestamp: March 17, 2019, 02:04:42 pm
content: and here:https://www.welectron.com/EEVBlog-121GW-Data-Logging-Multimeter-mit-Bluetooth

author: hgg
author_rank: Frequent Contributor
timestamp: March 17, 2019, 02:06:44 pm
content: Yes, definitely cheaper than buying it from Australia.Thanks.

author: Apochrom
author_rank: Contributor
timestamp: March 17, 2019, 02:09:05 pm
content: I'm just noticing, Welectron gw121 delivery time 22days...