Brymen 257s - low resistance measurement  - Page 1
Forum section: electronics / repair

author: mzdenkov
author_rank: Regular Contributor
timestamp: August 05, 2024, 02:19:18 pm
content: Greetings,I recently bought BM257s DMM. When measuring on sub 100Ohm resistances, values are a bit off the reading compared to myRigol DM3058E (still has factory calibration).While accuracy of BM257 is 0.5%+4d -> 600 Ohm range, its +- 0.3 ohm (im ignoring the +4d), all measurements are ~0.3 ohm lower.i.e:RIGOL 2W/4W : 4.04 Ohm/ 4.006; BM: 3.7 Ohm;RIGOL 2W/4W : 38.529 Ohm/ 38.487; BM: 38.2Ohm;Is it possible to calibrate only 600 Ohm range?Would it be possible with the "DIY" precision resistor made lake on schematic bellow?- R1: 309R 1%- R2: 10k + 500R multi turn pot.OR is it just me and my OCDBest Regards.

author: giosif
author_rank: Frequent Contributor
timestamp: August 06, 2024, 06:01:45 pm
content: Only responding to the measurement differences part of your post, but have you used the same set of leads between the two multimeters and/or have you zero-ed out the resistance of the leads when taking these measurements?

author: mzdenkov
author_rank: Regular Contributor
timestamp: October 15, 2024, 08:40:31 pm
content: Hello,I did. All measurements were off by -0.3 ohm -> 1.2R was measured as 0.7.I know that in low ohm range 2W mode dsnt work well.After i made my "precision" resistor, which value i checked with my RIGOL DM3058E 4W mode,I've callibrated the Brymen on the 600 Ohm range where DMM asked for 300.00 Ohm resistor.After that, i compared all measurements with my FLUKE, Rigol, UNI-T DMMs and it all checks out.Best Regards.

author: GAVER
author_rank: Newbie
timestamp: October 17, 2024, 05:51:57 am
content: 1) Turn Rotary Knob to "OFF" position.2) Press and hold "SELECT" and "HOLD" buttons, and then turn "Rotary Switch" from "OFF" to "" function position within one second.3) "000.0" is displayed4) Input 000.0, press "SELECT" and then "REL" buttons simultaneously5) Wait till reading is stable, press "SELECT" and then “HOLD” buttons simultaneously.6) “300.0” is displayed7) Input 300.0, press "SELECT" and then "REL" buttons simultaneouslyWait till reading is stable, press "SELECT" and then “HOLD” buttons simultaneously.9) “3.000k” is displayed10) Input 3.000k, press "SELECT" and then "REL" buttons simultaneously11) Wait till reading is stable, press "SELECT" and then “HOLD” buttons simultaneously.12) “30.00k” is displayed13) Input 30.00k, press "SELECT" and then "REL" buttons simultaneously14) Wait till reading is stable, press "SELECT" and then “HOLD” buttons simultaneously.15) “300.0k” is displayed16) Input 300.0k, press "SELECT" and then "REL" buttons simultaneously17) Wait till reading is stable, press "SELECT" and then “HOLD” buttons simultaneously.18) “3.000M” is displayed19) Input 3.000M, press "SELECT" and then "REL" buttons simultaneously20) Wait till reading is stable, press "SELECT" and then “HOLD” buttons simultaneously.21) “30.00M” is displayed22) Input 29.80M, press "SELECT" and then "REL" buttons simultaneously23) Wait till reading is stable, press "SELECT" and then “HOLD” buttons simultaneously.24) Turn to OFF to terminate the calibrationAttached is the procedures to calibrate BM257 resistance function. If the problem of your unit is only for 600 OHM range, you may turn meter off right after proceeding with "Procedure 8th". Please be careful. Wrong calibration operation may lead to ..... .

author: mzdenkov
author_rank: Regular Contributor
timestamp: October 17, 2024, 04:43:48 pm
content: Thaks.When this was still a problem, I've found the video by "mjlorton" youtuber.All the procedure was as he showed.Only 600Ohm range was the problem, other worked well compared to my other DMMs.Anyways thank you a lot.