Brymen BM257 - Low readings - Page 1
Forum section: electronics / testgear

author: cs.dk
author_rank: Unknown
timestamp: March 26, 2016, 09:12:57 am
content: Hi,I have been wondering some time. Each time i grab my BM257, the readings seems to be a bit on the low side.As i dont have some sort of voltage standard, i just measures batteries, PSU's, etc. and compare with other meters.If i calculate correctly it is just within spec, but nothing more than that.Some examples:Li 18650 cell;BM235: 4.120BM257: 4,116BM869: 4,1231Car battery, not fully charged:BM235: 12,50BM257: 12,47BM869: 12,503TDK Lambda PSU at 49,4V (At the digital readout)BM257: 49,35BM869: 49,442Same PSU at 49,6VBM257: 49,52BM869: 49,600The PSU is charging batteries, so the voltage climbing slowly up, but the measurements are taken same time.I'll try to test on other ranges later today. Positive to see that the EEVBlog BM235 meter and my BM869 does agree.

author: Lightages
author_rank: Unknown
timestamp: March 26, 2016, 10:41:50 am
content: If it is in spec then there isn't much to say. Yes it could be closer. How old is it?

author: cs.dk
author_rank: Unknown
timestamp: March 26, 2016, 10:55:30 am
content: Quote from: Lightages on March 26, 2016, 10:41:50 amI can live with it, not so much of a problem. But it have always read a little to the low side. Will check ohms, amps etc. to.It is from October 2015.Most multimeters are bang on, on DC volts. This one just meets it's claimed specs, thats what i wonder about. Does anyone else have a BM257 for comparison?

author: Wytnucls
author_rank: Super Contributor
timestamp: March 26, 2016, 11:58:08 am
content: Manufacturers usually specify worst guaranteed accuracy over a time period after calibration. Could be 24hrs, 30 days, etc...Portable DMMs are mostly rated for a year, like Fluke, Hioki, Gossen, Uni-T and others:'Accuracy is given as ±([% of reading] + [number of least significant digits]) at 18° C to 28° C, with relative humidity up to90 %, for a period of one year after calibration.'A new meter should be very accurate, at least within 1/4 of its stated yearly accuracy figure.Strangely, it looks like Brymen doesn't have a time period specified in their manual. Accuracy could only be valid for a month.However, if your figures are correct, the meter is probably defective and should be sent back for a new calibration.Correction: Brymen does specify a one year accuracy validity. (calibration paragraph)

author: cs.dk
author_rank: Unknown
timestamp: March 26, 2016, 12:13:08 pm
content: Thanks for the infoIt seems strange, that the is no time period, i agree.Quote from: Wytnucls on March 26, 2016, 11:58:08 amAs I don't have any voltage standard for reference, it's not some precision-work.. But if ie. 4 meters agree, and one falls out, i do trust the 4 meters more.I'll try the same measurements with more meters, just to compare. Also on more ranges. The TDK Lambda PSU goes to 600V DC to see the higher range.I wont bother returning the meter, the shipping from DK to PL would probably be the same cost as a new meter, and I don't do some mV precision work.If someone from DK are reading here, and they have some sort of standard i could borrow for a week or so, then drop me a PM.

author: 3db
author_rank: Frequent Contributor
timestamp: March 26, 2016, 12:52:43 pm
content: I have a BM257 about 3 months old.I just gave it a quick test on DC Volts measuring 2.5,5.0,7.5 and 10 Volts.I used a reference of dubious quality and compared it with a couple of other meters.The Brymen seems fine and did not read lower than the others.Hope this is of help.

author: Sjokolade
author_rank: Regular Contributor
timestamp: March 26, 2016, 01:31:25 pm
content: I had to have my 257s calibrated as it was out of specification -https://www.eevblog.com/forum/testgear/brymen-257s-lost-calibration-data/

author: cs.dk
author_rank: Unknown
timestamp: March 26, 2016, 07:00:07 pm
content: Strange - The initial tests were at ~15C in my auto workshop. The meter seems to behave now?When i did this test, i have raised the temperature to ~18-19C. Either the meter need a power-on period to settle, or it is extremely sensitive to temperature, else i don't know whats going on.I usually just flip the switch, take a measurement, and switch the meter off again.The PSU is a TDK Lambda Gen600-2.6 - Under this test it is without any load.There are a few decimal errors, as I had to set Excel to 4 digits for the 869s. I have manually edited some, as i remember the meterscale. The* with one of the instruments are, that the meter is not capable of measuring 200 V on a 200V scale, had to raise it to 600V.Note: The picture of the meters and the measuring ins't at the the same time..