DMM's  NOISE  -  ( uCurent GOLD  +  Metrix MTX3293-BT a powerful combination ) - Page 1
Forum section: electronics / testgear

author: bozidarms
author_rank: Regular Contributor
timestamp: July 23, 2017, 09:25:30 pm
content: Hi to group,Recently, i got a uCurent GOLD, and have measure noise(offset) in nA range.Due to many posts about this in forum, i wondered how noisy is mine?The result is relay good, noise is between -9 and -23uV (picture 1).At the same time i have measure the noise of MTX3293 too (picture 2).After 25 min. warm up time, noise vary between - and + 1uV,i think one excellent result for a DMM, and both together are a very capable combination.In forum is lot written about noise in bench multi-meters, and almost nothing about noise in DMM's.It would be interested to know, what is the value of noise in others DMM's,so please, share yours experiences (measurements).

author: Kleinstein
author_rank: Super Contributor
timestamp: July 24, 2017, 08:14:42 am
content: Noise measurements are difficult with meters that do not have a PC interface or at least logging feature. So it does not work with most handheld meters. Quite often in handheld meters the noise is at or below the resolution limit - for manual reading it is kind of inconvenient if the last digit is constantly changing - this adds quantization effects. Depending on the value read the output may stick to a value or show the 1 digit jumps - both cases hide the true noise.A 1 µV resolution with low noise is rather good for a handheld meter.

author: Fungus
author_rank: Super Contributor
timestamp: July 24, 2017, 09:17:19 am
content: Quote from: bozidarms on July 23, 2017, 09:25:30 pmHandheld DMMs only update the screen a few times per second and the displayed value is usually the average of several samples. Noise will be moot.You may be able to measure noise on true RMS meters by selecting AC volts mode and shorting the input terminals. It won't tell you anything about the characteristics though and I expect it will depend on the range selection (so don't expect to know how much noise is on the 100V range by selecting the mV range to measure it).I think the only thing you can say with confidence is that it should be slightly less than 1 digit on anyTrue Scotsmeter.

author: alm
author_rank: Super Contributor
timestamp: July 24, 2017, 04:58:50 pm
content: Quote from: Fungus on July 24, 2017, 09:17:19 amI think this is a bad test on a true RMS meter. True RMS converters like the AD636 (as used by probably all handheld meters that can do true RMS, unless you can point to one using a thermal converter or direct sampling) have a DC offset. This offset becomes negligible as the AC voltage increases, due to \$\sqrt{x^2 + y^2} ~ x\$ for \$x >> y\$. By shorting the inputs, you are focusing on this offset, which would be irrelevant if you measured above 5% or so of full scale (as specified in the datasheet), and which may or may not be very stable.I can not think of a way to quantify noise on a handheld without communication interface outside of something very labor intensive (recording values by hand) or complicated (pointing a camera at the display and running that through image recognition or hooking a logic analyzer to tap the signals). Even decent statistics, like standard deviation, appears to be missing in pretty much all handheld meters.