Suggestions for a millivolt DMM  - Page 1
Forum section: electronics / testgear

author: Sultanpepper123
author_rank: Regular Contributor
timestamp: October 20, 2019, 11:04:24 pm
content: Hello everyone, I'm having a hard time in selecting a suitable multi meter that should measure AC voltages as low as 100 micro volts @ 50 Hz with steps of 50 microvolts. I've searched for quite some time andherethey seem to have a problem in that range i suppose. My research shows that i can use Fluke's 8808A, 8845A, 287 or 289 , I may be betting on too high specs or vice versa. I would appreciate if someone sheds some light on some suggestions.EDIT: This might be useful to some who tried to reach the reference but found out the link is dead, a screenshot from the deadlink of Gellar Labs link which illustrates the dead zone of the agilent 34401A DMM can be foundhereRegards

author: EEVblog
author_rank: Unknown
timestamp: October 21, 2019, 04:54:57 am
content: What you might need is a "millivoltmeter"Analog ones are still handy:https://www.alibaba.com/product-detail/MVT-171-Analog-Millivoltmeter-Electrical-Meter_60732310848.htmlMost digital meter will only have a 200-500mV AC range full scale, so you need a 50,000 count meter to get 10mV resolution. 500,000 count to get 1mV resolution.Some like the 121GW have a 50mV range.Here is a digital one:https://www.alibaba.com/product-detail/UNI-T-UT632-digital-AC-millivoltmeter_62341154520.html

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: October 21, 2019, 09:44:53 am
content: Well I learned something today; I was going to suggest the Keysight 34461A which is my flagship, best in house, expensive, reference, calibrated multimeter but, on checking the specs, I find that the lowestACVolts range is 100 mV and it can 'only' measure down to 0.3% of range (on AC) which is 300 uV which misses the OP's requested resolution by a lot.That begs a question - What's the point of having a 6.5 digit multimeter if you can only get down to the 4th digit for any kind of measurement? Or am I missing something?

author: EEVblog
author_rank: Unknown
timestamp: October 21, 2019, 10:39:26 am
content: Quote from: Gandalf_Sr on October 21, 2019, 09:44:53 amIt's only an issue with AC, that's a special snowflake.

author: EEVblog
author_rank: Unknown
timestamp: October 21, 2019, 10:46:00 am
content: https://www.aliexpress.com/item/32594363735.html

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: October 21, 2019, 10:48:25 am
content: Quote from: EEVblog on October 21, 2019, 10:39:26 amYes, my wording wasn't the best but thanks anyway for the clarification.

author: Sultanpepper123
author_rank: Regular Contributor
timestamp: October 21, 2019, 11:19:05 am
content: Quote from: EEVblog on October 21, 2019, 04:54:57 amThank you Dave for the help and guidance. Just to let you know how ecstatic i am right now since i'm a fanboy of your channel and since a considerable part of reason where i am right now is due to watching your videos.Just one question, which brand would you recommend as a reliable brand ( i prefer it to be digital one tbh ) ?.RegardsOmar

author: Fungus
author_rank: Super Contributor
timestamp: October 21, 2019, 12:01:45 pm
content: Those Aneng 8008 multimeters have a 10mV AC range with 1uV resolution.$20 on Aliexpress:https://www.aliexpress.com/item/33001360039.html(image from Dave's video review)

author: Performa01
author_rank: Super Contributor
timestamp: October 21, 2019, 12:17:32 pm
content: Quote from: Fungus on October 21, 2019, 12:01:45 pmCan you demonstrate the measurement of a 100µV signal with reasonable accuracy as requested by the TO?

author: Fungus
author_rank: Super Contributor
timestamp: October 21, 2019, 12:19:55 pm
content: Quote from: Performa01 on October 21, 2019, 12:17:32 pmDave did:https://youtu.be/xdGQEVdxmQQ?t=689(at 11:28)

author: Performa01
author_rank: Super Contributor
timestamp: October 21, 2019, 12:30:12 pm
content: Quote from: Fungus on October 21, 2019, 12:19:55 pmSorry, I can only see 9.66mV (and higher) there.

author: evava
author_rank: Regular Contributor
timestamp: October 21, 2019, 12:40:33 pm
content: Quote from: Fungus on October 21, 2019, 12:19:55 pmIt is known problem with RMS converter, he only gives reasonable values from few % of range upwards.If only we could switch off RMS conversion, then we could use full resolution of DMMs.

author: 2N3055
author_rank: Super Contributor
timestamp: October 21, 2019, 12:50:33 pm
content: At 50 Hz you could also use amplifier to amplify signal and then measure after amplifier...

author: Fungus
author_rank: Super Contributor
timestamp: October 21, 2019, 01:00:03 pm
content: Quote from: evava on October 21, 2019, 12:40:33 pmMaybe somebody could try it. I don't have anything calibrated that goes that low.Quote from: 2N3055 on October 21, 2019, 12:50:33 pmThat, too.

author: evava
author_rank: Regular Contributor
timestamp: October 21, 2019, 01:24:23 pm
content: Quote from: Fungus on October 21, 2019, 01:00:03 pmTake Fluke 287/289 for example:when 100uV at 50Hz, manual stated accuracy 0.3% +- 45counts, see picture.Maybe it is actually better, who knows.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 21, 2019, 01:50:10 pm
content: Analog RMS converter have a problem if the signal gets too small (e.g. below some 1% of full scale). The problem starts with the rectification part detecting the sign - first it gets slower (reducing the BW at lower amplitude) and finally fails. Some version also get a rather sluggish response at low levels.Things are better (or at least can be), with usually expensive (though it does not have to) DMMs that use digital methods for RMS. So the Keysight 34461 could actually work well even below 1 mV, though the specs do no include this. The advantage here is that there is no need for a separate sign detection. So the BW can be constant and no magic limit where things break down. Residual noise compensation is also easier in software than in analog HW.100 µV are still 1 % of the 10 mV range of the cheap meter. So chances are it could still work - at least for low frequency. However such a test can vary from unit to unit - some may work better than others.Turning off RMS is easy, just use the DC range. Of cause this does not solve the problem unless the meter is really fast and can do the math (like man DSOs can).

author: egonotto
author_rank: Super Contributor
timestamp: October 22, 2019, 04:24:26 am
content: Hello,I try my AN8009.I feed a 50Hz sine wave so that the AN8009 shows about 50 µV.Than i double the input and the AN8009 shows about 75 µVMy AN8008 shows with the above settings about 70 µV and 90 µV.Best regardsegonotto

author: evava
author_rank: Regular Contributor
timestamp: October 22, 2019, 06:49:21 am
content: Quote from: Kleinstein on October 21, 2019, 01:50:10 pmThis multimeterhttps://lygte-info.dk/review/DMMKyoritsu%20KEW1062%20UK.htmlKyoritsu KEW1062 can switch RMS on and off:QuoteI think in this case it could be useful.EDIT: maybe I am not right, see picture: accuracy stated in manual is also in MEAN value detection from 10% of range!P.S. Thank you very much for your reviews, lygte-info!

author: EEVblog
author_rank: Unknown
timestamp: October 22, 2019, 08:29:29 am
content: Quote from: Fungus on October 21, 2019, 12:01:45 pmForgot about that, great!Limited bandwidth though of course.

author: Fungus
author_rank: Super Contributor
timestamp: October 22, 2019, 08:54:23 am
content: Quote from: EEVblog on October 22, 2019, 08:29:29 amHow low do they go? Some people are doubting they still work with a an input signal of 100uV (or lower).Maybe you could do a quick test to prove them wrong...(I'd do it but I don't have the equipment)

author: BravoV
author_rank: Super Contributor
timestamp: October 22, 2019, 09:07:00 am
content: You should try to find your local market for those old analog millivolt meter, scored one last year locally as the crowd are flocking into digital meter, their lost.A GWInstek analog, at 300uV range has accuracy about +/- 3% from 20 Hz to 200 kHz, not bad.

author: TurboTom
author_rank: Super Contributor
timestamp: October 22, 2019, 12:32:36 pm
content: I just tested the low AC ranges of three "cheapo" Angeng meters and an RM303 4.5 digit instrument with probably the same chipset:All the instruments perform identically with only sub-percent deviation between them. 1mV 50Hz sine is accurate on all of them within maybe two or three least digits tolerance. At 100µV 50Hz they all indicate a little low, maybe by 3%. At 50µV, indication is 30µV with strong fluctuations. Below 30µV results in a displayed value of plain zero. The frequency ranges up to approx. 2kHz (sine) where the displayed value virtually doesn't differ at all from the readings at 50Hz, above that it quickly drops to zero (within one octave).Seems like 100µV is the lowest AC value that can be measured decently accurate with the Aneng (and siblings) family of cheapo-multimeters.Just for interest, my venerable Fluke 89 IV isn't usable at that low levels at all. Even though it has a mV AC range with 1µV resolution, it just dithers around heavily at signal levels below 5mV.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: October 22, 2019, 12:55:24 pm
content: I just a very quick and basic test with my Aneng 8008 fed by a DG1062Z, the lowest output I can get is 800 uV rms and, at 500 Hz the Aneng reads within 2%.

author: dom0
author_rank: Super Contributor
timestamp: October 22, 2019, 04:23:15 pm
content: HP 3400A has a noise floor of something like 60 µVrms. It's also a true RMS indicating meter. Supports very high crest factors.For pure sine signals there aremanymore options, since it's easier to measure these simply by using a good amplitude detector. Look for "HF Millivoltmeter". For example, Philips PM 2554 covers a similar range as the 3400A (~50 µV - 300 V). Practically every instrument manufacturer built these, with varying sensitivity, accuracy and bandwidth.Preamplifier for a scope is another option.

author: SilverSolder
author_rank: Super Contributor
timestamp: October 22, 2019, 04:34:48 pm
content: If the source impedance is low... the world famous uCurrent actually works as a decent amplifier at these kinds of frequencies.

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 22, 2019, 05:18:19 pm
content: Quote from: BravoV on October 22, 2019, 09:07:00 amHey! The scale goes up to 11.My apologies to all "Spinal Tap" fans.

author: 001
author_rank: Super Contributor
timestamp: October 22, 2019, 05:46:43 pm
content: Quote from: egonotto on October 22, 2019, 04:24:26 amWHY?

author: Gyro
author_rank: Super Contributor
timestamp: October 22, 2019, 06:27:55 pm
content: Quote from: 001 on October 22, 2019, 05:46:43 pmDIFFERENT NOISE FLOORSP.S.Pleasestop shouting in your posts, alcohol fuelled or not.

author: Gyro
author_rank: Super Contributor
timestamp: October 22, 2019, 06:30:19 pm
content: The venerable Datron 1030A True RMS voltmeter has a noise floor of ~80uV wideband (1MHz) and <30uV with the 10kHz band limit filter engaged. They're hard to find though.

author: macboy
author_rank: Super Contributor
timestamp: October 22, 2019, 06:31:06 pm
content: Quote from: 001 on October 22, 2019, 05:46:43 pmBecause: NoiseThe reading is a summation of the inherent noise of the meter plus the input signal. These add as root-sum-of-squares.If the input signal was about 32.2 mV initially, then double that (64.4 mV) for the second test, and the inherent noise floor of the meter is 38.2 mV, then the readings make sense.test 1: sqrt( 32.22+ 38.22) = 49.96 ~= 50 mVtest 2: sqrt( 64.42+ 38.22) = 74.87 ~= 75 mVIf the signal is at least 5x as high as the noise, then the noise makes little difference:sqrt( 2002+ 38.22) = 203.6 mVi.e. only 1.8% higher than the input of 200 mV. Note that although the meter contributes 38.2 mV of noise in addition to the signal, the reading is only 3.6 mV higher, not 38 mV higher. At a signal level of 400 mV, the reading is 401.8 mV, which is only 1.8 mV high, or less than 0.5% error.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 22, 2019, 07:20:43 pm
content: Noise is only part of the problem. To a certain limit the offset from noise could be compensated in software. With many RMS implementation another big problem is the precision rectification that does not work reliably anymore if the amplitude is too small. This also includes most (if not all) analog true RMS chips. A first consequence of lower amplitude is slower detection of the sign and thus reduced BW at low amplitude. So the simple noise calculation does no longer work with a real RMS converter.There are ways around this with a square law detector like used in RF power sensors or digital RMS. However I am still looking for a cheap meter with digital RMS. The square law detectors tend to be limited accuracy and also have some weakness at low amplitude.The main point for the small voltages is having suitable amplification / ranges.For a simple test, I would reduce the amplitude from the generator with a divider and this way get a low voltage test signal. Even a crude divider tends to be better than comparing 2 meters way outside the specified range.

author: Andreas
author_rank: Super Contributor
timestamp: October 22, 2019, 08:18:29 pm
content: Hello,I made a AC linearity comparison on a K2000, a HP34401A in 100mV AC range and my scope.The clear winner is the scope (except for the noise floor at zero).with best regardsAndreas

author: Gyro
author_rank: Super Contributor
timestamp: October 22, 2019, 08:35:05 pm
content: A couple of articles on meter AC low level linearity from Joe Geller....https://web.archive.org/web/20150301064705/http://www.gellerlabs.com/34461A%20AC%20zero.htmhttps://web.archive.org/web/20121104004609/http://www.gellerlabs.com/34401A%20AC%20zero.htm(Also including useful Agilent tech note links)

author: Terry01
author_rank: Frequent Contributor
timestamp: October 22, 2019, 08:36:36 pm
content: Brymen BM867S or BM869s ?

author: BravoV
author_rank: Super Contributor
timestamp: October 23, 2019, 03:19:31 am
content: Quote from: schmitt trigger on October 22, 2019, 05:18:19 pmAnticipating 10% overshoot ?

author: Fungus
author_rank: Super Contributor
timestamp: October 23, 2019, 06:52:40 am
content: Quote from: Terry01 on October 22, 2019, 08:36:36 pmI thought of those as well but the lowest range is 500mV with 0.3% accuracy, 10uV resolution.Granted they seem to beat their rated specs by a wide margin but somebody would need to try it. I suspect that if they don't go lower than 500mV then it's for a reason...

author: Terry01
author_rank: Frequent Contributor
timestamp: October 23, 2019, 07:10:50 am
content: Quote from: Sultanpepper123 on October 20, 2019, 11:04:24 pmQuote from: Terry01 on Yesterday at 09:36:36 pmBrymen BM867S or BM869s ?I thought of those as well but the lowest range is 500mV with 0.3% accuracy, 10uV resolution.Granted they seem to beat their rated specs by a wide margin but somebody would need to try it. I suspect that if they don't go lower than 500mV then it's for a reason...I have the 867s but don't have anything that goes down to uV to use as a test

author: Fungus
author_rank: Super Contributor
timestamp: October 23, 2019, 07:54:44 am
content: Quote from: Terry01 on October 23, 2019, 07:10:50 amMe too.(actually 857s but it's the same specs)

author: 2N3055
author_rank: Super Contributor
timestamp: October 23, 2019, 08:10:14 am
content: At 50 Hz attenuator is just 3 plain resistors...

author: Terry01
author_rank: Frequent Contributor
timestamp: October 23, 2019, 08:11:34 am
content: Quote from: Fungus on October 23, 2019, 07:54:44 amI'm sure one of the guys here will have the meter and the necessary equipment to test uV and they can let us know if it's up to the task or not. If the OP only needs the said resolution for 1 project or whatever the Brymen has to be one of, if not the best $$$'s solution out there?I will still love mine even if it's not up to the task! The Brymen's are a quality meter.

author: Terry01
author_rank: Frequent Contributor
timestamp: October 23, 2019, 08:18:45 am
content: Quote from: 2N3055 on October 23, 2019, 08:10:14 amI have a sig gen that can put out 50Hz but 1 mV is as low as it goes and I doubt that could be trusted as it's just 1 of those cheap feeltech things

author: EEVblog
author_rank: Unknown
timestamp: October 23, 2019, 08:20:54 am
content: Quote from: schmitt trigger on October 22, 2019, 05:18:19 pmI need one now!

author: BravoV
author_rank: Super Contributor
timestamp: October 23, 2019, 08:32:27 am
content: Quote from: EEVblog on October 23, 2019, 08:20:54 amQuick grab them while they are still reasonable priced, before Dave makes a new video about this.

author: Fungus
author_rank: Super Contributor
timestamp: October 23, 2019, 08:40:50 am
content: Quote from: Terry01 on October 23, 2019, 08:18:45 amGrab a potentiometer and hook it up. See what happens.How low can you go before it visibly/obviously goes wrong?

author: Fungus
author_rank: Super Contributor
timestamp: October 23, 2019, 09:11:42 am
content: Quote from: PeDre on October 23, 2019, 08:57:01 amI see you still have some unpushed buttons, can you increase the attenuation to 86dB and see if it says 50uV?What does it read if you use the standard multimeter probes instead of fancy connectors?

author: evava
author_rank: Regular Contributor
timestamp: October 23, 2019, 09:31:31 am
content: Quote from: PeDre on October 23, 2019, 08:57:01 amIs it possible? Reading RMS value at 0.02% of range?When manufacturer states in manual accuracy from 5% to 10% of range is 0.3%+100 counts?What for are manuals then?

author: Terry01
author_rank: Frequent Contributor
timestamp: October 23, 2019, 09:37:32 am
content: Thanks Peter.Your set up is way better than my "feeltech special"

author: nctnico
author_rank: Super Contributor
timestamp: October 23, 2019, 09:44:42 am
content: Quote from: BravoV on October 23, 2019, 08:32:27 amYou can buy these new. Lowest price (180 euro) I could find is from TME:https://www.tme.eu/be/nl/details/gvt-417b/analoge-multimeters/gw-instek/

author: Fungus
author_rank: Super Contributor
timestamp: October 23, 2019, 11:10:43 am
content: Quote from: evava on October 23, 2019, 09:31:31 amYes.Those numbers aren't "garanteedinaccuracy", they're the outer limits of the bell curve on the production line.Those bell curves also allow for extremes of temperature, and temperature makes abigdifference to handheld meters with this many digits. If you're measuring at the same temperature as the factory's calibration room then you'll get much better accuracy than if you're measuring at freezing (or hot) temperatures, which is where those outer limits of accuracy will come into play.Bottom line: In practice, and at ordinary temperatures, these Brymens will domuchbetter than those specs. I've compared mine to a fancy 6.5 digit bench multimeter and it matched it perfectly.Quote from: evava on October 23, 2019, 09:31:31 amTo know when there's something seriously wrong with the meter.(and when the manufacturer will accept a return under warranty).

author: Fungus
author_rank: Super Contributor
timestamp: October 23, 2019, 11:17:57 am
content: Quote from: nctnico on October 23, 2019, 09:44:42 amJeez, that's massive. It looks like a little handheld meter in the photo - not so!

author: joeqsmith
author_rank: Super Contributor
timestamp: October 23, 2019, 12:14:55 pm
content: I used a 100mVrms (set with the 34401A) as a reference. I stepped this down to 1mV using 40dB fixed attenuators, along with a step attenuator to get into the 100uV 60dB), terminated to 50ohms.The 34401A is not even in the ballpark.Fluke 189 #1, 0.108mV (My friends old meter)Fluke 189 #2, 0.107mV (Cosmetically the show queen)Fluke 189 #3, 0.108mV (PCB from black meter that was transient tested)UNI-T UT181A, 0.093mV (Damaged from ESD, modified PCB and OEM regulator)Brymen BM869s #1, 0.02mV (Newer unit from Brymen, switch was life cycled, transient tested, different transistor clamp)Brymen BM869s #1, 0.06mV (my original meter, damaged from testing but repaired with OEM parts)Gossen Ultra, 0.00mV (Added shielding)Yokogawa TY820, 0.175mV (Damaged during testing. Repaired with OEM parts)TPI 194II, 0.04mV (Damaged attenuator, not repaired)All of the meters require several seconds to stabilize.Using the Fluke #260dB, calculated 100uV, reads 107uV61dB, calculated 89.1uV, reads 89.1uV*** I suspect I wrote down the wrong number for this reading. Checking today with the same setup I measure 96uV***62dB, reads 85uV63dB, reads 73uV64dB, reads 68uV70dB, calculated 31.5uV, reads 37uV******Added picture of setup and included a few other meters. Also, I should note that none of these meters have ever been aligned outside of the factory that I am aware of. It's possible that the used Flukes had been at one time.I looked at the other meters I thought may have a mV range that could read down this low. Most can't resolve to the uV. Of course there is the Gold Standard of ALL meters, the Fluke 87V. Voted best meter ever for electronics. Oh yea, sorry, no mV AC range.I looked at the 121GW prototype and it appears it could resolve down to 1uV. Because of the amount of modifications I have made to this meter after it was damaged, then having aligned it at home and it being a prototype, to avoid confusion I'll let Dave post some actual numbers for his meter. I would expect it to throw up some decent numbers.That UNI-T UT181A seems to be the big surprise once again.

author: maginnovision
author_rank: Super Contributor
timestamp: October 23, 2019, 05:08:56 pm
content: I tried my fluke 5200a at 50Hz and 100uV(calibrated as 108uV since it can't be adjusted with sense lines). 1252B read 102uV, 1282A read 110uV. They both responded to 10uV step changes with a 10uV change in reading. Initial settling was a few seconds, changes were about 3 seconds. I didn't bother with single uV changes since I don't have the equipment to go lower than 100uV and didn't have a better meter hooked up nearby to verify the reading. Neither meter was able to determine the frequency with the low amplitude signal.EDIT: Just tested 1242C, totally useless. Noise floor of about 660uV.

author: Fungus
author_rank: Super Contributor
timestamp: October 23, 2019, 05:31:30 pm
content: Looks like Dave's been busy as a result of this thread...

author: Fungus
author_rank: Super Contributor
timestamp: October 23, 2019, 05:35:40 pm
content: Quote from: joeqsmith on October 23, 2019, 12:14:55 pmKeeping us in suspense...?

author: egonotto
author_rank: Super Contributor
timestamp: October 23, 2019, 06:49:54 pm
content: Hello,it is no DMM but a great meter: Meratronik V640.Voltage from 1.5 mV to 1500 V full scale.At 1.5mV +- 3% for 30Hz to 10 kHzAll other +- 1.5%Best regardsegonotto

author: joeqsmith
author_rank: Super Contributor
timestamp: October 23, 2019, 11:57:12 pm
content: Quote from: Fungus on October 23, 2019, 05:35:40 pmI didn't think so. The data for it was in that same post. It's 7uV low vs my closest Fluke 189 at 7uV high. None of my other handheld meters can resolve to 1uV and come as close as these two. Too bad that UNI-T hasn't come out with an improved version of the 181A.

author: evava
author_rank: Regular Contributor
timestamp: October 24, 2019, 07:58:55 am
content: Quote from: joeqsmith on October 23, 2019, 12:14:55 pmThank you for your measurement data.IMHO Fluke 87V in HiRes mode on V~ has got range/resolution to 0.00 mV (10uV) (same as Brymen 869s) - that's sufficient for showing 0.10 mV, 0.11mV, 0.09mV or so.Could you please check also this meter?

author: Electro Detective
author_rank: Super Contributor
timestamp: October 24, 2019, 08:49:08 am
content: I haven't got mine here to check, but IIRC the 87V has a High Res mode on turn on.Surely that should drag in some seriously low level AC mV action

author: Electro Detective
author_rank: Super Contributor
timestamp: October 24, 2019, 09:28:04 am
content: A lot of comparison tests are wishful thinking come speculation,unless there's a freshly calibrated real deal AC reference generator and or meter to compare low levels vs frequency performanceand then there's the TRMS vs Averaging vsthing too.Chuck in a bit of distortion and superimposed crap on that 'how low can you goluv u long time' millivolt signal and...wellgood luck and don't stop believin..

author: maginnovision
author_rank: Super Contributor
timestamp: October 24, 2019, 09:44:48 am
content: Quote from: Electro Detective on October 24, 2019, 09:28:04 amI used a calibrated 5200A for the meters I tested.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 24, 2019, 12:17:26 pm
content: Quote from: evava on October 24, 2019, 07:58:55 amAn 87V fan?Because I feel so bad for you, I'll do you one better.I want you to get some idea on the 87V's settling time so I have put together a short video where I compare it with the 189. I purchased this 87V brand new for the sole purpose of testing it. It's SN 409xxxxx. It was transient tested up to 12KV where one of the clamps started to exhibit enough leakage to throw off some of the readings. Part was replaced with OEM. Meter was then subjected to 50,000 full rotations of the rotary switch. While it was grinding at the end of the test, the meter still worked fine. Since then I have cleaned the contacts as I had used the meter for some other tests.You may notice the time jump at the end of running the 87V. While I sped up the video, I wanted to make sure that the 87V had settled. To help speed the video, I removed the section where nothing was happening.https://youtu.be/NPvq5i0z_8s

author: hgjdwx
author_rank: Regular Contributor
timestamp: October 24, 2019, 01:21:06 pm
content: HIOKI DT4282 can only measure the ac voltage above 1mv, and the voltage below 1mv is forced to be zero (actually, all ac ranges within 1000 words return to zero).

author: Kleinstein
author_rank: Super Contributor
timestamp: October 24, 2019, 03:02:43 pm
content: The lower level on how far down the AC mode still works can depend on the rectifier internal offset. So different units can have a different limit, quite often better than the specs, but not always. So a single meter of a type working well at low voltage does no say other will be the same. There can be lucky ones with a low offset.

author: Fungus
author_rank: Super Contributor
timestamp: October 24, 2019, 06:20:14 pm
content: Quote from: joeqsmith on October 23, 2019, 12:14:55 pmQuote from: PeDre on October 24, 2019, 08:59:47 amI wonder why your Brymen appears so much better than Joe's.(maybe joe is in Winter)

author: alm
author_rank: Super Contributor
timestamp: October 24, 2019, 07:24:45 pm
content: There's a big difference between measuring 1 mV with 1 uV resolution, and measuring a 100 uV signal with 1 uV resolution. The latter may be outside the linear range of the true RMS converter. If the analog true RMS converter has a 100 uV offset, it will measure sqrt(100e-6^2 + 100e-6^2) = 141 uV with a 100 uV input, and sqrt(100e-6^2 + 1e-3^2) = 1.005 mV. So the error for small signals is much larger.I would indeed suggest an AC millivoltmeter. HP, Philips and Fluke (8920a/8921a/8922a) made them. Not sure about current models. A DMM that digitizes the AC signal and has a low enough range would be a more expensive alternative.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 24, 2019, 11:59:41 pm
content: Quote from: alm on October 24, 2019, 07:24:45 pmThat's true.Quote from: Sultanpepper123 on October 20, 2019, 11:04:24 pmI was running well below OP's requirements just to get a feel if any of my meters could pull off a measurement like this.Quote from: Kleinstein on October 24, 2019, 03:02:43 pmTrue.What I have done, now that I have an idea how far out my attenuator stack is, I compensated for that error and repeated the test running from -50 to -70dB for all four of my old Fluke meters. I also included the UNI-T UT181A as it was really the only other meter that came close, even though it takes a fair amount of time to settle compared with the Flukes.No it's not nearly as slow to settle as the Golden Standard of all electronics meters that we worship. Also shown is the ACmV specs for the 189/187.Office temperature was 21.8 degrees C.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 25, 2019, 12:11:10 am
content: Quote from: Fungus on October 24, 2019, 06:20:14 pmIt's possible that my meters have suffered from all the abuse. It's possible they have drifted in this range. It could be something different with the test setup. I've made attempts to validate my results using the equipment I have to run cross checks.

author: Fungus
author_rank: Super Contributor
timestamp: October 25, 2019, 12:51:00 am
content: Quote from: hgjdwx on October 24, 2019, 01:21:06 pmI has a sad.

author: Fungus
author_rank: Super Contributor
timestamp: October 25, 2019, 12:56:14 am
content: Quote from: joeqsmith on October 24, 2019, 11:59:41 pmConclusion: The only Fluke worth owning is the one they don't make any more.

author: hgjdwx
author_rank: Regular Contributor
timestamp: October 25, 2019, 02:57:44 am
content: Quote from: Fungus on October 25, 2019, 12:51:00 amI've been sad about this for a long time.And it does not have mV range of AC+DC mode and no current AC+DC mode

author: Electro Detective
author_rank: Super Contributor
timestamp: October 25, 2019, 09:15:47 am
content: Quote from: Fungus on October 25, 2019, 12:56:14 amNo contest therebut a 289, 28-11, orgold holstered87V will get the job done good enoughtill some'Flukes worth owning'pop up on Ebay,and the repair, battery leakage nightmares and cal dramas begin..

author: EEVblog
author_rank: Unknown
timestamp: October 25, 2019, 09:23:22 am
content: Quote from: joeqsmith on October 24, 2019, 12:17:26 pmIt's only the best selling multimeter of all time, with a lifetime warranty. Yeah, those 87V fanboys are so weird

author: Fungus
author_rank: Super Contributor
timestamp: October 25, 2019, 09:51:11 am
content: Quote from: Electro Detective on October 25, 2019, 09:15:47 amA 289? Who wants a meter the size of a laptop with a dedicated "Help!" button, "multi-language user interface" listed as afeature, and several threads on here telling people how to fix it whenever it springs an oil leak?

author: joeqsmith
author_rank: Super Contributor
timestamp: October 25, 2019, 10:27:23 am
content: Quote from: EEVblog on October 25, 2019, 09:23:22 amGary Dahl sold a lot of rocks with a lifetime warranty but they were not gold.Do you have some time to show off a few of the 121GWs?

author: Electro Detective
author_rank: Super Contributor
timestamp: October 25, 2019, 10:32:28 am
content: Quote from: Fungus on October 25, 2019, 09:51:11 am..what I thought too, till I scored an unloved 289 cheap, and realized it's a lot of meters rolled into oneThe logging function that requires no outboard gear,live min max average (all three at once, plus actual current status)the centered -/+ DC meter modeLow-Z and some novel continuity/buzzer modes etc etcare just tips of the iceberg for what thisOBESEsmartphone sized meter can do, that many others can'tCome on, it ain't that big, surely..

author: joeqsmith
author_rank: Super Contributor
timestamp: October 25, 2019, 10:37:17 am
content: Quote from: Electro Detective on October 25, 2019, 09:15:47 amI'm not sure 3 minutes settling to get a >50% error answer, is good enough for what the OP has in mind or not.

author: Fungus
author_rank: Super Contributor
timestamp: October 25, 2019, 10:48:22 am
content: Quote from: Electro Detective on October 25, 2019, 10:32:28 am22.2 cm x 10.2 cm x 6 cm

author: BravoV
author_rank: Super Contributor
timestamp: October 25, 2019, 11:05:50 am
content: Yeah, 287/289 is quite big, here comparisons ...

author: Electro Detective
author_rank: Super Contributor
timestamp: October 26, 2019, 03:18:21 am
content: The 289 fits in the tech's palm just fineand I'll bet he not complaining what the boss gave him to use on the jobbut he should be worded up about a decent insulation tester (1507 please) to sort out that motor properly,if a power down is an optionFWIW: remember what they say about guys with big hands or big meters..

author: maginnovision
author_rank: Super Contributor
timestamp: October 26, 2019, 05:34:15 am
content: They have thick glasses? Can't see small meters so get a big one, and big hands can't have dainty glasses.

author: 001
author_rank: Super Contributor
timestamp: October 27, 2019, 09:14:30 am
content: Quote from: macboy on October 22, 2019, 06:31:06 pmGreat answer! Thanx a lot!In this cause it looks not bad for a $20 meter, isn`t it?

author: Fungus
author_rank: Super Contributor
timestamp: October 27, 2019, 01:36:26 pm
content: Quote from: 001 on October 27, 2019, 09:14:30 amHaven't you got one? I thoughteverybodyhere had at least one Aneng 8008.At that price you can have two.

author: 001
author_rank: Super Contributor
timestamp: October 27, 2019, 06:20:54 pm
content: Quote from: Fungus on October 27, 2019, 01:36:26 pmNo I haven`t. No reason to change wellknown gear. But I read here about this strange goodies.

author: Sultanpepper123
author_rank: Regular Contributor
timestamp: October 27, 2019, 07:53:50 pm
content: Quote from: joeqsmith on October 25, 2019, 10:37:17 amSo a 289 has a settling time of 3 minutes ? , it's alot but as long as it's reading within spec i'll take it. So realistically the closest i can get "New" is a 289 am i correct ?Quote from: joeqsmith on October 24, 2019, 12:17:26 pmWell let me tell you that i contacted fluke's distributor here in my country and to my surprise seems they've recommended this 87V as a solution based on the given requirementsQuote from: joeqsmith on October 23, 2019, 12:14:55 pmThank you very much, I appreciate the incredible work done, really appreciate the effort and the shared dataQuote from: 2N3055 on October 21, 2019, 12:50:33 pmBy any chance would you recommend a ready solution , thank you in advanceQuote from: dom0 on October 22, 2019, 04:23:15 pmI'm sorry i may sound like a young player at home, which i am . But is it a case that bench top DMMs like keysight's lineup ( 34460A, 34461A, 34465A, and 34470A) or fluke's 8845A do a better job than most / any handheld DMM like the fluke 289 ?Quote from: PeDre on October 23, 2019, 08:57:01 amThank you sir for the valuable data, much appreciated

author: joeqsmith
author_rank: Super Contributor
timestamp: October 27, 2019, 08:29:22 pm
content: Quote from: Sultanpepper123 on October 27, 2019, 07:53:50 pmI do not show any data for the Fluke 289. The only ones I tested are the ones where I posted their date. If you like, I could borrow a friends and see how it behaves.Quote from: Sultanpepper123 on October 27, 2019, 07:53:50 pmI'm not sure why they would recommend this meter as its certainly not a good application for it. Your distributor may just be in sales and have no technical knowledge. Hailing it as the holy grail for all applications certainly won't help the end users or the companies' reputation in the long run.Quote from: Sultanpepper123 on October 27, 2019, 07:53:50 pmNo response from Dave on how the 121GW performs with these lower voltage levels. I was hoping that he would demonstrate it out performing my antique Flukes. My original plan was to wait a year to look at it but I really wanted them to get that switch ironed out, but another year has passed and I haven't heard anymore about it. If people would like to see how the current flavor of it stacks up, I'll pick up a couple to run.

author: Sultanpepper123
author_rank: Regular Contributor
timestamp: October 27, 2019, 09:18:46 pm
content: Quote from: joeqsmith on October 27, 2019, 08:29:22 pmThat would be wonderful , of course as long as it is not a problem(i'm feeling a bit pushy, if so then my apologies)Quote from: joeqsmith on October 25, 2019, 10:37:17 amI'd love to see how it performs against the fluke 189's and other digital DMM's , if someone does it or maybe if dave does a video on it that would be quite interesting

author: joeqsmith
author_rank: Super Contributor
timestamp: October 28, 2019, 12:16:10 am
content: Quote from: Sultanpepper123 on October 27, 2019, 09:18:46 pmNo problem. I will ask them tomorrow about their 289. I've borrowed their meter before when I reviewed the UT181 and as long as I promise not to blow it up, it should be fine.Getting Dave's meters will take some time but I don't see a problem with running some tests on a couple of the them. I've been curious myself about them.

author: bson
author_rank: Unknown
timestamp: October 28, 2019, 12:55:38 am
content: Quote from: Fungus on October 25, 2019, 10:48:22 amWTF is he doing with that probe... did he stick the common lead in a motor?

author: Fungus
author_rank: Super Contributor
timestamp: October 28, 2019, 09:29:39 am
content: Quote from: bson on October 28, 2019, 12:55:38 amThe display shows 1.5 Ohms so....

author: joeqsmith
author_rank: Super Contributor
timestamp: October 28, 2019, 05:00:41 pm
content: I forgot how bad the display is on these.I made an attempt to repeat my previous tests, using the exact same setup. I verified the setup using one of the 189s. Looking at the 289, it's not even close. At -50dB with a 100mV source, compensating for the errors in the attenators as before, it should read around 316uV but it reads roughly 546uV. It's also very unstable. The readings wander 20uV or so. It does seem to settle about as fast as the 189s I have.The SN# for this meter is 1736xxxx. It was calibrated (not aligned) early this year and passed. The meter belongs to a friend of mine and I doubt it has seen any abuse.At least from my testing, I would say both the 289 and the gold standard 87V are not good enough to make the OP's measurements. I wonder why those 189s work so well in this lower range.I've placed an order for a couple of Dave's meters and will post the results once they arrive.

author: Sultanpepper123
author_rank: Regular Contributor
timestamp: October 28, 2019, 07:09:27 pm
content: Quote from: joeqsmith on October 28, 2019, 05:00:41 pmThank you very much for making the tests, really appreciate it. Seems now 289 is out the window. Would you recommend / have in mind any of the bench DMM's ( say keysight's, keithley, fluke ) if they have a better chance in meeting the requirement ? . And i thought after reading datasheet of 289 that its all happy daysRegardsSultan

author: joeqsmith
author_rank: Super Contributor
timestamp: October 28, 2019, 11:27:02 pm
content: Glad to help.I don't normally offer recommendations when it comes to test equipment. In your case, I would need to know more about the application to even take a guess.A handheld DMM (a good one anyway) can handle a fair amount of abuse. This is why I was guessing you wanted to use a DMM rather than something a bit more specialized. If you were to gain up the signal as suggested for example, your amplifier may not be as robust as a good DMM's front end. I have a home made amp that I use for low frequency, low voltages that I put together on some perf board. The gain can be set to 10, 100 and 1000. The attached picture shows the 100uV 50Hz signal after the 50 ohm terminator, being amplified by 10X. Of course this amplifier has no protection.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 28, 2019, 11:49:29 pm
content: My original Fluke 101 that has survived everything I have ever thrown at it, measuring 100uV 50Hz with the amplifier set to 1000X.But again, just to be clear, if I were to use this amplifier to say try and measure AC ripple on a 900V plate supply, even with a capacitor to block the DC, it may very well fail. That's not what I use it for.

author: Electro Detective
author_rank: Super Contributor
timestamp: October 29, 2019, 07:44:00 am
content: 4 pages later, with no shortage of Fluke 289 and 87V tall poppy syndrome bashing...Let's meander back to OP Sultanpepper123 "Suggestions for a millivolt DMM"Hello everyone, I'm having a hard time in selecting a suitable multi meterthat should measure AC voltages as low as 100 micro volts @ 50 Hz with steps of 50 microvolts.I am going to assume OP Sultanpepper123 needs ANY meter that does just that, and does not care or want to pay for any other bells and whistles featuresi.e. if there's a multimeter around that does that, cheap or too much. with decent specs and dita at everything else, please comment/suggest here

author: Fungus
author_rank: Super Contributor
timestamp: October 29, 2019, 08:05:44 am
content: Quote from: joeqsmith on October 28, 2019, 05:00:41 pmI assume that if they had any chance of working that Dave would have said so in the very first reply in this thread. He didn't... he suggested a bunch of other meters instead.Quote from: Electro Detective on October 29, 2019, 07:44:00 amPeople need to know. You'd think they'd do the job from reading the spec sheet, but nooooo...Quote from: Electro Detective on October 29, 2019, 07:44:00 amI'm not sure what happened to the ANENG 8008, some people said it worked then it just vanished from the thread.The conclusion seems to be that nothing so far has worked with 100% certainty. There's two paths left:a) Buy somthing with "millivoltmeter" written on the front (which nobody here seems to own).b) Use a combination of ordinary multimeter+amplifier, which is now being discussed.

author: maginnovision
author_rank: Super Contributor
timestamp: October 29, 2019, 08:54:04 am
content: 100uV in 50uV steps at 50Hz both my keysights worked fine. My Prema 5017 bench meter worked fine. My Prema 8017 did NOT work fine, the noise floor is about 200uV for some reason, it goes back to Prema soon. I could check some of my Datrons but I'd need to finish calibrating a tektronix 475A first to get some room to do so.

author: deadlylover
author_rank: Frequent Contributor
timestamp: October 29, 2019, 09:58:41 am
content: Hmm very interesting, I tried this with Godzilla (Advantest R6581).I can only generate down to 30uV with the ShibaSoku audio analyser, and I lost my calibration short so I don't know if I can null out the 7ish uV error offset. Resolution is no problem, I can adjust it by 1uV and it tracks without issue. (the analyser lets me adjust by 10nV steps, that's nuts)I think in AC coupling mode it was not good at all and it needed at least 0.5mV or so.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 29, 2019, 11:14:32 am
content: Quote from: Fungus on October 29, 2019, 08:05:44 amThat would be my guess as well but it's good to see the data.After watching so many of Dave's harsh and critical DMM reviews, I'm interested in seeing for myself what he is willing to put his name on. After two years, I assume it's as good as it's going to get and this was as good of an excuse as any to finally have a look.

author: Sultanpepper123
author_rank: Regular Contributor
timestamp: October 29, 2019, 01:38:09 pm
content: Quote from: Fungus on October 29, 2019, 08:05:44 amIf i would go with option (b) would that be something like aμcurrent gold+ an ordinary multimeter ? if not, would you recommend something prebuilt ?RegardsSultanQuote from: maginnovision on October 29, 2019, 08:54:04 amWould you kindly share the model number of both keysights that worked ?RegardsSultan

author: joeqsmith
author_rank: Super Contributor
timestamp: October 29, 2019, 05:27:42 pm
content: Quote from: Sultanpepper123 on October 29, 2019, 01:38:09 pmI think that would depend what you are trying to do. If you are attempting to read AC riding on some potentially lethal high voltage DC source or something else that is totally safe and you understand what you are doing. Building a simple amplifier would not pose much of a problem if you are working in low voltage circuits. Obviously, what I have shown has zero risk for me or the test equipment. Post some details about what you are trying to do.

author: Electro Detective
author_rank: Super Contributor
timestamp: October 30, 2019, 08:48:30 am
content: Quote from: joeqsmith on October 29, 2019, 11:14:32 amNot only were "Dave's harsh and critical DMM reviews" most welcome from a buyer choice perspectiveand a way overdue safety aspect heads up> no thanks to meter manufacturers on thatmany of these reviews IIRC were made way before any EEVblog meter was plannedAnd isn't there the price point to consider too?DJ isn't flogging a $1000+ bells and whistles meter that falls short on the AC low mV specs as many big dollar meters do anywaynor do I think the initial design intentions had really low AC mV requirementsBesides, AC millivolts down that low is sub audio territory anyway isn't it?i.e. buy a dedicated low millivolt AC meter if you really need one, as it's not gonna happen with most 'All In Ones' at any price

author: joeqsmith
author_rank: Super Contributor
timestamp: October 30, 2019, 11:26:41 am
content: Quote from: Electro Detective on October 30, 2019, 08:48:30 amI wouldn't say that OP is working in audio as there are certainly applications where we are interested in even lower noise levels having nothing to do with audio. This particular measurement is just one small aspect of what I will be looking at with the 121GW.Having looked at the early meter and uncovering several problems, I am very interested in seeing how it has changed. I was following the firmware updates for a while, but I am really interested in the hardware.The 121GW's switch was a weak point with the early version. While Dave made a video showing a switch life cycle test, when looking at pictures various people had posted, it appeared that they had used various contact designs.While I do mention the price of the products, it really has no bearing on how I conduct my tests. The free meters from Harbor Freight are treated the same as a $900 Gossen for the data I collect. After testing so many products, I have my favorite brands. I certainly didn't start out being pro Fluke but the data changed my view. Point being that I really don't care how the meters perform and the test jigs have no brand bias. So while people will tell me I am on witch hunt while I am looking at their favorite brand, the data speaks for itself.Safety wise, I would have no idea, nor do I care. IMO, the best thing anyone could do would be to check the reports and see how often the company inspects their products. If you designed a new product, had it certified, then started changing the design, you will normally go through the process again. You may find companies performing annual tests. The cost can be significant. Perhaps this is why no frills meters like the Fluke 101 that have a very limited feature set, cost $50. The Aneng meters may cost half that with far more features but if safety is really important, what one would you want to use?****Too little coffee. Fixed some grammar problems.

author: Sultanpepper123
author_rank: Regular Contributor
timestamp: October 30, 2019, 02:25:39 pm
content: Quote from: joeqsmith on October 29, 2019, 05:27:42 pmCurrently I'm working on an Energy utility meter and i'm trying to periodically measure the current transformer's output after the burden resistor where readings start from 119.68uV , so as far as i can tell as long as the burden is there and both CT terminals are connected, this is considered "safe" . I'm also reading mains voltage which is referenced to neutral ( voltage divided ) to around 140 mV. the concern here is at the CT which will be giving out very small readings which the microcontroller will read but form time to time i'll need to make sure the metrology front end is reading things correctly, should someone jump in and say that DMM is not useful in this case and an oscilloscope is , i currently have a Siglent SDS1104X-E but i'm sure it wont be able to read those numbers unless introduced to a LNA or Dave's uCurrent ? right now i'm thinkning out loud. Would really appreciate sharing your thoughts.RegardsSultan

author: SilverSolder
author_rank: Super Contributor
timestamp: October 30, 2019, 03:29:20 pm
content: Quote from: Sultanpepper123 on October 30, 2019, 02:25:39 pmHow many ohms is the burden resistor for the CT, and how many ohms are the two resistors in the high voltage divider?Knowing that would help find the most cost effective way of measuring the values you are looking for (including figuring out if a uCurrent would work).

author: Sultanpepper123
author_rank: Regular Contributor
timestamp: October 30, 2019, 04:07:46 pm
content: Quote from: SilverSolder on October 30, 2019, 03:29:20 pmThe CT is 1:2500 , starting current is 40 mA till 110 A. with a load resistance rating of 10 ohm CT, my burden resistor is 7.48 ohms . The voltage divider is 10 in series 165K ohm resistors (1.65 M ohm total) as the top resistor and lower resistor in the V.divider is 1K ohm.RegardsSultan

author: joeqsmith
author_rank: Super Contributor
timestamp: October 30, 2019, 04:49:03 pm
content: So 40 mA is roughly 120uV and 110A is 330mV. Sounds like you would really want to just gain up the voltage then. Even if the sense opens, it seems like it's fairly limited as far as having the amp survive.The problem may be that say you use a 1000X amplifier, it would be wanting to put out 330V.Assuming you are testing steady state and can manually change the gain, you could almost use that amplifier I show the pictures of. I have 10,100 and 1000X, and using the 10X or 3.3V output wouldn't be a problem with a different battery pack. Maybe just a couple of back to back diodes to clamp the inputs if you open the sense for some reason.Another option may be something like Tektronix's ADA400A which has up to a 100X gain.http://w140.com/tek_ADA400A.pdf

author: SilverSolder
author_rank: Super Contributor
timestamp: October 30, 2019, 05:39:11 pm
content: ...and just to comment on the uCurrent, it could be pressed into service as a low level voltmeter in this situation but you would have to put a resistor in series with it to read all of the wide range you are interested in. Or, you could use it directly as Dave intended, i.e. as a current meter and measure the current through your resistors - but that would require breaking into the circuit on the board so would be for bench testing only.Personally, since I already own a uCurrent, I would go right ahead and use it - but if you have to go out and buy stuff, a high impedance voltage amplifier as suggested by @joeqsmith (I haven't used that specific model) is more convenient for this specific use case.

author: tautech
author_rank: Super Contributor
timestamp: October 30, 2019, 07:33:53 pm
content: Quote from: Sultanpepper123 on October 30, 2019, 02:25:39 pm119.68uV will be right down in the channel base noise however if you select a p-p measurement and engage Statistics you might get some usable data. Give it a try. Of course you'll need to have 1x probe and input selected.

author: Sultanpepper123
author_rank: Regular Contributor
timestamp: October 30, 2019, 09:43:25 pm
content: Quote from: joeqsmith on October 30, 2019, 04:49:03 pmI've never used one of those, looks interesting. Personally option A would be a pretty good exercise. But since this is work related and i'm not going to pay for it, I'm leaning towards buying a ready made differential preamplifier, the ADA400A looks to have a proprietary connector. Nevertheless, i've realised a new tool type but after searching a bit i've stumbled uponthis, based on your experience would this suffice ? Also correct if i'm wrong, we are now going into the track of using an oscilloscope + differential preamplifier , correct ? or does it work on a multimeter ( i currently have a modest UT61E , will that work ? ). Again massive thanks and appreciation for sticking around and the help and sharing your experience and thoughtsRegardsSultanQuote from: SilverSolder on October 30, 2019, 05:39:11 pmWouldthisbe considered a step up / suitable for the application ? , Please let me know if there are other alternatives.RegardsSultan

author: SilverSolder
author_rank: Super Contributor
timestamp: October 30, 2019, 10:19:43 pm
content: The amp you linked looks like it would do the job - just never feed it more than 400mV on its input in DC mode.Looks like a pretty cool product, the only thing I thought was a little bit disappointing is the 1% gain accuracy.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 30, 2019, 10:28:08 pm
content: Hence my back to back diode comment. Same applies to this amp.I was thinking 1% was pretty decent when you consider the stackup for the transformer, shunt, meter. If they need 1% total, they may need to do some tricks but I doubt that's the case.

author: maginnovision
author_rank: Super Contributor
timestamp: October 30, 2019, 10:35:33 pm
content: You could characterize it too so that you know what the gain is, it's pretty flat across the range but with multiple ranges 1% is pretty conservative. I have two of them and they work fine as long as you don't use the included supply.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 01, 2019, 01:20:49 am
content: As promised, two brand new, out of the box, 121GWs. I used the exact same setup as before, compensating for the errors in the attenuators. It was then rechecked against one of the Fluke 189s. The office is 20.8 degC.It doesn't appear to be all that great which may be why Dave didn't present data for it but it was better than a lot of the meters I looked at.I think you get much better results using the amplifier. Good luck with your testing.

author: Andreas
author_rank: Super Contributor
timestamp: November 01, 2019, 05:53:42 am
content: Quote from: Sultanpepper123 on October 30, 2019, 02:25:39 pmfor that application I would use a low noise high resolution oscilloscope e.g.:https://www.picotech.com/oscilloscope/4262/picoscope-4262-specificationsor if it has to be more accurate something like this:https://www.dewetron.com/products/power-analyzer/dewe2-pa7/with best regardsAndreas

author: BravoV
author_rank: Super Contributor
timestamp: November 01, 2019, 06:02:07 am
content: Guys, before suggesting anything, consider that the OP is living in Iran, choices are very limited, even OP can afford it.

author: Sultanpepper123
author_rank: Regular Contributor
timestamp: November 01, 2019, 11:42:19 am
content: Quote from: SilverSolder on October 30, 2019, 10:19:43 pmThank you very much Sir, i think i will go with the amplifier solution.RegardsSultanQuote from: SilverSolder on October 30, 2019, 05:39:11 pmThank you very much for sharing your thoughtsRegardsSultanQuote from: joeqsmith on October 30, 2019, 10:07:43 pmNoted, that gives the amplifier (which is differential input ) an advantage , correct ?RegardsSultanQuote from: joeqsmith on November 01, 2019, 01:20:49 amVery interesting data. Kudos to you sir for the huge effort and sharing your results with us here and i must say it was really a pleasure.BTW it turns out i've watched a few videos from your youtube channel a few years back while trying to test my boards with, really interesting videos i must say, keep up the good work.RegardsSultanQuote from: BravoV on November 01, 2019, 06:02:07 amEgypt actually. But i agree with the rest of statementRegards

author: SilverSolder
author_rank: Super Contributor
timestamp: November 01, 2019, 11:54:14 am
content: One thing to try is to use the Averaging acquisition mode on your scope (assuming it has it!), and see if it can pick a signal out of the noise floor. You might be surprised how powerful averaging can be! Don't use x10 probes, connect the signal straight in with coax cable to give the best chance of picking something up. Set the averaging as high as you can, and let'er rip!

author: Performa01
author_rank: Super Contributor
timestamp: November 01, 2019, 02:46:06 pm
content: Quote from: SilverSolder on November 01, 2019, 11:54:14 amActually a SDS1004X-E can do this with its true 500µV/div sensitivity, even without averaging.For best results, the setup should be tweaked a little, but even so you cannot expect a stellar accuracy for a number of reasons:The high voltage tolerant split-path input buffer of modern DSOs exhibits a lot of noise at low frequencies. The already weak signal gets divided down by 10-20dB, then amplified back up to its original level by a (MOS)FET OpAmp. The global LF feedback and offset control introduces some additional very low frequency noise.One vertical division on the DSO is equivalent to just 25LSB of the 8bit ADC. Signals that are less than one division peak to peak certainly cannot be measured with great accuracy, even if there was no noise.A DSO isn't a precision instrument from the outset...Keeping the above in mind, you'd need to be prepared for errors up to 10% when dealing with microvolt signals.I've simulated the situation described by the OP. The strong (100mVrms in my example) voltage signal goes into channel 1 and this also needs to be the trigger channel, since even the excellent trigger system in an SDS1004X-E cannot deal with a noisy 100µVrms signal.Channel 2 is set to 500µV/div and bandwidth limited to 20MHz.Max. record length is limited to 70kpts in the Acquire menu in order to get the sample rate down and reduce the bandwith even further by this.Use standard deviation measurement (aka AC-RMS) for estimating the RMS voltage - or, even better, cycle standard deviation measurement, as I've found this to be a bit more accurate in the given situation.The first screenshot SDS1104X-E_50Hz_100uVrms_Avg16.png illustrates the measurement with 16 times averaging acquisition. Look at the mean value of the measurement statistics.The 2nd screenshot SDS1104X-E_50Hz_100uVrms_Norm.png shows the same scenario without averaging. Yes, the signal trace doesn't look as pretty as before, but Cycle Stdev measurement accuracy is hardly affected. So it is possible to get a reasonably quick measurement when needed.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 01, 2019, 08:51:33 pm
content: I wonder how linear it is. Some time ago I was attempting to use over sampling with my scope to improve the resolution. It was really non-linear. I ended up making a model of the errors and used that to apply a correction. It worked alright but I doubt I could get down to these levels.

author: Performa01
author_rank: Super Contributor
timestamp: November 02, 2019, 12:14:13 am
content: Quote from: joeqsmith on November 01, 2019, 08:51:33 pmA legitimate question - and there is a reason why I've stated that we have to expect up to 10% error...I've done another test run and this time the measurements were different - the error was higher.Here are the results:As can be seen, the error is consistently between +3% and +7%, hence <4% linearity error.Yet I wondered where the constant error comes from and did a long term observation on the DSO, where I noticed some ultra low frequency interference, with a peak to peak amplitude almost 10% of the measured value.I checked the 1mV test signal with a Keithley 2015 THD bench meter and sure enough, the reading was unstable there as well, with readings between 950µV and 1.047mV.Finally I realized what's going on and changed the frequency to 60Hz, thus clearly separating it from the mains frequency. Lo and behold, the DMM reading was suddenly a fairly stable 1.017mV.The ultra low frequency interference component was just the difference frequency between 50Hz from the AWG and the 50Hz mains, and that difference was just too low to cancel out within a reasonable number of signal periods. On the DSO, I could use the line trigger and the trigger point moved very slowly - slower than the minute hand of a clock...I can't be bothered to repeat the test with 60Hz right now, but might do it eventually. Anyway, because of this the results of my test run could be taken as some sort of worst case scenario - and serve as a warning at the same time, that measuring mains related signals might include some interference that is hard to detect and cannot be separated.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 02, 2019, 05:02:03 pm
content: If we can amplify the signal to get a stable trigger, then we may as well work with the amplified signal.I doubt my DSO would allow me to use the average at this low of a signal (because of the trigger). Maybe I could capture several cycles in a sweep then in software derive a reference to pull each cycle apart, overlay and do the average. I would still want to model the DSO's errors to get the most out of it. Seems like a lot of work to with little gains.How well does your DSO do if you use the 100uV signal for the trigger and try to average?

author: Kleinstein
author_rank: Super Contributor
timestamp: November 02, 2019, 05:32:22 pm
content: For the trigger one does not need to amplify the actual signal, just a signal in phase (e.g. same generator / mains if mains signal) would be good for the trigger.Just using a longer data window can also be an option, though it includes more higher frequency noise. So ideally one would want a lower than 20 MHz BW limit.Using a high degree of averaging and a rather short data window (e.g. 1 or 2 periods) nearly turn the DSO into a lock-in amplifier.

author: SilverSolder
author_rank: Super Contributor
timestamp: November 02, 2019, 06:00:09 pm
content: Quote from: Kleinstein on November 02, 2019, 05:32:22 pmI use my scope as a null detector in a bridge, synced to the generator, and using a uCurrent to amplify the current into a ratio transformer "variable tap". I am getting 0.1ppm resolution by looking at the phase relationship over 1 period - the ability to average the noise out of a noisy AC waveform is definitely a killer feature of a DSO, I can't think of any other instrument that could do this.

author: Performa01
author_rank: Super Contributor
timestamp: November 02, 2019, 07:34:27 pm
content: I have repeated the test with the Siglent SDS1104X-E and a 60Hz signal.This time the output signal at 100mV was calibrated using a Keithley 2001. Apart from the calibration error (which is insignificant for this test), only the accuracy of the internal attenuators in the Siglent SDG6052X arbitrary waveform generator remain an issue. From other tests I have every reason to believe that the attenuator in this device contributes less than 0.5% error to the net result, so I can present my findigs with reasonable confidence:SDS1104X-E_Linearity_60HzThis looks certainly much better now, with less than 1% absolute and 1.7% linearity error down to 500µVrms and still good 1.3% accuracy and 2.1% linearity down to 300µVrms. Below that, the error increases a lot.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 02, 2019, 07:41:36 pm
content: I thought I was making it clear that I was assuming there is only the 100uV source to work with. Sounds like I wasn't clear enough. Obviously if there is access to a higher voltage source that is in sync with the signal of interest that could be used for a trigger, this wouldn't be a problem.

author: Performa01
author_rank: Super Contributor
timestamp: November 02, 2019, 07:58:34 pm
content: Quote from: joeqsmith on November 02, 2019, 07:41:36 pmI think most of us have referred to the situation as described by the OP in his reply #106:https://www.eevblog.com/forum/testgear/suggestions-for-a-dmm/msg2761686/#msg2761686It sounds like there is a strong 140mV signal from the same source available.Quote from: joeqsmith on November 02, 2019, 05:02:03 pmAs already stated, it does not do it at all, since it cannot trigger a 100µV RMS signal.It does work with a 200µV RMS signal though:SDS1104X-E_60Hz_200uVrms_Avg16The expected reading would be about 205µV, and the error is in line with my previous test.EDIT: Please notice the low standard deviation of the result in the measurement statistic ...Btw, just to be safe: "my" DSO happens to be also the DSO of the thread opener. Therefore I thought this demonstration might be helpful in his situation. Otherwise I would not recommend any DSO (not even a PicoScope 4262) without suitable external preamplifier for measuring low frequency microvolt signals.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 02, 2019, 07:59:45 pm
content: Quote from: SilverSolder on November 02, 2019, 06:00:09 pmThe classical instrument to measure small AC signals including phase to a reference is a lock in amplifier, especially the better 2 phase version. Compared to an DSO modern digital Lock-ins tend to use higher resolution ADCs, but lower speed. The other related old time instrument is a box car integrator - the equivalent to the averaging mode one an DSO. This one could also be done in analog for a limited number of channels.A good working averaging mode can be an important and very useful feature on an DSO.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 02, 2019, 08:56:09 pm
content: QuoteQuoteI missed that part. Even at 200uV, it seems impressive.

author: SilverSolder
author_rank: Super Contributor
timestamp: November 02, 2019, 09:20:57 pm
content: Quote from: Kleinstein on November 02, 2019, 07:59:45 pmUsing a DSO, you can act as a "human lock-in amplifier" by varying the capacitance across one of the bridge arms until the waveforms show that you have nulled out both the real and quadrature currents. You can even act as a human capacitor if the circuit is somewhat high impedance (e.g. 100K), playing it like a Theremin to balance it out!Ghetto metrology!Just for fun, I tried inputting a nice noisy 100uV signal on an Agilent 54622D, which (unlike the Siglent) only has a 2mV/division vertical amplifier (the 1mV setting is "faked").Without averaging:With averaging:100uV amplitude is too low to measure properly - but good enough to see the phase!Further experiments showed that you can get down to about 5uV - 10uV and still just about make out that there is a signal there...If you put Dave Jones' uCurrent in front of this not particularly sensitive scope, with accurate amplification of x100, you can actually peek into the nanovolt region!7 digit resolution is possible (has been achieved in the basement) this way, and with another x10 more amplification, that elusive 8:th digit might be within reach using the DSO method...But, who knows, perhaps there is a lock in amplifier or a box car averager in the future!

author: joeqsmith
author_rank: Super Contributor
timestamp: November 02, 2019, 11:29:58 pm
content: Using the same setup I used with the handheld meters, but using a separate signal for the trigger, my vintage DSO is about 10% out at 100uV. The Fluke 101 with a simple amplifier would easily out perform it at a much lower cost. Not too surprised.

author: Frex
author_rank: Regular Contributor
timestamp: November 03, 2019, 07:09:47 am
content: hello all,For those who want make low level AC measurements, i designed few months agoa small wide-band low noise amplifier to do power supply wide-band noise measurements.It include two stages with x10 and x100 gain output with flat bandwidth over 20Hz - 20 MHz.It accept DC offset of + or - 20V max. The total bom count is about 30€,and the full project is open source and available on Githubhere.You can also lookherewhere i describe the project with some measurements results.Regards.Frex