We Can Make Multimeter Reviews Better - Page 1
Forum section: electronics / general

author: Richard_S
author_rank: Contributor
timestamp: December 17, 2023, 10:18:06 pm
content: I want to start by paying tribute to those that care about safety. Making sure that the meter has fuses and protection and will keep me safe when I probe around in that electrical substation is genuinely a good thing. Only I don't have an electrical substation nor three-phase at my house. I can't even remember the last time I measured mains voltage. I know that these things matter even when you are on the far side of the transformer, but even that is rare for me.What I measure predominantly are small ac voltage signals and it is here that multimeters are pretty useless. What may surprise people more, is that even the expensive high-performance models are poor at small-signal ac measurements. Not all of them, but most.Yet, I cannot remember reading or watching a review that took a look at small-signal ac measurements. I'm sure there are some, but they are far from the norm. We get loads of detail on the high-voltage, high-current side of things and that is great alongside lots of attention to dc accuracy, but ac precision and how useful a meter is for small signal work is regularly omitted altogether. What we all need to do is to balance our coverage of multimeters by mentioning the higher bandwidth and lower voltage signals alongside the bigger signals and dc performances we cover now.AccuracyIts not uncommon to find that a very expensive high-precision bench multimeter reading dc to better than 0.03% has an accuracy of worse than 1% for ac voltages. A much prized 6.5 digit meter may well perform significantly worse than another much cheaper device with only 4.5 digits. It is very hard to find meters even amongst the elite that prioritise ac accuracy. The poor ac accuracy performance is missed in so many reviews so we should make a point of discussing ac accuracy and especially for small signals..RangeWhen it comes to small signals, the situation is made even worse because of the lack of low-level ranges. Meters that have a dc millivolt range or even stray into microvolts sometimes start 5, 10 or even 30 times this for ac signals. This disparity is rarely mentioned and we really should. The combination of poor accuracy and the absence of low measurement ranges interact to make many meters singularly useless for small signal measurement, yet we almost never say.BandwidthIt is rare to find a meter that will handle the full audio bandwidth which is what I am most interested in. Meters often retain their accuracy only in the tens of Hertz or hundreds of Hertz. There are meters that are good for this, and this is one area where paying more often helps, but you have to look for them and you can't take it for granted. Again, this shortcoming is rarely mentioned in our reviews. While audio is what matters to me, people working on servo systems and dc motor drives as well as all sorts of sensor and drive circuits need wider bandwidths, in some cases way beyond the audio range I'm looking for. I am amazed that ac accuracy, ac ranges and ac bandwidth are not standard talking points in every multimeter review.RMSI am often shocked at people talking about the RMS capability of a multimeter without mentioning bandwidth. People will recommend looking for RMS capability for use with audio for example. Why do they do this? In most cases the meter does not cover the audio range and so whether it measures true RMS or not is irrelevant. Secondly, true RMS is unnecessary when measuring things like gain and line-up levels using tone. Keep in mind that meters are always less accurate when measuring true RMS, so where the meter has a choice, you are generally better off turning this function off. Where RMS is at its most useful is when measuring noise, but yet few multimeters have the range to usefully measure noise in audio equipment (or servo systems for that matter). If they could, fewer still have A-weighting which you may well need at some point, for sound at least. We make far too much fuss about RMS and rarely explain how limited its use really is. How many multimeter reviews have you read where the author never draws attention to the limited bandwidth?DecibelsThe ability to present the reading in dB is often scored well in reviews when in practice, I find that it is rarely useful. If you want to line a piece of equipment up, then you can convert from dB first and simply measure in volts. Where direct reading of decibels does become useful is when tracking changing values and most multimeters are too slow for their dB reading displays to be relevant.Please throw rocks at my thinking here. Tell me I'm wrong. Point out that all this stuff is regularly covered. Happy to be shown to be incorrect on this if I am.

author: bdunham7
author_rank: Super Contributor
timestamp: December 17, 2023, 11:04:05 pm
content: Quote from: Richard_S on December 17, 2023, 10:18:06 pmRTFM.And don't consider products that don't have reasonably complete specifications in that manual. Reviews are no substitute for proper specifications.A few things about specific points you made:AC accuracy is an order of magnitude or so more difficult to be precise with than DC, even more so at high or low frequencies or complex signals. But I can't think of any decent meters that have as wide of a disparity between them as you claim. Any examples?As far as BW, meters intended for mains power applications may have reduced BW, but most decent meters with separate TRMS converter chips will cover at least to 20kHz, at least in voltage. Where they almost all fall down is BW for AC current. The otherwise modestly performing BK Precision 2831E was specified to do current with reasonable accuracy out to 20kHz, which exceeds most of its competitors.Being able to switch between average-responding RMS reading and true RMS isn't a feature I've ever seen and A-weighting really wouldn't be appropriate for an RMS-reading DMM. It is true that many use cases don't require TRMS, but I'm not sure why you think they are necessarily more accurate without it.Decibel readings may not be a big thing to you or most people, but the function is very easy and cheap to implement so there's no savings to be had by eliminating it.Your issue with small-signal AC readings is probably residual counts and the lower specified threshold (in the manual, of course) that prevents you from getting any meaningful readings below 1-5% of the lowest range. A review will only tell you how that particular unit does on that particular day, the actual performance will vary between units and is only guaranteed to meet the spec. As an example, take the Fluke 289 on the 5VAC range reading a 1kHz test signal. The meter is specified for accuracy from 2% to 100% of the specified range, meaning over 100mV. One example displayed about 230 residual counts (with zero input) equivalent to 23mV, another showed 0 residual counts and doesn't start showing any reading at all until the signal reaches about 16mV. Both meters are well within spec above 100mV. But two reviewers with two different meters might come to different conclusions.b/t/w, to reinforce your point about TRMS, my average-responding Fluke 27 (3.2V range) will read that same 1kHz signal all the way down to 1mV within 1 count accuracy.

author: TheDefpom
author_rank: Frequent Contributor
timestamp: December 17, 2023, 11:36:56 pm
content: You obviously haven’t seen my reviews where I do things like check detection threshold’s and accuracy for the entire voltage range, including bandwidth vs accuracy.I do this on a Datron 4700 calibrator.

author: alm
author_rank: Super Contributor
timestamp: December 18, 2023, 12:10:04 am
content: The problem with testing accuracy in reviews is that accuracy and bandwidth is generally based on probability distributions, and you won't learn much about a probability distribution from a single sample. Yet manufacturers are not likely to ship say a hundred meters for a review, never mind the amount of work in collecting data on 100 meters. If you are just talking about specifications, then surely you don't need a reviewer to read the specifications?I can understand low voltage AC response, though I agree with bdunham7 that you really shouldn't be relying on the meter performing better than the guaranteed specs. And particularly should not expect because a single sample exceeded the specifications by a certain amount, that a meter you buy a year later will do the same.Quote from: Richard_S on December 17, 2023, 10:18:06 pmDo you have a reference for that? Any 5.5+ digit bench meter I'm familiar with is true RMS and has better accuracy than lower end meters. One meter I remember that can switch between true-RMS and average responding is theKeithley 2001-M, but the average responding mode has a lower accuracy than true RMS mode. I think the average-responding mode was just added for a military customer that had procedures based on avergage-responding meters, not for better accuracy. If anything, an average-responding meter makes more assumptions about signal shape and distortion. Any lab-grade ACV standard I'm familiar with, likethermal voltage converters, are true RMS.

author: rsjsouza
author_rank: Super Contributor
timestamp: December 18, 2023, 12:40:03 am
content: Maybe we are few and far between. Although I don't perform accuracy AC measurements in small signal scenarios as defpom does, in my reviews I usually measure bandwidth and try to educate the audience on its applicability to audio and how TRMS influences measurements of non-sinusoidal waveforms.Regarding accuracy, alm and bdunham7 mentioned very important points, especially due to the variability of each unit and the wide variance of accuracy across the range.

author: bdunham7
author_rank: Super Contributor
timestamp: December 18, 2023, 04:07:15 am
content: Quote from: alm on December 18, 2023, 12:10:04 amI think the superiority of the average responding meters is only evident at the very low end of the scale where the residual counts start to matter, at least if we're talking about comparing meters in roughly the same class. But in most cases involving 5.5+ digits, average responding meters are older models that don't have the lower ranges on ACV. The Fluke 8800A, for example, responds fairly accurately all the way down to the bottom of its 2VAC range, but competing 5.5+ digit TRMS meters like the 8842A have a 200mVAC range.On meters that are switchable or based on TRMS models, if they simply use the averaging feature of the TRMS chip along with different calibration constants, you may get an average-responding meter with all the disadvantages and none of the benefits of a dedicated average-responding converter.

author: J-R
author_rank: Super Contributor
timestamp: December 18, 2023, 06:09:10 am
content: What minimum voltage are you actually targeting?The features mentioned seem somewhat niche, so I can understand why reviewers might not be focused on them. The DMM is a multifunction device so there are going to be strengths and weaknesses due to cost/design/market. Plenty of forum members have some specific DMM due to an aspect it excels at.For audio repair older analog AC millivolt meters still seem popular. The "best" one I have currently is the Lodestar MV-3100A which has a 300uV range and 1MHz bandwidth. My various bench DMMs were OK down to around 500uV at 100kHz, and in some cases to 200uV and 300kHz and beyond. For regular measurements of these and smaller inputs, perhaps I'd get a nanovolt amplifier.

author: 2N3055
author_rank: Super Contributor
timestamp: December 18, 2023, 07:53:16 am
content: Quote from: Richard_S on December 17, 2023, 10:18:06 pmFrom your writing, I would gather you need to measure voltage in audio range. Probably for audio amplifiers stuff.What you need is probably specialty low voltage AC voltmeter.There are many articles and reviews that mention small AC measurements.I would be curious to know what application needs better than 0.06% accuracy in audio range at levels of 10 µV RMS.Accuracy: It depends on your definition of "high-precision bench multimeter". Even my "not very fancy" Rigol DM3068 (6 1/2 digit meter) has 0,06% accuracy on AC range (10Hz-20kHz) on 200 mV range. Simillary from Siglent and oodles of others. Also 5 1/2 digit meters from Siglent and Rigol will do 0.2% in audio range... TTi 1908 will too.. and bunch of others..Range: There are meters (like I said, those are specific instruments) that have sensitivity you need. Standard multimeters with their unshielded banana connectors and probes are not fit for this purpose. You need coaxial, shielded inputs and probes for this. Maybe differential, even...BW: I have 3 multimeters that have way more than audio BW: DM3068 (300kHz), MTX3293 (200kHz) and BM869S (100kHz). There are very many meters that have very wide BW.dB: dB measurements are simple recalculation. On well implemented meter you can specify load impedance and get direct dBm reading. Speed will be defined by meter AC measurement speed. On DM3068 (for instance) i can specify AC RMS filter and in fastest setting, I get maybe 10 measurements per second. Enable dBm and voila.... Realtime response.But you are correct. Most multimeters are not audio meters. Audio meters are specialized instruments, which multimeters are not.To add, I also have a 16 Bit picoscope that is best AC voltmeter you can buy. 5MHz BW, scope, meter, and several dozens of measurements, spectrum etc...People also use audio analysers for accurate level measurements.If you want a simple and inexpensive solution, a preamplifier and decent meter does a good job too.Or shall we take this question and set it differently?How about you lay out what problem you need fixed ( "I need to measure this and this within these and these parameters and constraints. What you guys can recommend?") and I'm sure some solution will come out of it...

author: Kleinstein
author_rank: Super Contributor
timestamp: December 18, 2023, 07:14:38 pm
content: For the general accuracy, this something that can not be tested with a few meters in a short time. Here one can only check of the samples actually meet the claimed accuracy specs, which they should all do with some margin for drift.A problem with just looking at the specs is that even for the manufacturer with 100s of meters to test it is hard to estimate the accuracy. Different companies may use different guard factors and even than they are sometimes off in either direction for some meters. Often only time tells which meters are very stable and which tend to drift or fail early.How far one may go down and still get a sensible reading can vary between units - can't use 1 or 2 meters to really judge on this. It can make a difference how the RMS readings are done. There are now also some handheld meter that do RMS the digital way. This often comes with a limited BW, fast response (rarely specified - so need to actually test), reasonable good performance at low frequency and small fraction of the range (at least if done right). So one can usually tell from a test and sometimes the specs.The analog RMS chips are tricky with small amplitudes: the smaller the voltage the smaller the bandwidth of the RMS chip. Another somewhat tricky point is the performance at lower frequency - that is less than some 40 Hz. Accuracy can suffer already quite a bit at 20 Hz. For the meters based on the analog RMS chips there is compromise between the low frequency performance and response time - it could be interesting to see on which side they are: relative fast response and poor LF accuracy or good accuracy also at 20-40 Hz and than a more sluggish response.

author: armandine2
author_rank: Frequent Contributor
timestamp: December 18, 2023, 08:51:49 pm
content: we can make Multimeter reviews betterI've mentioned before that I don't believe there areOscarsfor this line of work - but for content makers their viewing figures seem to suffice.

author: bdunham7
author_rank: Super Contributor
timestamp: December 18, 2023, 11:36:56 pm
content: Quote from: Kleinstein on December 18, 2023, 07:14:38 pmThat compromise is sort of baked into the problem and it is there even if you don't use an analog TRMS chip. Better and newer meters (think HP 34401A and up/newer) have selectable AC filters and work pretty well down to 3Hz or so.

author: Richard_S
author_rank: Contributor
timestamp: December 19, 2023, 05:21:36 am
content: Well, thanks everyone, what an interesting set of replies! I still think making reviews even better, even more effective, address a wider range of users, is a laudable aim though I am beginning to think that may be an unpopular view. Firstly, to those who say here that "I have got a great meter for..." Well done to you. I'm not sure that really speaks to the issue though. As for "reading the f-ing manual", is that really a response to reviews not being as well constructed as they could be?Look at a bunch of multimeter videos and see how often they say "it's got a basic dc accuracy of..." but do not point out that its ac voltage accuracy is also very good, or perhaps more importantly when it is not. The dc accuracy is the banner headline figure but the ac accuracy is always worthy of discussion, always should get a mention. Always in the context of how the low ac ranges stack up against the dc too because having acceptable accuracy but no low ranges is just as much a problem.Several times people mention that it is harder to achieve precision on ac. Is that a reason not to direct the viewer or reader to understand the performance of an individual meter? I would have thought if anything that it makes it more important.I would just ask whether you think enough reviews make a big enough effort to explain the meter's basic ac accuracy and characterise it as good or bad?

author: Kleinstein
author_rank: Super Contributor
timestamp: December 19, 2023, 08:56:08 am
content: For many uses the accuracy of the AC measurements is not that important. Anything mains related is a bit variable anyway. There are a few exceptions, especially with audio. The more relevant part for AC are the limitations is the frequency and crest factor. Not all DMMs can measure 20 Hz or 10 kHz AC reasonably well - this could still be an acceptable limitation as most measurements tend to be main frequency and maybe the 2xmains frequency ripple after a rectifier. A point not always clear in the specs is that some meters have AC mV with DC coupling only. This can be anoying when looking at ripple.Quote from: bdunham7 on December 18, 2023, 11:36:56 pmThere is a principle limitation, but the analog RMS chips are quite a bit slower than the limit that can be reached in the digital solution. Ideally digital RMS the response takes the actual frequency into account and can react from one period to the next. Even with just a fixed filter it is the difference between a finite response time (FIR filter like running average) and an exponential decay (and sometime worse) for the analog RMS. Switching the filter speed with analog RMS is more like a work around to have the choice. The newer KS bench DMMs (3446x - not sure about the 34410) use digital RMS.One can quite clearly see the difference when measuring an AC voltage and than remove the probes / turn off the source. With digital RMS one usually gets one reading in between and than a zero. Analog RMS takes several samples to get down and sometimes several seconds to really reach zero.

author: 2N3055
author_rank: Super Contributor
timestamp: December 19, 2023, 09:10:38 am
content: Quote from: Kleinstein on December 19, 2023, 08:56:08 amKS 34410AKS 34401A uses RMS chip from AD. But34410/34411A did have digital measurements and that architecture is probably the basis for 3446x series....EDITED error. Sorry.

author: EEVblog
author_rank: Unknown
timestamp: December 19, 2023, 09:40:14 am
content: Quote from: Richard_S on December 19, 2023, 05:21:36 amGood thread topic.One of hte problem is that a decent review is already long enough, and adding (and explaining the importance/lack of importance of low level AC signal measurmeents and bandwidth you could argue adds excess length to the video for what most would consider little benefit. Sure it might be very important, maybe the most important parameter for some people, the number fo people in the catgeory is arguably low.I think most reviewers know this and is why they tends to skip or gloss over such things.And I know some poeple will say " just use timestamps", but the fact is video length matters.Every reviewer also has a set of their own personal interests, and so they tend to focus more on those things. Joe Smith for example is mostly focussed on electrical and physical robustness and comparison, and for some poeple that may be the most important factor, but for others it could be way down the list.

author: Micke
author_rank: Regular Contributor
timestamp: December 19, 2023, 10:26:31 am
content: Quote from: 2N3055 on December 19, 2023, 09:10:38 amBoth HP/A/K 34410A and 34411A uses Digital sampling for ACV and ACA. Crest factor can be up to 10:1

author: 2N3055
author_rank: Super Contributor
timestamp: December 19, 2023, 10:30:19 am
content: Quote from: Micke on December 19, 2023, 10:26:31 amYou are right... Idiot dyslexic me confused 34401 and 34410...I used 34411 so that one I know how it works... I completely forgot about 34410...Post corrected. Thank you !

author: bdunham7
author_rank: Super Contributor
timestamp: December 19, 2023, 09:42:16 pm
content: Quote from: Richard_S on December 19, 2023, 05:21:36 amI suppose it all depends on what the overall goal of a review is. If it is to characterize a single example of a meter that either doesn't have detailed specifications or for viewers that don't read manuals or don't understand those specifications, then perhaps some attempt to discuss the subject might be worthwhile. But there have been extended discussions here about the particulars issues with various meter's AC performance and those get quite complex and detailed. IMO, there's not much use in trying to simplify these issues enough to cram them into a reasonable length YouTube review. At some point, simple becomes wrong.So here's what you'd need to include in order to have any reasonable claim of covering the subject, IMO:1) Input impedance characteristics, including whether or not they change on each range. This includes resistance, capacitance, AC or DC coupling and the lower cutoff frequency of that coupling.2) The type of AC RMS conversion--separate digital, analog chip, on-chipset digital etc. Then the bandwidth of the system, as well as residual counts and lower thresholds. I'd want to know whether the meter goes to zero whenever it is below a threshold, if the BW is lesser at lower levels, what minimum % of scale you need to acheive reasonable accuracy, maximum crest factor and more things I can't think of at the moment.3) The performance of the input divider/amplifer--at what point does it clip/protect, if it is DC coupled is it possible to saturate it with DC and get a wrong reading instead of OL, and again more things as they occur to the reviewer.4) The performance of the DC system (ADC + conditioning circuitry) after the AC conversion, if applicable. How often does the display update, settling time, accuracy on all the ranges, etc.5) Perhaps comparison of the example with the specifications, if the specs are detailed enough. However, I did give a concrete example above of exactly how this could not be all that helpful with only one sample.Unless you cover all of that, IMO, you aren't covering the AC subsystem. At best, what you seem to be proposing would be to review the performance of a particular meter in a specific use case that you have in mind, such as measuring some relatively low-impedance, low-voltage audio signal such as perhaps a line-out or something. Characterizing a meter as "good" or "bad" would be an example of simplifying something until it is wrong.

author: Richard_S
author_rank: Contributor
timestamp: December 19, 2023, 09:55:33 pm
content: Thank you to everyone that is contributing. I'm finding this a very rewarding discussion. I hope others are too.I know that some think adding a bit of detail on ac signal measurements would be time consuming in reviews, but could we not just add "basic ac voltage accuracy" to compliment the "basic dc voltage accuracy" that is so beloved of the manufacturers themselves as well as the community? Add to this a clear statement about the lowest ac range and I think you have defined the small signal performance. A few tens of seconds at most.I have found it interesting that people think low-level ac signals are very niche. They may well be. Because they are so vital for me, it's difficult for me to see how many, or how few, others also need it. I have to confess that I am surprised though. It would seem to me that many people have at some point built, refurbished, or repaired a piece of audio gear. Maybe that's just the people I know. As well as the sound, loads of servo systems use signals that are both vaguely in the same frequency range, and also share signal levels with sound equipment. Lots of the systems in cars and airplanes for example. While a lot of power supply ripple falls into the same frequencies and voltages. If there is one thing that I have found more educational than any other here, it is that small ac signals are a very specialist interest.On the RMS topic, I completely get why power users need to know RMS values, to help them understand what real power is being delivered, expended, lost or whatever. For small audio signals I was making the point that RMS is useful for two things. Knowing the realtime operational level of an audio signal and noise. All too often I read or watch someone saying that a multimeter "has to have RMS" for audio applications. Well, for realtime measurements of complex signals a multimeter is totally unsuitable, so its only real benefit is for measuring noise. Here it is a great asset but I wanted to point out that often the meter:does not have the bandwidth to make audio measurementsdoes not have a range low enough for noiseis required to assess a weighted measurement (almost always A) and multimeters just don't have weighting circuitsMeaning that users can be driven to buy totally unsuitable RMS-reading meters without understanding their limitations. That it would be useful to educate people that an average reading unit may well have suited them better, if it had a lower ac range and greater ac accuracy. It seems to me, and please say if I am wrong on this, that away from the very high-class and consequently high-priced (when new) meters, RMS is a relatively costly option that often reduces accuracy.

author: alm
author_rank: Super Contributor
timestamp: December 19, 2023, 10:10:09 pm
content: Quote from: Richard_S on December 19, 2023, 05:21:36 amThe problem is that a review can not make any statements about performance like accuracy or bandwidth beyond performance beyond "the performance of this meter is consistent with the published specifications". Just like you can't conclude from measuring the height of one person from Australia and one person from the US if people in Australia are taller than people in the US. In both cases you need to describe the entire population based on a representative sample of sufficient size. Asking this from a reviewer is unreasonable. So the manual or data sheet is the best information you're going to find. If the data sheet is incomplete or unreliable, then don't buy a meter from that manufacturer if performance is important to you.Quote from: Richard_S on December 19, 2023, 09:55:33 pmCan you explain? Anything within the bandwidth and crest factor of the DMM should be represented reasonably well. There are plenty of DMMs with bandwidth well beyond the audio bandwidth.Quote from: Richard_S on December 19, 2023, 09:55:33 pmCan you show examples of two DMMs in the same price class, one average responding with higher accuracy and lower ranges, and one true RMS with lower accuracy? Or is this just a hypothetical? This "RMS is a relatively costly option" was true up to maybe twenty years ago, but I think you'd be hard-pressed to find any decent average-responding DMM these days.

author: Richard_S
author_rank: Contributor
timestamp: December 19, 2023, 10:33:56 pm
content: Quote from: bdunham7 on December 19, 2023, 09:42:16 pmGreat thoughts and thanks for taking the time and sharing them bdunham7. Thankfully, I think for audio (but also to some degree for stuff like servo systems, sonar and other similar signals) life is a lot simpler.1) Audio output impedances tend to vary from a few ohms to a few hundred ohms while inputs are a few thousand to a few tens of thousands. As best I know, this means that unless the meter is particularly incompetently designed, its resistive impedance is going to be sufficiently high for it not to matter. Then as for the reactive part; well audio is close enough to dc that it too just won't matter either. So very different to RF measurement thankfully.2) The bandwidth matters, and absolutely needs to be discussed. Excluding the really high-priced examples, many meters just do not have the bandwidth required. I'm not sure the question of how the RMS is converted does matter though, its more the performance that needs addressing. I don't think audio test is that demanding. Thankfully for audio, crest factor is largely irrelevant. Either you are trying to measure operational levels - how loud the sound is - where crest factors cab be extreme in audio but also where a multimeter is no use (so we don't care), or you are measuring test tones (which when measuring level, will be sine waves), or you are measuring noise. If you are measuring noise then crest factor does not play a significant role (or if it is significant, it means that the noise is so high you no longer care about the exact level).3) These things could theoretically be a problem I guess, but I have just never met these issues in practice.4) Once again, we are lucky in audio. Settling time is largely irrelevant because operational measurement where it would matter can't be done with a multimeter anyway. For test tones and noise, contrary to some other signal types, longer is better. So more or less, whatever the meter can do, it will be sufficient.

author: bdunham7
author_rank: Super Contributor
timestamp: December 19, 2023, 10:41:18 pm
content: Quote from: Kleinstein on December 19, 2023, 08:56:08 amMaybe this isn't the right thread, but I'd protest that things are not as simple as that. The apparent settling time of a particular DMM using analog TRMS is not necessarily due to the response time of the analog TRMS system. The DC system afterwards integrates over a period of time as well and often has a smoothing function. Very few meters allow you to change the AC TRMS filter speed and the DC aperture independently (although I do have one that does) so this shows up as an apparent difference in settling times. A quick experiment using two roughly equivalent meters, the HP 34401A and the Fluke 8846A, shows me that with the default 20Hz AC filter and reading a 5VAC 60Hz signal, the HP does take a few readings to settle but the 8846A will settle with one intermediate reading, whether from 5VAC to 1VAC or from 5VAC to residual counts (all using a fixed range).One thing to realize is the the AC filter, whether expressed in Hz or ms,is not a high pass filter. The TRMS converter will typically function down to DC if you can get past the blocking capacitor. If you set the AC filter to a setting much higher than the input frequency but then use a long DC aperture (or averaging) you then get something closer to an average reading than RMS. This is just a result of the nature of AC and the exact same thing happens in a digital system if you aren't careful.Any AC measurement is necessarily a gated, computed result and one big difference between digital and analog is the shape of the gate. However, there's a reason HP retained the option of analog TRMS in the 3458A and that is because a digital system with a rectangular gate (if you use one) has it's own issues. You mentioned synchronizing the gate to the period of the signal for a fast response and when that works it's fine--but it doesn't always work. The folks at HPAK and Keithley have put a lot of work into getting those digital subsystems to work appropriately and you still need the right gate time.My Fluke 8505A, which is not an integrating meter in the typical sense, gives me the option of manually setting a TRMS settling time of 100ms or 500ms and another separate option of how many samples to acquire and average for each displayed reading. The default, IIRC, is 27, but you can select any number from 1 to 217samples per reading (it takes 240 samples per second). Using this, I can pretty readily demonstrate that the settling time of the TRMS converter is a non-issue for human-readable results. If you were looking at logging faster changes in higher frequency signals, then perhaps you'd want a shorter gate/faster settling time, but that would be acheivable with either type of system.

author: EEVblog
author_rank: Unknown
timestamp: December 20, 2023, 02:10:37 am
content: Quote from: bdunham7 on December 19, 2023, 09:42:16 pmThat's the thing. If you spent say 10 minutes of a review fully charctering the AC performance and then compared it to say the best performing model on the market, may people without knowing better might think that's "bad", when in every other (likely more important) way the meter is better.This is why to me, arguing over whether or not a meter survives Joe Smith's overload tests slighter better than some other meter is likely moot for most people. So it's likely better to simply say in a review that it's UL tested, tick, do a few basic tests like 1000V and 240V on the ohms range and that's that, tick, and they design and layout physically looks ok, tick.I'd put AC performance of a meter so far down the list of things to consider for Joe Average that it's just not worth adding to a review.That doesn't mean there isn't a niche market for that, just like Joe has found for his overload testing, many people enjoy those comparisons and find them useful.So nothing to stop someone becoming the go-to channel for detailed AC performance test comparisons. But I just don't think it's something that needs to be in every review.

author: EEVblog
author_rank: Unknown
timestamp: December 20, 2023, 02:21:43 am
content: Quote from: alm on December 19, 2023, 10:10:09 pmYes, the spot accuracy test in a review is essentially just a "warm fuzzy" test to potentially spot an issue.Any decent meter will be calibrated adjusted at the factory, so if you review test a meter with a 0.5% spec and you measure 0.4% out then you can certainly go "somethingsup here..."But you can't take two reviews of different meters with one showing 5.000 and one showing 5.002 and say that one is "more accurate" than the other, that's not a thing.Unfortunately the other issue with reviews is that can't keep having a detailed explanation in every review video of how accuracy works etc, the videos wouldn't become too long and convoluted. So you have to link to different videos on this topics and leave it up to the viewers to ensure they know what it all means.One good example of this, even know not electronics, is Thunderf00t's style of debunking videos. The video will be about X, but his style is to include full detail on X, Y, and Z etc in the same video just in case that's the only video of his you'll ever watch. The result is a much longer video that repeats so much stuff from other videos. There is some merit to that of course, but if you are a regular viewer it's all redundant.

author: Richard_S
author_rank: Contributor
timestamp: December 20, 2023, 04:13:59 am
content: Quote from: alm on December 19, 2023, 10:10:09 pmHi Alm and thanks for taking the time to think about this and respond. I genuinely do not understand your first point and it is I am sure my fault.Maybe I can explain what I find frustrating in meter reviews. I note that reviewers will almost always mention the maximum ac voltage that a meter's manual will claim it can handle. They will always mention the claimed basic dc accuracy. Not only that, they will use this figure to classify the meter. Finally, they will often then mention the minimum dc voltage range.By contrast I note that the minimum ac voltage range gets mentioned less frequently. Even though its maximum almost always gets a look in. My overall point here is that while there are many people servicing electrical substations and three-phase motor drives and that kind of high-voltage gear, there are some that work on small signal stuff too and I think they get left out. It would seem from what people say here though that more are working on the big high-power systems like electrical substations or three-phase motors than would ever want to fix an audio amplifier, radio, or audio interface unit. A fact I genuinely found surprising.My contention was that because it is frequently ignored, small-signal ac performance does not get put in perspective. I never hear the phrase "basic ac accuracy" for example. Why? In your reply here, you would seem to be saying, and I am sure I must have got this wrong, that mentioning the quoted basic dc accuracy is straightforward, but to mention the quoted ac accuracy is inappropriate without testing many examples of the same model of meter. If that is so, why? What is different between ac and dc in this regard?As for operational audio measurement, I am happy to explain. If you want to do this you need a special meter, the dynamic response of which needs to be dedicated to the task. These dynamics were often called the ballistics of the meter. As well as a particular meter, the user also needs to have been trained to understand what the reading means and it is the movement of the needle (or other analogue indicator) that they will read, not just its position. So, no one can or would use the digital display of a DMM for this and any multimeter's analogue bar graph will not carry the correct ballistics. DMMs will also generally not update frequently enough, and rarely have the resolution required.I'll search out some example meters. I note a feeling though that for a lot of contributors here, their own favourite meter is in the $1,000 to $2,000 (US) class and this is what they think of as a typical mutimeter. In my world, such meters are rare, and I think that the vast majority of people looking for help are buying $100 to $200 units.

author: EEVblog
author_rank: Unknown
timestamp: December 20, 2023, 04:52:22 am
content: Quote from: Richard_S on December 20, 2023, 04:13:59 amThe perspective is that for most users, small signal AC performance is not that important. As I said, for some like yourself it may be THE spec you are after, but for most people it's just not, and that's why reviews have evolved to not even bother measuring it. Anyone with experience with RMS converter chips knows that small signal perfornace is usually poor, the bandwidth drops and so can the accuracy, so you avoid doing that if possible.I'm not saying it's not a worthy test, it's just that most people aren't going to care and so the review community has evolved to not care that much and focus is spent elsewhere.

author: IanJ
author_rank: Unknown
timestamp: December 20, 2023, 05:20:02 am
content: Improving DMM testing?…….then I’ll throw in my DMM Continuity tester, a free design for anyone to make up.https://www.ianjohnston.com/index.php/projects/124-project-062-dmmcontinuityIt’s a device that puts numbers to and replaces the ‘clacking the probes together as fast as the DMM can handle’ in continuity mode.I sent one to The Defpom, he uses it in all his DMM reviews…….albeit he really should update the firmware in his hint hint…..LOL!Ian.

author: nonlinearschool
author_rank: Contributor
timestamp: December 20, 2023, 08:37:04 am
content: Hi.This may be an incredibly dumb question.why not use a scope? you are talking about AC signals and audio frequency range. How would a DMM that meet's your desired specs be better?Or, maybe it is the frustration of how everyone does multi meter reviews. I may be new here, but I have watched an awful lot of electronics videos.The small, new, and major YouTube channel creators in electronics. I get curious and go back to their beginning videos. What I have noticed is that early on, Dave kind of set the standard format of how to review them. Afrotechmod got it going, others did their various method or style...Then slowly they all began to emulate Dave's style.Dave is right. add too much and a video can get really long. However, I rarely see reviews that review a pieced of kit specifically for Audio, and very low level work. I know all you electronics YouTube content creators are on this forum. Right?How about trying out doing a video or two in a different format that caters to this "limited" interest? it might just lead to more review videos catering to other specific areas and needs!Uh, so DO I have the lingo right? "piece of kit"? "YouTube channel creator"? or "content creator"?

author: J-R
author_rank: Super Contributor
timestamp: December 20, 2023, 09:02:52 am
content: While I do think it's a valid conversation to discuss the AC capabilities of various DMMs, unfortunately what was primarily asked for is that every review be perfect. But so what if they extensively cover AC capabilities. Maybe another person comes along and wants to know how many Newtons it takes to flatten the DMM's stand. You're just asking for this one area of interest to be focused on.So I would propose pivoting the thread to some real world testing, result aggregation and problem solving instead.With regard to the concept that analog meters are superior in certain areas, I do see that of course with the AC millivolt meter I mentioned earlier that the 300uV range was an advantage, but wouldn't say the fact that it is analog is automatically also an advantage.If there is some criteria that must be tested, then there is no reason for someone to have to develop some specific skill with an analog meter. There are plenty of digital meters that can sample the same signal for automated analysis and do a far better and consistent job than a human watching a twitchy pointer.It's true that most handheld DMMs are made for some very specific use cases, and I'd actually suspect that perhaps over 90% of handheld DMMs are sold to the average person on the street who wants to check some basic stuff around the house or on their car. Out of hundreds of friends and family that I can recall at the moment, all of them fit this. These are the folks that try to "measure the amps" of their doorbell transformer or car battery, for example.

author: alm
author_rank: Super Contributor
timestamp: December 20, 2023, 09:31:20 am
content: Quote from: Richard_S on December 20, 2023, 04:13:59 am"Basic DC accuracy" is more fundamental specification because every DMM is a DC voltmeter with circuits strapped on to convert ACV, Ohms, current etc to a DC voltage. So it gives an upper bound on accuracy. No range is going to be more accurate. For a good meter at least Ohms performance will be fairly close to DCV performance."Basic AC accuracy", as in best AC accuracy based on the data sheet could easily be mentioned, although there is usually more variation in AC accuracy over ranges and frequency than for DC. Also lowest AC range could easily be mentioned, although like others mentioned the trick with a review is to extract the specifications most important for the intended audience. They could also mention how the AC accuracy is specified from 5% of the range, if that's in the data sheet. But why not read the data sheet? I think the value in reviews is in information that's not in the data sheet, like mechanical construction or user interface, or how quickly it responds to a change in value.The problem I see is with measuring unspecified things, like how low can it really meaasure ACV or over what bandwidth. That partly depends on the noise of the RMS converter (if analog), for example, and that may vary between samples. So I see limited value in such testing. For testing specified metrics you can at least verify if they are consistent with the specifications.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 20, 2023, 11:07:20 am
content: Quote from: nonlinearschool on December 20, 2023, 08:37:04 amMany AC measurement can be done with a scope, but most scopes are not portable, not really suitable for direct mains reading and usually come at a high price point.At the high end, when there is already a graphical screen anyway one could prefer a scope view (even if low sampling rate / BW), but this more one the wishlist and actually found with common DMMs.Looking at properties not specified is a 2 sided thing. It is problematic with properties that are (or likely can be) quite different with different units . This would be something like the drift on turn on, the low end for AC when using analog RMS, the actual accuracy of the meter at hand. So the common point is most previews of showing the meter spot on at 2 V or 10 K is more like a useless part. It would only be a point if a meter is significant off (e.g. more than half the accuracy spec).Other properties are the interesting ones, like the speed for autoranging or the beeper and they will likely not vary much and are just missing in the spec sheet. The BW for AC is more one of the 2nd kind - usually similar between units and not allways given in the specs. However it needs some care (e.g. BW may depend on the range, amplitude) and it can get lengthy covering it all.For the accuracy the Ohms part may actually be better than the DC voltage part as a different reference is relevant, though this is more like an exception.

author: Richard_S
author_rank: Contributor
timestamp: December 20, 2023, 12:17:41 pm
content: Quote from: EEVblog on December 20, 2023, 04:52:22 amThat is absolutely fair enough. Because it is an area I am interested in does not mean that anyone else is, or at least thatmanyother people are. I get that. I still think that it is fair for me to ask though. Let's say there were more than just a few other people who cared about small signal ac performance, how would we know unless we all speak up? What else can I do but ask?As part of a pitch that the minute or two it takes to talk about the basic ac accuracy is time worth spending, here are my thoughts. The quality of dc measurement is summed-up by our term "basic dc accuracy". It will change according to the range and sometimes within a range for example. Yet we still mention it even though the detail is generally omitted. It is why we even have the phrase I believe. It communicates that there is more to know but that this figure gives you a simple overall summary. The couplet of stating a basic dc accuracy and lowest range really define a meter for low-voltage dc work without drowning in detail.So, this is probably me just being dense (I often am), but aren't the challenges of giving a basic ac view not much the same? Aren't all the arguments that it is an incomplete picture still just as true for dc? For ac it would have to be three elements, basic accuracy, lowest range, and then bandwidth as well. So, one more number. I get that not everyone cares about ac performance, though can I ask, is there also not a case that it acts as a bell-weather for all users regarding design quality, even those not directly interested?And thanks so much for engaging on this. I have learned loads. I hope it has helped others too.

author: mendip_discovery
author_rank: Super Contributor
timestamp: December 20, 2023, 05:35:10 pm
content: Quote from: IanJ on December 20, 2023, 05:20:02 amHow about adding a sound sensor that can listen for the beep and provide a time from clack to beep.EDIT: Just read the full page Ian posted to and noticed that he has already thought of that.

author: mendip_discovery
author_rank: Super Contributor
timestamp: December 20, 2023, 05:55:26 pm
content: My general feeling is there is room out there for a more in-depth review of meters on YT but it's got to be from someone with some tasty stuff that can test the various elements with a good degree of confidence. But also to avoid being a brand snob and asking too much from a hungflug cheap meter. I must admit it is hard to get information on the performance of a meter when you are looking to buy as there is a lack of unbiased info out there, but each person has a different use case depending on what they plan to use the meter for. I wish more of my customers spent some time thinking about the gear they are buying as most of the time it is a non-tech person who goes on RS and just buys something that will do what they want for not a lot.My issue is it is within the spec new and also a year or two after working out in the real world?How does it handle as a daily tool?I see cheap ass meters turn up at work and they are OK but not convinced of the result they want to show you. Then expensive known brands that make their mind up quickly and neatly, as well as expensive brands with lots of digits but the extra digits are a waste as wander about soo much. Though I am cheating as I am confident of the source and unsure of the meter, normal people are sure of the meter and unsure of what they are measuring so I see 2 or 3 digits out as being not great.

author: Richard_S
author_rank: Contributor
timestamp: December 20, 2023, 06:33:51 pm
content: Quote from: nonlinearschool on December 20, 2023, 08:37:04 amThat is a fair question and in some cases, a scope would work just fine. Starting with measuring sine wave test signals then... Of course, the first issue may well be that the user does not have a scope. Apart from that it is convenience, balanced signals, and accuracy I think. Oscilloscopes are more cumbersome and do not just give you a singular direct reading in the way a meter does. It is really straightforward to use a meter. You are likely to need to measure other things like resistance and the multimeter can be turned to multiple tasks easily. Where the signal is balanced (common in audio), a battery-powered multimeter can easily be used across the two conductors while for a scope it is a bit more tricky (though not an awful lot these days). Finally, the scope, at best, is about the same accuracy as the most basic of meters meaning that for the price its accuracy is poor.For more complex signals, the performance depends so much on the scope and what measurement functions it has built in. What you always want to know about any complex signal is their power and therefore you need their RMS voltage. The accuracy is still a limitation for complex signal waveforms - at least compared to a reasonable multimeter.

author: 2N3055
author_rank: Super Contributor
timestamp: December 20, 2023, 09:28:38 pm
content: Quote from: Richard_S on December 20, 2023, 06:33:51 pmScopes absolutely give you discrete measurements and actually dozens of them at the same time.AC RMS, AC+DC RMS, DC component, frequency, P-P value etc.In addition to time domain waveform view also spectrum and other things..At the same time you see if signal is what you expect.I prefer to use scope for most voltage measurements first, and break out multimeter only to measure with more accuracy...And contrary to what you wrote, with complex signal good scope will actually do much better than most meters.It has much wider BW and built in measurements will do very good job.

author: Rax
author_rank: Super Contributor
timestamp: December 21, 2023, 02:53:56 am
content: I admit not reading all posts in detail, but what I've seen I think misses the paradigm shift the "low level audio measurements" universe requires. This may just be the wrong place to ask those questions.The gold standard for this type of endeavor is the Audio Precision systems. R&S and Keysight makes some similar units, but I don't think anyone else than AP can claim the top spot.The issue with this type of measurements is:They're "dB" precise, not "ppm" precise. When analyzing audio signals, "ppm" accuracy is irrelevant.The whole deal with this type of analysis is that, to be relevant ("dB" levels response, distortion, FFT, intermodulation, phase accuracy, group delay, etc.) it simply doesn't need to employ the same accuracy exigencies as metrology would require. Absolutely all of the relevant data harvesting is disjunct with that mindset. 100% of the professionals involved in "low level ACV audio signals" analysis need relevance and interpretations that don't really intersect with metrology, 5.5 digits + levels.My point being oftentimes there's just no "pull" for utility the actual audience is not looking for.

author: Rax
author_rank: Super Contributor
timestamp: December 21, 2023, 03:04:01 am
content: One exception to the lack of intersections I mention that I am aware if is the Keithley 2015 (and I feel there were a couple of others I can't recall now) that does THD, but most, if not all, people doing work in this field will not resort to what I personally feel is a compromised solution and resort to the heavyweights such as AP.Anyone working in this field that experiences an AP box for the first time feels they've had both legs and arms tied behind their back until they got that box. It's a whole other universe.

author: Richard_S
author_rank: Contributor
timestamp: December 21, 2023, 05:31:16 am
content: Quote from: 2N3055 on December 20, 2023, 09:28:38 pmAre we presenting contrary arguments? I don't see that myself.Seeing the waveform can be an big plus and that is a good point to make. For audio test signals it tends to be irrelevant much of the time because the levels of distortion being observed do not show up to the human eye. For audio noise, well there is rarely anything meaningful to see in the waveform. The spectrum by contrast would be valuable, but oscilloscopes typically do not have the resolution (frequency resolution) required to display what is going on (you need considerably less than one Hertz for sound). To be fair, a lot of specialist audio gear and software lacks it too. For measurements like pulse-width drives though, observing the waveform can be a huge boon.Bandwidth for RMS measurements is a rather moot point isn't it? The struggle with so many multimeters is that their RMS bandwidths are too narrow. They can be in the hundreds of Hertz. Then when you do get an instrument, like a digital scope, that can measure bandwidths in the hundreds of kilohertz and even megahertz, the bandwidth is often too wide. RMS is about inferring power, power is the ability to do work, higher frequencies often can't be used to do work. The upper frequencies are irrelevant to say audio signals, because you can't hear them, while they are irrelevant to motor drives, because the motor will not apply that energy, and so on. So, ironically meters often have too little bandwidth and scopes too much (for the application).

author: Richard_S
author_rank: Contributor
timestamp: December 21, 2023, 06:11:02 am
content: Quote from: Rax on December 21, 2023, 02:53:56 amThank you for the contribution Rax. Yes, I think you are suffering from not reading the posts.In summary, reviews of multimeters that cost in the region of $100, to $200 would be more informative if they included their basic ac accuracy just like they include their basic dc accuracy.An AP unit is not pocketable and two orders of magnitude more costly.I loved the phrase "accuracy exigencies", never been prompted to think of accuracy in terms of its urgency before.For audio we are really talking 0.1dB precision rather than dB precise I think, suggesting an ideal accuracy of 0.11% (roughly one tenth of 0.1dB) with still-workable accuracies up to around 0.3% or 0.5% at a push.Metrology is the study of measurement is it not? Difficult to follow the concept that measuring with either less than, or more than, a certain number of digits is no longer measurement. Or did I misunderstand?

author: David Hess
author_rank: Super Contributor
timestamp: December 21, 2023, 08:47:08 am
content: Quote from: Richard_S on December 17, 2023, 10:18:06 pmI recently found dB to be advantageous when tuning speaker cabinets because it made the measurements more sensitive.Quote from: bdunham7 on December 17, 2023, 11:04:05 pmThe old Tektronix handheld multimeters have a configuration option to switch between average responding AC and true RMS AC readings, while always displaying true RMS for the AC+DC mode. When I was first using precision square waves to do AC calibration, all three of these measurement modes on my Tektronix DMM916 read exactly what they should have to the last digit. I ended up using average reading AC mode because the settling time was faster.With the most common analog true RMS conversion circuit, the difference between average AC and true RMS AC is a single wire.Quote from: Rax on December 21, 2023, 03:04:01 amI never understood what market Keithley was aiming for with that expensive meter supporting THD measurements.QuoteI suspect it is like the first time you use a low frequency network analyzer, or a time domain reflectometer that has picosecond resolution.

author: TUMEMBER
author_rank: Regular Contributor
timestamp: December 21, 2023, 11:17:59 am
content: Quote from: Richard_S on December 21, 2023, 06:11:02 amMany problems with the "shape" of voltage can be "skipped" by using analog meters with electro-magnetic conversion. A laboratory-grade analog meter may meet your requirements and will cost much less than super-advanced DMMs.In this presentation you can see the surprising results achieved in the "duel" between the "old" and the somewhat modern, much more expensive Rigol.Niestety filmik nie ma automatycznej translacji na angielski.Unfortunately, the video does not have automatic translation into English.Fortunately, "the tables are international".

author: Kleinstein
author_rank: Super Contributor
timestamp: December 21, 2023, 12:27:59 pm
content: Many of the analog meters us a simpler rectifier and not true RMS. For mechanical averaging there are moving iron meters that actual come close to RMS response, but they are far from ideal (e.g. limited BW from eddy currents, magnetic hysteresis, nonlinear scale). With the analog scale it is hard to read much better than 1% and the meter movements are somewhat temperature sensitive. To reduce loading one may also want an electronic amplifier up front.The better of the analog RMS meters often use similar RMS to DC converter chips as the DMMs, just the needle instead of an ADC.The only really better way are thermal RMS converters, but these are slow and expensive, and thus more a thing for CAL labs.

author: Rax
author_rank: Super Contributor
timestamp: December 21, 2023, 02:45:39 pm
content: Quote from: Richard_S on December 21, 2023, 06:11:02 amWell, that's a little unfair, and also incorrect. Did you think my point was misplaced, or maybe unclear?I didn't say I didn't read the posts, I said I didn't read them in as much detail as I would have liked to. I am an extremely close and attentive reader, but don't always have as much time as I'd like to achieve that result, was essentially my point.So, I re-read the thread and I still think my point is pertinent. There was one mention of "audio analyzers" (2N3055's post) but that's it.Quote from: Richard_S on December 21, 2023, 06:11:02 amI was making a different point - similarly with RF measurements, AF measurements typically follow logarithmic scales. A "level generator" such as the 3335A is linear to about .1dB. How much would that translate in ppm? If you look at AC performance (typically evaluated from the perspective of "logarithmic linearity") in actual V (mV, uV), it's all full of mountains and valleys.Quote from: Richard_S on December 21, 2023, 06:11:02 amBoth are measurements, but priorities are everything. See my points above. I did a quick search on the Metrology group for "Audio Precision" and the results are very few (and a good proportion are mine...). I just think there's little intersection between specialists in audio analysis (though there's a whole, massive chunk of the internet catering for those crowds) and the voltnuts.

author: TUMEMBER
author_rank: Regular Contributor
timestamp: December 21, 2023, 03:44:46 pm
content: Quote from: Kleinstein on December 21, 2023, 12:27:59 pmI value your knowledge because it is gigantic.But you are wrong here - some of the LABORATORY MIRROR meters had a class of 0.2.ll your objections are valid, but 20 years of "patterning" in the old days have not allowed me to forget about it.And for my friend who started this topic, the only thing left to do is buy a Fluke 8050A on eBay and send it to the service center for adjustment. It will be "relatively cheap", although the measurement class is so-so.

author: bdunham7
author_rank: Super Contributor
timestamp: December 21, 2023, 06:27:58 pm
content: Quote from: David Hess on December 21, 2023, 08:47:08 amWas that average-responding but RMS corrected? Or did it display the actual average voltage?

author: TheDefpom
author_rank: Frequent Contributor
timestamp: December 21, 2023, 08:16:11 pm
content: As someone that actually does these review videos, I can say there is only so much time I am willing to put into doing one.I spend up to 3 hours recording the actual footage (depending upon the features of the meter, plus whatever playing around I do before hand to learn the meter a bit), then at least two to three times that time to edit it down to something more concise, and even then the videos are still usually over 30 minutes long.It is a LOT of work, and whilst I dont mind doing that so much for a higher priced meter such as a Fluke or Keysight as the value of the meter makes it worthwhile (plus I would not be selling one of those afterwards), the budget meters are hard to justify committing that much time to, yes I still put a lot of time into those reviews, but if I can only sell the meter for $20 afterwards (as I have no need for budget meters), I don't want to spend 3 days making a video for it, plus the final video would be WAY too long for the target audience, people looking for a budget meter are not going to be interested in the finer details of edge case usage, sure that may be the case for higher cost meters though.

author: joeqsmith
author_rank: Super Contributor
timestamp: December 21, 2023, 09:26:06 pm
content: Quote from: EEVblog on December 20, 2023, 02:10:37 amSure, drag me into this mess...I don't check meters for their accuracy as part of my reviews. I don't often check all their features. Rare I even look at current measurements. Rather I focus on stressing the meters to failure. Life cycling their rotary switches, exposing them to chemicals, dropping them, and of course subjecting them to some low level transients. It all takes time.I don't normally accept donations so there is the cost of the product (which is going to be trashed). But that pails to the time required. No Pateron, begging people to join the channel, ring that bell or what ever YT wants. It's a total loss channel. Then the content is sparse and dry.I run the tests I want to see and make them available for free. That about sums it up. Don't like the content, plenty of it out there.

author: David Hess
author_rank: Super Contributor
timestamp: December 22, 2023, 03:25:02 am
content: Quote from: bdunham7 on December 21, 2023, 06:27:58 pmAverage responding for a voltmeter always means RMS corrected for a sine source, which means it reads 11.11% high for a square wave compared to the RMS reading.

author: alligatorblues
author_rank: Regular Contributor
timestamp: December 22, 2023, 03:28:11 am
content: I know the premiere and most sought after audio tech in Los Angeles. He's booked for five years. He has a mod for the Fluke 8840A/8842A AC add-on board that makes it perfect for audio. It's not a difficult mod, but thinking it up might have been.I have to search in my email for his phone#.

author: EEVblog
author_rank: Unknown
timestamp: December 22, 2023, 07:24:37 am
content: Quote from: joeqsmith on December 21, 2023, 09:26:06 pmTo be clear, Ilikeyour content Joe, I find it interesting and valuable. Just pointing out that probably for most people, something like high voltage overload testing comparisons are a bit moot for most once you pass a certain generally acceptable point. So it's an example just like the OP is discussing here with low signal level AC. Sure, small signal AC would be an interesting test and comparison, but for most people it's probably moot in the decision making process.

author: joeqsmith
author_rank: Super Contributor
timestamp: December 23, 2023, 07:15:11 pm
content: Quote from: Richard_S on December 17, 2023, 10:18:06 pmI had saved an old 1980's Fluke 8506A thermal RMS meter from scrap and repaired it. Once working, I used my HP34401A as a reference to align the DC stages. See the following thread for background:https://www.eevblog.com/forum/testgear/some-old-school-instruments-showing-how-its-done-(hp-3325a-and-fluke-8506a)/When it came to the AC alignment, I left it alone because of the reason you mention. The accuracy and MHz bandwidth specs are nothing I could match. The AC specs for this meter may be found in the manual.https://pearl-hifi.com/06_Lit_Archive/15_Mfrs_Publications/15_Fluke/Fluke_8506A.pdfNote the drift in table 1-3.I think if I wanted to verify the cheap handheld meters AC performance, I would start by having this meter aligned and calibrated. I had looked for source at the time I was doing the repairs but didn't find anyone I would trust and don't believe Fluke would still support it. I would guess the cost for the work, including a report would have exceeded what I would be willing to pay. It's all pots, then the time for things to stabilize. If they told be a >$1000 USD, I wouldn't be too surprised.

author: bdunham7
author_rank: Super Contributor
timestamp: December 23, 2023, 07:38:00 pm
content: Quote from: joeqsmith on December 23, 2023, 07:15:11 pmLast I checked Fluke would calibrate it (no repair service offered however) and the cost was indeed more than $1000. The proble with 'regular' cal labs is I think they would only do the front-panel software calibration and consider any knob-twiddling as "repair". I'm putzing with mine right now as I'll soon have the opportunity to compare it to a 3458A and 5200A. Wish me luck. But I'm not sure you'd actually need to go to these extremes, at least for any handhelds I've seen. For extreme low-level testing, I think an in-cal 34401A and a ratio transformer would suffice?

author: joeqsmith
author_rank: Super Contributor
timestamp: December 23, 2023, 10:00:43 pm
content: Good to hear you are still working on yours. I gave up trying to reverse engineer their firmware and shelfed the meter. I have thought about taking it to work and comparing it with a calibrated 3458A. Maybe I could then go through the AC alignment. My problem would be coming up with a suitable source. Post how it works out for you.Hard to say when it comes to reviewing the cheap meters. I don't watch very many reviews and see little value in the typical unboxing, connect them to a battery and resistor then giving them 5 stars. They serve a purpose for people who love to have their purchasing decisions validated. I liked Dave's reviews because of the humor.The only reason I make any measurements is to show that a meter has changed (normally damaged), not how accurate it is or that it meets the manufactures claims. I may make the same measurements 10 or more times during a video looking for that one time where it shifts, signaling a problem.

author: joeqsmith
author_rank: Super Contributor
timestamp: December 24, 2023, 01:38:13 am
content: Specs for some of the left over hand helds that I could still test. Sorry Keysight, your meter didn't come close to surviving and could not be repaired. The 121GW was saved by the fact I bought two of them and never exposed one of them to any potential destructive tests. The crappo TPI required a new controller IC. The 181A required a new power supply IC. The Yokagowa required several ICs but all were common. The BM869s required new transistors for the high speed clamp. Fluke 189, tested a beat up used one but no idea what it would take to damage it. Typical of Flukes later products.Nothing comes even close to matching specs of a high end meter or even the Fluke thermal RMS relic previously mentioned. If calibrated, I could certainly use it to show the accuracy of these low cost meters.**The Ultra/Prime what ever Gossen calls it now, costs over $1100 USD today. But consider that old Fluke was over $10,000 back in the early 80s when it was made. It's all relative.

author: bdunham7
author_rank: Super Contributor
timestamp: December 29, 2023, 05:29:50 am
content: Quote from: joeqsmith on December 23, 2023, 10:00:43 pmWell, surprisingly enough the 8506A is fixed and now appears to be within specs as close as can be determined using a 3458A, a 5200A, a ratio transformer and other assorted instruments.However, it also turns out to be not very suitable for testing low-level AC peformance of handhelds, at least not directly. One unfortunate aspect of the Thermal RMS sensor is that it doesn't perform well at the low end of the scale and this is way worse than a TRMS chip would be. It has reduced accuracy below 25% of full scale and is not specified below 10%. This is apparently why they have the .100/.300/1/3/10/30 etc ranges--to keep the sensor above the 25% level, at least when autoranging. The meter is not specified for reading anything below 12.5mVAC. According to the explanation in the manual, the excessive residual counts error below the specified minimums are due to 1/f noise, but the meter also picks up all sorts of RF and line-conducted noise. With a LSD of 1µV and a BW >1MHz, this isn't too surprising as an AM radio station can be under 1MHz and provide 100µV or more with even a poor antenna. I had to rearrange my bench, eliminate my UPS and turn a bunch of stuff off to even get close to proper low-level performance.But now perhaps I can try some meters. I'm open to suggestions as to what the test standards should be for low-level performance. I was going to start at 1kHz and determine the minimum voltage for a meter to be accurate to within 1% or 1 count, whichever is greater. Or since the OP wanted to look at audio, I could also look at 20Hz and 20kHz, both of which are performance verification test points for the 8506A.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 29, 2023, 10:21:56 am
content: For a low level test signal one could use a voltage divider (resistors or transformer). So the source and ref. meter would be at a higher voltage, like 100x the small signal. This way one would not have an issue with rather small values. For the moderately low frequencies a DDS based signal generator should be quite stable and flat in the frequency response, expecially if there is no AC coupling at the low end.The low amplitude performance may scatter between units, depending on the internal offsets at the analog RMS chip and how they try to compensate (at least to some approximation) for the meters own noise.At the lower frequency end, like 20 Hz one can expect some deviations with different waveforms. So it may be worth looking at a sine and square wave (maybe also half wave rectifier from an arb generator) for the low frequencies. I would expect some deviation at low frequencies, especially with meters that have a relatively fast response and thus not so slow filter at the RMS chip.Good thermal converters are still the standard, but not all thermal converters are that good. A good meter with digital RMS (e.g. KS 3446x or Keithley DMM6500) may be the more practical reference meter for a small AC signal, at least for the lower frequencies. At least in principle they can compensate for the own noise and get good performance also at a small fraction of the range. The thermal converters are more thing for higher frequencies, not so much small signals.

author: joeqsmith
author_rank: Super Contributor
timestamp: December 30, 2023, 07:23:15 pm
content: Quote from: bdunham7 on December 29, 2023, 05:29:50 amGood to hear you have it sorted out. Looks like Richard lost interest. Odd as they were the ones asking.

author: Svgeesus
author_rank: Regular Contributor
timestamp: December 31, 2023, 12:48:39 am
content: Quote from: EEVblog on December 20, 2023, 04:52:22 amAnd for others, audio bandwidth and microvolt measurements is theprimaryuse case and frankly we couldn't care less about high voltage safety because we are measuring on ±15V systems (what the op-amp providers now call "high voltage") all the time; if we have some need to probe a 400V system we will call in a professional, who will have their own Fluke or whatever.Not that we would expect a review to omit that - but we would likely skip over that part.

author: bdunham7
author_rank: Super Contributor
timestamp: December 31, 2023, 12:55:42 am
content: Quote from: Svgeesus on December 31, 2023, 12:48:39 amOK, then what levels, BW and accuracy are you looking for? µVAC is pretty tough for a regular DMM and even tougher if you want TRMS. I don't have many handheld DMMs to test, but I can try what I have--but I'm not sure what parameters would be most important.

author: bdunham7
author_rank: Super Contributor
timestamp: December 31, 2023, 04:03:29 am
content: Quote from: joeqsmith on December 30, 2023, 07:23:15 pmPerhaps, or perhaps just busy with the holidays. In any case, I found a relevant white paper courtesy of the U.S. Army.https://www.govinfo.gov/content/pkg/GOVPUB-C13-83cb89e6828c42f3920d25f1c0c1001c/pdf/GOVPUB-C13-83cb89e6828c42f3920d25f1c0c1001c.pdf

author: miro123
author_rank: Frequent Contributor
timestamp: December 31, 2023, 10:42:15 am
content: Quote from: Richard_S on December 17, 2023, 10:18:06 pmThe short answer is look athttps://www.youtube.com/@N8FDYIf you prefer text review use the github linkhttps://github.com/TomWilkinson/Multimeter-Reviews/tree/mainTake all those reviews with grain of salt if you are interested in accuracy. The most multimeters reviews are kind of "one night stand ". Evaluation requires to use single multimeters for long time. Unfortunately this group of people are not youtubers nor web posters.

author: joeqsmith
author_rank: Super Contributor
timestamp: December 31, 2023, 04:30:59 pm
content: Quote from: bdunham7 on December 31, 2023, 04:03:29 amPerhaps. I wouldn't put in a lot of effort unless it is something you are personally interested in. Thanks for the link.

author: bdunham7
author_rank: Super Contributor
timestamp: January 01, 2024, 06:40:16 pm
content: Quote from: miro123 on December 31, 2023, 10:42:15 amA grain of salt indeed. Tom certainly has a wide assortment of multimeters and I have to applaud him for providing the written reviews as well as his straightforward approach. There are, however, some errors interpreting specifications and he also comes to the conclusion that certain models do not meet their specifications, which I think may be erroneous. The Fluke 289, Fluke 177/179, Greenlee 860A and UNI-T 181A reviews may potentially have these errors, and perhaps others since I didn't read them all. However, even these questionable conclusions raise some substantial issues, just not the ones that they appear to be at first glance.The only one I actually have is the 289, so naturally I looked at that one and saw that he claims that it does not meet its DC accuracy specifications at 1mVDC and at various points from ~300-500VDC. The error at 1mVDC is because the 289 has a 50mVDC range with an additional x10 gain stage and the specifications state (in the fine print) that the tolerances for this range are statedafter nulling any offset--IOW you have to zero it first. He states that he does not have reference standards but instead relies on unidentified power sources and a Keithley DMM6500 in parallel as a reference. He has a picture comparing a number of meters reading a source in parallel, all showing noticeable error with some in-spec and some out depending on the particular meter and its tolerances. I can think of one possible cause for this (other than the meters being out of spec), but I'll wait to state until others can make some suggestions.

author: guenthert
author_rank: Frequent Contributor
timestamp: January 06, 2024, 09:42:13 am
content: Quote from: bdunham7 on January 01, 2024, 06:40:16 pmI'm always uncomfortable measuring a source with multiple meters in parallel / simultaneously. If the source is not ofverylow impedance, the bias current (might average to a few pA, but easily spikes in the nA range) rakes havoc on those measurements. For handheld DMMs, it's probably more the limited (and not all that well defined) input resistance which gets in the way.Regarding True RMS measurements: in the early 70s, -hp- published a pamphlet warning of the traps of average converting meters:http://hparchive.com/Application_Notes/HP-AN-124.pdfFor the Datron/Wavetek 1271 (I suppose also for the 1281) there is a True RMS option board, which doesnotuse a thermal converter (because, as they claim, that would be too slow); instead they use a hairy assembly of squaring, log- and antilog circuits (the instrument is old enough that the digital circuitry was too slow for the sampling approach). The claim good accuracy down to 1%FS with 100mV the lowest range.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 06, 2024, 10:27:59 am
content: A parallel connection of voltmeters should not be an issue. The bias and loading from normal impedance, like 10 M or even lower with analog meters is effecting all the meters in the same way and is thus no issule - it would only be a problem if the cables are rather high resistance - so no real issue with less than 9 digits.The switching glitches may be an issue with some high end bench meters at high resolution. The lower resolution meters usually have input protection with enough resistance to filter out the spikes and both ends. A good meter should also be somewhat tolerant to some spikes / variations in the signal. If the parallel connection causes problems there should be 2 meters at fault: one causing interference and one being a bit sensitive.The RMS circuit in the Datron meters is kind of the old form (maybe a little better) of what is more commonly found inside the RMS-DC onverter chips, like the AD637 and similar and still used in quite some meters. There is nothing really wrong with this. Thermal RMS is old style and slow and thus no longer used from practical multimeters. It is still a thing for high frequencies and maybe the metrology side. The digital sampling method is getting increasingly popular, but not necessary better (especially not in the common low power versions found in handheld DMMs) - it has different pros and cons. So it helps to know which method is used.

author: 2N3055
author_rank: Super Contributor
timestamp: January 06, 2024, 10:48:52 am
content: Quote from: guenthert on January 06, 2024, 09:42:13 amLoading the source will change absolute value, but you still can see accurate relative comparison to reference voltmeter.With AC measurements, it usually creates more problem that most meters have no well defined complex impedance, mainly input capacitance, and fact that it changes all the time between the ranges.Capacitances will easily be in hundreds of pF and will be considerable load...Both MTX3293 (260/68 pF) and BM869S (98/75pF) change capacitance between low and high range.DM3068 (155pF) is very stable. It does not change through the ranges..As for resistive part of input impedance, that is well defined in datasheets on all meters I have.But as stated before, multimeters are not made to be excellent wideband AC voltmeters.They are Swiss Army knifes of the T&M industry.

author: David Hess
author_rank: Super Contributor
timestamp: January 06, 2024, 02:02:07 pm
content: Quote from: Kleinstein on January 06, 2024, 10:27:59 amSome combinations of meters, even lower resolution ones, will have problems with charge injection from the automatic zero or chopper cycle. Usually I see this when measuring the input resistance of one meter using another, but it also shows up with high impedance sources.I keep a couple of old multimeters which do not produce charge injection for sanity measurements. They use brute force with precision matched JFET input stages instead of automatic zero or chopping.Quote from: 2N3055 on January 06, 2024, 10:48:52 amI would be really careful about that, especially with handheld automatic ranging meters. They often specify 1 or 10 megohm input resistance even when it varies significantly because of how the switching for the input divider is configured. They use a divider where different taps are grounded, which causes the input resistance to change. Moderate source resistances, or a high voltage probe, will then allow the reading to change on different ranges by an amount greater than the accuracy rating of the meter.Most datasheets just say 1 or 10 megohms without specifying this. The alternative constant input resistance meters (1) sometimes specify 10 megohms with a tolerance like 1% or 0.1% which is much tighter than the variable input resistance case which is more like 10%.This postshows what is going on with variable input resistance decade dividers on autoranging multimeters.(1) Bench multimeters or manual ranging handheld multimeters, with some exceptions. I have yet to find a handheld automatic ranging multimeter which has constant input resistance, but I assume they exist. It is practically impossible to tell without measuring it.

author: 2N3055
author_rank: Super Contributor
timestamp: January 06, 2024, 02:58:01 pm
content: Quote from: David Hess on January 06, 2024, 02:02:07 pmThank you for your good intentions and good advice. But I'm careful.I don't do Kaiweets or something like that.I have Metrix, Brymen, Fluke and Rigol.They all have detailed datasheets and yes, I'm like you and verified it myself.If you noticed, I said that ohmic resistances are well defined (and verified to be true) but capacitance does vary and have provided a measured data.But I think we might have a slight disconnect here.I'm not saying all these meters necessarily have single, unchanging ohmic resistance. It changes but it is well documented and verified to be such.MTX 3293 even shows it right there on the screen as you go through ranges when on DC :100mV (Imp 10MΩ)1000mV (Imp 11MΩ)10V (Imp 10.5MΩ)100V (Imp 10.05MΩ)1000V (Imp 10MΩ)OTOH DM3068 is rock solid 10,026MΩ 200m/2/20V and 10,014MΩ 200/1000V

author: David Hess
author_rank: Super Contributor
timestamp: January 06, 2024, 03:24:04 pm
content: Quote from: 2N3055 on January 06, 2024, 02:58:01 pmFluke is one of the manufacturers which does not accurately document the input resistance of their meters. They have an application note which is included with their high voltage probes which has an incomplete list of which of their meters have compromised accuracy because their input resistance changes. They suggest applying a correction factor. I know Brymen does the same thing. I searched their entire line of multimeters for one with a constant 10 megohm input resistance and as far as I can tell, they have none.All of my high end autoranging handheld multimeters specify 10 megohms, but their input resistance changes as described in the post that I linked.B&K autoranging handheld multimeters sometimes have detailed specifications with different resistance specified for different ranges, and sometimes simply say 10 megohms. Do the later ones have a constant input resistance? I have no idea, but at least they seem to be distinguishing the two unlike Fluke and Brymen.

author: bdunham7
author_rank: Super Contributor
timestamp: January 06, 2024, 10:16:15 pm
content: Quote from: guenthert on January 06, 2024, 09:42:13 amThere can be issues when using meters in parallel, but usually it is the best of several imperfect choices. The problem as I see it is that even when in parallel, a disagreement between meters doesn't necessarily result only from calibration issues. I don't know what happened in the tests that are mentioned above, but I do know that there is a huge difference in the normal mode rejection spec for the Fluke 289 (which has been deemed "out of spec" by the reviewer) and the Keithley DMM6500. If everything is set up optimally, the stated values are 60dB for the 289, 100dB for the DMM6500, both at 60Hz respectively. The reviewer makes no mention of the voltage source other than to say that he doesn't have reference standards.There are many other experimental errors that can crop up using a parallel meter as a reference, but most of those don't really apply to measuring 490V with a handheld DMM. Differing responses to common or normal mode AC or noise is about the only thing I can think of.