EEVblog #1051 - 121GW Multimeter Mass Turbulence - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: January 06, 2018, 09:59:09 am
content: Some quick sanity testing of the newly arrived 121GW multimeters

author: tautech
author_rank: Super Contributor
timestamp: January 06, 2018, 10:12:36 am
content: At 8.17, whats the spec on the pad next to R77 ?

author: Brumby
author_rank: Unknown
timestamp: January 06, 2018, 11:51:28 am
content: The "No bulls**t packaging" graphic looks familiar!I'd nudge Dave for a sample unit .... except he's already compensated me for the design back when the BM235 was released.Still saving my pennies up for one (but my carison the road legally).

author: Brumby
author_rank: Unknown
timestamp: January 06, 2018, 11:54:23 am
content: More importantly - it's a wonderful sight. The product is now real and on the shelf!

author: klunkerbus
author_rank: Unknown
timestamp: January 06, 2018, 01:22:29 pm
content: Congrats on the new arrival.Got a chuckle out of the "Sydey" Australia markings on the outer box. Hopefully the meter QC is better...Edit: Well, I am of course assuming there really is no Sydey, Australia.

author: wraper
author_rank: Unknown
timestamp: January 06, 2018, 02:10:38 pm
content: Looks like solder blob squeezing from under QFN. And there is barely any solder on the pads on the right side of the same IC. I'd say that solder paste was applied with misaligned stencil.

author: b_force
author_rank: Super Contributor
timestamp: January 06, 2018, 02:20:58 pm
content: Finally they arrived.Nice looking meters Dave!Jonestronics?Btw, I saw that some people already mentioned it in the video as well, but this is a nice opportunity to use and explain the importance of the standard deviation.aka. how much of a tolerance spread you may expect from the sample you took.Many engineers are pretty sloppy with that, but in some cases it can explain a lot about certain issues in the end.From your notes, I calculated that your 5V range is 5.0000 ± 0.0004 V (with 3? = 99.8%)Or 5.000 V ± 0.01%Which is nicely within specs.

author: massivephoton
author_rank: Contributor
timestamp: January 06, 2018, 05:47:06 pm
content: How could Dave dare to turn them on before tearing 'em apart!

author: AustinTxBob
author_rank: Contributor
timestamp: January 06, 2018, 06:13:14 pm
content: When will they be available to purchase?

author: Brumby
author_rank: Unknown
timestamp: January 06, 2018, 10:43:36 pm
content: Quote from: AustinTxBob on January 06, 2018, 06:13:14 pmGood question.Dave has mentioned a component shortage (at non-inflated prices) and there are still around 2,000 units required for the Kickstarter campaign.I'm sure Dave will let us know when he will have stock on the shelf available.

author: mc172
author_rank: Frequent Contributor
timestamp: January 07, 2018, 12:51:04 am
content: What's with the large discrepancy on what I assume is room temperature?Very nice, though! Top marks mate.

author: ataradov
author_rank: Super Contributor
timestamp: January 07, 2018, 01:13:54 am
content: It does not show all segments on after turning on. Living on the edge?

author: rs20
author_rank: Super Contributor
timestamp: January 07, 2018, 01:45:08 am
content: Quote from: b_force on January 06, 2018, 02:20:58 pmPossibly a bit hypocriticalQuote from: b_force on January 06, 2018, 02:20:58 pmWhat are you even on about?The standard deviation of the provided datais 0.00013One of the values is 4.9994V, so the observed range is within 5.0000 ± 0.0006 V, not ± 0.0004 V.Multimeter specs are not given as standard deviations, they are absolute limits. Same with engineering drawing dimensions. The only time I see X ± Y where the Y means standard deviations is political polls, but that is the exception rather than the rule. The 3 sigma = 99.8% rule applies to normal distributions, and only when you calculate the standard deviation correctly...So why you wrote 5.0000 ± 0.0004 V (with 3? = 99.8%) is completely beyond me. Even if you misread the 4.9994 as 4.9999, the fact that 3 sigma = 99.8% is utterly irrelevant when no standard deviation is being given.

author: dragondgold
author_rank: Newbie
timestamp: January 07, 2018, 01:58:58 am
content: Hi! Is it possible to order one of this now? I totally missed the Kickstarter campaign

author: Brumby
author_rank: Unknown
timestamp: January 07, 2018, 04:39:15 am
content: Dave's got around 2,000 on the equivalent of "On Back Order and Paid" as it is right now. I sincerely doubt he is going to start taking more back orders.Also, it is a rocky place to be when you don't have any idea of delivery date - Just look at the minor delays that hit the first batch! In general, customers get impatient once they've parted with their cash - and it's not a pleasant place to be if something goes wrong and more delays are encountered. Some will wait, but others will get upset and there will be those who will want their money back. This is a lot of grief and effort for Dave with no reward. It is much easier to wait until they are in his hands.And it's not as if ordering earlier will get you your 121GW any earlier. It won't. The only benefit to you will be that you've got your name down and paid the price at the time.There is another issue for Dave - pricing. The first batch and the Kickstarter units had "introductory pricing". For ongoing sales, Dave will have to determine his retail price - which is going to depend on several factors. I would say getting the Kickstarter units sorted is a step down this path.

author: Tom45
author_rank: Frequent Contributor
timestamp: January 07, 2018, 04:18:25 pm
content: No test leads in "the very first one"?

author: IanB
author_rank: Super Contributor
timestamp: January 07, 2018, 04:58:40 pm
content: Quote from: Tom45 on January 07, 2018, 04:18:25 pmAs I recall it comes with test leads, case and thermocouple.

author: b_force
author_rank: Super Contributor
timestamp: January 07, 2018, 05:01:15 pm
content: Quote from: rs20 on January 07, 2018, 01:45:08 amAnd this is why a proper lesson in statistics is in place, because you are making a lot of mistakes mister.First of all, the standard deviation is indeed 0.00013. but that's only valid for one sigma, or in other words,68% change that a value will fall within the first standard deviation of the distribution.This number is pretty low and typically 3 sigma is pretty standard to use (although 2 sigma might be fine for most practical engineering examples).In big scientific research experiments, people use typically even 5 sigma (= 99.99994% certainty)So 3 times that value will give you 0.0004 (actually it's 0.0005 I made a little typing error).But most of all, you are totally missing the point of what a data sample is and how you can statistically use this to get a very good estimate for all possible outcomes.Or in other words how a 32 data sample can be representative for a couple of hundreds (or even thousands) of multimeters.The absolute WRONG way of doing it, is the way you did it. Since you don't know if there will be other meters that will be worse than that or how many of them will.But I stand to be corrected myself, because I made a writing mistake here.My correct answer had to be that the correct value is; 4.9998 ± 0.0005 V, again with 3 sigma which gives a 99.7% certainty.So based on this little data sample it shows that these meters by default will be off by -0.0002V on average.What does this practically mean?Well based on THIS data sample taken by David, people can expect that 99.7% of the multimeters will measure 4.9998V when a 5V voltage is applied with a tolerance of 0.0005VLast point, yes by DEFINITION things are given in standard deviations.Why? Because science is a statistical way of measuring things.I have worked for companies that do calibrations and there standards work exactly this way.But like I said before, most engineers are pretty sloppy using it correctly (or not at all actually)

author: IanB
author_rank: Super Contributor
timestamp: January 07, 2018, 05:12:56 pm
content: Given that it is a sample of meters from a large population one should compute the sample standard deviation rather than the normal standard deviation.One should then quote the sample mean \$\bar x\$ and the sample standard deviation \$s\$ and allow the reader to do their own interpretation and estimates of confidence intervals as they wish.

author: Keith Ward
author_rank: Newbie
timestamp: January 07, 2018, 05:35:11 pm
content: That "blob" is a test point (TP6) that is somehow tinned but yet all of the others are not. If the test point is merely connected to the pin next to it there are no issues, but if not ...

author: rs20
author_rank: Super Contributor
timestamp: January 07, 2018, 07:03:38 pm
content: Quote from: b_force on January 07, 2018, 05:01:15 pmYou'd be wise to realise that part of the reason people don't follow your messages here is because your use of statistical language is so incredibly vague. Granted, I missed that what you had done was pre-multiply by 3* to give one of the most amateurish "tolerance intervals" I've seen in a while. But because you called it a "range" rather than a "tolerance interval" or anything else, I didn't interpret it as such, and was completely thrown.* And then attach that to 5, rather than the sample mean? What? You can't honestly blame me for doubting your credentials at that point.Quote from: b_force on January 07, 2018, 05:01:15 pmYep, I totally didn't get the hint that you were calculating tolerance intervals and calling them "ranges".Quote from: b_force on January 07, 2018, 05:01:15 pmAre you serious! I didn't do anything, other than state a number of facts that remain perfectly true: The standard deviation is X, the observed range is Y, and I couldn't understand what you were talking about. All true at the time.Quote from: b_force on January 07, 2018, 05:01:15 pmNo. The datasheet specs might be prepared behind the scenes using statistics similar to the statistics you described, but what theymeanis absolute limits that are not to be interpreted using assumptions of normal distribution, let alone standard deviations. Calibration of 9 digit super high-end multimeters, sure, there's going to be statistics involved there -- but I'm seeing no evidence at all that the basic datasheet specs of 121GW-level multimeters is anything other than guaranteed simple limits. Datasheet limits are often much looser than the samples statistics would suggest (take the results for this meter, for example), since future process changes could screw with things (a possibility that is completely beyond the ability of naive 3 sigma statistics to estimate.)Quote from: IanB on January 07, 2018, 05:12:56 pmTrue enough, I'd have been happy with either those raw statistics or an explicitly called-out TI.Regarding sample standard deviation, I don't disagree (although I'm not sure the difference is non-negligible even with as few as 30 samples) -- however, there is yet another assumption that has been made here. What istrueis that for normally distributed data, 99.7% ofpopulationitems fall between(populationmean) - 3 (populationstandard dev) and (populationmean) + 3 (populationstandard dev)One of the most rife mistakes in statistics, IMHO, is when people take thesamplestandard dev and plug it in to the formula above. You might be thinking "eh, what does it matter, it'll be a little bit high sometimes and a little bit low sometimes, so some intervals will be a little bit more generous and others will be a little bit too tight, but it'll all cancel out, right?" Answer: no. Turns out you make more mistakes with the erroneously tight intervals than can possibly be made up for by the generous intervals. This is where the t-distribution comes in; and is why you actually need to use Student's t-test in many situations that seem naively amenable to nonsense like 'take "the" mean and add/subtract 3 times "the" standard deviation'.And everything above is all about generating a 99.7% confidence interval for the populationmean-- we haven't even started generating intervals that contains 99.7% of units in the population (which are called tolerance intervals rather than confidence intervals, by the way -- and that's not just a pedantic difference, the numbers are completely different -- CIs shrink with more data, TIs don't.)Anyway, my point to all this is that whether the sample standard deviation should be used is a rather long way down the list of things that need to be sorted out here. (Edit: but to be clear, you're absolutely correct that the sample standard deviation is much more correct in most/all circumstances)

author: Dr. Frank
author_rank: Super Contributor
timestamp: January 07, 2018, 08:48:59 pm
content: Quote from: wraper on January 06, 2018, 02:10:38 pmThat's not a QFN package, that has ordinary Gullwing legs, therefore also no solder from under the package.It looks odd, anyhow, obviously UEI do not use AOI.This excess solder does no harm, obviously, as the package has 4x5legs, and maybe TP6 is connected to the last pin, anyhow.Frank

author: ataradov
author_rank: Super Contributor
timestamp: January 07, 2018, 08:54:42 pm
content: Looks like QFN-20 to me. And TP6 is under the package. There is TP3 on the other end of the package that is not soldered.So there is a short between that pin and TP6. But it looks like they are electrically connected anyway.Still pretty poor soldering quality.

author: EEVblog
author_rank: Unknown
timestamp: January 07, 2018, 09:27:52 pm
content: Quote from: Brumby on January 06, 2018, 10:43:36 pmI have explained this countless times now.UEi can't magically make a zillion units, and all stock they are making goes toward KS backers first before I have any spare left over for others to order.

author: EEVblog
author_rank: Unknown
timestamp: January 07, 2018, 09:32:27 pm
content: Quote from: Brumby on January 07, 2018, 04:39:15 amAll correct, taking more pre-orders on units without having proven anything haszeroupside for me at this point.

author: IanB
author_rank: Super Contributor
timestamp: January 07, 2018, 09:33:24 pm
content: Quote from: EEVblog on January 07, 2018, 09:27:52 pmI'm curious about the situation where some components seem to be in short supply/have long lead times. Were there strong technical reasons for including those components in the design, since it seems a curious design decision to use rare parts?

author: EEVblog
author_rank: Unknown
timestamp: January 07, 2018, 09:33:32 pm
content: Quote from: Tom45 on January 07, 2018, 04:18:25 pmUEi do not supply the leads, I get those from Brymen.

author: EEVblog
author_rank: Unknown
timestamp: January 07, 2018, 09:35:25 pm
content: Quote from: IanB on January 07, 2018, 09:33:24 pmYes there were good reasons.And there may not have been a shortage at the time.And UEi had no idea how many would be sold, so it's not like they were going to commit to buying 5000 or something, these aren't cheap parts.

author: riyadh144
author_rank: Unknown
timestamp: January 08, 2018, 07:25:11 am
content: You should start a bug thread, because these are the issues that need to be mentioned so they can get fixed.

author: rs20
author_rank: Super Contributor
timestamp: January 08, 2018, 07:39:50 am
content: Just one little addendum to the statistics discussion -- I decided to dig a little deeper into tolerance intervals (which, for example, given a bunch of multimeter observations, lets you answer a question like "what interval will contain 99.7% of other units in the population, i.e., future multimeters).I followed the instructionshere. It turns out you have to providetwothings: a percentage of population units that you want your interval to capture (I chose 3 sigma, i.e., ~99.7%), and the confidence level with which you want your interval to be correct (in the style of confidence intervals, I chose 99%). So, in short, I'm answering the question: "Based on the sample data, what interval will 99.7% of future meters fall within? I want my interval to be sufficiently large in in 99% of parallel universes."The answer is (AFAICT) 4.99975 ± 0.00054 (unreadable spreadsheet), which is a significantly larger range than the naive 3 sigma method, even though this interval provides "only" 99% confidence. To get 99.7% confidence would widen the interval even further (and require access to chi-squared tables that I didn't immediately have to hand!)To preempt a couple of questions:So why can't I use the 3 sigma rule?I touched on this before, but that rule is only legit when you havepopulationmeans and standard deviations to hand. When you have onlysamplemeans and standard deviations, those are onlyestimatesof the population statistics, and that's where the chi-squared distribution comes in.How do you make sense of, or choose, the two parameters?Unfortunately that's a question of interpretation that the science of statistics is not particularly concerned with answering. All that statistics has to say is that it istruethat in 99% of possible samplings/parallel universes, ~99.7% of meters in the population fall within an interval computed in the same fashion as above. In the other 1% of parallel universes, you'll get an unlucky sampling that is way out of whack and you'll have no idea that that's even happened. Deal with it. How you choose to make decisions based on that information is entirely up to you.

author: IanJ
author_rank: Unknown
timestamp: January 08, 2018, 12:09:29 pm
content: Quote from: EEVblog on January 07, 2018, 09:35:25 pmI've been hit by the same.........and from what I know the manufacturers don't keep the world stocked with expensive high end parts continuously, it's a case of: if demand is high again then they'll switch over the production lines and manufacture a few tens of thousands.......and repeat.Some of the waiting times are up to 3 months......and I've found RS/Farnell/Digikey to be pretty good with their estimates of when they'll have stock again.End result is you do get caught out from time to time........and there's not much you can do about it unless you have deep pockets!Ian.

author: WaveyDipole
author_rank: Frequent Contributor
timestamp: January 08, 2018, 05:34:58 pm
content: Also disappointed to have missed the Kickstarter campaign. No news for months, no responses to questions about specs and all of a sudden this thread and the Kickstarter campaign has been and gone in ten days without so much as a whisper. Guess I will have to wait until the next batch..... Looks like a very nice meter.

author: Tom45
author_rank: Frequent Contributor
timestamp: January 08, 2018, 05:50:50 pm
content: Quote from: WaveyDipole on January 08, 2018, 05:34:58 pmWhile you are waiting, you can read the user manual at:http://www.eevblog.com/files/EEVblog-121GW-Manual.pdfThat manual needs a proof reader.

author: WaveyDipole
author_rank: Frequent Contributor
timestamp: January 08, 2018, 08:45:18 pm
content: Yes, I saw that on the Kickstarter page and have been contenting myself with having a look it. The meter has some interesting functions including the display of burden voltage. I recently had occasion to do some current measurements and found the readings on a Fluke 45 I was using some 20% adrift of what was expected. The reason turned out to be related to burden voltage which led to my raised awareness of the subject. The meter turned out to be accurate and the expectation correct.

author: EEVblog
author_rank: Unknown
timestamp: January 08, 2018, 08:54:50 pm
content: Quote from: WaveyDipole on January 08, 2018, 05:34:58 pmApart from the video on my channel and all my social channels announcing the thing

author: EEVblog
author_rank: Unknown
timestamp: January 08, 2018, 08:59:37 pm
content: Quote from: riyadh144 on January 08, 2018, 07:25:11 amhttps://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/

author: orion242
author_rank: Unknown
timestamp: January 08, 2018, 09:05:11 pm
content: Quote from: EEVblog on January 08, 2018, 08:54:50 pmLol, reminds me of this.https://youtu.be/S34_19FASHc?t=4m38sSeems they have scrubbed the internets of the original video.

author: WaveyDipole
author_rank: Frequent Contributor
timestamp: January 08, 2018, 09:51:25 pm
content: Quote from: EEVblog on January 08, 2018, 08:54:50 pmMy fault I guess for not subscribing to your video channels! Its not something that I have ever done nor do I have accounts on Facebook or Twitter. I quite delierately keep away from this invasive social media stuff. However I am a regular visitor to this site and I have kept looking on the main site page at fairly regular intervals for information. I came across this thread via a Google search today. Each time I have searched for '121GW' on this forum I only found older threads about the prototypes and now, of course, this one. Since I now know that there was a Kickstarter project I had a look in the EEVBlog Kickstarter forum and sure enough there is a mention of the project. This is not a section I have ever visited before nor did I ever think to look there. After all, I didn't know this meter would be introduced via a Kickstarter project. I just thought it would come up in the shop when it was ready and there would be an annoucement on the main site page. The only videos I can find at the moment are related to the repair of a prototype. I've had a lot of illness over the last few weeks so I have not been as regular visitor as I might have been during much of November and December. Had I known at the time, I would have gladly supported the Kickstarter project with my contribution. I am still willing to do so when the opportunity next arises.

author: nctnico
author_rank: Super Contributor
timestamp: January 08, 2018, 10:00:55 pm
content: Quote from: EEVblog on January 07, 2018, 09:35:25 pmI'd call that a luxury problem. Nice to see it is doing well and it will be a good test to see how an open source ecosystem will work for a professionally produced piece of test equipment.

author: Muttley Snickers
author_rank: Unknown
timestamp: January 08, 2018, 11:47:48 pm
content: I suspect there is a problem with the time and date on mine, I replaced the rtc battery but it didn't help much.

author: Brumby
author_rank: Unknown
timestamp: January 09, 2018, 12:12:25 am
content: Looks fake to me...

author: NexusKoolaid
author_rank: Contributor
timestamp: January 09, 2018, 03:23:21 pm
content: Quote from: WaveyDipole on January 08, 2018, 09:51:25 pmThis thread came up for me today:https://www.eevblog.com/forum/crowd-funded-projects/announcement-121gw-multimeter-on-kickstarter/msg1365882/#msg1365882It was #12 on the list - probably would have been #10 or higher were it not for more recent threads.QuoteI don't know if there was any 'main site' discussion, but the store vs. Kickstarter question was answered at least once in February:https://www.eevblog.com/forum/testgear/new-eevblog-branded-multimeter-coming/msg1139966/#msg1139966I sincerely hope that your illness is behind you and you're feeling better now.Cheers

author: Mike Warren
author_rank: Unknown
timestamp: January 10, 2018, 06:15:29 am
content: Quote from: Muttley Snickers on January 08, 2018, 11:47:48 pmAs Brumby said, that one looks fake. The giveaway is the 2 knobs. If you look at photos posted by Dave you'll notice the genuine one only has one knob.

author: b_force
author_rank: Super Contributor
timestamp: January 12, 2018, 02:26:31 am
content: Quote from: rs20 on January 08, 2018, 07:39:50 amWell this subject was hammered into on my studies, so it basically flows through my veins.Maybe it's better that I write a different topic about it, because you're clearly mixing a few things up (and it's going to be very offtopic)Based on a taken sample (with a minimum of 5), you can have two things to look at.1 - how accurate you know the average, which is the standard error (SE)2 - how much 'spread' you can expect based on your samples, which is the standard deviation (SD)Although you calculate them almost the same way, they are two very different things.You can easily recognize them, since you need to divide by the amount of samples with the first one.By definition that means that the number will get smaller.In this case you don't really care about the average, but you are interested about the spread.

author: MegaVolt
author_rank: Frequent Contributor
timestamp: January 12, 2018, 09:24:43 am
content: Tell me where you can see his scheme?

author: rs20
author_rank: Super Contributor
timestamp: January 13, 2018, 10:15:37 am
content: Quote from: b_force on January 12, 2018, 02:26:31 amI look forward to it. A couple of points though: I don't care where you worked or what you studied, this is statistics so we cantestour theories; we don't need to appeal to/claim authority. Also, it'd be appreciated if you stopped repeatedly attacking my correctness without actually quoting specific things I said and pointing out how they are wrong. Just writing out some different words does not constitute useful constructive feedback.* I'll be bringing MATLAB scripts verifying the correctness of the method I used to a high degree of precision using virtual populations of hundreds of thousands of "multimeters"; I look forward to seeing what you bring.* I regularly see people arguing on the internet when both people are right, and just wording things differently. I wonder if this is happening here.

author: b_force
author_rank: Super Contributor
timestamp: January 13, 2018, 04:17:17 pm
content: Quote from: rs20 on January 13, 2018, 10:15:37 amI guess this is a matter of a cultural difference maybe?I am used to that if someone quotes the way I did, it means that you don't follow the whole basic principles (and differences) of it.It doesn't matter, it's not bad or something. People have all kinds of different backgrounds.Therefore it made me realize it's easier to start a new topic about it.Give me some time to get a story together that's understandable for all kinds of people.Enough offtopic