EEVblog #1051 - 121GW Multimeter Mass Turbulence

[IanB]

I 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.

I'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?

[EEVblog]

No test leads in "the very first one"?

UEi do not supply the leads, I get those from Brymen.

[EEVblog]

I 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.

I'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?

Yes 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.

[riyadh144]

You should start a bug thread, because these are the issues that need to be mentioned so they can get fixed.

[rs20]

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 instructions here. It turns out you have to provide two things: 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 have population means and standard deviations to hand. When you have only sample means and standard deviations, those are only estimates of 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 is true that 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.

[IanJ]

I 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.

I'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?

Yes 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.

I'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.

[WaveyDipole]

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.

[Tom45]

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.

While you are waiting, you can read the user manual at:

http://www.eevblog.com/files/EEVblog-121GW-Manual.pdf

That manual needs a proof reader.

[WaveyDipole]

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.

[EEVblog]

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.

Apart from the video on my channel and all my social channels announcing the thing 

[EEVblog]

You should start a bug thread, because these are the issues that need to be mentioned so they can get fixed.

https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/

[orion242]

all my social channels announcing the thing 

Lol, reminds me of this.

https://youtu.be/S34_19FASHc?t=4m38s

Seems they have scrubbed the internets of the original video.

[WaveyDipole]

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.

Apart from the video on my channel and all my social channels announcing the thing 

My 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.

[nctnico]

I 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.

I'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?

Yes 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.

I'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.

[Muttley Snickers]

I suspect there is a problem with the time and date on mine, I replaced the rtc battery but it didn't help much.   

[Brumby]

Looks fake to me...

[NexusKoolaid]

Each time I have searched for '121GW' on this forum I only found older threads about the prototypes and now, of course, this one.

This thread came up for me today:

https://www.eevblog.com/forum/crowd-funded-projects/announcement-121gw-multimeter-on-kickstarter/msg1365882/#msg1365882

It was #12 on the list - probably would have been #10 or higher were it not for more recent threads.

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.

I 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/#msg1139966

I sincerely hope that your illness is behind you and you're feeling better now.

Cheers

[Mike Warren]

I suspect there is a problem with the time and date on mine, I replaced the rtc battery but it didn't help much.   

As 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.

[b_force]

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 instructions here. It turns out you have to provide two things: 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 have population means and standard deviations to hand. When you have only sample means and standard deviations, those are only estimates of 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 is true that 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.

Well 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.

[MegaVolt]

Tell me where you can see his scheme?

[rs20]

Well 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)

I 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 can test our 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.

[b_force]

Well 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)

I 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 can test our 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.

I 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