Author Topic: EEVblog #1051 - 121GW Multimeter Mass Turbulence  (Read 10789 times)

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EEVblog #1051 - 121GW Multimeter Mass Turbulence
« on: January 06, 2018, 09:59:09 am »
Some quick sanity testing of the newly arrived 121GW multimeters


 
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Offline tautech

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #1 on: January 06, 2018, 10:12:36 am »
At 8.17, whats the spec on the pad next to R77 ?
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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #2 on: January 06, 2018, 11:51:28 am »
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 car is on the road legally).
 

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #3 on: January 06, 2018, 11:54:23 am »
More importantly - it's a wonderful sight.  The product is now real and on the shelf!
 

Offline klunkerbus

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #4 on: January 06, 2018, 01:22:29 pm »
Congrats on the new arrival. 

Got a chuckle out of the "Sydey" Australia markings on the outer box. Hopefully the meter QC is better...  :-DD

Edit: Well, I am of course assuming there really is no Sydey, Australia. 
« Last Edit: January 06, 2018, 01:26:05 pm by klunkerbus »
 

Online wraper

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #5 on: January 06, 2018, 02:10:38 pm »
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.



« Last Edit: January 06, 2018, 02:20:43 pm by wraper »
 
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Offline b_force

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #6 on: January 06, 2018, 02:20:58 pm »
Finally they arrived.
Nice looking meters Dave!
Jonestronics?  :-DD


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.  :-+

« Last Edit: January 06, 2018, 02:35:18 pm by b_force »
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Offline massivephoton

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #7 on: January 06, 2018, 05:47:06 pm »
How could Dave dare to turn them on before tearing 'em apart!  :palm:
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Offline AustinTxBob

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #8 on: January 06, 2018, 06:13:14 pm »
When will they be available to purchase?
 

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #9 on: January 06, 2018, 10:43:36 pm »
When will they be available to purchase?

Good 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.
 

Offline mc172

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #10 on: January 07, 2018, 12:51:04 am »
What's with the large discrepancy on what I assume is room temperature?

Very nice, though! Top marks mate.
 

Offline ataradov

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #11 on: January 07, 2018, 01:13:54 am »
It does not show all segments on after turning on. Living on the edge?
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Offline rs20

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #12 on: January 07, 2018, 01:45:08 am »
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...

Possibly a bit hypocritical :P

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.  :-+

What are you even on about?
  • The standard deviation of the provided data is 0.00013
  • One 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.
 
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Offline dragondgold

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #13 on: January 07, 2018, 01:58:58 am »
Hi! Is it possible to order one of this now? I totally missed the Kickstarter campaign  |O
 

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #14 on: January 07, 2018, 04:39:15 am »
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.
 
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Offline Tom45

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #15 on: January 07, 2018, 04:18:25 pm »
No test leads in "the very first one"?
 

Offline IanB

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #16 on: January 07, 2018, 04:58:40 pm »
No test leads in "the very first one"?

As I recall it comes with test leads, case and thermocouple.
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Offline b_force

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #17 on: January 07, 2018, 05:01:15 pm »
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...

Possibly a bit hypocritical :P

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.  :-+

What are you even on about?
  • The standard deviation of the provided data is 0.00013
  • One 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.
And 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 0.0005V

Last 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)
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Offline IanB

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #18 on: January 07, 2018, 05:12:56 pm »
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.
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Offline Keith Ward

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #19 on: January 07, 2018, 05:35:11 pm »
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 ...
 

Offline rs20

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #20 on: January 07, 2018, 07:03:38 pm »
And this is why a proper lesson in statistics is in place, because you are making a lot of mistakes mister.

You'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.

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.

Yep, I totally didn't get the hint that you were calculating tolerance intervals and calling them "ranges".

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.

Are 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.

Last 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)

No. The datasheet specs might be prepared behind the scenes using statistics similar to the statistics you described, but what they mean is 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.)

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.

True 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 is true is that for normally distributed data, 99.7% of population items fall between

(population mean) - 3 (population standard dev) and (population mean) + 3 (population standard dev)

One of the most rife mistakes in statistics, IMHO, is when people take the sample standard 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 population mean -- 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)
« Last Edit: January 07, 2018, 07:10:00 pm by rs20 »
 

Offline Dr. Frank

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #21 on: January 07, 2018, 08:48:59 pm »
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.



That'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
« Last Edit: January 07, 2018, 08:51:33 pm by Dr. Frank »
 

Offline ataradov

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #22 on: January 07, 2018, 08:54:42 pm »
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.
Alex
 

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #23 on: January 07, 2018, 09:27:52 pm »
When will they be available to purchase?

Good 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.

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.
 

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Re: EEVblog #1051 - 121GW Multimeter Mass Turbulence
« Reply #24 on: January 07, 2018, 09:32:27 pm »
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.

All correct, taking more pre-orders on units without having proven anything has zero upside for me at this point.
 


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