EEVblog #852 - Multimeter Mass Turbulence

[drussell]

The more interesting Part for Professionals would be the long term aspects of the calibration values, the reliability in general, the reputation, the availability of pare parts, Robustness etc.

Precisely!

While it is good (and totally expected) that they met (and vastly exceeded) their published specifications from the factory, the much more important question is how they hold up over time with use and abuse! 

These meters have essentially the same class of accuracy specifications as my 25 year old Amrel model 37 (4000 count) meter has:



(Sorry for the garbage image) of 0.3% + 3 counts on the DC ranges, for example... 

It's still damn close, at least the last time I had it near a much more accurate instrument to check it, even after being thrown in the truck or a toolbox, frozen in winter for days or weeks, scorched in the heat of the sun for hours, blasted with high voltages (it starts to beep at you when you get to 1050 or 1100 volts despite being rated for 1000), the 20A current range fuse being blown to smitherines more times that I care to admit, etc....

... and this thing is is calibrated with potentiometers and has never needed to be adjusted yet!  It always meets spec (WAY exceeds spec, actually) every single time I've checked it against iinstruments that are an order of magnitude more accurate!!...

Will the Brymen hold up?  Probably quite well, I would expect, but the more telling thing than 40 out-of-the-box meters is:

When Dave has the first 40 come back for returns, service or calibration, will they STILL meet spec?

Any cheap Chinese $5 meter can meet the spec out of the box...  Will these units hold up?!!

Is Dave even doing the returns and service?  Do you have to send it back to China to be recalibrated? 

He certainly has the instrumentation to be able to have people send his exclusive EEVBlog meter back to him if they have problems and check them out.  THAT will certainly be interesting to see the results of!!    Hopefully some people send a few back to him at some point for a check-up!

Until then, it's just

Dave didn't calibrate them. As far as I could tell he was just checking them for consistency. But he didn't make any adjustments.

No, but having a second level quality control test is totally a bonus! 

[drussell]

I do not have the software cal adjustment procedure.

IMHO, if you're the exclusive distributor of this model of meter, you should get that from Brymen!

[retrolefty]

So are these meters now not brand new, but rather slightly used.   

No, they are not used ! They have been calibrated by Dave personally. I hope he gives out a EEVblog Cal certificate with this limited series meter

Dave didn't calibrate them. As far as I could tell he was just checking them for consistency. But he didn't make any adjustments.

 Haven't you kept up with the many 'calibration' Vs 'adjustment' threads around here. There are two camps of opinion:

Camp 1. Calibration is not adjustment. Calibration is comparing with 'provable' testing standards and equipment and stating the differences seen on the various ranges and functions of the device being 'calibrated' and printing a report and/or sticker for the tested item.

Camp 2. What camp 1 calls calibration we call that verification or certification only. We feel a calibration is when adjustments are made, either open/closed/firmware/trim pots/whatever, to align the device being checked to match the 'provable' standards and equipment stated values. A published report should state the 'as found readings' and the 'post calibration/adjustment' readings.

Dave in one of his videos stated that "calibration is not adjustment", so I guess he is a firm camp 1 member. Or perhaps he is just stating what it means to the firms he has dealt with. Pick your camp I guess.

[f4eru]

Calibration and adjustment is often mixed.
Usually, when you get your instrument to a cal lab, they never adjust it, (it would be an out of calibration, and a repair).
Adjusting minor deviations (in spec) is bad practice, because it breaks long term reproducibility with that instrument.

[gardner]

A really interesting video.  Thank you.

I've compared a couple of really cheap meters against my Keithley 195A, which is the most accurate meter I own.  I have been surprised at the basic accuracy -- even really junky ones are basically bang on.  The things I am curious about are the temperature stability and the accuracy of non-basic functions that I don't have reliable standards for myself.

Temperature-wise I find I have to use my portable multimeter out in the bush in the middle of winter at -25C to debug some radio gear, or in the 35C summer sun or something.  I would be interested in how these meters read after sitting on the front seat of a locked car all afternoon at 60C or after sitting in your deep freeze at -17C for 24 hours.  Are they anything like accurate at extremes, and is there a lot of unit to unit variation?

I would also be interested in how accurately they measure a 100kHz frequency standard and how accurately they measure a 1 mic cap.  My most accurate frequency and capacitor meter is an Amprobe 34 that has a specified accuracy of 5%+10 digits for caps.  It's not like super accuracy is likely to be really important in these functions, but it would be interesting to know if typical units outperform their specs in these aspects too.

[Brumby]

I was just using the term calibration in the same sense Dave did when he said "I haven't asked Brymen how they actually calibrate these things." or "They can actually software calibrate these things".

Context means a lot on this subject - hence the request for clarification.

[nctnico]

So are these meters now not brand new, but rather slightly used.   

No, they are not used ! They have been calibrated by Dave personally. I hope he gives out a EEVblog Cal certificate with this limited series meter

Dave didn't calibrate them. As far as I could tell he was just checking them for consistency. But he didn't make any adjustments.

 Haven't you kept up with the many 'calibration' Vs 'adjustment' threads around here. There are two camps of opinion:

Camp 1. Calibration is not adjustment. Calibration is comparing with 'provable' testing standards and equipment and stating the differences seen on the various ranges and functions of the device being 'calibrated' and printing a report and/or sticker for the tested item.

Camp 2. What camp 1 calls calibration we call that verification or certification only. We feel a calibration is when adjustments are made, either open/closed/firmware/trim pots/whatever, to align the device being checked to match the 'provable' standards and equipment stated values. A published report should state the 'as found readings' and the 'post calibration/adjustment' readings.

Dave in one of his videos stated that "calibration is not adjustment", so I guess he is a firm camp 1 member. Or perhaps he is just stating what it means to the firms he has dealt with. Pick your camp I guess.

My Websters English dictionary says that calibration means checking AND adjusting a piece of test equipment.

[EEVblog]

I was just using the term calibration in the same sense Dave did when he said "I haven't asked Brymen how they actually calibrate these things." or "They can actually software calibrate these things".

Brymen do a closed case calibration adjustment on the 50mV an 500mV ranges. They rely on the divider for the rest.

[EEVblog]

My Websters English dictionary says that calibration means checking AND adjusting a piece of test equipment.

This is not something you want to trust the dictionary on.
At most companies running a proper quality system and take calibration seriously, if you sent a bit of gear for "calibration" and asked them to perform a calibration adjustment, then you'll get booted out the door pretty quick, or slapped over the head. Why? because you just ruined the calibration and drift history of that instrument.
When you send something to a cal lab "for calibration" they will just measure it and give you a report. They will only adjust it if you ask them to.

[nowlan]

News to me. Ive never done it, but for most people I think they would expect a device to be corrected if out.

[EEVblog]

News to me. Ive never done it, but for most people I think they would expect a device to be corrected if out.

Then they have no idea nor do they care about proper professional calibration procedures.

Any serious gear you send for calibration should not be "out". If it is out of spec then the unit is faulty and you have a potentially big issue on your hands.
I've seen this cause panics in companies - When did it fail? By how much? Is it intermittent? Was it used for production testing?, or qualification? How many units tested weer effected? It can lead to huge formal investigation.
If the calibration company simply tweaks if back into spec for you then that company would lose their calibration contract instantly!

I know this sounds a bit ridiculous to Joe Average electronics enthusiast, but it's the way calibration is done professionally in the industry, and there are very good reasons for it.
Calibration should not include adjustment unless specifically done so under your advisement.

[retrolefty]

My Websters English dictionary says that calibration means checking AND adjusting a piece of test equipment.

This is not something you want to trust the dictionary on.
At most companies running a proper quality system and take calibration seriously, if you sent a bit of gear for "calibration" and asked them to perform a calibration adjustment, then you'll get booted out the door pretty quick, or slapped over the head. Why? because you just ruined the calibration and drift history of that instrument.

 

I've read that argument before but don't understand what is being 'ruined'? As long as they record the 'as found before adjustment' readings and the 'after adjustment' readings what data is lost? You still have the drift value from the prior calibration interval so one knows the drift between those two dates. As a user I'm not interested in tracking unadjusted calibration drift over many years but rather from the last 6 month or yearly calibration interval. 

When you send something to a cal lab "for calibration" they will just measure it and give you a report. They will only adjust it if you ask them to.

And of course pay them some amount above their 'normal calibration' quotation I would have no issue with this subject if the calibration services would just quote two types of service, validation (at a lower cost) and calibration (at higher costs) so one clearly knows what they are getting for their money. Can anyone show us a DMM manufacture that discusses calibration procedures in their owners manual that doesn't involve some kind of hardware or software 'adjustment' ?

I know this sounds a bit ridiculous to Joe Average electronics enthusiast

 A bit? it's an abuse of the word calibration. My Fluke model 45 service manual clearly states what they mean by verification and calibration:

This chapter of the Service Manual provides performance tests that can be used at any
time to verify Fluke 45 operation within published specifications. A complete calibration
procedure is also included. The performance test and, if necessary, the calibration
procedure can be performed periodically and after service or repair.

 Why does various Joe Blow 'calibration service' company get to redefine the word calibration to be contrary to common sense and Fluke, Webster, and to Joe average enthusiast.
 I supervised a Instrument Shop at a refinery for a couple of years and had to deal with 3rd party agreements, local quasi government inspectors, and incident investigations, etc. All that was ever questioned was is the calibration sticker expired or not.   

[EEVblog]

I've read that argument before but don't understand what is being 'ruined'?

The long term drift record is "reset" once the unit is adjusted.

As long as they record the 'as found before adjustment' readings and the 'after adjustment' readings what data is lost? You still have the drift value from the prior calibration interval so one knows the drift between those two dates. As a user I'm not interested in tracking unadjusted calibration drift over many years but rather from the last 6 month or yearly calibration interval.

Once you adjust it you have lost the ability to see the long term drift trend over years. i.e. will if keep drifting in one direction, or will it come back. Does it cycle? etc.
Once you adjust the instrument you should throw that data out the window and start again.
If that's what you want to do, then hey, that's your choice, but IME it's not how any large organisation I've worked for does it.
Buy hey, it's all what you want to achieve.

And of course pay them some amount above their 'normal calibration' quotation I would have no issue with this subject if the calibration services would just quote two types of service, validation (at a lower cost) and calibration (at higher costs) so one clearly knows what they are getting for their money.

They quote whatever you ask them to quote.
They'll tweak the EEpots nude whilst listening to wale songs if you pay them enough money.

[rrinker]

They quote whatever you ask them to quote.
They'll tweak the EEpots nude whilst listening to wale songs if you pay them enough money.

 This is why I love this place.

Having done precision mechanical measurement (QC checking jet engine parts), you don't want to mess with a given tool's history because that traceability becomes incredibly important. Parts we made were for several different engines, but mostly stuff that went into the F15. The production of many of these parts is traceable completely back to the day it was made, on which machine it was made, and who did the final check before shipping it out the door. Very precise stuff, down to the nearest 0.0001" (in DaveSpeak - less than half a bee's dick). What made it funny was that the owner of the business was an old time German machinist, used to doing hand work, not CNC stuff, at an order of magnitude or more looser tolerances and sometimes had trouble understanding why this stuff had to be kept so tight. The best was when the local US Navy development center brought us this sample of an aluminum casing with a weird pattern inside that the wanted us to duplicate, to a very tight tolerance. They wouldn't (and likely couldn't) tell us what it was, but I got a look at it and it was obviously a microwave waveguide of some sort. The owner and his right hand man (another old time German machinist) kept going on after the Navy people left about why does this stupid little box need to be made that precise... 

[Abbas]

Dave maybe you could also try out testing them all at once in parallel! It would be something great and maybe also fun!

And also I am curious what will happen if you connect all of them in series for a current measurement? World's largest chain current mesurement

[Brumby]

And also I am curious what will happen if you connect all of them in series for a current measurement? World's largest chain current mesurement

Burden voltage demonstration.

Would be an interesting one to do, actually.  We can calculate the answer - but a graphic picture might make more of an impressionon some viewers.....

[Abbas]

Burden voltage demonstration.

Would be an interesting one to do, actually.  We can calculate the answer - but a graphic picture might make more of an impressionon some viewers.....

Yeah that's what I thought of. Connecting 40 or more multimeter in series with a current load would show in a obviously way how burden voltage can affect the readings. It would be exactly appropriate since Dave has a mass of multimeters available at the moment

Hitting some birds with a stone [emoji41]

[tggzzz]

(0.3% isn't a very good spec for something with a 22000-count chipset that displays 5 digits on screen)

Agreed, but if other conditions hold it might just be useful.

A company I once worked for sold a very expensive attenuation meter with a 0.1dB accuracy and a 0.001dB stability and repeatability. The stability was important since it was used to detect small changes in attenuation over the course of a week or so.

[Fungus]

(0.3% isn't a very good spec for something with a 22000-count chipset that displays 5 digits on screen)

Agreed, but if other conditions hold it might just be useful.

A company I once worked for sold a very expensive attenuation meter with a 0.1dB accuracy and a 0.001dB stability and repeatability. The stability was important since it was used to detect small changes in attenuation over the course of a week or so.

The UT61E has data logging at a very low price so I guess you could use it for stuff like that if you calibrate the setup properly.

But ... does the UT61E have the right stability for that? I don't know.

I do know they skimp on every possible part to get the price down so I'm not confident.

[hopski]

I use a couple of  UT61E's for data logging. I check them every month with a DMM plus tester and other references, no noticable drift for the last few months, but it they do drift as least I'll know by how much.

[SeoulBigChris]

Regarding your engineering note pad, Australia uses seven-ring notebook binders?