Two DVMs...

[chrisq]

On 8/19/23 18:04, Fred Bloggs wrote:

On Saturday, August 19, 2023 at 1:24:16 PM UTC-4, John Larkin wrote:
On Sat, 19 Aug 2023 10:11:57 -0700, John Larkin
jla...@highlandSNIPMEtechnology.com> wrote:

On Sat, 19 Aug 2023 12:43:24 -0400, ehsjr <eh...@verizon.net> wrote:

On 8/19/2023 9:49 AM, John Robertson wrote:
On 2023/08/18 7:25 p.m., John Larkin wrote:
The Keithley 2001 is obsolete, so our test department is moving on to
a Keysight. They\'ll have to add a driver into our Python library.

They loaned me one to evaluate.

https://www.dropbox.com/scl/fi/vv1u2r1whendlxioihoma/Two_DVMs.jpg?rlkey=y0pbb1xhjl5na4004lfjoih6c&raw=1

Not too bad, considering that my Fluke hasn\'t been calibrated in human
memory.

I had to take six pics to get the numbers on the Fluke. Its VF display
heterodynes with my phone camera and makes a cool comet effect.



Is the Fluke meter not quite showing yet another digit in the photo?
Might that be an 8 or 9 as the .00000X digit?

If so, then indeed, it isn\'t doing badly!

John :-#)#

Maybe it\'s the Keysight that\'s off by ~10 uV


Ed

I think there was one more digit that the phone camera missed.

But they agree to 1 PPM!

I have a request to design a board that will be a couple-of-PPM
accurate programmable voltage source. That\'s scary.

I\'m thinking of using several (or many) ADR420-series parts,
temperature controlled. Or a few LM199s, except it\'s obsolete.

ADR1000 is still available.

REF-01 is remarkably stable.

I wonder what those DVMs use.


The Fluke uses a \"reference transistor\", which is an NPN with a zener
in the emitter.

I seriously bet that\'s using \'mathematical\' compensation of some kind.

Fluke used the reference amplifer, transistor / zener
combination in a whole range of test gear. Original part
was in the 1969 General Electric Transistor manual, so
idea had a very long life. Looking at the the Fluke 731B
voltage standard, doesn\'t look anything special in the
circuitry, but the reference zener / transistor devices
came as a selected pair, device and resistor. Bet Fluke
also designed so that the various tempcos of the resistors
all cancelled out. Fluke were masters of analog design,
but takes a lot of work to get that sort of performance
from such innocent looking circuitry. Special sauce,
indeed...

 

[Anthony William Sloman]

On Sunday, August 20, 2023 at 9:36:38 PM UTC+10, chrisq wrote:

On 8/19/23 19:39, John Larkin wrote:
On Sat, 19 Aug 2023 15:05:16 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

On 2023-08-19 14:43, John Larkin wrote:
On Sat, 19 Aug 2023 17:49:52 -0000 (UTC), Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:
On Sat, 19 Aug 2023 10:11:57 -0700, John Larkin
jla...@highlandSNIPMEtechnology.com> wrote:

On Sat, 19 Aug 2023 12:43:24 -0400, ehsjr <eh...@verizon.net> wrote:

On 8/19/2023 9:49 AM, John Robertson wrote:
On 2023/08/18 7:25 p.m., John Larkin wrote:
The Keithley 2001 is obsolete, so our test department is moving on to
a Keysight. They\'ll have to add a driver into our Python library.

They loaned me one to evaluate.

https://www.dropbox.com/scl/fi/vv1u2r1whendlxioihoma/Two_DVMs.jpg?rlkey=y0pbb1xhjl5na4004lfjoih6c&raw=1

Not too bad, considering that my Fluke hasn\'t been calibrated in human
memory.

I had to take six pics to get the numbers on the Fluke. Its VF display
heterodynes with my phone camera and makes a cool comet effect.



Is the Fluke meter not quite showing yet another digit in the photo?
Might that be an 8 or 9 as the .00000X digit?

If so, then indeed, it isn\'t doing badly!

John :-#)#

Maybe it\'s the Keysight that\'s off by ~10 uV


Ed

I think there was one more digit that the phone camera missed.

But they agree to 1 PPM!

I have a request to design a board that will be a couple-of-PPM
accurate programmable voltage source. That\'s scary.

I\'m thinking of using several (or many) ADR420-series parts,
temperature controlled. Or a few LM199s, except it\'s obsolete.

ADR1000 is still available.

REF-01 is remarkably stable.

I wonder what those DVMs use.

The Fluke uses a \"reference transistor\", which is an NPN with a zener in the emitter.

At a SWAG, three LTZ1000s and some software.

Great longterm stability. Maybe they\'ve been aged.

$93 from Digikey.

Could be. They\'re probably a bit cheaper if you buy lots at a time, but there\'s obviously a lot of TLC involved.

Stabilizing the temperature adequately will require some care, for sure.

And if you want long term stability, you stabilise the temperature at the lowest leven you can get away with. Peltier junctions are better than resistive heaters for that.

> >> I sometimes put voltage references on paddles routed out of the PCB. This is mostly to avoid shifts due to mechanical stress on the package, but could come in very handy to (more or less) eliminate temperature gradients.

The more rabid temperature stabilisation freaks stabilise an external block at the desired temperature just to minimise temperature gradients in the central core.

> >> A nice analytically-calculable geometry, e.g. a paddle within a paddle, joined with two pairs of thin bars, would let one put two nested temperature control zones in a small space.

It\'s in the literature. It didn\'t sweep the world.

> >> Some nice squeaky styrofoam, and maybe a bit of wraparound metal here and there to get rid of incidental vertical gradients, would probably do a good job.

If you knew exactly what you were doing.

I\'m thinking about a baby board with some mosfet heaters in the
corners and a clever arrangement of references and thermistors towards
the middle. It could go on my main board on spacers, with a cover.
That could attenuate external temp changes by 50:1 maybe.

Four refs would cut the noise in half.

I could mux a nanovolt-resolution differential delta-sigma ADC between multiple references and see if any is an outlier.

The potential customer has been talking about this for over a year. In typical form, when they finally place an order they will want it in three weeks.

The LTZ1000 data sheet talks about thermocouple voltages from kovar-to-copper connections. The cure might be worse than the disease.

> I would use a cheaper reference of known characteristics and use software correction. Anyone can throw $100 LTZ1000 at the problem, but there must be a smarter way...

Analog Device wouldn\'t have bothered to keep on offering the LTZ1000 if there was.

If you want to use software correction you have to characterise your cheaper part very accurately, which takes time and costs money. there is no free lunch.

--
Bill Sloman, Sydney

 

[John Larkin]

On Sun, 20 Aug 2023 11:36:30 +0000, chrisq <devzero@nospam.com> wrote:

On 8/19/23 19:39, John Larkin wrote:
On Sat, 19 Aug 2023 15:05:16 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-08-19 14:43, John Larkin wrote:
On Sat, 19 Aug 2023 17:49:52 -0000 (UTC), Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:
On Sat, 19 Aug 2023 10:11:57 -0700, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:

On Sat, 19 Aug 2023 12:43:24 -0400, ehsjr <ehsjr@verizon.net> wrote:

On 8/19/2023 9:49 AM, John Robertson wrote:
On 2023/08/18 7:25 p.m., John Larkin wrote:
The Keithley 2001 is obsolete, so our test department is moving on to
a Keysight. They\'ll have to add a driver into our Python library.

They loaned me one to evaluate.

https://www.dropbox.com/scl/fi/vv1u2r1whendlxioihoma/Two_DVMs.jpg?rlkey=y0pbb1xhjl5na4004lfjoih6c&raw=1

Not too bad, considering that my Fluke hasn\'t been calibrated in human
memory.

I had to take six pics to get the numbers on the Fluke. Its VF display
heterodynes with my phone camera and makes a cool comet effect.



Is the Fluke meter not quite showing yet another digit in the photo?
Might that be an 8 or 9 as the .00000X digit?

If so, then indeed, it isn\'t doing badly!

John :-#)#

Maybe it\'s the Keysight that\'s off by ~10 uV


Ed

I think there was one more digit that the phone camera missed.

But they agree to 1 PPM!

I have a request to design a board that will be a couple-of-PPM
accurate programmable voltage source. That\'s scary.

I\'m thinking of using several (or many) ADR420-series parts,
temperature controlled. Or a few LM199s, except it\'s obsolete.

ADR1000 is still available.

REF-01 is remarkably stable.

I wonder what those DVMs use.



The Fluke uses a \"reference transistor\", which is an NPN with a zener
in the emitter.



At a SWAG, three LTZ1000s and some software.

Cheers

Phil Hobbs

Great longterm stability. Maybe they\'ve been aged.

$93 from Digikey.



Could be. They\'re probably a bit cheaper if you buy lots at a time, but
there\'s obviously a lot of TLC involved.

Stabilizing the temperature adequately will require some care, for sure.
I sometimes put voltage references on paddles routed out of the PCB.
This is mostly to avoid shifts due to mechanical stress on the package,
but could come in very handy to (more or less) eliminate temperature
gradients.

A nice analytically-calculable geometry, e.g. a paddle within a paddle,
joined with two pairs of thin bars, would let one put two nested
temperature control zones in a small space.

Some nice squeaky styrofoam, and maybe a bit of wraparound metal here
and there to get rid of incidental vertical gradients, would probably do
a good job.

Cheers

Phil Hobbs

I\'m thinking about a baby board with some mosfet heaters in the
corners and a clever arrangement of references and thermistors towards
the middle. It could go on my main board on spacers, with a cover.
That could attenuate external temp changes by 50:1 maybe.

Four refs would cut the noise in half.

I could mux a nanovolt-resolution differential delta-sigma ADC between
multiple references and see if any is an outlier.

The potential customer has been talking about this for over a year. In
typical form, when they finally place an order they will want it in
three weeks.


I would use a cheaper reference of known characteristics and use
software correction. Anyone can throw $100 ltz1000 at the problem,
but there must be a smarter way...

We can correct for tempco, and probably will, but not for noise or
ageing.

$100 would not be a big deal here, although there is a case for using
one or several $10 chips, if we feel that they are stable long-term.

We used to buy a Motorola zener diode that came with a graph of 1000
hours of voltage history. It came in a presentation-quality plastic
tube with signed certificates, for the price of a nice dinner for
four. The optimum current was noted.

 

[John Larkin]

On Sun, 20 Aug 2023 11:50:18 +0000, chrisq <devzero@nospam.com> wrote:

On 8/19/23 18:04, Fred Bloggs wrote:
On Saturday, August 19, 2023 at 1:24:16?PM UTC-4, John Larkin wrote:
On Sat, 19 Aug 2023 10:11:57 -0700, John Larkin
jla...@highlandSNIPMEtechnology.com> wrote:

On Sat, 19 Aug 2023 12:43:24 -0400, ehsjr <eh...@verizon.net> wrote:

On 8/19/2023 9:49 AM, John Robertson wrote:
On 2023/08/18 7:25 p.m., John Larkin wrote:
The Keithley 2001 is obsolete, so our test department is moving on to
a Keysight. They\'ll have to add a driver into our Python library.

They loaned me one to evaluate.

https://www.dropbox.com/scl/fi/vv1u2r1whendlxioihoma/Two_DVMs.jpg?rlkey=y0pbb1xhjl5na4004lfjoih6c&raw=1

Not too bad, considering that my Fluke hasn\'t been calibrated in human
memory.

I had to take six pics to get the numbers on the Fluke. Its VF display
heterodynes with my phone camera and makes a cool comet effect.



Is the Fluke meter not quite showing yet another digit in the photo?
Might that be an 8 or 9 as the .00000X digit?

If so, then indeed, it isn\'t doing badly!

John :-#)#

Maybe it\'s the Keysight that\'s off by ~10 uV


Ed

I think there was one more digit that the phone camera missed.

But they agree to 1 PPM!

I have a request to design a board that will be a couple-of-PPM
accurate programmable voltage source. That\'s scary.

I\'m thinking of using several (or many) ADR420-series parts,
temperature controlled. Or a few LM199s, except it\'s obsolete.

ADR1000 is still available.

REF-01 is remarkably stable.

I wonder what those DVMs use.


The Fluke uses a \"reference transistor\", which is an NPN with a zener
in the emitter.

I seriously bet that\'s using \'mathematical\' compensation of some kind.

Fluke used the reference amplifer, transistor / zener
combination in a whole range of test gear. Original part
was in the 1969 General Electric Transistor manual, so
idea had a very long life.

I wonder if it was monolithic. More likely two dies.

 

[chrisq]

On 8/20/23 13:07, Anthony William Sloman wrote:

<snipped>

Analog Device wouldn\'t have bothered to keep on offering the LTZ1000
if there was.

It\'s supposed to be the best, so one variable a manufacturer can
ignore, if the end price justifies it. They would still need
to do a lot of work to get the performance, as other issues start
to dominate at sub microvolt levels. Analog probably have a
reference design for the pcb layout, and choice of resistors.
Buying in thousands, they will get a price good enough to
make them a viable choice.

> If you want to use software correction you have to characterise your
cheaper part very accurately, which takes time and costs money. there is
no free lunch.
>

Agreed, but if done right, say with batching to take care of spreads,
that work only needs to be done once. Fine tuning with experience on
actual performance just means a software update. Manufacturers can
also specify tighter tolerancing for incoming parts, or get the
vendor to do the work on curvature and aging.

Solartron and others got good results using such an approach. The
Solartron 7081, 8.5 digit dvm. mid 1980\'s for example...

 

[Joe Gwinn]

On Sat, 19 Aug 2023 15:35:31 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

On Sat, 19 Aug 2023 18:07:52 -0400, Joe Gwinn <joegwinn@comcast.net
wrote:

On Sat, 19 Aug 2023 10:11:57 -0700, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:

On Sat, 19 Aug 2023 12:43:24 -0400, ehsjr <ehsjr@verizon.net> wrote:

On 8/19/2023 9:49 AM, John Robertson wrote:
On 2023/08/18 7:25 p.m., John Larkin wrote:
The Keithley 2001 is obsolete, so our test department is moving on to
a Keysight. They\'ll have to add a driver into our Python library.

They loaned me one to evaluate.

https://www.dropbox.com/scl/fi/vv1u2r1whendlxioihoma/Two_DVMs.jpg?rlkey=y0pbb1xhjl5na4004lfjoih6c&raw=1

Not too bad, considering that my Fluke hasn\'t been calibrated in human
memory.

I had to take six pics to get the numbers on the Fluke. Its VF display
heterodynes with my phone camera and makes a cool comet effect.



Is the Fluke meter not quite showing yet another digit in the photo?
Might that be an 8 or 9 as the .00000X digit?

If so, then indeed, it isn\'t doing badly!

John :-#)#

Maybe it\'s the Keysight that\'s off by ~10 uV


Ed

I think there was one more digit that the phone camera missed.

But they agree to 1 PPM!

I have a request to design a board that will be a couple-of-PPM
accurate programmable voltage source. That\'s scary.

Here there be dragons - and madness:

.<https://lists.febo.com/empathy/list/volt-nuts.lists.febo.com

Joe Gwinn

I will add that Volt-Nuts is a good source of circuit ideas and
suggestions of components to investigate.

Yes, we\'d need one of those crazy expensive system DVMs to test and
calibrate units.

Really? A Keysight 34461A Digital Multimeter, 6.5 Digit, Truevolt DMM
costs about $1,500 list, and the 34465A 6.5 Digit Multimeter, Truevolt
DMM costs about $1,900 list. 75 ppm and 30 ppm respectively.

There is also a 7.5-digit option, 34470, for $4.400 list. Probably
cherry-picked from the run of 34465A production. 16 ppm.

And then there is the 8.5 digit option, the 3458A Multimeter, for
$14,400 list. 0.1 ppm


>I could imagine an automated test/cal cycle taking a full day.

How good does this simple little voltage reference really need to be?
Given what it takes Keysight to get to the above accuracies, is there
any hope of getting anywhere close with just a hand full of
components, even with calibration?

Joe Gwinn

 

[bitrex]

On 8/19/2023 3:38 PM, Liz Tuddenham wrote:

John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:

[...]
Not too bad, considering that my Fluke hasn\'t been calibrated in human
memory.

I have a Philips PM2518 which lost its fine calibration when the memory
battery ran out. It pre-dates the takeover by Fluke of Philips
Instruments and this one had stickers showing it was last calibrated by
the Luftwaffe in 2003.

Earlier this year I sent it off to Instrotech of Watford, who took a bit
of persuading that it was worth recalibrating. They succeeded, despite
a lack of information, and returned it to me promptly at a sensible
price with a proper Calibration Certificate.


Disclaimer: I have no connection with Instrotech other than as a
satisfied customer.

I had my HP3478A calibrated & adjusted last year, MIT student lab
surplus. I\'m unsure if it was ever calibrated since it left the factory,
there was no cert on it anywhere when I bought it.

It was within spec on everything except one test in the 3 Meg resistance
range:

<https://imgur.com/a/5UKCYhm>

The work was done by Essco in Lowell, MA, about 30 miles north of
Boston. total cost for the job was $170, about three times what I paid
for the 3478A..

 

[Anthony William Sloman]

On Monday, August 21, 2023 at 1:09:24 AM UTC+10, John Larkin wrote:

On Sun, 20 Aug 2023 11:36:30 +0000, chrisq <dev...@nospam.com> wrote:
On 8/19/23 19:39, John Larkin wrote:
On Sat, 19 Aug 2023 15:05:16 -0400, Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote:
On 2023-08-19 14:43, John Larkin wrote:
On Sat, 19 Aug 2023 17:49:52 -0000 (UTC), Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote:
John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:
On Sat, 19 Aug 2023 10:11:57 -0700, John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:
On Sat, 19 Aug 2023 12:43:24 -0400, ehsjr <eh...@verizon.net> wrote:
On 8/19/2023 9:49 AM, John Robertson wrote:
On 2023/08/18 7:25 p.m., John Larkin wrote:

We used to buy a Motorola zener diode that came with a graph of 1000 hours of voltage history. It came in a presentation-quality plastic tube with signed certificates, for the price of a nice dinner for four. The optimum current was noted.

That would have been the 1N829.

https://www.microsemi.com/document-portal/doc_view/125462-lds-0220-datasheet

You had to get the current to precisely 7.5mA to get the promised temperature stability. The one occasion where I saw one designed in, the engineer clearly hadn\'t bothered to get it precise enough - because the breakdown voltage at 7.5mA is in the range 5.89V to 6.51V and while he\'d put in a trimpot to let him trim the output voltage to 10.000V exactly, he hadn\'t put a trimmer on the resistor that set the current to let him get that to exactly 7.5mA. It was pretty silly.

The integrated circuits that incorporate buried zeners presumably use laser trimming or on-chip zapping to sort this out on a chip-by-chip basis (which isn\'t cheap),

--
Bill Sloman, Sydney

 

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