Re: [volt-nuts] Matched resistors

[Charles Steinmetz]

Andreas wrote:


But for the 100uVpp I have to ask for the measurement conditions.
Is the source (reference) connected via (long cable) and supplied 
with another mains line


No


or on the same pcb with the same power supply (or battery supplied).


Yes.  (And I have extensive design experience with ultra-low noise 
power supplies, decoupling, RFI prevention, and low-noise grounding.)



Was the pcb cleaned before measurement to keep leakage low?


Yes, it was freshly built and cleaned upon completion (vapor-phase), 
although that really has no bearing on commutation noise (charge 
injection) internal to the switched capacitor circuit, which is where 
all of the cyclical noise is generated.  Can it be filtered 
out?  Perhaps, but not easily without raising some other noise or 
drift problem.


How much noise did the reference generate? 1uV output measurement is 
quite low with
typical 0.6ppm/V of a buried zener multiplied by 2 and a amplifier 
with 1.6uVpp (referred to input).


I was using the ADR4520 (1uVp-p noise in the 0.1-10Hz band), with 
post-filtering.  When I said "about 1uVpp" output noise, I was 
thinking order of magnitude for purposes of comparison to 100uV, not 
precise value (which was more like 2-3uVpp).


Best regards,

Charles



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Re: [volt-nuts] Matched resistors

[Dave M]

Do you have easy, low cost access to an old Fluke 801 or 803 differential 
voltmeter?  These meters have a Kelvin-Varley divider inside that is 
composed of strings of resistors that are highly matched in value and 
tempco.  If I remember correctly, the highest decade is filled with a string 
of 40K resistors, each succeeding smaller decade value is 1/5 of the next 
higher decade, but all very well matched. They should all be very well aged 
by now too. (Just like wine... they get better with age).
Perhaps you could mix & match values to come up with suitable resistors for 
your project.  If your project is a one-off deal, then perhaps that approach 
could prove viable.


Cheers,
Dave M



From: Tony 



Randy,

Have you considered using multiple identical resistors to reduce the
variance? Depending on who you believe, you can reduce the variance of
the overall resistance by SQRT(N) where N is the number of resistors
in series/parallel. Its not that easy to create a good search query
for
this but here is one such explanation:

http://paulorenato.com/joomla/index.php?option=com_content&view=article&id=109:combining-resistors-to-improve-tolerance&catid=4:projects&Itemid=4

Ideally they should all come from the same batch - ie. manufactured by
the same machine from the same batch of materials. Obviously there's
no
way to guarantee that without close liaison with the manufacturer (you
did want 10 million parts at $.10 each didn't you!) but hopefully a
set
of resistors which come off the same reel would come close.

The absolute value isn't important however, but 'statistical gain'
will also apply to the TCR and stability of the overall divider. The
following assumes that both factors are similarly improved by SQRT(N),
but in fact they may be rather better than that.

That80? or $108 for one sealed Vishay foil divider will buy a lot of
lower spec parts: 



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Re: [volt-nuts] Matched resistors

[Randy Evans]

Tony,

I should have mentioned that I am primarily referring to stability, not
accuracy.  As i stated before, accuracy is relatively unimportant but
stability is essential.

Randy


On Wed, Jul 23, 2014 at 8:22 PM, Randy Evans 
wrote:

> Tony,
>
> Your improvement factor of SQRT(n) assumes that each resistor in the group
> has random changes uncorrelated to all others in the group.  For similar
> type resistors, I would think that is not likely to be true. For shelf life
> stability it is likely that they all "age" in a similar way.  Unless the
> resistors are in a hermetic package, humidity would impact all the
> resistors in a similar manner.
>
> Randy
>
>
> On Wed, Jul 23, 2014 at 6:36 PM, Tony  wrote:
>
>> Randy,
>>
>> Have you considered using multiple identical resistors to reduce the
>> variance? Depending on who you believe, you can reduce the variance of the
>> overall resistance by SQRT(N) where N is the number of resistors in
>> series/parallel. Its not that easy to create a good search query for this
>> but here is one such explanation:
>>
>> http://paulorenato.com/joomla/index.php?option=com_content&;
>> view=article&id=109:combining-resistors-to-improve-
>> tolerance&catid=4:projects&Itemid=4
>>
>> Ideally they should all come from the same batch - ie. manufactured by
>> the same machine from the same batch of materials. Obviously there's no way
>> to guarantee that without close liaison with the manufacturer (you did want
>> 10 million parts at $.10 each didn't you!) but hopefully a set of resistors
>> which come off the same reel would come close.
>>
>> The absolute value isn't important however, but 'statistical gain' will
>> also apply to the TCR and stability of the overall divider. The following
>> assumes that both factors are similarly improved by SQRT(N), but in fact
>> they may be rather better than that.
>>
>> That80€ or $108 for one sealed Vishay foil divider will buy a lot of
>> lower spec parts:
>>
>> Approx 12558 x Susumu RR0510P .5%, 25ppm 0402 (Digikey, $86/10k). 6279 in
>> series and parallel in each leg of the 1:1 divider> com/photos/Susumu%20Photos/RR%200402%20SERIES.jpg> might reduce the
>> variance to 25ppm/SQRT(6279) = .32ppm. Can't see any spec for stability,
>> but it may also improve similarly. Would take a while to solder them onto
>> stripboard though!
>>
>> Slightly more sensible might be 1078 x TE Connectivity RP73 1%, 10ppm
>> 1206 (Digikey, $100.18/1K).  Stability .5% (no qualifers in datasheet)
>>  => 10ppm/SQRT(539) = .43ppm, stability => 215ppm
>>
>> Or 372 x KOA Speer RN731JTTD4021B5 .1%, 5ppm (Mouser, $29/100). Stability
>> not on data sheet but typical endurance is +/- .02% for 1000 hrs @ 70C
>> on/off 1.5hours/.5hours.
>> => 5ppm/SQRT(138) = .37ppm, endurance => 14.7ppm (Stability should be
>> rather better than that). Note that the Mouser part no. is for a 25ppm part
>> but their manufacturer's part number is the 5ppm part as is the
>> description. Also, the price is way too high for 25ppm parts.
>>
>> Or 28 x Susumu RG2012L .01%, 2ppm (Digikey, $39.6/10). Stability not
>> quoted but typical Load Life is .01% (1000 x 1.5hours on/.5hours off at 85C)
>> => 2ppm/SQRT(14) = .53ppm, endurance => 27ppm
>>
>> You could also use multiple resistor networks. Eg:
>>
>> 104 x Susumu RM2012B-103/103-PBVW10 .1%, 5ppm tracking, 2
>> resistors/device (Digikey $104/100). Stability not quoted, endurance 500ppm
>> (1000 x 1.5hours on/.5hours off at 85C)
>> => 5ppm/SQRT(104) = .49ppm, endurance => 49ppm
>>
>> 35 x TT Electronics SFN08B4701CBQLF7, .25%, 5ppm tracking 7
>> resistors/device (Digikey, $76/25) . Stability not quoted, high temperature
>> exposure < 1000ppm
>> => 5ppm/SQRT(122) = .52ppm
>>
>> 33 x TT Electronics 668A1001DLF .5%, 5ppm tracking 8resistors/device
>> (Digikey, $82/25). Stability not quoted, load life < 1000ppm
>> => 5ppm/SQRT(33 * 4) = .45ppm
>>
>> 16 x Vishay DFN .1%, 3ppm tracking with 4 resistors/device (Digikey,
>> $5.24/1). Shelf life ratio stability is specced at 20ppm (1 year at 25C).
>> (That may be a typical rather than a maximum - your parts may all be much
>> worse than typical). The 3ppm tracking TCR may also be a typical figure as
>> its headlined in a section titled 'TYPICAL PERFORMANCE' but in the
>> specification table its not qualified with '(typical)' as they sometimes do
>> in other datasheets. Its hard to tell.
>> => 3ppm/SQRT(32) = .53ppm shelf life stability => 3.5ppm
>>
>> 5 x Vishay DSMZ metal foil dividers, .5ppm tracking max (probably
>> performs rather better than this over restricted temperature range, but
>> don't believe the Vishay typical figure of < .1ppm/C) (Digikey, $22.93/1).
>> Shelf life ratio stability not quoted but 'typical limit' for Load Life
>> ratio stability is 50ppm (2000 hours at 70C). Who knows what a typical
>> limit is? Again, probably best to treat Vishay 'typical' figures with a
>> pinch of salt given the experience of another poster on volt-nuts.
>> => .5ppm/SQRT(5) = .22ppm

Re: [volt-nuts] Matched resistors

[Randy Evans]

Tony,

Your improvement factor of SQRT(n) assumes that each resistor in the group
has random changes uncorrelated to all others in the group.  For similar
type resistors, I would think that is not likely to be true. For shelf life
stability it is likely that they all "age" in a similar way.  Unless the
resistors are in a hermetic package, humidity would impact all the
resistors in a similar manner.

Randy


On Wed, Jul 23, 2014 at 6:36 PM, Tony  wrote:

> Randy,
>
> Have you considered using multiple identical resistors to reduce the
> variance? Depending on who you believe, you can reduce the variance of the
> overall resistance by SQRT(N) where N is the number of resistors in
> series/parallel. Its not that easy to create a good search query for this
> but here is one such explanation:
>
> http://paulorenato.com/joomla/index.php?option=com_content&;
> view=article&id=109:combining-resistors-to-improve-
> tolerance&catid=4:projects&Itemid=4
>
> Ideally they should all come from the same batch - ie. manufactured by the
> same machine from the same batch of materials. Obviously there's no way to
> guarantee that without close liaison with the manufacturer (you did want 10
> million parts at $.10 each didn't you!) but hopefully a set of resistors
> which come off the same reel would come close.
>
> The absolute value isn't important however, but 'statistical gain' will
> also apply to the TCR and stability of the overall divider. The following
> assumes that both factors are similarly improved by SQRT(N), but in fact
> they may be rather better than that.
>
> That80€ or $108 for one sealed Vishay foil divider will buy a lot of lower
> spec parts:
>
> Approx 12558 x Susumu RR0510P .5%, 25ppm 0402 (Digikey, $86/10k). 6279 in
> series and parallel in each leg of the 1:1 divider com/photos/Susumu%20Photos/RR%200402%20SERIES.jpg> might reduce the
> variance to 25ppm/SQRT(6279) = .32ppm. Can't see any spec for stability,
> but it may also improve similarly. Would take a while to solder them onto
> stripboard though!
>
> Slightly more sensible might be 1078 x TE Connectivity RP73 1%, 10ppm 1206
> (Digikey, $100.18/1K).  Stability .5% (no qualifers in datasheet)
>  => 10ppm/SQRT(539) = .43ppm, stability => 215ppm
>
> Or 372 x KOA Speer RN731JTTD4021B5 .1%, 5ppm (Mouser, $29/100). Stability
> not on data sheet but typical endurance is +/- .02% for 1000 hrs @ 70C
> on/off 1.5hours/.5hours.
> => 5ppm/SQRT(138) = .37ppm, endurance => 14.7ppm (Stability should be
> rather better than that). Note that the Mouser part no. is for a 25ppm part
> but their manufacturer's part number is the 5ppm part as is the
> description. Also, the price is way too high for 25ppm parts.
>
> Or 28 x Susumu RG2012L .01%, 2ppm (Digikey, $39.6/10). Stability not
> quoted but typical Load Life is .01% (1000 x 1.5hours on/.5hours off at 85C)
> => 2ppm/SQRT(14) = .53ppm, endurance => 27ppm
>
> You could also use multiple resistor networks. Eg:
>
> 104 x Susumu RM2012B-103/103-PBVW10 .1%, 5ppm tracking, 2 resistors/device
> (Digikey $104/100). Stability not quoted, endurance 500ppm (1000 x 1.5hours
> on/.5hours off at 85C)
> => 5ppm/SQRT(104) = .49ppm, endurance => 49ppm
>
> 35 x TT Electronics SFN08B4701CBQLF7, .25%, 5ppm tracking 7
> resistors/device (Digikey, $76/25) . Stability not quoted, high temperature
> exposure < 1000ppm
> => 5ppm/SQRT(122) = .52ppm
>
> 33 x TT Electronics 668A1001DLF .5%, 5ppm tracking 8resistors/device
> (Digikey, $82/25). Stability not quoted, load life < 1000ppm
> => 5ppm/SQRT(33 * 4) = .45ppm
>
> 16 x Vishay DFN .1%, 3ppm tracking with 4 resistors/device (Digikey,
> $5.24/1). Shelf life ratio stability is specced at 20ppm (1 year at 25C).
> (That may be a typical rather than a maximum - your parts may all be much
> worse than typical). The 3ppm tracking TCR may also be a typical figure as
> its headlined in a section titled 'TYPICAL PERFORMANCE' but in the
> specification table its not qualified with '(typical)' as they sometimes do
> in other datasheets. Its hard to tell.
> => 3ppm/SQRT(32) = .53ppm shelf life stability => 3.5ppm
>
> 5 x Vishay DSMZ metal foil dividers, .5ppm tracking max (probably performs
> rather better than this over restricted temperature range, but don't
> believe the Vishay typical figure of < .1ppm/C) (Digikey, $22.93/1). Shelf
> life ratio stability not quoted but 'typical limit' for Load Life ratio
> stability is 50ppm (2000 hours at 70C). Who knows what a typical limit is?
> Again, probably best to treat Vishay 'typical' figures with a pinch of salt
> given the experience of another poster on volt-nuts.
> => .5ppm/SQRT(5) = .22ppm, load life => 22ppm
>
> Interestingly Digikey quote a price of only $5400 for 1k parts for the
> similar DSM divider (1ppm tracking), which is a huge difference from
> $22.93. Might be worth considering a bulk buy if there enough volt-nuts
> with the same problem. They aren't stocked though so that price might not
> be 'real'. However:
> 

Re: [volt-nuts] Matched resistors

[Tony]

Randy,

Have you considered using multiple identical resistors to reduce the 
variance? Depending on who you believe, you can reduce the variance of 
the overall resistance by SQRT(N) where N is the number of resistors in 
series/parallel. Its not that easy to create a good search query for 
this but here is one such explanation:


http://paulorenato.com/joomla/index.php?option=com_content&view=article&id=109:combining-resistors-to-improve-tolerance&catid=4:projects&Itemid=4

Ideally they should all come from the same batch - ie. manufactured by 
the same machine from the same batch of materials. Obviously there's no 
way to guarantee that without close liaison with the manufacturer (you 
did want 10 million parts at $.10 each didn't you!) but hopefully a set 
of resistors which come off the same reel would come close.


The absolute value isn't important however, but 'statistical gain' will 
also apply to the TCR and stability of the overall divider. The 
following assumes that both factors are similarly improved by SQRT(N), 
but in fact they may be rather better than that.


That80€ or $108 for one sealed Vishay foil divider will buy a lot of 
lower spec parts:


Approx 12558 x Susumu RR0510P .5%, 25ppm 0402 (Digikey, $86/10k). 6279 
in series and parallel in each leg of the 1:1 
divider 
might reduce the variance to 25ppm/SQRT(6279) = .32ppm. Can't see any 
spec for stability, but it may also improve similarly. Would take a 
while to solder them onto stripboard though!


Slightly more sensible might be 1078 x TE Connectivity RP73 1%, 10ppm 
1206 (Digikey, $100.18/1K).  Stability .5% (no qualifers in datasheet)

 => 10ppm/SQRT(539) = .43ppm, stability => 215ppm

Or 372 x KOA Speer RN731JTTD4021B5 .1%, 5ppm (Mouser, $29/100). 
Stability not on data sheet but typical endurance is +/- .02% for 1000 
hrs @ 70C on/off 1.5hours/.5hours.
=> 5ppm/SQRT(138) = .37ppm, endurance => 14.7ppm (Stability should be 
rather better than that). Note that the Mouser part no. is for a 25ppm 
part but their manufacturer's part number is the 5ppm part as is the 
description. Also, the price is way too high for 25ppm parts.


Or 28 x Susumu RG2012L .01%, 2ppm (Digikey, $39.6/10). Stability not 
quoted but typical Load Life is .01% (1000 x 1.5hours on/.5hours off at 85C)

=> 2ppm/SQRT(14) = .53ppm, endurance => 27ppm

You could also use multiple resistor networks. Eg:

104 x Susumu RM2012B-103/103-PBVW10 .1%, 5ppm tracking, 2 
resistors/device (Digikey $104/100). Stability not quoted, endurance 
500ppm (1000 x 1.5hours on/.5hours off at 85C)

=> 5ppm/SQRT(104) = .49ppm, endurance => 49ppm

35 x TT Electronics SFN08B4701CBQLF7, .25%, 5ppm tracking 7 
resistors/device (Digikey, $76/25) . Stability not quoted, high 
temperature exposure < 1000ppm

=> 5ppm/SQRT(122) = .52ppm

33 x TT Electronics 668A1001DLF .5%, 5ppm tracking 8resistors/device 
(Digikey, $82/25). Stability not quoted, load life < 1000ppm

=> 5ppm/SQRT(33 * 4) = .45ppm

16 x Vishay DFN .1%, 3ppm tracking with 4 resistors/device (Digikey, 
$5.24/1). Shelf life ratio stability is specced at 20ppm (1 year at 
25C). (That may be a typical rather than a maximum - your parts may all 
be much worse than typical). The 3ppm tracking TCR may also be a typical 
figure as its headlined in a section titled 'TYPICAL PERFORMANCE' but in 
the specification table its not qualified with '(typical)' as they 
sometimes do in other datasheets. Its hard to tell.

=> 3ppm/SQRT(32) = .53ppm shelf life stability => 3.5ppm

5 x Vishay DSMZ metal foil dividers, .5ppm tracking max (probably 
performs rather better than this over restricted temperature range, but 
don't believe the Vishay typical figure of < .1ppm/C) (Digikey, 
$22.93/1). Shelf life ratio stability not quoted but 'typical limit' for 
Load Life ratio stability is 50ppm (2000 hours at 70C). Who knows what a 
typical limit is? Again, probably best to treat Vishay 'typical' figures 
with a pinch of salt given the experience of another poster on volt-nuts.

=> .5ppm/SQRT(5) = .22ppm, load life => 22ppm

Interestingly Digikey quote a price of only $5400 for 1k parts for the 
similar DSM divider (1ppm tracking), which is a huge difference from 
$22.93. Might be worth considering a bulk buy if there enough volt-nuts 
with the same problem. They aren't stocked though so that price might 
not be 'real'. However:
20 x Vishay DSM dividers, 1ppm (Digikey, $5400/1000) Load life ratio 
stability 'typical limit' 50ppm

=> 1ppm/SQRT(20) = .22ppm, load life => 11ppm

Multiple LT5400 networks could also be used and may give the best 
results, but the much larger absolute tolerance, +/-15% would cause 
those with the highest value for series connected/lowest for parallel to 
dominate and reduce the statistical improvement. Do your own calculations.


Its interesting that all these different components end up providing 
pretty much the same performance for the same cost - in ot

Re: [volt-nuts] Solartron 7071 noisy

[Jean-Louis Noel]

Hi Bill,

From: "BIll Ezell" 


That's a little high, a bit worse that what I remember mine being.

So I will try to replace IC201 (ICL7650) as stated in the Service Manual.
But, if it so I fear that the calibration will be lost.


Question, what was your warmup time? These really take about 24 hours to

At least 48 hours.

But, don't try to recalibrate the actual reference voltage unless you have 
a very good standard, of which a single Weston cell is not one of.
It's a Transvolt 9154C actually (4 cells with t° stabilized at 0.01°C) but, 
I

don't wish to calibrate it because it's still under calibration.

Thanks.

Bye,
Jean-Louis 


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Re: [volt-nuts] Matched resistors

[Andreas Jahn]

Hello,

the 50uV loss is plausible to me.

But for the 100uVpp I have to ask for the measurement conditions.
Is the source (reference) connected via (long cable) and supplied with 
another mains line

 or on the same pcb with the same power supply (or battery supplied).
Was the pcb cleaned before measurement to keep leakage low?
How much noise did the reference generate? 1uV output measurement is 
quite low with
typical 0.6ppm/V of a buried zener multiplied by 2 and a amplifier with 
1.6uVpp (referred to input).


As every CMOS input is susceptible against noise (getting rectified over 
the input protection diodes)

you can easily shift the input voltage by an offset due to RF noise.
For LTC1043 inputs which are connected via external line I use a 1nF filter
capacitor against ground to keep the influence of the RF noise low.

With best regards

Andreas

Am 23.07.2014 02:40, schrieb Charles Steinmetz:

Randy wrote:

I agree that there are potentially some serious unknown issues with 
drift

due to time and temperature due to changes in leakage current, charge
injection, etc.  I would think some serious characterization would be
needed before this approach could be used.


I have used LTC1043s in the voltage-multiplier configuration, and 
based on that experience I believe you will find there are too many 
surprises hiding there to reach your error budget.  First, there are 
losses in the conversion -- IME, even when driving nothing but the 
non-inverting input of an LTC1050 chopper-stabilized opamp used as a 
follower, the output voltage of an LTC1043 doubler is quite a bit 
(50uV or more) less than [Vin * 2].  Second, the output of the 1043 + 
buffer is about 100x noisier than the output of the same reference 
followed by a non-inverting gain-of-two LTC1050 (on the order of 
100uVp-p for the 1043 + buffer, about 1uVp-p for the non-inverting 
gain-of-two amplifier in a 10Hz bandwidth, IME).  Also, the 1043 noise 
is not symmetrical, so different DC meters may give readings that 
differ by 50uV from one another.


If you try the LTC1043, I'll be interested to see what you find.

Best regards,

Charles



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Re: [volt-nuts] Solartron 7071 noisy

[BIll Ezell]

That's a little high, a bit worse that what I remember mine being.
According to the specs, you should expect about 0.1/0.6/4 uV for those 
ranges.

So, your 10V seems a bit noisy.
Question, what was your warmup time? These really take about 24 hours to 
fully stabilize.
Do you have the service guide? There are several internal adjustments 
that affect the total noise, might just need tweaking.


But, don't try to recalibrate the actual reference voltage unless you 
have a very good standard, of which a single Weston cell is not one of.


I'll give mine a check.

On 7/23/2014 12:00 PM, volt-nuts-requ...@febo.com wrote:

Hi Everyone,

I have a problem. I bought a Solartron 7071 on Ebay.
That Voltmeter seems working properly but I think it's too noisy.
It passes Self Test and Initialize and the reading is consistent against
a Weston Cell to the µV.
But, when left with a short circuit as input the noise (maximum during 5
min) is:
0.2µV for 0.1V scale
0.4µV for 1V scale
8µV for 10V scale

Is it acceptable?
Thanks for your help.

Bye,
Jean-Louis



--
Bill Ezell
--
The day Microsoft makes something that doesn't suck
will be the day they make vacuum cleaners.

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