Andreas,
The current environment is an uncontrolled home lab. Great variation in
temperature and humidity, hence the primary design will use the vhd200 oil
filled hermetic package resistor arrays. I plan on evaluating for
stability and accuracy to see if I need to ovenize it to meet my voltage
s
Hello Randy,
until now you have not written about your design accuracy needs and
about your environment conditions.
(humidity + temperature controlled lab or industrial environment or
simply your uncontrolled "lab" at home).
In your measurements you should also regard humidity as a significan
I would like to thank all those you supplied ideas for matching resistors.
I have decided to test three approaches for now, the first is using Vishay
vhd200 hermetically sealed foil resistors (three each at around $26 each),
the second is using LTC5400 resistor arrays, the third is a hybrid approa
Randy,
You might want to look at:
Digikey PN 749-1052-1-ND (qty 1, $0.89)
or
Digikey PN Y4485-5K/5KBCT-ND (qty 1, $22.93)
Both parts are from Vishay.
My advice is to build something and then measure that something.
You are the best judge of your immediate design problem and measurement
capa
At risk of being flamed for suggesting scrapping an instrument, selecting
the best pair from the K-V divider of an old Null Voltmeter may be an
option. A simple bridge with the test resistors in a heated oil bath and
the other pair kept constant will give an indication of match. Take care
not to me
Tony,
Sorry for not reading further. I will give it some thought. Interesting
idea.
Randy
On Thu, Jul 24, 2014 at 5:13 AM, Tony Holt wrote:
> Randy,
>
>
> On 24/07/2014 04:22, Randy Evans wrote:
>
>> Tony,
>>
>> Your improvement factor of SQRT(n) assumes that each resistor in the group
>> ha
Randy,
On 24/07/2014 04:22, 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.
Yes/,/ I'm well aware of that w
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
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 40
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 eac
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
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
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
Charles,
For the design I am contemplating, the accuracy of the X2 in not important,
only the stability. For example, if the output of the X2 is 50uV low, I
don't care so long as its always 50 uV low +/- a few ppm over time and
temperature. The noise could be filtered but its must also be stable
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
> > Gesendet: Montag, 21. Juli 2014 um 20:28 Uhr
> > Von: "Bob Smither"
> > An: "Discussion of precise voltage measurement"
> > Betreff: Re: [volt-nuts] Matched resistors
> >
> > On 07/17/2014 10:26 AM, Randy Evans wrote:
> > >
ther"
> An: "Discussion of precise voltage measurement"
> Betreff: Re: [volt-nuts] Matched resistors
>
> On 07/17/2014 10:26 AM, Randy Evans wrote:
> > Frank,
> >
> > The high cost is my concern, although high performance demands high price
> > typicall
Bob Smither"
> An: "Discussion of precise voltage measurement"
> Betreff: Re: [volt-nuts] Matched resistors
>
> On 07/17/2014 10:26 AM, Randy Evans wrote:
> > Frank,
> >
> > The high cost is my concern, although high performance demands high price
> >
On 07/17/2014 10:26 AM, Randy Evans wrote:
> Frank,
>
> The high cost is my concern, although high performance demands high price
> typically. I am trying to double the voltage reference from either an
> LM399 or LTZ1000, hence the need for precision matched resistors for a x2
> non-inverting ampl
Andreas,
Of course, I would also expect the leakage currents to change over
time/temperature and I would expect them to be the dominant error source.
Randy
On Mon, Jul 21, 2014 at 9:38 AM, Randy Evans
wrote:
> Andreas,
>
> Since you are familiar with the LTC1043, do you know what stability ov
Hello Randy,
I have no experience with a voltage doubler.
From theory the output impedance gets halved by a 2:1 divider
and gets doubled with a X2 multiplier.
So I would expect around a factor 4 more influence of error sources.
But this is only a best guess.
The leakage current of the buffer is
Andreas,
Since you are familiar with the LTC1043, do you know what stability over
time and temperature one could expect for the X2 circuit, assuming a high
quality low leakage capacitor was used? Since the circuit does not appear
to be sensitive to the capacitor value, the primary change over ti
Hello Randy,
some information you will get on eevblog. (its much easier to post
(larger) pictures there).
Namely within the LTZ1000, LM399 and T.C. Measurements threads:
http://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/
http://www.eevblog.com/forum/projects/lm399-based-1
Andreas,
Thanks for the information. Do you have the drift chart, etc. posted
anywhere? that would be very interesting reading.
Thanks,
Randy
On Fri, Jul 18, 2014 at 10:11 PM, Andreas Jahn
wrote:
> Hello Randy,
>
> I think the only difference is in oscillator section (and thus power
> cons
http://www.vishaypg.com/foil-resistors/list/product-63036/
http://www.vishaypg.com/doc?63036
Am 19.07.2014 06:07, schrieb Randy Evans:
I figured out that VPG is Vishay Precision Group but I have not managed to
identify the vhd hermetic divider. Could you point me to the location on
the Vishay w
I figured out that VPG is Vishay Precision Group but I have not managed to
identify the vhd hermetic divider. Could you point me to the location on
the Vishay web site?
Thanks,
Randy
On Fri, Jul 18, 2014 at 9:00 PM, Randy Evans
wrote:
> I am not familiar with "vpg" or "vhd" terms. I assume
I am not familiar with "vpg" or "vhd" terms. I assume the former is a
company (European?) and the latter is a model type? Do you have a URL or
other information to get followup information. The 0.1 ppm tracking is
exactly what I am looking for and I don't need absolute accuracy.
Thanks,
Randy
Andreas,
That is good information, I appreciate it. I have contacted LT application
support but they have yet to get back to me on my questions except they did
recommend to use the LTC6943 instead of the LTC1043. Later generation I
guess.
I think i am going to try both the LTC6943 and the LT540
randy,
re. vpg: they offer an hermetic divider (vhd) with typ. 0.1ppm tracking of
tempco. if you are ok with lowest available abs. accuracy it will be well
priced, I remember having asked them for a price and it was below 50€ for
standard lead time (which can be very long). it is also fair to a
Hello Randy,
I am using the LTC1043 in 1/2 VIN or 1/3 VIN configuration.
A matching of the caps is not necessary.
In the 1/2 VIN or 1/3 VIN configuration a matching would give
the advantage that the settling time of the cirquit is reduced.
But in 2* VIN or inverting configuration a matching gives
I am not sure if Fluke had matched tempco spare parts, but you can look at
some NOS resistors from Fluke on ebay. They may be a good start and some of
the pricing isn't bad.
Todd
On Thursday, July 17, 2014, Randy Evans wrote:
> Frank,
>
> The high cost is my concern, although high performance d
Frank,
The high cost is my concern, although high performance demands high price
typically. I am trying to double the voltage reference from either an
LM399 or LTZ1000, hence the need for precision matched resistors for a x2
non-inverting amplifier (using a LT1151 precision op amp). An alternati
Hi Randy;
I would look at Visha Foil resistors
http://www.vishaypg.com/docs/63120/hzseries.pdf
Hope that helps.
Cheers;
Thomas Knox
> Date: Wed, 16 Jul 2014 17:44:10 -0700
> From: randyevans2...@gmail.com
> To: volt-nuts@febo.com
> Subject: [volt-nuts] Matched resistors
>
> I am building a 10V
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