Author Topic: Best out-of-the-box 10V reference?  (Read 65577 times)

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Offline The Soulman

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Re: Best out-of-the-box 10V reference?
« Reply #25 on: January 06, 2017, 09:47:29 pm »
A non-volt-nut here with a question.

 Why must there be a 10vdc output standard with all the added complexity and variation of the opamp stage. Why not just output the zener's natural reference voltage? Just measure and record it's voltage upon manufacture of the standard for future tracking with proper calibration standards.

One just ends up with a voltage number either way suitable for measurement, trending with time, etc, and should be usable via mapping calculations for any user's need? Is there not value in eliminating sources of variation altogether. OK maybe a buffer X1 opamp might still be desirable?

I'm having the same idea, long term stability is a must, and it appears a part based on a zener and in
a hermetically sealed case are best.
Maybe LM399? https://www.conrad.at/de/pmic-spannungsreferenz-linear-technology-lm399hpbf-shunt-fest-to-46-4-1256340.html

Or actually in my case I would only like to know if my 30.000 count bench meter is still accurate (on 3 volt dc range) I know it's close
and it is stable when compared to my 20.000 count meter, they only differ 0,01% at most (no I'm not a voltnut and not planning on to becoming one..).
So for me I'd rather build a small simple and stable 2,5 volt (With 2,5 volt I use most of the meters resolution)  reference and have it measured by someone who is a voltnut, or maybe someone that is still in denial and "only" has a 7,5 digit meter. :)
Are LM136AH-2,5 any good?

For 6000 or 60.000 count meters a 5 volt reference would be better suited.

 

Offline guenthert

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Re: Best out-of-the-box 10V reference?
« Reply #26 on: January 06, 2017, 10:05:11 pm »
A non-volt-nut here with a question.

 Why must there be a 10vdc output standard with all the added complexity and variation of the opamp stage. Why not just output the zener's natural reference voltage? Just measure and record it's voltage upon manufacture of the standard for future tracking with proper calibration standards.

One just ends up with a voltage number either way suitable for measurement, trending with time, etc, and should be usable via mapping calculations for any user's need? Is there not value in eliminating sources of variation altogether. OK maybe a buffer X1 opamp might still be desirable?
Generally speaking 10V is just a convention (in the age of Weston cells it used to be 1.018V).  Important is only that you have multiple references with the same nominal voltage so that you can compare them using a Null voltmeter.  A null meter is much simpler in construction and (hence) much cheaper than a long scale DMM for the same sensitivity.  It also doesn't need to be accurate other than at 0V (and you can easily calibrate that yourself, which reduces maintenance costs).

If all you want to do is to verify that a given DMM operates still within specification (of a given DC voltage range), then you need only a voltage reference calibrated to a remaining uncertainty (some argue four times, some argue 10 times) smaller than the DMM.  For a 4.5 digits DMM that can be a cheap AD584 which offers multiple voltages ...
 

Offline The Soulman

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Re: Best out-of-the-box 10V reference?
« Reply #27 on: January 06, 2017, 10:52:42 pm »
For a 4.5 digits DMM that can be a cheap AD584 which offers multiple voltages ...

A AD584KH "out of the box" has maximum deviation of 0,16% on 2,5 volt range, my meter is specced at 0,05%.
Yes a AD584 can be used to verify there isn't something majorly wrong with the meters accuracy, but adjusting
a meter like this would require something much more accurate, max 0,01% or so.
 

Offline David Hess

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Re: Best out-of-the-box 10V reference?
« Reply #28 on: January 06, 2017, 11:06:11 pm »
Are LM136AH-2,5 any good?

For less cost there are references with initial accuracy much better than the LM136's 1%.  At 1/10th the price, an 2.5 volt LM4040A would have 10 times better initial accuracy.

An expensive hermetic through hole package would make more sense for a more precise reference like an LM339 or LTZ1000 where physical strain would be more apparent.

For "out of the box" reference accuracy, the accuracy and temperature coefficient of the internal voltage divider is already taken into account in the specifications.  So it may pay to use a higher voltage reference if it results in a better initial accuracy expressed in parts per million.

I would look for something like a 5.000 volt MAX6250A in an 8 pin plastic DIP package which is 0.02% and 1ppm/C at 5 volts for about $10, and then put it into a circuit which operates it under the nominal conditions specified in the datasheet.

My actual search for a part would involve a spreadsheet with price, tolerance errors from various sources, temperature coefficient from various sources, and then maximum total unadjusted error over some nominal temperature range.
 
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Offline The Soulman

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Re: Best out-of-the-box 10V reference?
« Reply #29 on: January 06, 2017, 11:08:54 pm »
To the OP, the AD584 has the capability to output four different voltage's, 2,5, 5, 7,5 and 10Volt
and are available in different accuracy grades (like most voltage reference ic's).
The AD584TH and AD584KH are the most accurate versions and have maximum 0,1% deviation on the 10 Volt range.

http://www.analog.com/media/en/technical-documentation/data-sheets/AD584.pdf
 

Offline The Soulman

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Re: Best out-of-the-box 10V reference?
« Reply #30 on: January 06, 2017, 11:23:34 pm »
Are LM136AH-2,5 any good?

For less cost there are references with initial accuracy much better than the LM136's 1%.  At 1/10th the price, an 2.5 volt LM4040A would have 10 times better initial accuracy.


I'm not the OP and come to think of it maybe I'm kinda hijacking this thread  :-[
For me initial accuracy of even 0,02 is not good enough and would like to get below 0,01%.
My plan is to build something around a stable 2,5 Volt zener reference and ship it to someone who is
able to measure it within that 0,01% uncertainty and then have it shipped back and compare it to my 4,5 digit meter.

Maybe something like this would also work for the OP.
 

Offline pitagorasTopic starter

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Re: Best out-of-the-box 10V reference?
« Reply #31 on: January 06, 2017, 11:39:08 pm »
The original post is about accuracy: "out of the box" without calibration known voltage.
Then there is the second important aspect that is precision, which is related to drift, short term and long term.
I think in this last aspect it is somewhat well stablished that LTZ1000 is king and LM399 is the prince. However you need some mean for calibrate them (which I don't have).
On the other hand, the zener discussion is also very interesting and might well continue here, but if you decide to open a thread, let us know :)
So zener is better than the king?
 

Offline Conrad Hoffman

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Re: Best out-of-the-box 10V reference?
« Reply #32 on: January 07, 2017, 12:18:47 am »
FWIW, my Data Precision / Analogic 6.5 digit voltage standard is quite good, drifting a couple ppm per year at most. What does it use for a reference? LM399!
 

Offline The Soulman

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Re: Best out-of-the-box 10V reference?
« Reply #33 on: January 07, 2017, 12:21:26 am »
The original post is about accuracy: "out of the box" without calibration known voltage.
Then there is the second important aspect that is precision, which is related to drift, short term and long term.
I think in this last aspect it is somewhat well stablished that LTZ1000 is king and LM399 is the prince.

It indeed appears to be so.

Quote
However you need some mean for calibrate them (which I don't have).

I've been searching online and looking at many different datasheets and it appears 0,02% is the best you can get "out of the box" (the 5 Volt MAX6250A as suggested by David Hess).
Other option might be a build up module and measured by voltagestandard.com, or one of the onehunglow equivalants.

Quote
On the other hand, the zener discussion is also very interesting and might well continue here, but if you decide to open a thread, let us know :)
So zener is better than the king?

No, there are two different types of voltage reference IC's (that I know of, I'm not an expert) one that uses a bandgap (common in almost everything that needs a low power and ok voltage reference) and the other (including LTZ1000 and LM399) use a topology around a zener diode (inside the IC) and the rest of the IC circuitry is there to pamper that diode to the max.
There are also actual plane bare zener diodes designed specifically to be used as voltage reference but must be driven
by a stable constant current and kept at a (fairly) constant temperature to perform well, couldn't
find those at all in online stores :-//

What type of volt meters do you have and what accuracy do you want?
 
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Offline guenthert

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Re: Best out-of-the-box 10V reference?
« Reply #34 on: January 07, 2017, 01:05:00 am »
For a 4.5 digits DMM that can be a cheap AD584 which offers multiple voltages ...

A AD584KH "out of the box" has maximum deviation of 0,16% on 2,5 volt range, my meter is specced at 0,05%.
Yes a AD584 can be used to verify there isn't something majorly wrong with the meters accuracy, but adjusting
a meter like this would require something much more accurate, max 0,01% or so.
Ah, I guess I missed the "out of box" qualifier.  I don't know of any voltage references which have initial accuracy anywhere close to their long term stability.  You'll find voltage references for less than $50 which are claimed to have been calibrated (their actual value measured and noted) using a sufficiently precise (and hopefully calibrated) DMM.  It's a bit of a trust issue though.  Best to bring that module to a friend with a calibrated DMM ...
 

Offline bingo600

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Re: Best out-of-the-box 10V reference?
« Reply #35 on: January 07, 2017, 01:06:36 am »

I would take a AD587UQ

with best regards
Andreas

I'd go with Andreas suggestion , Joe Geller used it.

Or if on a tight budget , maybe try the - AD587KNZ DIP-8
http://www.ebay.com/itm/AD587KN-AD587KNZ-DIP-8-/270986206419

Get an AD587 that's "Old Stock" , rumours are that the newer ones are not as stable


http://pdf1.alldatasheet.com/datasheet-pdf/view/48072/AD/AD587JQ.html


/Bingo
« Last Edit: January 07, 2017, 01:27:44 am by bingo600 »
 

Offline SvanGool

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Re: Best out-of-the-box 10V reference?
« Reply #36 on: January 07, 2017, 01:12:33 am »
@guenthert

Quote
Quote
I like the idea of buying a bunch of references and building something but you can get an already calibrated 0.01% voltage reference for $30 from VoltageStandard.com.
Well, you might want to read  https://www.eevblog.com/forum/metrology/calibratory-d-105-dc-precision-voltage-reference-standard/ first.

The VoltageStandard.com have, in general, good feedback. I think you are mixing up with http://www.ebay.com/itm/10-Volt-10-V-DC-Prec-Voltage-Reference-Standard-Nulled-to-Fluke-732A-or-732B-/251756273626 which is indeed in detail discussed in the thread you mentioned.

If not, can you elaborate a bit?
# Don't hurry, the past will wait. #
 

Offline pelule

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Re: Best out-of-the-box 10V reference?
« Reply #37 on: January 07, 2017, 01:18:53 am »
You will learn something new every single day
 

Offline guenthert

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Re: Best out-of-the-box 10V reference?
« Reply #38 on: January 07, 2017, 01:43:05 am »
@guenthert

Quote
Quote
I like the idea of buying a bunch of references and building something but you can get an already calibrated 0.01% voltage reference for $30 from VoltageStandard.com.
Well, you might want to read  https://www.eevblog.com/forum/metrology/calibratory-d-105-dc-precision-voltage-reference-standard/ first.

The VoltageStandard.com have, in general, good feedback. I think you are mixing up with http://www.ebay.com/itm/10-Volt-10-V-DC-Prec-Voltage-Reference-Standard-Nulled-to-Fluke-732A-or-732B-/251756273626 which is indeed in detail discussed in the thread you mentioned.

If not, can you elaborate a bit?
Yes indeed I have and I'm terribly sorry about that. :-//
Really odd blunder, as I do actually have his "DMM check" product, which includes a 5V reference, which is well constructed and for all I know works as advertised.
« Last Edit: January 07, 2017, 01:48:27 am by guenthert »
 

Offline IconicPCB

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Re: Best out-of-the-box 10V reference?
« Reply #39 on: January 07, 2017, 01:45:28 am »
@ Conrad Hoffman

First of all Thank You for a very common sense approach to the metrology lab project.

I was wondering if You had any words on  aging the resistors and components prior to selection in order to ensure a more predictable outcome at the end of assembly?

And now for another three letter acronym... TIA
« Last Edit: January 07, 2017, 01:49:31 am by IconicPCB »
 

Offline David Hess

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Re: Best out-of-the-box 10V reference?
« Reply #40 on: January 07, 2017, 05:53:08 am »
I'm not the OP and come to think of it maybe I'm kinda hijacking this thread  :-[
For me initial accuracy of even 0,02 is not good enough and would like to get below 0,01%.
My plan is to build something around a stable 2,5 Volt zener reference and ship it to someone who is
able to measure it within that 0,01% uncertainty and then have it shipped back and compare it to my 4,5 digit meter.

The selection process for the reference would be different in the case where you are going to trim and/or measure it against a standard.  Drift and various other errors become more important than absolute tolerance from the manufacturer.
 

Online Andreas

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Re: Best out-of-the-box 10V reference?
« Reply #41 on: January 07, 2017, 08:23:19 am »

I'd go with Andreas suggestion , Joe Geller used it.

Get an AD587 that's "Old Stock" , rumours are that the newer ones are not as stable


Hello,

Joe Geller used the AD587LQ (0..70 deg C). But this grade is now obsolete (no longer produced).
The AD587UQ is specified from -55 to 125 deg C.
And it is clear that when you trim the overall (average) T.C. at the temperature extremes
a device with a larger temperature range is likely to have a larger gradient (slope) near room temperature.

I think the rumours result from the different behaviour of the LQ and UQ type at room temperature.
But this is only relevant if you are looking into ppm stabilities.

The selection process for the reference would be different in the case where you are going to trim and/or measure it against a standard.  Drift and various other errors become more important than absolute tolerance from the manufacturer.

Thats true. In this case I would select for zero T.C. / hysteresis / ageing drift and low noise.


With best regards

Andreas
 

Offline Conrad Hoffman

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Re: Best out-of-the-box 10V reference?
« Reply #42 on: January 07, 2017, 04:44:50 pm »
...words on  aging the resistors and components prior to selection

One can get really crazy with this stuff, as evidenced by the LTZ1000 threads. I don't have the equipment to do much beyond about 1-2 ppm. Even when I had ovenized standard cells, I'm not sure I could have done much better. I heat with wood, so my lab temperature tends to vary by 5-10 degrees. All I can say is the original MML voltage references remained very stable over time, 1-2 ppm/year, using common 1% metal film resistors selected for matched tempco. One has to be careful soldering, as it often causes a permanent value change. I would typically power the units and age them for a couple weeks before final calibration. Even if you aged the individual parts, you'd still have to age the assembled unit, so it wouldn't gain you much.

It's too bad the metal can references are getting scarce. They have the thermal emf problems of Kovar leads, but are mechanically pretty good. The plastic versions are mechanically terrible, changing voltage with any flexing or stress on the pc board. What you have to do is float them above the board on three (or whatever the minimum needed is) wires, each with a small stress relieving "s" bend. Then, mount the pcb with three wires and no other supports. It's all about kinematics and avoiding bimetal bending effects as the temperature changes.

Don't underestimate individual temperature compensated zeners if you can find them. The original common one was 1N821, but there are many other similar ones. If you do the classic opamp circuit with an op-07 or similar, that supplies the zener current from the regulated output, and ovenize it, you can compete with some of the best ICs. Stay with the optimum zener voltage of something like 6.8 V and experiment with current to find the zero TC point.
 
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Offline pitagorasTopic starter

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Re: Best out-of-the-box 10V reference?
« Reply #43 on: January 07, 2017, 07:06:22 pm »

Don't underestimate individual temperature compensated zeners if you can find them. The original common one was 1N821, but there are many other similar ones. If you do the classic opamp circuit with an op-07 or similar, that supplies the zener current from the regulated output, and ovenize it, you can compete with some of the best ICs. Stay with the optimum zener voltage of something like 6.8 V and experiment with current to find the zero TC point.

Do you have some information on this? Specially in building the "oven".
 

Offline Conrad Hoffman

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Re: Best out-of-the-box 10V reference?
« Reply #44 on: January 07, 2017, 09:56:42 pm »
There should be info on ovens on-line somewhere, and again the level of crazy is up to you. My old JRL standard cell oven consisted of an inner box, aluminum, with some resistance wire wrapped around it, or maybe flat heater pads. Control was with a mercury thermoregulator, but today you'd use a thermistor or other sensor of your choice, and a control circuit. They then put that inside another aluminum box, wrapped with resistance wire and controlled the same way. The inner oven ran a bit hot, 37C I think, and the outer oven a few degrees less. It's like using double voltage regulators- no ambient is going to affect that inner box. I've built simple single ovens that held a few millidegrees, and I don't think that's needed here. Look for a Jim Williams Linear Technology app note with a temp control circuit. Hewlett Packard made a 1N821 based voltage standard years ago, visually similar to the Fluke 731- so old I can't find a picture of one. The diode circuit was on a small and not-too-special pcb that lived inside a small drawn aluminum can- wrapped with resistance wire and stuffed in a block of foam for insulation. You just need to get a few degrees higher than the highest ambient you ever expect, and hold it within a tenth degree or so. If I were doing one today I'd probably get some 1" copper pipe and copper end caps. Wrap it with insulated resistance wire (or use a Kapton heater pad- eBay is loaded with them), glue a sensor to it, and make a simple proportion control. I wouldn't use a nice PWM control because of the noise. Install some feedthrus for wire and stick it a block of Styrofoam for insulation.
 
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Offline pitagorasTopic starter

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Re: Best out-of-the-box 10V reference?
« Reply #45 on: January 08, 2017, 02:38:34 am »
Look for a Jim Williams Linear Technology app note with a temp control circuit.
This one?
http://cds.linear.com/docs/en/application-note/an89.pdf
 

Offline David Hess

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Re: Best out-of-the-box 10V reference?
« Reply #46 on: January 08, 2017, 04:33:11 am »
Look for a Jim Williams Linear Technology app note with a temp control circuit.
This one?

http://cds.linear.com/docs/en/application-note/an89.pdf

That would work but he was thinking of something a little simpler.  Check figure 5 on page 3 of Linear Technology application note 12.
 
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Online Andreas

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Re: Best out-of-the-box 10V reference?
« Reply #47 on: January 08, 2017, 05:38:45 am »
Hello,

although I think that for your needs a oven is overkill ...

the simplest cirquit for a small oven I have found is at the bottom of this page:
http://www.techlib.com/electronics/ovenckts.htm

with best regards

Andreas
 
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Offline pitagorasTopic starter

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Re: Best out-of-the-box 10V reference?
« Reply #48 on: March 09, 2017, 04:18:41 am »
Ok... 2 pieces AD587KR are on the way...
Having 2 pieces can be used to improve noise figures? Where can I read about that?
Thanks
 

Online Andreas

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Re: Best out-of-the-box 10V reference?
« Reply #49 on: March 09, 2017, 07:30:42 am »
Hello,

what application do you have that noise plays a role?
What stability do you want to reach?

Individual references may have up to factor 10 difference in noise.
(see the LT1027DCLS8-5 thread with popcorn-noise).

https://www.eevblog.com/forum/metrology/t-c-hysteresis-measurements-on-brand-new-lt1027dcls8-5-voltage-reference/msg970876/#msg970876
against
https://www.eevblog.com/forum/metrology/t-c-hysteresis-measurements-on-brand-new-lt1027dcls8-5-voltage-reference/msg972153/#msg972153

So buying 2 references and hope that the averaging will reduce noise by a factor 1.4 makes no sense for me.
I would at least buy 10 references and select the 2 with the lowest noise for averaging.

with best regards

Andreas


 


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