Author Topic: Best out-of-the-box 10V reference?  (Read 65575 times)

0 Members and 1 Guest are viewing this topic.

Offline Conrad Hoffman

  • Super Contributor
  • ***
  • Posts: 1928
  • Country: us
    • The Messy Basement
Re: Best out-of-the-box 10V reference?
« Reply #75 on: April 11, 2017, 04:27:53 pm »
Don't know if it would work well with the meters, but with my bridges I make several passes through a big tape wound toroid core with the detector coax to kill common mode stuff.
 

Offline pitagorasTopic starter

  • Regular Contributor
  • *
  • Posts: 116
  • Country: fr
Re: Best out-of-the-box 10V reference?
« Reply #76 on: April 18, 2017, 04:44:53 pm »
Well, my two AD587KR finally arrived. 

Those are SOIC 8 epoxy, so not ideal... I know I'll have to live with humidity drift...

In the other aspects I think there is still something that can be done.
1) For temp drift I'll be building the thermistor compensated circuit.
2) I'd like to know if, to mitigate mechanical stress, for the mounting I should be doing something different than for any other standard SOIC 8

Before digging into the PCB design, I accept all suggestions.
Cheers
 

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 14076
  • Country: de
Re: Best out-of-the-box 10V reference?
« Reply #77 on: April 18, 2017, 06:16:01 pm »
Mechanical stress can be a problem with SO8. Stress can be from bending the board and expansion (thermal and humidity) of the board.

One way to reduce stress is to put the chip close to the corner / edge of a board or even better use cut out on 3 sides. Another more DIY like option would be to try a kind of through hole mounting of the SO8 with extra wires. So floating the chip something like 3 mm above the board. Chip on flex might be an option for a more production like solution.

 

Online David Hess

  • Super Contributor
  • ***
  • Posts: 16547
  • Country: us
  • DavidH
Re: Best out-of-the-box 10V reference?
« Reply #78 on: April 18, 2017, 07:41:40 pm »
Another important thing that is missing in the schematic is a 100nf capacitor on the output (pin 6 to 0V). Without that the SVR is very EMI sensitive as I have seen a lot of times in my lab before I understood that. I also normally use ferrite beads to the connecting pins (in and out)


This can show up when you reverse the leads at the DMM... From my discussion about it at the time: "To my surprise, I read -9.989XX (I don't recall the XX).  With the leads the normal way, I'm seeing 9.9998X with the X depending on temperature drift in the 'lab'".

After using twisted pair leads for both power and output to the DMM (an HP 3455A), I found a 4.7 nF film capacitor on the SVR output was sufficient to fix it in my case, but before the twisted pair leads, using standard mini-grabber leads, it took 0.33uF to make the 3455A read the same with the leads swapped!

I never really worked out why the AD587/HP 3455A did that - I had no problem with an HP 3456A.

I have seen the same kind of problem with high resolution DMMs when reading low impedance sources like strain gauge bridges and strain gauge amplifiers.  Besides adding LC filtering at the DMM, one solution was to use passive speed control on the fans in the temperature chamber so no EMI was generated.

Two problems I have run across include:

1. While the inputs are floating, they are not symmetrical.  The common input has a lot more common mode coupling to ground.  They make special meters with differential inputs and a separate common for shielding the test leads but they are not general purpose instruments.

2. Some "modern" DMMs and especially handheld ones suffer from excessive charge pumping at their inputs just like chopper stabilized amplifiers.  Usually I see this show up when two DMMs are connected to the same source (like each other) and intermodulation of the charge pumping causes a DC offset but some circuits can produce the same problem.  I keep a couple of old DMMs which have JFET input buffers around to make measurements when I need a sanity check.
 

Offline tszaboo

  • Super Contributor
  • ***
  • Posts: 7307
  • Country: nl
  • Current job: ATEX product design
Re: Best out-of-the-box 10V reference?
« Reply #79 on: April 18, 2017, 07:58:20 pm »
I have seen the same kind of problem with high resolution DMMs when reading low impedance sources like strain gauge bridges and strain gauge amplifiers.  Besides adding LC filtering at the DMM, one solution was to use passive speed control on the fans in the temperature chamber so no EMI was generated.

Two problems I have run across include:

1. While the inputs are floating, they are not symmetrical.  The common input has a lot more common mode coupling to ground.  They make special meters with differential inputs and a separate common for shielding the test leads but they are not general purpose instruments.

2. Some "modern" DMMs and especially handheld ones suffer from excessive charge pumping at their inputs just like chopper stabilized amplifiers.  Usually I see this show up when two DMMs are connected to the same source (like each other) and intermodulation of the charge pumping causes a DC offset but some circuits can produce the same problem.  I keep a couple of old DMMs which have JFET input buffers around to make measurements when I need a sanity check.
A fan have rotating magnets, or magnetic field, with coils in it, so so much for not generating EMI.

And yes, DMMs can be nasty loads. Just place a DMM and a scope on the same testpoint in a circuit, something with high source impedance.

Mechanical stress can be a problem with SO8. Stress can be from bending the board and expansion (thermal and humidity) of the board.

One way to reduce stress is to put the chip close to the corner / edge of a board or even better use cut out on 3 sides. Another more DIY like option would be to try a kind of through hole mounting of the SO8 with extra wires. So floating the chip something like 3 mm above the board. Chip on flex might be an option for a more production like solution.
In my experience the 3 way milling is enough. The other important thing is to get rid of ceramic capacitors near high impedance nodes, like any RC filter, and place there film capacitors. Panasonic has reasonably priced SMD film capacitors in 1210 and smaller packages.
 

Offline pitagorasTopic starter

  • Regular Contributor
  • *
  • Posts: 116
  • Country: fr
Re: Best out-of-the-box 10V reference?
« Reply #80 on: April 18, 2017, 08:04:15 pm »
In my experience the 3 way milling is enough. The other important thing is to get rid of ceramic capacitors near high impedance nodes, like any RC filter, and place there film capacitors. Panasonic has reasonably priced SMD film capacitors in 1210 and smaller packages.

What do you mean by 3-way milling?
 

Offline tszaboo

  • Super Contributor
  • ***
  • Posts: 7307
  • Country: nl
  • Current job: ATEX product design
Re: Best out-of-the-box 10V reference?
« Reply #81 on: April 18, 2017, 09:12:16 pm »
The PCB around the reference is milled on 3 sides, in a U shape, so it flexes less. "3 way" is probably not the good wording for it.
http://cds.linear.com/docs/en/application-note/an82f.pdf
Figure 11.

mod: fixed link
« Last Edit: April 19, 2017, 08:31:07 am by NANDBlog »
 
The following users thanked this post: bck

Offline Vgkid

  • Super Contributor
  • ***
  • Posts: 2710
  • Country: us
Re: Best out-of-the-box 10V reference?
« Reply #82 on: April 19, 2017, 01:33:37 am »
Heres one most have heard about.
Burr Brown Ref101. All the down to 1ppm/c and .005v accurate.
If you own any North Hills Electronics gear, message me. L&N Fan
 

Offline ocw

  • Regular Contributor
  • *
  • Posts: 248
  • Country: us
Re: Best out-of-the-box 10V reference?
« Reply #83 on: April 19, 2017, 03:08:26 am »
The REF101 has long been discontinued, is hard to find, expensive when you do find and because of that stands a good chance of being counterfeit.
A REF102CP is still made and is available from reputable stores for around $10.  Since it is +/-2.5 mV 2.5 ppm/C it will be more accurate "out-of the-box" than a REF101 at normal room temperatures.  The one that I have measured 10.00051 volts without any correction efforts being made.
 

Offline Vgkid

  • Super Contributor
  • ***
  • Posts: 2710
  • Country: us
Re: Best out-of-the-box 10V reference?
« Reply #84 on: April 19, 2017, 03:28:07 am »
I have a k-specced 101 sitting in its ovenized tomb, where it was sitting for decades.
If you own any North Hills Electronics gear, message me. L&N Fan
 

Online David Hess

  • Super Contributor
  • ***
  • Posts: 16547
  • Country: us
  • DavidH
Re: Best out-of-the-box 10V reference?
« Reply #85 on: April 19, 2017, 03:47:48 am »
In my experience the 3 way milling is enough. The other important thing is to get rid of ceramic capacitors near high impedance nodes, like any RC filter, and place there film capacitors. Panasonic has reasonably priced SMD film capacitors in 1210 and smaller packages.

What do you mean by 3-way milling?

Mill a channel around 3 sides of the part so it sits on a peninsula.  Now any strain in the printed circuit board is directed around it.
 

Offline ocw

  • Regular Contributor
  • *
  • Posts: 248
  • Country: us
Re: Best out-of-the-box 10V reference?
« Reply #86 on: April 19, 2017, 04:12:40 am »
Quote
I have a k-specced 101 sitting in its ovenized tomb, where it was sitting for decades.
While that ovenized 101K will have better frequency stability, its specification sheet shows less accuracy promised (unless it has a correction circuit which violates the "out-of-the-box" condition) than a $10 REF102CP sitting at typical room temperature.
 

Offline not1xor1

  • Frequent Contributor
  • **
  • Posts: 716
  • Country: it
Re: Best out-of-the-box 10V reference?
« Reply #87 on: April 19, 2017, 05:11:07 am »
The REF101 has long been discontinued, is hard to find, expensive when you do find and because of that stands a good chance of being counterfeit.
A REF102CP is still made and is available from reputable stores for around $10.  Since it is +/-2.5 mV 2.5 ppm/C it will be more accurate "out-of the-box" than a REF101 at normal room temperatures.  The one that I have measured 10.00051 volts without any correction efforts being made.

what about AD588BQ?
it is in ceramic case so should be insensitive to humidity variations
according to the datasheet it should produce 10V +/- 1mV, +/-1.5ppm/K (0-70°C), 15ppm long term stability (and/or other voltage values according to the connections)

I bought several of them from various ebay suppliers
so far I got only one from Germany and it looks like a real one
it has a 1325 mark... 25th week of 2013?

unfortunately my best DMM is just a fairly new Brymen 867S which measures 10.0017V (and 5.00038-5.00080 from 3 different new MAX 6250ACPA+ with 0.02% initial accuracy)

now I'm waiting for some more from China and Hong Kong, they should be second hand and so already aged (provided they are not fake)
I just hope I can average the values to have a rough idea of the real voltage
so far it looks like the Brymen is within specifics but a bit of a mV on the high side
 

Offline Vgkid

  • Super Contributor
  • ***
  • Posts: 2710
  • Country: us
Re: Best out-of-the-box 10V reference?
« Reply #88 on: April 19, 2017, 05:41:08 am »
Quote
I have a k-specced 101 sitting in its ovenized tomb, where it was sitting for decades.
While that ovenized 101K will have better frequency stability, its specification sheet shows less accuracy promised (unless it has a correction circuit which violates the "out-of-the-box" condition) than a $10 REF102CP sitting at typical room temperature.
True, those ref102's are impressive.
If you own any North Hills Electronics gear, message me. L&N Fan
 

Offline tszaboo

  • Super Contributor
  • ***
  • Posts: 7307
  • Country: nl
  • Current job: ATEX product design
Re: Best out-of-the-box 10V reference?
« Reply #89 on: April 19, 2017, 08:50:14 am »
The REF101 has long been discontinued, is hard to find, expensive when you do find and because of that stands a good chance of being counterfeit.
A REF102CP is still made and is available from reputable stores for around $10.  Since it is +/-2.5 mV 2.5 ppm/C it will be more accurate "out-of the-box" than a REF101 at normal room temperatures.  The one that I have measured 10.00051 volts without any correction efforts being made.
You know, that the REF102C does not mean ceramic package?
The picture I have in the thread is a REF102 reference, it is OK, not brilliant.

If you want a modern, hermetically sealed 10V reference, there isn't one. You need to make your own.
Its actually not that hard, just place two LTC6655BHLS8-5 on top of each other (in series... well not really). By the looks of it, it does not like load, so buffering the bottom one will be necessary. Since it has a sense pin, you can negate the output buffers offset voltage. It is somewhat analog black magic, but precision analog was always difficult, and it requires some crazy BOM cost. Starting with 28EUR just for the two reference.
 

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 14076
  • Country: de
Re: Best out-of-the-box 10V reference?
« Reply #90 on: April 19, 2017, 09:26:19 am »
If you don't need modern, there are still a few 10 V references in a metal can: LT1013, AD581.

Modern reference chips are more like 2.5 or 5 V and often not in a metal can any more. Two of the 5 V refs in series is an option.

The LTC6655 is good when it comes to noise and TC, but not that good when it comes to hysteresis and long term drift. So it depends on the requirements.
 

Offline tszaboo

  • Super Contributor
  • ***
  • Posts: 7307
  • Country: nl
  • Current job: ATEX product design
Re: Best out-of-the-box 10V reference?
« Reply #91 on: April 19, 2017, 09:33:40 am »
If you don't need modern, there are still a few 10 V references in a metal can: LT1013, AD581.

Modern reference chips are more like 2.5 or 5 V and often not in a metal can any more. Two of the 5 V refs in series is an option.

The LTC6655 is good when it comes to noise and TC, but not that good when it comes to hysteresis and long term drift. So it depends on the requirements.
Because they are made for ADCs and DACs obviously. long term drift can be solved by aging, and temperature cycling. hysteresis with keeping it indoors. I think it is a lesser issue, my home has only 5-10 degrees temperature change during a year. And I'm only saying this for others, because you will know this.
 

Offline pitagorasTopic starter

  • Regular Contributor
  • *
  • Posts: 116
  • Country: fr
Re: Best out-of-the-box 10V reference?
« Reply #92 on: April 19, 2017, 01:04:53 pm »
Ok I will be building the circuit attached, if I interpreted correctly @lars indications.
PCB will be 2 layers, one of them ground.
Will try to mill the "U" te relief stress.
The reference will be trimmed at a local EE faculty metrology lab. I'll try to perform some stress bending as suggested in the link by @NANDBlog

 

Offline tszaboo

  • Super Contributor
  • ***
  • Posts: 7307
  • Country: nl
  • Current job: ATEX product design
Re: Best out-of-the-box 10V reference?
« Reply #93 on: April 19, 2017, 01:38:00 pm »
If you want to hear my 2 cents:
Adding a 7815 on the input can reduce the line regulation issues almost entirely.
Adding a TVS diode on the input and output makes sure you dont fry the circuit. An ESD event can drift your reference, and you never notice it, until calibration.
Make sure you can place a film capacitor for C2, at least as an alternative.
Place an LED on the input
Leave space for extra input output capacitors.
RV2 should be 10 turns pot
none of these is necessary for proper operation
 

Offline pitagorasTopic starter

  • Regular Contributor
  • *
  • Posts: 116
  • Country: fr
Re: Best out-of-the-box 10V reference?
« Reply #94 on: April 19, 2017, 07:50:07 pm »
Yes I want as many cents as you have :)
I attach new version of schematic.


 

Online The Soulman

  • Frequent Contributor
  • **
  • Posts: 949
  • Country: nl
  • The sky is the limit!
Re: Best out-of-the-box 10V reference?
« Reply #95 on: April 19, 2017, 08:35:26 pm »
Do you need the adjustment options?
How and when are you going to dial it in just right?
If not set just right they're potentially a source of error.
I'm not an expert, just asking..  :popcorn:
Also might want to add a polarity reversal protection diode on the input (1n4001 or something).
 
 

Offline Andreas

  • Super Contributor
  • ***
  • Posts: 3222
  • Country: de
Re: Best out-of-the-box 10V reference?
« Reply #96 on: April 19, 2017, 09:33:49 pm »
If you don't need modern, there are still a few 10 V references in a metal can: LT1013, AD581.

Modern reference chips are more like 2.5 or 5 V and often not in a metal can any more. Two of the 5 V refs in series is an option.

The LTC6655 is good when it comes to noise and TC, but not that good when it comes to hysteresis and long term drift. So it depends on the requirements.

Hello,

the AD581 is only a bandgap reference. So it has about factor 5 more noise (with comparable current) and more ageing drift than a buried zener.
LT1031 (not 1013) and LT1021 (H-package) are metal can buried zener references.
 
When I measure a LTC6655 (5V) it usually has about the same noise than a  buried zener 5V reference. (all in hermetically LS8-packages).
But the hysteresis is really bad for the LTC6655 even near room temperature.

The AD588BQ should play in the same game as AD587xQ. But if you do not need a dual voltage output the price is too high.

Ok I will be building the circuit attached, if I interpreted correctly @lars indications.

Depending on positive/negative T.C. of the AD587 you might have to put the thermistor either to ground or the output of the reference.
The resistor/trimmer in series to the 100K thermistor needs probably more than 20K.
The output voltage trimmer is around 200R to 1K depending if you take the default values of the other 2 resistors or if you carefully adapt them to the raw output voltage.

see also parts list of standard SVR reference:
http://www.gellerlabs.com/SVR%20M.html

Adding a 7815 on the input can reduce the line regulation issues almost entirely.
I second this. I am usually using a LT1763 low noise regulator as low drop/low power pre regulator (thermally isolated from the reference). (Note: max 20V input)

Also might want to add a polarity reversal protection diode on the input (1n4001 or something).

of course yes if you do not have a voltage regulator with reverse polarity protection.

With best regards

Andreas



« Last Edit: April 19, 2017, 09:54:13 pm by Andreas »
 

Online David Hess

  • Super Contributor
  • ***
  • Posts: 16547
  • Country: us
  • DavidH
Re: Best out-of-the-box 10V reference?
« Reply #97 on: April 19, 2017, 11:56:10 pm »
Adding a 7815 on the input can reduce the line regulation issues almost entirely.

Or bootstrap the reference using an operational amplifier and single transistor if necessary.
 

Offline nuno

  • Frequent Contributor
  • **
  • Posts: 606
  • Country: pt
Re: Best out-of-the-box 10V reference?
« Reply #98 on: April 21, 2017, 05:10:08 pm »
If we buy a few chips of same output voltage and initial accuracy, can't we "average" their values and mathematically work "backwards" to get a higher accuracy for each? (assuming there is some minimum degree of variability between them)
« Last Edit: April 21, 2017, 05:12:31 pm by nuno »
 

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 14076
  • Country: de
Re: Best out-of-the-box 10V reference?
« Reply #99 on: April 21, 2017, 06:22:20 pm »
With more units one might be able to to reduce the uncertainty to a certain degree. There is no magic way to all unknown factors out (like in measuring noise levels or efficiency of reversible transducers). So with 4 units equal quality but uncorrelated error one might on average end up with half the tolerance  - however the worst case error is not getting better, only less likely.

With 4 equal units from the same type and series, chances are the error is in the same direction - thus averaging will be less effective. The can be (and will be to some extend) systematic errors in a hole series.

Before getting something like 4 refs at $10 each, it might be easier to find someone to do a more or less unofficial calibration.
 
The following users thanked this post: nuno


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf