Author Topic: Geller Labs SVR and SVR-T  (Read 35014 times)

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Offline Andreas

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Re: Geller Labs SVR and SVR-T
« Reply #75 on: December 20, 2015, 10:36:52 pm »
Hello,

The picture (of SRV) is on page 1 of this thread.
I do not see any SM-components.

R04 has to be adjusted to the T.C. of the uncompensated reference.

With best regards

Andreas


 

Online HighVoltage

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Re: Geller Labs SVR and SVR-T
« Reply #76 on: December 20, 2015, 10:40:46 pm »
Hello,

i'm just trying to build a SVR-T, using a chinese AD587LQ.
Does anybody know the dimension of the fixed resistor R04 who is in series to the 100k thermistor THR1?
Are both resistors SMD?
I tried to use a little glas-thermistor in series with a 1 meg trimmer but i got no success, the output voltage ist drifting like a rally car.
Without that "compensation" the output is rocksolid for the actual temperature...

Thanks in advance

Frank

You can find descriptions here:
http://www.gellerlabs.com/svr%20series.htm
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Offline F64098

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Re: Geller Labs SVR and SVR-T
« Reply #77 on: December 20, 2015, 11:16:26 pm »
Hello,

The picture (of SRV) is on page 1 of this thread.
I do not see any SM-components.

The description says: "After installation of the thermistor and gain resistor on the underside of the board,"
I think, they are SM-components.

Quote
R04 has to be adjusted to the T.C. of the uncompensated reference.

I know, but i'm not sure, if R04 must have 50kOhms or 200kOhms e.g.
I tried some constellations but i got heavy drifting, maybe produced by the little thermistor which i placed between the socket and the housing of the AD587 and the resulting bad thermal coupling.
A SMD-thermistor, solded near the pins of the AD587 would be the better solution.

Best regards

Frank




 

Online Gyro

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Re: Geller Labs SVR and SVR-T
« Reply #78 on: December 20, 2015, 11:18:37 pm »
The thermistor and resistor on the SVR-T are mounted on the back of the PCB, the resistor is a fixed value T/H (like the other black ones on the board) rather than a trimmer (of dubious TC). Joe selected the resistor value during cycling in his oven. Once tested, he covered both parts with blue thermally conductive resin.

The temperature trimming process is described here:

http://www.gellerlabs.com/SVR_TempcoTest.htm

EDIT: The temperature compensation was adjusted at the customer requested operating temperature - it is only good for a few degrees either side.
« Last Edit: December 20, 2015, 11:26:46 pm by Gyro »
Chris

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Offline lars

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Re: Geller Labs SVR and SVR-T
« Reply #79 on: December 21, 2015, 02:59:04 pm »
Hello Frank

As I have been through this, my recommendation is to first check what temperature coefficient you have before adding the NTC + resistor. Normally the useful range for temperature compensation is up to 3ppm/C in the SVR-T. That is also the normal TC´s for the LQ as it has the S-shaped temperature curve adapted for 0-70C, this is probably also the reason the UQ is not so well suited for the room temperature range.

Next step is to check with a 1Mohm resistor instead of the NTC + resistor. It shall move the output voltage 25+-5ppm. If so a rough estimate are to use a resistor of about 250kohm for 1ppm/C, 150kohm for 2ppm/C and 100kohm for 3ppm/C. I set up an Excel sheet for this. Joe used Labview for his automated procedure.

Using a small NTC is not recommended if no other way is used to get a long time constant. I used a through hole NTC like Digikey BC2302-ND. I think Joe also did that. I attached it close to the 587LQ and also boxed the SVR board. Joe used epoxy to get a close coupling to the board that gave more time constant.

Lars
 

Offline ltz2000

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Re: Geller Labs SVR and SVR-T
« Reply #80 on: December 21, 2015, 03:49:46 pm »

The same basic circuit, but more compact layout. The thermistor glued on the top of the reference gives very good thermal tracking.

https://www.eevblog.com/forum/projects/diy-compact-dc-voltage-standard/msg805614/#msg805614



 

Online Gyro

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Re: Geller Labs SVR and SVR-T
« Reply #81 on: December 21, 2015, 07:35:51 pm »
Hello Frank

As I have been through this, my recommendation is to first check what temperature coefficient you have before adding the NTC + resistor. Normally the useful range for temperature compensation is up to 3ppm/C in the SVR-T. That is also the normal TC´s for the LQ as it has the S-shaped temperature curve adapted for 0-70C, this is probably also the reason the UQ is not so well suited for the room temperature range.

Next step is to check with a 1Mohm resistor instead of the NTC + resistor. It shall move the output voltage 25+-5ppm. If so a rough estimate are to use a resistor of about 250kohm for 1ppm/C, 150kohm for 2ppm/C and 100kohm for 3ppm/C. I set up an Excel sheet for this. Joe used Labview for his automated procedure.

Using a small NTC is not recommended if no other way is used to get a long time constant. I used a through hole NTC like Digikey BC2302-ND. I think Joe also did that. I attached it close to the 587LQ and also boxed the SVR board. Joe used epoxy to get a close coupling to the board that gave more time constant.

Lars

Lars,

Many thanks for posting the details. I had been wondering about the compensation relationship myself and I suspect several others had too.  :-+

Chris
Chris

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Offline F64098

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Re: Geller Labs SVR and SVR-T
« Reply #82 on: December 21, 2015, 09:18:04 pm »
Hello Lars,

i say also thank you for this excellent explanation. :-+
Using a 220k resistor in series with the thermistor should perfectly work for my AD587.

I'm also working on an layout for a small PCB, fitting into a TEKO tin-box (45*48mm).
I will use a small capacitor on the output and connect the output wires directly to small solder pads,
putting some ferrite beads over them, to reduce EMI problems and avoid additional solder joints.
There are also additional pads for 3 types of precision trimmers and for paralleling the trim resistors R01 and R03.

What do you think about a complete ground plane for increasing the "heat" dissipation?
Joe's boards don't use a complete plane. Instead he uses 2 Oz. traces " to minimize errors caused by trace voltage drops".
The whole circuit runs at 2 mA, so i think doing this would be very volt-nutty?!

Best regards

Frank

 

Offline lars

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Re: Geller Labs SVR and SVR-T
« Reply #83 on: January 16, 2016, 08:18:31 am »
Hello Frank

About the ground plane I think it is mostly for bypassing not so much for heat as it is so thin compared to the glass fibre.

Be careful about DC current not going in the output wires. I think it is a good idea to take them close to pin 4 respectively pin 6 of the AD587. But as you say 2mA is not a lot and also not changing if you don´t put load on the output as I think you aren´t.

Lars
 

Offline lars

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Re: Geller Labs SVR and SVR-T
« Reply #84 on: January 16, 2016, 08:23:50 am »
I just tested three AD587JQ I ordered from Digikey and all three seems to have low temperature drift. Of course it is a risk as the spec is so bad but my three at least is useful for experiments with SVR-T like boards.

As AD not makes AD587LQ and KQ anymore some JQ probably will be as good as the LQ and KQ I guess.

Lars
 

Offline Andreas

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Re: Geller Labs SVR and SVR-T
« Reply #85 on: January 16, 2016, 11:21:49 am »
Hello Lars,

I also got recently 3 AD587JQ (from RS).
But have not done any measurements yet.
Mine are all with DateCode 1342 (Philippines)

Which datecode do you have?

With best regards

Andreas

 

Offline lars

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Re: Geller Labs SVR and SVR-T
« Reply #86 on: January 16, 2016, 01:22:30 pm »
The date codes on the AD587JQ from Digikey was 1517 and Philippines.

Lars
 

Offline F64098

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Re: Geller Labs SVR and SVR-T
« Reply #87 on: January 16, 2016, 01:32:36 pm »
About the ground plane I think it is mostly for bypassing not so much for heat as it is so thin compared to the glass fibre.
Hello Lars,

but i think it may help to egalize "hot spots" or to thermally connect grouped parts.

Quote
Be careful about DC current not going in the output wires. I think it is a good idea to take them close to pin 4 respectively pin 6 of the AD587.
When you look at my PCB in the other thread, you see a strictly star ground, centered on Pin 4 of the AD587.
Both groundplanes (pictures of the PCB not shown) are only connected to this point.
And also the trace to the output is placed on the top layer while the trace to the trim circuit is on the bottom layer.

Quote
But as you say 2mA is not a lot and also not changing if you don´t put load on the output as I think you aren´t.
All things that will be connected to the output, are only a load for my purse  :-DD

With best regards

Frank
 

Offline zlymex

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Re: Geller Labs SVR and SVR-T
« Reply #88 on: March 13, 2016, 12:54:56 pm »
Hi,
Since this is AD587 and voltage standard related topic, I'll put something here.
Look at what I got today:

More than 300 recycled AD587KR. I've tested 100 of them and they are all good with voltages between 9.996V to 10.002V. I plan to use them in a two stage parallel(of 64 to 100 units) to achieve the lowest noise of a solid state reference :)
 

Offline lars

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Re: Geller Labs SVR and SVR-T
« Reply #89 on: March 14, 2016, 08:09:57 pm »
Nice to parallel up to 100 AD587 to get low noise. I have done the same with 12 in parallell. With just 12 in parallell it is critical that all has the same low noise otherwise it is of no use. With 100 it may be less critical. As I have had several units from two different batches (via Digikey and RS) with very high noise I have tested all individuals but it takes very long time. The noise was about 4ppm pp random over seconds so even 100 in parallell may be affected. The noise was so high that I saw it with just a six-digit DMM during initial tests.

Lars
 

Offline Andreas

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Re: Geller Labs SVR and SVR-T
« Reply #90 on: March 14, 2016, 10:22:58 pm »
Hello Lars,

from theory the typical noise of a AD587 should be around 6uVpp. (0.6 ppm peak-peak).
So what happened here with 4 ppmpp = 40 uVpp?

The 3 AD586 that I have measured (similar only 5V instead of 10V) are all below 3 uVpp (0.6 ppmpp).

with best regards

Andreas
 


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