Author Topic: Ultra Precision Reference LTZ1000  (Read 882244 times)

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Offline alex-sh

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Re: Ultra Precision Reference LTZ1000
« Reply #2775 on: October 01, 2019, 01:17:33 am »
Would you mind telling or showing more details, like PCB,mechanical and thermal design, choice of resistors?
If prerequisites are ok, I offer to do the T.C. trimming, and determination of output voltage(s)

Frank

This is the board I have - your design :)  The resistors are Vishay. The two critical resistors are hermetically sealed.
Here is another link - https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg2514555/#msg2514555
Very much appreciate your assistance.

 

Online Dr. Frank

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Re: Ultra Precision Reference LTZ1000
« Reply #2776 on: October 01, 2019, 08:15:09 am »
Would you mind telling or showing more details, like PCB,mechanical and thermal design, choice of resistors?
If prerequisites are ok, I offer to do the T.C. trimming, and determination of output voltage(s)

Frank

This is the board I have - your design :)  The resistors are Vishay. The two critical resistors are hermetically sealed.

Very much appreciate your assistance.


Well, fine,  :-+, so I'm familiar with that board, at least.
So what is the T.C. of these resistors, the Vishay and the other ones?
Did you determine these T.C.s?

How is the PCB assembled, or is this the current state?

It's not feasible to trim this naked PCB, as the mechanical/thermal assembly also influences the T.C.
Also be aware, that the trimmed 10V output has to be re-trimmed, because T.C. trimming by this nominal 200k resistor changes the LTZ1000 output voltage.

My offer persists, if you would have made a proper assembly.
Frank
 
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Offline alex-sh

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Re: Ultra Precision Reference LTZ1000
« Reply #2777 on: October 01, 2019, 09:05:18 am »
Would you mind telling or showing more details, like PCB,mechanical and thermal design, choice of resistors?
If prerequisites are ok, I offer to do the T.C. trimming, and determination of output voltage(s)

Frank

This is the board I have - your design :)  The resistors are Vishay. The two critical resistors are hermetically sealed.

Very much appreciate your assistance.


Well, fine,  :-+, so I'm familiar with that board, at least.
So what is the T.C. of these resistors, the Vishay and the other ones?
Did you determine these T.C.s?

How is the PCB assembled, or is this the current state?

It's not feasible to trim this naked PCB, as the mechanical/thermal assembly also influences the T.C.
Also be aware, that the trimmed 10V output has to be re-trimmed, because T.C. trimming by this nominal 200k resistor changes the LTZ1000 output voltage.

My offer persists, if you would have made a proper assembly.
Frank

Non-critical resistors are 0.01% 5ppm 0.5W Vishay SFERNICE Foil resistors T.C +/-5ppm/C
Critical resistors are 0.01% 0.3W RADIAL Vishay Metal Foil seal resistors (VH102K and VHD200 used as a single resistor) - I think these have T.C. +/- 1ppm/C and 2ppm/C respectively.

The board was assembled by hand. Resistors and LTZ1000 was soldered with an extra care trying not to overheat these components.
I left long legs for LTZ1000 - not sure if it was the right decision. It's been a long debate here about the legs length and TCR.
 
Currently, the board is in the Hammond enclosure (LTZ1000 has been isolated for air drafts) running 1500h+
No, I did not determined the T.C.

Thank you once again.
« Last Edit: October 01, 2019, 09:07:01 am by alex-sh »
 
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Online Dr. Frank

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Re: Ultra Precision Reference LTZ1000
« Reply #2778 on: October 01, 2019, 11:01:55 am »


Non-critical resistors are 0.01% 5ppm 0.5W Vishay SFERNICE Foil resistors T.C +/-5ppm/C
Critical resistors are 0.01% 0.3W RADIAL Vishay Metal Foil seal resistors (VH102K and VHD200 used as a single resistor) - I think these have T.C. +/- 1ppm/C and 2ppm/C respectively.

The board was assembled by hand. Resistors and LTZ1000 was soldered with an extra care trying not to overheat these components.
I left long legs for LTZ1000 - not sure if it was the right decision. It's been a long debate here about the legs length and TCR.
 
Currently, the board is in the Hammond enclosure (LTZ1000 has been isolated for air drafts) running 1500h+
No, I did not determined the T.C.

Thank you once again.

Well,  I also left the legs long... successful.

Everything sounds good, maybe you have a picture of the completed device, including power supply.

Anyhow, if nobody else in your country (UK?) gives an offer, you may send it to me.. just send me a PM to clarify details.

Frank
 
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Offline MiDi

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Re: Ultra Precision Reference LTZ1000
« Reply #2779 on: October 01, 2019, 12:33:11 pm »
Non-critical resistors are 0.01% 5ppm 0.5W Vishay SFERNICE Foil resistors T.C +/-5ppm/C
Critical resistors are 0.01% 0.3W RADIAL Vishay Metal Foil seal resistors (VH102K and VHD200 used as a single resistor) - I think these have T.C. +/- 1ppm/C and 2ppm/C respectively.

The most critical resistors are the boost resistors for 7->10V.
Their tracking TCR and drift are only attenuated ~3x, whereas all other are >=100x.
The Datasheet seems to be wrong for the relevance of the impact of resistor changes.

Put your money wisely  ;)
 
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Offline alex-sh

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Re: Ultra Precision Reference LTZ1000
« Reply #2780 on: October 01, 2019, 04:00:23 pm »


Non-critical resistors are 0.01% 5ppm 0.5W Vishay SFERNICE Foil resistors T.C +/-5ppm/C
Critical resistors are 0.01% 0.3W RADIAL Vishay Metal Foil seal resistors (VH102K and VHD200 used as a single resistor) - I think these have T.C. +/- 1ppm/C and 2ppm/C respectively.

The board was assembled by hand. Resistors and LTZ1000 was soldered with an extra care trying not to overheat these components.
I left long legs for LTZ1000 - not sure if it was the right decision. It's been a long debate here about the legs length and TCR.
 
Currently, the board is in the Hammond enclosure (LTZ1000 has been isolated for air drafts) running 1500h+
No, I did not determined the T.C.

Thank you once again.

Well,  I also left the legs long... successful.

Everything sounds good, maybe you have a picture of the completed device, including power supply.

Anyhow, if nobody else in your country (UK?) gives an offer, you may send it to me.. just send me a PM to clarify details.

Frank

Thank you
PM sent
 

Offline alex-sh

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Re: Ultra Precision Reference LTZ1000
« Reply #2781 on: October 03, 2019, 03:12:46 am »
Does anyone have a spare LTZ1000 PCB? I would favour a board based on a design by Dr Frank and branadic?
Please send me a PM
 

Offline notfaded1

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Re: Ultra Precision Reference LTZ1000
« Reply #2782 on: October 04, 2019, 03:01:55 pm »
I'd also like advice on source for a PCB either from member here or from online board house that has a design.  I, sadly don't have 4 LTZ1000 but only two older 2001 and 2004 LTZ1000ACH.  Is there anyone that has some PCB's ready that I could purchase?  This seems to be the best route to a nice precision reference vs just buying one (and it's good learning experience for this computer scientist).  You guys have put so much effort into this and hats off  :clap: I want in please?  Wow TIN that PCB looks sweet!  I hope you'll post some stats and graphs from it.  After going through hand selecting that many resistors to make your quad... perhaps you've got enough decent resistors left over for a single board set you could part with?

Best Regards,

Bill
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Offline RandallMcRee

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Re: Ultra Precision Reference LTZ1000
« Reply #2783 on: October 04, 2019, 03:35:43 pm »
Your wish is our command:
https://github.com/pepaslabs/px-ref

Notice that there is a link in the readme to OSH boards, under Purchase. I have built six and they work well.

BTW your older LTZ1000A are fine, like fine wine, it seems.

addendum: The PX board is the work of Mr. Pepas; as you can see from the github url and the readme therein. I just thought I should publicly acknowledge that this is all his (and others!) great work and we are grateful for it!
« Last Edit: October 04, 2019, 03:44:37 pm by RandallMcRee »
 
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Offline imo

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Re: Ultra Precision Reference LTZ1000
« Reply #2784 on: October 04, 2019, 06:23:15 pm »
There is Dr. Frank's recreation as well
https://github.com/pepaslabs/dr-frank-ltz1000
 
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Offline 3roomlab

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Re: Ultra Precision Reference LTZ1000
« Reply #2785 on: October 06, 2019, 04:58:51 am »
theoretical mitigation of 1/f noise by guarded capacitors simulation
using the LTspice (white) function to create flicker noise, i spew 10uV pp noise from a 7v supply.

the first 2 are test simulations of 1RC filter and 2RC filters, reduce 10uV to 1uV pp. this is assuming guard drive is noiseless, which is impossible. this 2 stage RC helps me to understand that the size of the the cap needs to be large enough in one single stage to capture the very very low Hz flicker.

the 3rd, accounting for a 2 sources of noisy guard, +noisy vref (all @ 10uV p-p).
the size of the capacitor need to be around 2F each and require about 8-10 days to settle, and the guard drive will need to be way way higher than the vref output by nearly 2mV. so it in theory mitigate 1/f by 10x.

it looks ... plausible ? 2F ? huge and leaky ... and the magnitude of madness of the idea (derived from blackdog's LT1021 vref) ...

edit
looking at digikey crazy stock list of supercap, if we go for highest 2k hrs 85C lifespan and grab a vishay 25F series it to get 8.1v WV, the simulation shows the stack will take about 37 days to settle off, but the 1/f noise gets attenuated down to somewhere @ 0.4uV. a 1:25 reduction from 10uV pp
come to think of it, this might be worth a shot for a LT1021 unit which is already very stable, and added as an addon
no of course this is not feasible ... but the noise reduction needs another angle of approach

edit
like andreas said below, SC are terrible. the TC is over 1% per C
« Last Edit: October 07, 2019, 10:46:27 am by 3roomlab »
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Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #2786 on: October 06, 2019, 06:30:34 am »
Mhm,

do you think that the capacity does not change within 37 days with room temperature?
If you pull the plates of a capacitor apart (e.g. rising temperature) the voltage will increase.

with best regards

Andreas
 
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Offline 3roomlab

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Re: Ultra Precision Reference LTZ1000
« Reply #2787 on: October 07, 2019, 08:43:43 am »
being distracted by the thread https://www.eevblog.com/forum/metrology/forum-crowd-project-simple-10v-ltz1000-plugnplay-box-(with-1k10k-hermetic)/
i took a peek at the ordering site, and noticed the ROHS and temp range confusion

digikey/mouser list theirs as -55~+125C and it is ROHS complaint. there is apparently no such unit on ADI website. (at the time of this writing, see pic)

edit
as an extension to my "curiosity on the temperature range
i had a look at the LT1021 as well, the LM399 and LT1021 in TO5 have leaded parts that are specified down to -55C and are NOT ROHS complaint.

update
some ADI bloke replied in their forum says the ADI website is in error (oct 2019).
as a "reply" to the below post by  "Magnificent Bastard". the question was not about the heater. LT1021 have no heater, and yet it has ROHS and non ROHS parts of which the best part is the TO5 which is non ROHS. i am very sure you will not call it moot if you were to choose 1 yourself.
« Last Edit: October 26, 2019, 11:32:52 am by 3roomlab »
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Offline Magnificent Bastard

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Re: Ultra Precision Reference LTZ1000
« Reply #2788 on: October 07, 2019, 04:41:05 pm »
being distracted by the thread https://www.eevblog.com/forum/metrology/forum-crowd-project-simple-10v-ltz1000-plugnplay-box-(with-1k10k-hermetic)/
i took a peek at the ordering site, and noticed the ROHS and temp range confusion

i just have to ask everyone here

when you bought your LTZ1000 CH/ACH
did you know it was a
1) 0~70C unit? (ROHS complaint)
2) or a -55~+125C unit ? (non ROHS complaint)

digikey/mouser list their as -55~+125C and it is ROHS complaint. there is apparently no such unit on ADI website.

This is a "moot" point.  Since this is an internally heated device, there is an upper and lower bound on the ambient temperature anyway for proper operation.
 

Offline essele

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Re: Ultra Precision Reference LTZ1000
« Reply #2789 on: November 15, 2019, 04:55:54 pm »
I thought I'd post my exploits with building a battery-backed LTZ1000 reference unit ... this has been done with a huge amount of input from this forum -- so a massive thanks to just about everyone! I'm sure there are a long list of things I've done wrong, a few I've worked out myself, and probably hundreds I'm not aware of ... any improvements would really be welcome.

This is a board based on the 10V one from Dr Frank, and using a (very slightly) modified version from the one that Cellularmitosis posted (and hosts on GitHub.)

The reference board is contained in the Teko 393 tuner enclosure which you can see in the middle of the outer enclosure. I used modelling foam which should be a good insulator to build the internal compartments.

The power supply board, which is really meant to keep the batteries charged, is based on a tps7a4901 along with another LDO 3.3v regulator to supply the front panel. The batteries are charged in parallel pairs using MCP73831's powered from isolated DC/DC converters, all powered from a mains AC/DC converter.

The batteries should last three or four days for the reference, and the AVR uses an average of 0.5mA in non-alarm mode, and 1.5mA in alarm mode, so that will last for weeks (it has a separate battery.)



The rear panel is a PCB which I only used since it's easier than trying to cut holes in anything else.



The front panel is also a PCB, but has an atmega328p on the back along with a couple of resistor dividers for the analog inputs, two rear-mount LED's, and a small SMD piezo sounder. This keeps an eye on whether external power is connected or not, flashes the LED's to show battery levels when charging, and then alarms if the battery level starts to get low ... it also gives you a helpful set of tones when mains is applied or removed (yes, I had fun with that!)



I've made up a few reference boards with different resistor sets on (this one is Sfernice 2ppm ones from eBay, but I also have a 5ppm version, and one with Edwins PWW's), so my intent is to build out a few more enclosures ... but I've got a few lessons learned from this one to include...

- The LiPo chargers get a bit warm, so I will see if I can move them to the other side of the board so they are closer to the vent holes ... this isn't really an issue since it's only really a problem if the batteries are particularly low (I could also reduce the charging current, but it's only 170mA at the moment anyway.)

- I get some blips when turning power on or off ... they can be in excess of 10uV ... I'm not sure if this is related to changes in the 12V power supply or some kind of noise. I need to do some more experiments ... interestingly there aren't showing up since everything is in the enclosure??

- I used a simple header and crimp connector on the front panel with no polarisation, and 16.8v on one pin ... yes - one dead avr. Some polarisation needed, would probably switch to an IDC one with a box (also saves the crimping!)

- There are no power switches, so nothing can be switched off ... so to turn off the alarm once the battery gets low (assuming you don't want to plug the power in) is a big disassembly job. I think a couple of rear mounted slide switches on the front panel with cut-outs should work -- one for the 12V supply to the ref, the other to turn off the AVR.

- I soldered the wires onto the Pomona 3770 jacks ... it didn't go particularly well, will probably need to redo them ... do others solder, or use crimp terminals?

And finally, I can't really measure the stability of any of the references yet ... my 34470A seems to be awful, it wanders all over the place (well 1-2ppm in the space of a day, lots of noise at the start of any temp increase), on ratio mode (which hopefully eliminates any issues with the meter) with a Datron 4000A it seems much more steady, with only a very minor temperature based delta ... but I have no idea which of them is the cause yet. I have a Prema 6048 which is away for calibration with Keysight, but they are taking an eternity, I think it's the first one they've had. Next project is a switching unit, so I can do some sensible data gathering from multiple devices.
 
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Offline MiDi

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Re: Ultra Precision Reference LTZ1000
« Reply #2790 on: November 15, 2019, 05:11:11 pm »
It looks very nice  :-+
Are there (invisible) earth connections directly screwed on all parts of metal case?
If not, you should add them for safety.
 

Offline essele

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Re: Ultra Precision Reference LTZ1000
« Reply #2791 on: November 15, 2019, 06:05:49 pm »
It looks very nice  :-+
Are there (invisible) earth connections directly screwed on all parts of metal case?
If not, you should add them for safety.


Thanks -- I missed that off of my list of lessons learned ... the rear panel actually has a copper pour and through hole plating on the four main fixings and one of the fixings for the power supply board, so that was supposed to do the trick, however it's not working. I'm not sure why yet ... I was just enjoying the thing being in one piece for a while before I dismantle it again!

Actually I hadn't really considered the top and bottom panels (which are separate) ... so maybe this isn't a good case choice, they do a single piece version which I think has the same dimensions, just may be more challenging for assembly.

EDIT -- so I mounted the back panel the wrong way around -- sigh, and so the plated hole that supposed to line up with the earthed stand-off doesn't ... I'll need to switch that around, but still doesn't solve the top and bottom issue. And actually the IEC socket fixings are earthed, so they would have been a better place to put the through hole plating (which I didn't!)
« Last Edit: November 15, 2019, 06:22:06 pm by essele »
 
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Offline MiDi

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Re: Ultra Precision Reference LTZ1000
« Reply #2792 on: November 15, 2019, 06:32:56 pm »
And actually the IEC socket fixings are earthed, so they would have been a better place to put the through hole plating (which I didn't!)

That would have been my next suggestion  ;)
I am not shure if the earth connections for the sides are appropriate, I guess not.
 

Offline alex-sh

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Re: Ultra Precision Reference LTZ1000
« Reply #2793 on: November 15, 2019, 07:54:41 pm »

- I soldered the wires onto the Pomona 3770 jacks ... it didn't go particularly well, will probably need to redo them ... do others solder, or use crimp terminals?


Very nice! Well done mate
Pomona 3770-0 - I use these ones too for my LTZ1000 project and I solder wires to them. Make sure you have the correct heat temp and they absorb a lot of heat.
 

Offline martinr33

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Re: Ultra Precision Reference LTZ1000
« Reply #2794 on: November 15, 2019, 09:05:04 pm »
It is really hard to measure the performance of a good reference. For example, you could use a 3458a, but it doesn't have the stability of a dedicated 10V reference, so it is hard to tell what you are looking at.

If you build a second unit, the delta between them can give you some ideas.
 

Offline essele

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Re: Ultra Precision Reference LTZ1000
« Reply #2795 on: November 29, 2019, 09:19:52 am »
Ok, so I finally got my Prema 6048 back from Keysight, all calibrated and happy.

I'm still working on my USB switching unit, so I've just done some overnight measurements comparing the 34470A and the 6048 measuring the reference from the posts above.

The top orange line is the measurement from the 34470A and the blue line is the 6048. The lower orange line is the temperature ... I pretty much melted the BME280 when trying to get the bloody thing to solder onto my board, so I'm not entirely convinced about the absolute temp, relative seems to be ok though.

The scale for the main measurements is ((v/first_v)-1)*1000000. So this should show ppm deviation from the original reading in each case.

You can see the 34470A is a bit all over the place (well, from +0.4ppm to -1.2ppm) although still easily within its 24h spec, it does show the marked different to the 6048 which is sitting in +/- 0.3ppm range.

The 34470A is in 100PLC, AZ on, fixed 10V range, no filter. Powered on for weeks.
The 6048 is on 20s sampling (8.5 digit), 20V range, no filter. Powered on for about 90mins at the start, so may still be warming.

Measurements are in a loop with no other delays, so that works out at approximately 1 measurement every 24 seconds.

Clearly there isn't enough information in this to make any concrete assertions, and the data set is a bit too short, but I thought it was an interesting initial set of data.

I should be able to get the switching going in the next few hours, then the intention is to sample two LTZ1000's and a Datron 4000A on both DMMs.
 

Offline HighVoltage

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Re: Ultra Precision Reference LTZ1000
« Reply #2796 on: November 30, 2019, 09:48:22 am »
Very interesting, essele!

The 34470A has some known flaws.
My biggest complaint was the ACAL drift.
Actually the 7 1/2 digit 34470A is much worst than the 6 1/2 digit 34465A, even worst than some of my older 34401A.

Keysight is working on a solution....
https://www.eevblog.com/forum/metrology/keysight-34470a-calibration-and-acal-problems/

There are 3 kinds of people in this world, those who can count and those who can not.
 
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Offline maginnovision

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Re: Ultra Precision Reference LTZ1000
« Reply #2797 on: November 30, 2019, 05:49:28 pm »
That looks pretty good! I wish Keysight could handle the 8017. I'm guessing the lack of english manual is why they "can't". In fact the only place I know of that can is Prema which means paying 350$ return shipping alone. Does it get more stable at higher integration times or nearly the same output?
 

Offline essele

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Re: Ultra Precision Reference LTZ1000
« Reply #2798 on: November 30, 2019, 06:30:53 pm »
I’ve now got my usb switch working but I saw some very strange behaviour.

I was switching between two 10v refs, and reading one 20s reading from the Prema each time ... the readings slowly converged, very weird ... I initially suspected my switch (since I built it!) but after some testing it looks like there is some kind of filtering going on in the Prema (despite the digital filter being off) ... it really does look like a rolling average.

It seems to be related to the number of readings and not elapsed time, so I now run it in 4s continuous mode for 20s before switching to a 20s single reading and it seems much better.

I’ve just rehoused the second reference in a similar case as above (but v2 with some improvements) and I’m about to kick off a new set of measurements, I will try some variations of the above and longer integration times as well as it seems a bit more jittery than the single measurement above.
 

Offline notfaded1

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Re: Ultra Precision Reference LTZ1000
« Reply #2799 on: November 30, 2019, 06:42:18 pm »
Which of the LTZ1000 reference PCB do you think is the most evolved and includes ability to do the 7V to 10V?  Or... do you think the 7.x to 10V is better done outside the reference container or inside it?  It seems a stable 7.x volt reference with boost to 10V trimmed output is the ideal. From your experience what do you suggest?

Bill
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