Author Topic: Ultra Precision Reference LTZ1000  (Read 990654 times)

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Online Dr. Frank

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Re: Ultra Precision Reference LTZ1000
« Reply #3050 on: October 14, 2020, 09:14:50 pm »

it's wound common mode, like a CAN bus choke, and it's the cheapest lacquered TDK ferrite (B64290L38X830) I got from voelkner/Conrad, about 1.8µH, or so.

Hello Frank,

so 1 winding on each side? (cannot see it exactly on the photo).

with best regards

Andreas
yes, quite randomly.
 
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Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #3051 on: October 14, 2020, 09:46:35 pm »
https://www.changpuak.ch/electronics/Arduino-Shield-BHUMI.php

Its a pity.
All those costly parts and then the temperature setpoint with 11:1 (below room temperature).
And a switchmode supply.

with best regards

Andreas
 

Offline openloop

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Re: Ultra Precision Reference LTZ1000
« Reply #3052 on: October 25, 2020, 12:51:18 am »
Quote
All those costly parts and then the temperature setpoint with 11:1 (below room temperature).

I've crunched some numbers, for the fun of it.

And, according to two dudes named Ebers and Moll, to keep temperature the same as for 12:1 ratio, for 11:1 R3 needs to be 13K7  :o

I do not know what consequences of increasing collector current to .5mA will be. Will the whole thing stay in regulation? Will somewhat increased self-heating of the temperature sensing transistor screw things? Will the additional voltage drop on pin7 be noticeable?

On another hand, dividers can be made out of them cool LT5400s ...  8)
« Last Edit: October 25, 2020, 01:46:31 am by openloop »
 

Offline uski

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Re: Ultra Precision Reference LTZ1000
« Reply #3053 on: October 26, 2020, 05:00:51 am »
Hi,

Did anyone hear about a group buy of LTZ1000A ?
It is out of stock anywhere but AD sells directly for $54.50 each for a pack of 20.

Any other way to get my hands on one ?
If someone wants to make a group buy I'd happily order one.

Or if multiple are interested maybe we could get a group buy going ?

Thanks
 

Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #3054 on: November 22, 2020, 07:43:49 pm »
Hello,

I finally have adjusted the T.C. of my LTZ#9 (LTZ1000 non A version)

first measurement on 03.11.2020 without R9: gives -128 ppb /K
from my rule of thumb (derrived from the LTZ1000A measurements) that each 1 Meg resistor compensates  +40 ppb/K
So I tried a 330K resistor.

measurement on 06.11.2020 shows clearly some over-compensation giving +31 ppb/K
So it seems on the LTZ1000 (non A) I have to calculate with 53 ppb/K for each 1 Meg resistor.

The first measurements with 402K  (e.g. 10.11.2020) where somewhat drifting so I had to wait until the measurements stabilized.
(perhaps I shouldnt have used a cheap 1% metal film resistor)

Now on 21.11.2020 the final result is 1 ppb/K in average. But of course due to the non linearity introduced by the temperature compensation there is some "Box T.C." of around 45 ppb/K over the temperature range of 12-38 deg C measured on top of the housing of the LTZ.

with best regards

Andreas

 
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Online Kleinstein

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Re: Ultra Precision Reference LTZ1000
« Reply #3055 on: November 23, 2020, 08:11:37 am »
The drift only looks bad because the scaling of the graph changes. In absolute numbers the curve without the resistor looks similar. One can also see that the resistor only has a really small effect on the voltage. So drift of the compensation resistor (even with cheap 1% resistors) should not be an issue.
The visible drift and hysteresis is more from the other resistors. Chances are this is still in the early hours for the parts and thus still in the initial drift after soldering / cleaning.

The compensation is nonlinear. So the right size of the compensation resistor would depend on the heater power / set temperature and likely also the thermal design.  With a higher set temperature and thus more heater power the heater voltage will change less with temperature and thus a smaller compensation resistor is expected. Similar more isolation could prefer a smaller resistor.
I would expect the right compensation resistor to be about inverse proportional to the heater voltage at a fixed temperature.
 

Offline openloop

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Re: Ultra Precision Reference LTZ1000
« Reply #3056 on: November 26, 2020, 03:03:24 am »
Andreas,

What is the time scale of your temperature sweeping graphs?
I mean, what is the total elapsed time?
 

Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #3057 on: November 26, 2020, 05:33:19 am »
Hello,

Setpoint temperature ramp speed is 0.12 deg C / minute.
(Actual temperature at the top of the aluminium housing of the PCB follows more ore less).
I usually start from 25 deg C down to cold, ramp up to hot and do another cold phase until minimum reaching 25 deg again.
In this case I did another hot phase and switched off the cooler during last phase.

Attached a different graph over time from first and last measurement.
So total time takes 1500 - 1900 minutes (so 25 - 30 hours) in this case.

with best regards

Andreas
 
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Offline branadic

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Re: Ultra Precision Reference LTZ1000
« Reply #3058 on: November 26, 2020, 08:34:40 am »
Hello Andreas,

we recently had a discussion about the temperature slope the other day. Even though I use 0.1K/min for the slope, which is the minimum that my Arroyo 5305 can do automatically, this is still to large to reach thermal equilibrium across the board and components. TiN uses a maximum slope of 0.02K/min and a minimum slope of about 0.0084K/min, so we are talking about a factor of 10 smaller value. This is achieved by a software controlled temperature profile and available here:

https://xdevs.com/guide/teckit

GitHub repository:
https://github.com/tin-/teckit

My explaination of the "open eye" (or hystersis if you want to call it like that) in your but also my measurements is, that thermal resistance and capacitance come into play if the slope is too fast. Thus, run up and run down are different. Solution, decrease the slope.

One thing that I don't like about the standard datasheet circuit of LTZ is, that tc-compensation and amplification to 10V are correlated and not independent from each other. This (let's call it) issue was solved in a commercial product of a voltage reference though.

-branadic-
Computers exist to solve problems that we wouldn't have without them. AI exists to ask questions, we wouldn't ask without it.
 
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Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #3059 on: November 26, 2020, 08:54:17 pm »
Hello branadic,

you are right (at least for a normal lab).

But in my case in summer I have up to 2 deg C / hour temperature rising. (from 22 deg to 33 deg C in a few hours).
So testing at 7.2 deg C / hour is only testing something like the "worst case".

On the other side: my battery pack within the LTZs limits the test time to a maximum of ~2 days.
So setting the ramp speed to below 0.05 deg C / minute is not really a option.

with best regards

Andreas
 

Offline niner_007

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Re: Ultra Precision Reference LTZ1000
« Reply #3060 on: December 01, 2020, 12:01:47 am »
Hey folks, I finished the layout of my LTZ1000 reference module. It is built around an 3458A reference form factor. 6 layers, uses mostly through hole parts, the divider is VHD200, the other sensitive resistors are VHP202Z, I also use MKP capacitors, and plan on using the free space for a few LMT70 temperature sensors, a USB interface and microcontroller for tracing and calibration.

I appreciate any feedback on the layout, specially around grounding.

P.S. each cell in the picture is 1mm, so that makes the thickest trace 1mm, an the thinnest trace 0.4mm.
« Last Edit: December 01, 2020, 12:41:38 am by niner_007 »
 

Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #3061 on: December 01, 2020, 05:47:31 am »
Hello,

for me it looks like you have to populate the LTZ on the bottom side of the PCB.
Is this intended?

with best regards

Andreas
 

Offline niner_007

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Re: Ultra Precision Reference LTZ1000
« Reply #3062 on: December 01, 2020, 06:04:20 am »
it is not meant to be populated on the bottom, perhaps orientation is not visible well
 

Offline niner_007

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Re: Ultra Precision Reference LTZ1000
« Reply #3063 on: December 01, 2020, 06:10:50 am »
I'm wondering if there is any concern in routing sensitive signal path in the inner layers, or whether it should always be routed on the top or bottom. Maybe surface contamination on the inner layers can't be as well controlled as on the top layer or bottom layers, which can receive a good cleaning at any time, hmm? Or am I overthinking.
 

Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #3064 on: December 01, 2020, 07:28:19 am »
perhaps orientation is not visible well
ok my fault.
I expected the nose on the top side of the PCB.

with best regards

Andreas
 

Online Kleinstein

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Re: Ultra Precision Reference LTZ1000
« Reply #3065 on: December 01, 2020, 07:58:59 am »
I'm wondering if there is any concern in routing sensitive signal path in the inner layers, or whether it should always be routed on the top or bottom. Maybe surface contamination on the inner layers can't be as well controlled as on the top layer or bottom layers, which can receive a good cleaning at any time, hmm? Or am I overthinking.

The traces are to a large part protected by the solder-mask. So surface leakage is mainly at the solder joints, and these have to on the outer layer anyway. The circuit is not that high in  impedance for most parts - so leakage is not very critical, it is not about pA currents.
The layout looks nearly like 1 layer, so there is essentially no need or advantage to go with 4 or more layers. 2 layers should be good enough. More layers add to possible mechanical stress in the board.

The traces are relatively wide and this way give quite some heat conduction paths around the LTZ1000.
The ground star point is a tricky part. Electrical is may be still OK with the relatively thick path to LTZ1000. Thermally this is not a good solution.  The alternative solution is to have the critical low side sense directly from the pin of the LTZ1000 and keep the rest separate with thinner traces.  It depends on the circuit around the reference (and off the board) how the ground connection should be.
 

Online Noopy

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Re: Ultra Precision Reference LTZ1000
« Reply #3066 on: December 01, 2020, 07:45:05 pm »
Any LTZ1000-fans here?  ;D

By popular request I have "designed" a LTZ1000 coffee cup:

https://www.redbubble.com/de/i/tasse/Referenzspannungsquelle-LTZ1000-von-Richis-Lab/63614214.9Q0AD

 8)

The LTZ1000 clock looks quite interesting...  ;D
 
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Offline niner_007

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Re: Ultra Precision Reference LTZ1000
« Reply #3067 on: December 02, 2020, 05:16:31 am »
I'm wondering if there is any concern in routing sensitive signal path in the inner layers, or whether it should always be routed on the top or bottom. Maybe surface contamination on the inner layers can't be as well controlled as on the top layer or bottom layers, which can receive a good cleaning at any time, hmm? Or am I overthinking.

2 layers should be good enough. More layers add to possible mechanical stress in the board.
What’s the mechanism by which that would happen? That seems surprising to me. I went for more layers just for layout neatness. This is not meant to be efficient economically, I am using VHD200 after all, which is overkill for an LTZ1000 design with its high ppm attenuation factor.
« Last Edit: December 02, 2020, 05:49:37 am by niner_007 »
 

Offline niner_007

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Re: Ultra Precision Reference LTZ1000
« Reply #3068 on: December 02, 2020, 08:04:31 am »
Mr. Kleinstein, made few updates, how's this? Replaced SMD diodes with thru hole diodes. Added ground plane for VCC and AGND. And made traces smaller. I think I could also add equalized "ballast" thermal pads for each trace around the LTZ1000 as well ala Datron. As is, does it lift your concern about thermals?

With the space I have, I don't know if better can be done  :'(
« Last Edit: December 02, 2020, 09:29:27 am by niner_007 »
 


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