Author Topic: Ultra Precision Reference LTZ1000  (Read 985980 times)

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Offline Galaxyrise

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Re: Ultra Precision Reference LTZ1000
« Reply #1300 on: February 07, 2016, 08:29:02 pm »
What FETs do you use. P-Channel are relatively rare.
MMBFJ177LT1G. I got 10, characterized them for 100uA, and choose the closest match for Q1 and Q2.

Quote
Would be nice if you could provide a larger image of the cirquit diagram. The numbers are hard to read.
Done.  I turned on part names, used a clearer font, and left if at the native resolution.  Updated the image in my earlier post  (the _Flip is because I swapped the positive and negative inputs on the schematic symbol.)

Quote
So for me there must be a different explanation for the 90 mV.
Using chuckb's images I computed about 42 "squares" along the trace to pin 4, which would be a resistivity around 0.5 ohm/sq to cause that shift.  That seemed high but not impossible, and it fit the nice linear relationship of the voltage shift to current.  Ah well :)

Thanks
« Last Edit: February 07, 2016, 08:33:01 pm by Galaxyrise »
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Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #1301 on: February 08, 2016, 07:19:00 am »
Sure, here we go...

 :-+

which would be a resistivity around 0.5 ohm/sq to cause that shift.  That seemed high but not impossible, and it fit the nice linear relationship of the voltage shift to current.

So if I understand you right you should be able to measure the 22 Ohms of pin 4  in series to the zener and also in series to the base/emitter of Q1.
The zener would be easy to measure. The datasheet states a typical zener voltage change of 80 mV for a 1 to 5mA difference. (so around 20 Ohms for both sides of zener + the zener itself).
But usually discrete zeners (directly contacted) in that voltage range have also dynamic resistances around 10 Ohms.

The base / emitter would be more difficult. In normal operating the base current should be around 1uA.
But I think that up to 50 or even 100uA you will be on the safe side.

With best regards

Andreas


 

Offline alanambrose

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Re: Ultra Precision Reference LTZ1000
« Reply #1302 on: February 08, 2016, 03:02:23 pm »
Hi,

Interesting results when we were away for the weekend (the whole graph is updated in my previous message above):

+ the temperature was very stable
+ there were still a few noise excursions - I'm suspecting mains noise
+ there were a couple of interesting artifacts (below) - I'm suspecting mains voltage droop. Exactly how this gets into the reading I'm not sure - atm the ref heater is powered by a E3631A and the ref by an Advantest R6144. I'm not logging these right now.

Otherwise the coefficients were similar to before -



- although you can see the time drift starting to mean revert be more square root like (rather than linear). I guess its possible to repeat this analysis this with a square root model for time drift. Interestingly whereas we're normally interested in high R squared, low R squared is what we're looking for here i.e. ideally the readings tend towards random processes with the coefficients all zero.

TiN - if you give me a link to your data I can do a preliminary analysis - you could copy the existing file without stopping the test. Were you impacted by the earthquakes?

p.s. >>> So you ordered 8051 chip alone? Mine REV? says 9,2. You got me thinking...

? :)

A.

« Last Edit: February 08, 2016, 03:21:03 pm by alanambrose »
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Offline TiN

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Re: Ultra Precision Reference LTZ1000
« Reply #1303 on: February 08, 2016, 03:48:07 pm »
Alan,

My data CSV is here. Graph here (takes long time to draw due to number of points, sorry).
There are many delays due to abnormal hangs of linux-gpib or my python capture app, so it's not that consistant :(.
-3ppm drop at start of NPLC2 data capture was due moved cable from reference to DMM.
It was just slight shake in Taipei, nothing like south part, so here everything is alright, except GPIB datalog stopped same moment 3:20am, perhaps cable got lose. :)

I'm trying now crude air thermal chamber test with 55W TEC module and K2510, to get setup for temperature cycling of references and resistors.
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Offline Galaxyrise

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Re: Ultra Precision Reference LTZ1000
« Reply #1304 on: February 08, 2016, 08:39:02 pm »
The zener would be easy to measure. The datasheet states a typical zener voltage change of 80 mV for a 1 to 5mA difference. (so around 20 Ohms for both sides of zener + the zener itself).
But usually discrete zeners (directly contacted) in that voltage range have also dynamic resistances around 10 Ohms.
Heh, the datasheet actually calls out this behavior! If you look at the "Zener Voltage vs Current" chart, it shows the sum of zener + Q1 going up more slowly than just zener alone--Q1 must be going down as zener current increases.  That chart has a non-linear change for Q1 below 2mA, though; too bad the datasheet doesn't explain the mechanism ;).  A resistor there may suffice for a spice model.

I wonder if my LTZ is 80mv or is up towards the datasheet max of 240... perhaps I'll try to measure it some day. 


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Offline alanambrose

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Re: Ultra Precision Reference LTZ1000
« Reply #1305 on: February 08, 2016, 10:19:23 pm »
OK a quick check. I've just taken the 1st day for the time being before the big 4ppm move. I'm getting -0.4ppm per day and -0.9ppm per K. For comparison MM's 3458A-8451 meter had +0.1ppm per day and -0.3ppm per K vs. a 732 (if I remember correctly) and my 3458A-1704 also 0.1ppm per day and +0.2ppm per K vs. an old A9 board. Your data is vs. one of your own ref boards? How aged is the LTZ on that one? Wow you guys in Taipai were lucky not to be near the centre.

(edit - actually looking at this graph more closely (see blue circle and black trend line) - the reading is moving before the internal temp of the meter suggesting that it's the ref that's shifting)

>>> I'm trying now crude air thermal chamber test

Yes thermal chamber is the way to go - I'm getting bored with my home lab being either freezing or stifling as I'm running these tests :) ... and you can't separate out the tempco of the meter from the tempco of the ref.

A.

« Last Edit: February 08, 2016, 10:30:05 pm by alanambrose »
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Offline TiN

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Re: Ultra Precision Reference LTZ1000
« Reply #1306 on: February 09, 2016, 01:25:57 am »
There is another issue with thermal box, as seem that EMI from TEC cause readings to jump a bit (1Meg 4W OHMF), even with Guard terminal of DMM wired to metal box with resistor.
Now since I can get temperature stable to ~0.005°C, let's try same test with LTZ ref. Yes, it's one of my early reference modules. It's Rev A01 PCB, LTZ1000ACH, LTC2057, 13K/1K heater.
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Offline alanambrose

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Re: Ultra Precision Reference LTZ1000
« Reply #1307 on: February 09, 2016, 10:05:12 am »
To determine tempco vs time drift and also calc RH and pressure coefficients, of course, we want variations in the 'independent variables'. So, some temperature jumps, ramps etc would be good - the kind of thing you might do if you were characterising a filter or other transfer function in the time domain. As an initial approximation, the tempco relationship seems pretty fast and somewhat linear, which is helpful for characterisation. I am also seeing a fall off in time drift with larger time scales which I'm putting down to 'square root' behaviour. (I will post some data presently - I need to write some more code.) With more data I should be able to fit these relationships fine. Actually, the 'better' the ref/meter / the more the variations are down to random fluctuations rather than easily observed xfer functions / the harder it will be to pull the relationships out of the noise. I don't think we're anywhere near that point yet though. I'm hoping to get a thermal chamber device set-up here also over the next couple of weeks.

A.
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Offline TiN

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Re: Ultra Precision Reference LTZ1000
« Reply #1308 on: February 10, 2016, 06:44:56 am »
Seems like I have hard time measuring tempco of LTZ module.
At first glance everything was okay, but when I got temp 4K up, i had strange -0.5ppm dip. Then bumped temp another +7K, it was bit stabilized.
Drop to original +24C (-11K) output barely changed, if take just two nearest hours with 11K temperature delta - simple math gives 0.009ppm/K.
Temperature of 3458A was measured as +0.118ppm/K due to sun in the morning, warming up meter 3.4K. ACAL brought signal back 0.7ppm down.

Should I crank chamber temp to +50°C, so we can see something ?

Details about setup covered in this EEVBlog thread.



« Last Edit: February 10, 2016, 07:07:02 am by TiN »
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Offline alanambrose

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Re: Ultra Precision Reference LTZ1000
« Reply #1309 on: February 10, 2016, 01:21:11 pm »
OK will take a look at that data.

For amusement, here is the plot of regression coefficients vs elapsed time from the beginning of my drift experiment.

(see https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg858685/#msg858685)

This suggests:

+ a simple linear model isn't bad (as these coefficients are fairly stable)
+ the time-drifty meter is stabilising a bit

I'm going to swap out the 8051 on that one and see if anything changes.

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Offline TiN

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Re: Ultra Precision Reference LTZ1000
« Reply #1310 on: February 10, 2016, 01:33:21 pm »
If I would be you, I'd perhaps created separate 3458A thread, and first thing would be to measure A9 output of drifty meter with stable one, to confirm it's not the ref (maybe it was done before?).
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Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #1311 on: February 10, 2016, 07:46:27 pm »
Hello Tin,

Seems like I have hard time measuring tempco of LTZ module.

Should I crank chamber temp to +50°C, so we can see something ?


yes it is no easy task.
There are different influences on the LTZ.
First you have temperature gradients which also have a influence
(see my PSRR experiment and the heat gun experiment).
Further there is shurely some influence from mechanical stress of the PCB.
Which might also vary over time when the Epoxy "flows" or soaks some humidity.

And that is also the reason why I do a slow ramp (around 0.1 deg C / minute)
down to 10 deg C up to 40 deg C and back to room temperature.
The shift from gradients appears as hysteresis in that case and can be averaged out.
See attached pictures of my LTZ#1 versus ambient temperature and PCB sensor temperature (which are quite different).

50 deg C might be too much for your temperature setpoint.
If you fall out of regulation the tempco will increase to 50 ppm/K.

with best regards

Andreas

« Last Edit: February 10, 2016, 07:50:34 pm by Andreas »
 

Offline TiN

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Re: Ultra Precision Reference LTZ1000
« Reply #1312 on: February 11, 2016, 07:05:00 am »
So your total test time is 5 hours?

What I see is that voltage output jumps caused by non-temperature related effects are far larger than change of temperature itself, to isolate tempco from other effects.
I'll test second module, and then will test both in same chamber. Perhaps differential measurement of two LTZs in chamber would be more useful, to avoid own DMM's effect impact results.
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Offline alanambrose

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Re: Ultra Precision Reference LTZ1000
« Reply #1313 on: February 11, 2016, 12:43:08 pm »
Hey Andreas,

Very interesting results. If I understand correctly:

+ no hysteresis between ambient and the outside of the ref
+ some thermal hysteresis between the outside and inside of the ref measured with Vbe
+ apparently some unaccounted for hysteresis in the ref itself
+ some non-linear ref tempco but approx -0.03 ppm per K (assuming the meter is at a stable temp)

Is that right? 6K per hour is quite a rapid temp rise for a lab in practice of course. Does the hysteresis loop change much if you increase/decrease the ramp speed? Could the apparent hysteresis in the ref just be an artifact from time-based meter drift?

p.s. a left scale in ppm nominal ref voltage would be easier to read :)

Hi TiN,

>>> If I would be you, I'd perhaps created separate 3458A thread, and first thing would be to measure A9 output of drifty meter with stable one, to confirm it's not the ref (maybe it was done before?).

I don't think anything could top your repair thread :) mine would be dead boring in comparison. I only mention the drifty meter for amusement's sake btw - I'm focused more on LTZ drift measurement and characterisation. Hence all the dull stats. I have a 4xLTZ test coming up.

Alan
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Offline TiN

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Re: Ultra Precision Reference LTZ1000
« Reply #1314 on: February 11, 2016, 12:47:24 pm »
Let the clash of LTZs begin :)  Perhaps we can have some specific test list and conditions which all of us can try to run? Would be more interesting to compare more "apple-apple" scenario..
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Offline alanambrose

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Re: Ultra Precision Reference LTZ1000
« Reply #1315 on: February 11, 2016, 01:19:42 pm »
>>> Perhaps we can have some specific test list and conditions which all of us can try to run? Would be more interesting to compare more "apple-apple" scenario..

Good point. I'm planning on logging mean voltage and noise (say 2NPLC/azero on) from 4xLTZ1000A (as unmodified A9 boards) with LTC2057 followers supplied by lowish noise supplies using my 3D printed thermal covers / plus supply voltage and ambient temp / switched with a standard K2000 scan card / measured by a 3458A / logged on a PC with C#. No special EMF or thermal shielding / no special thermal EMF precautions / no temperature chamber / fairly stable home lab temperature environment with a few planned ambient temperature excursions / running for a week or so. The intention is to observe, compare and characterise the time drift / get an overall (meter plus ref) tempco. I'm expecting that regressions and some kind of n-cornered hat analysis (which I haven't figured out yet) will help.

A.
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Offline TiN

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Re: Ultra Precision Reference LTZ1000
« Reply #1316 on: February 11, 2016, 02:05:29 pm »
Challenge accepted.  :bullshit: :box:
 I had similar idea, with exception of thermal box and using TCSCAN-2001 card in 2001. And using my own LTZ modules. I think I can get forth back from unsuccessful K2001 conversion.

Changed to second module, took a photo. Here's my module setup:



This one is LTZ1000CH (2014 week 16), LTC2057 opamp, 12K/1K for low temperature setpoint.
Battery powers MAX6610 sensor, located on bottom side at center.

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Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #1317 on: February 11, 2016, 10:45:57 pm »
So your total test time is 5 hours?

its more 12-15 hours.
ramping down and up and with 1 hour rest at minimum and maximum temperature + some overlapping because at the beginning the ramp speed starts at zero and behaves different when finally ramping down.

Hey Andreas,

Very interesting results. If I understand correctly:

+ no hysteresis between ambient and the outside of the ref
+ some thermal hysteresis between the outside and inside of the ref measured with Vbe
+ apparently some unaccounted for hysteresis in the ref itself
+ some non-linear ref tempco but approx -0.03 ppm per K (assuming the meter is at a stable temp)

Is that right? 6K per hour is quite a rapid temp rise for a lab in practice of course. Does the hysteresis loop change much if you increase/decrease the ramp speed? Could the apparent hysteresis in the ref just be an artifact from time-based meter drift?

p.s. a left scale in ppm nominal ref voltage would be easier to read :)


I think you are mis-interpreting the diagrams.
They are both the same except for the x-axis.
In one case (tPCB) the NTC near the LTZ on the PCB is on the x-axis.
Since I did not remove the Y-axis for this sensor he shows no hysteresis but the other sensor.

In the other case (tAMB) I have a second NTC outside of the aluminium case of my reference as x-axis.
So this sensor shows no hysteresis but the PCB-sensor lags against the ambient temperature.

Vbe is never measured in the diagrams (This would change the setpoint of the LTZ).
The hysteresis on the reference appears mainly because the temperature is neither the same of the one or other NTC.
The other part could be some effect due to temperature gradient.

I think you did not mention the 2:1 divider in the measurement (so you should not divide by 7200 mV but by 3572 mV
when calculating T.C. (around 0.06 ppm/K).

My "meter" is a LTC2400 based ADC with temperature compensation in this case.
It is rather noisy (the ADC itself + the around 0.1ppm quantisation noise of temperature compensation giving around 0.25ppm standard deviation) but has almost no drift over time.

Changeing the ramp speed has it´s limits.
Increasing is not possible for the whole temperature range (the peltier cooler is at its limit with 0.1 K/minute).
Slowing down would need running over night or splitting the measurement over several days.

With best regards

Andreas




« Last Edit: February 11, 2016, 10:51:10 pm by Andreas »
 

Offline TiN

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Re: Ultra Precision Reference LTZ1000
« Reply #1318 on: February 12, 2016, 06:05:04 am »
Well, second module was no good:



+0.67 ppm/K, from 10K change. Something definately not right on this one. I see no point of testing this one any more before issue is fixed.

Also I forgot that I had Rev.B module in 3245A, so I cannot test it directly.

-----------------------------

Changed to 3rd module (still Rev.A, 13K/1K setting, ACH-zener, different opamp this time, LT1097):



Next tests will be more interested, with old LTZ chips and sockets, and also wirewound resistors instead of Vishay foils.  ;)
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Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #1319 on: February 12, 2016, 05:48:12 pm »
Hello,

here some results from my tilting experiment.
The LTZ is oriented in all directions.
The output voltage is measured as voltage difference between
LTZ#3 and #5 in the 100mV range with 100NPLC. (averaged over 1 minute).
One reference in normal position and the other is changed in orientation.

0 = N = Normal (all pins down)
1 = 4 = Pin 4 pointing up
2 = O = up side down
3 = 8 = Pin 8 pointing up
4 = 6 = Pin 6 pointing up
5 = 2 = Pin 2 pointing up

LTZ#3 has around 0.6 ppm difference through the orientations.
LTZ#5 has around 0.15-0.2 ppm when calculating out the drift.

So the question is: is the larger difference of #3 due to the LT1013A or is it a feature of the LTZ itself.

For the drift probably the treatment with the setpoint change is a reason.
So I will repeat the measurement this weekend after 1 week with constant setpoint.

With best regards

Andreas




« Last Edit: February 12, 2016, 08:19:37 pm by Andreas »
 

Online Kleinstein

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Re: Ultra Precision Reference LTZ1000
« Reply #1320 on: February 12, 2016, 06:51:05 pm »
Even though the change in voltage is only about 2 µV at the output from the normal position, the OPs should not show that much effect. To get 2 µV at the output, the offset at the OP must change by 400 µV or about 1 mV. The more likely source is the temperature abound the Pins of the LTZ1000. One could check this be repeating with a different cover.

The difference between the two modules might be due to the different position of the OPs as a heat source.

Another possible factor could be the earths magnetic field - though likely not a big factor. At least I have not seen data on this.
 

Offline branadic

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Re: Ultra Precision Reference LTZ1000
« Reply #1321 on: February 13, 2016, 06:22:54 pm »
My LTZ1000CH, based on the PCB from Andreas and resistors from Edwin Pettis, is alive. My meter shows 07.200V. Have to verify the exact value with different meters right know.
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Offline Macbeth

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Re: Ultra Precision Reference LTZ1000
« Reply #1322 on: February 13, 2016, 08:44:38 pm »
My LTZ1000CH, based on the PCB from Andreas and resistors from Edwin Pettis, is alive. My meter shows 07.200V. Have to verify the exact value with different meters right know.
What kind of ballpark figure is a set of hand made resistors, like yours, from Edwin going to set me back? Or is it "if you have to ask, it's too expensive for you!"  :-DD

Any stock wirewounds that could be available?
 

Offline branadic

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Re: Ultra Precision Reference LTZ1000
« Reply #1323 on: February 13, 2016, 09:56:36 pm »
Quote
ou might want to obtain a small amount of "down" [or a synthetic version of it like the stuffing for sleeping bags], and put some inside the metal box.  Not a lot-- you are not trying to insulate, but to stop convection currents in the air surrounding the LTZ and other components.  I'm assuming that there is a metal lid for the metal box.

Sure, there is a lid for the metal box and yes, there will be some cotton batting put inside. My LTZ is already sitting on a small 3D printed plastic spacer, as can be seen here:

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg841924/#msg841924

Only a small part on this spacer at the solder junction is senitive for possible air flow problems.

Quote
What kind of ballpark figure is a set of hand made resistors, like yours, from Edwin going to set me back? Or is it "if you have to ask, it's too expensive for you!"  :-DD

Any stock wirewounds that could be available?

They were affordable and fast available, nothing fancy, but I could have used Econistor:

https://www.rhopointcomponents.com/components/resistors/precision-through-hole/wirewound-econistor-3ppmc-8e16-8g16-series.html

or Miniohm instead too:

https://www.rhopointcomponents.com/components/resistors/precision-through-hole/wirewound-miniohm-3ppmc-5e10-5g10-series.html

Maybe they are any good for you too. Frank is pretty happy with his Econistors.
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Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #1324 on: February 13, 2016, 11:35:46 pm »
Maybe they are any good for you too. Frank is pretty happy with his Econistors.

How do you know that?

https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg624931/#msg624931

With best regards

Andreas
 


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