Author Topic: Ultra Precision Reference LTZ1000  (Read 958929 times)

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Offline alex-sh

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Re: Ultra Precision Reference LTZ1000
« Reply #2850 on: January 30, 2020, 01:56:41 pm »
What kind of controller is used? Temperature control works quite well with a PI controller.

A simple P-Controller.
However, the problem is not in controller, but in placement of NTCs.
I had to place one NTC right next to the source and I failed - this gave me oscillation 
 

Offline alex-sh

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Re: Ultra Precision Reference LTZ1000
« Reply #2851 on: January 30, 2020, 04:13:46 pm »
Made a stupid mistake last night while burning the midnight oil - applied +15V to the buffer output +10.000000V (Dr Frank's PCB).
Now both the BUF and BUF 10.000000V outputs are dead. VREF on the LTZ1000 is giving me 7.08823V (just like before this accident). So I guess LTC1052 was killed?  |O

I paid the price for staying very late  >:(
« Last Edit: January 30, 2020, 09:53:23 pm by alex-sh »
 

Offline guenthert

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Re: Ultra Precision Reference LTZ1000
« Reply #2852 on: January 31, 2020, 05:19:28 pm »
But volt-nuts would rather avoid digital+pwm close to their lovely reference :) Therefore the idea with analog PI even it would be difficult (we do it not because it is easy..).
Whoa, that's a slippery slope there, ending with batteries, potentiometers and galvanometers like it's 1899. 

Just because PWM is easy for the uController, there doesn't have to be a high (EMI indcucing) current PWM to the heater.  Nothing stops you from adding a cap or two before the series pass transistor (assuming a sufficiently capable transistor of course) ...
« Last Edit: February 01, 2020, 01:48:38 am by guenthert »
 

Offline imo

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Re: Ultra Precision Reference LTZ1000
« Reply #2853 on: January 31, 2020, 06:30:04 pm »
But volt-nuts would rather avoid digital+pwm close to their lovely reference :) Therefore the idea with analog PI even it would be difficult (we do it not because it is easy..).
Whoa, that's a slippery slope there, ending with batteries, potentiometers and galvanometers like it's 1899. 
Edit: It took me 2 hours to wire and simulate :)
Added the temperature difference between the heated case and board.
The TIP121 has to be thermally isolated from the case  :-[
« Last Edit: January 31, 2020, 08:15:18 pm by imo »
 

Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #2854 on: January 31, 2020, 07:46:10 pm »
Nothing stops you from adding a cap or two before the series pass transistor (assuming a sufficiently capable transistor of course) ...
Ok I forgot to mention that I use a rather slow automotive power stage (BTS432) which is optimized to EMI with turn on/off times around 100 us.

with best regards

Andreas
 

Offline 3roomlab

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Re: Ultra Precision Reference LTZ1000
« Reply #2855 on: February 01, 2020, 06:29:17 am »

Edit: It took me 2 hours to wire and simulate :)
Added the temperature difference between the heated case and board.
The TIP121 has to be thermally isolated from the case  :-[

you can try very quick and dirty approx numbers
each 1g of plastic thermal mass C = 1F ~ 2F
metals are sissies, each 1g = about 0.4~ 0.5F
water is about 3.9F per 1g

each cm sq of box is approx 800C/W
each cm sq of PCB is approx 800C/W

eg inside pcb 5x10cm, 2 side = 100sq cm ~ 800/100=8C/W
inside of box recieving heat from PCB 10x10x10 ~ 600sq cm ~ 800/600=1.3C/W

pcb to box inside is about 1.3+8 = 9.3C/W
external box to air is 1.3C/W

instead of simulate heat going out, try and see what happens when the ambient goes up and down. it will ruin your entire day of simulations
overclocked CPU and GPU are a waste of energy and time, it is highly energy + calculation inefficient vs watts. there is an entire influencer industry milking users off it, they call it "premium" but lifespans are short, oxymoronic crap , more like single use.
 
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Offline imo

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Re: Ultra Precision Reference LTZ1000
« Reply #2856 on: February 01, 2020, 09:11:45 am »
Sure, the simulation of the thermostated box for the Vref is off topic here, therefore I stop with the below picture - I've moved the thermistor (the heater one) a bit off the heater - I get a nice oscillation :)

PS: added a version with 2x TIP121 as the heaters with added white phonon noise :)
« Last Edit: February 01, 2020, 11:10:17 am by imo »
 

Offline alex-sh

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Re: Ultra Precision Reference LTZ1000
« Reply #2857 on: February 05, 2020, 12:00:30 pm »
I wonder if this is due to the oven not being properly insulated?
I fear that the NTC for the temperature controller is too far from the heat source.

Thats why I typically use 2 temperature sensors.
One for the heater and one for the point of interest.

With best regards

Andreas

Hi Andreas,

I managed to obtain temperature stabilisation between 34.81C to 34.93C which is within around 0.1C.
I used two NTCs - one attached right next to the heating resistor and one is next to LTZ1000A.
I am using 2  x TE Connectivity GA10K3A1A (+/-0.1C tolerance, B value tolerance 0.5%).
Do you think this is sufficient? The enclosure is covered in one layer of insulation. I think I have to work more on insulation putting the second layer.

Thanks
Alex
 

Offline alex-sh

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Re: Ultra Precision Reference LTZ1000
« Reply #2858 on: February 16, 2020, 09:26:23 am »
I can see from time to time these spikes (marked in red in the photo). This is a new ltz1000ach ageing, but the measurements were taken (a) in the temperature oven (b) in the shielded enclosure (c) powered by a battery pack. The only thing which comes to my mind are cables. I’m using ordinary 22AGW cables rather than shielded ones. However, from the DMM I’m running banana to BNC shielded cable with hooks at the end.

What do others think? Where these spikes are coming from? What cables are you using for your boards please (links to Digi-Key would be appreciated)
 

Offline imo

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Re: Ultra Precision Reference LTZ1000
« Reply #2859 on: February 16, 2020, 09:32:53 am »
Your DMM6500 Vref is an LM399.. Popcorn?
 

Offline hwj-d

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Re: Ultra Precision Reference LTZ1000
« Reply #2860 on: February 16, 2020, 09:42:31 am »
@alex-sh
Looks like typical popcorn noise. That's the LTZ itself. Should decrease over the months, but should be observed. My LTZ are reasonably quiet after 18 months.
 
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Online Kleinstein

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Re: Ultra Precision Reference LTZ1000
« Reply #2861 on: February 16, 2020, 09:48:06 am »
There are several possible reasons for just a single out-layer. One possibly source could be EMI (e.g. mobile phone sending a rather strong sync signal once in a while,  radar).  Popcorn noise of the DMM reference would usually look different and would not be visible near zero.

With just a relatively low impedance reference to a DMM the cables are not that critical - a poor choice could give some thermal EMF, but this is more a problem with the connectors that the cable itself.  BNC connectors may not be the best choice for DC.

What is exactly measured ? It does not look like directly reading the 7 V with the DMM. This would not make that much sense anyway as the DMM internal reference would dominate.
 
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Online dietert1

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Re: Ultra Precision Reference LTZ1000
« Reply #2862 on: February 16, 2020, 10:09:26 am »
You seem to have 1.5 uV drift in 10 minutes, which is a lot and may indicate there is something else going on besides ageing. Or is the plot in hours?

Regards, Dieter
 

Offline imo

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Re: Ultra Precision Reference LTZ1000
« Reply #2863 on: February 16, 2020, 11:22:51 am »
The Vref based on a selected LM399AH inside the DMM6500 may walk (random walk) 5uV p-p at constant temp.
Edit: added "AH"
« Last Edit: February 16, 2020, 11:51:57 am by imo »
 

Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #2864 on: February 16, 2020, 11:51:28 am »
What do others think?

... you need more meters.
otherwise you cannot distinguish wether it is from the LTZ or from the meter.

my K2000 also has from time to time (at certain temperatures) some popcorn noise.
Of course there can also be many other reasons like EMI from mains into the reference or the meter.

of course popcorn noise (at least short duration events) from the reference can also be measured with a 1/f (0.1-10 Hz) amplifier

with best regards

Andreas
 
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Offline hwj-d

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Re: Ultra Precision Reference LTZ1000
« Reply #2865 on: February 16, 2020, 12:37:47 pm »
You seem to have 1.5 uV drift in 10 minutes, which is a lot and may indicate there is something else going on besides ageing. Or is the plot in hours?

Regards, Dieter
Minutes. Looks like a relative fresh assembled new kit to me.
 

Offline Dr. Frank

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Re: Ultra Precision Reference LTZ1000
« Reply #2866 on: February 16, 2020, 02:47:15 pm »
I can see from time to time these spikes (marked in red in the photo). This is a new ltz1000ach ageing, but the measurements were taken (a) in the temperature oven (b) in the shielded enclosure (c) powered by a battery pack. The only thing which comes to my mind are cables. I’m using ordinary 22AGW cables rather than shielded ones. However, from the DMM I’m running banana to BNC shielded cable with hooks at the end.

What do others think? Where these spikes are coming from? What cables are you using for your boards please (links to Digi-Key would be appreciated)

Alex,
I assume you are using the same PCB and circuit like your already running LTZ1000 reference board?
Have you ever observed these spikes on this non-A version reference with this DMM?
Frank
« Last Edit: February 16, 2020, 02:57:35 pm by Dr. Frank »
 

Offline alex-sh

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Re: Ultra Precision Reference LTZ1000
« Reply #2867 on: February 16, 2020, 03:40:35 pm »
You seem to have 1.5 uV drift in 10 minutes, which is a lot and may indicate there is something else going on besides ageing. Or is the plot in hours?

Regards, Dieter
Minutes. Looks like a relative fresh assembled new kit to me.

It's correct. It is minutes and this has been assembled recently. This is LTZ1000ACH
 
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Offline alex-sh

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Re: Ultra Precision Reference LTZ1000
« Reply #2868 on: February 16, 2020, 03:53:41 pm »
I can see from time to time these spikes (marked in red in the photo). This is a new ltz1000ach ageing, but the measurements were taken (a) in the temperature oven (b) in the shielded enclosure (c) powered by a battery pack. The only thing which comes to my mind are cables. I’m using ordinary 22AGW cables rather than shielded ones. However, from the DMM I’m running banana to BNC shielded cable with hooks at the end.

What do others think? Where these spikes are coming from? What cables are you using for your boards please (links to Digi-Key would be appreciated)

Alex,
I assume you are using the same PCB and circuit like your already running LTZ1000 reference board?
Have you ever observed these spikes on this non-A version reference with this DMM?
Frank


Hallo Dr Frank,

No, this is a different PCB producing a buffered 7.1V. This is the LTZ1000ACH
The idea is to have several LTZ1000 and LTZ1000ACH and then I can monitor the drift against the recently calibrated ones.
Unfortunately, my gear is too useless to monitor
I was conducting some tests with the temperature oven when I noticed this peak noise. I cannot remember observing it with a non-A version.

However, I must admit that the reference has not been aged yet. It probably has to sit on the PSU for months before doing any tests

Thanks
Alex
 

Offline alex-sh

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Re: Ultra Precision Reference LTZ1000
« Reply #2869 on: February 16, 2020, 03:56:41 pm »
What do others think?

... you need more meters.
otherwise you cannot distinguish wether it is from the LTZ or from the meter.


I completely agree with you.
However, we are looking into an expensive territory.
I can do ratio measurement on my DMM between a calibrated LTZ1000 and a new LTZ1000 (after aging it).
Or maybe you can advise on how to measure it properly without spending $$$ for the equipment?
 

Offline exe

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Re: Ultra Precision Reference LTZ1000
« Reply #2870 on: February 16, 2020, 04:15:46 pm »
The Vref based on a selected LM399AH inside the DMM6500 may walk (random walk) 5uV p-p at constant temp.
Edit: added "AH"

Afaik the reference inside is SZA263 .
 

Offline hwj-d

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Re: Ultra Precision Reference LTZ1000
« Reply #2871 on: February 16, 2020, 05:40:19 pm »
Something to compare. This is 10V PX LTZ-CH, now ca. 20 month at 15V. Such a peek happens ca. 1/month last 6 month.
Weather is quite stormy, last 2h.

« Last Edit: February 16, 2020, 05:44:47 pm by hwj-d »
 
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Offline alex-sh

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Re: Ultra Precision Reference LTZ1000
« Reply #2872 on: February 16, 2020, 06:17:08 pm »
Something to compare. This is 10V PX LTZ-CH, now ca. 20 month at 15V. Such a peek happens ca. 1/month last 6 month.
Weather is quite stormy, last 2h.

So it is a 20 months old Vref? 31uV p-t-p!!!
Do you think it has been caused by a storm? I remember reading a thread where MisterDiodes mentioned that LTZ1000 was picking up a train several blocks away.
 

Offline Conrad Hoffman

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Re: Ultra Precision Reference LTZ1000
« Reply #2873 on: February 16, 2020, 07:44:35 pm »
I don't know if this applies to buried zeners but a friend used to build commercial instruments with voltage references. He selected his TC zeners based on noise. The zeners with the lowest noise were also the most stable over time. This was in the days of 1N82x types. I believe popcorn noise is the result of defects in the crystal lattice and I'd be surprised if it improved over time. Naturally at the level we're talking here, noise can sneak in from anywhere and everywhere! As for that LT1052 failure some posts above, I always found they were quite fragile and managed to pop more than a couple. They also aren't very good at driving their own feedback network, preventing the use of low values for low noise. Regardless, the zero drift makes up for everything else.
 
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Offline hwj-d

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Re: Ultra Precision Reference LTZ1000
« Reply #2874 on: February 16, 2020, 07:51:52 pm »
Something to compare. This is 10V PX LTZ-CH, now ca. 20 month at 15V. Such a peek happens ca. 1/month last 6 month.
Weather is quite stormy, last 2h.

So it is a 20 months old Vref? 31uV p-t-p!!!
Do you think it has been caused by a storm? I remember reading a thread where MisterDiodes mentioned that LTZ1000 was picking up a train several blocks away.
This PtP is the single popcorn peak. Std Dev under this circumstances with 10V upward regulation is 1.77µV, without popcorn <1.5µV for this 10V-PX, without upward regulation <1.3µV.
Think about, this DMM6500 isn't better. The PtP limit of this meter itself isn't better than ~ 10 to 12µV. Below that, you are looking to the limit of your 6.5 meter, not the DUT.  ;)
 


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