Author Topic: LT1021CMH based mini-reference  (Read 18766 times)

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Offline Alex Nikitin

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LT1021CMH based mini-reference
« on: January 31, 2017, 10:37:09 am »
I've worked on that project slowly over half a year now and at last the reference is boxed and working quite well. It is built on a bit of a stripboard and as I only have enough bits to build one more, I am not planning to make a pcb for it. Most components are from eBay, the main exception is Pomona CuTe connectors. The reference is very simple, containing the LT1021CMH chip, a 20K multi-turn pot, few resistors and diodes for an additional temperature compensation (without it the tempco was over 10ppm/C, now it is around 1ppm/C), a reverse polarity protection diode on the P/S connector, a P/S capacitor, an LED, a 3-position switch and a nice VBF 10K/1.111111K divider in a hermetic case. This unit can provide 10V, 1V, 10K and 1K reference values with a reasonable accuracy and (hopefully) a decent long-term stability (better than 50ppm looks about right). The switch connects the output terminals to the voltage reference in one position, disconnects it in the middle and shorts the terminals in the third position. The divider is wired permanently to the output terminals providing 1V reverence from 10V output, so with the voltage reference disconnected, the resistance between two red terminals is either 10K or 1K. I will now measure the voltage and resistance values over a period of time (probably a couple of weeks) and my plan is to use this unit as a travelling reference. There is a space left for an output buffer to give the reference better load capabilities and a better short-circuit protection (right now it will survive a short, but most likely would suffer a hysteresis shift after that) so I will install it as a next step.

Cheers

Alex
« Last Edit: January 31, 2017, 11:03:37 am by Alex Nikitin »
 
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Re: LT1021CMH based mini-reference
« Reply #1 on: January 31, 2017, 11:35:38 am »
Your DMM is unhappy though.

Nice little box. How about 10V noise? Also it's small enough to be fit into little heater box, do you plan running tempco tests as well?
I'm in for travel comparisons, if you need victims. :) VHD divider from hifi-guy? I remember he had this value dividers in his shop.
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Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #2 on: January 31, 2017, 11:51:50 am »
Your DMM is unhappy though.

Error 103 was left after a remote operation   :palm: .

Nice little box. How about 10V noise? Also it's small enough to be fit into little heater box, do you plan running tempco tests as well?
I'm in for travel comparisons, if you need victims. :) VHD divider from hifi-guy? I remember he had this value dividers in his shop.

The noise (at NPLC100  ;) ) is below 1ppm p-p, the tempco is estimated from the overnight run - see the graph below - the temperature change was about 6C max-min, so the tempco is about +1ppm/C). And yes, the divider is from that source. I've bought several items from him, including two of these dividers specifically for that box.

Cheers

Alex
« Last Edit: January 31, 2017, 11:56:17 am by Alex Nikitin »
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #3 on: January 31, 2017, 01:47:51 pm »
I've added a buffer using OP97 (so now short circuits are not a problem) and run a quick test on NPLC1 to look at the noise. Here is the result for a 90 seconds run, the vertical scale 0.2ppm/div . I suppose it is OK for this kind of a reference. The current consumption is less than 4mA unloaded, the load regulation on the output terminals with a buffer is less than 3ppm/mA (<3mohm output resistance).

Cheers

Alex
« Last Edit: January 31, 2017, 02:02:47 pm by Alex Nikitin »
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #4 on: January 31, 2017, 03:42:56 pm »
And here is another measurement for 80min at NPLC10, in the lab at about 23C room temperature, with 10K load placed on the output terminals for 15min.

Cheers

Alex
 

Online Andreas

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Re: LT1021CMH based mini-reference
« Reply #5 on: January 31, 2017, 03:48:27 pm »
Is this battery powered or mains connected?

With best regards

Andreas
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #6 on: January 31, 2017, 03:53:37 pm »
Is this battery powered or mains connected?

With best regards

Andreas

Right now it is powered from mains through a simple switcher adapter  ::) . It can certainly run from a couple of 9V batteries in series. For what it should do it is good enough as it is. I might add an internal 15V LDO regulator though.

Cheers

Alex
 

Online Andreas

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Re: LT1021CMH based mini-reference
« Reply #7 on: January 31, 2017, 04:02:38 pm »
Hello,

At least in the 2nd Diagram the noise seems to be rather high to me. (10uVpp).
After my understanding the 0.1-10 Hz noise should be 6uVpp typical.
With 10 NPLC (5 Hz) it should be even sligthly below.

With best regards

Andreas
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #8 on: January 31, 2017, 04:18:26 pm »
Hello,

At least in the 2nd Diagram the noise seems to be rather high to me. (10uVpp).
After my understanding the 0.1-10 Hz noise should be 6uVpp typical.
With 10 NPLC (5 Hz) it should be even sligthly below.

With best regards

Andreas

Hi Andreas,

The power supply right now is not very good, without question, just something that was at hand in the lab. I will try a battery run and a different (linear stabilized) supply possibly tomorrow. The "typical" values in the datasheet however are not a guarantee of performance. The "typical" tempco for the LT1021CMH is shown as 5ppm/C with maximum 20ppm/C in the temperature range. In fact the one I'm using in this unit has a tempco over 10ppm/C around 23C, fortunately quite linear so I could correct it with a simple diodes chain.

Cheers

Alex
« Last Edit: January 31, 2017, 04:21:15 pm by Alex Nikitin »
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #9 on: February 06, 2017, 09:39:42 am »
I am running the reference now from a nice linear 24V regulated supply however the 0.5ppm "jumps" are still present and I suppose that is the LT1021 chip itself. Still OK for the application intended. The VBF divider 10K/1K111111 is reasonably stable, below the results from the 68hours run over the weekend on the divider output giving 1V reference, the temperature dropped from +26C at the start to +20C at the lowest point, making the tempco a bit over +1ppm/C, plus a zoomed-in 1h graph to show the "jumps". Also attached the current schematics. The five diodes chain is selected for the particular reference (each diode gives about -2ppm tempco correction in this configuration, with the resistor R7 changed accordingly to keep the output at 10V). VR1 provides a fine trim. Output terminals switched by a three position switch, in one position only SW1.1 and SW1.2 closed, in the second position all switches are open and in the third only SW1.3 is closed, providing a short on the output to connect 10K and 1K111111 resistors in parallel, giving 1K reference value.

Cheers

Alex
« Last Edit: February 06, 2017, 10:20:48 am by Alex Nikitin »
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #10 on: February 06, 2017, 02:45:59 pm »
One more graph - 10K output measured over 15min (NPLC100 on HP3458A).

Cheers

Alex
 

Online Andreas

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Re: LT1021CMH based mini-reference
« Reply #11 on: February 06, 2017, 03:18:01 pm »
I am running the reference now from a nice linear 24V regulated supply however the 0.5ppm "jumps" are still present and I suppose that is the LT1021 chip itself.

Hello,

looks like popcorn noise.
I had also 1 extreme candidate (besides some other) in my LT1027DCLS8 thread.

What NPLC did you use on the measurement?

With best regards

Andreas
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #12 on: February 06, 2017, 03:32:43 pm »
I am running the reference now from a nice linear 24V regulated supply however the 0.5ppm "jumps" are still present and I suppose that is the LT1021 chip itself.

Hello,

looks like popcorn noise.
I had also 1 extreme candidate (besides some other) in my LT1027DCLS8 thread.

What NPLC did you use on the measurement?

With best regards

Andreas

Hi Andreas,

It is a pop-corn noise  :( , however I think it is acceptable for this unit  ::) . I use NPLC100 most of the time for long-term logging, with some earlier graphs taken at NPLC1 and NPLC10 (noted in the relevant messages) . Here is another graph taken (at NPLC100) during a warm-up from a non-powered state on 10V output - 5ppm/div vertical and 1min/div horizontal. So far the stability is OK, I may try to run the unit in my improvised "Happy Reptile" temperature chamber to look at the tempco.

Cheers

Alex
« Last Edit: February 06, 2017, 06:49:32 pm by Alex Nikitin »
 

Offline Kleinstein

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Re: LT1021CMH based mini-reference
« Reply #13 on: February 06, 2017, 08:39:42 pm »
Even with some popcorn noise, the noise level is very good (e.g. 0.6 µV for the 1 h run).
The steps are only like 200-300 nV - so hard to tell with a less sensitive meter.
You also have to take into account that some of the observed noise is from the reference inside the meter.
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #14 on: February 09, 2017, 10:13:42 am »
I did a 23C-15C-45C-23C run in my "temperature chamber" on the 1010B reference and will post some graphs later. Few things transpired during that run.

First, there is a noticeable lag between the reference itself and the temperature compensating diodes, as the diodes are placed on the board and not in a direct thermal contact with the case of the reference. It is only noticeable during reasonably fast temperature changes, as the diodes react faster than the reference, so if the temperature rises fast, the voltage can actually drop by 5-10 ppm before rising again some minutes later.

Second, the tempco measured after the voltage is settled at a particular temperature is reasonably constant at +1...+1.5ppm/C over the whole 15C-45C range, so with a better temperature compensation circuit this could be adjusted closer to zero. I won't bother with this unit though, it is good enough for it's intended application as a travelling reference that could be posted cheaply.

Third, the hysteresis was not readily measurable over that run, less than 1ppm variation after settling down at the same 23C temperature as at the start. It is also worth noting that the reference was transported at an outside temperature below 5C and did not exhibit any voltage shifts. The control run will be after the weekend when I'll bring it back to HP3458A.

I will also run a proper temperature test for the internal 10K reference resistor. A preliminary estimate from few points is below 2ppm/C.

Cheers

Alex

« Last Edit: February 09, 2017, 10:17:51 am by Alex Nikitin »
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #15 on: February 20, 2017, 12:38:49 am »
Here is the second run in a "temperature chamber", this time with few "stops" - again, there is a visible lag on the thermal compensation, essentially no hysteresis, +1ppm/C tempco and a bit of a popcorn noise, still visible though the voltage was measured with the Keysight 34465A.

Cheers

Alex

 

Offline Kleinstein

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Re: LT1021CMH based mini-reference
« Reply #16 on: February 20, 2017, 04:57:43 pm »
The popcorn noise look much stronger than in the earlier measurement. So maybe it is from a different source, like the DMM.
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #17 on: February 20, 2017, 05:05:50 pm »
The popcorn noise look much stronger than in the earlier measurement. So maybe it is from a different source, like the DMM.

Not really, the popcorn noise is about the same 0.5ppm p-p. Vertical scale is 2ppm/div. Other "jumps" are from the thermal lag between the tempco correcting diodes and the reference IC.

Cheers

Alex
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #18 on: February 27, 2017, 03:19:16 pm »
I've measured the reference again with the HP3458A after three weeks and some temperature changes powered and not powered between 5C and 40C - the 10V output has drifted less than 3ppm. I suppose it is good enough for that reference.

Cheers

Alex
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #19 on: March 02, 2017, 03:26:54 pm »
Here is the latest from a 48 hours run with the room temperature variations between 21C and 24.5C. On a longer scale the popcorn noise type variations are about 1ppm p-p, which is still acceptable for this kind of a travelling reference, I think, as the stability with time, temperature and humidity variations appears to be good.

Cheers

Alex
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #20 on: March 06, 2017, 03:34:36 pm »
I've done a little update on the 1010B last week, adding a DMOS FET to bootstrap the supply voltage on the LT1021. The main reason was the supply voltage variation affecting the output too much due to the self-heating of the LT1021. With the FET in the circuit the supply voltage on the reference chip is 11.3V and does not change with the external voltage supplied from 13 to 28V. As a nice side effect the power dissipation in the LT1021 is halved and so is the warm-up drift (from 40ppm to 20ppm). The rest of the parameters seems to be unaffected.

Cheers

Alex
 
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Offline Gyro

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Re: LT1021CMH based mini-reference
« Reply #21 on: March 06, 2017, 08:18:51 pm »
Just looking at the LT1021 datasheet, I hadn't realised there was an LT1021-7 which does not include internal scaling resistors (or trim pin). The thing that surprised me is that its long term drift is quoted at a mere 7ppm/kh typ versus 15ppm for the other variants, marginally lower than the LT LM199 spec (8ppm/kh). Presumably this is for the H package only.

I'm just curious that it's the lowest drift I've seen quoted for any IC reference. It's also quieter than the LM199 and with the benefit of a buffered output. Ok, the TC is higher than the LM199 but much lower than an unheated LM329. It looks as if it could work very well in a low temperature oven. Anybody tried it?
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Offline Kleinstein

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Re: LT1021CMH based mini-reference
« Reply #22 on: March 06, 2017, 09:03:54 pm »
It looks like there is no (more) LT1021-7 in a metal case. At least LT does not have is for sail in small quantity.
 

Offline Gyro

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Re: LT1021CMH based mini-reference
« Reply #23 on: March 06, 2017, 09:19:42 pm »
Hmm, a good point (sadly). It's still just about possible to find genuine LM329H on ebay (and other LT1021H variants) but no sign of LT1021-7. An idea behind its time then.  :(
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Online Andreas

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Re: LT1021CMH based mini-reference
« Reply #24 on: March 06, 2017, 10:07:04 pm »
It looks like there is no (more) LT1021-7 in a metal case. At least LT does not have is for sail in small quantity.
How can you tell that?
Arrow has more than 1000 LT1021DCH-7 stocked.
And sells in single quantities.

Besides this:
The stated long term drift (the first 1000 hrs after soldering) usually is much higher than that what you can measure after a 10000 hrs run in phase.
I normally measure 1-2 ppm/year for good hermetically references after that.
So for me a T.C. larger than 1 ppm/K hurts much more since a compensation of T.C. is never perfect (perhaps a factor 10 improvement) when the compensation is outside the reference chip.

With best regards

Andreas
 
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Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #25 on: March 07, 2017, 09:14:56 am »
Just looking at the LT1021 datasheet, I hadn't realised there was an LT1021-7 which does not include internal scaling resistors (or trim pin). The thing that surprised me is that its long term drift is quoted at a mere 7ppm/kh typ versus 15ppm for the other variants, marginally lower than the LT LM199 spec (8ppm/kh). Presumably this is for the H package only.

I'm just curious that it's the lowest drift I've seen quoted for any IC reference. It's also quieter than the LM199 and with the benefit of a buffered output. Ok, the TC is higher than the LM199 but much lower than an unheated LM329. It looks as if it could work very well in a low temperature oven. Anybody tried it?

You need to be careful about datasheet figures, it is not something to rely on from my experience, especially in regard to the noise, tempco and long term stability. At best it is a rough guide. My examples of LM1021CMH are relatively noisy (noisier than a good LM399), with a rather large tempco (~10-15ppm/C) though the long term stability and hysteresis after one month appear to be very good. I have chosen this chip for a travelling reference mostly because it provides 10V with internal (i.e. placed in a hermetic case) resistors, so all critical bits (the reference, the step-up network and the resistor reference/divider) are in a hermetic packaging. OK, it is relatively noisy with 1ppm p-p of a pop-corn "jumps" but the long term stability appears to better than 1ppm/month (how much better only the time will tell) and it proved so far to be quite insensitive to travelling and temperature cycling from 5C to 40C.

I have ten LM129AH in a hermetic packaging, perhaps I'll build the next reference with that one (or 2-3 in parallel, or maybe 3 in series for ~20V main reference voltage) and see how that will work. Another option is my JVR metal can JFET based reference, which appear to be very stable (less than 5ppm drift over more than a year, essentially less than I could measure reliably) and has a low tempco around room temperature. It does rely upon some good resistors though and doesn't have a particularly low noise (~0.5ppm p-p).

Cheers

Alex

 

Offline Gyro

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Re: LT1021CMH based mini-reference
« Reply #26 on: March 07, 2017, 10:07:09 am »
Quote
You need to be careful about datasheet figures, it is not something to rely on from my experience, especially in regard to the noise, tempco and long term stability.

Oh absolutely. It just struck me as strange that LT would go to the 'trouble' of stating half the typical long term drift for the 7V version rather than just sticking with the more or less universal 15ppm/khr. It effectively implies that [Edit: the ratio drift of] the on chip resistive divider used on the other variants contributes typ 8ppm/khr, not something you would expect them to want to draw attention to.

I was wondering how your JFET reference was doing, I hadn't seen an update for quite a while. It sounds way better than your initial expectations.
« Last Edit: March 07, 2017, 10:19:58 am by Gyro »
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Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #27 on: March 11, 2017, 05:54:18 pm »
The reference is on its way to one of the forum members in Netherlands, anybody else would like to be next to use/measure it?

Cheers

Alex
 

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Re: LT1021CMH based mini-reference
« Reply #28 on: March 16, 2017, 04:26:36 pm »
Quote
The reference is on its way to one of the forum members in Netherlands

That is me and I just picked it up today.  :)

Two questions for Alex:
  • Did you calibrate at 23°C or another temperature?
  • Is R5 (200k) a low tc resistor, I saw it has quite some impact when temperature changes?
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Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #29 on: March 16, 2017, 05:10:04 pm »
Quote
The reference is on its way to one of the forum members in Netherlands

That is me and I just picked it up today.  :)

Two questions for Alex:
  • Did you calibrate at 23°C or another temperature?
  • Is R5 (200k) a low tc resistor, I saw it has quite some impact when temperature changes?

1) Yes, 23-24C ambient. It should be written on the label.

2) 200K is MELF 0.1% , ± 15ppm/°C . It should not have any noticeable influence on the output  v temperature. The temperature compensating diodes are right next to it though.

Cheers

Alex
« Last Edit: March 16, 2017, 05:20:11 pm by Alex Nikitin »
 

Offline SvanGool

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Re: LT1021CMH based mini-reference
« Reply #30 on: March 17, 2017, 12:49:10 pm »
I received and unpacked it, thanks a lot Alex !

I did some first experiments with the traveling standard with my HP 34401A (close to 1 year cal), Alex used a HP 3458A 002 for measuring the travelling standard, before sending it.

Questions popping up, I am trying to imagine the possibilities of this travelling standard and I'm still learning:
  • What does it mean if my HP 34401A is displaying 10.00038k (23C) when the travelling reference has 10.00045k on the label? Is this HP 34401A 10k range at least 10ppm (HP 3458A 002 accuracy) + 25ppm (0.0020% + 0.0005%, HP 34401A 24h accuracy) + 3ppm (travelling standard 1ppm noise + 2ppm 1C temp. accuracy) + 7 ppm (difference in meter readings) = +45/-31 ppm accurate  for the next 24 hours?
  • Would it mean, that if I would calibrate (assuming the travelling standard was stable since its first check with the HP 3458A 002) the HP 34401A with the travelling standards 10K and enter 10.00045 as calibration value, in that range, that the HP 34401A would have a minimum accuracy, for that 10k range, of 10ppm (HP 3458A 002 accuracy) + 25ppm (0.0020% + 0.0005%, HP 34401A 24h accuracy) + 3ppm (travelling standard 1ppm noise + 2ppm 1C temp. accuracy)= 38 ppm for the next 24 hours, in stead of the current 110 ppm (HP 34401A 1 Year 23C+/-5C accuracy)-25 ppm(24h 23C+/-1C ) = 85 ppm more worse minimum accuracy I have now?
  • What would this mean for the HP 34401A 90 days and 1 year accuracy after 24 hours and 90 days, is it correct that e.g. the 1 year accuracy would become 110+10+3=123 ppm in stead of the 110ppm when I would officially re-calibrate the unit? So the price of using the traveling standard (in stead of officially calibrating) would be 13ppm for the involved ranges, but the calibration times would be reset again, for those ranges.
Of course (for now when we don't know the exact behavior yet of the traveling standard) I would have to do the above exercise with my own LTC1021 voltage reference, VHP202Z 10K000 0.1% resistor and VHP202Z 1K0000 0.05% resistor, that I would measure simultaneously and would use those ones for calibrating when Alex has verified the standard completely again, on return. To mitigate the risk that I would ruin my current calibration, for those ranges, when the standard seems not to be stable upon return, assuming that my own references and meter have small aging drifts meanwhile.
« Last Edit: March 17, 2017, 12:51:21 pm by SvanGool »
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Offline ap

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Re: LT1021CMH based mini-reference
« Reply #31 on: March 17, 2017, 03:02:38 pm »
Without having verified the detail ppm levels you state for each of the meters and cases, your logic is right. If you have a travelling standard with a certain total uncertainty (its cal value uncertainty, its possible temperature drift error, its aging related drift, anything else such as e.g. noise from surrounding; you need to establish all that), then you can use this reference to calibrate your 34401, and going from there, t0 starts again for your 34401. The uncertainty of that cal resistor adds to the time-depending uncertainties of the 34401.
Be carefull when establishing the basic uncertainty of the resistor (you say 10ppm). The 3458A opt 002, btw, is no better doing resistance measurements than a standard 3458A. The 1 year 3458A uncertainty would be 10+0.5+3ppm absolute, if a standard cal was done as per cal manual of Keysight. They do have calibrations that are more precise than the 3ppm though. But if not done at Keysight, it may as well be worse. I have seen people calibrating a 3458A with a Fluke 5500...
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Offline lars

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Re: LT1021CMH based mini-reference
« Reply #32 on: March 17, 2017, 05:56:23 pm »
Hello Alex,

I like your small box. Very clever use of the 10+1.111k with the switch! Even if I prefer NTC compensation,  diodes also works very well ;)
Your idea to send it around to get statistics is very good I think. Guess I should PM you.

Hope the discussion on uncertainty will give good answers. That is one of the most interesting things for me. Having no volt nut friends nearby or access to sufficient good calibrated equipment getting low uncertainty is a problem for me (and many others).

In December I think I wrote a long post in the Calibration club thread but hesitated to send it. TiN´s questions (provocation) about uncertainty really is important. Using GUM (Guide to Uncertainty of Measurements) for DIY is probably as useful as for my professional work, but how to get statistics???

As far as I understand from my professional work: When I send eg a 34401 for calibration the uncertainty for the next 1 year will be the specification assuming the calibration lab says "pass"! An interesting discussion I have had with myself for my hobby is what say 34401 10k resistance that is off 7ppm at latest calibration and the last years have been say 10, 4, 15ppm. Can I conclude something?? (Of course I have characterized the aging, temperature and humidity sensitivity (takes long time) :)

Lars
 

Offline Kleinstein

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Re: LT1021CMH based mini-reference
« Reply #33 on: March 17, 2017, 06:29:05 pm »
With many parts the drift follows a simple curve, often getting slower the older the part and moving in one direction. With some parts (e.g. voltage ref. chips) it is even known from experience in which direction and about as fast they usually drift.  With high end parts, there is however the problem, that the readings during calibration also has some uncertainty and this may be more like random scattering (if it was a known trend, they should have corrected it). So you instrument history reflects both the instrument aging and the scattering and maybe drift of the calibration lab(s).

For a meter send in to calibration, one has to distinguish between an calibration with adjustment and a pure check / reading. You only get the tighter short time specs if there was an adjustment or if you use the actual readings during calibration for correction. The direct reading from the display are not getting better from just a calibration that says still in specs (which?) without an adjustment.

With some instruments (especially high end ones) it is also that the quality level of calibration can make a difference - not every calibration will bring you back to the stated short time specs.
 

Offline SvanGool

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Re: LT1021CMH based mini-reference
« Reply #34 on: March 28, 2017, 12:36:31 pm »
I finished my measurements on Alex's LT1021CMH based "Travelling reference":

Equipment used:
  • 6.5 Digit multimeter HP34401A:
    • Last calibration: Dec 2014 (16 months over 1 year calibration accuracy)
    • Settings: 10GOhm DCV input imp., 100PLC, manual range, 4-wire resistance measurement
    • Specified accuracy DCV  10.00000 V:           40 ppm (1 yr)
    • Specified accuracy DCV  1.000000 V:           47 ppm (1 yr)
    • Specified accuracy Res. 10.00000 KOhm:  110 ppm (1 yr)
    • Specified accuracy Res. 1.000000 KOhm:  100 ppm (1 yr)
  • Oregon temperature meter TWR800: accuracy 0.5°C
  • Racal Dana 9232 Lineair Laboratory Power Supply:
    • Output voltage: 15.16 V
    • Load regulation: <0.01%
    • Ripple and noise: < 1 mV
    • Output impedance: <5 mOhm @ 1 kHz
Result:
  • 10 VDC:    09.99999 V (@23.3 °C), HP3458A calibration: 10.00000 V, difference -1 PPM
  •   1 VDC:    1.000033 V (@23.3 °C), HP3458A calibration:   1.00004 V, difference -2 .. -12 PPM
  • 10 KOhm: 10.00037 K (@23.5 °C), HP3458A calibration: 10.00045 K, difference -8 PPM
  •   1 KOhm: 1.000093 K (@23.5 °C). HP3458A calibration:   1.00010 K, difference -2 .. -12 PPM

Recommendations:
  • Also specify the calibration for a lower temperature (e.g. 20°C), it was difficult to reach 23 °C in the cold North  :).
  • Assess why it was not possible to get a stable 6.5 digit reading for the 1.000000 VDC and 1.000000 KOhm ranges on the HP3458A (on the HP34401A on "slow 6 digit", it was no problem).
  • Consider to include wiring, to exclude measurement error addition by the wiring.

Conclusion:

if Alex verifies the calibration still to be intact on return of the reference at his place, it proves that the reference is behaving excellent and I can conclude that the accuracy of my equipment would be within 124 ppm or less, for these ranges again for the next year, if I would calibrate it now (see also my previous posting).

I find this a very good result and it looks very promising for achieving the goal of this travelling standard.
Thanks a lot Alex, very good job!

Large fast picture of measurements.

« Last Edit: March 28, 2017, 12:43:50 pm by SvanGool »
# Don't hurry, the past will wait. #
 
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Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #35 on: March 28, 2017, 12:49:45 pm »
Thank you, good results!

Cheers

Alex
 

Offline Squantor

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Re: LT1021CMH based mini-reference
« Reply #36 on: April 02, 2017, 02:24:47 pm »
Hello Alex,

I am measuring the traveling standard as we speak. I am doing measurement runs but I am yet to bring my logging facility up.

I am testing with the following requipment: HP34401A, Two Keithley 2700's and a Keithley 2000. Too bad all their calibration statuses are unknown. So I have no idea what my contribution will be, maybe just academic interest :). I am measuring everything in my server room where it is a balmy 26 degrees centigrade, this is measured with a Klockis Ikea multifunctional clock, alarm, timer, temperature measurement thingy.

More information coming up.
 
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Offline The Soulman

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Re: LT1021CMH based mini-reference
« Reply #37 on: April 19, 2017, 08:51:15 pm »
How is the reference doing?
I'm interested in the drift caused by shipping, temperature changes, etc.
Only Alex can tell...
 

Offline Squantor

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Re: LT1021CMH based mini-reference
« Reply #38 on: April 20, 2017, 07:15:31 am »
I was really busy at work and other private matters. While measuring with my hp34401 calibration date unknown I noticed at 23C it was spot on with the reference! Very impressive! The cables that SvanGool made worked very well too. Did some quick tests with thermal EMF's with my recently repaired hp419a. It was about 200nV but not logged it for a longer period. I wanted to compare it to a battery of keithley 2002's that we have lying around but I could not find time due to overtime I have to put in these weeks.

I will arrange with SvanGool to return the reference and first work on my own measurement setup to enable automated measuring and make a few extra references based on this design. Then if Alex is willing reship it to me to compare and measure again, maybe with the keithley 2002's from work.
 
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Offline SvanGool

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Re: LT1021CMH based mini-reference
« Reply #39 on: May 06, 2017, 02:57:10 pm »
Hello,

I got the "Alex" LTC1021CMH reference back from Squantor and measured again with the same setup (@23.4 °C, 15.16V input, HP34401A 10GOhm DCV input imp., 100PLC, manual range, 4-wire resistance measurement)
as here: https://www.eevblog.com/forum/metrology/lt1021cmh-based-mini-reference/msg1172332/#msg1172332 after three hours warming up and same cabling.

The results, 5 weeks after the first measurement:
  • 10 VDC:    10.00001 V, +2 PPM on first measurement,         +1 PPM HP3458A
  •   1 VDC:    1.000033 V,   0 PPM on first measurement, -2 .. -12 PPM HP3458A
  • 10 KOhm: 10.00032 K,  -5 PPM on first measurement,         -13 PPM HP3458A
  •   1 KOhm: 1.000089 K,  -4 PPM on first measurement, -6 .. -16 PPM HP3458A

Still not bad at all.

I will now send the unit back to Alex in the UK, who will get his (re-calibrated ?) HP3458A also back this week  :-DMM
« Last Edit: June 25, 2017, 09:19:15 am by SvanGool »
# Don't hurry, the past will wait. #
 
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Offline The Soulman

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Re: LT1021CMH based mini-reference
« Reply #40 on: June 25, 2017, 05:05:26 pm »
And?  :popcorn:
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #41 on: June 25, 2017, 06:46:23 pm »
And?  :popcorn:

The reference is not back to me yet.

Cheers

Alex
 

Offline SvanGool

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Re: LT1021CMH based mini-reference
« Reply #42 on: June 25, 2017, 07:19:33 pm »
But it will be this week  :)

I kept it to check also a HP3457A, I just repaired, which took a bit longer then expected, the last results:
  • HP34401A (last calibration Dec 2014):
    • @24.1 °C: 10.00005 V
    • @24.1 °C: 1.000041 V
    • @24.1 °C: 10.00023 K
    • @24.1 °C: 1.000081 K
  • HP3457A (last calibration Dec 2013):
    • @23.7 °C: 10.00023 V
    • @23.7 °C: 1.000047 V
    • @23.8 °C: 10.00047 K
    • @23.8 °C: 1.000084 K

Comment: the HP3457A has a nonadjustable 10 MOhm input impedance on the >=10V range and >10GOhm on the <10V range. On the HP34401A I used the >10 GOhm setting on all ranges.
I'm curious for your HP3458A results.
# Don't hurry, the past will wait. #
 

Offline The Soulman

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Re: LT1021CMH based mini-reference
« Reply #43 on: June 25, 2017, 08:13:19 pm »
Thanks, looks like this little reference is holding up pretty well.
I'm also interested to see the results on the 3458, but is has to cross the pond first...
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #44 on: June 25, 2017, 08:28:30 pm »
Comment: the HP3457A has a nonadjustable 10 MOhm input impedance on the >=10V range and >10GOhm on the <10V range. On the HP34401A I used the >10 GOhm setting on all ranges.
I'm curious for your HP3458A results.

Thank you. In this case the input impedance at 10V does not matter, as the output impedance at 10V output is a fraction of an Ohm, and at 1V output the output impedance 1K, however both meters are at a high impedance input at that range.

Cheers

Alex
 

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Re: LT1021CMH based mini-reference
« Reply #45 on: June 29, 2017, 10:45:52 am »
Yesterday I've received the reference back and today took it to the lab and after 2h warm-up measured it with the freshly calibrated (9 May 2017) HP3458A Opt 002 (after ACAL ALL):
Here are the results @24C:

10.000043V
1.000044V
10.00045K
1.000096K

The wiring offset was less than 0.5uV. The popcorn noise "jumps" in the voltage are about 0.5ppm, as before.

It looks like the reference drifted about +4ppm on 10V and 1V, with no visible drift on the resistance values (less than 1ppm) over the time period of about four months and some international travel  :-+ .

The calibration results for the HP3458A show +1ppm error on 10V and 1V DC gain.

Cheers

Alex
« Last Edit: June 29, 2017, 11:29:14 am by Alex Nikitin »
 
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Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #46 on: July 03, 2017, 06:44:02 pm »
Well, the 1010B reference is now available on loan to the forum members in the UK and Europe, the only conditions are to pay postage and to return the reference in a good state in 2-3 weeks time.

The reference provides stable 10V, 1V, 10K and 1K - measured with better than 10ppm accuracy. In the UK I can provide a good 24V DC wall-wart supply, otherwise a reasonable quality 15-30V DC supply is required.

Cheers

Alex

P.S. Update - the reference is booked for the next two weeks or so. Please PM me if you would like to join the queue  ;) .
« Last Edit: July 03, 2017, 09:32:46 pm by Alex Nikitin »
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #47 on: July 26, 2017, 09:14:07 am »
Another update after the reference has traveled to Italy and back. Here are the measurements results, using the same HP3458A Opt 002 after ACAL. The lab temperature was 24.5C.

10.000040V
1.000043V
10.00044K
1.000095K

The reference is again available.

Cheers

Alex
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #48 on: July 26, 2017, 03:40:39 pm »
Here is a 3 hour run today in the lab for 10V output. 1ppm/div vertical scale

Cheers

Alex
 
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Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #49 on: August 07, 2017, 10:50:31 am »
The reference is booked for another two weeks.

Cheers

Alex
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #50 on: November 03, 2017, 11:39:22 am »
The 1010B reference is back in my hands and after a 2 hours warm up at 24C in the lab the HP3458A (after ACAL ALL) measures 10.00002V on 10V output. I will log the 1010B over the weekend and post a graph next week, together with the resistance measurements and 1V output value. The residual offset in the measuring system is less than 0.5uV.

The reference will be available again at the end of next week.

Cheers

Alex
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #51 on: November 06, 2017, 04:32:58 pm »
The voltage readings are about -1ppm from what I've measured in August at the same temperature, both for 10V and 1V outputs. I suppose it is stable enough (the popcorn noise is still about 1ppm p-p) .

Cheers

Alex
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #52 on: November 09, 2017, 12:16:35 pm »
The latest measurements at 24C :

10.00002V
1.000041V
10.00044K
1.00010K

The reference is again available.

Cheers

Alex
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #53 on: November 10, 2017, 12:01:06 pm »
Here is the overnight measurement on 10V output with the temperature of the unit measured by a thermocouple. The tempco in this range of temperatures is about +1.25ppm/C .

Cheers

Alex

 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #54 on: March 01, 2018, 03:46:14 pm »
The 1010B is back in my lab after another travel and again available. The measured values are holding inside +/- 5ppm for last six months or so, measured by the same HP3458A Opt 002.

Cheers

Alex
 

Offline TheUnnamedNewbie

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Re: LT1021CMH based mini-reference
« Reply #55 on: March 13, 2018, 09:38:16 am »
The reference just arrived in Belguim! I'll maybe shoot some video of it, unless you prefer me not to.
The best part about magic is when it stops being magic and becomes science instead
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #56 on: March 13, 2018, 10:43:36 am »
The reference just arrived in Belguim! I'll maybe shoot some video of it, unless you prefer me not to.

No problem with a video as long as you don't open the reference, it will ruin the calibration.

Cheers

Alex

 

Offline TheUnnamedNewbie

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Re: LT1021CMH based mini-reference
« Reply #57 on: March 13, 2018, 10:48:26 am »
The reference just arrived in Belguim! I'll maybe shoot some video of it, unless you prefer me not to.

No problem with a video as long as you don't open the reference, it will ruin the calibration.

Cheers

Alex



Ofcourse! I was not planning on opening it because of that reason.

Thanks again for making this possible. Seeing my Keithley read 10.00007 has given me a lot more confidence in future measurements. Will start logging tonight.
The best part about magic is when it stops being magic and becomes science instead
 
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Offline TheUnnamedNewbie

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Re: LT1021CMH based mini-reference
« Reply #58 on: March 24, 2018, 09:57:14 am »
Had a quite busy week so unfortunatly couldn't get as much data as I was hoping to, and haven't been able to make it to the post on Friday. However, I'll send it back on Monday or Tuesday.
Sorry for going over my 2 week slot!

The best part about magic is when it stops being magic and becomes science instead
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #59 on: March 24, 2018, 12:22:12 pm »
Had a quite busy week so unfortunatly couldn't get as much data as I was hoping to, and haven't been able to make it to the post on Friday. However, I'll send it back on Monday or Tuesday.
Sorry for going over my 2 week slot!

Not a problem whatsoever, take your time, another week if you need it, there is no queue  at the moment!

Cheers

Alex
 

Offline guenthert

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Re: LT1021CMH based mini-reference
« Reply #60 on: March 31, 2018, 12:09:30 pm »
My HP34401 showed 10.00000V (+1/-2 over N=100, NLPC=10) at about 23°C (can't currently measure temperature with much confidence), which is quite astonishing given that it has not been calibrated in the last two years (if ever).

My Datron Wavetek 1271 showed between 9.999,9752 to 9.999,9766V (min, max each average over 10).  Not sure, whether the variance is due to low frequency noise of the DUT or the one of the internal reference or some draft across the contacts.  My home 'lab' is not suitable for sub-ppm measurements.  This result too is IMHO quite remarkable, given that the instrument was calibrated in 1993 (or at least nobody since bothered to update the calibration time stamp in the NVRAM).

I think this goes to show that with some luck old instruments can be very stable and much more accurate then the nominal specification suggests.
 

Offline ap

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Re: LT1021CMH based mini-reference
« Reply #61 on: March 31, 2018, 12:44:36 pm »
I think this goes to show that with some luck old instruments can be very stable and much more accurate then the nominal specification suggests.

There is a reason why many cal labs prefer old, aged precision instruments, such as the 3458A, 732 and 1281 (anyway not available new anymore) over new ones
Metrology and test gear and other stuff: www.ab-precision.com
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #62 on: May 25, 2018, 07:57:18 am »
The 1010B is back in my lab after another travel to Europe and again available.

It looks like my little unit holds the values really well, the difference from the values I've measured a month ago is below what I can measure reliably (HP3458A measures all four values at less than +/-2ppm difference).

Cheers

Alex
 

Offline borghese

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Re: LT1021CMH based mini-reference
« Reply #63 on: May 25, 2018, 09:47:58 pm »
I was the last user of the reference, and I used it to calibrate my two HP3456, previous calibration date unknown; surprisingly they were out of tolerance less than 20ppm; excellent and easy to repair instruments.
Alex, maybe you could add the resistance value of 1.111k resistor so to have six digits of resolution; I estimated 1111.210 ohm
Thanks again Alex
Cheers
Cheers
Borghese
 

Offline Alex Nikitin

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Re: LT1021CMH based mini-reference
« Reply #64 on: August 09, 2018, 09:51:07 am »
The 1010B is back in the lab after a trip to Scotland, re-measured (with essentially the same results) and available again.

Cheers

Alex
 

Offline stijena1973

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Re: LT1021CMH based mini-reference
« Reply #65 on: May 31, 2019, 07:56:29 am »
Are there some new data on the mini reference?

Also did You keep track on resistor ratio separately from the reference voltage?

If You did then You probably have some statistical data on the quality of the resistors  internal to the chip...?
 


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