PX Reference

[ap]

After burn in a couple of weeks, i need a calibration of one or some of them.
(as free as possible, except shipping costs of course.  )
Who can I address then, medium term, if possible in Germany or EU?
I know, maybe a difficult question...

Calibrating your LTZ reference after stabilization burn-in against a 3458A does not make much sense. A standard 3458A has a 1 year uncertainty of 8+ ppm, so effectively arround 10ppm. Your LTZ, if properly build and stabilized, should be arround 1 or 2 ppm pa. So if you e.g. do two consecutive CALs, 1 year appart, against calibrated 3458As in their one-year accuracy cycle, to evaluate the stability of your LTZ, you will know nothing. Any drift of your LTZ will be hidden in the 3458As' uncertainties. It deserves a much tighter cal. If you are ready with burn-in feel free to send me a PM.

[TiN]

I still hold KX project calibrations for willing participants, and to support community I can offer one time PX ref calibration (DCV value and tempco as received) too, at shipping cost. Calibration vs unknown history 3458A indeed does not provide uncertainty better than 10ppm, but verified known stable 3458A can do 4ppm without much problem. Both of my 3458A drifted <2ppm from last year, however I'd stress out this is NOT an official or legally traceable calibration, and my meters are not standard stock boxes.

I do my verifications for 10V range in my homelab using bank of 6 x LTZ1000 references and 4 x LTZ1000A-based DMMs versus annually calibrated 732B (unc 0.55ppm). So my safe lab guesstimate is 4ppm/annual, 2 ppm if you hit a lucky day.  . Good verified stable 3458A is great to do DCV-DCV transfers over a day or even week with sub-ppm uncertainty (I have one verified vs 732B).

[cellularmitosis]

Very generous TiN!  Time to assemble my KX board!

[hwj-d]

@ap, @TiN, @Echo88, @cellular and all the others here and over the world,

what can i say now,

here with you, i feel in safe hands. 

After burn in, i will PM you.
Maybe one goes to ap, one to TiN, if i know, whether there are import export customs problems or not.

Thanks so much to all

[eurofox]

Hi PX builders,

I would like to get your input, what do you think about my measures taken on a Keithley 7 1/2 digit, 100 averages:

Max: 07.065917 V
Min: 07.065843 V

For me it does not look very stable 

eurofox

[hwj-d]

Hi PX builders,

I would like to get your input, what do you think about my measures taken on a Keithley 7 1/2 digit, 100 averages:

Max: 07.065917 V
Min: 07.065843 V

For me it does not look very stable 

eurofox

If you switch it on first time, the voltage drops. That's normal. Let it stabilize a couple of hours, days, weeks without turning it off. Don't connect chassis/PSU ground to measurement -Vz. Use a noiseless PSU. Watch the used current, that should be < 30mA (26-27mA).
€: Measure without greater ambient temperature fluctuations for the first time.
€€: Don't use clips, crokodiles etc. with measurement cables. Twist them.

 

[eurofox]

Hi PX builders,

I would like to get your input, what do you think about my measures taken on a Keithley 7 1/2 digit, 100 averages:

Max: 07.065917 V
Min: 07.065843 V

For me it does not look very stable 

eurofox

If you switch it on first time, the voltage drops. That's normal. Let it stabilize a couple of hours, days, weeks without turning it off. Don't connect chassis/PSU ground to measurement -Vz. Use a noiseless PSU. Watch the used current, that should be < 30mA (26-27mA).
€: Measure without greater ambient temperature fluctuations for the first time.
€€: Don't use clips, crokodiles etc. with measurement cables. Twist them.

 

It is on my lab desk not connected to ground, powered by an HP lineair power supply and use less than 30mA.
It is only powered for a few hours, have to build it into a "container" with a dedicated power supply.
I would like to add a opamp to raise the voltage to 10V.

eurofox

[cellularmitosis]

Hi PX builders,

I would like to get your input, what do you think about my measures taken on a Keithley 7 1/2 digit, 100 averages:

Max: 07.065917 V
Min: 07.065843 V

For me it does not look very stable 

eurofox

Hi eurofox,

I have found that my LTZ's have been more sensitive to EMI / waving my hand near the circuit, etc, than my LM399 circuits.

The most quiet results I have obtained so far were:

- With the LTZ board inside of an aluminum Hammond 1590B enclosure

- Measuring the difference between one LTZ and another

- With both LTZ's powered by independent batteries / regulators

I have other boards on-hand (a clone of Dr. Frank's board, and a KX board), but I have not assembled them yet (still characterizing resistors and I'd like to measure the 1/f noise of my LTZ's before soldering them in).  When I get those other boards assembled, I'll be able to compare the EMI / hand-waving sensitivity of the different board designs.

[d-smes]

I have found that my LTZ's have been more sensitive to EMI / waving my hand near the circuit, etc, than my LM399 circuits.

Why don't more folks pour a ground fill in their circuit board layouts and stitch them top to bottom with via holes to improve localized shielding against EMI?

[Dr. Frank]

Why don't folks use more of Andreas RF/EMC blocking capacitors?

Single sided PCB is also fully sufficient, but a Guard / shield enclosure required.

My 'new' circuits / assemblies are completely immune against common hand-waving, SMPSU, or mains disturbances.

Frank

[cellularmitosis]

I have found that my LTZ's have been more sensitive to EMI / waving my hand near the circuit, etc, than my LM399 circuits.

Why don't more folks pour a ground fill in their circuit board layouts and stitch them top to bottom with via holes to improve localized shielding against EMI?

You mean like this?

[hwj-d]

I have found that my LTZ's have been more sensitive to EMI / waving my hand near the circuit, etc, than my LM399 circuits.

Why don't more folks pour a ground fill in their circuit board layouts and stitch them top to bottom with via holes to improve localized shielding against EMI?

That's strange. I've build four PX'es now, and none has this EMI sensitiveness. See attached pictures. Nearby i'm designing/building a little compact 2x15V PSU. That's worstcase  for EMI, normaly. Simultaneously measurement with 10 PLC; 10 µV Y-Achsis.

[hwj-d]

You mean like this?

Does it go inside a TEKO 371

[cellularmitosis]

You mean like this?

Does it go inside a TEKO 371

Nope, a 1590B 

I should put a disclaimer: I haven't actually made nor tried that board yet, and it is also missing one of Andreas' capacitors (his C15, I think), so you'd have to bodge that in.

[hwj-d]

You mean like this?

Does it go inside a TEKO 371

Nope, a 1590B 

I should put a disclaimer: I haven't actually made nor tried that board yet, and it is also missing one of Andreas' capacitors (his C15, I think), so you'd have to bodge that in.

Don't be fooled.
Your PX V2.4 is very good, in my opinion.
These EMI issues must be due to external circumstances. 

[Kleinstein]

I have found that my LTZ's have been more sensitive to EMI / waving my hand near the circuit, etc, than my LM399 circuits.

Why don't more folks pour a ground fill in their circuit board layouts and stitch them top to bottom with via holes to improve localized shielding against EMI?

Ground fill is often a poor solution for precision circuits, as one looses the control over the ground connection. A ground plane can be low impedance, but not low enough when it comes to ppm range.

One might use an extra plane just for shielding, e.g. add an extra shield layer to an otherwise single sided layout.
Close to the LTZ1000 one may not want the extra thermal conduction everywhere, so it would end up with a circle around the LTZ without an shield.  One downside with partial shields is that they tend to concentrate interfering fields near the edge. So a partial shield might be worse than non at all.

[quarks]

After burn in a couple of weeks, i need a calibration of one or some of them.
(as free as possible, except shipping costs of course.  )
Who can I address then, medium term, if possible in Germany or EU?
I know, maybe a difficult question...

Thanks

because I caught a bad cold I am a little late, but feel free to contact me, if you need another meassurement of your LTZ1000A.
BTW very nice build, so thanks for sharing

[hwj-d]

Thank you very much for your offer, will come back to that after burn in a few weeks more. 

Get well. 

[cellularmitosis]

Version 2.4.1

Just a few trivial changes:

I found the TO-99 too difficult to solder, so I made the pads a bit larger.

I also added footprints for an input and output capacitor directly on-board (I had been mounting these caps across the binding posts).

https://oshpark.com/shared_projects/hUZKe65r

https://github.com/pepaslabs/px-ref/tree/master/kicad/releases/v2.4.1

[WillTurner]

@Cellular
  I wasn't quite sure where to put this, but since it's a derivative of your LTZ1000 symbol, I thought you'd most likely find it here.

  Below is a Kicad LTZ1000 schematic symbol broken into heater and zener elements. I'm planning on moving the schematic back to being closer to the reference circuit.

  Here is the heater.



  And here is the rest of the component.


Edit: inserted images inline.

[aronake]

For version 2.5 and 2.6 what connector is intended to be used for the two big areas of the PCB?

[cellularmitosis]

For version 2.5 and 2.6 what connector is intended to be used for the two big areas of the PCB?

ah, 2.5 and 2.6 were "beta" boards which happened at about the same time that my volt-nut disease went into remission.  They were both designed to fit in the next larger size of TEKO case.

The two big areas on the PCB are for the large tubular ferrite chokes as used in the cal club's px ref, but you can attach the chokes to the board instead of just stuffing them into the case.

If I recall, 2.5 was simply the 2.4 series but with the chokes on-board, and also a couple of footprints for larger 1uF red box wima caps on input and output.  I don't think I ever got around to populating one.

2.6 was an experimental board I made after getting my hands on some OHMTEK 132077 hermetic multi-resistor chips, which I probably found on taobao, and thought "I should build an LTZ around this".  I seem to recall it didn't work correctly, but I never got around to debugging it.

I've attached a photo from 2018.

edit: recalling a bit more of this now: the jumpers on 2.6 (at least in theory) allowed you to make many combinations of R4 and R5, thus dialing in different temperature set points.  I wrote a little script back then to spit out all of the combinations, which I just threw into a gist.

I doubt anyone could get their hands on any OHMTEK 132077 chips today, so that's a bit of a dead end.

[Grandchuck]

hey CM...nice to see you posting again!

[Conrad Hoffman]

CM, your projects make me feel better about mine. My interests fade in and out over several year cycles. Metrology for a while, photography for a while, health issues for a while, family issues for a while, 3d printing for a while, then around again. 

[cellularmitosis]

CM, your projects make me feel better about mine. My interests fade in and out over several year cycles. Metrology for a while, photography for a while, health issues for a while, family issues for a while, 3d printing for a while, then around again. 

Rock on, Conrad!  You've certainly been an inspiration to me.