USA Cal Club: Round 2

[Echo88]

Id like to participate in the EUCalClub as well. 

[hwj-d]

It would be a good topic for stuttgart to organize an eu-calclub.

[mimmus78]

EUCalClub consider me in

[hwj-d]

See https://www.eevblog.com/forum/metrology/eu-calclub/msg2410806/#msg2410806

 

[vindoline]

As HJW-d announced, the USA CalClub reference has arrived back in the USA! The package arrived yesterday and I haven't had time to do anything but power it up. It's looking good so far and I'll monitor it for 24 hrs or so. I'm still expecting the other new reference from TiN. My current thinking is to wait for both references so we can send them around together. I expect most people would like to be able to use and compare the two. 

[bitseeker]

Ok, now it's time to lift the veil, what I did with the lid.

Now there are two precise resistors 1k and 10k under it, with the ability to take a real 4-wire measurement, but without changing the dimensions of the tekko housing. I put little but precise 4-wire measurement cabels in the package, hoping that was a good and usefull idea. Some pictures:

(edit translation)

I like it!

It's also exciting to see interest spring up for an EU Cal Club. Thanks, HW!

[bitseeker]

Some info from Dr. Frank regarding LTZ references (from the new EU Cal Club thread):

Hello,
we may discuss the stability problems in depth on the Metrology Meeting.
I've had bilateral exchanges of LTZ references and resistors already with a number of volt-nuts.

I usually have sent one LTZ1000, un-powered, and one VHP202Z, 10k, with built-in temperature sensor, allowing precise resistance calculation over temperature.

That fits in a small DHL packet at low cost.

Transfer is not possible during winter, as the LTZ especially at temperatures < 0°C shows hysteresis of several + ppm, but during spring .. harvest, it will retrace its nominal value within < 0.5ppm.

Round trip measurements are necessary to confirm successful transfers, as well as systematic data evaluation.

[CatalinaWOW]

I would think this would threaten transfer year round as most shipping methods have an air transport leg, and the cargo hold can easily reach this temperature.

[nikonoid]

Shipping powered reference is more expensive as it adds weight, size and requires quicker shipments.

What about doing hysteresis recovery procedure after shipping, like in Pickering patent? It has expired, I believe, so free to be used.

This way we can ship references unpowered year round.

[hwj-d]

CatalinaWOW

You'd think. In reality we now have a LTZ1000 Ref, which has already been transported twice across the "big pond". Now it depends on the extent to which the measured values actually differ. Certainly also the demand of accuracy plays a role.

 

[Dr. Frank]

Shipping powered reference is more expensive as it adds weight, size and requires quicker shipments.

What about doing hysteresis recovery procedure after shipping, like in Pickering patent? It has expired, I believe, so free to be used.

This way we can ship references un-powered year round.

Yes, the LTZ 1000 can be recovered by cycling the temperature, following the Pickering Patent. For personal use, this method has always been 'free'.

I assume, that this method did never work properly in the Datron 7000 application, as its oven temperature is described as being 45°C, and symmetric temperature sweeps of +/- 40°C, as described in this patent US 5369245 then would never be achievable at usual room temperatures.

The LTZ 1000 shows an asymmetric hysteresis behavior, though.
The hysteresis at low temperatures is bigger, than at higher temperatures. This is also indicated inside a paper about the Datron 7000.

Therefore, such a technique has to be run kind of asymmetrically, and the correct procedure (contrasting the original patent) has to be evaluated.

Otherwise, a temperature logger could be added to the packet, and a mandatory round-trip-measurement might detect hysteric shifts, that is to consequently measure the voltage before and after the travel at the same laboratory.

Frank 

PS: demonstration of this problem, with Pickering document:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1882325/#msg1882325

[TiN]

I'm sorry about all the delays, reference module for US Cal Club is shipped today.
Initial calibration data and measured stats:



My lab will get new SI Volt (doing JJA cal for my refs soon), so I will be able to confirm/deny the absolute uncertainty of my setup. Two 3458A and K2002 were used to perform all measurements.



Output provided by two Pomona 3770 low thermal EMF posts. Input power and auxilary circuitry using circular shielded connector (fanout cable included in package).

Power requirements : +11 to +15VDC, -2 to -15VDC, current limited at least 80mA. Power input is protected by 125mA fuse and TVS.
Optional PCB temperature sensor : MAX6610 (U4 on PCB), with isolated power +5V.
Optional ROM data storage: I2C EEPROM with isolated +3.3V power (ground shared with temp sensor).
Calibration data provided for temperature range +20 °C to +50 °C



Chip is LTZ1000A, setpoint 12.5/1K TCC VHP200 divider. Onboard regulator for LTZ1000A section is LT3042. Schematics is otherwise same as Linear's datasheet.



Output amplifier is Analog ADA4522-2 chopper, together with bipolar transistor driver. Reference can survive short at the output for indefinite time.
FX module output driver can sink or source up to 20mA, but here module cannot maintain output accuracy because kelvin sense lines are not routed to the binding posts.

Inline fuses are hidden in yellow tube. Suggest not to break them
Just realized, somebody melted few film cap casing 



Looking forward to see results on this by US members. I would recommend not to open the box to avoid magic ppms leaking out 

[bitseeker]

Exciting! Definitely worth the wait. Thank you, TiN! I promise not to let any ppms escape.

[hwj-d]

 

Ok, I'll sign in again...     

[hwj-d]

To provide it against high import customs, declare it as 10$ selfmade electronics scrap ...

        

(edit: excuse my joke TiN, the reference is overwhelmingly well done)

[vindoline]

reference module for US Cal Club is shipped today. . . .
Looking forward to see results on this by US members. I would recommend not to open the box to avoid magic ppms leaking out 

Wow! Just, wow. This is going to be exciting! A huge 'thank you' TiN!

[JBeale]

Just read through the xdevs.com/article/792x/ page about that reference board; what a project!  Impressively photographed as well. I'm curious how the PCB is held mechanically inside the metal case, assuming it does not simply float. Is there some compression gasket around the edge?

[TiN]

It is kinda floating, suspended in foam and pads. Rigid mechanical coupling to metal case could translate into board stress and cause problems.
No gasket around the edge, it's not hermetically sealed.

[JBeale]

Thanks. It looks like you leave nothing to chance so maybe you have measured it already, I'm just curious if the foam may have a measurable conductance (especially if ambient humidity rises) if it contacts any traces, untented vias etc? Normally I would guess "many megohms" and not consider it further, but normally I have never encountered an analog circuit which is measured at the sub-ppm level!

[vindoline]

Alien technology has landed in upstate NY! A huge thanks to Cellularmitosis for starting the USA Cal Club and providing so much of its initial enthusiasm, momentum, and the references! Also I can't thank TiN enough for his donation of an FX reference. I feel like our club is now world-class! hjw-d also donated precision resistors and Kelvin connections - thank you!

Compared to the more experienced and knowledgable participants, I'm just a beginning volt-nut. My "best" meter is an HP3456A (6.5 digit) I also have a Keithly 196 and a recently acquired Fluke 8506A. Also, my budget is more limited - a 3458A is not to be considered! I'm adding a donation of a rugged Nanuk shipping case for the references and a DIY Prologix style GPIB-USB adapter. Thanks to forum member WaveyDipole for re-writing the firmware! The GPIB adapter works great in my hands. I hope people find it useful.

The full kit contains:

An FX 10 volt ref and its power input cable
A PX 7 volt ref with a variety of input and output connectors
A 12 volt regulated power supply for the PX
Precision Vishay 1K and 10K resistors along with a custom Kelvin connection cable
An Arduino based temperature and humidity monitor with sensor cable
A USB-GPIB adapter with WavyDipole's AR488 firmware
Two blank USB-GPIB PC boards - if anyone decides they want to build and keep one!

The Gear ships out Monday morning!

[hwj-d]

Hi vindoline,

have you measured the PX? Because it was going abroud/oversea, had the ref relevant deviations from my measurements in the EU?

Background, see the discussion to the EU-Calclub
https://www.eevblog.com/forum/metrology/eu-calclub/msg2458485/#msg2458485
(and following)

Thanks a lot,
H.-W.

[Conrad Hoffman]

Looks great, can't wait to see it. My meters are also just 6.5 digit, but I've got three Fluke 731 references that I inter-compare, plus a few others. I can do good differential measurements, but haven't had a proper cal in many years. Probably still within 50 ppm or so. My meters are on a Prologix GPIB controller, but anything else can be plugged in as well. Subterranean lair/lab is usually cool, but very stable.

[vindoline]

hwj-d, yes. I measured the PX reference before and after I calibrated my HP346A with TiN's FX. I'll post the data soon!

[bitseeker]

I've got my eyes peeled for the new cal package. Thanks, vindoline, for putting it all together and taking the lead. Of course, I second all the thanks that you itemized, as well.

With regard to meters, my highest-resolution ones are also 6.5 digits. I'm also a volt-noob, having only started my metrology experience with this club. So, no worries.

One question about your HP meter. It seems to have lost a digit somewhere. So far, it's been referred to as a 345 and a 346. Perhaps by merging what we know thus far about it, might its true model be 3456?

[vindoline]

All these model numbers make my old eyes spin! It's an HP 3456A 6.5 digit meter. It's great!