Electronics > Metrology

USA Cal Club: Round 2

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Ok, enough delays!  Time to start round 2 of the cal club.   :scared:

This round will use a 7V LTZ1000 board (PX-ref v2.4).

Good things about this round / improvements over last round:

* The ref is an LTZ1000, woohoo!  :-+
* This particular LTZ chip shows lower-than-typical 1/f noise (see date code 9811 in this page)
* Reverse polarity protection (schottky on positive input)
* Output short protection (LTC2057 buffer)
* Standardized on a common set of connectors
* Low EMI sensitivity (ferrite common-mode chokes on supply and output)
* Steel TEKO case (provides some amount of magnetic shielding)
* Star-pattern shipping (should detect shipping-induced hysteresis)
* Light weight package (about 9 oz.) == cheap shipping (about $4)
Things which aren't ideal about this round:

* Due to a mishap I lost the ~3 months of ageing on the LTZ which I had intended to use for this round  :-BROKE
* ...which means I also lost Doug's (voltagestandard.com) measurement using his calibrated 3458A  :palm:
* This LTZ has only been ageing for a week (but has only moved 1 count on a Keithley 2015 in that time)
* Tempco of the ref hasn't been measured / adjusted via the 400k resistor
But you know what, it's never going to be perfect -- there will always be more tweaks to be made and work to be done.  Time to get the show on the road!


This time, we'll use a star-pattern: the ref will get shipped back to me at each leg of the round.  Hopefully we can use this technique to detect any hysteresis / drift picked up during shipping.

Shipping is going to be pretty cheap (about $4), so here's how I'll approach it: I'll include a return-shipping label for convenience, and if you want to drop me a few bucks in paypal, that's great.  If not, no big deal -- the shipping is going to be a relatively small amount of money anyway, so I'm not worried about it.

Certainly, if you have calibrated gear, I don't think you should worry about shipping -- you're doing the rest of us a big favor just by participating  :-+


I'm not sure I have a complete list of everyone who wanted to participate in this round, so please chime in if you don't see your name!

* Muxr
* technogeeky
* VintageNut
* vindoline
* Conrad Hoffman
* dr.diesel
* CalMachine
* CatalinaWOW
* kj7e
* bitseeker
* RandallMcRee
* nikonoid
* martinr33
* orin
* Vacuuminded
* Vgkid
* MaxFrister
* SirAlucard
* flittle
* hwj-d
* rhb
* ArthurDent
* edavid
* GEOelectronics
* Svgeesus
...and I think I might be sending the ref to a few surprise guests internationally as a "thank you" for being excellent contributors to the forum  :-+

I think I'll choose the shipping order using a random sort, which is equally fair / unfair for everyone  ::)

Some additional detail about the ref:

Supply voltage:

Valid supply voltage range is from about 9.1V (the LTZ falls out of temperature regulation below this point) to 15V (max specified supply voltage for the LT1013).  Let's standardize on 12V for this round.

Supply connection:

The ref has a 2-pin 0.1" female header socket for the supply connection, and will ship with two "pigtails": one with banana plugs and another with croc-clips.

The pigtail connector has been colored silver on the positive lead.  The CAT5 wire is solid-color for negative and white/stripped for positive.  The banana plug heat-shrink is yellow for positive and black for negative.  The croc clips are red for positive and green for negative.

Output connection:

The output pigtail connection is made using a paired set of Mil-Max machine pin headers with solder-cup termination.  These are gold-plated beryllium copper.  With a wrap of tissue, etc, these should track thermally and present minimal thermal EMF.



Two pigtails will be supplied for the output connection: one with a Pomona 4892 dual banana plug (gold-plated beryllium copper spring, brass body), and one with bare copper wires.


Thanks for putting this together and kicking off a new round. Looking forward to it. What all do you want us to capture/upload/post about the ref when we receive it?


By the way: with single supply the LT1013 will go up to 30V so it is not the limitation.

It would be also a good idea to put a voltage regulator directly to the cirquit so that everyone has the same voltage (since PSRR is not infinite).

Rhats why I always use a LT1763 based regulator in my cirquits either on board or also off board with the little single sided PCB that I have already shown.

With best regards


As much as possible, we should standardize our testing method.  ie polling frequency, instrument setup, log file format etc.

That would make it much easier to compare/analyze results.


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