[volt-nuts] Best reference after LTZ1000

Andrea Baldoni erm191ba3 at ermione.com
Tue Aug 24 22:43:17 UTC 2010


On Sun, Aug 22, 2010 at 01:37:11PM -0400, Marvin E. Gozum wrote:

> Yes, as for transfer reference, if you have access to a calibrated  
> reference you can adjust your 34401 too, you don't need such.  But, I  
> recall you mentioned earlier you didn't have a calibrated reference for 
> your precision DMM.  At least empirically, Geller's reference has been 

Unfortunately, I have it not.

Calibration of 34401A costs around 150EUR here. It's more than the cost of
the Geller's reference, but the full calibration could not be done with
just a 10V voltage source.

Anyway, could I trust that this little board, after a travel overseas,
would bring to me any precision? It has a trimmer on it. Better would have
been if he just measured the untrimmed output of the reference and noted
on paper, like the folks of HP do with their LTZ1000-based board...

But at this point he would just be selling me a measure, because the chip
itself cost around 10$ and it works without any external component...

> around since 2004, he now has longevity statistics on his side that his 
> board is a capable of at least a 1 month transfer of 10. 000 00 Vdc 
> reference from his lab to you, if so inclined. Malone doesn't detail much 
> on the site beyond the basic specs of the original chip.

How could the Geller's board be better than the chip over it?
If the chip itself is good enough to reach alone a stability worth to transfer
a calibration good enough for a 34401A, would be very interesting to simply
measure chips by putting them in a suitable ZIF socket, put a note on them,
and sell them as they are. No trimmer, no PCB, no resistors. If I could
claibrate a 34401A against a 10.00000V, I could calibrate without any
problem against a 10.12345V.

> Sorry for a reply delay, but I was intrigued enough to get one and  

I am just going abroad for a fair for a couple of weeks, so I will also reply
late.

> measure it as soon as possible, lest it drift!  Sure enough, under the 
> same temperature conditions, its accurate to my calibrated 8456A,  
> reading 10.000 00 Vdc.  I am now gathering stats on its performance.

You are doing an interesting work. Interesting also would be
to buy a barebone chip and measure it untrimmed.

> It is a bit unusual, but in the article he wrote for a hobbyist  
> magazine, detailing this device, he does describe that he didn't expect 
> this response either, from the chip.  But it seems the heater of the 399 
> responds in a way not well characterized, so he seized the moment.

I just read the patent. Substantially, what he patented is the fact he's using
the heater of a voltage reference of a LM399 kind as a sensing element, and
that the circuitry is composed by operational amplifiers, resistors, etc.

I never patented it, but once, while developing a low power switching supply,
I used a common house lamp bulb as a load.
Measuring the voltage on the lamp (the switching was a current source) I was
able to determine the wind around the bulb. I am not joking.
The lamp filament was kept just glowing red and bringing away heat from the
bulb made a noticeable change in his resistance.
The simple fact that an anemometer could also be done with a lamp bulb and
a circuit comprised of operational amplifiers, I think, is not the kind of
innovation that deserve a patent. The use of a lamp, or the use of a
heater of a voltage reference, would not make actual hot wind anemometers
any better :)

> don't think anyone who can afford a new HP 3458A to use as a hobby will 
> unlikely be making a living selling electronic kits.

I think you are right, maybe he's just making kits also for hobby.

Best regards,
Andrea Baldoni



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