[volt-nuts] Best reference after LTZ1000

[Marvin E. Gozum]

At 06:36 AM 8/16/2010, Andrea Baldoni wrote:
>On Sun, Aug 15, 2010 at 03:34:29PM -0400, Marvin E. Gozum wrote:
>
> > What do you think of Geller's work?  He uses the AD587 as a voltage
> > reference, and writes of results > = the AD specs.
>
>I think the same of voltagestandard.com. These boards adds nothing to the
>original chips they use (the chips are not selected)... they may
>eventually just degrade performance with layout/mechanical stresses/passive
>components.
>The calibration service they offer, because it is applied to this kind of
>references, is not useful as a "transfer" to anyone with already decent
>instruments (with better references inside).

Hello Andrea,

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 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.

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


> > Your need seems close to the principle used in his thermal anemometer,
> > which he patented.  IIRC, it measures temperature change as changes in
> > the stable voltage response of a reference, which is then proportionate
> > to air current.
>
>As far as I can see from the circuit, he uses that poor LM399 just as
>heater resistor and RTD. The reference diode is unconnected.
>The reference of the wheatstone bridge is the +15V power.
>
>I don't see what kind of principle he could have patented. Hot wire 
>anemometers
>are not a new and this is the worst one I could imagine.

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'm not so sure how the well it measures cfm, but the setup is so 
simple and cheap, one can easily breadboard the device and see of 
what value it is.


>Maybe he has tried to use the LM399 to sell voltage references, he has failed
>to obtain good results (it's not so easy to use as the AD587) and having
>already bought some (and probably having burned the diode...) he recycled them
>in this kit...
>Best regards,
>Andrea Baldoni

Its interesting this has come up for his services several times, the 
issue of sales.  But I think differently.  I don't know him, but you 
can easily find out what he does for a living via google, As an 
aside, I 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.

Cheers!



Sincerely,



Marv Gozum
Philadelphia, PA