[volt-nuts] Best reference after LTZ1000
Marv Gozum @ JHN
marvin.gozum at jefferson.edu
Tue Aug 24 17:37:12 UTC 2010
Thanks for the links and the insight. Sorry for delay, but was also
reviewing the old commentary on time-nuts about the Geller
references, his patents, and more on voltage standards not on this
Overall though, the more important item is taken as a whole is this
box with the patented stabilizing circuit a better reference than
something else, assuming this is what your friend has?
I agree with your criticism of the circuit function. See the
schematic on the patent. There is a novel item, notice that the
supply voltage for the LM399 comes from the vref output of the AD587
op amp, rather than V+ as expected? This provides an ultra stable
supply for the LM399, compared to one from a standard regulator or
battery, while also putting a continuous load on the op amp. Not
sure what this does to the ppm/oC over time, so I would think Geller
should characterize such as effect better to capitalize on it.
Geller does offer the patented circuit on a stabler and more costly
version of SVR, but you have to ask him for it. Its near $300
compared to the $35 SVR.
But I think there are more conventional ways to achieve stability
without the uncertainty of this circuit's function.
If others aren't aware, the Time Nuts archives around 2008/9 have
discussions about WarrenS's modification and his experience with
Geller boards and chips, mailed to-fro East and West coast USA, and
his experience with its stability. There are other posts affirming
Geller and Malone's boards at least for short term stability as
transfer references, no time statement what short means, I presume at
minimum the time it takes to receive US mail from coast to coast.
Thanks a bunch again, for the leads and comments.
At 05:03 PM 8/22/2010, Charles P. Steinmetz wrote:
>>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.
>>Its interesting this has come up for his services several times,
>>the issue of sales. But I think differently.
>Geller has a patent covering a method of improving the temperature
>coefficient of an AD58x or similar monolithic reference using an
>LM399 or other ovenized reference
>(http://www.pat2pdf.org/patents/pat7382179.pdf). A friend has a
>little reference box he bought from Geller that claimed to use a
>circuit based on the patent. However, according to the patent,
>Geller didn't use opposite tempcos to offset each other, he
>essentially just swamped the internal reference and used the AD58x
>as an output scaling amplifier for the ovenized reference. So why
>use an AD58x in the first place? You could do significantly better
>with a precision op amp and the ovenized reference, with a little
>attention to details. So, the patent appears to be what we used to
>call a puff patent.
>I notice that his current offering is just a PCB with an AD587 and a
>(http://gellerlabs.com/SVR%20schematic.pdf). Apparently, he
>concluded that his patented circuit didn't improve things over the
>current AD parts enough to be worthwhile.
>This is not to say that his references aren't any good, or don't do
>what he says, or aren't good value. They are certainly reasonably
>priced, and he is very clear about what they are and are not
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