Ye Olde HP3458A
Greetings volt-nuts,
My first post to the list...
I am considering buying a HP3458A, possibly new, but am hesitant about
forking out so much for such an old design. I suppose I am used to
picking up 1980's gear on ebay for <5% of its list price :)
What are peoples opinions on the likelihood of a newer model coming out
soon? Surely they can't keep making it for much longer?
--
John Devereux
In message 87y5z97jwe.fsf@devereux.me.uk, John Devereux writes:
What are peoples opinions on the likelihood of a newer model coming out
soon?
p=0.
Read the HP Journal article carefully, and you will realize that if
you want to build a DVM an order of magnitude better than the 3458
it will have connectors for both "power" and "helium", because such
a instrument will crash directly into the thermal noise.
The only place where you could drastically improve on the Hp3458,
is the two internal references, and this is where much of the
"value add" of Flukes 8508a comes from.
I am somewhat dubious if we will ever see compact high-temperature
superconductor based josephson voltage references and quantum resistance
standards, but if they appear on the market, it would be pretty trivial
to retrofit a HP3458 with them, provided they can fit in the box.
The other argument for buying an HP3458A is that it is a much more
interesting instrument to play with, up to and including downloading
and running your own M68k programs on it.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
"Poul-Henning Kamp" phk@phk.freebsd.dk writes:
In message 87y5z97jwe.fsf@devereux.me.uk, John Devereux writes:
What are peoples opinions on the likelihood of a newer model coming out
soon?
p=0.
Read the HP Journal article carefully, and you will realize that if
you want to build a DVM an order of magnitude better than the 3458
it will have connectors for both "power" and "helium", because such
a instrument will crash directly into the thermal noise.
:)
I have read that article before and was suitably impressed. But it was
not clear to me where their 100nV/rtHz "theoretical limit" came from. It
seems arbitrary rather than fundamental - it is the noise of a 600k
resistor.
There are plenty of opamps (and transistor front ends) with <1nV/rtHz
noise. And plenty of resistors less than 600k:).
Also while digging around I found some patents that appear to improve on
the architecture. For example 4951053 describes a summing node switching
scheme that seems obviously superior to that illustrated in the journal
article. (In fact it predates it, maybe the article is not quite right?)
The only place where you could drastically improve on the Hp3458,
is the two internal references, and this is where much of the
"value add" of Flukes 8508a comes from.
I am somewhat dubious if we will ever see compact high-temperature
superconductor based josephson voltage references and quantum resistance
standards, but if they appear on the market, it would be pretty trivial
to retrofit a HP3458 with them, provided they can fit in the box.
The other argument for buying an HP3458A is that it is a much more
interesting instrument to play with, up to and including downloading
and running your own M68k programs on it.
Hey that sounds fun :) I wire wrapped a homebrew 68k board around then
too.
--
John Devereux
John Devereux john@devereux.me.uk writes:
"Poul-Henning Kamp" phk@phk.freebsd.dk writes:
In message 87y5z97jwe.fsf@devereux.me.uk, John Devereux writes:
What are peoples opinions on the likelihood of a newer model coming out
soon?
p=0.
Read the HP Journal article carefully, and you will realize that if
you want to build a DVM an order of magnitude better than the 3458
it will have connectors for both "power" and "helium", because such
a instrument will crash directly into the thermal noise.
:)
I have read that article before and was suitably impressed. But it was
not clear to me where their 100nV/rtHz "theoretical limit" came from. It
seems arbitrary rather than fundamental - it is the noise of a 600k
resistor.
There are plenty of opamps (and transistor front ends) with <1nV/rtHz
noise.
(replying to myself)
Actually not so many at ~DC :)
And plenty of resistors less than 600k:).
Also while digging around I found some patents that appear to improve on
the architecture. For example 4951053 describes a summing node switching
scheme that seems obviously superior to that illustrated in the journal
article. (In fact it predates it, maybe the article is not quite right?)
The only place where you could drastically improve on the Hp3458,
is the two internal references, and this is where much of the
"value add" of Flukes 8508a comes from.
I am somewhat dubious if we will ever see compact high-temperature
superconductor based josephson voltage references and quantum resistance
standards, but if they appear on the market, it would be pretty trivial
to retrofit a HP3458 with them, provided they can fit in the box.
The other argument for buying an HP3458A is that it is a much more
interesting instrument to play with, up to and including downloading
and running your own M68k programs on it.
Hey that sounds fun :) I wire wrapped a homebrew 68k board around then
too.
--
John Devereux
I looked into this a few years ago when units came into eBay between
$1K-3K. Currently, they are in 2-3x that range.
Consider its maintenance cost too, you can track the past discussions
on volt-nuts. For a 20 year old design, there have been changes in
newer production models through the decade:
http://litstation.marketing.agilent.com/litapp/SearchSN.do?method=openExternalSNSearch&prodNum=3458A
Geller Labs has a summary of various vintages:
http://www.gellerlabs.com/HP%203458A%20DMM.htm
I don't think there will be a new 8.5 DMM model any time soon, as the
number of players in this sector is very small, daresay tiny, and the
few reviews that compare what little exists against each other
suggests the 3458a remain tops. From a Chinese website in 2008, not
sure I posted this before:
At 02:47 AM 8/4/2011, John Devereux wrote:
Greetings volt-nuts,
My first post to the list...
I am considering buying a HP3458A, possibly new, but am hesitant about
forking out so much for such an old design. I suppose I am used to
picking up 1980's gear on ebay for <5% of its list price :)
What are peoples opinions on the likelihood of a newer model coming out
soon? Surely they can't keep making it for much longer?
Sincerely,
Marv Gozum
Philadelphia, PA
Sorry, the links to the China site is wrong, corrected:
At 11:03 AM 8/4/2011, Marvin E. Gozum wrote:
I don't think there will be a new 8.5 DMM model any time soon, as
the number of players in this sector is very small, daresay tiny,
and the few reviews that compare what little exists against each
other suggests the 3458a remain tops. From a Chinese website in
2008, not sure I posted this before:
Sincerely,
Marv Gozum
Philadelphia, PA