[volt-nuts] External Freq Reference Mod for 3458A?
phk at phk.freebsd.dk
Fri Jun 5 15:49:13 EDT 2015
In message <COL130-W405514A623341979406897DFB20 at phx.gbl>, Tom Knox writes:
>Does any of the Volt-Nuts brain trust have any experience adding
>an external Frequency Reference on the 3458A.
The only reference I have seen to this is that NIST modified a HP3458A
this way in order to be able to sample a sine-wave approximation from
a Josephson junction voltage standard after the transitions had settled.
>There is a 20MHz reference on the A/D board but externally clocking
>it has affected linearity collecting data off a 10VDC reference
>that looks a little like a hanging bridge I have seen before between
>GPS and oscillator sync. Is there another clock? Thanks for any
You want to be 100% sure you don't inject any ground reference into
the A/D board. Whatever you do, you *must* isolate the signal.
Agilent isolated the serial port between the A/D and the main
processor with 20cm of (plastic) optical fiber, and I think a
significant clue should be taken from that: Optocouplers and
transformers are unlikely to be good enough.
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at 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.
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