[volt-nuts] 34401A Why 10M ohm default i/p resistance?

Poul-Henning Kamp phk at phk.freebsd.dk
Thu Apr 10 16:59:21 EDT 2014

In message <534704F7.3030101 at toneh.demon.co.uk>, Tony writes:

>Very unlikely I'd have thought - the relay (K104) which selects between 
>the high and low voltage ranges also selects the  I/P resistance. It 
>wouldn't get used any more than the identical relay |(K102) which 
>switches when changing between 10 and 100V ranges.

If you leave your 34401A on 10G input with nothing connected in
a dry atmosphere, it is going to build up charge and trigger the
autorange relay.  Anti-wear-out mechanisms are certainly relevant.

A similar mechnism is documented in one of the 3458A manuals.

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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