[volt-nuts] hp3457a low voltage range behavior

frank.stellmach at freenet.de frank.stellmach at freenet.de
Wed Sep 4 05:10:50 EDT 2013

in the 3457A schematics there's C101 = 220pF in the DCV (30mV .. 3V) input path.
If your instruments takes about 5min. to charge that capacitor from zero to 3V, the input current is about 2.2pA, or about 1.4 TOhm, very good!
This capacitor will probably not discharged by the 100:1 divider, so you should not leave the jacks open, otherwise the relais K106, K107 might wear out, if the autorange quickly switches back and forth .
Congratulations for that fine instrument.

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