[volt-nuts] hp3457a low voltage range behavior

Frank Stellmach frank.stellmach at freenet.de
Tue Sep 3 17:21:13 EDT 2013

The more important parameter is Ibias, the input current, vs. the input 

Neither Input Resistance, nor input bias current, nor input capacitance 
are specified for the 3457A.

Input current is on the order of a few pA, up to 20pA, and input 
capacitance, I would guess, several dozen pF, or you'll have to study 
the CLIP, if there's a bigger cap in the front end.

Even this would be 100nF, you can calculate, that the input  will charge 
quickly with open input jacks, and then will actuate the 100:1 divider 
by relais, if 3V were exceeded. The 10MOhm then will quickly discharge 
the input cap again.


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