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

Brent Gordon volt-nuts at adobe-labs.com
Thu Apr 10 17:52:13 EDT 2014

On 4/10/2014 3:18 PM, Tony wrote:
>    Gordon wrote:
>> Pure conjecture:  So that the reading on the 34401A matches that on a 
>> $20 DVM.
> I assume you mean when the DVM is disconnected - otherwise you 
> wouldn't spend more than $20 on a meter! But I said that in my 
> original post:
Actually, I meant while connected.  For example, you want to do a 
quick-and-dirty check on a voltage.  Say you had previously set the 
voltage to a specific value using the 34401A .  Sometime later you want 
to check the voltage but the 34401A is not available.  So, you use your 
10 M-Ohm Fluke handheld DVM.  If your source impedance is high and you 
set the voltage with the 34401A set to 10 G-Ohm you would get a 
significantly different reading with the Fluke.  If the voltage was set 
with 34401A in 10 M-Ohm mode, you should get the same reading (within 
the accuracy of the Fluke).


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