[volt-nuts] HP 3456A Setup

[ws at Yahoo]

woops, corrected "3456A"

> If the meter has a zero error, you need to correct it

True, if the zero error is more than a few microvolts. If it is, then there
is likely something broken, but assuming you have a normal working HP5456A, 
then
As far as zeroing the meter with its leads shorted, using "Math Null" (aka
Tare) is the only way to zero the 5456A's small offset that is left over
after "auto zero".
When using the Null command with the 5456A's  slow update rate, high
resolution, and filter off, you can measure voltages down to 0.1 uv if
you're real careful.
I find the digital "Null" is also very useful when measuring changes in the
differences between two similar but not exactly the same values or measuring
changes that occurred in a single device.
When desired the digital zero offset being used can be read out at any time
using "Recall", "Z" or any  new value can be stored using "Value_desired", 
"Store", "Z".
I find when making meaningful Sub PPM voltage measurements, ANY Zero offsets
in the meter and leads have to be taken into account, and using the digital
null mode helps a lot.

ws

**************
>
>
> [volt-nuts] HP 3456A Setup
> Charles P. Steinmetz charles_steinmetz at lavabit.com
>
>>>1) Select "DC volts"
>>>2) "Guard button" IN
>>>3) "Auto Zero" ON
>>>4) "Filter" OFF
>>>5) "Auto Range" Selected
>>>6) "INT" selected
>>>7) enter-keys "6", "Store", "N DIG DISP" (#9 key)
>>>8) enter-keys "100", "Store", N Cycles Int" (CHS key)
>>>9) with Inputs shorted push "Math" "Off" (#0 key)
>>>9a) then push "Math" "Null" (#3 key)
>
> Note that step 9a turns on what other manufacturers call a "relative"
> or "tare" function -- it subtracts a reading taken immediately after
> the function is activated from all subsequent readings (untill Math
> Null is deactivated).  This is handy for cancelling the lead
> resistance for resistance measurements, for example.  But it is
> probably not what you want for normal DC measurements.  Instead,
> leave Null off and just let Autozero zero out the residual for each
> measurement.  If the meter has a zero error, you need to correct it
> -- not just subtract the zero error you got a while ago from the
> current reading.
>
> Regarding the correct connection of the guard terminal, HP
> Application Note AN-123 provides a thorough discussion of what to do
> and why.  Connecting it to the Low input (as by pushing the Guard
> button in) is often suitable, but not always.
>
> Best regards,
>
> Charles
>
>