[volt-nuts] Tilt effect on Keithley 2000

[Charles P. Steinmetz]

Andreas wrote:

>I am playing around with some reference voltages and found out that my LM399
>references have 20-30 uV change in output voltage depending on the
>orientation of the reference.
>
>So when calibrating my voltage references with a Keithley 2000
>I found out that the reading changes on the Keithley too
>depending of the orientation of the instrument.

What is the time constant?  Slowish (i.e., could be thermal) or rapid 
(presumably gravitational/mechanical stress)?

I have operated Fluke 732As and 5440Bs in various orientations and 
have not noticed any changes.  With the 732s I was specifically 
looking for changes with orientation, and didn't see any to the limit 
of my methods (around 0.1 ppm).  With the 5440B I wasn't specifically 
looking for an orientation effect, but I think I'd certainly have 
noticed 1 ppm.  Of course, neither instrument uses an LM399 or LTZ1000.

Best regards,

Charles