[volt-nuts] Tilt effect on Keithley 2000

[Andreas_-_Jahn]

Hello,

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.

For example a 5 V reference is showing 4.99998 V with Keithley flat on the
table.
On the right edge of the instrument the reading is 4.99991 V
On the left edge I get 5.00004 V.
All in all the difference is 130 uV or 26 ppm!!
A second Keithley shows similar effect with 120uV difference.

Has anyone observed similar effect on other precision instruments
like Solartron, Agilent or Flukes.
Is this effect restricted to LM399-based instruments like the Keitley 2000
or are other references like LTZ1000 affected too?

best regards

Andreas