[volt-nuts] HP 3456A AC cal

[Richard Moore]

I'm trying to get my head around the AC cal procedure for the HP 3456A 
-- there is no full-scale cal, just some extremely finicky tweaks for 
the bottom ends of three of the four ranges. I really don't understand 
how this is supposed to work, especially since it is very accurate on 
all DC ranges (up to 500V -- above that some heating of the divider R 
seems to occur and it loses accuracy as the voltage increases). But on 
AC, the tweaks don't result in anything like an accurate level reading 
compare to my 3458A -- at 10VAC it is off by hundreds of ppm. Anybody 
shed any light on this? Is there a way to get full scale cal points in 
AC mode? Any mods to fix this -- lovely meter otherwise; I much prefer 
it to the 34401A I used to have, except for the overall bigness....