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....

On 12/09/2014 00:30, Richard Moore wrote: > 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.... > Hi Richard, Does the meter have a DC to RMS converter chip in it, because if it does you have to account for the self noise and offset of the gilbert cell at the heart of the converter.

>From what I remember: The 3455A has a good AC front end but is a real pain to calibrate with a lot of adjustment (read flexibility). I think HP gave up a lot of accuracy for a simpler calibration. The 3457A seems to do AC a lot better than the 3456A. Nether meter come close to doing what the 3458A does. On Fri, Sep 12, 2014 at 12:04 AM, M K <m1k3k1@hotmail.com> wrote: > On 12/09/2014 00:30, Richard Moore wrote: > >> 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.... >> >> Hi Richard, > > Does the meter have a DC to RMS converter chip in it, because if it does > you have to account for the self noise and offset of the gilbert cell at > the heart of the converter. > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/volt-nuts > and follow the instructions there. > -- *John Phillips*

On 12/09/2014 08:36, John Phillips wrote: > From what I remember: The 3455A has a good AC front end but is a real pain > to calibrate with a lot of adjustment (read flexibility). I think HP gave > up a lot of accuracy for a simpler calibration. The 3457A seems to do AC a > lot better than the 3456A. Nether meter come close to doing what the 3458A > does. > > On Fri, Sep 12, 2014 at 12:04 AM, M K <m1k3k1@hotmail.com> wrote: > >> On 12/09/2014 00:30, Richard Moore wrote: >> >>> 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.... >>> >>> Hi Richard, >> Does the meter have a DC to RMS converter chip in it, because if it does >> you have to account for the self noise and offset of the gilbert cell at >> the heart of the converter. >> >> _______________________________________________ >> volt-nuts mailing list -- volt-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/ >> mailman/listinfo/volt-nuts >> and follow the instructions there. >> > > I downloaded the service maual from the BAMA archive, it is an absolute value circuit followed by a logging anp, not quite the AD634 gilbert cell, but still prone to the same offset and noise creating a non-linearity at the bottom of each range.