Hi guys, I read carefully all your debates about the voltage references and internal constructions of the famous 3458A or 34401A, but I wonder why nobody ever speaks about the 34420A. According to the datasheet, it seems to outperform the 3458A with small signal measurements. Does anybody have some experience with this meter or know what's inside ? Is it a tuned 34401A or something different ? Sam.

Samuel DEMEULEMEESTER wrote: > Hi guys, > > > > I read carefully all your debates about the voltage references and internal > constructions of the famous 3458A or 34401A, but I wonder why nobody ever > speaks about the 34420A. According to the datasheet, it seems to outperform > the 3458A with small signal measurements. Does anybody have some experience > with this meter or know what's inside ? Is it a tuned 34401A or something > different ? > > > > Sam. > > The service manual schematics indicate that its essentially an enhanced 34401 with a higher gain lower noise dc amplifier, a few tweaks to the ADC and close attention to minimise thermal emfs in the input circuitry. The dc amplifier input stage is a darlington cascoded differential JFET input stage (bootstrapped to the input device source common mode) with an active load whereas the 34401 merely used a pair of JFET source followers with bootstrapped drains. Bruce

Hello Sam, I do not own the 34420, but looked at the 34420A some time ago. It comes down to resolution versus accuracy. The 34420 can resolve to 1pV while the 3458a to 10nV. But the 34420 is ~ 20 ppm, at 10Vdc, 90 days. Its other ranges span between 20-60ppm for 90 days. You can compare accuracy on your own from 24h up to 1 year, as their spec sheets provide. For the same time frame, the 3458a is 4.6 ppm, and between 4-6ppm for all the Vdc scales, and this is without the high accuracy board. As the last digits of all meters are the subject of most of the uncertainty, without tight accuracy, you repeat the measurement, you don't want to get something else. As Bruce suggests the 34420 is a modified 34401, its basic platform has limitations. At 05:09 PM 8/25/2010, Samuel DEMEULEMEESTER wrote: >Hi guys, > > > >I read carefully all your debates about the voltage references and internal >constructions of the famous 3458A or 34401A, but I wonder why nobody ever >speaks about the 34420A. According to the datasheet, it seems to outperform >the 3458A with small signal measurements. Does anybody have some experience >with this meter or know what's inside ? Is it a tuned 34401A or something >different ? > > > >Sam. > >_______________________________________________ >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. Sincerely, Marv Gozum Philadelphia, PA