Very impressive Ed. Looking forward to seeing more detail on the 417 front end solid state conversion when you are ready to publish.
Did a quick search on the net for Keithley 417, but nothing came up. I wanted to see if the circuit is similar to the Keithley 610B. Lou On Wed, Jul 8, 2020 at 11:03 AM ed breya <[email protected]> wrote: > I just did a quickie experiment to get higher resolution. I rigged up an > external meter movement about the same size as the internal one, hooked > to the monitor out, which is 3V FS. The external meter is set up for > about ten times the sensitivity, so 300 mV FS. I wanted to see how the > noise looks, with similar meter ballistics, and expand the zone around > zero to assess the bias current. The net result is the external meter > reads about 10 fA FS, and the noise and drift are still low enough to be > quite usable. The latest bias current estimate is about 50-100 aA, > slowly dithering around less than plus one percent of FS, with > occasional jumps to about 500 aA or less. I can't tell yet if these > jumps are part of the 1/f noise, or line noise and transients getting > through the power supplies. > > Anyway, presuming I didn't make any mistakes in my measuring and > figuring, this is quite impressive. I hope I just didn't get lucky with > one particular part, but I think the others will be similar. I will > eventually be checking them all, and other part types, in test setups. > > For reference, I confirmed the scaling. With the 417 set up for maximum > sensitivity, it's 100 fA FS. Putting the suppression supply at 100 mV > through the top 1E12 resistor, it reads near full scale. Setting at 10 > mV, the internal meter reads ten percent of FS, and the external meter > reads near its full scale. BTW I can set the suppression directly with > mV resolution. Long ago, I changed the last digit pot to a ten-turn > precision type with a kilodial indicator - it's nice. > > This is now over a hundred times better than the original spec for the > 417's grid current. When it's all said and done, I'll likely add a 10X > meter switch arrangement in the 417, to get a 10 fA FS range capability > too. It may be good even at much higher sensitivity, but 10X is pretty > good, and I likely won't need any more, practically speaking. Besides, > putting a DVM (and some filtering) on the output can expand it even > more, if ever necessary. > > One problem I did find, is there's some line ripple appearing in the > output signal, which I need to investigate. It's pretty small - about > one percent FS - and the meters don't notice it, but it still bugs me, > since it's way bigger than the apparent random noise. > > Ed > > _______________________________________________ > volt-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/volt-nuts_lists.febo.com > and follow the instructions there. > _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/volt-nuts_lists.febo.com and follow the instructions there.
