On the picture, 06:00 is 6 minutes.
As far as the number of digits, the 34461A returns the full floating point number for the measurement over SCPI (i.e. ADC + calibration function), so it has plenty of digits and there is quite a bit more effective resolution than the 6.5 digits on the display.
IIRC, the 34401A returns what is on the display, so no gravy.
Hi,
That's not correct!
The 34401A also returns one more digit for each single measurement, i.e. 7 digits, over the bus .
Also the statistics function delivers 7 digits, which are really useable when averaged over an appropriate time.
Generally, ALL HP bench meters deliver one or two digits more over the bus, than displayed .
BenchVue also displays this additional resolution.
The 3458A outputs up to 9 digits, and at least 8 digits also for functions which were displayed to 7 or 6 digits only.
All other 6 1/2 and 7 1/2 bench instruments up to now were very similar, or exact copies, concerning the A/D topology, including the reference.
That can be seen also by the Multi Slope III or IV designation, where obviously mostly software related improvements were made.. if you study the schematics in contrast to that.
So the length of the raw A/D output words was always very similar, something like 24..25 Bits (>30 bits for the 3458A.)
I also think, that even the new 34461 reused the A/D from the 34410A, only the user interface, graphical and statistical functions and interfacing was greatly improved.
And I'm curious about the 34465A, 34470A, if further improvements on reference and A/D were made, or if they only reused again.
Indicator for latter assumption is, that the A/D linearity still is on the order of 1ppm only, like the old 34401A, although 7 1/2 digits would urgently require something like 0.1ppm, which is only possible by the A/D in the 3458A (which has down to 0.02ppm linearity).
Well, if you would like to judge about the stability of the additional digits of the 6 digits instruments, you would best make a longer series of measurements on a known stable reference, and then calculate the Allan stability deviation, like we've done in a recent thread.:
https://www.eevblog.com/forum/projects/project-kx-diy-calibrator-reference-sourcemeter/msg592440/#msg592440It will probably turn out, that NPC 100 does not give useful results, but at about 12 seconds averaging time, this additional digit can be used.
Frank