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HP / Agilent 34401A hidden menu
coromonadalix:
can you compare it with the 34970 brother ???
iMo:
Theoretically the mystery "mode 9" could be the Capacitance measurement (see the 34410A).
It works the same as the 2W resistance method - feeding a current into the capacitor, but measuring the ramp (ie. either measuring the time from V1 to V2, or, via a sampling of X DCV samples and calculating the ramp's slope..).
The available 34401A charging currents range is the same as with 34410A.
iMo:
The question with the Capacitance measurement is how to define the starting point for the measurement, as the charging the capacitor via the 0.5uA to 1mA current source is made in time, and the optimal option is to have the capacitor discharged to zero volts. Then you simply make DCV sampling with a NPLC speed (class 0), till the voltage reaches a max voltage, or, you may do a fixed number of DCV samples within a sweep. Then you calculate the slope of the sampled voltage ramp and from that you get the capacitance. The autoranging from 1nF to 10mF (34410A) would require to alter the constant current value and perhaps NPLC before the ramp sweep to stay in an "optimal" DCV range. The question is how to discharge the capacitor, or how to define the "start" of a sweep. There is a lot of switches inside, they may use a lot of tricks..
PS: for example the const current 0.5uA charges 1nF in 20ms to 10V, while 1mA charges 10mF in 1s to 100mV (all from a discharged capacitor).
alan.bain:
Sadly examining the CONF? command output on the 34410A (why didn't I think of this sooner) shows that mode 9 isn't capacitance but DC voltage ratio
CONF VOLT:DC:RAT range, res
Capacitance would have been much more useful... now I still need an HP4262/3 :-)
alan.bain:
Looking at my old notes there's another interesting AC mode on these meters
diag:poke 27,0,1
enables 10kHz AC filter mode (in addition to the usual 3Hz, 20Hz and 200Hz filters) so you can select this with
det:band 10000
This works pretty much like DC measurement off the back of the RMS converter and allows very fast readings to be made (the normal ac modes include a software filter and sum of squares calculation, taking longer for the lower frequency knee). I don't have one of those nice Fluke AC calibrators like the 5200A so I'm not able to check how accurately it works (or test my bench for strength).
This mode doesn't seem persistent over power cycles, although the poke to set it does write NVRAM.
I'm sort of amused that in the 7-5-2 firmware the flag works by storing 34401 in 0x168c. I didn't notice this at first from a hex listing.
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