On Jun 24, 2007, at 1:58 PM, Michel Jullian wrote:
Nice (I am really impressed by the ASCII art)
Gee, you're easily impressed. 8^)
but R2 is superfluous Horace. Current is the same at all points of the circuit, so R1 (or R1 and R3) is sufficient to measure the discharge current, whatever the nature (filament, drops, ions...) of the discharge. Agreed?
No. The *average* will obviously work out, but this is a dynamic circuit which involves connection to the environment through ground. There is, or can be, a delay carrying the current from the needle to the plate. If a drop is charging there will be a charging current through R2 not fully reflected by a current in R1. There is an induced charge on the plate, but also to the general environment. The full current to the plate is delayed until the drop completes the trip.
This does point out a nice improvement. A grounded metallic ring could be placed axially aligned with the emitter needle and between the plates and needle. It would have to be big enough that it would not directly attract the jet/drops to itself. Properly sized this ring should increase the signal for drops, and likely diverge both a drop and ion beam. An ion beam would be in part attracted to the ring in any case. It would not carry the full current through the ring, while a filament would. A filament should also carry most of low frequency signal through the ring to the plate because it is nearly neutral so capacitive linkage with the ring should be small.
----------------- | | V Emitter | P _ Plate | | T1 | | | | -o-R1---G---R2-o- | | | o o o V1 G V2 Fig. 1 - Circuit diagram for drop/thread detection
Regards, Horace Heffner
