On Jun 24, 2007, at 1:58 PM, Michel Jullian wrote:
Nice (I am really impressed by the ASCII art) 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.
----------------- | | 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
