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?
Michel ----- Original Message ----- From: "Horace Heffner" <[EMAIL PROTECTED]> To: <vortex-l@eskimo.com> Sent: Sunday, June 24, 2007 9:16 PM Subject: Re: [Vo]:Air threads >I just noticed the thread name changed. > > ----------------- > | | > V Emitter | > P > _ Plate | > | T1 > | | > | | > -o-R1---G---R2-o- > | | | > o o o > V1 G V2 > > Fig. 1 - Circuit diagram for drop/thread detection > > P is a smooth DC power supply floating above R2 and T1 (one technical > difficulty with this approach). The plate current goes through R1 to > ground G. This gives two current proportional voltages V1 and V2 > close to ground and thus easily amplified (a major advantage). If > the current is carried by charged droplets then the current signals > will be wildly different in timing. If the current is carried by > conductive filament then the signals should be comparatively flat. > It may be possible, depending on needle choice and humidity, and/or > possibly CO2 concentration, to generate either mode. If the needle > emitter is in conductive filament mode, then it should be possible to > instantly send a HF signal injected by transformer T1, and which is > not received at the same magnitude when there is no filament. > Further, if the plate is bifurcated, (and another current sense > resistor R3 added) and the emitter moved from above one plate to > above the other, then a droplet beam (or dry air dry needle signal) > should transition current from R1 to R3 more gradually and smoothly > than a conductive filament (or set of multiple simultaneous > filaments, which would give a step function). > > The emitter and plate can exchange places. Since the power supply is > floated, possibly with an isolation transformer, P and T1 can > exchange places. If P is a small van de Graaf, then T1 has to be > between P and the tip. It is also possible to locate T1 between R1 > and the plate. > > Some handy pre-amp circuits for anyone interested. (Note: I am not an > electrons guy!) > > > True full wave signal amp: > > +Vdd (Drain) > | > | > | > I---- > Gate I > Input---> I---- > | > R1 > | > o----->Output > | > I---- > Gate I > ---> I---- > | | > | R2 > | | > ---------| > | > -Vss (Source > > > Two NTE455 MOSFET's, Dual Gate, N-Ch, TV UHF RF Amp (gate Protected), > gfs - 22,000 micromhos Typ, BVdsx 20 V min, Idss 0.5-8 mA, Pd00 mW > Max, Vgs(off) - G1=2, G2=0.7 V, Ciss 3.5 pF Max, Crss 0.03 pF Max. > Gates tied together. R1 = R2 = 2.2 k. +Vdd and - Vss supplied by > two opposed 9 V batteries. I have never actually tried this. > > For a capacitor isolated (and thus differential) signal at about half > the cost (and I've tried this, thanks to John Schnurer): > > > > +Vdd (Drain) (Vdd = +9 V) > | > R2 (22 ohms) > | > |---------------C1---Ground (C1 = 1000 pF) > | > I---- > In Gate I NTE455 > o--C2-o-> I---- > | | (Source) > R3 | > | o------------------->Out > o | > R1 (2.2 k) > | > Ground > > To avoid charge build up on the gate R3, as large a resistor as > possible (e.g. 20 Mohm), can shunt to ground. If the signal is too > small this can be temporarily removed while looking at the signal. > > Regards, > > Horace Heffner >
