On 6 March 2018 at 09:40, Dr. David Kirkby <drkir...@kirkbymicrowave.co.uk> wrote:
> Sorry this is not precision voltage measurement, but it is not unrelated. > > As a radio club project, we are building a simple electroscope, with no > active components. The gold leave variety would work, but two bits of > alluminum foil do too. > > My plan was to go one better, and build a Bohnenberger electrometer. > For what it is worth, this is my design: http://www.kirkbymicrowave.co.uk/tmp/G8WRBs-electrometer.jpg There's 600 V DC between two strips of PCB material. A 600 V 47 uF capacitor was charged to 600 V. A small bit of aluminum foil, between the plates, then moves to the left or right, depending on whether the charge is positive or negative. The big capacitor, which is 2.2 nF 15 kV is not doing much apart from being a structure to hold other parts. It has large lugs on it, where multiple M6 screws can be fitted, so it is nice electrical insulator. Its actual capacitance (2.2 nF) is insignificant when in parallel with 47 uF. Under sufficient applied field, and with sufficient charge, it is possible to get the foil to oscillate from side to side like a pendulum. I believe what happens is if a negative charge is applied to the foil, it gets attracted to the positive plate, which causes them to touch, so the foil receives a positive charge - the opposite of what it had before. This causes it to move in the other direction. It is possible to get it to oscillate back and forth. I expect, with a sufficient mass and very high electric field, a pendulum could be made to make a clock, but with a little bit of tin foil, the foil would clearly break quite quickly. A more substantial structure would be required, which I suspect would need some very high voltages. A Google of 'electrostatic clocks' does indicate they exist, although I have not looked into how they work. But I believe a sufficiently high electric field could make a pendulum swing, and that of course could make a clock. Anyway, it was interesting playing with this. I am wondering if there's any way to detect the polarity of a charge, without having any power source. Clearly the gold leaf electroscope can detect charge, but does not need a power supply. The Bohnenberger electrometer can detect polarity too, but needs a power supply. I was wondering if the charge could be applied to two diodes, which were each connected to a plate. The it may be possible to charge one plate only, as only one diode would conduct, so only one plate would be charged. The the leaf would be repelled from whatever plate has the same charge. Dave _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.