From: "Terrell W. Fritz"
Date: Wed, 03 Jan 2001 12:14:00 -0700
Subject: Re: [TSSP] NSVPI - Terminated Coil Results
Hi Bert, Paul, I measured the junction capacitance of the diode at 20pF. If the contact capacitance is say only 1pF it would be a 20:1 attenuator and the diode will not turn on which is what I suspect will happen. I got a small 100mH choke today and 10Meg resistor so I will try it. I now see Paul's thinking in removing the contact capacitance as a big voltage drop. Perhaps a TL082 based circuit would do the trick. I have the surface mount types. One would have to keep the batteries and all that from affecting the circuit much but direct testing could still be done against the present NSVPI. Any thought on how to make or build such a device is welcome. Obviously, having to tap directly into the secondary is a real problem for everyone else. Cheers, Terry At 06:40 AM 1/3/2001 -0600, you wrote: >Terry, > >I suspect that you are indeed correct - the combination of the >relatively low capacitance to the signal source, diode drop, and diode >junction capacitance are all conspiring against being able to make this >work. The cure for all of these woes would be a precision fullwave >rectifier (or absolute value) circuit made up of a pair of Op Amps, one >or two diodes and some resistors - check out Art of Electronics or a >book on Op Amps for detailed schematics. > >-- Bert -- >-- >Bert Hickman >Stoneridge Engineering >Email: bert.hickman@aquila.net >Web Site: http://www.teslamania.com > >"Terrell W. Fritz" wrote: >> >> Hi Paul, >> >> At 10:46 AM 1/2/2001 +0000, you wrote: >> >Terry, All, >> > >> >You might like to try the following modification to the NSVPI >> >gradient probe, in attempt to get it to work without requiring >> >electrical contact with the coil. The idea is to add in an RF >> >choke to provide a DC path for the diode to charge the storage >> >cap. >> > >> > | pt >> > | ----||--- <-------------[diode]-- >> > | pc | | >> > | | | >> >sec | -[choke]- --- storage cap >> >coil | | --- >> > | pt | | >> > | ----||--- <---------------------- >> > | pc >> > | >> > >> >'pc' are the 'contact capacitances' of the two probe terminals 'pt', >> >[choke] is an RF choke wound on a miniature toroidal ferrite >> >core - this so that inductive coupling with the secondary is >> >minimised. Alternatively, use a high value resistance instead, and >> >allow time for the storage cap to charge. >> >> Originally, I tried this as shown at: >> http://hot-streamer.com/TeslaCoils/Misc/PaulNich/oldNSVPI.jpg >> >> It seemed the contact capacitance was so small (perhaps compared to the >> diode's junctions capacitance) that it would not charge. I just didn't >> seem to be able to get the diode to charge the cap even with germanium >> diodes. The junction just would not conduct. Would the chock help this?? >> >> > >> >We could do to figure out a way to make an absolute top volts >> >measurement. Terry's toroided coil Q of 164 gives a predicted >> >voltage gain of 168.5, but the cumulative gradients, with 0.12 >> >diode drop added, gives around 155 volts, so we have a discrepancy >> >here which appears larger than either the measurement or prediction >> >errors. >> > >> >Note that for the bare coil case, Q=60, Vgain predicted is 68.5 >> >and the cumulative voltage was 69.72 - within limits. >> > >> >> I think I just need to fix the ground plane again and drop a scope probe >> down onto the top of the coil. I have a 3pF 1000:1 probe that should do >> minimal loading both from capacitance and resistance. It also has a real >> long cable. It will add some C to the top and change Fo a little but maybe >> that won't be a problem. I assume both toroid and non-toroid cases are >> wanted. Time is short tonight, but I'll try tomorrow. Let me know if that >> is what you had in mind? >> >> Cheers, >> >> Terry >> >> >Cheers, >> >-- >> >Paul Nicholson, >> >Manchester, UK. >> >-- >
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.