REFLECTOR: Magneto P-lead pickup circuit
Jim Agnew
jim_agnew_2 at yahoo.com
Sun Mar 13 13:09:29 CST 2005
Brian,
First it depends on what mag you are using, Slick or Bendix. I have High
Altitude (read high output) Bendix Mags and their P-lead wave form drove my
electronic tac nuts requiring a change in the filtering circuit.
The wave form is basically a very sharp peaked sine wave of decreasing
amplitude (ringing) and some fixed number of cycles depending on the mag. If I
remember the Slicks had about 5 cycles and the Bendix 7 or 8. It was a long
time ago and a lot of time with an oscilloscope.
Jim
--- Brian Michalk <michalk at awpi.com> wrote:
> I am working on my backup EFI circuit, and am considering a pickup off the
> magneto P-lead as one of the RPM inputs.
>
> I machined a collar that mounts on the crankshaft that feeds the crank
> position signal to the Autronic, an off the shelf engine computer. The
> Autronic provides spark and injection. My backup spark is a magneto. My
> backup fuel injection is a system I designed myself. It takes RPM and MAP
> to determine commanded fuel flow, and then a fuel flow input to make it
> closed loop. I will be taking one signal off the tach drive, and wanted
> another signal. I can get it from the above mentioned collar, or from the
> magneto.
>
> My thinking is that an alternator belt could fail, thrashing about and cause
> my RPM sensor to fail. Does anyone have a schematic on picking up a tach
> signal off the magneto? I have no idea what that waveform looks like.
>
> Brian Michalk <http://www.michalk.com>
> Life is what you make of it ... never wish you had done something.
> Aviator, experimental aircraft builder, motorcyclist, SCUBA diver
> musician, home-brewer, entrepreneur and barely single
>
>
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James F. Agnew
Jim_Agnew_2 at Yahoo.Com
Tampa, FL
Velocity 173 Elite Aircraft Completed & Flying
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