Knock Sensors

[orin at WOLFENET.com]

> this is assuming that the mic is an electret mic (is it ???).
> If it is just a dynamic or crystal (piezo) and has no active
> impedance matching drivers inside it, it should not be polarized.
> (reason I question whether it's an electret is that all electrets
> I've worked with -- and I've actually purchased sheets of the plastic
> used to make them -- use a metallized plastic that has been stressed
> so that it's permanently 'charged' so it can simulate a condensor
> mic.  anyway, the plastic is easily damaged by heat -- wonder
> if it could stand up to engine temps -- maybe there's some
> new substance since I worked with it in the mid-80's ??)

I believe the older Bosch knock sensors are piezo and have a screened cable
going to them - two signal wires and a screen.  I wouldn't think that
the signal wires would be polarized.  This is what I remember from
the diagrams for my 86 Audi 5000 CS quattro.

Orin.