knock dection

[VIBISH]

I have made a knock sensor using PVDF. It is sensing the knock while knocking on it the output I checked in CRO. Till now I didn’t test in engine...The problem that I am getting the signal mix with noise... the noise is of 50Hz and the amplitude is 250mv...can any one sagest me the solution for this problem and what all testing I have to do and the circuit diagram.....
i want to know the frequency range

[lozo]

The problem that I am getting the signal mix with noise... the noise is of 50Hz and the amplitude is 250mv...can any one sagest me the solution for this problem and what all testing I have to do and the circuit diagram.

Could you possibly provide more details about your testing jig. What is your power source, how is it set up? What are your parameters of testing?

The fact that the "noise" you're receiving seems to occur at very specific frequency and is of a fairly large amplitude level implies a poor circuit design that may be letting some other external factors influence it. Could you put up your circuit diagram too?



can any one sagest me the solution for this problem and what all testing I have to do and the circuit diagram.

Not without any more info mate.


i want to know the frequency range

Wha?

BTW: A quick search on google returned a couple of research papers examining the implementation of piezo based knock sensors. Have you looked at any of these yet? Here's one of them. http://www.pipitone.dima.unipa...les/MECA%20%2702.pdf (http://www.pipitone.dima.unipa.it/files/MECA%20%2702.pdf)


Cheers
Richie Wong
University of Auckland Formula SAE

[Brianson]

Without knowing more about your particular set up, it is hard to give any specific advice.

50Hz sounds like interference from mains power, which can be avoided by properly done wiring.

A good place to start reading about how to cut out noise is at http://zone.ni.com/devzone/cda/tut/p/id/3344