Knock Sensors

Discussion in 'General Electronics Chat' started by Tree1, Feb 28, 2011.

  1. Tree1

    Thread Starter Member

    Nov 30, 2010
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    Can someone explain the flat frequency response of knock sensors.
     
  2. Tree1

    Thread Starter Member

    Nov 30, 2010
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    Or can anyone please explain the relationship between acceleration and frequency for knock sensors ? How does one affect the other?
     
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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  4. Tree1

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    Nov 30, 2010
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    I'll check it out. Thanks
     
  5. Tree1

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    Nov 30, 2010
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    And yes, I've googled knock sensors. I do have a lot of info. but I'm still confused as to the relationship between these two parameters and voltage.The sensor is senstive to acceleration. If the acceleration is constant and the frequency is increased what happens to the output ?? Is there a direct relationship between the two? I just really want to what happens to acceleration as frequency is increased or vice versa.
     
  6. KMoffett

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    Dec 19, 2007
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    Is the knock sensor sensitive to acceleration?... or is it just that the engine computer inputs a knock signal from the knock sensor, and interprets acceleration from a speed sensor?

    Ken
     
  7. Tree1

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    Nov 30, 2010
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    Hmm, well technical info. that I have indicates that the sensitivity is measured in mV/g. Sensitivity at 5kHz 26 (+/_ 8) mV/g. It seems to be sensitive acceleration.
     
  8. KMoffett

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    Dec 19, 2007
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    The acceleration (i.e. at 5KHZ) is probably indicating the sensor response to motion due the detonation in the cylinder, not motion of the vehicle. Do you have a link to the datasheet?

    Ken
     
  9. Tree1

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    Nov 30, 2010
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    Yes, http://www.bosch-motorsport.de/pdf/sensors/knock/KS-P.pdf. Yes I agree with your last statement but whether its acceleration of the sensor or vehicle. I just wanted to know the relationship between frequency and acceleration for these type of sensors. If the frequency of the vibrations increases does that mean the acceleration will increase. Is there direct relationship between the frequency of the knock and the acceration of that vibration creating that knock ?
     
  10. KMoffett

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    Dec 19, 2007
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    Within limits, the frequency and the acceleration will be independent of each other. The output voltage amplitude will be proportional to the acceleration. Frequency will determine whether it's knock, as opposed to other vibrations of the engine. Acceleration will determine how severe the knock is.

    Ken
     
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  11. Jaguarjoe

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    Apr 7, 2010
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    Vibration acceleration increases proportional to the square of vibration frequency.
     
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  12. debe

    Well-Known Member

    Sep 21, 2010
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    A Knock sensor on an engine is listening for pre ignition knocks, these signals are sent to the ECU & filtered. The resulting signal is used to alter IGN timing. In Fords which i trained on, the ECU ramps up the timing untill there is pre inition which the Knock sensor detects, then the timing is retarded, the process is then repeated. All this happens very quickly. The knock sensor is only a piezo transducer being used as a microphone so to speak. It is not an acelleration sensor on an engine.
     
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  13. Tree1

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    Nov 30, 2010
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    Thank you!!!!!!!!!!!!!!!!!!!!! Soo much guys!. Thanks for this clarification! A special thanks to Kmoffett.
     
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