IC engine knock detector circuit for capacitive sensor - compares filtered and unfiltered demodulator outputs and requires no tuning

摘要

The device for the detection of knocking in internal combustion engines contains few and economical components and requires no ref. window. If a window is reqd. only one measurement window is necessary. The exact knock frequency does not need to be known for tuning purposes. The time history of the knock signal amplitude is obtd. via a demodulator circuit whose output is filtered by a low pass filter. The outputs of the demodulator and filter are compared in a comparator whose output is tested against an adjustable measurement window. A capacitive detector is used and its impedance may form part of a high-pass or band-pass filter. The low-pass filter and demodulator circuit ref. levels are adjustable. The demodulator may be a rectifier or squarer.