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15-18
IM 701210-06E
Explanation
When the value of the computed channel is greater than the elimination level, filter
computation is performed. If the value is less than the elimination level, the computed
result is set to 0. This filter is effective such as when extracting only the knocking
components from the pressure inside the engine cylinder.
Trigger
Pressure inside
the engine cylinder
Extracts only the knocking section
Knocking
Eliminates valve noise
Valve noise
Noise elimination level
(elimination level)
Computed Channels
CH1 to CH16 and DSP1 to DSP6 (optional)
The computed result of a DSP channel can be specified as a computation source of
another DSP channel, but only DSP channels with a channel number smaller than itself
can be specified.
Digital Filter That Can Be Used in the Knocking Filter
The following three digital filters can be specified. (For details, see appendix 6.)
Sharp, IIR (Butterworth), and Diff (differentiation)
Filter Format
Characteristics
Filter Type
Computation
Type
SHARP
Attenuation slope of the frequency response is HPF*
FIR
steep (–40 dB per octave)
Linear phase and constant group delay
BPF*
Ripple exists in the passband
Stop band is comb-shaped
IIR (Butterworth)
Attenuation slope is between SHARP and
HPF
IIR
GAUSS
Not linear phase and group delay not constant BPF
No ripple in either passband or stopband
Close to the characteristics of an analog filter
Cutoff frequency can be set lower than
SHARP/GAUSS
Diff (differentiation) Performs the same computation as the differentiation described in section
15.4.
*
HPF: High-pass filter, BPF: Band-pass filter
15.6 Using the Knocking Filter (DSP Channels)