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15-8
IM 701210-06E
15.3 Using Filters (DSP Channels)
Explanation
A digital filter is used to perform the computation.
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.
Setting the Digital Filter
The following four types of filters are available. For details, see Appendix 6.
Sharp, Gauss, Mean (moving average), and IIR (Butterworth)
Filter Format
Characteristics
Filter
Computation
Type
Type
Sharp
Steep attenuation slope (–40 dB per octave)
LPF
1
FIR
Linear phase and constant group delay
HPF
1
Ripple exists in the passband
BPF
1
Stop band is comb-shaped
Gauss
Gentle attenuation slope
LPF
FIR
Linear phase and constant group delay
No ripple in the passband
There is no overshoot in the step response.
Low order and small delay
MEAN
Comb-shaped characteristics
LPF
FIR
(Moving Average)
There is no overshoot in the step response.
Linear phase and constant group delay
IIR
Attenuation slope is between SHARP and GAUSS
LPF
IIR
(Butterworth)
Not linear phase and group delay not constant
HPF
No ripple in either passband or stopband
BPF
Close to the characteristics of an analog filter
Cutoff frequency can be set lower than SHARP/GAUSS
1. LPF, HPF, and BPF denote low-pass filter, high-pass filter, and bandpass filter, respectively.
The cutoff frequency, center frequency, and pass band can be specified in terms of
percentages of fs (sampling frequency).
Type
Filter Band
1
Cutoff Frequency
2
Center Frequency
3
Pass Band
4
Sharp
LPF
2.0% to 30.0%
-
-
HPF
2.0% to 30.0%
-
-
BPF
-
3.0% to 30.0%
2% of fs
-
4.6% to 30.0%
5% of fs
-
7.0% to 30.0%
10% of fs
-
9.6% to 30.0%
15% of fs
-
12.0% to 30.0%
20% of fs
Gauss
LPF
2.0% to 30.0%
-
-
IIR
LPF
0.2% to 30.0%
-
-
HPF
0.2% to 30.0%
-
-
BPF
-
0.6% to 30.0%
1% of fs
-
1.2% to 30.0%
2% of fs
-
2.6% to 30.0%
5% of fs
-
5.2% to 30.0%
10% of fs
-
7.6% to 30.0%
15% of fs
-
10.2% to 30.0%
20% of fs
1.
LPF, HPF, and BPF denote low-pass filter, high-pass filter, and bandpass filter,
respectively.
2.
The cutoff frequency (CutOff) can be specified only when LPF or HPF is selected.
The resolution is 0.2%.
3.
The center frequency can be specified only when BPF is selected.
The resolution is 0.2%.
4.
The pass band can be specified only when BPF is selected.
You can select the pass band from 1%, 2%, 5%, 10%, 15%, and 20%.