YOKOGAWA SL1400 - Page 577

App-27
IM 701240-01E
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App
App
Index
Appendix
Filter Characteristics (Time Delay) of the Smoothing Filter
The smoothing filter is a moving average filter in which computation is performed in
realtime. The computation interval of moving average is 40 µs (25 kHz). It is constant
independent of the sampling rate of the SL1400.
The moving average order (the number of points of moving average) is specified in time.
The maximum value is 25000 order (when set to 1000 ms).
The characteristics of the smoothing filter are as follows:
• The filter is a low-pass filter.
• Pass band is flat.
• Has linear phase characteristics and constant group delay by filter order.
The group delay is derived using the following equation.
Group delay = (the number of points of moving average – 1) × 40 µs/2
• Has comb-shaped bandwidth characteristics.
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0f 0.1f 0.2f 0.3f 0.4f 0.5f
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MEAN (Moving Average) Frequency Characteristics
dB
(f: sampling frequency [Hz])
The figure below shows the result when the smoothing filter is applied to a waveform that
changes in steps. The switching filter setup time follows the step change.
Waveform after applying
the smoothing filter
Waveform before applying
the smoothing filter
Smoothing filter setup time
Appendix 11 Measurement Principles (Measurement Method and Update Rate) of the Frequency Module