Appendix
Filter Characteristics (Time Delay) of the Smoothing Filter
The smoothing filter is a moving average filter in which computation is performed in real time. The computation
interval for moving averages is 40 μs (25 kHz). It is constant independent of the sample rate of the DL850E/
DL850EV.
The moving average order (the number of averaged points) is specified in terms of time. The maximum value is
25000 points (when the time is set to 1000 ms).
The characteristics of the smoothing filter are as follows:
•
The filter is a low-pass filter.
• The pass band is flat.
• The filter has linear phase characteristics. The group delay is
constant for a given filter order.
The group delay can be derived through the following equation.
Group delay = (the number of averaged points − 1) × 40 μs/2
• The filter has comb-shaped bandwidth characteristics.
The figure below shows the result of applying the smoothing filter to a waveform that changes in steps. The
smoothing filter setup time follows the step change.
Smoothing filter setup time
Waveform before the
smoothing
filter is applied
Waveform after the
smoothing filter is
applied
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