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The Basics of Numerical Filtering
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Автор:  san [ 23 серпня 2014, 00:22 ]
Тема повідомлення:  The Basics of Numerical Filtering

The Basics of Numerical Filtering
Creative number crunching can smooth out data in a control loop.
http://e-ditionsbyfry.com/Olive/ODE/CTL ... w=document
Цитата:
To coffee drinkers and auto mechanics, “filtering” extracts unwanted contaminants from a stream of valuable material. Control engineers, on the other hand, use numerical filters to extract streams of valuable data from measurement noise and other extraneous information (see the “Filtering the feedback” graphic).
The “Running average” sidebar shows how the most basic numerical filter—a running or moving average—can extract the average value from a sequence of recent process variable measurements. Averaging is an especially effective method for determining the true value of a process variable when the measuring device is prone to unpredictable fluctuations commonly described as noise. Measurement noise affects all industrial instruments to one degree or another. Variations in ambient conditions (especially temperature) or interference from nearby electrical sources can cause an unfiltered instrument to report a skewed reading. Sometimes the measurement technology itself is not entirely accurate, causing unfiltered measurements to deviate from the process variable’s true value.
If deviations are brief, random, and equally distributed between positive and negative values, the noise will contribute no net effect to the average of recent measurements, so the readings reported by a filtered instrument will be accurate. Even if the noise is not strictly random and has a non-zero average or mean, an averaging filter can compensate by detecting the mean and subtracting it from the instrument’s readings.

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