Many processes have inherent noises that obscure the true underlying values (Fig. 1). These values range from the movement of stock prices to DCS-measured temperature values in a chemical plant. The intent of a filter is to attempt to reduce the amount of noise and reveal more of the true process behavior. As a rule in controls, a significant move for the output for a controller loop is when the process variable changes at least 10 times the noise band or, in other words, a signal-to-noise ratio greater than 10.1 One downside is that most filter techniques impose a delay, which makes applying them for control and real-time decision-making difficult.
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