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The low-pass filter is used to create a smoother flow of a point. Take for example a setpoint here which goes first from 14 to 20°C and then back down. The filter smoothens the flow of the setpoint.

The internal working of the low pass filter is based on the principle of a time constant as characteristic of a decaying exponential function. An input step-profile that goes from 0 to 1 instantaneously at t=0s, will reach 63.21% (1-e^-1) at t=𝜏 with 𝜏 the time constant.

In Hysopt, you can define a separate time constant for an upramping change and a downramping change.

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Example

This component is very useful when it comes to valves and energy centers to create a more sensible behavior.