In the manual reference that"Typically, the Output Filter can be set to a value close top the natural frequency of the system. For example, if a system tends to oscillate at 10 Hz, a good starting value for the Output Filter is 10 or higher.
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How should i get the value of natural frequency of the system?
The tuning wizard can show this. After the wizard obtains plots, it calculates the system model. At this point, click the Advanced button and choose to allow second order. Then look at the model parameters. One of them is the Natural Frequency. Make sure to unselect allow second order model before continuing.
Under what circumstances can be use second order model .
It can be used anytime, although it is best to use it only when necessary. That is when the medium between the applied force and the measurement location acts like a spring.