You can use the PID Control Input Filter VI to filter unwanted, high-frequency noise from measured values in a control application. For example, if you are measuring process variable values using a DAQ device, you can use the this VI to filter noise from input values in the control loop before passing the values to control functions such as the PID VI.
When filtering noise, set the sampling rate of the control system to at least 10 times the fastest time constant of the physical system. This ensures that any frequency components of the measured signal greater than 1/10 of the sampling frequency are a result of noise in the measured signal. Gains in the PID controller can amplify this noise and produce unnecessary wear on actuators and other system components.
The PID Control Input Filter VI uses a lowpass fifth-order finite impulse response (FIR) filter. The cutoff frequency of the lowpass filter is 1/10 of the sampling frequency, regardless of the actual sampling frequency value.
You can use the Filters PtByPt VIs or the LabVIEW Digital Filter Design Toolkit to perform additional filtering tasks. Refer to the National Instruments website for more information about or to purchase the Digital Filter Design Toolkit.