Frequen-cy asked questions

Many modern servo filters provide some facility for frequencydependant filtering. This is useful for compensating for mechanical systems that have a resonance at a certain frequency or speed, or to reduce high frequency noise.

The most common implementation of such a filter is known as a bi-quad filter, shown in figure 6. By choosing the right values for A1, A2, B0, B1, and B2 this filter can function as a notch filter, band-pass filter, high or low-pass filter. If you are not familiar with use of a bi-quad filter, there are a number of facilities that provide information including the website www.octave.org. This website includes a tool that lets you calculate values for A1, A2, etc. based on the frequency filtering characteristics you want for your system.

Biquad algorithm flow

Bi-quad filter