Second

order filter. A smoothing filter in which the output follows the input, only more slowly; It is usually implemented in software as a difference equation of period T. When the second-order filter is used in avionics, it is commonly to smooth data, and to wash out transients at mode change. Usually, a first-order filter suffices, and it being less expensive, is chosen over a second-order filter. Typical values for omega sub n, a, and b are 0.1-2 rad/s, and zeta 0.1-0.9. It should also be noted that two first-order filters can be chained together to form a second-order filter that is critically damped or overdamped. When implementing a second-order filter on normalized variables, such as angles, the discontinuities require special treatment.