9 - Measuring Frequency Response

Abstract

Many instruments have been developed to measure frequency response, but they are expensive and difficult to integrate in a digital control system. To solve this problem of integrating a control system analyzer into a system, interfaces are built into the software for collecting and analyzing the necessary data on PC. There are a number of facets for measuring frequency response: The system is excited with the correct sinusoidal waveform, and the resulting system behavior is collected and the relevant frequency response data is extracted from it. The chapter describes the two methods used primarily for measuring frequency response: measuring in isolation and in-loop measurement. The chapter also discusses the ways to overcome the effects of noise and nonlinearities, which are the two inevitable real-world issues of measuring frequency response. The chapter illustrates an example set of software that can be used to integrate the control system analyzer into the system.