A digital phase-shift-keyed technique for narrowband system identification

Abstract

Maximum-entropy binary test signals using microcomputer software are used for real-time interrogation of control systems to evaluate frequency response information. The most commonly used of these test signals spread their energy among known baseband frequencies of octave and/or decade ratios starting with the fundamental. Digital phase-shift-keyed modulation is used to design new zoom binary test signals, which use either a finite squarewave or a compact octave binary modulating signal. A zoom factor, or zoom factors with multiphase-shift-keyed modulation, are used to concentrate the test signal energy in an ever decreasing bandwidth on either side of a selected suppressed carrier. This allows a more selective system identification by a microcomputer in the form of frequency information, with high spectral resolution, about a specified central frequency. These novel binary interrogation signals are used to 'zoom in' on the closed-loop maximum magnification of a lightly damped DC position servo and highlight the gain margin of an air temperature control system.