VALIDITY OF DESCRIBING-FUNCTION TECHNIQUES FOR THE ANALYSIS OF THIRD-ORDER RELAYOPERATED SERVOMECHANISMS.
MASSACHUSETTS INST OF TECH CAMBRIDGE DYNAMIC ANALYSIS AND CONTROL LAB
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The relay-operated servomechanism oscillates at finite amplitudes and frequencies with its input equal to zero. These amplitudes and frequencies can be predicted by a special technique which replaces the relay by a quasilinear model called the describing function. To gain confidence and understanding in this type of technique, an analog computer was used to obtain exact solutions for the system and these were compared to solutions obtained by the describing function technique. In this thesis the solution comparisons are presented in a graphical form along with relay characteristic gain-phase plots, motor load gain-phase plots and an explanation of the describing function technique. Describing function predictions were found to be within ten percent of computer solutions for the great part, however, in the region of incipient oscillation results were consistantly poor. Author