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Feedback system testing

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1 Author(s)
White, C. ; Naval Research Laboratory, Washington DC, USA

An analog method of servo system performance testing applicable to experimental analysis and system development and to go-no-go production and maintenance tesfiug has been devised. For a servo system with a forward transfer function Geoand a feedback transfer function Gouthe loop actuating signal equals the loop input signal divided by1+G_{eo}G_{ou}. The loop actuating signal becomes exactly equal to a test signal if the test signal is multiplied by the factor1+G_{eo}G_{ou}before application to the servo system. The difference between the loop actuating signal of the closed-loop servo system and the arbitrary test signal is continuously zero for the system exactly meeting the specificationG_{eo}G_{ou}function simulated in the signal generator. Sinusoidal testing methods are most effective with the servo system loop open. Transient testing (single-event time-domain input) is usually performed on servo systems with the loop closed. The analog method described, as distinguished from transient and sinusoidal methods, uses time-domain signals (a step-function signal generator input is found suitable) to obtain frequency-domain parameters in a method effectively making an open-loop test of a closed-loop servo system. The1+G_{eo}G_{ou}signal generator is conveniently realized using an analog computer of the operational amplifier type. An alternative mechanization of the signal generator uses only passive elements. Nonlinear as well as linear servo systems may be tested by the method. Single-integrator, angle tracking, and range-tracking servo systems have been analyzed. The range-tracking transfer function was employed in an analog computer experiment. Recordings of both the loop actuating signal and the difference between the loop actuating signal and the signal generator input were made for 0, ± 6 db, and ± 12 db departures from correct gain and for 0, ± 1, and ± 2 octave departures from correct corner frequency. A study of these recordings revealed potentialities for control of adaptive servo systems.

Published in:

Automatic Control, IRE Transactions on  (Volume:6 ,  Issue: 1 )