A computational compensation for measuring system dynamics

This paper is concerned with the general problem of de termining the time history of an unknown input signal, given only the recorded response of a known physical sys tem excited by the unknown input. The particular case considered is determination of true thrust from the re corded test stand response, with the physical system re sponse noise superimposed upon the thrust data. Passive or numerical filtering can smooth the trace, but these methods will attenuate the signal within a particular fre quency band, and thus may distort the data content of the recorded response.

The paper describes analog computer techniques that can be used to reconstruct data distorted by such physical system response. The data may be recovered through an "active filtering" process, even when it contains compo nents of a higher frequency than the response noise being removed. Several examples are shown, including one case where the original signal was recovered intact even though the input signal excited a system resonance by passing through the natural frequency of the simulated test stand.

The method described is not restricted to linear systems, but can take into account such nonlinearities as changing rocket booster mass, and nonlinear damping and spring force versus deflection relationships. The major require ment is to obtain sufficient information to permit deriva tion of a realistic mathematical model of the physical sys tem used for test and measurement purposes.