Importance

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Abstract

The control loop instability detection and correction apparatus monitors an error signal produced by a control system to detect any instability in the control loop before the instability significantly affects the performance of the controlled apparatus. This is accomplished by monitoring the error signal to detect a change in the error signal greater than a predetermined limit and to tabulate the number of times the change in the error signal is in excess of the predetermined limit over a fixed period of time. Whenever the change in the error signal is in excess of the predetermined limit, it is reduced in magnitude to a predetermined value and this resultant signal is applied to the controlled apparatus in place of the originally generated error signal. In addition during each sampling time interval, the result of this comparison is used to increment or decrement a counter. If the change in the error signal is in excess of the predetermined limit, the counter is incremented to indicate the number of times that the change in the error signal has exceeded the predetermined limit. If, on the other hand, the change in the error signal is less than the predetermined limit the counter is decremented to indicate that the error signal is within the allowable limits of magnitude. If this count tabulated by the counter exceeds a predefined threshold, an alarm indication is activated to note possibility of instability in the operation of the controlled apparatus.

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First Claim