ABSTRACT
In asymptotically process-stable systems, any infinitesimal increment to the input process causes only an infinitesimal increment of the output process. Acceptable levels of process instability can be translated into certain boundaries on the Nyquist diagram, so they can be accounted for in a necessary and sufficient way by appropriate sizing of the stability boundaries. The bounds for process instability are found for sinusoidal test signals. Process instability manifests itself in sudden bursts of oscillations or jumps in the output signal. These phenomena contribute to the output error and therefore need to be limited. The amplitude and shape of the periodic output signal are generally multivalued functions of the periodic input signal parameters, and depend on the input signal prehistory. Particularly, the output might depend on whether the current value of the input signal was arrived at by gradually increasing or gradually decreasing the input signal amplitude.
