Comments on `Optimal gain for proportional-integral-derivative feedback' by S.A.K. Al-Assadi and L.A

This comment concerns the comparison of tuning parameters for proportional-integral-derivative (PID) controllers proposed in the above paper (ibid., vol.7, no.6, p.16-19, 1987). The commenters focus on the time-delay example and the resulting table contained in the above paper. They remark on some fundamental points regarding PID controllers that have been misunderstood in the above paper as well as in T.B. Kinney (Chem. Eng., p.67, Sept. 1983), which serves as one of its principal references. >