Abstract
In this paper a method of optimum setting for the PI controller in a process control system is presented.
A stepwise disturbance to the control system will produce a pair of characteristic figures, i. e., the amount of overshoot and the amplitude damping ratio. They are used as performance indices of the optimum setting of the controller. A 20 percent overshoot will be optimum in the sense that it gives the smallest ISE among the responses with the same amplitude damping ratio. On the other hand a desirable value of the amplitude damping ratio will be 0.25 which is recommended by J. G. Ziegler and N. B. Nichols. In this paper it is shown that an amplitude damping ratio being 0.2∼0.25 makes the quadratic performance index smallest for the controlled system of the first order lag system with delay.
The adjusting device is built as a trial. The impulse response of control system for the disturbance is identified by means of the correlation technique using the M-sequence signal. Two performance indices, the amount of overshoot and amplitude damping ratio, are evaluated from the impulse response. The proportional gain and the reset time of PI controller are simultaneously adjusted with the pulse motors in inverse proportion to the error of the amplitude damping ratio and the reciprocal of the overshoot respectively.
Simulation studies are carried out on a analogue computer and give satisfactory results.
