Process control, automatic frequency response

Automatic control has long been a significant feature of the process industries, but only very recently has there been any attempt to treat process control problems quantitatively. It is now clear that the theoretical developments in the field of servomechanisms and governors are generally applicable to process control problems. The great simplification in treatment that results from frequency response characterization, makes possible a quantitative appraisal and design of process control systems. 

Chapters 2, 3, and 4 deal with the distillation variables, and Chapter 5 covers distillation process control strategies. Chapter 6 describes some of the constraints on distillation variables and separation capabilities. Chapter 7 introduces the concepts that are critical to product quality and the measurements that evaluate performance criteria such as frequency of failure. Chapter 8 describes the concepts and nomenclature that are fundamental to PID control loops. Chapter 9 covers the concepts of tuning process controllers when they are operating in automatic output mode. Chapter 10 is about measuring the response of process variables when the controller is in manual output mode, that is, with no feedback from the process variable. 

Automatic tuning needs identify the dynamics of a certain process. Usually Relay was mainly used as an amplifier in the fifties and the relay feedback was applied to adaptive control in the sixties. The exciting to a process loop make it reach the critical point. The critical point, i.e, the process frequency response of the phase lag of pi(it),has been employed to set the PID parameters for many years since the advent of the Ziegler-Nichols(Z-N) rule. From then several modified identification methods are... 

For that purpose, the quartz crystal is simultaneously excited at two frequencies. The response at the lower frequency is processed by a feedback loop dedicated to measure and automatically compensate Cq. The response at the higher frequency is processed by a phase-locked loop that continuously maintains and tracks oscillations at/s. The voltage waveform V hl is the sum of the two sinusoidal signals V h. with frequency/h generated by the voltage controlled oscillator VCO, and Vl, with frequency/, lower than/n, generated by the auxihary oscillator OSC. The frequency/r of the signal Vu is taken as the output frequency/out of the whole circuit. In the frequency domain, the ex-... 

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