Velocity deadband method

Chapter 22 provides equations for typical process controllers and control valve dynamics. The controllers considered are the proportional controller, the proportional plus integral (PI) controller and the proportional plus integral plus derivative (PID) controller. Integral desaturation is an important feature of PI controllers, and mathematical mc els are produced for three different types in industrial use. The control valve is almost always the final actuator in process plan. A simple model for the transient response of the control valve is given, which makes allowance for limitations on the maximum velocity of movement. In addition, backlash and velocity deadband methods are presented to model the nonlinear effect of static friction on the valve. 

Modelling static friction the velocity deadband method... 

It is interesting to compare the backlash description of static friction with the velocity deadband model. Equation (22.56) was programmed for the velocity deadband method, while equations (22.58) and (22.59) were programmed for the backlash description. The half-deadband/half-backlash width, b, was chosen as the largest likely value of 0.05. The two models were subjected to a controller output consisting of a damped oscillatory output of period 150 seconds. The exciting... 

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