a) Antilock brake systems use feedback control to manipulate a valve controlling
ID: 3348735 • Letter: A
Question
a) Antilock brake systems use feedback control to manipulate a valve controlling the pressure applied to the hydraulic brake. The speed of the wheel is measured, compared to set point and fed into an automatic controller whose output is used to manipulate the valve. Draw a block diagram showing the basic elements of the control system. (2 marks) b) In a particular feedback control system, the error signal increases linearly for the first five seconds from 0% to 10% and stays at 10% for the next five nds. After this period the error signals decrease slowly at 1%/s. A PID controller is responding to the signal. Show schematically (i) how controller output would vary with the proportional signal alone for the first 15 seconds and (ii) how the controller output would vary with derivative action alone for the first 15 seconds. (4 marks) c) For the case above, when would you expect the integral action of the controller to reach zero? Justify your answer (2 marks) d) Briefly outline how to use the "process reaction tuning method" to tunea PID controller, It is not necessary to reproduce the formulae for determining the various constants, rather describe the approach and basic concept of the method. (4 marks)Explanation / Answer
Tuning process
A. Controller should be placed in the manual and we need to wait for the process to settle
B. Minor percentage change should be made in the controller output and wait for the process variable to settle to a new value.
C. Calculate the change in process value and convert it into the percentage.
D. Maximum slope of process curve helps us to find out dead time and time constant.
E. Repeat the test 2-3 times to obtain good process characteristics.
F. Check the settings of new controller and compare it with the old one .
F.
Implement and test the new controller settings and monitor the new controllers performance.
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