41081 Chapter Notes - Chapter 10: Rise Time, Embedded System
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Chapter 10 - Control Systems
Introduction to Control Systems
• A control system is a type of embedded system that regulates the behaviour of a
physical device by seeking to match a system value to a desired value.
• The device being controlled is the plant.
• The desired output value is an input into the system, and the difference between
the desired, and the actual output is known as the error.
• An actuator is the part of the machine which is responsible for moving or controlling
the system.
• A controller strives to reduce the error by changing the value of the actuator input in
response to the error values.
• On-Off control is a simple control mechanism that either completely enables or
disables an actuator.
• There are some undesirable features that occur with this control mechanism, such as
overshooting (where the latency that occurs causes the value to be larger than
wanted). Another issue that occurs is oscillation which is where the value goes
above and below the desired value.
Proportional Control
• One way to reduce issues surrounding control systems is to set the changing aspect
of the system to be proportional to the resulting error.
• A proportional controller sets the actuator input value equal to the error times a
constant:
• The best value for the constant can be determined through experimentation or
through mathematical equations and analysis.
Proportional-Derivative Control
• The issues initially mentioned, or overshoot, oscillation and the slow rise time can be
further reduced by having the controller consider the rate of change of the output
value, as it approaches the desired value.
• It considers both the output error and the output rate of change.
Proportional-Integral-Derivative Control
• An undesirable feature in a control system is steady-state error wherein the actual
output value never actually reaches the desired output value.
• This value can be approximated by summing past error values computed for each
sample, which can be done through integration.
• PID is short for Proportional Integral Derivative, which is a controller that uses the
following equation:
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