Lecture 2 Flashcards
Give the key components of a block diagram
signals, systems, feedback, inputs, outputs
What are signals?
variables that are a function of time, normally have a physical unit and dimensions
What is a system?
elements that are interconnected with signals,
it is something that responds to signals
What is a disturbance signal?
a signal we cant control
an unwanted input that affects the systems output signal
What is an input signal?
a signal we can control
How do you decide what the system is in a block diagram?
the system will be something we are interested in
How is a signal represented on a block diagram?
Always as an arrow, with the direction representing the input and output flow of the signal to systems
What is a process?
A special name for a system that we are trying to control
How do we mathematically connect input and output signals?
Output signal = f(input signals) where the function f defines the sytem
ie the output signal is a function of the input signals
Give the different types of signal
Electrical signal - value of the voltage in a cable relative to ground
Sensor signals - typically an electric signal representing a physical measurement
physical quantities - eg the height of something
When setting up a block diagram what is often the easiest way to start?
Consider how manual control might work (ie via an operator)
Give an overview of manual control of a tank liquid height
Operator observes fluid height (sensor)
Operator mentally compares fluid height to desired position and decides how to adjust flow (controller)
Operator adjusts input flow accordingly (actuator)
What is a summing/difference block and how is it represented?
Drawn as a circle Used to compare a desired signal with an output signal
What is an error signal?
desired signal - output signal
What is a negative feedback system?
a negative feedback system is one in which we are taking away the output signal of a system from the desired signal to give an error signal
Why is automated control better than manual control?
Operator is bored, unreliable and expensive, often the systems that a manual operator might to control could be fast, complex, dangerous and inaccessible
What is the general progression of system blocks?
desired output response and measurement output -> comparison, controller, actuator, process -> actual output and feedback
What is a multi input multi output system?
a system with multiple inputs and outputs that are monitored and controlled all in one loop
What is a multiloop system?
a system with multiple loops - inner loop and outerloop
to control a number of signals
In an electric motor, what is assumed about the speed and input signal? (voltage)
Motor speed is proportional to the input signal
motor speed = G x input signal
Draw a simple block diagram from motor speed control
See lecture 2
What is proportional control
Proportional control is where an error signal e is multiplied by a constant K to give the control signal c
ie c = K x e
In proportional control what is controller gain?
Controller gain is the constant used to multiply the error signal by to give the control signal,
it must be chosen by the engineer
Derive the equation for the control signal for motor speed model given
desired speed = sd
motor speed = sa = Gc = const G * input signal c
measured motor speed = sm
error value = e
controller gain = K
sa = sd * GK/ (1 + GK)
We want GK/ (1 + GK) -> 1
Therefore K must be as large as possible
Give the issues with the motor speed control system described in these flashcards and their result
-No dynamics
-Assumed instantaneous change in motor speed
-Infinite angular acceleration
-Infinite torque
These assumption cause transient behaviour and instability
