Lecture 7

Question 1

What is the process behind coming up with a block diagram for a tank level

Answer 1

You have a desired height, you compare that to the current height to give an error signal, you have to pass this through a controller to give a usable signal in the actuator which affects the process which you’re trying to control, a sensor is then used to record the new height level

Question 2

How could the height of a tank of fluid be detected

Answer 2

Using ultrasound at the top of the tank reflecting off the bottom
Using a pressure sensor at the bottom of the tank if the density of fluid is known

Question 3

What is a linear system

Answer 3

Superposition (x1(t)+x2(t)) = f(x1(t)) + f(x2(t))
Y=x^0.5 is non linear
9 + 16 = 25
But 3+4 not = 5
And
Homogeneity f(Bx(t)) = B f(x(t))

Question 4

Why is a system required to be linear

Answer 4

The Laplace transform requires

Question 5

How do you know if a system is non linear

Answer 5

It does not follow the rules of superposition or homogeneity

Question 6

If a system does not follow rules of homogeneity how can we alter it to do so

Answer 6

Linearise the system ie y = mx + c assumed to be y = mx, can then treat constant c as an input to the linear system

Question 7

What does the time constant define

Answer 7

The speed of response of a 1st order system
Tau

Question 8

What is the settling time

Answer 8

Step response reaches +- 2% of the final value
Equal to 4*the time constant

Question 9

After one time constant the step response

Answer 9

Reaches 63% of its final value

Question 10

How do you rearrange block diagrams

Answer 10

Using the examples from the equation sheet

Question 11

As proportional gain increases what happens to the time constant

Answer 11

It reduces