Week 3 - Control System Security

Question 1

Control System

Answer 1

A system of devices that manages, commands, directs, or regulates the behavior of other devices or systems to achieve a desired output.

Aim of controller is to make sure the response of the system matches a desired value, known as the reference or setpoint, by automatically adjusting the input.

Question 2

Automatic control

Answer 2

Helps with achieving optimal performance, it improves productivity, it simplifies and facilitates tasks, it reduces human error, makes tedious manual tasks automated.

It enables engineering, industrial and scientific advancements.

It is an essential part of high-tech industries such as: space- vehicles, vessels, airplanes jet fighters (fly-by-wire), self-driving vehicles, missile guidance, robotic systems, (nuclear) power plants, manufacturing, HVAC, and industrial processes

Question 3

Application of automatic control

Answer 3

• Automated industrial robots.
• Auto pilot system and flight control computers (FCC)
• Speed governance.
• Dynamic positioning system (DPS) for vessels.
• Temperature, pressure, flow and humidity control.

Controlled systems are parts of our daily life: from as simple as a fridge (or room) temperature controller to sophisticated ones such as self-driving vehicles.

Question 4

Concept of Automatic control

Answer 4

Control systems for short are comprised of different elements:

Control systems monitor a processes or plant to make sure it does not vary from pre-set limits.

This is performed by changing the manipulated variables (inputs) within their specified range to maintain the controlled variable (output) at some desired value.

For example, changing the fan speed (manipulated variable) to keep the CPU temperature (controlled variable) within its safe operation range.

Question 5

Automatic Control: Stages

Answer 5

1. Measurement
2. Comparison
3. Computation
4. Correction

Question 6

Plant

Answer 6

Part of a system that is going to be controlled or regulated is called a plant.

This could be a piece of equipment or a set of machine parts.

The purpose of a plant is to perform a particular operation. (air cooled CPU and heatsink)

Question 7

Process

Answer 7

Any operation to be controlled (turning on the fan)

Question 8

Controller

Answer 8

An element of the system which controls the plant or the process.

Question 9

Input

Answer 9

An external signal applied to the control system in order to generate a specified output.

Question 10

Output

Answer 10

The response obtained from the control system when the input signal is applied.

To understand the behavior of the system to the input, it is important to acquire the output. Control system behaviour (how the output corresponds to input changes)

Question 11

Disturbance

Answer 11

This is an undesired signal that adversely impacts the value of the output.

Unavoidable in real-life systems, not in our control.

Internal disturbance, External disturbance.

One of the main reasons of using control systems is the presence of disturbance.

Question 12

Control System Types

Answer 12

1. Natural: the planet and human body
   are natural control systems.
2. Manmade: any control system made
   by humans.
3. Manual: it is not automatic (example:
   light switch)
4. Automatic: human body temp, room temp.
5. Open-loop: no feedback from the process. Example washing machine, toaster.
6. Closed-loop: these systems receive some information from the controlled process. Example fridge, auto pilot.
7. Linear & non-linear: output has a linear relation with the input (increasing the input by x would increase output by x), whereas non-linear does not.
   * Example of linear system: toaster, 1 bread needs 1 minute, 2 breads takes 2 minute …
   * Example of non-linear system: force
   required to open or close a bottle. Fuel
   efficiency vs speed
8. Time variant vs time invariant: when the parameters of the system and hence its behavior does not change with time it is time-invariant. When they do alter with time the behavior changes with-time and it is called time-variant.
   * Battery charging: many cycles -> less charge
   * Car engine: output power -> acceleration
   * Smart traffic light: delay -> traffic

Question 13

Open loop control system

Answer 13

Output of the system is not compared with the reference input therefore the accuracy of the system depends on the calibration.

Adversely impacted by the presence of disturbance. It is only practical for simple systems where the input and output relation is known and there are no internal/external disturbances.

Systems that rely on time are often open-loop for example, traffic light, toaster, washing machine, microwave-oven

Question 14

Open loop control system: Adv.Disadv.

Answer 14

Advantages:
– Simplicity to design and therefore cheap and economical.
– Useful when output is difficult to measure.
– Easy and cheap maintenance.
– No feedback stability issues.

Disadvantages:
– Accuracy depends on calibration accuracy.
– Inaccurate if there are variations in external environment.
– Regular maintenance and recalibration required to maintain the quality and accuracy of the system.

Question 15

Closed loop control system

Answer 15

This systems maintain a predefined relationship between the output and the input by means of comparing them. This is also called a feedback control system

Feedback control and closed-loop are used interchangeably

The input and output both are depending on each other.

Feedback is always used to better control the action and reduce the system output error.

The error is fed to the controller, so it controls the system such that the error is reduced to zero.

Question 16

Closed loop control system: Error

Answer 16

The error is 𝑒(𝑡) = 𝑟 𝑡 ± 𝑏(𝑡);

When the feedback (b) is positive system is called a positive feedback system and if b is negative its called a negative feedback system.

The controller proportionally adjusts the error signal to generate the manipulated signal (m) to keep the process under control.

m(t) is generated such that to reduce the error to zero, this signal is used to control the process such and generate the controlled output c(t)

Question 17

Closed loop control system: Adv.Disadv

Answer 17

Advantages:
– High accuracy as the output is constantly monitored and manipulated signal is generated to reduce the error.
– Internal/external disturbance impact is mitigated, as changes are sensed by the controller to modify the error accordingly.
– No regular recalibration or maintenance is required as system can adjust.

Disadvantages:
– Complicated, time consuming, and expensive design (as requires more sensors).
– A bad design could lead into incorrect feedback, therefore pushing the controller to overcorrect/undercorrect and make the system unstable.
– Overcorrection and instability is one of the biggest challenges of the design.

Question 18

Ideal control system

Answer 18

1. Accuracy,
2. Sensitivity,
3. Noise Tolerance,
4. Stability,
5. Bandwidth,
6. Speed,
7. Oscillation

Question 19

Industrial Control Systems

Answer 19

Used for managing, directing, and regulating the behavior of automated industrial processes. A term that encompass several types of control systems, but all these systems have some basic traits in common. Their job is to produce a desired outcome, typically maintaining a target state or performing a certain task in an industrial environment. They carry out this function using sensors to gather real-world information. They then compare this data with desired set points, and compute and execute command functions to control processes through final control elements, such as control valves, to maintain desired states or complete tasks.

Question 20

Sensors and Actuators

Answer 20

Both the devices that manipulate the mechanical components to which they are attached (e.g., valves, switches, relays) as well as the sensors that report field data to the controllers. This is the point that bridges the cyber environment with the physical world.

Question 21

Controllers

Answer 21

The devices that receive input from sensors and adjust the actuators based on their programming.

Question 22

Local Supervisory Systems

Answer 22

Systems enabling operators to supervise, monitor, and control the physical processes. These interfaces may use commodity operating systems like Windows but are frequently simpler devices like touch screens.

Question 23

Management Systems

Answer 23

Servers and workstations at the top level of the industrial control network. The end point of all ICS control and monitoring and tie-in point for business systems, these systems have broad visibility into the entire ICS environment, often across multiple geographic regions.

Question 24

Business Systems

Answer 24

Corporate-level services that use ICS operational data and telemetry for business applications like billing, modeling, trending, and reporting. These systems are not considered part of the industrial control network.