Control Systems

The Control Room of a Nuclear Power Station

A control system is a system of hardware and software that controls the function of a piece of equipment, e.g. a radio controlled car is an example of a basic control system. Other examples include…

Traffic Lights

Lifts

Microwave

Air Conditioning Systems

Theme Park Rides

Automatic Doors

Burglar Alarm

Train Networks

Robots

What is a Control System?What is a Control System?

Security Lights

In their simplest form, control systems take in data as input, process the data, and then send out signals as output…

The Parts of a Control SystemThe Parts of a Control System

In their simplest form, control systems take in data as input, process the data, and then send out signals as output…

The Parts of a Control SystemThe Parts of a Control System

There are two main types of control system…

Open LoopSystem

Closed LoopSystem&

Types of Control SystemTypes of Control System

The open loop system is the simplest type of control system, as it does not take account of the output. The input data is processed, then sent as output,e.g. an automatic door…

Open Loop SystemOpen Loop System

A person stepson a pressure pad,

and the pressure pad sends a signal tothe control box

The control box processes the

data, and sendsa signal to the electric door

The door opens in time for the person

to walk through

Open Loop SystemOpen Loop System

The open loop system is the simplest type of control system, as it does not take account of the output. The input data is processed, then sent as output,e.g. an automatic door…

A person selects the microwave power and the time for

cooking. This input is sent to the

embedded computer

The embedded computer

processes the data, and sendsa signal to the

microwave generator

The microwave generator cooks the food for the required time at the required

power

Open Loop SystemOpen Loop System

Another example of an open loop system is the control system for a microwave oven…

The problem with this open loop system is that the microwave oven will keep cooking the food, even ifit is already burnt – there is no account of output.

A closed loop system uses feedback provided by sensors. Feedback is where information from the output gets used as part of the input. A feedback loop provides extra data, which is processed withthe input data.

Closed Loop SystemClosed Loop System

Closed Loop SystemClosed Loop System

A closed loop system uses feedback provided by sensors. Feedback is where information from the output gets used as part of the input. A feedback loop provides extra data, which is processed withthe input data.

The pilot operates the control to put the aircraft into a

steep turn.Feedback also forms

part of the input.

The plane’s control box (a large computer)

processes this data and sends signals to the

wing flaps and engines.

The wing flaps and engines make the

necessary adjustments.

Most control systems are closed loop systems, e.g.a flight control system…

Sensors monitor the tilt of the aircraft and send this information to the control box. This becomes part of the input. When the required amount

of tilt has been reached, the computer sends signals to thewing flaps and engine to stop any further adjustments.

Closed Loop SystemClosed Loop System

Timings are set at the control box for

the heating to come on and off, and the thermostat on the

wall is turned to the correct temperature.Feedback from the thermostat forms part of the input.

The control box processes these

settings and sends signals to the boiler

and water pump.

The boiler and water pump operate

together to warm the house to the

correct temperature.

Another example of a closed loop system is a central heating system…

The thermostat is a heat sensor which detects the temperature in the room. The thermostat sends signals to the control box, which will

switch the water pump off if the house is warm enoughand on, if the house is too cold.

Closed Loop SystemClosed Loop System

What different control systems might there be onboard this yacht?

Engine Management

Air conditioning

Navigation

Control TechnologySome of the most advanced control technology is used in cars and airplanes.

Control TechnologyControl Technology

This car’s control systems include:

ABS (Anti-lock Braking System)

Engine Management

Rain detecting windscreen wipers

Darkness detecting headlights

Anti-lock Brake SystemAnti-lock Brake System

Draw an input-output diagram for the flow of data in an anti-lock brake system…

The driver applies the brakes firmly in an emergency.

Feedback fromthe sensors in the wheel also forms part of the input.

The control box processes the data and

either allows the braking to go ahead or sends a

signal to the calliperto release a wheel.

The calliper either grabs or releases the wheel and the car slows down as quickly as possible without skidding.

Sensors monitor the motion of the wheels. If any of the wheels stops turning, i.e. starts skidding, the control box sends a signal to the brake calliper to release the brake on that wheel for a fraction

of a second, just until the wheel starts turning again.

Rain-detecting Windscreen WipersRain-detecting Windscreen Wipers

Draw an input-output diagram for the flow of data in a rain-detecting windscreen wiper control system…

Sensors in the windscreen detect the moisture level

and send data to the control box. The driver may alsoset the wipers

manually.

The control box processes the data and sends a signal to the windscreen wipers,

controlling the precise speed of movement.

The wipers move at a rate which

removes the water efficiently, whilst distracting the driver as littleas possible.

Sensors in the windscreen continue to send data to the control box, e.g. if the car slows down, less rain will hit the windscreen so the moisture

level will go down. This data is fed back to the control box,which would then slow down the wipers.

Fly-by-Wire

Fly-by-WireFly-by-Wire

Fly-by-wire is a complex control system that controls and monitors:

Thrust (force produced by the engine)

Lift (upwards force produced by the wings)

Pitch and yaw (the tilt of the aircraft)

Flight plan (weight, destination, route, weather conditions)

Fly-by-WireFly-by-Wire

Fly-by-wire creates a huge amount of data which is passed from sensors, to the onboard computerto be processed, then onto the output devices.

The computer processes the pilot’s instructions from the joystick and other cockpit controls, then sends signals to the rudders, engines and wing flaps inorder to achieve the desired results.

There are no physical links, such as cables from the cockpit directly to the rudders, engines, etc.

Fly-by-WireFly-by-Wire

If the pilot pulls too heavily on the joystick, thesystem may issue a warning to the pilot, or override the pilot’s instruction, to prevent an accident.

Modern aircraft are so complex, that it would not be possible tofly them withoutfly-by-wire technology.

Control systems can work 24 hours a day, 7 days a week. They don’t need a break, they don’t complain and they don’t need paying – unlike humans.

Advantages of Control SystemsAdvantages of Control Systems

They can be relied upon to respond quickly and precisely to data from many different sensors at the same time.

They can be used in inhospitable and dangerous situations, e.g. inside Nuclear power stations.

The software and hardware can be expensive because it may have to be produced specifically for a particular job.

Disadvantages of Control SystemsDisadvantages of Control Systems

If a computer fails, the whole system will fail. For this reason, important control systems, such as fly-by-wire, or those inside a nuclear power station, are protected with emergency backup systems ready to take over in case the main system fails.

The computer cannot react to unexpected events, only those events which have been programmed in, whereas a human would be able to take action.

Keyword Activity 1Keyword Activity 1

Drag the missing words to the correct place in the sentences…

Keyword Activity 2Keyword Activity 2

Drag the missing words to the correct place in the sentences…

WordsearchWordsearch

CrosswordCrossword

QuizQuiz

After viewing this presentation, you should…

Understand the terms control system, input, processing and output.

Understand the difference between an open loop system and a closed loop system.

Be able to list several examples of computer controlled systems, e.g. traffic lights, burglar alarm.

Be able to describe feedback.

ObjectivesObjectives

Be able to draw input-output diagrams to explain what happens at each stage of input, process, output and feedback for common control systems.

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