Control SystemsIGCSE ICT

Objectives

True control system is when the computer is controlling the output dependent on information from sensors about what is happening.

Be able to describe a number of uses, giving the hardware and software requirements.

Be able to describe the applications that these uses can be put to.

Computers can control systems far more accurately, and respond to changes far more quickly than a human could

IPO (INPUT PROCESS OUTPUT)What is the role of the processor in any control system?

What is a control system?

Uses microprocessors or computers to control certain physical conditions Sensors take

measurements, then A/D converter converts them into digital signals

The measurements are compared to stored (predefined) values

Processor makes a decision based on the comparison

Control output devices will be used

Turtle Graphics (LOGO) Control of Lights and Lamps

Traffic Control System Control of Washing Machines Robotics Burglar Alarms Central Heating Video Recorders Microwave Ovens Control of Automatic Cookers Central Air Conditioning Computer-controlled Greenhouses

Examples of control systems

Usually measured by Sensors Physical conditions

(variables) that are controlled by computer/microprocessors include: Temperature Pressure Humidity Light Moisture etc

Hardware requirements: Input

Numeric KeypadPush buttons/switchesTemperature sensorMoisture sensorPressure sensorLight sensor

Processor

ADC (A/D Converter)

DAC (D/A Converter)

TimerAlgorithms to

compare data from sensors to predefined values or ranges

Signals sent to control output devices

Hardware requirements: Output

RobotFansHeatersBoilersBuzzer/alarmLightsLED displayMotors

Computer-Controlled Greenhouse

A light sensor to detect how much light the plants are getting

A temperature sensor to see how cold/hot the greenhouse is

A moisture sensor to se how wet/dry the soil is Lights to illuminate the plants if it gets too dark A heater to warm up the greenhouse if it gets

too cold A water pump for the watering system A motor to open the window if it gets too warm

inside

ADC

IPO Computer-Controlled Greenhouse

Inputs Processes Outputs

Light Sensor Sensors monitor amount of light , moisture, temperature

continuously

Light

Moisture SensorAnalogue data from sensors

converted to digital using ADCWater Pump

Temperature sensor

Temperature compared to preset range/value

Heater

Signal sent to turn on heater and use motor to close

window if too cold

Motor

Signal sent to turn off heater and use motor to open windows if too warm

Signal to actuator to turn water pump on if soil dry or off

is soil is moist

Air conditioning

Sensors are needed to monitor temperature (continuously)

Microprocessor compares the temperature with a preset value/range

Depending on result microprocessor causes the fan motor to speed up or slow down

Fan motor switched on or off

IPO Central Air Conditioning

Inputs Processes Outputs

Buttons/touchscreen

Sensors monitor temperature continuously

LED display

Contact switch Analogue data from sensors converted to digital using ADC

Fan

Temperature sensor

Temperature compared to preset range/value

Buzzer

Pressure sensor Signal sent to actuator to switch fan on or off

Closed Loop system

Output directly affects the input

No human intervention is necessary

Good for situations where control is required 24/7, or in a dangerous/difficult environment

Refrigeration

Sensors continuously monitor temperature

Microprocessor compares the temperature with a preset value/range

Depending on result microprocessor causes the fan motor to speed up or slow down

Fan motor switched on or off

IPO Refrigeration

Inputs Processes Outputs

Contact switch (door)

Sensors monitor temperature continuously

LED display

Pressure sensor (door)

Analogue data from temperature sensor converted

to digital by ADC

Compressor

Number pad or dial Temperature compared to preset range/value input by

user

Buzzer

Temperature sensor

Signal sent to actuator to switch compressor on if temp

is too high

Signal sent to actuator to switch compressor off if temp

is OK

Central heating

Sensors are needed to monitor temperature (continuously)

Microprocessor compares the temperature with a preset value/range

Microprocessor controls two actuators one opens gas valves in the

boiler the other switches the pump on

IPO Central Heating

Inputs Processes Outputs

Touch screen Sensors monitor temperature continuously

LED display

Number pad or dialAnalogue data from

temperature sensor converted to digital by ADC

Radiators

Temperature sensor

Temperature compared to preset range/value input by

user

Signal sent to actuators to switch pump on & open valves

if temp is too low

Signal sent to actuator to switch pump off/close valves if

temp is OK

Automatic Cooker (Microwave Ovens

are very similar, more features, most can be set to turn themselves on and off at particular times)

2 User inputs: Desired temperature Length of cooking time

Sensor measures the temperature in the cooker

Microprocessor controls a heating element to keep the temperature constant

Microprocessor controls a buzzer to inform the user when the time is up.

IPO Automatic Cooker

Inputs Processes Outputs

Touch screen/Keypad

Sensors activated

Temperature Sensor

Checks if temperature greater than the temperature from the

sensor

Buzzer

Timer Heater

Analogue data from sensors converted to digital by ADC

Burglar Alarm

User inputs a code to set the alarm when they leave the house and a code to stop the alarm being triggered when they re-enter the house

Detects when a door or window is open using a simple magnet and contact switch

If the movement sensor senses something, the computer can immediately decide what to do

IPO Burglar Alarm

Inputs Processes Outputs

Touch screen/Keypad

Sensors activated

Light SensorChecks if lights have been

turned onBuzzer/Alarm

activated

Movement Sensor (senses infra-red

light changes)

Detects if something is moving within a certain range

Magnet/Contact Switch

Checks if doors/windows are open

Analogue data from sensors converted to digital by ADC

Software requirements

Control software