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