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Control Systems

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  1. IGCSE ICT Control Systems

  2. 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

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

  4. 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

  5. Examples of control systems • 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

  6. Usually measured by Sensors • Physical conditions (variables) that are controlled by computer/microprocessors include: • Temperature • Pressure • Humidity • Light • Moisture etc

  7. Hardware requirements: Input • Numeric Keypad • Push buttons/switches • Temperature sensor • Moisture sensor • Pressure sensor • Light sensor

  8. Processor • ADC (A/D Converter) • DAC (D/A Converter) • Timer • Algorithms to compare data from sensors to predefined values or ranges • Signals sent to control output devices

  9. Hardware requirements: Output • Robot • Fans • Heaters • Boilers • Buzzer/alarm • Lights • LED display • Motors

  10. 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

  11. IPO Computer-Controlled Greenhouse

  12. 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

  13. IPO Central Air Conditioning

  14. 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

  15. 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

  16. IPO Refrigeration

  17. 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

  18. IPO Central Heating

  19. 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.

  20. IPO Automatic Cooker

  21. 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

  22. IPO Burglar Alarm

  23. Software requirements • Control software