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Introductory unit on systems

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  1. 1. Systems Approach Universal System <ul><li>We use a systems diagram to analyse technology. </li></ul><ul><li>All systems can be analysed and simplified in terms of their inputs , process and outputs </li></ul><ul><li>The UNIVERSAL SYSTEMS DIAGRAM consists of these three basic elements. </li></ul><ul><li>This process is known as the “BLACK BOX” approach to technology </li></ul>PROCESS INPUT OUTPUT
  2. 2. Systems Diagrams <ul><li>To analyse a system more fully, we can list the inputs and outputs from the system. </li></ul><ul><li>As an example, consider an electric kettle, </li></ul>OUTPUTS: KETTLE Water and Electricity Hot water, Noise and Steam Water and Electricity. Hot water, noise, steam. INPUTS:
  3. 3. Pupil Problems Here are some problems for you to try, <ul><li>Battery powered torch </li></ul>Torch Chemical energy Light energy Heat energy <ul><li>Vacuum cleaner </li></ul>Vacuum Electrical energy Dirt Noise, Heat, Clean carpets
  4. 4. Pupil Problems <ul><li>Washing machine </li></ul>Washing M/C Water, Dirty clothes, Electrical energy Hot water, Noise, Steam, Clean clothes <ul><li>Television </li></ul>TV Electrical energy, Digital signal Picture, Sound, Heat
  5. 5. Sub-Systems Sometimes it is necessary to break the PROCESS down into smaller pieces. <ul><li>To enable this we consider the system’s </li></ul><ul><li>SUB SYSTEMS </li></ul>Example: A battery powered torch Switch Bulb Chemical energy Light and Heat energy System Boundary
  6. 6. Pupil Problems 1) A microwave oven Timer Magnetron Electrical energy Heat, Light, Hot food On/Off Turntable Food 1 st Inputs 2 nd Subsystems 3 rd Boundary 4 th Flow of information arrows 5 th outputs Set time
  7. 7. Pupil Problems 2) Washing machine Heater Motor Electrical energy Clean Clothes Control Dirty clothes Pump Drum Water Hot water,etc. Set Cycle
  8. 8. Control Systems <ul><li>All types of system need some form of control to operate </li></ul><ul><li>There are 2 main types of control, </li></ul>OPEN LOOP <ul><li>In an OPEN LOOP system the input causes the output </li></ul><ul><li>The output operates independently of the input </li></ul>CLOSED LOOP and <ul><li>Open loop system are cheap but not very accurate </li></ul>Light switch Bulb Action Light
  9. 9. Control Systems <ul><li>In a CLOSED LOOP system, the output is compared with a reference value </li></ul><ul><li>Closed loop systems are more accurate, but also more expensive </li></ul><ul><li>The self monitoring action of closed loop is achieved through a FEEDBACK loop </li></ul>On/Off Motor Fan Heater Thermostat Set temp Elect Heat
  10. 10. Control Systems Tap Handle Valve Water level Water Person Flood Manual Open Loop
  11. 11. Control Systems Tap Handle Valve Water level Water Eyes / Brain Hand Correct level Manual Closed Loop
  12. 12. Control Systems Automatic Closed Loop Start Switch Valve Water level Water Level Sensor Control Unit Correct level Press
  13. 13. Pupil Problems <ul><li>State three examples of manual open-loop control. Draw a system diagram for each one and show the system boundary. </li></ul><ul><li>State three examples of manual closed-loop control. Draw a system diagram and show the system boundary. </li></ul><ul><li>State three examples of automatic closed-loop control. Draw a system diagram and show the system boundary. </li></ul>
  14. 14. Control Diagrams Example: Temperature control in a gas oven We could draw a systems diagram for the gas oven, but it is sometimes necessary to draw a more accurate control diagram Temperature sensor Oven Burner Gas Valve - + Set value Correct temperature Actual value
  15. 15. Error Detector Symbol - + Set value Actual value Error How the error detector works: If SET VALUE (+) is bigger than the ACTUAL VALUE (-) the ERROR SIGNAL is ON (Raising the oven temperature) If the SET VALUE (+) is less than the ACTUAL VALUE (-) the ERROR SIGNAL is OFF (Cooling the oven temperature)
  16. 16. Pupil Problems <ul><li>Explain the following terms when applied to control systems: </li></ul><ul><li>Open loop </li></ul><ul><li>Closed loop </li></ul><ul><li>Negative feedback </li></ul><ul><li>Positive feedback </li></ul><ul><li>Error detector </li></ul>
  17. 17. Pupil Problems <ul><ul><ul><li>Draw a control diagram showing the manual closed-loop control system for a cyclist steering a bicycle. </li></ul></ul></ul><ul><ul><ul><li>Draw a control diagram showing the automatic closed-loop control system for the cruise-control in a car. </li></ul></ul></ul>