Systems Approach Universal System INPUT PROCESS OUTPUT All systems can be analysed and simplified in terms of their inputs, process and outputs The UNIVERSAL SYSTEMS DIAGRAM consists of these three basic elements. This process is known as the “BLACK BOX” approach to technology We use a systems diagram to analyse technology. INPUT PROCESS OUTPUT

As an example, consider an electric kettle, Systems Diagrams To analyse a system more fully, we can list the inputs and outputs from the system. As an example, consider an electric kettle, Water and Electricity. INPUTS: OUTPUTS: Hot water, noise, steam. Hot water, Noise and Steam Water and Electricity KETTLE

Pupil Problems Here are some problems for you to try, Battery powered torch Chemical energy Light energy Heat energy Torch Vacuum cleaner Noise, Heat, Clean carpets Electrical energy Dirt Vacuum

Pupil Problems Washing machine Water, Dirty clothes, Electrical energy Hot water, Noise, Steam, Clean clothes Washing M/C Television Picture, Sound, Heat Electrical energy, Digital signal TV

To enable this we consider the system’s Sub-Systems Sometimes it is necessary to break the PROCESS down into smaller pieces. To enable this we consider the system’s SUB SYSTEMS System Boundary Example: A battery powered torch Light and Heat energy Chemical energy Switch Bulb

Pupil Problems 1) A microwave oven 2nd Subsystems 1st Inputs Timer Set time 5th outputs Magnetron Electrical energy Heat, Light, Hot food On/Off Turntable 3rd Boundary Food 4th Flow of information arrows

Pupil Problems 2) Washing machine Set Cycle Electrical energy Hot water,etc. Control Water Heater Motor Pump Drum Clean Clothes Dirty clothes

Control Systems OPEN LOOP and CLOSED LOOP All types of system need some form of control to operate There are 2 main types of control, OPEN LOOP and CLOSED LOOP In an OPEN LOOP system the input causes the output The output operates independently of the input Open loop system are cheap but not very accurate Action Light switch Bulb Light

Control Systems Set temp Heat Elect In a CLOSED LOOP system, the output is compared with a reference value Closed loop systems are more accurate, but also more expensive The self monitoring action of closed loop is achieved through a FEEDBACK loop Set temp Thermostat Heat On/Off Motor Fan Heater Elect

Control Systems Manual Open Loop Water Flood Tap Handle Valve Water level Person

Control Systems Manual Closed Loop Correct level Tap Handle Valve Water level Water Eyes / Brain Hand

Control Systems Automatic Closed Loop Water Correct level Press Start Switch Valve Water level Level Sensor Control Unit

Pupil Problems State three examples of manual open-loop control. Draw a system diagram for each one and show the system boundary. State three examples of manual closed-loop control. Draw a system diagram and show the system boundary. State three examples of automatic closed-loop control. Draw a system diagram and show the system boundary.

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 Set value Gas Valve Burner + - Temperature sensor Oven Correct temperature Actual value

Error Detector Symbol + - How the error detector works: If SET VALUE (+) is bigger than the ACTUAL VALUE (-) the ERROR SIGNAL is ON (Raising the oven temperature) Set value + Error If the SET VALUE (+) is less than the ACTUAL VALUE (-) the ERROR SIGNAL is OFF (Cooling the oven temperature) - Actual value

Pupil Problems Explain the following terms when applied to control systems: Open loop Closed loop Error detector

Pupil Problems Draw a control diagram showing the manual closed-loop control system for a cyclist steering a bicycle. Draw a control diagram showing the automatic closed-loop control system for the cruise-control in a car.