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Systems Approach
Universal System
We use a systems diagram to analyse technology.
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
PROCESSINPUT OUTPUT
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,
OUTPUTS:
KETTLEWater and Electricity
Hot water, Noise and Steam
Water and Electricity.
Hot water, noise, steam.
INPUTS:
Pupil Problems Here are some problems for you to try,
1) Battery powered torch
TorchChemical energy
Light energy Heat energy
2) Vacuum cleaner
VacuumElectrical energy
Dirt
Noise, Heat, Clean carpets
Pupil Problems3) Washing machine
Washing M/C
Water, Dirty clothes, Electrical energy
Hot water, Noise, Steam, Clean clothes
4) Television
TVElectrical energy, Digital signal
Picture, Sound, Heat
Sub-SystemsSometimes it is necessary to break the PROCESS down into smaller pieces.
To enable this we consider the system’s
SUB SYSTEMS
Example: A battery powered torch
Switch BulbChemical energy
Light and Heat energy
System Boundary
Pupil Problems
1) A microwave oven
Timer
MagnetronElectrical energy
Heat, Light, Hot food
On/Off Turntable
Food
1st Inputs 2nd Subsystems
3rd Boundary
4th Flow of information arrows
5th outputsSet time
Pupil Problems
2) Washing machine
Heater Motor
Electrical energy
Clean Clothes
Control
Dirty clothes
Pump
Drum
Water
Hot water Clean Clothes
Set Cycle
Control Systems
All types of system need some form of control to operate
There are 2 main types of control,
OPEN LOOPIn an OPEN LOOP system the input causes the output
The output operates independently of the input
CLOSED LOOPand
Open loop system are cheap but not very accurate
Light switch BulbAction Light
Control Systems
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
On/Off Motor Fan Heater
ThermostatSet temp
Elect
Heat
Control Systems
Tap Handle
Valve Water levelWater
Eyes / Brain
Hand
Correct level
Manual Closed Loop
Control Systems
Automatic Closed Loop
Heating Switch
Valve
Water
Temp
SensorControl
Unit
Correct Temp
Required Temperature
Boiler
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.