1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

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

8. 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

9. 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

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

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

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

13. 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.

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

15. 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

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

17. 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.