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 level

Water

Person

Flood

Manual Open Loop

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.