Engineering Science Introduction to Systems, Lecture notes of Engineering

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Engineering Science

Introduction to Systems

System Diagrams

INPUT PROCESS OUTPUT

Assignment 1 - Open Loop Control

Redraw the systems diagrams shown below, filling in the missing inputs, processes

and outputs into your jotter.

Torch

Cash Machine

Gas Fire

DVD Player

Microwave

Vending Machine

Sub-Systems

The Universal System can be broken down into a number of sub-systems. For

example, a sub-systems diagram of a washing machine could look like this.

A systems boundary is drawn with a broken line. It represents the limits of the

system. Note that the inputs and outputs are the only things that cross the

system boundary.

A full sub-systems diagram of the washing machine could be a bit more

complicated.

On/Off Switch Water Heater Drum Motor

Dirty Clothes

Clean Clothes

System Boundary

On/Off Switch

Drum Motor

Water Heater

Dirty Clothes

Clean Clothes

System Boundary

Drum

Water Pump

Door Closed (^) Powder Dispenser

Manual Control

Electricity Electricity (^) Clean Water

Washing Powder

Waste Water

Control Unit

Programme Selector

For example, the light level in a room could be controlled with a dimmer switch.

The light level in the room can be measured by a human eye and the switch

adjusted manually to give exactly the light level required. This is fully described

as Manual, Closed Loop Control.

A Closed Loop Control system can always be identified by the presence of a

feedback loop. The feedback and control can either be Manual or Automatic. An

Open Loop Control system never has a feedback loop.

Manual^ Set Light level^ Electric^ Wiring^ Light Bulb Input

Desired Light Level

System Boundary

Manual Observation

Feedback Loop

Assignment 2 - Closed Loop Control

Redraw the systems diagrams shown below, filling in the missing sub-systems into

your jotter.

Fridge

Central Heating

Stadium Roof

Control Unit Fridge Coolant

Manual Input

______

_________________

____

_________ Boiler _______

_______ Desired Temperature

Temperature Sensor

Temperature Setting

Control Unit ______

Manual Input

___________

Limit Switch

___________ (^) Driver

Homework

1. A) Draw the Universal Systems Diagram.

B) Draw a systems diagram for the cement mixer

shown. Show all inputs and outputs.

2. A manufacturer wants to use a cruise control system to keep a car’s speed

constant even when it goes up and down hills. The system should allow a

driver to take their foot off the accelerator once the desired speed has been

set.

A) Complete the systems diagram below for the cruise control system.

B) This control systems makes use of a feedback loop. State the type of

control produced by this automatic system.

3. Give 3 further examples of Open Loop Control. Draw a systems diagram for

each, showing all inputs and outputs.

4. Give 3 further examples of Closed Loop Control. Draw a systems diagram for

each, showing all inputs and outputs.

Problems—From past papers

1. A petrol driven mini-moto is shown below.

(a) Complete the system diagram below for the mini-moto by adding the

main input energy and the main output energy.

(b) The main parts of a mini-moto drive system are shown in the diagram

below.

(i) (A) separates the system from the outside world. State the name of

this part of the diagram.

(ii) The whole system can be broken down into several parts labelled

above as (B). State the name given to these parts.

Mini-moto

………………………… Energy ………………………… Energy

Input Energy Engine^ Gearbox^ Chain Drive^

Output Energy

A

B

3. Hair straighteners are shown below.

(a) Complete the system diagram below for the hair straighteners by adding

one main input energy and one main output energy.

(b) The main parts of the hair straighteners are shown below.

(i) (A) separates the system from the outside world. State the name of

this part of the diagram.

(ii) The whole system can be broken down into several parts labelled

above as (B). State the name given to these parts.

Hair Straighteners

………………………… Energy ………………………… Energy

ON/OFF

Switch

Heating Element

Ceramic Plates

A

B

4. A CD player is shown below.

(a) Complete the diagram below for the CD player by adding one main input

and one main output. One input has been provided for you.

(b) Draw the Universal System Diagram.

CD Player

Switch ON (Electricity) ………………………… ………………………….

7. An air conditioning system is operated by closed loop control.

(a) Complete the diagram below.

(b) State a suitable electronic component which could be used for the

output driver sub-system.

Set temperature

Control Unit Output Driver

___________

_______

__________________

8. The temperature of a steam room in a leisure centre is controlled

automatically.

A valve opens to release steam when the temperature is below the set level.

When the temperature of the room is hot enough, the valve is closed.

(a) State the type of control produced by this automatic system.

(b) Complete the diagram.

Set temperature

Control Unit ___________ Valve^

Desired temperature

Temperature Sensor