City & Guilds 2330 Certificate of Electrotechnical Technology Level 2 Unit 2 Outcome 1 Session 1

1. Principles of electrotechnology City & Guilds 2330Certificate of Electrotechnical TechnologyLevel 2Unit 2 Outcome 1 Session 1

2. Outcome 1 Describe the application of the basic units used in electrotechnology Session 1 Basic S.I units and their multiples Aims and objectives of this session • To be able to identify the S.I. Unit, multiple, sub-multiple, symbol and quantity commonly used in electrotechnology • To be able to state why S.I. units are used and how quantities are managed. 2

3. Where did S.I units come from? The S.I system is the modern form of the metric system and is the most widely used system of measurement. The metric system was first implemented during the French revolution in the 1790s with just the ‘metre’ and ‘kilogram’ as the standards of ‘length’ and ‘mass’. In 1948 an overhaul of the metric system resulted in the development in the “Practical system of units” which when it was published in 1960, it was given the name “The International System of Units” .

4. SI Units To make it easier for everyone to understand each other a common standard has been adopted. Le Systeme international d'Unitesor SI Units officially came into being in October 1960 and has been officially recognised and adopted by nearly all countries. 4

5. Definitions of S.I. units Below are the fundamental units from which others are derived 5

6. Derived Units All units can be derived or ‘made’ from these fundamental units These units cannot be broken down into smaller elements A metre is always a metre. If we want to measure 5 centimetres we are sub-dividing the metre . If we want to measure kilo-metres we are multiplying the metre. The same applies to seconds, grams etc 6

7. Units and symbols 7

8. S.I. prefixes The SI allows the sizes of units to be made bigger or smaller by the use of appropriate prefixes. The electrical unit of a watt is generally used in terms of 1000 watts at a time. The prefix for 1000 is kiloso we use kilowatts kWas our unit of measurement. For makers of electricity, it is common to use megawatts MW or even gigawatts GW. 8

9. Try this on your calculator. To find a negative power: • Enter your number i.e. 2 • Press X10x button then (-) button • Press the number of negative powers i.e. 3 • Press = button • Answer should be 1 over 500 • Press ENG button • Answer should be 2x10-3 • Press SHIFT button then ENG button and then repeat • Answer should be 0.002 To find a positive power: • Enter your number i.e. 2 • Press X10x button • Press the number of positive powers i.e. 6 • Press = button • Answer should be 2000000

10. Power of 10 All prefixes are based on the power of ten. A power of 10 is positiveif for numbers larger than 10 and negative for numbers less than 1. It is usually written as M x 10n Where M = any number n = any power 10

11. Standard Form The reason why we do this becomes clearer when we start to do calculations. Instead of talking about an appliance being rated at 5.837x 103 W, we say 5.837 kW. The k is used to mean 103 or 1000 and so on as in the table. Standard form is when there is one and only one digit to the left of the decimal point 5.873x 103 InEngineering form we would write 5.837 k and can have more than one number in front of the decimal place. Theindex can be positive or negative depending on which side the decimal point has been moved from. End of session 1 11