Good Practice Guide No 132 Beginner’s Guide to …

1 good Practice Guide No 132 Beginner s Guide to measurement in electronic and electrical engineering The National Physical Laboratory (NPL) NPL is the UK s National measurement Institute, and is a world-leading centre of excellence in developing and applying the most accurate measurement standards, science and technology available.

2 NPL's mission is to provide the measurement capability that underpins the UK's prosperi ty and quality of life. NPL Contributors Fiona Auty Jonathan Williams Rachael Stubbins Find out more about NPL measurement training at or our new online study programme at National Physical Laboratory Hampton Road Teddington Middlesex TW11 0LW United Kingdom Telephone: +44 (0)20 8977 3222 Institution of engineering and Technology (IET) The IET is working to engineer a better world through our mission to inspire, inform and influence the global engineering community, supporting technology innovation to meet the needs of society.

3 It is the Professional Home for Life for engineers and technicians, and a trusted source of Essential engineering Intelligence . The IET has nearly 160,000 members in 127 countries, with offices in Europe, North America, South Asia and Asia-Pacific. IET Contributors Barry Brooks Amanda Weaver Mike Cunningham Tony Whitehead Mike Cash The Institution of engineering and Technology Michael Faraday House Six Hills Way Stevenage Hertfordshire SG1 2AY Telephone: +44 (0)1438 313 311 Fax: +44 (0)1438 765 526 Contents Foreword.

4 1 Introduction .. 3 good measurement Practice .. 5 International System of Units (SI) .. 6 measurement in 12 Uncertainty analysis .. 20 Introducing a defined measurement procedure .. 29 Reading instrument specifications .. 30 Case studies .. 33 Next steps .. 44 Further reading .. 45 Key to icons: Need to know Nic e to know Checklist 1 Foreword Mr Barry Brooks BSc (Eng) CEng FCGI FIMarEST FIET (President of the IET 2013-2014) measurement is a multidisciplinary, cross-sector topic critical to all engineering and control systems and to quality of life.

5 Although life in the 21st century relies heavily on precision measurement , often we are not even aware of it. Satellite navigation systems are dependent on ultra-stable clocks; different electrical components work together in personal electronic goods; and food producers use the optimal temperature necessary for perfection to prevent energy wastage. Precision measurement is at the heart of each of these products and services, many of which we take for granted. All engineers measure things, but do you know what use will be made of the measurements?

6 Are you making the right measurement and using the right tools? Do you know the SI rules? Do you understand the need for planning your measurement ? Do you know the effects of instrument performance limitations? This beginner s Guide will open your eyes to the significance of good measurement and will help you to understand how to use this to best effect in your area of engineering . Through the practical application of theory, alongside lively, interesting and relevant case studies, you will learn how electrical and electronic engineers measurements relate to national standards.

7 And you will see how good measurement Practice is necessary for you to make the most appropriate measurements. For over 140 years, the IET has been inspiring, informing and influencing the global engineering community, supporting technology innovation to meet the needs of society and, as such, we are delighted to have worked with NPL on this joint publication a publication that shares and advances knowledge to enable you to make a positive difference as an electrical or electronic engineer. This Guide will equip you with the guiding principles and good Practice to measurement in electronic and electrical engineering .

8 The IET: working to engineer a better world. 2 measurement in electronic and electrical engineering The business or study of designing and building electrical systems, especially those that use power and control machines or are involved in communication and the use of equipment. The action of measuring something where measuring ascertains the size, amount or degree (of something) by using an instrument or device marked in standard units. The world of the electronic and electrical engineer. Introduction 3 Introduction Life in the 21st century relies heavily on precision measurement .

9 Often we are not even aware of it: Satellite navigation systems depend on ultra -stable clocks, as any small err or in timing can throw navigation a long way off course. electrical components ordered from different suppliers will work together in your personal electrical goods. Food producers know the optimal temperature for preparing biscuits perfectly, so that they do not waste any unnecessary energy. Precision measurement is at the heart of each of these experiences, and many more that we often take for granted. NPL has a special role in measurement .

10 Every measurement is a comparison between a quantity we want to know about and a standard amount of that quantity. In the UK, NPL is responsible for maintaining these standard quantities and making them available to industry throughout the country, giving UK businesses a competitive advantage. When it all goes wrong: even simple measurement mistakes can be very costly! The Great Kersten Blunder. Software controlling the Vigor space probe, on course for Venus, used instead of to convert millimetres to inches. The error meant that the probe missed Venus completely, and $2 billion worth of technology was lost.