This Handbook is aimed at Electrical and Instrument Technician level. This advisory book gives Technicians the knowledge of how electronic components actually work and how to fault find on electronic circuits. There are limitations on Atex equipment on what can be changed. The author is an Electrical Training Consultant with 38 years experience with BP Hull, seven of those years as their site Instrument/Electrical Training Officer and after retirement 16 years as a Electrical Training Consultant carrying out Training and Assessing for the Complex Scheme at Humberside Off shore Training Association ( H O T A)