Measurement and Control Basics Fourth Edition

Chapter 3 - Electrical and Electronic Fundamentals

Introduction

The design of programmable control systems requires a thorough
knowledge of the basic principles of electricity and electronics. This
chapter will discuss the fundamentals of electricity and magnetism and
then examine the electrical and electronic circuits that are commonly
encountered in process control. We will also discuss the operation and
purpose of electro-magnetic and electronic devices, such as transformers,
power supplies, electromagnetic relays, solenoid valves, contactors,
control switches, and indicating lights.

Fundamentals of Electricity

Electricity is a fundamental force in nature that can produce heat, motion,
light, and many other physical effects. The force is an attraction or
repulsion between electric charges called electrons and protons. An electron
is a small atomic particle having a negative electric charge. A proton is a
basic atomic particle with a positive charge. It is the arrangement of
electrons and protons that determines the electrical characteristics of all
substances. As an example, this page of paper contains electrons and
protons, but you cannot detect any evidence of electricity because the
number of electrons equals the number of protons. In this case, the
opposite electrical charges cancel, making the paper electrically neutral.

If we want to use the electrical forces that are associated with positive and
negative charges, work must be performed that separates the electrons
and protons. For example, an electric battery can do such work because its
chemical energy separates electrical charges to produce an excess of
electrons at its negative terminal and an excess of protons at its positive
terminal.

 

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