TABLE OF CONTENTS Before beginning a detailed discussion of the various electrical components and their uses, a discussion of the basics of measuring the three major electrical quantities is in order. In Chapter 1 the basic physics of an electric circuit were discussed. This unit will build on those principles and illustrate the how and why of measuring current, voltage, and resistance.
To measure current, voltage, and resistance you must have:
A measuring instrument with the correct range.
A mental or physical diagram of the circuit to be measured.
A knowledge of the correct procedure for the measurement desired.
It might seem obvious that if you are going to measure voltage you would have a voltmeter, for current, an ammeter, and for resistance, an ohmmeter. However, due to the relationship between the three quantities (as discussed later in this unit), you may measure voltage indirectly by determining the current through a resistance and through similar procedures. Regardless of which measurement you are going to take, the meter must have the expected value within its range of safe operation. The meter leads must be appropriate for the quantity to be measured; for example, when measuring high-potential, the meter leads should meet certain insulation specifications.
It is always preferable when measuring electrical quantities to have an up-to-date circuit diagram (or schematic) in front of you. This is not always possible. In the real world, one is occasionally called upon to measure electrical quantities without benefit of documentation. This should
