TABLE OF CONTENTS This chapter discusses the measurement of DC voltages and DC voltmeters as well as voltmeter calibration and some protective circuitry for voltmeters. As with the following chapter on current meters, it is vitally important that you have a good, thorough understanding of voltmeters their properties and constraints since measuring any electrical property normally requires a voltage reading.
Though digital meters are commonly used across industry, you may still find their predecessor, the analog voltmeter, in use. We dwell almost entirely on an analog voltmeter in this first section for several reasons. First, the disadvantages of analog voltmeters are precisely why digital meters excel they overcame these intrinsic disadvantages. Second, because analog meters are relatively scarce, you may actually have to adapt an analog meter for your use using one of the methods we describe here, particularly when replacing old but still functional equipment. And finally, this section continues the application of Ohm's Law from the last chapter as well as providing some basic calibration principles.
The most common form of analog voltmeter, which is basically a d'Arsonval meter movement (explained in more detail in Chapter 5), is a current-activated meter. That is, by passing a current through the meter coil, which is located in a magnetic field, a proportional to the current deflection of a pointer attached to the meter coil is obtained (see Figure 6-1).
The most important characteristics of this type of movement are the full-scale deflection current (fsd)...
