2-1
CHAPTER 2
MISCELLANEOUS MEASUREMENTS
LEARNING OBJECTIVES
Upon completing this chapter, you should be able to:
1.
Define and explain the use of the terms "dB" and "dBm" as they apply to power measurements.
2.
Describe the use of resistive loads, bolometers, and thermocouples in power measurements.
3.
Explain the measurement of mechanical rotation using the tachometer, stroboscope, and the
strobotac.
4.
Explain the measurement of frequency in various ranges using vibrating reeds, tuned circuits,
heterodyne frequency meters, absorption wavemeters, cavity wavemeters, and frequency
counters.
5.
Describe the use of frequency-measurement devices, oscilloscopes, and spectrum analyzers in
waveform analysis and maintenance.
6.
Describe semiconductor testing and applicable terms in maintenance.
INTRODUCTION
In chapter 1, you studied test equipment administration and the basic measurements that all
technicians are responsible for performing. Chapter 2 presents miscellaneous measurements that are fairly
common; keep in mind, however, that you may not routinely perform these measurements in your
particular job. This chapter introduces you to several test instruments and components found in those test
instruments. It will also serve as a review of some of the basics of electronic theory related to test
equipment.
POWER MEASUREMENTS
You may be required to check the power consumption and the input-signal power levels of electronic
equipment. The determination of dc power is fairly simple; recall that the unit of power, the watt, is the
product of the potential in volts and the current in amperes (P = E I).
As discussed in NEETS, Module 2, Introduction to Alternating Current and Transformers, the phase
angle of the voltage and current must be considered for accurate ac power measurements. The
measurement of ac power is further complicated by the frequency limitations of various power meters. If
there is no phase angle difference, you can compute ac power in the same manner as dc power; that is, by
determining the effective value of the product of the voltage and current.
For equipments that operate in the audio-frequency (af) range, power levels have to be determined in
the performance of routine checks and during corrective maintenance procedures.
