Upon completing this chapter, you should be able to:
1. Describe the basic theory of the galvanometer.
2. Describe the basic theory of the DArsonval meter movement.
3. State the proper procedure for connecting an ammeter to a circuit.
4. Define ammeter sensitivity.
5. State the proper procedure for connecting a voltmeter to a circuit.
6. Describe possible effects on a circuit caused by the connection of a voltmeter.
7. Define voltmeter sensitivity.
8. Describe the internal operation of an ohmmeter with the use of a block diagram.
9. Describe the operating procedure for using a megohmmeter.
10. Describe the use of the electrodynamometer-type meter as a voltmeter, ammeter, and wattmeter.
11. Describe the factors that limit wattmeter capability.
12. Describe an open circuit, a ground, a short, and the tests used to check for these conditions.
When troubleshooting, testing, or repairing electronic equipment, you will use various meters and
other types of test equipment to check for proper circuit voltages, currents, resistances, and to determine if
the wiring is defective. You may be able to connect these test instruments to a circuit and take readings
without knowing just how the instruments operate. However, to be a competent technician, you need to be
able to do more than merely read a test instrument. You need a basic knowledge of how test instruments
operate. This chapter discusses the operating principles of some of the test instruments you will use in
The best and most expensive measuring instrument is of no use to you unless you know what you are
measuring and what each reading indicates. Remember that the purpose of a meter is to measure
quantities existing within a circuit. For this reason, when the meter is connected to the circuit, it must not
change the condition of the circuit.