Chapter 13

1. Chapter 13 AC Measurements

2. Objectives • After completing this chapter, the student should be able to: • Identify the types of meters available for AC measurements. • Identify the types of meter movements used to make AC measurements. • Explain the function of an oscilloscope.

3. Identify the basic parts of an oscilloscope and explain their functions. • Demonstrate the proper setup of an oscilloscope. • Describe how to use an oscilloscope to make a measurement. • Explain how a counter works. • Identify the basic parts of a counter.

4. AC Meters • Moving-coil meter movement. • referred to as d’Arsonval meter movement. • designed to measure DC current. • AC current must be converted to DC current to be measured. • The process is called rectification. • The rectifiers convert the sine wave into a pulsating DC current.

6. Iron-vane meter movement • Does not require the conversion of AC to DC. • Consists of two iron vanes within a coil. • One stationary vane • One movable vane • Used primarily for 60 hertz applications.

8. Clamp-on meter • Uses a split-core transformer. • Used for measuring high values of AC current.

10. Oscilloscopes • Most versatile piece of test equipment available for working on electronic equipment and circuits. • Provides a visual display of what is occurring in the circuit.

12. Oscilloscopes provide: • The frequency of a signal. • The duration of a signal. • The phase relationship between signal waveforms. • The shape of a signal’s waveform. • The amplitude of a signal.

13. The basic parts of an oscilloscope are: A cathode ray tube (CRT). A sweep generator. Horizontal and vertical deflection amplifiers. Power supplies.

14. Cathode-ray tube (CRT) A phosphor screen. Deflection plates. An electron gun.

15. Faceplate • Marked in centimeters along the vertical and horizontal axis. • Can be calibrated with a known voltage before testing an unknown signal. • Called a graticule, and is separate from the oscilloscope. • Mounted in front of the CRT.

16. Power switch • Usually on the front panel. • May be a toggle, push-button or rotary switch. • Mounted separately or with another switch. • Used to apply line voltage to operate the oscilloscope.

17. Intensity switch • Also called brightness. • Controls the electron beam within the CRT. • It is a rotary control. • Too much intensity for too long can burn a hole or etch a line in the phosphor screen.

18. Focus and astigmatism controls • Connected to the electron gun. • Used to adjust the electron beam size and shape. • Rotary controls.

19. Horizontal and vertical position controls • Rotary controls. • Allows the electron beam to be positioned anywhere on the face of the CRT.

20. Horizontal block • Consists of: • A vertical input jack. • An AC/DC switch. • A volts/cm rotary switch. • The oscilloscope probe is connected to the input jack. • The probe is then connected to the circuit to be tested.

21. Horizontal block • Also called the time base. • Consists of: • A time/cm rotary switch. • A trigger-control switch. • A triggering level control.

22. Level control • Sets the amplitude that the triggering signal must exceed before the sweep generator starts. • Initial oscilloscope control settings: • Intensity: set to the center of range. • Focus: set to the center of range. • Astigmatism: set to the center of range. • Position: set to the center of range.

23. Triggering: INT + • Level: AUTO • Tine/cm: 1 msec • Volts/cm: 0.02 • Power: ON

24. Frequency counters • Measures frequency by comparing a known frequency against an input frequency. • Consist of: • A time base. • An input-signal conditioner. • A gate-control circuit. • A main gate. • A decade counter. • A display.

26. The electronic counter is used in/on: • electronics repair shops. • engineering departments. • ham radio shacks. • industrial production lines.

27. Wide use of the electronics counter can be attributed to the integrated circuit, which has: • reduced the size and price. • increased its accuracy. • increased its reliability. • increased its stability. • increased its frequency range.

28. Bode Plots • Named for H.W. Bode. • Used for studying amplifier feedback. • Required semi-log graph paper. • Required two graphs. • gain in decibels. • phase shift in degrees.

29. Bode plotters today • Computer simulations make them easier to use. • Used to measure voltage gain or phase shift of a signal. • Produces a graph of circuit’s frequency response. • Useful in analyzing filter circuits.

30. In Summary • Measuring AC current with: • A moving coil meter. • Iron-vane meter. • A clamp-on meter. • An oscilloscope provides: • Frequency of the signal. • Duration of the signal.

31. Phase relationships between signal waveforms. • Shape of the signal’s waveform. • Amplitude of the signal. • The basic parts of an oscilloscope are: • Cathode-ray tube (CRT). • Sweep generator. • Horizontal deflection amplifier. • Vertical deflection amplifier. • Power supply.

32. Frequency counters • Basic parts of a frequency counter are: • Time base • Input signal conditioner • Gate-control circuit • Main gate • Decade counter • Display • Bode plotters