Unit 9

Oscilloscopes

• Objectives– After completing this chapter, the student

should be able to:• Explain the function of an oscilloscope.

• 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.

• 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.

• 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.

• The basic parts of an oscilloscope are:– A cathode ray tube

(CRT).

– A sweep generator.

– Horizontal and vertical deflection amplifiers.

– Power supplies.

• Cathode-ray tube (CRT)– A phosphor screen.

– Deflection plates.

– An electron gun.

• 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.

• 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.

• 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.

• Focus and astigmatism controls– Connected to the electron gun.– Used to adjust the electron beam size and

shape.– Rotary controls.

• Horizontal and vertical position controls– Rotary controls.– Allows the electron beam to be positioned

anywhere on the face of the CRT.

• 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.

• Horizontal block– Also called the time base.– Consists of:

• A time/cm rotary switch.

• A trigger-control switch.

• A triggering level control.

• 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.

– Triggering: INT +– Level: AUTO– Tine/cm: 1 msec– Volts/cm: 0.02– Power: ON

• In Summary– An oscilloscope provides:

• Frequency of the signal.

• Duration of the signal.

• 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.