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
–
–
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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:
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–
–
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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.
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Triggering: INT +
Level: AUTO
Tine/cm: 1 msec
Volts/cm: 0.02
Power: ON
• In Summary
– An oscilloscope provides:
•
•
•
•
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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.