Oscilloscopes

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Unit 9

• Oscilloscopes

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• 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.

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• 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.

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• Oscilloscopes provide
• The frequency of a signal.
• The duration of a signal.
• The phase relationship between signal waveforms.
• The shape of a signals waveform.
• The amplitude of a signal.

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

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

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• 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.

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• 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.

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• 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.

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

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

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• 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.

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

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• 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.

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• Triggering INT
• Level AUTO
• Tine/cm 1 msec
• Volts/cm 0.02
• Power ON

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• In Summary
• An oscilloscope provides
• Frequency of the signal.
• Duration of the signal.
• Phase relationships between signal waveforms.
• Shape of the signals waveform.
• Amplitude of the signal

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• The basic parts of an oscilloscope are
• Cathode-ray tube (CRT).
• Sweep generator.
• Horizontal deflection amplifier.
• Vertical deflection amplifier.
• Power supply.