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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.