chapter 13
Post on 02-Jan-2016
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• 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.
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• 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.
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• 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.
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– 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.
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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 signal’s 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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• 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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• 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.
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• The electronic counter is used in/on:– electronics repair shops.– engineering departments.– ham radio shacks.– industrial production lines.
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• 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.
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• 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.
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• 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.
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• 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.
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• 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.
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