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1418-1, Capacitors
and Capacitive
Circuits
Experiment 7: Using Capacitors in
Filter Networks
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Objective
• To demonstrate that the combination
of a resistor and a capacitor can be
used to make a filter circuit.
• The circuit can either pass high
frequencies while rejecting low
frequencies or pass low frequencies
while rejecting high frequencies.
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Introduction
• The High- and Low-pass filters on the
previous slides, are examples of
capacitors used in a voltage-divider
circuit.
• Instead of using only capacitors, a
resistor and a capacitor is used in the
voltage divider network.
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• You learned in previous lessons about
Capacitive Reactance and how to
work with the following formula.
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• The arrangement of the components
(capacitor and resistor) forms a filter
network either to pass or reject a
given frequency.
• The rejection or passing ratio depends
upon the ratio of XC and R.
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• The voltage drops of these two
components are governed by the laws
of the series circuit, which uses the
following formula:
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• You will be calculating the calculated
voltage drop across both the resistor
and the capacitor at the designated
frequencies. Use the following
formula for the resistor voltage drop:
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ER is calculated with ckt at 100Hz.
ER is calculated with ckt at 10kHz.
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• You will be calculating the calculated
voltage drop across the capacitor at
the designated frequencies. Use the
following formula for the resistor
voltage drop:
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EC is calculated with ckt at 100Hz.
EC is calculated with ckt at 10kHz.
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Conversion Graph Follows
on next slide
• The following slide has graphs which illustrate the scales for
converting DC meter readings to AC effective values when used with
the Voltage Doubler.
• Remember: the Voltage Doubler converts the AC signal/voltage
to a DC Voltage.
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Build the above circuit
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Above is a wiring example
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Build the above circuit
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Above is a wiring example
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Calculate the Pass Ratio
• You will calculate the pass ratio for
both the High-pass and Low-pass
circuits using the following formulas:
• The next two slides will show the
formulas and the associated examples.
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Final Discussion
• We have seen a network consisting of
a resistor and capacitor is capable of
passing certain frequencies and
rejecting or blocking others.
• It may be necessary to use more than
one network to accomplish the desired
pass ratio.
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• Since the calibration of the frequency
generator used in this experiment
wasn’t exact, we were not able to
obtain a % of error.
• We were however able to prove, with
the pass ratios, our experiments were
successful by demonstrating the Low-
pass and High-pass characteristics of
the RC Filter.
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Questions?
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Resources
• Rubenstein. (2001). Lesson 1418:
Capacitors and capacitive circuits.
Cleveland: Cleveland Institute of
Electronics.
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The End
Developed and Produced by the Instructors in the CIE
Instruction
Department.
© Copyright 04/2012
All Rights Reserved / April 2012
