Transcript Wave, Filters

Laboratory 9:
Electrical Filters
General Engineering
Polytechnic University
Overview
• Objectives
• Frequency Response
Graph
• Filters
• Types of Filters
• Electrical
•
•
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Materials for Lab
Procedure
Written Assignment
Written Topics
Recitation Topics
Closing
Objectives
• Learn about the different types of filters and their
uses
• Implement circuit elements to create different filters
• Use your new knowledge to identify the filters based
on the graphs created
Frequency Response Graph
• Scale: Gain vs. Frequency
• Gain (db) = 20*log(Vout/Vin)
• Uses a semi-logarithmic scale, where the X-axis is
the logarithmic scale
gain (dB)
max gain in dB
(linear scale)
gain is 3 dB
lower than the
max
3 dB
3 dB point: output power
(Pout) = 1/2 input power (Pin)
Bandwidth: The range at
which the signal is still clear
f
Bandwidth
gain vs. frequency
(kHz)
(log scale)
Filters
• Used to get rid of unwanted frequencies
• It is impossible to build an ideal filter which
has sharp cutoff frequencies
• Instead, unwanted frequencies will be
passed, but at almost negligible amplitudes
0
0
-5
-10
-15
vs.
-20
-25
Gain (dB)
Gain (dB)
-5
-10
-15
-20
-25
-30
-30
1
10
100
1000
Frequency (Hz)
1
10
100
1000
Frequency (Hz)
Ideal
Non-Ideal
Types of Filters
•High-Pass
High-Pass Filter
•Allows high frequencies
to pass through
•Band-Pass
0
Gain (dB)
•Low-Pass
-5
-10
-15
-20
-25
-30
1
10
100
Frequency (Hz)
1000
Types of Filters
•High-Pass
Low-Pass Filter
•Low-Pass
•Allows low frequencies
to pas through
•Band-Pass
0
Gain (dB)
-5
-10
-15
-20
-25
-30
1
10
100
Frequency (Hz)
1000
Types of Filters
•High-Pass
Band-Pass Filter
•Allows a certain range of
frequencies to pass
through
•Low-Pass
•Band-Pass
0
Gain (dB)
-5
-10
-15
-20
-25
-30
1
10
100
Frequency (Hz)
1000
Electrical
• Electrical Terms
•Terms
•Elements
– Voltage (V) [unit = V for Volts]
• The work required to move charge
through an element
– Current (I) [unit = A for Amperes]
•Wiring
• The rate at which charge is moving
past a given reference point in a
specified direction
– Power (P) [unit = W for Watts]
• The rate at which energy is
converted into another form (i.e.
heat, motion)
• P=V*I
Electrical
•Terms
• Electrical Elements
– Resistor (R) [unit = W for Ohms]
•Elements
•Wiring
• Controls the amount of current
delivered to the rest of the circuit
– Capacitor (C) [unit = F for Farads]
• Stores and delivers electrical
energy when needed
– Inductor (L) [unit = H for Henries]
• Stores energy in a circuit or to
produce a magnetic field for use in
moving objects
Electrical
•Terms
• Electrical Wiring
– Series
•Elements
• Carries the same current to all of the
elements
•Wiring
– Parallel
• Has elements with a common voltage
across each of them
Materials for Lab
•
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Resistor
Capacitor
Inductor
Function Generator
Coax Cable
Alligator Clips
Breadboard
LabVIEW Oscilloscope and Digital Multi-Meter
program
Procedure
• Resistance Size
•Resistance
Size
•Voltagemax
•Filter Circuits
– Using the resistor chart and the color bands on the
resistor record the size of the resistance
– Open the Digital Multi-meter (DMM) in LabVIEW and
select the W (ohms) icon
– Measure the size of the resistor by connecting it to pins
1 and 9 of the DAQ board
– Compare the measured value of the resistance to the
value you calculated using the color bands
Procedure
• Voltagemax
•Resistance
Size
•Voltagemax
•Filter Circuits
– Turn the amplitude knob of the function generator all
the way to the right -- the maximum voltage
– Insert coaxial cable into the opening labeled “MAIN”
– Connect the cable to the DAQ board:
• red alligator clip to pin 1
• black alligator clip to pin 9
– Press the V~ icon on the virtual DMM
– Record voltage displayed (represents Vin for all
computations)
– Open the Oscilloscope program in LabVIEW
– Slowly adjust the buttons marked ‘Timebase’ and
‘Volts/Div’ until a recognizable continuous sine wave is
produced
Procedure
• Filter Circuits
– For each of the 3 circuits on page 84, do the following:
•Resistance
Size
•Voltagemax
•Filter Circuits
• Construct the circuit on the breadboard provided
• Connect the terminals of the function generator to where
the Vin in the circuit diagram is (the max voltage)
• Connect pins 1 and 9 of the DAQ board to where the Vout
is located in diagram
• Starting at a frequency of 1 Hz on the function generator
run the oscilloscope program
• Record the value of Vac in the Vout column of the table on
page 84
• Complete the table by increasing the frequency of the
Function Generator
• Calculate the gain and use Excel Spreadsheet to graph
the gain vs. frequency. Be sure to convert the x-axis to
log scale
• Analyze the graph to determine the type of filter created
Written Assignment
• Full Individual Report (one report per student)
• Use the guidelines on page 5 for help
• Include the Excel tables and a gain vs frequency graphs
for each of the mystery circuits
– Determine type of filter each circuit produced
– Label the frequency response graph with the correct
filter type
– Find the 3 dB point and bandwidth for each filter
• Make sure your instructor initials your original data
• Include the topics found on the next slide
• Remember to create a title page
Written Topics
• Each of the following topics must be addressed in the full
report and should be placed in the proper sections
– What does the 3 dB drop show about the filter?
– Discuss the importance of decreasing or increasing the
‘Volts/Div’ on the oscilloscope
– What can the DMM measure besides resistance?
– Discuss the affect of the graphs when a different
resistance or different capacitance is used
– What other applications can you think of where
frequency filtering would be useful?
Recitation Topics
• Discuss the different types of filters
• Discuss the importance of the 3 dB point in the filter
• Discuss the importance of the Volts/Div on the
oscilloscope
Closing
• Return the equipment back to your instructors
• Make sure you have all the original data, and it has
been signed by your instructor