General Engineering

1
Laboratory 9Electrical Filters

• General Engineering
• Polytechnic University

2
Overview

• Objectives
• Frequency Response Graph
• Filters
• Types of Filters
• Electrical

• Materials for Lab
• Procedure
• Written Assignment
• Written Topics
• Recitation Topics
• Closing

3
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

4
Frequency Response Graph

• Scale Gain vs. Frequency
• Gain (db) 20log(Vout/Vin)
• Uses a semi-logarithmic scale, where the X-axis
  is the logarithmic scale

3 dB point output power (Pout) 1/2 input power
(Pin) Bandwidth The range at which the signal
is still clear
5
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

vs.
Ideal
Non-Ideal
6
Types of Filters

• High-Pass Filter
• Allows high frequencies to pass through

• High-Pass
• Low-Pass
• Band-Pass

7
Types of Filters

• Low-Pass Filter
• Allows low frequencies to pas through

• High-Pass
• Low-Pass
• Band-Pass

8
Types of Filters

• Band-Pass Filter
• Allows a certain range of frequencies to pass
  through

• High-Pass
• Low-Pass
• Band-Pass

9
Electrical

• Electrical Terms
• Voltage (V) unit V for Volts
• The work required to move charge through an
  element
• Current (I) unit A for Amperes
• 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

• Terms
• Elements
• Wiring

10
Electrical

• Electrical Elements

• Terms
• Elements
• Wiring

• Resistor (R) unit W for Ohms
• 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

11
Electrical

• Electrical Wiring
• Series
• Carries the same current to all of the elements

• Terms
• Elements
• Wiring

• Parallel
• Has elements with a common voltage across each of
  them

12
Materials for Lab

• Resistor
• Capacitor
• Inductor
• Function Generator
• Coax Cable
• Alligator Clips
• Breadboard
• LabVIEW Oscilloscope and Digital Multi-Meter
  program

13
Procedure

• Resistance Size
• 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

• Resistance Size
• Voltagemax
• Filter Circuits

14
Procedure

• Voltagemax
• 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

• Resistance Size
• Voltagemax
• Filter Circuits

15
Procedure

• Filter Circuits
• For each of the 3 circuits on page 84, do the
  following
• 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

• Resistance Size
• Voltagemax
• Filter Circuits

16
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

17
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?

18
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

19
Closing

• Return the equipment back to your instructors
• Make sure you have all the original data, and it
  has been signed by your instructor