General Engineering Polytechnic University

1. Laboratory 9:Electrical Filters General Engineering Polytechnic University

2. Objectives Frequency Response Graph Filters Types of Filters Electrical Materials for Lab Procedure Written Assignment Written Topics Recitation Topics Closing Overview

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. gain (dB) (linear scale) max gain in dB gain is 3 dB lower than the max 3 dB f (kHz) (log scale) Bandwidth gain vs. frequency 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 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 • Terms • Elements • Wiring • 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

10. Electrical • Terms • Elements • Wiring • Electrical Elements • 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 • Terms • Elements • Wiring • Electrical Wiring • Series • Carries the same current to all of the elements • 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