1 General Engineering Polytechnic University Laboratory 9: Electrical Filters

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) = 20*log(V out /V in ) Uses a semi-logarithmic scale, where the X-axis is the logarithmic scale 3 dB point: output power (P out ) = 1/2 input power (P in ) Bandwidth: The range at which the signal is still clear Bandwidth 3 dB f (kHz) (log scale) gain (dB) (linear scale) gain vs. frequency max gain in dB gain is 3 dB lower than the max

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 –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 –Resistor (R) [unit =  for Ohms] Controls the amount of current delivered to the rest of the circuit

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  (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 Voltage max Filter Circuits

14 Procedure Voltage max –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 V in 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 Voltage max 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 V in in the circuit diagram is (the max voltage) Connect pins 1 and 9 of the DAQ board to where the V out is located in diagram Starting at a frequency of 1 Hz on the function generator run the oscilloscope program Record the value of V ac in the V out 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 Voltage max 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