Lab 1
Contents
1. agrees tolerably well with what you expect before proceding R Fig 1 1 A parallel LC Circuit A large R in series with an AC voltage course the signal generator simulates an AC current source But be careful of grounding Both ground clips of the scope probes are connected together within the scope They both go to earth ground Make sure that they are not connected to different points of your circuit b Set up the frequency sweep of the signal generator to display the frequency response and print it Instead of changing the frequency manually you can use the frequency sweep capability of the function generator In frequency sweep mode the function gen erator gradually changes the frequency output from f to fa passing through all intermediate frequencies The sweep time tsw determines how long it takes to pass through the frequency range from f to f After it reaches f it abruptly re Physics 326 Laboratory Manual Lab 1 turns to f and repeats the sweep If the sweep mode is linear then the frequency change from f is proportional to the time that has passed from the start of the sweep f f Wtsw 2 fi If the sweep mode is logarithmic then the frequency is proportional to the expo nential of the time and the rate at which it sweeps is proportional to frequency f f ekt where k In f f tew In logarithmic mode for example if the sweep is from 10 Hz to 1000 Hz it covers the range from 10 Hz to 100 Hz i2. reflects the scale changes Adjust the CH 1 scale to 1 V div Press CH 2 and investigate the VERTICAL SCALE adjustment as before and leave CH 2 on 1 V div Press CH 1 Play with the VERTICAL POSITION knob Turn the HORIZONTAL SCALE knob and note how the displayed waveform changes The legend beneath the display reflects the change in sweep rate Move the trace left and right with the HORIZONTAL POSITION control After you have changed a few settings you should be able to return to the original configura tion by pressing AUTOSET The result of AUTOSET depends on the signals which input to the oscilloscope so if you have changed the function generator output in any way AUTOSET will result in a different configuration Furthermore not all of the oscilloscope s function settings are 1 2 Physics 326 Laboratory Manual Lab 1 reconfigured by AUTOSET It is possible to save all settings of particular configuration for later recall from the oscilloscope s internal memory See the User s Manual for how to do this c Investigate the difference between AC DC and GND input coupling Press VERTICAL MENU Observe the signals when you choose AC DC and GND on the menu Normally you use DC even when you are measuring AC signals The purpose of the AC coupled input is to subtract a DC offset from a signal so that you can magnify the alternating component Add a DC offset to the signal by pulling the OFFSET button on the function genera tor You should notic
3. IG for the trigger source This frees CH 2 for observing another signal while still allowing the trigger signal to come from SYNCH of the function generator e Learn to measure frequency assuming that the horizontal time base is accurately cali brated Centre the displayed waveform about a horizontal line Measure the period from zero crossing to zero crossing and calculate the frequency Compare with the value obtained using the MEASURE menu and from the function generator readout f Generate Lissajous figures by applying two signals of different frequencies to CH 1 and CH 2 Use the transformer for one signal Choose the DISPLAY menu and switch to the XY display instead of the YT display If the HORIZONTAL SCALE setting is vastly inappropriate for the signal being displayed the Lissajous figure may be incomplete To see this try varying HORIZ SCALE when displaying a Lissajous figure to make sure at least one full cycle is being displayed g Invert a signal using the VERTICAL menu and add subtract multiply and divide two signals applied to the two channels using the MATH functions Use the function generator for one signal and the PROB COMP signal for another Lab 1 Physics 326 Laboratory Manual 1 3 h Printing You can print the scope display on a printer using the HARDCOPY function This is useful for recording results to put in your lab book Before using HARDCOPY you must ensure that the output port and printing options are correc
4. Introduction The experiments in this lab manual are designed to introduce various aspects of analog electronics starting from the simplest concepts such as Ohm s law and leading to practical electronic circuits including amplifiers integrated circuits oscillators voltage regulators and logic gates Each lab script is intended for a four hour lab period Some students may need more time to complete the labs especially at the beginning when the equipment is still unfamiliar Your time can be used more efficiently if you prepare in advance by reading the script and planning the procedure before coming to the lab There may be homework problems assigned which are intended to be done before the lab in order to prepare Each workstation in the lab has the necessary equipment an oscilloscope a function generator a multi meter and an experimental box The multi meter can measure voltage current resistance and capacitance The experimental box includes 12 V power supplies for operational amplifiers and a 5 V supply for logic chips The independent Anatek variable power supply includes a robust current limiting control For those circuits built from independent components not using integrated circuit IC chips it is better to use this power supply because it withstands abuse much better than the power supplies in the experimental box Insert jumpers to create a continuous bus from one side to the other Use the horizontal bus pins for the voltages
5. cope Simultaneously apply the SYNCH output signal of the function generator to Channel 2 Press in sequence the oscilloscope s AUTOSET CLEAR MENU and CH 1 buttons AUTOSET should configure the scope to measure the signals coming into the inputs The CLEAR MENU and CH 1 buttons en sure that the display is clean and your next operations will affect the CH 1 display The green light next to CH 1 should be lit You should see a 2 Vpp signal displayed on the CH 1 trace and a square wave displayed on the CH 2 trace What is the peak to peak voltage of the square wave Hint The function generator s output voltage display depends on the Zou setting of the function generator Zout can be set to either 50 Q or infinity If the setting is 50 then the displayed output voltage will be 1 2 the voltage produced by the function generator because it assumes it is driving a 50 Q load where the output voltage would be split evenly between its 50 Q output impedance and a 50 Q load If Zout is infinity then the display will show the full voltage produced by the function gen erator which is the voltage applied to a very high impedance load For this course the Zou setting should be infinity The Zou setting does not affect the actual output of the function generator it only changes the numerical display b Change the scale and position of the waveforms Turn the SCALE knob under VERTICAL Notice how the display changes The V DIV leg end beneath the display
6. e that AC coupling subtracts the offset from the displayed waveform Avoid AC coupling unless you need to subtract an offset at low frequencies AC coupling can distort the signal s display AC coupling puts a high pass filter on the input to remove the DC off set To see this put the coupling on AC and decrease the function generator s frequency until the signal starts to appear smaller in amplitude After you finish put the frequency back to its original value d Learn the operation of the scope s sweep and trigger controls Press TRIGGER MENU Make sure trigger source is CH1 Vary the level control to observe the effect of changing the trigger level There is a floating T on the screen to show you where the triggered position of the input signal is displayed There is also an arrow on the right hand side if the screen to indicate the trigger voltage level If either of these indicators are not visible they may have been turned off Consult the user s manual or an instructor to find out how to turn them on again Change the trigger source to CH 2 which displays the SYNCH signal What effect does changing the trigger level have now Change the trigger slope from positive to negative Note the difference There s a button labelled Set Level to 50 which is handy to quickly stabilize a signal on the screen when you don t know where the trigger level should be set Reconnect the SYNCH signal from the function generator to EXT TRIG Select EXT TR
7. esistance near the resonant frequency for purposes of analysis Rparaiei 1 R 1 Zic where Zic Ri jL where R stands for the real part of the argument 1 0 F 1 0 Z 2 5 gt gt 0 5 0 5 0 0 t o o iF 1 kHz 2 kHz 3 kHz 4 kHz 5 kHz 6 kHz 100 Hz 1 kHz 10 kHz 100 kHz 1 MHz 10 MHz Linear Sweep Fig 1 2 Logarithmic Sweep On the left is a hypothetical display of a linear frequency sweep with f 1 kHz and f 6 kHz On the right is another display made by a logarithmic sweep with f 100 Hz and fe 10 MHz Note that by assiduously choosing tsweep and the horizontal scale a convenient frequency scale is produced 3 Fourier Analysis Drive the circuit of Fig 1 1 with a square wave and carefully observe the frequency re sponse of the output voltage You will get peaks in the output sine wave response at the circuit s resonant frequency and at certain lower frequencies that have harmonics at the resonant fre quency This is a sort of backward Fourier analysis The first few terms of the Fourier expansion of a square wave should be roughly related to the peak frequencies and amplitudes Try using the sweep generator to display a series of peaks at once 4 Cascaded Filters Build a band pass filter by cascading a high pass and a low pass filter To avoid the filters affecting each other use the following design cri
8. n the same amount of time that it covers the range from 100 Hz to 1000 Hz In linear mode it covers the range from 10 Hz to 100 Hz in the same time that it covers the range from 100 Hz to 190 Hz and it would take 111 times longer to go from 100 Hz to 1000 Hz To set the sweep mode on the function generator follow these steps e Press SHIFT MENU to enter the function generator menus e Using the gt key select B SWP MENU e Pressing gives 1 START F e You can now specify the start of the frequency sweep using the knob e Use gt to select other submenus such as 2 STOP F 3 SWP TIME and 4 SWP MODE LINEAR OR LOG We suggest that START F should be near zero and STOP F should be high enough to conveniently capture the frequency range of interest e After you have entered in all the numbers depress SHIFT SWEEP to enter sweep mode The output of the function generator should now be sweeping through the specified frequencies You can display a picture of the frequency response of a circuit on the oscilloscope in the following way Trigger on the SYNCH signal from the function generator e Position the trigger point near the left hand side the of the display e Adjust the function generator s sweep time and the scope s HORIZ SCALE settings so that the end of the sweep is at the right hand side of the display You should choose the sweep time to be slow enough to allow for at least one cycle to take place before the frequency change
9. rding November 1990 Revised March 1994 Revised July 1996 Revised Nov 1998 Revised March 2002 Revised April 2005 General Purpose knob Miscellaneous controls Acquisition controls i so am Cursor control Tektronix TDS 340 Eime osuo za Um Menu Vertical Horizontal Trigger controls controls controls controls Lab 1 Physics 326 Laboratory Manual 1 1 LAB 1 Introduction to Equipment and Circuits The basics of Th venin s theorem and AC circuits are covered in Physics 231 You may wish to review that material before starting these labs Reading Malvino Ch 1 Hayes and Horowitz Class 1 Worked Examples and Lab 1 Note especially A preliminary note on procedure Malvino Ch 16 sections 9 10 11 16 17 18 19 20 Hayes and Horowitz Class 2 Worked Examples and Lab 2 Read A Note on Reading Capacitor values p51 H amp H 1 Oscilloscope and function generator These are a few warm up exercises in using the Hewlett Packard function generator and Tek tronix Digital Oscilloscope a Show two signals on the oscilloscope display Adjust the function generator to produce a sine wave set the AMPLITUDE to 2 Vpp Apply the sine wave signal from the function generator to Channel 1 of the oscillos
10. s significantly e Adjust the channel s zero volts position to the bottom of the display Increase the amplitude of the function generator s output so that a fre quency response graph fills the display You can fill in the trace by using the envelope mode Choose ENVE LOPE from the ACQUIRE MODE menu so that the screen will display Lab 1 Physics 326 Laboratory Manual 1 5 the accumulation of several sweeps The number of sweeps accumulated is controlled by the General Purpose Knob b Use the display to find the resonant frequency the bandwidth and Q of the circuit c Investigate what happens when you load the output with a load resistor Explain Note The parallel LRC circuit is analogous to the series LRC circuit Whereas the series circuit is drive with an alternating voltage source the parallel circuit is driven by a current source The calculations in both cases correspond with each other if in the parallel case one uses admittance complex conductance to calculate current instead of using imped ance to calculate voltages The function generator is a voltage source but you can make an approximate current source by placing a relatively large resistor in series with its output The signal generator behaves as a current source if R is much larger than the magnitude of the impedance of the parallel LC circuit Also be aware that the internal series resistance of the inductor Ri can be approximated as a parallel r
11. shown here These five holes are Joonnected together These are connected too but J not to the ones above These 25 holes are These 25 holes are connected connected e i to those on the left hand The breadboard area on the experimental box has holes for component leads 22 solid wire and IC pins Don t try to force larger wire into these hole because it will spring them too far and ruin the board The horizontal rows of holes on the top and bottom of the breadboard are connected together horizontally The left and right halves are independent We suggest that you use these horizontal rows for power supply voltages and ground You may wish to put a jumper wire between the left and right halves so that the voltages are the same across the board The vertical columns of holes are connected electrically in groups of five along a vertical line The top and bottom halves are independent Typically one inserts an IC chip straddling the centre trough There are then four empty holes for making connections to each IC pin When you plug ICs into the breadboard a common convention is to put pin 1 on the left For other components make sure the leads are not in the same column of five unless you want them connected together The oscilloscope has many knobs and buttons which may be confusing at first It helps if you read the introductory booklet and manual provided by Tektronix If nothing seems to be happening press AUTOSTART N Albe
12. terion the output impedance of the first filter should be about 1 10 the input impedance of the second filter Only resistive impedances are con sidered The resistor values should be 1 10 Measure its frequency response
13. tly configured Use the UTILITY I O menu to select the hardcopy port e g Centronics Layout e g portrait and Hard Copy format e g Epson printer BMP file There is a program which allows downloading the oscilloscope display to a computer at tached to the oscilloscope through the IEEE 488 interface You can either print this file on the printer or include it in a document Instructions should be provided in the lab 2 Frequency Sweep Analysis of a Parallel LC Circuit In this exercise you will use the frequency sweep feature of the function generator to gener ate a graphical display of the frequency response of a parallel LC filter a Construct the parallel resonant circuit of Fig 1 1 The parallel LC circuit is often called a tank Choose R to be several times larger than the impedance of the LC circuit at the resonant frequency Choose L and C so put the resonant frequency between 10 kHz and 100 kHz Measure the internal resistance of the inductor Ri The internal resistance that you measure is a Series resistance but in a parallel resonant circuit you can model it as a resistance in parallel with L with a value of W 2L7 R where wo is the resonant frequency For example if L 30 mH Wo 10 kHz and Ri 10Q then wo L Ri 9 KQ Thus the expected Q can be calculated After constructing the circuit manually tune the function generator to locate the resonant frequency and 1 2 power points Make sure the observed behaviour
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