Full manual - Physics Department
Contents
1. The additional input to the summing amplifier allows the noise generator signal to be added to another signal Vym Vin noise Vary the 10kQ potentiometer to obtain maximal noise amplitude Sketch the waveform observed on both sides of the coupling capacitor and at the output of the summing amplifier An oscilloscope time base of 20 us div is recommended Also observe the output of the summing amplifier at a sweep speed of 500 us div This output is labelled NM on the job board for Noise Mixer output Calculate the cut off frequency of the low pass filter in the NM What is the attenuation of this filter for the frequency component that results from transitions every 20 us 25kHz 1 Connect the NM output through a 100 kQ resistor to the summing point of the I to V con verter in the noisy signal source Observe the converter output with a scope and adjust the noise generator output from zero until the square wave becomes difficult to see Trigger the scope from a clean square wave or TTL output of the FG to avoid loss of synch Mea sure the DC output voltage of the lock in amplifier with the modulated LED on and then off Compare again the signal to noise S N ratios at the input and output of the lock in amplifier Explain why it is necessary to modulate the signal in order to obtain the improvement in S N through the lock in technique Experiment 6 An introduction to using microcomputers in a physics labor2. a large resistance 13 14 EXPERIMENT 3 BUILDING CIRCUITS WITH OP AMPS Using a signal diode 1N914 wire the following input circuit to measure the reverse bias current of the diode Select the value of Ry necessary to give a reasonable Vout Use reverse bias voltages V 1 2 and 5V 3 2 Inverting amplifier As seen in Section 3 1 the input offset voltage of op amps can introduce significant output errors Many op amps 351 741 have additional pins for adjusting the offset to zero O R AN Vin AMM E 351 6 5 Y Voce ULL 8 7 6 5 O 2 3 4 ULL Vec out ni 1 Es Wire the circuit shown with Ry 100 kQ and Ria 10 kQ gain 10 connect input to com mon and adjust the balance potentiometer until the op amp output is nearly zero lt ImV Set DMM to an appropriate scale Prior to every other experiment in this lab check in the same manner whether the op amp remains balanced it should Use a 1V supply as Vin disconnect the wire to common first Measure Vout for five or more val ues of Vin in the range 0 7V 1 Use the FG set at 1 kHz as Vn Use the two channels of the scope to monitor the inverting input of the op amp and Vout Slowly increase the amplitude of the input signal starting near zero Observe what happens at the inverting input as the amplifier saturates
3. processor control e 8088 8086 registers Table 6 2 shows a list of 14 internal to CPU memory locations with very fast access used to keep track of where in the program the CPU is Each register is 16 bit wide However General Registers see Table 6 2 can also be addressed in two 8 bit chunks xL and xH for Low and High bits respectively e SEGMENT OFFSET addressing 16 bits can address 65 536 locations size of segment 20 bits can address 1MB segment 16 bits offset 16 bits address 20 bits TOTP e IBM PC memory map is summarized in Table 6 3 This is just an example of a particular architecture IBM PC other microprocessors and micro controllers differ in the details but are fundamentally similar to the above description More to come 30 EXPERIMENT 6 USING MICROCOMPUTERS IN A PHYSICS LABORATORY Table 6 2 8086 8088 CPU registers 16bit segment high 8 bits low 8 bits comments General register o o OO AR AR JA aoee Doo TT Do sms 0 DOS To o To Code Segment pointer Data Segment pointer Ese ie gee EE E gt gt Sd t Flags consists of individual bits which flag certain conditions E g bit ZF on Zero Flag means the last instruction yielded a 0 as a result Table 6 3 IBM PC memory map 1 O BIOS Ram RAM for special purposes ROM Basic Program memory VGA video expansion IBM monochome video CGA video memory reserved for video expansion ROM usually not all instal
4. 100kQ Vv to i the gain of the amplifier until the Modulated Noisy I to V converter light source detector square wave component of 50 to 100 mV is obtained at the output Make note of the DC level the square wave amplitude p p and the approximate noise amplitude p p in the output signal Why is there a DC component in the output of the I to V converter from FG Be 10V 15 Sig l Mer from I to V 10 10 converter O 7 af AM AM O 5k0 1MQ MQ c AF 100 100kQ AD534 g 2 14 1 3 4 l 4 16 6 100kn tuned amplifier multiplier LP filter demodulator 1 Now connect the AF 100 tuned amplifier circuit to the output of the I to V converter Observe the tuned amplifier output with the scope Adjust the FG frequency to get the maximum output from the tuned amplifier Record your values of tuned amplifier output voltage p p waveshape appearance DC component of the output voltage and the FG frequency setting You should have observed a sine wave at the tuned amplifier output The input however was a noisy square wave with a DC component Explain the difference in input and output waveforms Y The analog multiplier and low pass filter phase locked demodulator should now be con nected The tuned amplifier output is multiplied by a square wave that is synchronous with the LED modulation Adjust the FG square
5. Compare your Vogset value to the x intercept above and comment on differences if any What causes a greater deviation from nominal gain Vogser or the resistor inaccuracy Optional Repeat the straight line fit to the data but this time force the intercept to be zero i e a one parameter fit This assumes Vofrse 0 Calculate and comment on error caused by this assumption Experiment 3 Building circuits with op amps The purpose of this experiment is to build several realistic op amp circuits We learn how to use op amps for signal conditioning in various measurements 3 1 Current to voltage converter gt Wy 1 353 on out Wire up the current to voltage converter cir cuit note that this corresponds to simply inter changing the input and ground connections in the circuit of Section 2 3 Here we emphasize the fact that the input is explicitly a current while the output is a voltage Vout Rylm Use a feedback resistor of 10 kQ Use a 10 MO precision resistor in series with a variable voltage supply as the current source In Vin x 107 for several five or more input currents in the nanoamperes to microamperes range Measure Vout with the DMM Iin Calculated Vo ES AAA Will the input offset voltage affect the measurement of small currents more a when the current source is a small voltage and a small resistance or b when it is a large voltage and
6. to noise S N ratio is to restrict the bandwidth of the amplifier in such a way that only the signal frequencies are transmitted This principle is illustrated using an active filter device The AF100 universal active filter is a versatile active filter device It has high pass HP low pass LP and band pass BP outputs simultaneously available and an uncommitted summing amplifier for making notch filters The centre frequency is tunable from 200 Hz to 10 kHz with two resistors The quality factor Q is variable from 0 01 to 500 by changing two additonal resistors The AF100 can be used in either an inverting or a non inverting configuration The pinout and the schematic di agram of an AF100 are as shown 10kQ Ry 1000pF Re 1000pF Fin Ra Ra and Re must be sup AMA ANA ANA Ml plied externally to AF100 see be 100kQ low All other components are in o gt a e M A s ternal Vin os E AO A Pi The gain and Q value of the filter R are determined by Rin and Ro The i centre frequency of the filter is de I termined by identical resistors Rg Re WORKS and Re according to O O O Highpass Bandpass Lowpass 50 33 x 108 fo in Hz f 22 5 1 ACTIVE FILTER 23 Wire up the non inverting mode filter using external resis 15V ic 9 15 Rn r O BP out tors of Ry Re Edd
7. Compare your results with the expected values 4 5 Logarithmic amplifier Using a non linear feedback element with an op amp e g a pn junction diode produces startlingly different transfer functions Logarithmic amplifiers serve as the basis for circuits such as analog multipliers studied in Section 4 6 Carefully balance a 351 op amp Then wire the logarithmic amplifier log amp Rin using a signal diode as the feedback ele O AM ment 3l 351 z Ei aut i gt 15V zo ly 1 Measure Vout as a function of Vi and Rin 20 EXPERIMENT 4 ADVANCED OP AMP DESIGNS Plot log Iin vs Vout For all but very small forward bias voltages the current through a diode varies exponentially with the applied voltage Io LE V T where 77 is an empirical parameter 2 for Si 1 for Ge diodes and J is the intrinsic current at zero bias Apply circuit analysis Simpson Sec 9 7 to your logarithmic amplifier and verify that the same relationship holds for the measured Ji and Vout Fit your data to the above equation and determine the parameters 7 and J for your diode Can you tell if this is a Si or a Ge diode 4 6 Analog multiplier Combining log amps with adding amps allows one to build analog multipliers and other components of analog computers for a review see Faissler Ch 30 Here we examine the transfer functions of one such commercial device AD534 15V A AD534 is inter
8. 10 7 AMA 100k0 and Rn s Rey Ro 100kQ Use 7 F AF 100 t O HP out precision resistors if Q 16 AMA possible D Re 8 O LP out 4 1 NM 15V 1 These external resistor values should give a centre frequency of 500Hz and a Q of slightly greater than unity Connect the FG output to Rin and use the scope in the two channel mode to observe both the FG output and the bandpass output of the filter Connect the FG TTL output to the digital counter for a readout of frequency Set the FG for a 1V peak to peak sine wave Observe the bandpass output as the FG frequency is varied through the centre frequency fo What happens to the bandpass output at fo 1 To measure fp accurately switch the scope to produce an xy plot Lissajous figure of filter output vs filter input At the centre frequency the bandpass output should be exactly 180 out of phase with the input signal Use the Lissajous figure to adjust the FG exactly to the centre frequency see Experiment 1 and or Malmstadt p 43 or Brophy p 63 for a discussion of Lissajous figures 1 Now switch the scope back to the dual trace mode and measure the peak to peak output voltage of the bandpass filter as a function of FG frequency over a range of 20 Hz to 20 kHz Record 10 15 values in this range including several near fo 1 Calculate and plot the filter gain in dB vs log frequency From the graph determine the rolloff rate of the filter in dB decade on both sides of fo Com
9. Is the assumption of virtual ground still valid 1 Keeping the amplitude of the input low and constant vary its frequency Can you estimate the maximum slew rate of the 351 3 3 Summing amplifier Inverting amplifier configuration may be used to perform several mathematical opera tions The summing amplifier provides an output related to the algebraic sum of two or more signals 3 4 OP AMP CHARACTERISTICS 15 D Wire up a summing amplifier as shown 100K0 1000 Use the 10V supply as V and the 1V V O A NW supply as Vo Measure Vout for six or more 5 combinations of input voltage values Keep V A one value constant for at least three values 2 31 gt o V 10k0 3j out of the other and vice versa E 15V 7 Plot Vout vs Va for constant Vi and Vout vs Vi for constant Vo Explain the values of the slopes and intercepts Disconnect the summing network from the 351 leave the balance pot and power connections in place for later use Design a circuit whose output represents 3V 4V2 Design and describe an inverting amplifier with a thermistor as one resistor such that the output voltage becomes more positive as the temperature inreases The thermistor resistance is 10 5 kQ at 28 C and 9 5 kQ at 23 C Choose the component values so that Vou changes 10 mV per C near room temperature Also include an offset circuit so that Vout 250 mV at 25 C Assume that the thermistor resistance change
10. input triangular wave Also record the amplitude of the square wave at the output Calculate the expected theoretical value for the differentiator output and compare it to the experimental value 1 Change the FG to square wave setting Sketch the observed waveforms 4 3 Difference amplifier The purpose of this section is to introduce precision amplifiers and to learn to distinguish differential and common mode signals Ref Simpson Ch 9 10 esp Sec 9 8 7 10 4 Faissler Ch 31 review Malmstadt et al Ch 8 1 18 EXPERIMENT 4 ADVANCED OP AMP DESIGNS 1 ame a Wire up the difference amplifier as shown vo AMA ANY Balance the op amp by connecting both V and V gt to ground and adjusting the offset 2 ELO potentiometer until Vout 0 Leaving Vz grounded vary V several val rele ues between 1V and 1V and measure Vout 100kQ O IMQ v Calculate the average gain of the amplifier In this measurement which components determine the gain of the amplifier How does the measured value compare with the theoretical one 1 Connect V gt to a constant 1V source and repeat the above two steps 1 Connect both V and V gt to the same variable voltage source measure Vou for several values of Vi Va between 1V and 1V Plot Vout vs Vi and determine the value of the common mode gain from the plot Interpret your data in terms of the imbalance of the resistance ratios
11. mode as the source in the squaring circuit wired above Connect the multiplier output to the vertical scope input and the FG output to the horizontal Use a 10 Hz sine wave signal Sketch the resulting display 1 Now use the dual trace mode to observe the waveforms of the input and output signals Sketch a representative display and indicate the position of OV for each waveform Explain the relationship of the frequencies and the DC components of the input and output waveforms Optional analog division 1 To obtain division connect the multiplier output to the Y gt input Now Z is no longer connected to the output and Za is no longer grounded In this configuration V Za V Z Vout 10 x f V X1 V X2 V Y Measure Vout for several values of V Z2 V Z1 and V X1 V X3 For simplicity you may want to ground Z1 X gt and Y Make sure you keep V X V X2 positive see the spec sheets of AD534 The output limits of AD534 are 11 V Calculate and plot the minimum value for V X1 V X gt as a function of V Z2 V Z1 over the V Z range of 10 V Experiment 5 Active filters and tuned amplifiers 5 1 Active filter Weak signals require special attention The techniques of separating signal from noise vary depending on the nature of the signal and of noise There are no general easy prescriptions When the frequencies of the signal and of the noise differ one way to increase the signal
12. of the two pairs of resistors determining the gain for the inverting and for the non inverting input Which pair has the higher gain and by how much How could this common mode gain be reduced Calculate the common mode rejection ratio CMRR for your difference amplifier Cal culate the maximum common mode signal the amplifier can accept if a 100 mV signal is to be amplified with an error of less than 0 1 4 4 INSTRUMENTATION AMPLIFIER 19 4 4 Instrumentation amplifier The purpose of this section is to combine the advantages of a difference input with the high input resistance of the voltage follower in a complete instrumentation amplifier 1 Wire up the instrumentation amplifier as shown add the input voltage followers to the existing circuit 2 100k0 IMQ 388 gt WW AWW Vo Oka E Sl 5 E E Not 0k0 1 18M Okt 5 353 Vo ll 100k0 MO gt Check the offset of the instrumentation amplifier and adjust the difference amplifier offset potentiometer if needed Measure Vou for various values of V and V2 so that you will be able to determine the difference gain and the common mode rejection ratio of the instrumentation amplifier Be sure you have taken sufficient data to perform your calculations Describe the reasoning you used in selecting the values for V and Vj From these data determine the gain and the CMRR Explain your interpretation of the data
13. water one at a moderately high temperature Immerse the thermistor mercury thermometer assembly into the hot one Modify your program to perform a frame grab of a large number of points Start the program and rapidly transfer the assembly into the ice water beaker Use your calibration data to plot true temperature as a function of time and analyze your data attempting to verify Newton s law of cooling the rate of cooling is proportional to the temperature difference Note and comment on the deviations from the exponential behaviour Appendix A Resistor colour code Ist 2nd 3rd 4th BANDS Second Band Third Band Silver is 10 tolerance Fourth Band Gold is 5 tolerance No band is 20 tolerance For example the resistance of a resistor whose bands are red red red silver is 22 x 10 2 2kM 10 33
14. Brock University Physics Department St Catharines Ontario Canada L2S 3A1 Phys 3P92 Experimental Physics I Electronics E Sternin Copyright Brock University 2006 2007 Abstract This is a senior undergraduate laboratory course 13 weeks in duration four hours per week Seven experiments running one or two weeks each are completed 1 Breadboard techniques and simple circuits errors introduced by instruments low pass filtering measuring phase shift Operational amplifiers basic concepts operational characteristics offset voltages and currents gain simple op amp circuits Building circuits with operational amplifiers current to voltage converter math operations op amp operational characteristics Advanced op amp designs op amps integrator and differentiator difference amplifier instrumentation amplifier log arithmic amplifier analog multiplier Active filters and tuned amplifiers active filters notch filter lock in amplifier Microcomputers in a Physics Laboratory basics of microcomputer design IBM PC registers and I O introduction machine language programming controlling PC LAB interface board Building and using a digital thermometer A D and D A conversion mixed language programming Each experiment requires a written lab report In addition a term project requiring at least three weeks of independent work by the student is completed and a fi
15. T 2 OPERATIONAL AMPLIFIERS BASIC CONCEPTS Note Voutput A x Vi V_ see Simpson pp 367 369 or Faissler p 247 248 2 2 Voltage follower V O in 2 353 e V out non inv inv Vec output input input 8 7 6 5 oN top 4 view o 2 5 4 output inv non input inv Vec input from MM VAN source Y WW A jumper 10k0 Y MAM 3 oA ARA 353 EAR NA jumper O 10k0 Wy Connect one of the 353 op amps as a volt age follower Use the 10 V as Vn and the DMM to mea sure Vou and Vi for five or more settings in the range 10 to 10V Calculate the gain 05 A 1kQ resistor will be used in series with the 10V output to simulate a voltage source with a 1k9 internal resistance A 10kQ resistor will be used to simulate the input resistance of the read out device used to measure the source voltage Wire the circuit on the left set the source voltage to a value between 1 V and 2 V and measure the voltage at point A with and without the 10kQ load connected Now connect an op amp voltage follower 353 to buffer the voltage source from the load resis tance Measure the follower output voltage with and without the 10k0 load resistor connected A transducer has an output resistance of 80kQ Describe how a follower could be used to decrease the loading error if the transducer output voltag
16. arly noted Results A tabulation of the experimental data graph s where appropriate derivation of the desired result plus an estimate of the random and systematic errors as well as numerical fit of theoretical curves to the experimental data points where appropriate If a computer program or a macro is used to analyze the data its listing should be attached as an Appendix to your report Discussion A discussion of the precision of the result how the experiment can be improved and its ultimate limitations possibly a comparison with other methods of obtaining the same result Conclusions As appropriate References All texts publications and other references used to assist in the experiment should be listed Handwritten reports will not be accepted You are encouraged to use TEX ETEX to write your reports A skeleton report is available for you to copy into your own filespace and to edit as appropriate Several different programs capable of data analysis and plotting are available on the PC s in the lab and on the University Unix servers including physica edgr gnuplot maple xmgrace and SigmaPlot All of these are capable of generating PostScript output which can then be included in your lab report Consult your instructor for details e The last three weeks of the course are reserved for your term project although you are encouraged to select one and start preliminary work on it as early as possible A list of available projects sho
17. atory To use microcomputers as laboratory instruments we need to learn the basics of their architecture and the ways to control them at the level of electrical signals We look under the hood of a computer based data acquisition system and learn how to control its hardware through low level programming Introduction Hardware e microcomputers as lab instruments computer A 1 1 I storage i i 1 1 I I signal processing A to D signal transducer Physics and display conversion conditioning experiment Physics e g oven e inside an IBM PC the mother board CPU RAM BIOS some I O amp timing circuits the I O bus expansion cards Note CPU often has a separate faster amp wider bus to access memory RAM I O card and the connection to the outside world operation of the computer boils down to controlled transfer and manipulation of bits digital on off 0V 5V levels among various components 27 28 EXPERIMENT 6 USING MICROCOMPUTERS IN A PHYSICS LABORATORY bel video disk serial keyboard network controller controller controller controller controller 20 address lines The bus 8 data lines more in later models 34 auxiliary lines ooooooooooOQO 0000 protoboard s Figure 6 1 Essential elements of a personal computer complex operations many clock cycles some devices may have to wait computer is not a real time
18. cheduled time Keep clear and complete records write down answers to the questions asked as well as your own observatons without waiting to be prompted Remember to describe the problems you encounter and how you solved them You might run into the same difficulty a few weeks later Make a preliminary measurement before you start to acquire your final results This way you will understand the operation of the equipment ensure that the equipment is working correctly establish the range of values so that you can choose the optimal settings on all your instruments find out what takes the most time and budget accordingly Graph the experimental curves and staple or glue them into the lab book Remember the importance of proper captions axes labels specification of units and definition of symbols These must be done as you go along do not wait until later as you will lose track of the settings once you change them in the course of an experiment Analyze your measurements and estimate the errors Keep your reports brief with an absolute maximum length of ten pages Reference your work do not copy text from manuals and books However make sure your reports are complete Always include properly annotated diagrams of your circuits make sure pinouts meter set tings and other trivial details are clearly marked Pay attention to these details what may seem obvious at the moment will be forgotten soon after you co
19. device but latency is small structure of a computer bus address lines which device is getting sending data auxiliary the timing of the transfer handshaking data lines ADO AD7 the data may be a real number a machine instruction a part of an address etc e A typical I O interface I O card inside a PC ribbon cables distribution module at the workstation optoisolators and separate commons 4x 8 bit input amp 4 x 8 bit output parts multiplexed 4 input 12 bit A D converter bipolar 10V 2x 12 bit D A outputs bipolar 10V counter amp timer circuits 29 Software e Programming languages see the summary in Table 6 1 Table 6 1 The hierarchy of programming languages EE 4th generation code generators Al large projects productivity High level Fortran Pascal Basic easy on humans hw independent Machine understood by the CPU Hardware bits 0 5V voltage levels ssi C bridges the two layers is a high level language but allows low level extensions Hs E Low level Assembler mnemonics hard but full control of hw e En e Compilers computer programs that translate the human readable source code into machine executable op codes e Op codes for example about 300 in six functional groups for 8088 8086 data transfer mov in out xchg arithmetic add sub inc dec mul div logical and or xor not string manipulation control transfer jmp call
20. e is to be measured with a 1 MQ input resistance oscilloscope and indicate the percent error avoided load Fix the input voltage at 10V Connect a 1kQ load resistor Riad to the follower output as shown and measure the output voltage with the DMM Remove Riaa and measure the no load voltage Repeat using the 100 Q and 47 Q load resistors Calculate the output current for each case 2 3 FOLLOWER WITH GAIN 11 Vout with load Vout without load Tout with load E PE o o R The small output voltage change observed with the 1kQ load indicates the very low output resistance of the voltage follower At lower load resistance it is possible to exceed the max imum output current capability of the op amp A significant loading of the output voltage occurs in such a case On the basis of the change in output voltage with a 1kQ load estimate the output resistance 2 3 9 of the voltage follower or if no change was observed place an upper limit on the output resistance e calculate the value the output resistance would have if the smallest observable change had been measured It may help to draw an equivalent circuit for the op amp see Simpson Fig 9 21 or Faissler Chapters 29 and 31 Calculate the maximum output current the op amp can supply based on your observations with the 100 Q and 472 loads Follower with gain Use a 353 op amp to wire the follower with gain 3 E E E E Vin O EE Y amplifier circu
21. ear on the screen The signals then appear as horizontal bands whose height is a measure of the signal amplitude The FG output can be adjusted if necessary to keep the Chl amplitude constant Use an FG amplitude of 5 to 10 V Express the gain G Vout Vin in decibels dB Voui Vin dB NU IESO IESO o T 30 Hz If you are using a computer program to do your calculations fill only the two middle columns of the above data table Plot the absolute value of the gain G in dB vs log frequency Determine the cutoff frequency and the attenuation slope in dB decade at high frequencies Review Simpson Sec 2 10 Using the nominal marked on the component values of C and R calculate and add to your plot the line representing the expected frequency response of this low pass filter Treat rT RC as a parameter and starting with the initial value given by the nominal component values fit a theoretical curve to your data Add this curve to the same plot Explain any differences observed 1 4 Observing phase shift with Lissajous patterns 1 With the FG at 100 kHz set the scope time base to observe 1 5 cycles Note that signal across the capacitor lags the signal across the function generator This phase shift can be measured as the fraction of a cycle delayed times 360 What is the phase shift at 100 kHz 1 Now measure the phase shift by means of Lissajous figures Switch the scope display to xy mode to observe the L
22. ee Sr eh Ge Grek Be ee ee dd LOCA amplifier ta A ee ee ee 6 Using microcomputers in a physics laboratory 7 Building and using a digital thermometer A Resistor colour code il Introduction In this course you will learn to build understand and debug working electronic circuits you will develop a basic understanding of the way modern laboratory instruments interface with micro computers and you will perform physical measurements using microcomputer controlled electronic devices built in the course of the lab To quote Brock Calendar the course covers operational amplifiers converters switches microcomputers and their application to physical measurements General Remarks Electronics is a tool Physics like everything else in everyday life is greatly influenced by the continuous explosive developments in electronics and one s success in physics like everywhere else often depends on mastering this tool That is why we study electronics as part of the physics curriculum The hope is that by understanding how our instruments work and what their limitations are we can use them to do better science One cannot learn electronics all at once Like in any complex subject gaining a reasonable level of electronic skills requires going back over the material several times Repetition and review are crucial in any learning situation This course will provide you with a small opening into a much larger world you will have to expand you
23. ensure that all integrated circuits IC s are powered lt gt with both Voc and Vec sd whenever an input signal is e supplied Failure to do this will destroy IC s to a E view Use 10V output from the job board as Vi unknown set it to any value between J EIGI 0 95 V and 0 95 V Connect 1 V out put of the job board to the inverting input of the op amp Use Veco 15V and Vcc 15 V 1 Use the scope to monitor the output and adjust the 1 V supply until a transition from one output voltage limit to the other occurs Measure and record the positive and the negative voltage limits of the op amp output 1 In the same circuit connect the DMM to the 1 V supply Adjust the potentiometer care fully to the value where the op amp output just begins to decrease from its positive limit as observed on the scope where it is as close to zero output as you can set it and where it is not quite at the negative limit Record these three values They may be very close to each other in this case estimate the upper limit on the change of the input voltage s that causes the output to jump from one limit to another Repeat these observations several times 1 Without changing any settings use DMM to measure V Estimate the open loop gain 4 of the op amp and its input offset voltage from the above measurements Compare with the nominal value 103 dB for 741 9 10 EXPERIMEN
24. gnals and to the ac waveforms generated by the FG 2 1000 ANN o C vouch jumper O Using a capacitor as the feedback element in the inverting amplifier circuit wire up the op amp integrator Use a 1 uF low leakage capacitor 10 tol erance or better Rin 1 MQ and set Vin 100 mV Q Measure the times required for the output to change by 1V 3V 5V and 8V Begin the timing when the touch jumper is removed Use the jumper to discharge the integrating capacitor i e to restart the integrator Repeat 1V measurement at least 3 times estimate the precision of your measurements standard deviation The above measurements require that the op amp be well balanced To test restart the integrator and quickly remove Vn when Vout 1V Does Vout remain constant after that If not re balance the op amp 1 Connect the input to ground reset the integrator and observe Vou on the most sensitive DMM scale Record your observations O 1000 MM o touch luF jumper 5V Y aid O O 16 Modify the circuit as shown turning it into a charge to voltage converter The circuit will be used to measure the capacitance of another capacitor Cy Discharge Cy 1 uF disconnect the touch jumper then carefully move the input jumper from 5V to the negative input of the op amp and observe changes in Vout Repeat several times 4 2 OP AMP DIFFERENTIATOR 17 Compare the measu
25. he signal observed on Ch2 at the frequencies in the table below Keep the Chl amplitude constant at 10 V Now connect a 10kQ resistor between the Ch2 input contact on the job board and common Repeat for a resistor of 1kQ Ch2 amplitude V noToad o one mB J Prone i om o o Poke _ _ Pima _ NB What you have observed is called cross talk It occurs when a signal in one conductor can induce a signal by capacitive inductive or electromagnetic coupling in another conductor The small currents induced in the receiving conductor produce voltages across the impedance between the conductor and common The larger the impedance the larger the voltage as your data shows When high impedance signal lines must be used they should be shielded Examples of shielded lines used in high impedance voltage measurements are BNC cables and oscilloscope probes 2See Faissler p 137 or the scope manual for a discussion of scope probes Experiment 2 Operational Amplifiers Basic Concepts The purpose of this experiment is to introduce op amp a key element of analog electron ics circuits Several configurations of a voltage follower will be built introducing the key characteristics of op amps 2 1 Null voltage measurement 1 Wire up the following circuit using a 741 i ras op amp E E E oi Care should be taken to Vi S e
26. issajous pattern as shown in figure below Consult the manual for your Isee Simpson p 81 for the definition of decibel 1 5 SHIELDING AND INDUCED SIGNALS 7 scope to find how to select the xy mode Be sure to note the sensitivity setting of each input in your measurement The amplitude values should be recorded in volts rather than divisions Set the sensitivities so that the major axis of the ellipse is at an angle of about 45 and several divisions in length The pattern should be centered on the screen so that the central chord of the ellipse c can be measured with the vertical centerline of the scope graticule An easy way to perform the measurement is as follows 1 Ground the vertical amplifier input with the input switch and align the trace with the horizontal center line 2 Switch the vertical amplifier to DC and ground the horizontal amplifier input Cen ter the trace horizontally Measure the length of that trace which is the quantity b i 3 Switch the horizontal amplifier to DC and measure c Repeat for the same frequencies a as before you may simply add columns to the table from the previous Section SO RO E INIA 00 O E S S Plot the phase angle 4 vs log frequency Again if you are using a computer program to plot the data you only need to fill out the columns for b and c On your plot add the line arctan w7T where again 7 RC using the nominal component value
27. it as shown You may find it con venient to use the precision resistor arrays for R R 100kQ and Ro 2 5 Use the 10V supply as Vin and vary the input L voltage in the range of 5 V For each value ac Ry 10k0 curately measure both Vi and Vout and calculate the observed gain Plot Vout vs Vin determine the region of linearity and fit that part of the data to a straight line to determine gain Note that you must allow for a non zero intercept thus use a two parameter fit Compare the gain you obtain with the values calculated at each data point and with the value you would expect for this circuit from the nominal resistor values Explain what limits the gain for large values of Vi Use the 1 V supply as input set at slightly below 10mV Vary the gain of the circuit by using different values of Ra 100 kQ 1 MQ and 10 MQ Compare the measured gains to those expected and explain any deviations Can a gain of less than 1 be obtained with this circuit Explain why or why not In the above plot the x intercept of the straight line corresponds to the input offset voltage Vortset It may be more clearly observed at low input voltages and high gains Examine this effect by connecting the follower input to common and measuring Vout for the same Ra values as above Be sure to disconnect the voltage source from the follower input before grounding the latter 12 EXPERIMENT 2 OPERATIONAL AMPLIFIERS BASIC CONCEPTS
28. led reserved for ROM Basic in ROM in the original IBM PC BIOS ROM Experiment 7 Building and using a digital thermometer Some things happen so fast that one simply cannot monitor them without help from a fast computer in the role of a data taker One example is a rapid quench which occurs when a hot body is immersed into a cold fluid Is the rate of cooling still proportional to the temperature difference add details here 1 Assemble the thermistor circuit as shown in Fig 7 1 O 5V Ry R OT offset O out eo 00 nc NO V N Ww A E offset in Figure 7 1 Thermistor circuit R Ry 10kQ Ry 10k0 potentiometer R thermistor R decreases as temperature increases 1 Immerse thermistor and mercury thermometer into a beaker of ice water at t 0 C Adjust Ry so that V 9 5 V at 0 C Calibrate V as a function of t Slowly heat the water so as to maintain thermal quasi equilibrium and measure V and t at 5s intervals Heat to 60 C Use little water for speed Use the program you have written to measure V record temperature readings from the mercury thermometer by hand 1 Plot and analyze your data and create the temperature calibration plot of the thermistor circuit 31 32 EXPERIMENT 7 BUILDING AND USING A DIGITAL THERMOMETER 1 Optional modify your program to report true temperature in C Prepare two beakers one with ice
29. ment on the values you obtain 1 Now connect the scope to the low pass filter output Convince yourself that the device acts as a low pass filter Accurately measure and record the 3dB frequency where gain G 0 707 x G lowfrequency and the phase shift at the 3dB frequency 1 Repeat for the high pass filter output 1 To get a filter with a higher Q use Rin 20kQ and Ra 1k0 Set the FG to give a sine wave with Vp p 0 5V Observe the bandpass output 1 Measure and plot the gain in dB us log frequency for the high Q bandpass filter LA useful physica trick fit G axf b f lt 480 will only fit G f for values of f 480 and below 24 EXPERIMENT 5 ACTIVE FILTERS AND TUNED AMPLIFIERS Estimate the Q of the two bandpass filters you have investigated Q can be measured as the ratio of the centre frequency fo of the bandpass output to the bandwidth the difference in frequency between the upper and the lower 3dB points 1 Return the AF100 to the low Q state Rin 100kQ Raq 100kQ Vary the feedback resistors and measure the centre frequency of the bandpass output Rs O o o E O 0 0 o RA AAA 5 2 Notch filter A special form of active filtering can be thought of as the reverse of bandpass filtering In analyzing a notch filter we concentrate on the noise rather than the signal 1 ada AF100 has one additional uncommitted 40kQ AN summing op amp It can be used to con HPo A MA struct a notch filte
30. mplete the experiment Your lab book should contain all of the information necessary to reproduce your experiments later and to write your lab reports away from your lab station You will be required to submit seven lab reports over the course of the first ten weeks of labs experiments 4 5 and 6 take two weeks each Each report is due one week after the lab date All of these lab reports together will account for 70 of your final mark Attempt to write your lab reports as if they were scientific papers To find out what format you are expected to follow see for example Canadian Journal of Physics Generally speaking you should address the following points clearly and explicitly Title The name of the experiment performed Abstract A brief summary of the most important factors in the experiment including the statement of the final result and conclusions Introduction Describe the motivation for doing the experiment the physical principles in volved how the technique used differs from other techniques etc Procedure A carefully labelled diagram of the apparatus with a description of its features a careful account of how the measurements were done including the precautions taken to eliminate systematic errors In simple cases it may be sufficient to simply state that the procedure as described in the Manual was followed exactly All changes in the procedure modifications of the circuit or of the component values etc must be cle
31. nal report written E Sternin lt ed sternin brocku ca gt Office H206 ext 3414 Lab B208 ext 4457 Contents 1 Breadboard techniques and simple circuits 1 1 Introduction to the workbench usais A A PA PTS BU RA 1 2 Errors introduced by the instruments gic yg eo ee Ge eG E ee Se E Wows pase Mtera ita pie e una mhend ete Sid wand oO a hd se alk amp ew Balas 1 4 Observing phase shift with Lissajous patterns 0 1 5 Shielding and induced signals e e 2 Operational Amplifiers Basic Concepts 2 1 Null voltage measurement dia dra ia e a A BA O Mo A RI A os eee 2 3 Followe r Wah Pat setg pisma eina ds A AN Se EU ARA 3 Building circuits with op amps 3 1 Current to voltage converter e 32 Invertinge Open A es 3 3 SUTIN Bin plier ea sys gt O ee as Gok a eve dep a ee E a 3 4 Op amp characteristics a E Spake o We o Dl a el Soltis a 4 Advanced op amp designs AN OPE IEA A ees ge Sate Sate Be Bok 4 2 Op amp differentiator as de a tes ee had eet nt See ent Ba ee Ang Difference amplifler ses Sica do da o dat ace Gab On ace an erara e bee 4 4 Instrumentation amplifier quis hr e Is eke ed ee a cats Ls Aso earithmic ampliher s soca eo ap a Elke Se oe oe IR AS a 4 6 Analog Miller s ss Aas sh e AAA AAA ds ed hc de od 5 Active filters and tuned amplifiers E ive Tuner sss bo 6 or TREO So ett ee ao cpa MENA og Me Ro A A D a D2 Nota MITEL ss dre tat ES hee Gig She Bee
32. nally trimmed and does not Xy 010 104 3 5 X 0 laesa 6 0Z require external trimmer potentiometers Y o3 Its pinout is shown on the left Y 0 4 5 8HV 15V T For multiplication use the fixed 10V supply from the job board as the X input and use several fixed voltages from the reference job board as the Y input 10V 10V 1V 1V Connect the Z input to the output Connect the X2 Y2 and Z inputs to common Test the multiplier in all four quadrants by applying voltages of both polarities in the range of 10V The multiplier transfer function should be Vout Vz x V 10 Include in your data set X1 Y1 values of 10 0 0 0 and 0 10 Offsets modify the multiplier equation Vout Vot 0 1 x Ve VO x Vy VOO where V Vi and Vou are the X Y and output offsets respectively Use your data to evaluate each of the offsets Explain how magnitude of offset induced errors changes with X and Y input levels 4 6 ANALOG MULTIPLIER 21 1 To obtain an output voltage proportional to the square of an input voltage connect both Xy and Y inputs to the same voltage source and the X and Y inputs to common The Z input remains connected to the output Test the circuit over a 10V range of voltages and compare to the expected Vou 0 1 x Vin 1 The squared voltage output can be plotted against the input with the xy mode of the oscilloscope Substitute the output of the FG set in the sine wave
33. r by summing the low 3 and high pass outputs as shown E 5 Wire up the above circuit Make sure Vout you disconnect the grounding wire from pin 3 Set the AF100 to fo 500Hz 100kQ S 1 Measure the frequency response of the notch filter Choose the frequencies of the FG wisely take a sufficient number of measurements to resolve the shape of the filters transfer function 1 Plot the gain vs log frequency What type of noise could be reduced using the notch filter Determine fo from your plot How does it compare with the expected value 5 3 Lock in amplifier One of the best ways to dicriminate against noise is to use a lock in amplifier It combines the techniques of signal modulation at the source band pass limitation and phase lock demodulation to provide ability to distinguish weak signals buried in the noise Because they actively modulate the source signal lock in amplifiers are capable of distinguishing signal and noise that have overlapping frequency spectra 5 3 LOCK IN AMPLIFIER 25 sn eee Connect a biased photodiode or paan Aa noise source a phototransistor to a I to V TIL out 2 converter Connect an LED to the DER EH ES TTL output of the FG set at about 100k0 500 Hz Do not connect the exter nal noise source NM on the job board yet Use the scope to observe the out put of the converter and adjust the position of the photodiode and or
34. r knowledge and enhance your expertise in electronics on your own Get your hands dirty This is a laboratory course and you will need to get actively involved You will be given few instructions on how to proceed and sometimes these instructions will be deliberately vague The results you get and the time you spend on experimental work will depend strongly on your ingenuity Use the best tools for the job For example you will be given access to personal computers you are encouraged to use them to plot and analyze your data and to prepare lab reports Often only the raw data needs to be filled in the tables in your lab book and all calculations can be done inside the computer program on the entire data set at once Safety is a state of mind Take this trite slogan to heart Be alert look out for possible dangers check your circuits and think before turning the power on Acquire and maintain good working habits around your workbench keep your work area tidy and free of loose wires and components Turn the power off before leaving Conducting an experiment e Begin by reading through the entire description of the experiment Make sure you understand the goals of the experiment before you begin Make note of and attempt to resolve all questions that may arise during preparation by consulting the references and or the instructor Do not perform experimental steps whose purpose you do not understand Aim to complete each experiment in the s
35. red value of the ratio C C with that obtained by a direct reading of the capacitance meter D 1000 391 O Me FC l E Z Y 1 Sketch and explain the observed waveforms 4 2 Op amp differentiator WK touch C jumper o Use FG to provide a square wave input to the integrator Use Rin 1 MQ and set the frequency to about 1 kHz Choose the Cf value appropriate for this frequency Moni tor both the input and the output with the scope Make sure you adjust FG to have a zero DC offset Alternatively you may want to use a small capacitor 1 uF in series with FG to remove the de compo nent from the input By interchanging the resistor and capacitor of the op amp integrator we obtain an op amp differentiator We will analyze its response to various waveforms of the FG Do not remove the circuit of the previous section you may want to re use it in Sec tion 4 3 2 60 3 5 out Wire up an op amp differentiator as shown In a dual 353 package you may choose either of the two op amps pins 2 3 1 or 6 5 7 The 100 pF capacitor is in cluded to provide noise stability For this circuit dVin dt Set the FG to 5V peak to peak 1 kHz tri angular wave and connect it as Vin Vout RC 1 Sketch the input and output waveforms including the proper scales Make sure your scope is on a calibrated setting Calculate and record the slope of the
36. riment References Numerous excellent introductory electronics books exist and you are encouraged to refer to them often Some selected titles are listed below with Brock Library calling numbers shown where appropriate Other references such as manufacturers data books and the equipment manuals should be consulted as needed Photocopies of selected parts of some of the references are available in the lab and other reference material can be obtained from the University Technical Services see your instructor if you require access You are encouraged to consult journals such as American Journal of Physics Electronics and Reviews of Scientific Instruments for further reading 1 H Austerlitz Data Acquisition Techniques Using Personal Computers Academic Press 1991 2 D Barnaal Analog and Digital Electronics for Scientific Applications Waveland Press 1982 TK7816 B34 3 J J Brophy Basic Electronics for Scientists McGraw Hill 1990 TK7815 B74 4 M M Cirovic Basic Electronics Devices Circuits and Systems 1974 TK7815 C53 A J Diefenderfer and B E Holton Principles of Electronic Instrumentation 3rd ed Saun ders 1994 5 W L Faissler An Introduction to Modern Electronics J Wiley amp Sons 1991 6 B Grob Basic Electronics 1989 TK7816 G75 7 P Horowitz and W Hill The Art of Electronics Cambridge University Press New York 1989 TK7815 H67 8 H V Malmstadt C G Enke and S R Crouch Elec
37. s Does it agree with the data As before treat T as a parameter and fit the theoretical curve to your data Compare the two curves and the data Are the results of this fit in agreement with the ones from Section 1 3 Explain the differences if any 1 5 Shielding and induced signals 1 Disconnect all signal inputs and outputs from the breadboard frame Connect a shielded cable to the scope input but leave the other end of the cable unconnected Observe the display and record the amplitude of any open circuit signal present Connect the cable to the breadboard frame and again measure the signal amplitude Now insert a job board and again measure the signal amplitude Also determine the signal frequency The signal can be further increased by connecting a wire to a job board contact to the scope connector and touching the other end of the wire The amplitude of the signal is also affected by whether you are touching the frame or other ground or not What is the source of the signal observed and why is it affected by the amount of unshielded conductor exposed EXPERIMENT 1 BREADBOARD TECHNIQUES AND SIMPLE CIRCUITS 1 Connect the FG signal output to a frame connector Connect the FG output to the Ch1 scope input through the contacts on a job board Set the FG for a 1 kHz 10 V sine wave Connect the Ch2 scope input to another frame connector but do not make any connections to the corresponding job board contact Record the magnitude of t
38. s linearly with T 1 3 4 Op amp characteristics It is important to recognize the limitations of op amps so that measurement errors may be avoided in instrumental applications We will explore two important characteristics of several different common integrated circuit op amps 1 To measure the input offset voltage Vogset connect the op amp as a voltage follower and connect the non inverting input to common The output voltage equals Vogser Perform this measurement for the three different types of op amps and include the data in the table Repeat for both of the LF353 dual op amps Note that the pinout of the 741 op amp is identical to that of the LF351 1 To measure the input bias current Las a 10 MQ resistor should be connected between the non inverting input of the voltage follower and common The IR drop across the resistor results from the bias current The output voltage Vout is the sum of the offset voltage Voffset and the IR drop across the resistor pias Vout Vofiset R Carry out this determination for each of the op amps under investigation tabulate and comment on the results Vottset Vout for Rin O Vout for Fin 10M0 MEE FE LF353 1 Experiment 4 Advanced op amp designs 4 1 Op amp integrator The purpose of this section is to wire up and analyze an analog integrator using a carefully balanced op amp and a low leakage quality capacitor We will observe the circuit response to both de input si
39. the DMM 1 2 Errors introduced by the instruments E For the circuit diagram shown what is the voltage between the point a and the ground RN What will be measured at point a with a voltmeter set to the 5 V A E range if the meter has a sensitivity of 10 000 0 V It may help to re draw the circuit diagram including the Th venin equivalent representation of this voltmeter 1 Using one or two resistors and the 5 V power supply of the breadboard system estimate the internal resistance of the DMM when used as a DC voltmeter Compare your result with the posted specs of the DMM 1 3 Low pass filter In this part of the experiment we compare the relative importance of various sources of error systematic errors due to differences between nominal and actual component values instrumental errors random scatter etc 5 6 EXPERIMENT 1 BREADBOARD TECHNIQUES AND SIMPLE CIRCUITS 1 Wire the circuit shown The FG and scope should O AN ES El be connected to the circuit using BNC or banana ats plug connectors on the frame Be sure all common connections are made especially if using the ba from FG Ros a ch2 nana connectors with BNC connectors the con dad nection to common is automatically made 1 Measure the input and output amplitudes as a function of frequency at least for the frequen cies shown in the table below An easy way to do this is to set the scope time base so that dozens of cycles app
40. tronics and Instrumentation for Scien tists Benjamin Cummings Publishing Co 1981 9 J O Malley Theory and Problems of Basic Circuit Analysis Schaum s Outline Series McGraw Hill 1992 TK454 046 10 M Plonus Electronics and communications for scientists and engineers Harcourt Academic Press San Diego 2001 11 R E Simpson Introductory Electronics for Scientists and Engineers 2nd ed Prentice Hall 1987 12 W F Stubbins Essential Electronics John Wiley and Sons New York 1986 13 J C Sprott Introduction to Modern Electronics John Wiley and Sons New York 1981 14 B G Thomson and A F Kuckes IBM PC in the Laboratory Cambridge University Press 1989 QC52 T46 This is the required text for PHYS 2P31 32 Experiment 1 Breadboard techniques and simple circuits 1 1 Introduction to the workbench Spend some time getting acquainted with the tools available at your workstation Make sure you understand their markings controls and limitations A few minutes spent now on learning your way through the oscilloscope s knobs and dials will quickly pay off 1 Become familiar with the breadboard socket connections 1 Investigate the power supply controls and the output voltages provided 1 Practice the techniques of connecting between devices on the breadboard and to devices not on it 1 Measure variable voltages on the job board over their full range 1 V and 10 V Use both the scope and
41. uld be posted in the lab early in the semester Unlike the step by step experiments in this lab manual you will be given a task and a minimum of instructions on how to proceed In lieu of a final exam you will be required to present your project and demonstrate its operation as well as to submit a written report on your work Several Faculty members and representatives from the Electronics Shop usually attend these final presentations Your project report may take the form of a lab report or that of a User s Manual for your particular device Under certain circumstances the report may be replaced by an interactive Help facility built into the software that you have written to support your device The term project including the report is worth 30 of the final mark Please refer to this outline and to this introductory chapter throughout the course of the experi ments The marking scheme used to evaluate your work is implicitly contained here Conventions used in this manual 1 Whenever you see a paragraph marked off with this symbol it indicates an experimental step You are expected to perform one or several operations and write down your results and observations in the lab book When you encounter this symbol it indicates a question or a problem You are expected to perform the necessary calculation and to provide a written answer and possibly a brief explanation in your lab book before you proceed to the next stage of the expe
42. wave output to supply a 10 V reference signal to the multiplier Observe the multiplier output Adjust the FG frequency carefully to obtain a waveform that most closely approximates a full wave rectified sine wave Draw the observed multiplier output waveform Label the axes 1 Connect the active low pass filter to the multiplier output Observe the DC output with the scope Record the DC level observed with the modulated LED on and off T Look again at the I to V converter output and measure the ratio of the square wave amplitude to noise amplitude Calculate the signal to noise S N ratio improvement obtained with the lock in amplifier 26 EXPERIMENT 5 ACTIVE FILTERS AND TUNED AMPLIFIERS 1 To better demonstrate the noise rejection capabilities of the lock in amplifier still more noise will be intentionally added to the signal This noise will be obtained from the noise generator circuit available on the reference job board The relevant part of the reference 200k job board circuit is shown The V ANA 0 001uF 5837 digital noise generator IC pro 4 duces 10 V pulses that have varying durations The pulse durations are random integer multiples of 20 ys ES NM The 10kQ potentiometer selects a O 3uF 150k fraction of the noise generator out put amplitude The noise signal NE is AC coupled into a summing am L gt plifier that also serves as an active low pass filter 15V 200kQ 5837 10kQ
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