EE1111 Lab Manual-Diploma - Lab 5

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Page i Diploma Program Course EE1111 LABORATORY MANUAL #5 Electrical and Telecommunications Engineering School of Electrical Engineering and Telecommunications Student Name: …………………… Student ID: …………………………

Contents Lab 5: First-order circuits .......................................................................................................... 3 Aims of this experiment ............................................................................................................ 3 Videos and guides for review .................................................................................................... 3 Lab 5: Pre-Lab work .................................................................................................................. 4 Lab 5: Part B. Hardware Explanation ........................................................................................ 4 Lab 5: Part C: Simulation and Discussion .................................................................................. 9 Required components ............................................................................................................ 9 I. RC transients – First measurements ................................................................................ 9 Page ii

Lab 5: First-order circuits Aims of this experiment The aim of this lab experiment is to examine the following features of first-order circuits: 1 Setup of the signal generator and oscilloscope for transient circuit measurements 2 Transient voltages and currents in simple RC circuits. Videos and guides for review List of suggested videos : Signal generator Oscilloscope List of suggested guides from Appendix:  Signal/Function generator  Oscilloscope Page iii

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Lab 5: Pre-Lab work Make sure you complete the online quiz for Lab 5 before attending your session. Note that this quiz can be found in Moodle in the Laboratory section. Lab 5: Part B. Hardware Explanation Please complete all the tasks given in this section during the lab session. Do not forget to watch the related lab videos and guides that are suggested for this lab experiment. 1. Annotate the diagram in Figure 5.2, on the next page, to show how you would set up the circuit in Figure 5.1 if you were in the lab. Assume that we wish to measure the transient voltage across L using the oscilloscope and want to measure the voltage of our source (signal generator) for this experiment. You may copy the image in Figure 5.2 into MS Paint, add your annotations, and then copy the annotated image back into this document. Refer to the Preface section in the Online Lab Manual for an example annotated image. The annotation in Figure 5.2 must show: (10 marks)  The components on the picture of the breadboard (use dark blue colour for all components).  Connections on the picture of the breadboard in red or black (or any other relevant colour) depending on the colour of the cable or wire insulation that you would use in a lab.  The cable connections between each piece of equipment and the breadboard and/or the components on the breadboard. Also, be prepared to explain to the lab demonstrator what connection type you would use at each end of the cable (i.e. banana plug, BNC, alligator clamp, etc.). It may be helpful to add text descriptions of this to your diagram. Figure 5.1: An RL circuit to observe the transient behaviour with the oscilloscope. Some helpful tips with this exercise are:  Ensure that annotated lines are thick enough to be easily seen, but not too thick that it becomes difficult to see what breadboard holes you are connecting wires to. Ensure that you understand why you have connected equipment in the particular configuration as lab demonstrators may ask you this question. Page 4

Figure 5.2: Part B. Equipment diagram for annotation exercise. Page v

2. Explain how you would set up the signal generator and oscilloscope in the following Answer Boxes. a. Include a comment to prove that you have checked that the estimated voltage across R does not exceed the rating of the oscilloscope. Note that we will assume that the rating of the oscilloscope is 150 V. Note that this is an important check that you should do whenever you connect an oscilloscope to a circuit! Think about the supply voltage in reference to the oscilloscope rating and make a comment in the Answer Box. (2 marks) b. Include equations to estimate what the maximum current draw from the signal generator should be and check that this does not exceed the signal generator maximum current limit . Note that the signal generator output resistance is 50 ohms. So, the maximum output current you would expect from the device is shown in the equation below. Note that this is an important check that you should do whenever you connect a signal generator to a circuit! Think about the steady-state current of the circuit and compare this to the maximum signal generator output current in the Answer Box. (3 marks) i max = v peak R o = 15 50 = 0.3 A c. For the signal generator, you should explain (do not worry about the TTL/CMOS option as we won’t connect to this port) (15 marks): i. Why do we always need to measure the signal generator output voltage using an oscilloscope? ii. How to set up to output a square-wave output. iii. How do we program the square wave to have an amplitude of 15 V? iv. How to program the frequency of the square wave including the decade options (also understand how to change this frequency from 1 kHz to 22 kHz). Bonus marks for detailing what check we should do before making this frequency change. HINT: Think about what we did in steps (a) and (b) here. v. What the duty cycle setting is and how it should be set to achieve a square wave. What if I want a wave that is 60% positive 15 V and 40% negative 15 V during a period, how should I set up my signal generator? vi. What does the offset button do? How should it be programmed for a square wave with +16 V and -14 V? Page vi Connect the “function output” output terminal of the function signal generator the CH1 signal input terminal of the oscilloscope and connect the AC power supply with a maximum voltage of 150V with an electrical appliance. And set the oscilloscope to a 1K Hz waveform. I = V / R_total = 15/ 1050 = 0.01428A < 0.3A

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d. .For the oscilloscope, you should explain (30 marks): i. How do I turn on (and off) the channel that I am measuring? ii. What buttons do I need to press to set up the scaling of the measurement? What scale ratio should you use here? iii. Use the image of the oscilloscope in Figure 5.3 to show how you would read the oscilloscope V/div and time/div off the display screen? Also, show how you would change the time/div of the screen using this image? How would you change the V/div of each channel? Does this resolution adjustment change the actual measurement? iv. Use the image of the oscilloscope in Figure 5.3 to show how you can shift the measured signals horizontally and vertically on the screen. Why might you want to do this shifting? Does this shifting change the actual measurement? v. What does triggering mean? Why do I need to use trigger mode when displaying periodic signals on an oscilloscope? What are the three modes of triggering? How do I adjust the trigger level? What does rising-edge and falling-edge triggering mean? vi. What are the run/stop and single buttons used for? vii. How can the measurement function be used to ensure that the signal generator voltage has an amplitude of 15 V? viii. What is ac and dc coupling? Which one should I use here? Page 7 1.Due to this is AC circuit, the voltage across signal generator changed every time and oscilloscope can show the value and change of voltage for a period of time. So it can be used. 2.press square-waveform function type knob 3.turning amplitude knob to 15V. 4.first press frequency decade you need, then turn the frequency knob. Also there are minimum and maximum value for different decade. 5.the percentage of positive and negative signal. Each is 50%. First set amplitude to 15V, then turn duty knob. 6.set amplitude constant(the center value). Rotate the offset knob

Figure 5.3: Picture of the oscilloscope 1.press power knob and channel 1 yellow light will turn on. Beside, press 1/2 will turn on/off 1/2 channel. 2.probe ratio should be 1:1 to be accuracy 3.5.00V/ is the vertical scale for V/div;2.000?/ is the horizontal scale for time/div. use horizontal large knob to change time/div. and vertical large knob to change V/div. No just change the display. 4.use vertical/horizontal small knob to shift in y/x axis. just change the display. 5.acquisition system begin acquiring. Define what something we need to display on screen and what data is available to make measurements. Normal mode, auto mode and single mode. Use trigger rotary knob 6.to catch the infrequent or non periodic events 7.use single tab 8.dc coupling will display dc and ac signal both. Ac coupling just display. Us dc here. Lab 5: Part C: Simulation and Discussion Please complete all the tasks given in this section during the lab session. Do not forget to watch the related lab videos and guides that are suggested for this lab experiment. Required components In this experiment you will be required to use the following components:  Your breadboard.  1 kΩ resistor.  220 μ F capacitor. Page 8

I. RC transients – First measurements Electrolytic capacitors have fixed polarity , as shown in Figure 5.4(a) (note the circuit symbol for capacitors sensitive to reverse voltage is in Figure 5.4(b)). If you connect the electrolytic capacitor the wrong way, it will explode. Note that some smaller capacitance capacitors are not sensitive to reverse voltage (see examples in Figure 5.4(c), and circuit symbol for generic capacitors in Figure 5.4(d)). (a) (b) (c) (d) Figure 5.4: (a) Electrolytic capacitor, (b) Reverse-voltage sensitive capacitor circuit symbol, (c) Polyester and ceramic capacitors, (d) Generic capacitor circuit symbol. 1 Build the RC circuit shown in Figure 5.5 on your breadboard. Use the polarized capacitor in Circuits in TinkerCAD, not the standard capacitor . Be careful to configure the polarized capacitor the correct way! Note that the signal generator should be used to produce a square wave with a maximum voltage of 5 V and a minimum voltage of 0 V. Figure 5.5: RC circuit to observe the transient behaviour with the oscilloscope. Take a screenshot of the oscilloscope reading with the appropriate time scale. From this waveform screenshot, estimate the time constant. Do not use the formula τ = RC as an answer here! HINT: There are two methods for doing this. Method 1: v c ( τ ) is 63.2% of the change from the initial value to the steady-state value. Find the time value at this voltage value v c ( τ ) to get the time constant. Method 2: Find the initial and steady-state values and get an equation for v c ( t ) . Then use the formula: v c ( τ ) = v c ( ∞ ) + [ v c ( 0 ) − v c ( ∞ ) ] e − τ τ = v c ( ∞ ) + [ v c ( 0 ) − v c ( ∞ ) ] e − 1 to find v c ( τ ) . Find the time value at this voltage value v c ( τ ) to get the time constant. Page 9

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Use method 2: v c ( 0 ) = 0V, v c ( ∞ ) =5V, v c ( τ ) = 5-5*(1/e)=3.16V From thinkercad we can see at t ~= 24s v_c ~= 3.2 So time constant is 24s. 2 Why can’t you change current instantaneously in an RL circuit? Why can’t you change the voltage across the capacitor instantaneously in an RC circuit? Lab work 5 Date: Assessor name and signature: Mark: Page 10 RL ： 1. If it is connected in series, the current is equal everywhere 2. it is in parallel, it needs to be connected to a current source, because this is mainly because the output voltage is equal to the input voltage. Therefore, the entire circuit does not act as a voltage signal filter. RC ： Since the capacitor has a storage effect on electric energy, the capacitor will slowly charge when it is energized, and the capacitor will discharge when there is no electricity, so the voltage across the capacitor cannot be changed instantly in the RC circuit.