Lab #1 Lab Introduction

Transcription

1 Cir cuit s 212 Lab Lab #1 Lab Introduction Special Information for this Lab s Report Because this is a one-week lab, please hand in your lab report for this lab at the beginning of next week s lab. The purpose of this lab is to allow you to become familiar with the laboratory equipment and processes. Labs will be performed in groups of two or three students. Each person will turn in his or her own copy of the required work for the lab. For this lab, one person from your group will need to check out the following from the EECS Shop. An analog probe kit with a breadboard (metal toolbox) Figure 1. A typical breadboard. The arrows indicate the direction of conduction. The 64 inner columns conduct vertically with an open break in the middle. The outer 2 rows on the top and bottom conduct horizontally (with an open break in the middle for some types of breadboards). Parts List 1-2 k Resistor 1-3 k Resistor 1-10 k Resistor Date Last Modified: 2/5/2018 5:57 PM 1

2 Definitions Voltmeter A device for measuring voltage between two points. A perfect voltmeter behaves like an open (infinite resistance) circuit. Voltage is measured by connecting the two voltmeter terminals to the two points of the circuit where the voltage (potential difference) is to be measured (see Fig. 4 below). Therefore, the voltmeter has no effect on the circuit because placing an (ideally) infinite resistance across any two points in the circuit will not affect its operation. Figure 2. Using a voltmeter for voltage measurement. Notice that no any change to the original circuit connections need to be done. We simply connect the terminals of the voltmeter across the component where the voltage is to be measured (resistor 4 in this case). Ammeter A device for measuring the electric current through a circuit path. A perfect ammeter behaves like a short (zero resistance) circuit like a wire. Current is measured by inserting the ammeter in series within the electric current flow path and, therefore, the ammeter has no effect on the circuit because it looks like a perfectly conducting wire (see Fig. 3 below). Figure 3. Using an ammeter for current measurement. Notice that we need to make a break in the circuit and connect this break by the two terminals of the ammeter, i.e., to interpolate the ammeter in the current path so that the electric current flows through the ammeter. Ohmmeter A device that measures the electric resistance between two terminals of a component or a circuit. If the resistance of a resistor is to be measured, the resistor should NOT be connected to an external circuit from both terminals. Date Last Modified: 2/5/2018 5:57 PM 2

3 Multi-meter A device that can function as an ammeter, voltmeter, or an ohmmeter. Most of modern multi-meters are digital multimeters (DMM s). There are generally two types of DMM s: hand-held DMM s and bench-top (or bench-attached) DMM s (like the ones attached to your benches in the lab). Function Generator (FG) A device that produces voltage signals as functions of time. Common signals that a FG can produce are sine waves, square waves, triangle waves, ramp waves, and noise. Common controls that a FG has include amplitude, frequency, and DC offset. Arbitrary Waveform Generator (AWG) A device that is like a function generator in that it produces voltage signals. However, an arbitrary waveform generator can produce any waveform (audio, television, digital data, sinusoids, etc.). AWG s have interfaces like FG s. They can generate analog signals from saved digital files (like signals generated by MATLAB or any other computer tool, or files of signals acquired from real analog signals by an oscilloscope) Digital Storage Oscilloscope (DSO) A DSO measures voltage signals as a function of time. The time-varying voltage can be recorded and saved as a data file (containing the voltage value at each sampling time) to be used for computer processing or regeneration when loaded to an AWG. Experiment 1. Using Multi-meters to Measure Voltage and Current Figure 4. Using your breadboard and provided circuit components, build the circuit shown in Fig. 4. The Hewlett-Packard power supply has three adjustable outputs. Use the +20V connection to supply 12V for V2 and the +6V connection to supply the 5V for V1. Select the appropriate meter and adjust the voltages before you connect power to the circuit. Use the COM terminal to provide the 0V potentials (this will be the ground point to your circuit). The green terminal is a connection Date Last Modified: 2/5/2018 5:57 PM 3

4 to common ground and is not necessary for this experiment. It will not be connected in most of our experiments. You will be using the bench-attached DMM to measure the voltage across R1 and the current through R1. When you use a meter to measure a parameter of a circuit, the meter becomes part of the circuit! When using the multi-meter as a voltmeter, it has a huge internal resistance on the order of 50M Ohms. When using the multi-meter as an ammeter (current meter) it offers almost zero internal resistance. Therefore, when measuring different parameters, you will connect the meter differently! To measure the voltage across R1, get a red cord and a blue cord from your probe kit. Insert the red cord in the jack designated for Volt readings. Insert the blue cord in the common (black) jack in the middle. Attach a red clip and black clip to the other ends of the respective cords. Clip the red clip to the side of R1 that you expect to have the highest potential. Clip the black clip to the opposite side. Make sure that the V button is depressed on your meter when measuring voltage. Your meter should now display the voltage across R1. If the reading is negative, the side with the red clip is at a lower potential than the side with the black clip. Record this reading in your lab notebooks. Because the voltmeter has such a huge internal resistance, almost no current was diverted through the meter when taking the above reading. However, when we are taking current readings this will not be the case! Because the ammeter has almost no resistance, if you connect it in the same fashion as above, almost all of the current will be diverted through the ammeter and it will not pass through R1. You will have then made a huge change to your circuit! The ammeter must be connected in series with R1 to determine the current flowing through it. To do this, first shut the power off to your circuit. Then remove the high side lead of R1 from the breadboard. Connect it to the black lead of the ammeter. Now connect the red lead to the portion of the circuit where the high side of R1 was. Now on the meter, move the red cord from the voltmeter jack to the ammeter jack. Also, depress the ma button on the meter when measuring current. When you are sure you have made the correct connections go ahead and turn on the power to your circuit. Your meter should now display the current flowing through R1 in milliamps. If there is a negative sign in front of the reading, the current is flowing the opposite direction of what you expected. Record this measurement in your lab notebooks. Note. The current through R1 can be measured anywhere in its current path. For example, the ammeter can be inserted with the upper or lower terminal of the resistor. Either way the same current flowing through the resistor will be flowing through the ammeter. Date Last Modified: 2/5/2018 5:57 PM 4

5 Experiment 2. Using the Function Generator and Oscilloscope In this experiment you will generate three different waveforms using the function generator (FG) and display these waveforms using the oscilloscope. These waveforms are: Signals to be generated and screen captured 1. A 1 V amplitude square wave with a 1ms period 2. 2sin(ωt), where ω=2 f, with f = 1.5 khz. 3. A 0.5 V amplitude triangle wave with a 20ms period and a DC offset of +2V Experiment 2 Deliverables The deliverables for Experiment 2 are labeled images of the three different waveforms screen-captured from the oscilloscope to the computer. The parts of the image that should be labeled are: 1. The major waveform characteristics: amplitude (Peak-Peak), period (Period), frequency (Frequency) and DC offset (Average N Cycles). 2. The Trigger Position indicator. 3. The Trigger Level. 4. The Ground Position Indicator. 5. The Volts/Div reading corresponding to the amplitude and Time/Div corresponding to the period The instructions that follow will show you how to set the FG and oscilloscope to display these waveforms, and then screen-capture the images of the waveforms to the computer. Using the BNC-to-BNC cable from your probe kit, connect the function generator (FG) output directly to the oscilloscope (use Channel 1) input as shown in Fig. 5 below. BNC-to-BNC Cable Figure 5. Date Last Modified: 2/5/2018 5:57 PM 5

6 Set the Frequency on the FG Press the Freq key on the FG to display the current frequency setting. To adjust this, you may do one of three things; you can use the arrows soft keys to adjust the frequency to the required number. Alternatively, you can turn the knob to increase or decrease the frequency. Or you can press the Enter Number key, then key in the desired frequency value following the green numbering beside the keypad and press the desired unit that is listed adjacent to the arrow keys. Set the Amplitude on the FG Now press the Ampl key on the FG to display its current value. Notice that is has the units of Vpp (voltage peak to peak). Therefore, if you want a sine wave with a ±1 Volt amplitude, you must enter 2 Vpp! Adjustments to this value are made the same methods as described above. Set the Type of wave on the FG The type (square wave, triangle wave or sinusoidal wave) of wave is set by pressing the key with the appropriate symbol. Set the Type of wave and the DC offset on the FG Finally, the DC offset is set by pressing the Offset key and adjusting the offset. If no offset is given, assume it is zero. Date Last Modified: 2/5/2018 5:57 PM 6

7 Steps to Manually Trigger and Display the Waveform on the Lab Oscilloscopes Waveform Measurements Channel Display Horizontal Control Run Control Green => Running Sampling Data Red => Stopped on current Sampled Frame Waveform Triggering Control General Selection Knob Vertical Control Power Key Softkeys Used to select options on the bottom of the digital display. Channel Inputs Where probes and other BNC input signal connectors are connected. Figure Turn on the oscilloscope, and check the Channel Display as shown in Fig If the Channel Display for channel 1 is not 1.00:1 change the input channel attenuation to 1.00:1. a. In the Vertical Control section of the oscilloscope, push the 1 key. b. Push the Probe softkey. c. Push the Probe X:1 softkey (X will be a number from 0.1 to 1000). d. Adjust the General Selection Knob until the attenuation for Channel 1 is 1.00:1. 3. If the Channel Display for channel 1 is not DC change the input channel coupling to DC. a. In the Vertical Control section of the oscilloscope, push the 1 key. b. Push the X Coupling softkey (X will be either AC or DC ). c. Adjust the General Selection Knob until Channel 1 is using DC coupling. 4. The 1 key in the Vertical Control section should be green, indicating that the channel 1 input data is being displayed. If it is not green, push the 1 key. Date Last Modified: 2/5/2018 5:57 PM 7

8 5. The Run/Stop key in the Run Control section should be green, indicating that the oscilloscope is sampling, and not frozen. If it is not green, push the Run/Stop key. 6. You will now configure the oscilloscope to trigger off the Channel 1 input. a. Push the Trigger key. b. Push the Source softkey. c. Select Source 1 using the General Selection Knob. 7. Next, think about the waveform you are trying to find. What is the wave amplitude, period and DC offset? 8. Now that the scope is triggering off of Channel 1, adjust the trigger Level knob in the Waveform Triggering Control section until a waveform appears. Notice the Trigger Position Indicator and the Trigger Level positions on the oscilloscope screen as shown in Fig. 7. The waveform should appear once the trigger level is in the range of the waveform signal swing (between the maximum and minimum values of the waveform). A good place for the trigger level to start is at the DC offset value of the waveform because this guarantees that your trigger level will be somewhere in the middle of the waveform you are trying to find. You may need to zoom out by increasing the Volts/Div in the Vertical Control section to be able to move the trigger level to the proper position. 9. Adjust the Volts/Div knob and the Position knob in the Vertical Control section to nicely fit the amplitude of the expected waveform. 10. Adjust the Time/Div knob and the Position knob in the Horizontal Control section to fit a full period or two of the expected waveform in the display. Trigger Position Indicator Time = 0 y-axis Y-Intercept at the Trigger Level Trigger Level Figure 7. Note: The Default Setup key will be used in future labs. This key returns the oscilloscope to its default settings, but it does not adjust the input attenuation. Date Last Modified: 2/5/2018 5:57 PM 8

9 This key is very useful, since you do not know what the person before did with the oscilloscope. Measuring Waveform Characteristics with the Oscilloscope Next, measure the waveform characteristics by pressing the Meas key, and then use the softkeys to select the following measurements: amplitude (Peak- Peak), period (Period), frequency (Frequency) and DC offset (Average N Cycles). Experiment 2 Deliverables The deliverables for Experiment 2 are labeled images of the three different waveforms screen-captured from the oscilloscope to the computer. The parts of the image that should be labeled are: 1. The major waveform characteristics: amplitude (Peak-Peak), period (Period), frequency (Frequency) and DC offset (Average N Cycles). 2. The Trigger Position indicator. 3. The Trigger Level. 4. The Ground Position Indicator. 5. The Volts/Div reading corresponding to the amplitude and Time/Div corresponding to the period Screen-Capture the Images from the Oscilloscope to the Computer 1.Go to All Programs on the computer and start the Keysight BenchVue. 2. Make sure your oscilloscope is detected and its icon is shown in the Instrument Panel at the bottom of the main window. 3. Start the bench Oscilloscope App by double-clicking the oscilloscope icon. 4. Go to the Screen Image tab from the top of the window and click on Get Current Screen button. The oscilloscope screen will be loaded and displayed in the current window. 5. Select the Save icon from the right bottom of the screen and then select Save Image. The saving dialog box will open; here s where you can write the file name and select the file format and directory for the image to be saved. Note: The Run/Stop key may become red while the images are being captured. Make certain the Run/Stop key is green again before performing more measurements. Date Last Modified: 2/5/2018 5:57 PM 9