EECS 318 Electronics Lab Laboratory #2 Electronic Test Equipment

Transcription

1 EECS 318 Electronics Lab Laboratory #2 Electronic Test Equipment Objectives: The purpose of this laboratory is to acquaint you with the electronic sources and measuring equipment you will be using throughout this course. During this lab, you will be asked to use these instruments to perform a variety of simple measurements of voltage and resistance. Equipment: 1 - Analog Probe Kit (YOU need to check out) 1 - DC Power Supply (Agilent E 3630A) 1 - Digital Multimeter (FLUKE 8050A) 1 - Function Generator (Hewlett Packard 33120A) 1 - Oscilloscope (Agilent) Components: 1-100Ω Resistor 1-1kΩ Resistor 1-10kΩ Resistor 1-100kΩ Resistor 1-5 kω Potentiometer 1 - Photodiode Procedure: 1. A digital multimeter (shown below) measures electrical voltage (AC and DC), current (AC and DC), or resistance. Digital Multimeter (FLUKE 8050A) Measure the voltage of a battery and note down the reading. Reverse the leads and observe what the meter does. Q1: What is the reading on the multimeter for the battery? What happens when the leads are reversed? 1

2 2. A DC power supply (shown below) supplies electrical DC power. Notice that this supply can generate three different voltages simultaneously in ranges: 0 to +6 V, 0 to +20 V, and 20 V to 0. Each of these voltages is generated from the respective positive terminal (note the labels) and the common (black) terminal. Note that the common terminal is the same for all three voltages. DC Power Supply (Agilent E 3630A) Set the multimeter to the 2-VDC range. Using jumper cables, connect the positive (red) and negative (black) terminals of the multimeter to the 0-6 V output terminal (red) and the com (black) terminal of the power supply, respectively. Select the +6 V meter setting on the power supply, and turn the +6 Voltage adjust knob to its fully counter-clockwise setting. Slowly increase the voltage control of the power supply from 0 to 6 V in 1 V increments. Compare the readings on the power supply meter with the multimeter. Q2: What happens to the multimeter display when the voltage exceeds 2V? How can this be avoided? It is a good practice when measuring a completely unknown voltage to start out on the highest range and move downward until the desired resolution is obtained. Try this with the voltage control turned up a little higher. 3. Using the multimeter, measure the resistance of each of the 4 fixed, twoterminal resistors (100Ω, 1kΩ, 10kΩ, 100kΩ) and record the measured resistance values along with the color code for each. Q3: Record the readings in the table below? Are all of the resistors within the tolerance indicated by the color code? 2

3 Indicated values Measured values Color Code Within tolerance (Y/N) 100Ω 1kΩ 10kΩ 100kΩ 4. Using the multimeter, measure the resistance between the two outer pins of the variable resistor using mini grips provided in the kit (5kΩ potentiometer). Q4: Does this resistance change appreciably (i.e. more than 1 kω when the slider is rotated? 5. Using the multimeter, measure the resistance between the inner pin and both of the outer pins of the potentiometer (inner and 1 st outer pin followed by inner and 2 nd outer pin) for few different settings of the slider. Q5: Does this resistance change when the plastic slider is rotated? For each slider setting, do the two resistances always add to the same value of 5 kω? Why? 6. With the multimeter set to DC volts, measure the voltage across the pins of the photodiode (the two-pin device with the circular, plastic window). Q6: Does this voltage change when you shield the window with your hand? Q7: What does this device seem to do? What could it be used for? 3

4 7. A function generator (shown below) produces a variety of voltage wave shapes (including the square wave and the sine wave) of various amplitudes and frequencies. It is often used as an AC voltage source in electronic measurements. Function Generator (Hewlett Packard 33120A) Note that the frequency and amplitude values can be set using the controls shown below: 4

5 8. An oscilloscope or scope" (shown below) is the basic instrument for dynamic measurements. The utility of this instrument lies in its tremendous flexibility. It can be used to observe voltage signals ranging in amplitude from a fraction of a millivolt to hundreds of volts at speeds from nanoseconds to as much as minutes. An oscilloscope can be used for many different purposes. This experiment will not cover the full functionality of the oscilloscope. Additional techniques will be taught in future experiments. Oscilloscope Note: the probe ratio for a BNC to BNC cable is 1:1. Make sure you set it up before doing any measurements. To do that, go to the menu button marked 1 (CH-1), select Probe; change the probe ratio to 1:1 using the push-to-select button. 9. In general, the oscilloscope has three major sections, which control the operation of the instrument. They are the VERTICAL" control section, the HORIZONTAL" control section, and the TRIGGER" control section. There are many other minor knobs controlling various functions. The first section is the VERTICAL" section, into which the outside signals are fed. The input signal controls the vertical position of the oscilloscope trace. Your scope has two channels (CH-1 & CH-2) to receive outside signals. Press 1 to activate display of the channel one input. Set the coupling mode to DC by changing the setting located at bottom left of screen. (This setting means that the vertical deflection will be determined by the total AC + DC input voltage.) The second section is the HORIZONTAL" control section. This section controls the rate at which the oscilloscope trace is scanned horizontally to stretch out the vertical deflection and make the trace look like a waveform. The third section is the TRIGGER" control section. Press Trigger and then 5

6 Press Edge, then select Type=Edge, Source=1, Slope=rising, Coupling=AC. (This setting means that the trigger circuit will ignore any dc component of the input signal) 10. Turn the function generator on and set it to generate a 1 KHz sine wave with a peak-to-peak voltage of 2.0 V and a DC offset of 0. Using a BNC-to-BNC cable, connect the output from the function generator to the CH-1 input of the oscilloscope. Press the default setup button on the oscilloscope. The default setup button is an important feature of the oscilloscope and is used to reset all settings to their default values. The default setup button can be used anytime when you make wrong adjustments. Change the horizontal and vertical setting to arrive at a reasonable sine wave display on the oscilloscope. There will be a display on the scope screen informing you about the settings and can be found on the upper section of the display. Q8: What are the horizontal and vertical settings that the default setup has chosen for this waveform? 11. The oscilloscope has a cursor feature that enables you to measure the amplitude and period (the time for one cycle of the wave) of the signal displayed on the screen. Use the CURSOR function to set cursors for the time durations and amplitude swings. To measure the peak to peak (p p) amplitude of the signal, press CURSOR menu then select mode=manual, Source=1, Cursors=Y1. Next, choose Y1, and rotate the entry knob so that the horizontal cursor rides on the top peak of the waveform. Next, choose Y2, and rotate the cursors knob so that the new horizontal cursor rides on the bottom peak. The p p voltage difference between the two cursors (in this case, the p p voltage) will appear on the screen. Q9: How does the measured signal amplitude on the oscilloscope shown as Y on the screen compare with the value shown on the function generator? Also note down the reading observed. 12. Press 1: select Probe; change Probe Ratio from 1:1 to 10:1. Q10: How does the measured signal amplitude on the oscilloscope compare with the value shown on the function generator? 6

7 13. Next set the mode to Normal by pressing the Mode/Coupling button found next to the Cursors button and then selecting the Normal mode found on the left bottom of the oscilloscope display. To measure the time (e.g., the period of the sine wave), press Source=1 and get into the cursor menu by pressing the CURSOR button. Next, choose X1, and rotate the cursor knob so that the vertical cursor intersects one of the zero-crossings of the waveform. Next, choose X2, and rotate the entry knob so that the new vertical cursor intersects a zero crossing one period after the first cursor. The Dt time difference between the cursors and the corresponding frequency f =1/ Dt will appear on the screen. Q11: How does this compare with the frequency indicated on the function generator dial? Also note down the reading observed. 14. Now, go back to the Trigger" section. Set the SLOPE control to the Falling setting and observe how the trace changes. Q12: What happens after the setting is changed to Falling? Reset Probe Ratio to 1:1. Set coupling mode to DC to include DC components measurement from the signal. Press the offset button on the signal generator and set the display value to This adds a +1.0 DC component to the sinusoidal output. Q13: How does the displayed waveform change? 15. Press the 1 button, set the coupling to AC. This sets the oscilloscope vertical section to ignore the dc component of the input signal. Q14: How does the displayed waveform change as the vertical coupling mode is changed from DC to AC? What advantage could you envision to using the AC coupling mode when displaying signals? 7