EENG-201 Experiment # 4: Function Generator, Oscilloscope

Transcription

1 EENG-201 Experiment # 4: Function Generator, Oscilloscope I. Objectives Upon completion of this experiment, the student should be able to 1. To become familiar with the use of a function generator. 2. To become familiar with the use of a digital stored oscilloscope. II. Material and Equipment 1- NYIT supplied Lab Kit 1- Function Generator 1- Oscilloscope 1-51 Ω, 1.5 kω, 2 kω, 5.1 kω, 0.1 µf, 4.7 uh III. Information Part I: Protek 9301 Function Generator The Protek function generator is a precise low distortion instrument, capable of generating sine, triangular, square, and ramp signals in the 0.1Hz to 32 MHz frequency range. The front panel and the main features are shown in Figure 4.1 and Table 4-1. Figure 4.1: Front panel of Protek function generator. Table 4-1 some features of the Protek function generator. No. Name Feature Description 1 CH1 Function Output 50 Ω square, triangle, sine wave output. 2 CH1 Sync Output Square wave output for driving digital logic. 3 Parameter Display Display the signal parameter values set for each channel. 4 Step The step key permits the operator to increase or decrease the selected parameter s step value. 5 Function Keys These keys choose the main waveform output. The Function [Up/Down] arrow keys select the output waveform. 6 Entry Keys The numeric keypad allows for direct entry. The value is entered by pressing one of the Unit keys. A typing error may be corrected by using the CLR key. 7 Units Keys The Units keys are used to enter numeric values. Simply press the key with the desired units to enter the value 8 Sweep/Modulation These keys control the modulation and sweep capabilities.

2 When the function generator is powered on the display parameter values that appear are: Display Description OUT FREQUENCY: indicates the frequency selected. AMPL: indicates the output voltage amplitude and units. OFFSET: indicates the dc offset output voltage. Operating Procedure Select the desired frequency by pressing the [FREQ] key and typing the value on the keypad. Complete the entry by pressing the appropriate units (Hz, khz, or MHz). The output frequency is displayed, on the LCD display. Select the output (FUNC menu) waveform (square, triangle, or sine) by pressing the FUNC Up/Down arrow keys until the desired function LED is lit. The SWEEP/MODULATE should be on LIN/SINGLE. The amplitude signal level can be set by pressing the [AMPL] key and typing in the value on the keypad. Complete the entry by pressing the appropriate units (Vpp, Vrms, or db). Part II. Tektronix TDS 2024 Oscilloscope The Tektronix TDS 2024 oscilloscope provides accurate real-time acquisition of signals. It supports features such as automatic measurement, peak detect, storage of four reference waveforms, and autoset. The front panel and the main features of the TDS2024 are shown in Figure 4.2. Figure 4.2: Front Panel of TDS EENG-201 Page 2

3 The VERTICAL Control relates to the vertical movement of the scope trace. This oscilloscope has four vertical sections so that it can be display four waveforms simultaneously. Figure 4.3: VERTICAL Control Table 4-2 VERTICAL Control Description. CH1, CH2, CH3 & CH4 (Menu) Display the channel input menu selections. CH1, CH2, CH3 & CH4 (Volts/Div) Selects calibrated scale factors. CH1, CH2, CH3 & CH4 (Position) Positions the waveform vertically. The HORIZONTAL Control relates to the horizontal movement of the scope trace. Figure 4.4: HORIZONTAL Control Table 4-3: HORIZONTAL Control Description POSITION Adjusts the horizontal position for all channels and math waveforms. SEC/DIV Selects the horizontal time/div (scale factor) for the waveform. The control buttons provide features to be used for all channels as listed in Table 4-4. Figure 4.5: Control Buttons EENG-201 Page 3

4 Table 4-4: Control Button Description SAVE/RECALL Displays the SAVE/RECALL menu for setups and waveform. MEASURE Displays the automated measurements menu. ACQUIRE Displays the acquisition menu. UTILITY Displays the UTILITY menu. CURSOR Displays the CURSOR menu. DISPLAY Displays the DISPLAY menu. AUTOSET Automatically sets the instruments control to produce a usable display of the input signal. RUN/STOP Starts and stops waveform acquisition. The connectors provide the input for the signal display as shown in Figure 4.6. Figure 4.6: Input Connector for waveforms. In addition to displaying waveforms, the display is filled with many details about the waveform and the oscilloscope control settings. Figure 4.7: Display of Two Waveforms Table 4-5: Display Description of Oscilloscope No. Name Feature Description 1 Horizontal Trigger Marker shows horizontal trigger position. Maker. 2 Width Trigger Marker shows Edge or Pulse Width trigger level. Marker. 3 Channel Indicator On-screen markers show the ground reference points of the Displayed waveforms. 4 Waveform Indicator An arrow icon indicates that the waveform is inverted. 5 Vertical Scale Selected vertical scale factors (Volts/Div). 6 Trigger Frequency. Readout shows trigger frequency. 7 Time Scale Readout shows main time base setting. EENG-201 Page 4

5 Part III. Probe Setting and Connections Probes are available with various attenuation factors which affect the vertical scale of the signal. The default setting for the Probe is 10X. Be sure that the Attenuation switch on the P2200 probe matches the Probe option in the oscilloscope. Switch settings are 1X and 10X. Attenuation switch Note: When the Attenuation switch is set to 1X, the P2200 probe limits the bandwidth of the oscilloscope to 7 MHz. To use the full 200 MHz bandwidth of the oscilloscope, be sure to set the switch to 10X. Figure 4.8: Probe Lead Setting Figure 4.9: Connection of Probe Lead Too Oscilloscope Figures 4.9 and 4.10 show how the oscilloscope is connected to a circuit. Figure 4.10: Probe Lead Connected to a Circuit EENG-201 Page 5

6 IV. Laboratory Procedure Part I. Display A DC Signal 1. Construct the circuit of Figure 4.11, with V S of the power supply set to 5 V. Set the VERTICAL scale for Channel 1 to 2 (Volts/Div). Draw what you see in the graph below, remembering to label all axes correctly. Explain what you are seeing on the oscilloscope. Figure Construct the circuit of Figure 4.12, with V S = 12 V, R 1 = 6 kω, R 2 = 2 kω. Set the VERTICAL scale for Channel 1 to 5 (Volts/Div). Measure V S using Channel 1and TP1 using Channel 2 of the oscilloscope. Draw what you see in the graph below; remembering to label all axes. Explain what you are seeing on the oscilloscope. Figure 4.12 EENG-201 Page 6

7 Part II. Display an AC Signal Figure 4.13: Display on scope Figure 4.14: Explanation of displayed waveform 1. Using Figure 4.13 and 4.14, answer the following questions: a. What is the setting on the Volts/Div? b. What is the peak voltage? c. What is the voltage peak to peak? d. What is the time base of the sec/div? e. What is the frequency of the signal (f)? EENG-201 Page 7

8 Part III. Taking Cursor Measurement You can use the cursors to quickly take time and voltage measurements on a waveform. Let s start by looking at the Figure As you can see, the oscilloscope is showing Vs displayed on Channel 1 and Va display on Channel 2. Construct the circuit of Figure 4.15, with the V S (the function generator) -5 V to 5 V (10 Vpeak-to-peak = 10 Vp-p) and a frequency of 20 khz, R 1 = 1.5 kω, C 1 = 0.1 µf, and L 1 = 4.7 µh. Setup the oscilloscope so that the voltage Vs can be displayed on Channel 1, and the voltage Va can be displayed on Channel 2. Figure 4.15 Measuring Peak-to-Peak Voltage Set the oscilloscope to read peak-to-peak Voltage for Channel 1: 1. Push the CURSOR button on the oscilloscope to bring the cursor menu. 2. In the CURSOR menu push the top option button called Type. Notice that the LED light under both vertical position knobs will turn on to indicate the use of cursor 1 and cursor 2 functions. 3. Turn the cursor 1 POSITION knob to place a cursor on the highest peak of the signal. Turn the cursor 2 POSITION knob to place a cursor on the lowest peak of the signal. 4. The peak-to-peak voltage is read as [Cursor 2]-[Cursor1] =Delta. a. What is the value of cursor 1? b. What is the value of cursor 2? c. What is the delta value? 5. Draw the displayed signal on the graph below. Be neat, to scale, and concise. 6. Repeat the above process for Channel 2. EENG-201 Page 8

9 Measuring Frequency Set the oscilloscope to read the frequency of Channel 1: 1. Push the CURSOR button on the oscilloscope to bring up the cursor menu. 2. In the CURSOR menu push the top option button call Type. 3. Turn the CURSOR 1 position knob to place the cursor on the center of the first peak of the waveform. 4. Turn the CURSOR 2 position knob to place the cursor on the center of the second peak of the waveform. 5. The period can be directly read as [Cursor 2]-[Cursor1] = Period. d. What is the value of cursor 1? e. What is the value of cursor 2? f. What is the period? 1 6. The frequency is. What is the frequency? Period 7. Draw the displayed signal on the graph below. Be neat, to scale, and concise. 8. Repeat the above process for Channel 2. Part V. Automatic Measurements Consider testing the circuit of Figure It is desired to measure the voltage peak-topeak at point V s and V a. as indicated in Figure To set the oscilloscope to read peak-to-peak Voltage for channel 1: 1. Push the MEASURE button on the oscilloscope to bring up the measure options. There are four options to use for any of the channels to be measured. 2. Push any of the four buttons to select the channel to be measured. 3. Push the Type option button and select the parameter to be measured, in this case Pk-Pk. 4. Repeat the process to measure frequency by pushing the Back button and choosing one of the other available options, look for channel 1, and set the Type to frequency. 5. Download the image of Channel 1 showing the voltage and frequency measurements. 6. Repeat the above process for Channel 2 not deleting the measurements for Channel 1. EENG-201 Page 9

10 Part IV: Downloading the Oscilloscopes Display On the lab computer desktop look for the Tek OpenChoice Desktop icon. Double click on it, and allow the program to load. Once the program has loaded, click on the Select Instrument button. A window will appear. Click on ASRL1::INSTR to select it and click the OK button. Notice that Get Screen icon has been activated. Double click on the Get Screen icon and allow time for the image to appear on the screen. It takes a minute for the image to appear, so be patient. Once the image has appeared, use the SAVE AS to save it on to your memory key. 1. Using Figure 4.15, download the following images: a. The voltage for Channel 1 showing the cursors for a peak voltage measurement. b. The voltage for Channel 2 showing the cursors for a peak voltage measurement. c. The frequency for Channel 1 showing the cursors for a time difference measurement of a quarter period. d. The frequency for Channel 2 showing the cursors for a time difference measurement. V. Questions 1. Suppose the function generator is set to a 1 MHz sinewave and the oscilloscope is set to 200nsec/div. Determine the number of squares that one period of the wave will occupy. 2. Repeat question 1 if the function generator is changed to a 1 MHz square wave. 3. What is the dc level of the waveform in Figure 4.18 below? 4. What is the frequency of the waveform in Figure 4.18 below? Figure 4.18 EENG-201 Page 10