Exp 2 Oscilloscope and Waveform Generator

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Universiti Sains MalaysiaElectrical & Electronic Engineering DepartmentBasic Circuits Laboratory EEE125

Oscilloscope Y-T Mode and Waveform GeneratorOBJECTIVE

To become familiar with using an oscilloscope and waveform generator.

To calculate, obtain, and measure the time varying signals, amplitude and duration(period) of various voltage signals.

To explore time domain and frequency domain representation of signals.

INTRODUCTION

Digital Oscilloscope

The oscilloscope is the most important instrument available to the practicing technician orengineer. It permits the visual display of a voltage signal that can reveal a range of informationregarding the operating characteristics of a circuit or system that is not available with a standardmultimeter. At first glance the instrument may appear complex and difficult to master. Be assured,however, that once the function of each section of the oscilloscope is explained and understoodand the system is used throughout a set of experiments, your expertise with this important toolwill develop quite rapidly.

Now that we have acquired a basic understanding of how the oscilloscope works, we canproceed to explore some of the most common tasks which can be accomplished with it. Theoscilloscope which we will be using in the lab is the InfiniiVision DSO-X 2002A Oscilloscopes , atwo channel (input) scope. Aside from the display itself, the oscilloscope consists of variouscontrol panels which give the user complete control of how the scope processes and displays its

inputs. In the section that follows we will describe each of the control panels and outline thefunctionality of each of the settings found therein.

The oscilloscope is basically a graph displaying apparatus and it represents an electrical signalsuch as voltage as a function of time. Our oscilloscope has two channels and the ability toperform the basic functions of Triggering and scaling both in the vertical and the horizontal axes.In the laboratory environment one usually finds oscilloscopes that perform a variety of specializedfunctions including various mathematical operations on signals. The features of our scopecorresponds to the most basic and important characteristics of these instruments.

The Front Panel Controls

On the front panel, keyrefers to any key (button) you can press. Softkeyspecifically refers to the

six keys that are directly below the display. The legend for these keys is directly above them, onthe display. Their functions change as you navigate through the oscilloscope's menus. For thefollowing figure, refer to the numbered descriptions that follows.


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Figure 1: InfiniiVision DSO-X 2002A Oscilloscope

The Oscilloscope Display

The oscilloscope display contains acquired waveforms, setup information, measurement results,and the softkey definitions.

Figure 2: Oscilloscope Display


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Frequency Measurement in Oscilloscope

The frequency of an unknown signal may be calculated from the oscilloscope very easily. Theperiod of the waveform is the product of the distance along the x-axis covered by one cycle andthe horizontal sweep setting. As an example, a sine-wave generator is set to 1000 Hz with thevoltage applied to the oscilloscope vertical. One cycle covers 9.95 cm, with a sweep speed (or

known as time/div) of 100 sec/cm. The period is T = (9.95)*(100X10

-6

)sec. The measuredfrequency is f= 1/T = 1005 Hz.

Figure 2: Frequency measurement

EQUIPMENTS

DSO-X 2002A Digital Oscilloscopes

USB data drive (bring this during lab session) Crocodile clips, BNC Connectors, Connection wires (single core)


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Experiment: Part ICalibrating the scopes probes and frequency measurement

1. Press the power switch. The power switch is located on the lower left corner of the frontpanel. The oscilloscope will perform a self- test and will be operational in a few seconds.

2. The first signal to input to the oscilloscope is the Demo 2, Probe Comp signal. This signalis used for compensating probes.

3. Connect an oscilloscope probe from channel 1 to the Demo 2(Probe Comp) terminal onthe front panel. Connect the probe's ground lead to the ground terminal (next to theDemo 2terminal).

4. Use [Auto Scale] to automatically configure the oscilloscope to best display the inputsignals. Press [Auto Scale]. You should see a waveform on the oscilloscope's displaysimilar to Figure 1a.

Figure 1a: Calibrated signal

5. Auto Scale analyzes any waveforms present at each channel and at the external trigger

input. This includes the digital channels, if connected. Auto Scale finds, turns on, andscales any channel with a repetitive waveform that has a frequency of at least 25 Hz, aduty cycle greater than 0.5%, and an amplitude of at least 10 mV peak- to- peak. Anychannels that do not meet these requirements are turned off.

6. Determine the number of divisions of X and Y. Record the volt/div and time/div from thedisplay, thus calculate the period, frequency and peak to peak voltage of the calibratedsignal.

Number of divisions, X = __________Number of divisions, Y = __________Volt/div = __________ VTime/div = __________ sPeriod = __________ s (calculated)Frequency, f = __________ Hz (calculated)Pk-Pk voltage, Vp-p = __________ V (calculated)

7. Do not turn off the oscilloscope as you will make automated measurement of thecalibrated signal in Part II of the experiment.


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Experiment: Part IIAutomated measurements and USB storage devices

1. The [Meas] key lets you make automatic measurements on waveforms. Somemeasurements can only be made on analog input channels. The results of the last fourselected measurements are displayed in the Measurements information area on the right-hand side of the screen.

2. Press the [Meas] key to display the Measurement Menu. Press the Source softkey toselect the channel. Press the Type softkey, then rotate the Entry knob to select ameasurement to be made.

3. Press the Add Measurementsoftkey or push the Entry knob to display the measurement.Cursors are turned on to show the portion of the waveform being measured for the mostrecently added measurement (bottom-most on the display). To view the cursors for apreviously added measurement (but not the last one), add the measurement again.

4. Measure the signals peak to peak voltage and its frequency. Compare with those in step6 of Part I.Frequency,f = __________ Hz (measured)

Pk-Pk voltage, Vp-p = __________ V (measured)

5. To turn off measurements, press the [Meas]key again. Measurements are erased fromthe display.

6. To stop making one or more measurements, press the Clear Meassoftkey and choosethe measurement to clear, or press Clear All. After all measurements have been cleared,when [Meas] is pressed again, the default measurements will be Frequency and Peak-Peak.

7. Most USB mass storage devices are compatible with the oscilloscope. However, certaindevices may be incompatible, and may not be able to be read or written to. When theUSB mass storage device is connected to the oscilloscope's front or rear USB host port,

a small four- color circle icon may be displayed briefly as the USB device is read.

8. Insert your USB into the host port. You do not need to "eject" the USB mass storagedevice before removing it. Simply ensure that any file operation you've initiated is done,and remove the USB drive from the oscilloscope's host port. Do not connect USB devicesthat identify themselves as hardware type "CD" because these devices are notcompatible with the InfiniiVision X- Series oscilloscopes. If two USB mass storagedevices are connected to the oscilloscope, the first one is designated "\usb" and thesecond one is designated "\usb2".

9. Image files can be saved to an external USB storage device. Press [Save/Recall] >Save> Format; then, turn the Entry knob to select 8-bit Bitmap image (*.bmp), 24-bit Bitmapimage (*.bmp), or 24-bit image (*.png).

10. Press the softkey in the second position and use the Entry knob to navigate to the savelocation. Press the Settingssoftkey. In the File Settings Menu, you have these softkeysand options. Set to Invert Gratthus the graticule in the image file has a white backgroundinstead of the black backgound that appears on- screen. Also choose Paletteand selectGrayscaleimages.

11. Finally, press the Press to Save softkey. A message indicating whether the save wassuccessful is displayed.


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Experiment: Part IIIWaveforms generator

1. A waveform generator is built into the oscilloscope. The waveform generator gives you aneasy way to provide input signals when testing circuitry with the oscilloscope. Waveformgenerator settings can be saved and recalled with oscilloscope setups.

2. To access the Waveform Generator Menu and enable or disable the waveform generatoroutput on the front panel Gen Out BNC, press the [Wave Gen ] key. When waveformgenerator output is enabled, the [Wave Gen] key is illuminated. When waveformgenerator output is disabled, the [Wave Gen] key is off. The waveform generator outputis always disabled when the instrument is first turned on.

3. The waveform generator output is automatically disabled if excessive voltage is appliedto the Gen Out BNC.

4. In the Waveform Generator Menu, press the Waveformsoftkey and turn the Entry knobto select the waveform type.

Figure 3a: Sample of waveform generators output

5. Depending on the selected waveform type, use the remaining softkeys and the Entryknob to set the waveform's characteristics.

6. Pressing a signal parameter softkey can open a menu for selecting the type ofadjustment. For example, you can choose to enter amplitude and offset values, or youcan choose to enter high- level and low- level values. Or, you can choose to enterfrequency values or period values. Keep pressing the softkey to select the type ofadjustment. Turn the Entry knob to adjust the value.

7. Notice that you can select between coarse and fine adjustments for frequency, period,and width. Also, pushing the Entry knob is a quick way to toggle between coarse and fineadjustments.

8. The Settings softkey opens the Waveform Generator Settings Menu which lets you makeother settings related to the waveform generator. For example to restore waveformgenerator defaults, press the Settings softkey. Then press the Default Wave Gen softkey.The waveform generator factory default settings (1 kHz sine wave, 500 mVpp, 0 V offset,High- Z output load) are restored.


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9. For our first experiment with the scope we will measure the various signals from thewaveform generator. Connect an oscilloscope probe from channel 1 to the Gen Out BNCusing extra BNC cable.

10. Start by setting the waveform generator to generate a sinusoidal signal with a peak topeak voltage and frequency of 5 Vp-p and 10 kHz respectively. Measure that signal onchannel 1 of your scope. Press [Auto Scale] and adjust the volt/div and time/div until yousee the signal. Draw your output signal in Figure 3b.

Figure 3b: 5 Vp-p, 10 kHz sinusoidal waveform

11. Set the volt/div to 1V/div and time/div to 25 us/div on the scope. Set the offset voltage to0 V. Determine the number of divisions of x-axis and y-axis.

Number of divisions, x-axis = __________ at 25us/divNumber of divisions, y-axis = __________ at 1V/div

12. A sinusoidal signal can also be represented by a mathematical function. Set thewaveform generator to generate a sinusoidal signal with a corresponding function. Drawyour output signal in Figure 3c. The function is V(t)= 2.5 sin 314t + 0.

Figure 3c: V(t)=2.5 sin 314t + 0 sinusoidal waveform


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13. Determine the number of divisions of x-axis and y-axis. Record the volt/div and time/divfrom the display, thus measure the period, frequency and peak to peak voltage as well asAC RMS-FS voltage of the calibrated signal using automated measurement.

Number of divisions, x-axis = __________Number of divisions, y-axis = __________Volt/div = __________ VTime/div = __________ sPeriod = __________ s (measured)Frequency, f = __________ Hz (measured)Pk-Pk voltage, Vp-p = __________ V (measured)AC RMS-FS voltage, Vac,rms = __________ V (measured)

14. The following signal is a PWM output obtained from an experiment. Determine the type ofthe signal, the number of divisions of x-axis and y-axis. Record the volt/div and time/divfrom the display, thus determine the period, frequency, peak to peak voltage and dutycycle of the signal.

Figure 3d: PWM output signal

Type of signal = __________Number of divisions, x-axis = __________Number of divisions, y-axis = __________Volt/div = __________ VTime/div = __________ sPeriod = __________ s (calculated)Frequency, f = __________ Hz (calculated)Pk-Pk voltage, Vp-p = __________ V (calculated)Duty cycle, k = __________ % (calculated)


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REVIEW QUESTIONS

1. List the uses of oscilloscope and waveform generator.

2. List the waveforms that can be generated via waveform generator.

3. Determine the period of 5 Vp-p, 1000 Hz sinusoidal waveform in milliseconds.Period = __________ ms

If the horizontal sensitivity of the scope is set to 2 ms/div, calculate the number of

horizontal divisions required to properly display one full cycle of the 1000 Hz signal.

Number of divisions = __________

If the vertical sensitivity of the scope is set to 0.2 V/div, calculate the number of vertical

divisions required to properly display full cycle of the signal. Can the oscilloscope do this?

Number of divisions = __________

TURN IN ONE REPORT PER GROUP AT THE END OF YOUR LAB SESSION.THERE IS NO TAKE HOME REPORT.

Exp 2 Oscilloscope and Waveform Generator

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