Lab 6 (Osci Triggering)

8/12/2019 Lab 6 (Osci Triggering)

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EEEB 111 ELECTRICAL/ELECTRONICS MEASUREMENT LABORATORY - UNITEN Exp. 6, Page 1/17

EEEB111

ELECTRICAL/ELECTRONICS

MEASUREMENT LABORATORY

Experiment 6:

Introduction to Oscilloscope & Phase Measurement


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EXPERIMENT 6

Introduction to Oscilloscope & Phase Measurement

Assessed OBE Course Objective:CO1 andCO4

OBJECTIVES

The objective of this laboratory experiment is to learn how to use the digital oscilloscope to displaytime varying signals and to understand the triggering method of the digital oscilloscope to display asteady waveform on the oscilloscope.

The phase relationship between two sinusoidal signals, using the Time Delay Method and Lissajous

Pattern Method are also studied.

INTRODUCTION

A. Oscilloscope, AC & DC VoltagesThe digital oscilloscope is one of the most useful and versatile instruments used to make electronicmeasurements. The primary use of the oscilloscope is to display variation of a voltage with respect to

time. In this experiment, the important control functions of the oscilloscope will be studied.

Two (2) types of waveforms from the direct current (DC) and alternating current (AC) voltages will

be observed. DC voltages do not vary with time and are characterized by its magnitude only.

Figure 6.1: Osci l l oscope r epr esent at i on of a DC Vol t age

AC voltages vary with timeand are characterized by its magnitude and frequency.

Figure 6.2: Osci l l oscope r epr esent at i on of an AC Vol t age


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Peak-to-peak amplitude (see Figure 6.2) is the voltage difference between the maximum andminimum of the waveform.

Zero peak-to-peak amplitude of the waveform is half of the peak-to-peak amplitude.

The period of the waveform is the time required for the waveform to complete one cycle; thereciprocal of the period is the frequency of the waveform.

Figure 6.3: Wavef orm Paramet ers

B. Triggering BasicsThe triggering mechanism of the oscilloscope determines the starting point of each horizontal

sweep. When a trigger source voltage passes through a particular voltage level (called thethreshold), the time base generator is triggered.

To get a stable waveform, the trigger source and input signal must be synchronized. (i.e. on samefrequency or multiples of the same frequency)

The three (3) trigger sources are:

1. Internal- used when the signal being displayed is the trigger source.

2. External- allows the user to apply an external signal to be used as a synchronization signal.

3. Line- utilizes the 50 Hz power line voltage from the power supply utility as the triggering

source.


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C. Phase MeasurementsThe phase of a sinusoidal is the displacement of that signal relative to a reference, usually anothersignal.

1. Time Delay Method

Figure 6.4: Phase Measur ement by Ti me Del ay Met hod

Consider the waveforms in Figure 6.4. Both waveforms have the same frequency, but onewaveform, V2, is shifted in time relative to the other waveform, V1. Thus, V2is said to lag V1.Similarly, it may be said that V1leads V2.

The phase angle may be computed using the equation:

=360

where

is the fraction of the period which V2is shifted in time relative to V1.

2. Lissajous pattern methodThis method requires the oscilloscope to display the variation of one signal voltage withrespect to a second signal voltage, rather than with respect to time.

In this application, the XY display capability of the signal oscilloscope is used. The reference

signal V1is applied to the horizontal (X) input, while V2is applied to the vertical (Y) input.

Given that the two signals have the same frequency, an elliptical Lissajous pattern will beformed. The phase angle may be computed from the Lissajous pattern by noting that:

=1

where A and B are quantities which may be read from the Lissajous pattern.

Figure 6.5 illustrates the input signals and the resulting Lissajous pattern.

T is the period of thewaveforms.

T is the distance betweenthe points where both V1and V2cuts the Time axis.


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Figure 6.5: I nput Si gnal s and Resul t i ng Li ssaj ous Pat t er n

PRE-LAB ASSIGNMENT

Download, read and print Introduction to Oscilloscope Measurement fromhttp://metalab.uniten.edu.my/~sulaiman/eeeb111.htm . Bring the printed material to lab to assistduring the experiment.

V

t

C

D

1 2 3 4 5 6 7

V1= C sin t

8

V

t

B

A

1 2 3 4 5 6 7

V2= B sin (t + )

B

A

-B

-A

-D-C

DC

V2

V1

A is the point where the ellipse cutsthe V2 axis.

B is the maximum point of theellipse.

Adjust the Ellipse waveform usingthe vertical adjusting knob ofChannel 1 to be centered at zero.Position (V1,V2) = (0V,0V)
http://metalab.uniten.edu.my/~sulaiman/eeeb111.htmhttp://metalab.uniten.edu.my/~sulaiman/eeeb111.htmhttp://metalab.uniten.edu.my/~sulaiman/eeeb111.htm


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UNIVERSITI TENAGA NASIONAL

Department of Electronics and Communication EngineeringCollege of Engineering

Semester: I / II / Special Academic Year: 20 .. / 20 ..

COURSE CODE: EEEB111 EXPERIMENT NO.: 6

LAB INSTRUCTOR: DATE: TIME:

TITLE: Introduction to Oscilloscope & Phase Measurement

OBJECTIVES:The objective of this laboratory experiment is to learn how to use the digital oscilloscope to display timevarying signals and to understand the triggering method of the digital oscilloscope to display a steady

waveform on the oscilloscope.

The phase relationship between two sinusoidal signals, using the Time Delay Method and Lissajous

Pattern Method are also studied.

PRE-LAB: MARKS:EXPERIMENTAL RESULTS:

Part A: Displays of High Frequency Sine Waveforms on DC and AC Couplings

Graph /2

Part B: Displays of Low Frequency Square Waveforms

Graph /2

Part C: Study of the Sensitivity Control

Graph /2

Part D: Study of the Sweep Time Control

Graph /2

Part E: Triggering Controls

Min & max trigger values /1

Graph slope triggers /1

Graph sync signal /1

Table 6.1 /3

Part F: Phase Measurements using Time Delay Method & Lissajous Pattern Method

Graph /2

Table 6.2 /1.5

Graph /2

Table 6.3 /1.5

POST-LAB:

Part A:

Q1 /1

Q2 /2

Part B

Q1 /1

Q2

Part C

/2

/1.5

CONCLUSIONS: /1.5

INSTRUCTORS COMMENTS:TOTAL:

/30

STUDENT NAME: STUDENT ID:SECTION:


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GROUP MEMBER: STUDENT ID:

EQUIPMENT1. Oscilloscope2. Function Generator (AC Power Supply)3. Oscilloscope Probes x 2nos.

4. BNC-Crocodile Clips Probe x 1no.

PROCEDURE

Part A: Displays of High Frequency Sine Waveforms on DC and AC Couplingsa. Take a BNC-Crocodile Clips probe, which has a probe setting of x1.

b. Connect the BNC end of the BNC-Crocodile Clips probe to the function generators MAIN

output.

c. Take an Oscilloscope probe, and set the probe setting to x10.

d. Connect the coaxial end of the Oscilloscope probe to the oscilloscopes Channel 1 input.

e. Attach the remaining ends of BNC-Crocodile Clips and the Oscilloscope probes together.Note that the metallic hook end on the Oscilloscope probe is the positive and the wire is thenegative.

f. Turn on the function generator and oscilloscope.

g. Set it to display, on the oscilloscope screen, a sine wave output of:

Frequency = 1 kHzPeak-to-peak amplitude = 8V

h. PressAUTOSCALE.

ThisAUTOSCALEfeature requires AC signals withfrequencies 50 Hz to function.

For frequencies < 50 Hz, manual scaling using the Horizontal (time) control knob must be

done.

i. Press theVertical Menubutton of Channel 1.

A menu will be displayed at the bottom of the oscilloscope screen.It shows the coupling options available on the oscilloscope.

j. Select the ground couplingoption.

Ground coupling determines the ground reference i.e. the zero voltage reference line.

k. Adjust the zero reference line using the vertical adjusting knob of Channel 1to be centered

at zero.

l. Select theAC couplingoption.

m. Save the resulting waveform to memoryMem 1.


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n. Repeat the ground couplingprocedure.

o. Display for the DC couplingoption.

p. Sketch BOTH resulting waveforms on the following graph, indicating title, proper couplingsand labeling axes.

Graph of High Frequency Sine Waveforms on AC and DC Couplings

Sens t v ty : Sweep T me:


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Part B: Displays of Low Frequency Square Waveformsa. Set the function generator to deliver a squarewave output of:

Fr equency = 5 HzPeak- t o- peak ampl i t ude = 8V

b. Adjust the Horizontal Sensitivity knob to get at least one cycle or completewaveform displayed on the screen.

As mentioned before the Autoscale feature does not function for frequency < 50 Hz,

therefore we need to use the Horizontal sensitivity knob to adjust manually.

c. Repeat the Ground coupling procedure.

d. Display theAC couplingwaveform.

e. Save to Mem 1.

f. Repeat the procedure with the DC coupling option.

g. Sketch BOTH resulting waveforms on the following graph, indicating title, proper couplingsand labeling axes.

Graph of Low Frequency Square Waveforms on AC and DC Couplings

Sens t v ty : Sweep T me:


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Part C: Study of the Sensitivity Controla. Set the function generator to deliver a sinewave output of:

Fr equency = 1 kHzPeak- t o- peak ampl i t ude = 8V

a. Turn theVerticalscale knob to adjust theVolts/Divsensitivity for Channel 1. Change

the sensitivity to 2 V/Divand save the resulting waveform toMem 1.

On the oscilloscope screen, the current sensitivity setting is displayed at the top left hand side,

next to the channel number.

b. Repeat the procedure for sensitivity setting of 5 V/Div save the resulting waveform toMem

2.

c. Sketch ALL resulting waveforms on the following graph, indicating title, proper couplingsand labeling axes.

d. Label the waveform according to the sensitivity settings: 2V/Div and 5V/Div.

Graph of 2V/div and 5V/div Sensitivity Controls

Sweep Ti me:


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Part D: Study of the Sweep Time Controla. Using a 500 Hz 8V peak-to-peak sine wave and a sensitivity setting of 2 V/div.

b. Turn the Horizontalscale knob to adjust the ms/div settings to 500s/div.

c. Save toMem 1.

d. Repeat to get the waveform with sweep settings of 1 ms/div.

e. Sketch ALL resulting waveforms on the following graph, indicating title, proper coupling andlabeling axes.

f. Label the waveforms according to the sweep settings.

Graph of 500s/div and1ms/div Sweep Time Controls

Sens i t i vi ty :


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Part E: Triggering Controls1. Set the oscilloscope-triggering mode to Automode. To do this, press the Modebutton at the

TRIGGERcontrol panel. Next, press the menu key at the bottom of the screen corresponding

to the Autoselection.

2. Select the trigger source to be channel 1. To do this, press the Sourcebutton and then, themenu key at the bottom of the screen corresponding to the Trigger Sourceselection. Finally,press the menu key corresponding to the channel 1selection.

3. Connect a 1 kHz, 4V peak-to-peak triangle wave to the oscilloscopes channel 1 inputconnector.

4. Set the trigger source to beAC Coupling Setting.

5. At the Trigger control panel, the trigger level may be adjusted using the corresponding Levelcursor knob. Vary the triggering level, by turning the knob, until the next waveform becomes

unstable (the current trigger level is shown on the screen).

6. Record the minimum and maximum trigger value, which seems to make waveform unstable(i.e. non-stationary).

Minimum Trigger value = ______________

Maximum Trigger value = ______________

7. Adjust the triggering level control to zero level i.e. make the waveform stable again.

8. Observe the effect of changing trigger slope setting. The slope setting is changed by first

pressing the Slope/Couplingbutton at the TRIGGER control panel.

9. Sketch the waveform for both instances of triggering.

Graph of Positive and Negative Slope Triggers

10.Display the synchronizing signal from the function generator (labeled SYNCor TRIG OUTonthe function generator) using Channel 1. Sketch the signal.

Sensitivity:

Sweep Time:


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Graph of Synchronizing Signal

11.Connect a 1 kHz, 4V peak-to-peak sine waveto the oscilloscopes channel 1input connectorin the AC Coupling Mode.

12.Set the trigger source to channel 1. Switch the trigger source to channel2, then to Line Modeand finally to External Mode(also called auxiliary). Observe and record the stability of eachdisplay.

13.With the trigger source set to Ext Mode, connect the SYNCoutput of the function generatorto the oscilloscope through the External Trigger input terminal at the bottom right of the

scope. Record the stability of the waveforms.

14.Finally, disconnect the SYNCoutput connection and select the Line triggering source andreduce the frequency of the sine wave to 50 Hz. Observe and record the stability of thewaveform.

15.Record all observations in the following Table 6.1.

Table 6.1: Resul t s f or Stabi l i t y of Tr i gger i ng Di spl ay

SineWaveform

Trigger SourceStability ofWaveform

1kHz

Channel 1

Channel 2

Line

Ext

Ext with Sync

50Hz Line

Sensitivity:

Sweep Time:


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Part F:Phase Measurements using Time Delay & Lissajous Pattern Method1. Construct the circuit shown in Figure 6.6.

Figure 6.6: RC Ser i es Ci r cui t

2. Use a 1 kHz sine wave with 8 V peak-to-peak amplitude as input V 1.

3. Connect V1to channel 1 and V2to channel 2 of the oscilloscope (as shown in Figure 6.6).

4. Be sure that the waveforms are centered about zero reference voltage by using the ACcoupling option (located under the VERTICAL control panel).

5. Select channel 1as the trigger source, which sets V1as the reference signal.

6. Sketch the signals and determine the phase of V2relative to V1by the time-delay method.

Graph of Time Delay Method Channel 1

7. To measure T, use the Cursors button located at the Measure control panel. Recordmeasurements.

8. Tabulate your measurements in Table 6.2.

Channel 1

Sensitivity:

Channel 2

Sensitivity:

Sweep Time:


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Table 6.2: Phase angl es usi ng Ti me Del ay Met hod

Note:

In situations where the input signal is very weak (i.e.: amplitude is very small), the waveform

displayed on the oscilloscope will be unstable. To overcome this problem, the External Triggering

Method using the SYNC signal from the Function Generator should be used for proper triggering of

the Oscilloscope.

9. At the HORIZONTALcontrol panel, press the Main/Delaybutton.

10.Next, press the menu key corresponding to the XYselection. The Lissajous pattern should bepresent on the display.

11.Sketchthe display, measure and record the distances 2A (from A to A) and 2B (from B to B), and compute the phase of V2with respect to V1.

Lissajous Pattern Method: 1 kHz frequency

9. Tabulate your measurements in Table 6.3.

Table 6.2: Phase Angl es usi ng Li ssaj ous Pat t ern Method

Frequency2A

=A1-(-A2)

2B=B1-(-B2)

=1

1kHz

Trigger Source T T =360

Channel 1


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POST-LAB ASSIGNMENT

Part A

1. State the proper coupling for the following AC wave form:

a. A high frequency sine wave : ________________

b. A low frequency square wave : ________________

2. Given the waveform shown below, answer the following questions, showing workings.

Vertical Sensitivity = 2 Volts/div

Sweep time = 500s/div

a. What is the peak-to-peak voltage of the triangular wave?

b. What is the period of the waveform?

c. What is the frequency of the waveform?

Vol t age

Ti me


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Part B

Theoretically,

=11

2

1. Determine the theoretical values for the phase shift of V2relative to V1for the circuit of Figure6.6 at 1 kHz.

1 kHz

2. Find the magnitude of the percentage error by comparing the theoretical values against measuredvalues of Lissajous pattern and Time Delay methods.

Lissajous Pattern Method Time Delay Method

Part C: Open Ended Question

1. How important an oscilloscope in the engineering field? Provide at least one sample ofapplication.______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

CONCLUSIONS:

Identify THREE (3) main understandings that you have gained from this experiment.

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

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Lab 6 (Osci Triggering)