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  USE OF THE OSCILLOSCOPE
      Science Learning Center
  University of Michigan – Dearborn


Modified from a presentation written by David Matzke by: Donald
Wisniewski, Dawn Wisniewski, Huzefa Mamoola and Angela Nolte

Under the direction of: Dr. Ruth Dusenbery and Dr. Paul Zitzewitz

With funds from the Office of the Provost, UM-D, and NSF CCLI
grant DUE#9952827 to RD and PZ.
            OBJECTIVES
In this module you will learn how use an
oscilloscope to:

 measure direct current (D.C.) voltage and

 measure alternating current (A.C.) voltage.
    Equipment
    Make sure that you
    have the following
    before you begin:

   an oscilloscope
   a function generator
   a six volt battery and
   two cables
CRT Screen                Control Panel




      Input Channel Selector
                Oscilloscope Screen

   Notice that the screen
    has ruled divisions
    both horizontally and
    vertically.
   The major divisions
    are marked off in
    centimeters, the
    middle lines also
    have minor divisions
    every 0.2 of a
    centimeter.
              Input Channel Selector
   This area is broken into two parts: the left half for
    channel A and the right half for channel B.
   In the center of this section lies the mode switch
    that determines which channel will serve as an
    input to the scope:A, B or Dual.
   For this module we will only be concerned with
    channel A.
          Channel A                     Channel B
                    Control Panel
   The section to the
    right of the screen
    contains the controls
    necessary to adjust
    the triggering and
    sweep time of the
    waveform.
   This section is
    generally used when
    measuring the period
    of A.C. waveforms.
          Turning the Oscilloscope ON
   Now turn the power
    switch located to the
    right of the screen to the
    ON position.

   Make sure the triggering
    level knob is pulled out
    for AUTO operation.

   A line or dot should
    appear on the screen.

   If not, check that the
    position switches and
    intensity dial point up.
                Set Mode Switch
   The oscilloscope is
    capable of measuring
    voltages from two
    different sources.

   The mode switch is used
    to alternate between
    sources.

   For the purposes of this
    module, set the mode
    switch to Channel A.
                Connect Cable
   A cable should be
    connected to the input
    of Channel A.

   The other end of the
    cable has 2 leads with
    alligator clips. These
    should not be
    connected to anything
    at this point (if they
    are, then disconnect
    them).
Sweep Time per centimeter Switch

   Look at the “sweep
    time per centimeter”
    knob.

   Turn the outer dial of
    the sweep time per
    centimeter to 2
    milliseconds (ms).
     Horizontal Position
   The horizontal line
    should be centered
    using the horizontal
    and vertical position
    knobs.

   Make sure the
    horizontal position
    knob is pushed in.
        Intensity and Focus Dials

   The intensity dial
    controls the
    brightness of the line.

   The focus dial
    controls the
    sharpness of the line.
Summary Measuring DC Voltage
To get started you should follow these steps:
 Set mode to channel A.

 Connect cable to input. Leads should be free.

 Turn power ON and wait for dot or line to appear.

 Pull Triggering level knob out.

 Adjust intensity and focus as needed.

 Set sweep time /sec knob till the line on the screen
  is seen clear and steady.
 Adjust horizontal and vertical position knob to
  make sure that the line is fully visible.
    Measuring a Direct Current Voltage

   Switch the A.C.-GND-D.C.
    switch to the D.C. position.

   Set the volts/cm dial on 1.

   Turn the beige dial
    clockwise all the way to
    put the volts/cm dial in the
    “calibrated” position.
                   Volts/cm Dial
   The volts/cm dial tells
    you the number of
    volts to be
    represented by each
    centimeter vertically
    on the screen.

   Here the outer dial is
    set to one, so each
    centimeter equals
    one volt.
   Checking Oscilloscope Calibration
Use the vertical
position dial to move
the baseline near the
bottom of the screen.
                   Connect Cables
   Now take the cable
    connected to the
    input and connect the
    black lead to the
    negative terminal of
    the 6 volt battery.

   Take the red lead and
    touch it momentarily
    to the positive post of
    the battery.
   The line on the
    oscilloscope should
    deflect upwards when the
    positive connection is
    made.

   The amount that the line
    deflects vertically tells us
    the voltage of the battery.

   Fasten the red lead to the
    positive post of the battery
    and read the voltage.

   The line should have
    deflected up about 6 cm
    (corresponding to 6 v).
   Disconnect the red lead.

   Set the baseline to the
    center position.

   Turn the volts/cm dial to 2.

   Fasten the red lead to the
    positive terminal again.

   The line on the
    oscilloscope should now
    deflect about 3 cm since
    each cm represents 2 v.
   Notice that the volts/cm dial does not change
    the voltage.

   It is a sensitivity dial that allows us to measure a
    wide range of voltages by telling us how much
    voltage is represented by each centimeter along
    the Y-axis.

   Disconnect the battery from the leads on the
    input cables.
Measuring a Time Varying (A.C.) Voltage
    Now look at the Function Generator. This
     device produces a voltage that changes over
     time.

    For purposes of this module, not all the features
     of the function generator will be discussed.
                      Initial Setup
   Before any work is to
    be done on the
    function generator, be
    sure that all the dials
    are turned completely
    clockwise and all
    buttons are in their
    outward position.
   There should also be a
    set of leads connected
    to the Main Output.
                    Amplitude Dial

   This dial is used to adjust the peak to peak voltage of
    the AC waveform from 0 to 25.

   Set the amplitude to max by turning the dial completely
    clockwise.
                   ATT Button
   This is the attenuation button. It is used to set the
    amplitude of the signal to a significantly smaller
    range.

   This button should be in the OUT position unless
    otherwise directed.
                   Function Buttons

   These button are located
    at the upper right corner
    of the generator.
    Selecting a button sets
    the type of voltage
    change over time as a
    square, triangular or sine
    wave.
   Press the button for the
    sine wave.
      Frequency Dial and Range Buttons

   The frequency dial
    and range buttons are
    used in conjunction
    when setting the
    frequency of the
    waveform.
   Pressing a range
    button will multiply
    the value of the
    frequency dial by that
    of the range button.
    Frequency Dial and Range Buttons
   Set the FREQUENCY dial to 1.0 and press the range
    button 10.
   The resulting frequency is 10 cycles/sec.
    Frequency and Frequency Multiplier
   Now set the FREQUENCY dial to 0.8 and the
    FREQUENCY MULTIPLIER to 1k.
   The resulting frequency is 800 cycles/sec.
     Connecting the Function Generator
            to the Oscilloscope
   Connect the
    alligator clip of
    the black lead
    from the function
    generator to the
    alligator clip of
    the black lead
    from the
    oscilloscope.

   Do the same with
    the red leads.
Measuring a Time Varying (A.C.) Voltage
    Set the volts/cm dial to 5,
     making sure the inner
     beige dial is turned fully
     clockwise.
    Remember each cm in the
     Y-axis represents a certain
     number of volts, in this
     case, 5/cm.
    Change the AC-GND-DC
     switch to A.C. and raise
     the image by adjusting the
     vertical position switch.
            Setting the Sweep Time
   The sweep time/cm knob
    contains two dials.
   The inner beige dial is a fine
    adjust and should be turned
    fully clockwise.
   The numbers corresponding
    to the outer dial represent the
    amount of time per cm in the
    X-direction.
   Set this to 2 ms.
   Now use the triggering
    level dial and the sync
    and source switches
    to steady the picture if
    necessary.

   Flip the source switch
    to INT in order to
    ensure that the sine
    wave starts from the
    same spot every time
    the electron beam
    sweeps across the
    screen.
                 Measuring Voltage
   Position the wave so
    that the bottom of a
    wave is lined up with
    one of the cm
    markings.

   Measure the number of
    cm’s from the bottom
    of the wave to the top.

   Multiply the number of
    cm’s by the volts/cm
    sensitivity to get the
    maximum peak
    voltage. This should
    be about 20-25 volts.     4.3 cm x 5 V/cm = 21.5 V
               Measuring Frequency
   Position the sine wave
    so that the beginning of
    the wave lines up with
    the cm position along
    the x-axis.
   Count the number of
    cm’s along the x-axis of
    one cycle and multiply
    by the sweep time per
    cm.
   You should get 10 ms
    or 0.010 sec. The
    inverse of this is the
    frequency, which is 100
    cycles/second.
                               5 cm x 2 ms/cm = 10 ms
      Changing the Oscilloscope Settings

   Remember that the
    function generator is
    producing the voltage
    and frequency. The
    oscilloscope is merely
    measuring the output.

   Change the volts/cm
    dial to 10 and the
    sweep time/cm dial to
    5 ms/cm.
     Changing the Oscilloscope Settings.
   Watch the wave form
    change as you change
    the volts/cm dial to 10
    and the sweep time/cm
    dial to 5 ms/cm.

   Adjust the triggering
    level knob if necessary
    to get a stable image.

   You should still be
    reading 20-25 V and 100
    cycles/sec.
Using the 5X Feature on Horizontal Knob
   Pull the horizontal
    knob OUT.

   Notice that it spreads out
    wave magnifying it 5
    times. We can use this
    feature to zero in on part
    of the wave.

   Push it back in before
    continuing.
Changing Function Generator Settings
      Now change the AMPLITUDE dial on the
       function generator.

      Notice that the reading on the
       oscilloscope changes.

      Dial in a different frequency.

      Remember that this changes the time for
       one wave on the oscilloscope.
                     Attenuation
   The attenuation button is used to output small
    voltages.
   Press the ATT button on the function generator to the
    IN position and observe the voltage on the
    oscilloscope.
   Adjust the controls on the oscilloscope if needed to
    properly observe the signal.
    Summary Measuring AC Voltage
   Turn on the function generator by pressing in the power
    button.
   Turn all dials completely clockwise and ensure all
    buttons are in the outward position.
   Press the function button of the desired wave function,
    i.e., triangle, square, or sine wave.
   Set the frequency dial and the press the range button of
    the function generator to achieve the desired frequency.
   Connect the leads of the function generator’s output to
    the leads of the oscilloscope’s input; red lead to red lead
    and black lead to black lead.
      Summary Measuring AC Voltage
   Flip the AC-GND-DC switch to AC on the oscilloscope.
   Set the VOLTS/CM dial to proper sensitivity; remember to
    twist the inner dial clockwise as far as possible.
   Set the sweep TIME/CM dial to proper sensitivity. Twist
    the inner dial clockwise as far as it will go.
   Make sure the picture is centered on the screen using the
    vertical and horizontal position dials.
   Flip the source switch to internal.
   If necessary, adjust the triggering level knob until you get
    a steady picture. The triggering level knob should be
    pulled out.
   Adjust the intensity and focus to get a good sharp image.
         Practice Problem #1

   Set frequency to 100 Hz.
   Set attenuation to 10.
   Find the peak to peak voltage and
   Find the time period for one cycle.
              Answer to #1

   Peak to peak voltage = 7 volts
   The time or period = 1 ms.
         Practice Problem #2

   Set frequency to 50 Hz.
   Set attenuation to 30.
   Find the peak to peak voltage and
   Find the time or period for one cycle.
             Answer to #2

   Peak to peak voltage = 0.7 volts
   Time or period = 20 ms.
  You have now completed the
     Oscilloscope Module.

 Obtain a Post Test and make
measurements using the assigned
  Function Generator settings


				
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posted:9/14/2012
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