Introduction to the Oscilloscope

1
Introduction to the Oscilloscope

• Professor Ahmadi
• ECE002

2
OBJECTIVES

• Review Electrical Signals
• D.C. (Direct Current) Signals
• A.C. (Alternating Current) Signals
• Explain Common Lab Equipment
• Oscilloscope, Function Generator, etc.
• Introduction to Oscilloscope Triggering

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Electrical Signal

• How do we classify the signals that we measure?

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Electrical Signals D.C. Signal

• A direct current or D.C. signal is one that only
  flows in a single direction.
• Typical Sources
• Batteries
• Agilent Power Supply in the ECE labs

5 2.5 -2.5 -5
What is the value at 5 Seconds? 20 Seconds?
YVOLTAGE (volts)
XTIME (seconds)
5 10 15 20
5
Electrical Signal A.C. Signal
5 2.5 -2.5 -5
YVOLTAGE (volts)
XTIME (seconds)
5 10 15 20

• A.C. or Alternating Current signals are ones that
  change direction over time.
• As time increases our voltage fluctuates up and
  down.
• Typical Sources
• Function Generators
• Electrical Outlets in Buildings
• So at time2.5s, what is the voltage?
• And again at 10seconds?...15 seconds?

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Electrical Signals

• DC Signals are usually characterized by their
  voltage.
• AC Signals are characterized by their
• Shape
• Frequency (Cycles Per Second)
• Period (Seconds Per Cycle)
• Amplitude

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Common Lab Equipment
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What is the purpose of an oscilloscope

• The purpose of an oscilloscope is to measure a
  voltage that changes with time and show it in a
  graphical format

1. Here is the oscilloscope in our lab

-Notice the X-Y axes
2) Here is our alternating voltage signal from
before
3) If we measure our signal with the scope, it
would look like this!
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What are the major components?

• Display Screen
• Displays an input signal with respect to time.
• Control Panel
• Adjusts how the input signal is displayed.

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What do we now know about the scope?

• What must the X-Axis represent?
• What must the Y-Axis represent?

• Sowhat do the dials do?

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Oscilloscope Screen

• Notice that the screen has ruled divisions both
  horizontally and vertically.
• The axes can be scaled, for example
• If each vertical division is worth 5 seconds,
  what time is represented by this point?
• If each horizontal line is worth 1 volt, what
  voltage is represented by this point?

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Oscilloscope Control Panel

• The section to the right of the screen contains
  the controls necessary to adjust how the waveform
  is displayed on the screen.
• The controls allow you to alter the sweep time,
  amplitude, and triggering method. (Note, these
  topics will be discussed later)

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Oscilloscope Input Channels

• How do we get the voltage into the scope?
• This area is broken into two parts
• Left Half for Channel 1 (X)
• Right Half for Channel 2 (Y)
• In the center is a switch that determines which
  channel will serve as the input to the scope 1,
  2, Dual or Add.
• Why would we want more than 1 channel?

Channel 2
Channel 1
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Equipment Function Generator

• Purpose Produces waves of different
• Shapes (sinusoidal, square, etc.)
• Amplitude
• Frequency
• Several available in the lab, but we will use the
  one built into the Instek Oscilloscope. (Shown)

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Equipment DC Power Supply

• Purpose Produces constant voltage or current
  signals.
• This DC Power supply is capable of generating
  voltages from -25V to 25V.

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Triggering

• Telling the Oscilloscope when to capture
  information.

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Triggering

• Electric signals change much faster than we can
  observe.
• To view a meaningful version of the signal, we
  must tell the Oscilloscope when to refresh the
  display.
• We accomplish this by setting a Triggering Level.

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Triggering
Without Triggering
With Triggering
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Triggering

• We want to tell the oscilliscope when it is the
  best time for it to refresh the display
• In our wave below, we tell the scope to trigger
  or capture the signal when it is going upward
  AND hits 2.0Volts

SO, trigger condition is When were
AND When at 2.0 Volts on our waveform!