1. Introduction to the Oscilloscope
Professor Ahmadi
ECE002
George Washington University

2. OBJECTIVES Review Electrical Signals Explain Common Lab Equipment
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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3. How do we classify the signals that we measure?
Electrical Signal
How do we classify the signals that we measure?

4. 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?
Y=VOLTAGE (volts)
X=TIME (seconds)
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5. Electrical Signal: A.C. Signal5
2.5
-2.5 -5
Y=VOLTAGE (volts)
X=TIME (seconds)
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 time=2.5s, what is the voltage?
And again at 10seconds?...15 seconds?
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6. 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

7. Common Lab Equipment

8. 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
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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9. 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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10. What do we now know about the scope?
VOLTAGE
TIME
What must the X-Axis represent?
What must the Y-Axis represent?
So…what do the dials do?
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11. 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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12. 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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13. 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 1
Channel 2
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14. 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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15. 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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16. Telling the Oscilloscope when to capture information.
Triggering
Telling the Oscilloscope when to capture information.

17. 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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18. Triggering Without Triggering With Triggering
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19. 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 we’re
Going up!
AND
When at 2.0 Volts on our waveform!
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