Transcript Introduction to the Oscilloscope

Introduction to the
Oscilloscope
Professor Ahmadi
ECE002
George Washington University
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
George Washington University
Electrical Signal
How do we classify the signals that we measure?
Electrical Signals: D.C. Signal
 A direct current or D.C. signal is one that only
flows in a single direction.
 Typical Sources
Y=VOLTAGE (volts)
 Batteries
 Agilent Power Supply in the ECE labs
5
What is the value at 5 Seconds?
20 Seconds?
2.5
-2.5
5
-5
George Washington University
10 15
20
X=TIME (seconds)
Y=VOLTAGE (volts)
Electrical Signal: A.C. Signal
5
2.5
-2.5
5
10 15
20
X=TIME (seconds)
-5
 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?
George Washington University
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
Common Lab Equipment
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!
George Washington University
What are the major components?
 Display Screen
 Displays an input signal with
respect to time.
 Control Panel
 Adjusts how the input signal
is displayed.
George Washington University
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?
George Washington University
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?
George Washington University
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)
George Washington University
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
George Washington University
Channel 2
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)
George Washington University
Equipment: DC Power Supply
 Purpose: Produces constant
voltage or current signals.
 This DC Power supply is
capable of generating
voltages from -25V to 25V.
George Washington University
Triggering
Telling the Oscilloscope when to capture information.
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.
George Washington University
Triggering
Without Triggering
George Washington University
With Triggering
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
George Washington University
When at 2.0 Volts on our waveform!