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Oscilloscope
Muhajir Ab. Rahim
School of Mechatronic Engineering
Universiti Malaysia Perlis
Introduction
• The oscilloscope is basically a graphdisplaying device.
• It draws a graph of an electrical
signal.
• In most applications the graph shows
how signals change over time.
• The vertical (Y) axis represents
voltage and the horizontal (X) axis
represents time
This simple graph can tell you many things about a signal.
• You can determine the time and voltage values of a signal.
• You can calculate the frequency of an oscillating signal.
• You can see the "moving parts" of a circuit represented by the signal.
• You can tell if a malfunctioning component is distorting the signal.
• You can find out how much of a signal is direct current (DC) or
alternating current (AC)
Types of Oscilloscope
There are two types of oscilloscope
1. Analog oscilloscope works by directly applying a voltage
being measured to an electron beam moving across the
oscilloscope screen. The voltage deflects the beam up
and down proportionally, tracing the waveform on the
screen. This gives an immediate picture of the
waveform.
2. Digital oscilloscope samples the waveform and uses an
analog-to-digital converter (or ADC) to convert the
voltage being measured into digital information. It then
uses this digital information to reconstruct the waveform
on the screen
Analog
Digital
So what is the advantages?
•
•
People often prefer analog oscilloscopes when
it is important to display rapidly varying signals
in "real time" (or as they occur).
Digital oscilloscopes allow you to capture and
view events that may happen only once. They
can process the digital waveform data or send
the data to a computer for processing. Also,
they can store the digital waveform data for
later viewing and printing.
How does an Oscilloscope
work?
How does an Oscilloscope
work?
• Like a televison screen, the screen of an oscilloscope consists of a
cathode ray tube.
• Although the size and shape are different, the operating principle is
the same. Inside the tube is a vacuum.
• The electron beam emitted by the heated cathode at the rear end of
the tube is accelerated and focused by one or more anodes, and
strikes the front of the tube, producing a bright spot on the
phosphorescent screen.
• The electron beam is bent, or deflected, by voltages applied to two
sets of plates fixed in the tube.
• The horizontal deflection plates, or X-plates produce side to side
movement.
• As you can see, they are linked to a system block called the time
base. This produces a sawtooth waveform.
• During the rising phase of the sawtooth, the spot is driven at a
uniform rate from left to right across the front of the screen. During
the falling phase, the electron beam returns rapidly from right ot left,
but the spot is 'blanked out' so that nothing appears on the screen.
How does an Oscilloscope
work?
• The signal to be displayed is connected to the input.
• The AC/DC switch is usually kept in the DC position (switch closed)
so that there is a direct connection to the Y-amplifier
• In the AC position (switch open) a capacitor is placed in the signal
path, in order to block DC signals but allows AC signals to pass.
• The trigger circuit is used to delay the time base waveform so that
the same section of the input signal is displayed on the screen each
time the spot moves across. The effect of this is to give a stable
picture on the oscilloscope screen, making it easier to measure and
interpret the signal.
What will signal look like?
• The oscilloscope has an illuminated dot that moves across the
screen. With no signal, it would look like the following.
What will signal look like?
• When a sinusoidal signal is applied, then the vertical position is
proportional to the voltage at any instant. If you applied a low
frequency sine signal, you would get a track like the one below
What will signal look like?
• If you have a sinusoidal signal that repeats every half millisecond - a
frequency of 2kHz - you would get a picture like this one.
• It would appear to be stationary on the oscilloscope screen, but it
really isn't. It's just that it repeats so frequently that you see it as a
constant image
How to use an Oscilloscope?
To use an oscilloscope, you need to adjust some basic
settings to accommodate an incoming signal:
• The attenuation or amplification of the signal using
the volts/div control to adjust the amplitude of the
signal before it is applied.
• The time base using the time/div control to set the
amount of time per division represented horizontally
across the screen.
• The triggering of the oscilloscope using the trigger
level to stabilize a repeating signal, as well as
triggering on a single event.
• Adjusting the contrast enables you to create a sharp,
visible display.
How to use an Oscilloscope?
• The front panel is divided into
three main sections labelled
Vertical, Horizontal, and
Trigger. Your oscilloscope may
have other sections,
depending on the model and
type.
• Notice the input connectors on
your oscilloscope. This is
where you attach probes. Most
oscilloscopes have at least two
input channels and each
channel can display a
waveform on the screen.
Multiple channels are handy
for comparing waveforms,
usually called ch1 and ch2.
Triggering Demo
Measuring Time Demo
Measuring Voltage Demo
Further Reading
https://www.cs.tcd.ie/courses/baict/bac/jf/labs/scope/index.html