BASICS OF LAB SCOPES
Scope Essentials
• Digital Storage Oscilliscope (DSO)
• Voltmeter that captures voltage samples & displays them
on a screen
• Voltage appears as a trace of light
• Trace moves up & down, displaying voltage
• Trace moves left to right, displaying time
• Digital Multimeters (DMM) take slower samples, displays
them as a numeric value
Scope Essentials
• DSO takes rapid fire samples (snapshots) of
voltage
• Samples are digitized & displayed on screen
• These digitized samples can be saved for
future use or transferred to a computer
The Waveform
• Waveform – the line traced
on the screen
• Scopes show voltage levels
over a period of time
(horizontal)
• Amplitude – difference
between a signals lowest and
highest value (0 – 5v)
(vertical)
• Frequency – rate at which a
signal repeats itself in one
second, measured in Hertz
Waveform Shape
• Signature of the
voltage signal
• When measuring
sensors, each has
it’s own unique
shape
The Scope Screen
• Divided into small
sections - Grids
• 8 x 10 grid Screen
• Voltage level
between grids is
adjustable
• Time base between
grids is adjustable
Voltage & Time Divisions
Trigger
• Voltage level that
the sampled signal
must cross to start
the horizontal sweep
that draws the
waveform across the
screen
• If voltage level is 2v
set trigger at 1v
Trigger & Slope
• Trigger sets the
voltage level that the
signal must cross to
start a sweep
• Positive slope –
triggers the sweep
on a rising voltage
• Negative slope –
triggers the sweep
on a falling voltage
Coupling
• Describes the type of signal being sampled
• DC coupling – for use with direct current
circuits (any unwanted AC voltage will be displayed)
• AC coupling – for use with alternating
current (blocks DC voltage)
AC Coupling
Sensor
location
DC Coupling
Pulse Width Modulated Signals
• Controlled switching of voltage on & off
• Fig. A – total cycle time is 35ms
– Injector is off 23ms
– Injector is on 12ms
• Fig. B –
– Injector is off 13ms
– Injector in on 22ms
Pulse Width Modulated Signals
• PWM values can be shown in milliseconds or as a
percentage
Glitch
• Intermittent malfunction in either a circuit
or a component
• Sudden change in voltage