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Introduction to theOscilloscope

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One of the most often used instruments in theelectrical engineering lab is the oscilloscopewhich notonly you can measure the waveform quantities, butalso it allows you to display the waveform as afunction of time.

The oscilloscope (or simply, scope) consists of adisplay tube on which one can trace the waveform. Anelectron beam which is generated by electron gunaccelerate toward the part of the display and isdeflected by electric fields, writes figures on thefluorescent screen.

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General principle of an oscilloscope showing the display tube

and the deflection system.

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A probe is a high quality

coaxial cable that hasbeen carefully designed

not to pick up stray

signals originating from

radio frequency (RF) or

power lines. Also a probe

has a large input

resistance which reducesthe circuit loading.

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If the voltage source to be measured has one

terminal grounded, make sure that the ground ofthe probe is connected to the ground of the voltage

source and not vice versa; otherwise, the source

will be shorted and may be damaged.

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Review the front Panel of the scope

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Review the Rear Panel of the scope

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Oscilloscope Basics

Channel 1 inputChannel 1 inputChannel 1 inputChannel 1 inputPower On/OffPower On/OffPower On/OffVertical Position

Volts/DivisionVolts/DivisionVolts/DivisionVolts/DivisionVolts/Division

Vertical PositionVertical PositionVertical Position

Time/DivisionTime/DivisionTime/DivisionTime/DivisionTriggeringTriggeringTriggeringTriggering

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Oscilloscope Settings

A typical display with correct settings:

Multiply 4 Div x Volts/Div to obtainthe peak-to-peak amplitude.

Multiply 5 Div x Time/Div to obtain

the period.

4 Div

5 Div

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Oscilloscope Settings

Volts/Division error (poor resolution)Volts/Division error (overrange)Vertical Position errorTime/Div error (too many cycles displayed)Time/Div error (only a part of one cycle displayBlank display can be caused by: no valid trig

position error, intensity (or brightness) turnedTrigger level set at 0 voltsTrigger level set negative

Trigger level set positive

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Oscilloscope Settings

If a waveform moves on the screen:

Check the trigger source, trigger level, trigger

mode, trigger slope, and the trigger coupling.

An example of a common error:

the trigger source is set for Channel 2

but the input signal is fed to Channel 1.

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Oscilloscope Quiz

The Volts/Div control is set at 100 mV/Div.

What is the peak-to-peak amplitude of thissignal?

800 mVP-P

Using the above, what is the RMS value

of this signal?283 mV

The Time/Div control is set at 50 ms/Div. What is the period

of this signal?

250 ms

Using the above, what is the frequency of this signal?

4 Hz

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Oscilloscope Quiz

The Volts/Div control is set at 1V/Div. What

is the dc amplitude of this signal?-3V

0 V

Using the above, what will be displayed if the

Volts/Div control is changed to 500 mV/Div?

Blank screen

What can cause the displayed waveform

to move on the screen?

No valid trigger

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Digital Oscilloscope Block Diagram

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The Digitizing Oscilloscope

1 0s 2 us/ 1RUN.00V

1

Setup memoryUndo Default

Status bar:

Vertical sensitivity

Sweep speedTrigger time reference

Channel(s) on

Run/stop

Softkey

labels

Calibrationsource

Power ON/OFF

Screenbrightness

Measure: Vrms, tr, ,f

Trace /Setup Memory

Display:grid, vectors,

averaging

Triggering:

Modes: Auto, Normal,TV

Sources: Ch1, Ch2, Ext, Line

Vertical position,

sensitivityMath on/off

Storage: Auto-store,

Erase, RUN/STOP

Horizontal:

Main Sweep Speed,Sweep Modes:

Delayed, XY, Roll

t = 0 Reference

fAutoscalePrint

Calibrate

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Main controls

Vertical

Volts/divisionVertical Position

Horizontaldelay

Time/division (sweep speed)

Trigger level Line is only

visible when you turn theknob. When signal is

smaller than trigger level,

scope stops sampling.

Display:

Grid full

Vectors off

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Vertical Controls

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Other Functions

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Other Functions (continue)

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Other Functions (continued)

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Other Functions (continued)

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Other Functions (continued)