Introduction to the Oscilloscope

Introduction to the Oscilloscope

Professor Ahmadi

ECE002

George Washington University

OBJECTIVESReview Electrical Signals

D.C. (Direct Current) SignalsA.C. (Alternating Current) Signals

Explain Common Lab EquipmentOscilloscope, Function Generator, etc.

Introduction to Oscilloscope Triggering


Electrical SignalHow 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 SourcesBatteriesAgilent Power Supply in the ECE labs


X=TIME (seconds)

Y=

VO

LTA

GE (

volt

s)

5 10 15 20

5

2.5

-2.5

-5

What is the value at 5 Seconds?20 Seconds?

Electrical Signal: A.C. Signal

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?


X=TIME (seconds)

Y=

VO

LTA

GE (

volt

s)

5 10 15 20

5

2.5

-2.5

-5

Electrical SignalsDC Signals are usually characterized by their

voltage.

AC Signals are characterized by their:ShapeFrequency (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!

What are the major components?

Display Screen Displays an input signal

with respect to time.

Control Panel Adjusts how the input

signal is displayed.


What do we now know about the scope?

What must the X-Axis represent?

What must the Y-Axis represent?


TIME

VOLTAGE

• So…what do the dials do?

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?


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)


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

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)


Equipment: DC Power Supply

Purpose: Produces constant voltage or current signals.

This DC Power supply is capable of generating voltages from -25V to 25V.


TriggeringTelling the Oscilloscope when to capture information.

TriggeringElectric 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.


Triggering


Without Triggering

With Triggering

TriggeringWe 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


Going up!

AND

When at 2.0 Volts on our waveform!

SO, ‘trigger’ condition is:When we’re

Documents

Introduction to the Oscilloscope