Introduction to the Oscilloscope Professor Ahmadi ECE002 George Washington University

OBJECTIVES Review Electrical Signals Explain Common Lab Equipment 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

How do we classify the signals that we measure? 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 Batteries Agilent Power Supply in the ECE labs 5 2.5 -2.5 -5 What is the value at 5 Seconds? 20 Seconds? Y=VOLTAGE (volts) X=TIME (seconds) 5 10 15 20 George Washington University

Electrical Signal: A.C. Signal 5 2.5 -2.5 -5 Y=VOLTAGE (volts) X=TIME (seconds) 5 10 15 20 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 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 Channel 2 George Washington University

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

Telling the Oscilloscope when to capture information. 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 With Triggering George Washington University

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 When at 2.0 Volts on our waveform! George Washington University