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Introduction to the Oscilloscope

Introduction to the Oscilloscope. Professor Ahmadi ECE002. OBJECTIVES. Review Electrical Signals D.C. (Direct Current) Signals A.C. (Alternating Current) Signals Explain Common Lab Equipment Oscilloscope, Function Generator, etc. Introduction to Oscilloscope Triggering. Electrical Signal.

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Introduction to the Oscilloscope

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  1. Introduction to the Oscilloscope Professor Ahmadi ECE002 George Washington University

  2. OBJECTIVES • Review Electrical Signals • 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

  3. Electrical Signal How do we classify the signals that we measure?

  4. 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

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

  6. 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

  7. Common Lab Equipment

  8. 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

  9. 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

  10. VOLTAGE TIME What do we now know about the scope? • What must the X-Axis represent? • What must the Y-Axis represent? • So…what do the dials do? George Washington University

  11. 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

  12. 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

  13. 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 2 Channel 1 George Washington University

  14. 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

  15. 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

  16. Triggering Telling the Oscilloscope when to capture information.

  17. 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

  18. Triggering Without Triggering With Triggering George Washington University

  19. Going up! 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 AND When at 2.0 Volts on our waveform! George Washington University

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