Lca-lab2.docx

Bahria University, Islamabad

Linear Circuit Analysis

LAB 02 Introduction of Oscilloscope Objectives: To familiarize students with the operation of Oscilloscope

Apparatus: 1. Oscilloscope 2. Function Generator (AC generator).

Introduction: In this lab you will learn the basics of how to use the oscilloscope. Then you will investigate time dependent circuits. These questions and lab activities are designed to help you to develop an understanding of these circuits, allowing you to address conceptual questions without plugging through the unnecessary mathematics. You will also see what these circuit components look like in real life.

Oscilloscope 1

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Reset the oscilloscope: Power on the oscilloscope, and disconnect any probes plugged into the ‘CH1’ input connector. Set all the levels, knobs and buttons to default position as indicated, if they are not already at default position. Set the CH1 Coupling mode switch to ground position.

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Linear Circuit Analysis

Turn down the intensity knob, if the signal line is too bright because to avoid burning out the screen. The signal line or dot should be clear but not too bright. Since CH1 is now “grounded” to zero volts, the oscilloscope should read zero on the vertical axis (using the coordinate axis centered on the screen). Adjust the CH1 vertical position knob so that the oscilloscope reads 0 volts. Calibration of oscilloscope: Now connect the probe with the connector of CH1. Connect the positive feed point of probe with the calibration point. The point at which 2Vp-p of 1 KHz is generated internally by the oscilloscope is called the Calibration point. See the square wave signal on the display screen of oscilloscope. Observe the signal that its amplitude is 2Vp-p and having the frequency of 1 KHz.

What the oscilloscope does: The oscilloscope graphs voltage vs. time, by sweeping an electron beam across the phosphorus screen. Whenever the beam hits the screen, it glows green. For most measurements, the beam sweeps right rightward at a constant rate. When the beam gets to the right-hand side of the screen, it jumps back to the left-hand side. In this way, the horizontal axis shows time period and the vertical axis shows the potential difference. i.e. the voltage between the two wires coming out of that probe. Measuring DC voltages, and using the Volts/Division setting: The point of this brief activity is to practice measuring a voltage with the oscilloscope, and to get a feel for what the Volts/division control do. Set the CH1 Volts/Division knob to 2V position. Set the CH1 coupling mode lever to DC level. Now use the oscilloscope to measure the voltage across a 1.5Volts battery. Make sure that you understand what the Volts/Division setting is doing. Students often make mistake in thinking in terms of Division/Volts instead of Volts/Division. To get a more precise reading of the battery’s voltage, should you turn the Volts/Division knob Clockwise or Counterclockwise? Why? Try it, to get a feel for how much precision can be gained.

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Bahria University, Islamabad

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Linear Circuit Analysis

Measuring AC voltages, and using the Time/Division setting: Now you will practice using a power supply, and will figure out what the Time/Division control do. The AC means (Alternating Current) that are the voltage put out by the power supply oscillate with a frequency that you set. Set the CH1 Time/Division knob to 0.5ms position. Set the CH1 Volts/Division knob to 5V position. Set the CH1 coupling mode lever to AC level. Turn on the AC signal generator. Set it to sinusoidal wave, having frequency of 1 KHz and make sure that the sweep width knob is all the way to the left, so that it clicks. Now connect the positive feed point of probe of oscilloscope with the positive output terminal and connect the ground point of oscilloscope with the ground terminal. Now you see the output of signal generator on the oscilloscope screen and the value of Amplitude and Time Period of the AC signal. After that you will use the Mathematical rules for the calculation of the voltage and frequency of AC signal. To get more precise measurement of the period of the oscillating voltage, should you turn the Time/Division knob Clockwise or Counterclockwise? Why? Try it, to get feel for how much precision can be gained.

Calculations: Frequency from Function Generation

Voltage(V)

Volt/Div No of Div

Time(ms)

Volt P2P

2KHz 5KHz 10KHz 15KHz

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Time/Div No of Div

Frequency Calculated (Hz) f=1/T Time period T