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lab1_u11_Res_Laws

# lab1_u11_Res_Laws - University of Florida Department of...

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University of Florida EEL 3111 — Summer 2011 Drs. E. M. Schwartz & R. Srivastava Department of Electrical & Computer Engineering Ode Ojowu, TA Page 1/6 Revision 0 20-May-11 Lab 1: Measurements In Resistive Networks And Circuit Laws OBJECTIVES To provide working knowledge of the voltmeter, ammeter, and ohmmeter as well as their limitations in making measurements in resistive networks. To understand how to use the myDAQ to provide the various above functions as well as others. Verification of Ohm's Law, Kirchhoff's Voltage Law, and Kirchhoff's Current Laws To understand the design and use of a potentiometer. To understand current and voltage division. MATERIALS Your myDAQ and entire lab kit Graph paper Read section 3.5 in the textbook. INTRODUCTION A voltmeter is used for measuring voltages. For the measurement of a voltage across a circuit component, a voltmeter must be connected in parallel with the component so that the voltage across the voltmeter is the same as that across the component. An oscilloscope is a special type of voltmeter that can display voltage as a function of time (usually). We will discuss and use an oscilloscope in some future laboratories. An ammeter is used for measuring currents. For the measurement of a current flowing through a circuit component, an ammeter is connected in series with the component so that the current flowing through the ammeter is the same as that flowing through the component. In other words, the branch must be disconnected, the ammeter inserted, and the branch reconnected. An ohmmeter is used for measuring resistances of resistors. If a resistor is in a powered circuit, one end of the resistor must be disconnected from the circuit before a resistance measurement is made. Then, the ohmmeter leads are connected to the resistor terminals. Never connect an ohmmeter to an energized circuit because the reading will be incorrect and the meter might be damaged. Using any of these meters can affect the operation of the circuit being measured. This is undesirable. Understanding how these meters affect the circuits in which they are used will allow you to minimize the effects that the meters have on the parameter being measured. In measuring a voltage or a current, always start at a high range setting and work down to a suitable range. This safety precaution will prevent the meter from being destroyed by an unexpected high voltage or current. An ideal voltmeter or an ideal oscilloscope has infinite input resistance; an ideal ammeter has zero internal resistance. Since such ideal meters do not exist, the effect of inserting a meter must be considered, i.e., the meter resistance must be included in the circuit analysis. Consider the circuit shown in Fig. 1 in which a voltmeter with input resistance R V is connected to measure the voltage across resistor R 2 . Ideally, if R V = , voltage division can be used to find the voltmeter reading of V IDEAL = V S * R 2 / (R 1 + R 2 ) .

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lab1_u11_Res_Laws - University of Florida Department of...

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