Lab2_ECE3710_MrC

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School

Georgia Institute Of Technology *

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3710

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Electrical Engineering

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Feb 20, 2024

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pdf

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© ECE3710, School of Electrical and Computer Engineering, Georgia Tech 1 Student: _____________________ Sign-off: __________________ Date: ________________________ ECE 3710 Lab 2: Resistor Networks and Wheatstone Bridge Objective: To reinforce understanding of • Solution methods for electrical circuit voltages and currents • Potentiometers • Sensors and Wheatstone Bridges Table of Contents: Materials Needed 1 Pre-Lab Assignment 1 Background 1 Systematic Solution Methods 1 Potentiometer 2 Wheatstone Bridge 3 Lab Procedures 3 Part A) Circuit 1 4 Part B) Circuit 2 4 Part C) Potentiometer 4 Part D) Position Sensor Using Wheatstone Bridge 6 Appendix 8 Materials Needed • 100Ω rotary potentiometer • 950Ω resistor • 4 x 1kΩ (1% tolerance) resistor • 2 x 2kΩ resistor Pre-Lab Assignment 1) Solve the circuits in the Appendix for the voltages and currents requested. Turn in your prelab with the rest of the lab and include all of your calculations. Circuit 1: i 1 = _____________, v 2 = _______________ Circuit 2: i 1 = _____________, v 2 = _______________ Da Cal Mr.

© ECE3710, School of Electrical and Computer Engineering, Georgia Tech 2 2) Read the Background section of this laboratory exercise. Background: Systematic Solution Methods Several different solution methods may be used to solve for voltage and currents in a circuit: Mesh Analysis, Node Analysis, Thévenin Equivalent circuit, and Norton Equivalent circuit. Both Mesh and Node analysis result in a set of simultaneous algebraic equations. • Mesh Analysis introduces intermediate variables called “mesh currents” and systematically implements Kirchhoff’s Voltage Law to solve for those mes h currents. • Node Analysis introduces intermediate variables called “node voltages” and systematically implements Kirchhoff’s Current Law to solve for those node voltages. • Thévenin and Norton Equivalent circuits replace a portion of a circuit with a simple source/resistance circuit that has the same current and voltage provided by the original circuit. Using Thévenin Equivalent and Norton equivalents, source transformation is a graphical method to replace a schematic with a simpler schematic in a series of substitutions. Potentiometer(or pot) A potentiometer is a variable resistor that varies its value proportional to the rotation of the shaft (rotary potentiometer) or a distance that a slider has traveled (linear potentiometer). Pots typically have three leads: two end points and the wiper . There is an externally adjustable trim that adjusts the position of the wiper with respect to the ends of the internal resistor. The symbol for a pot is shown on the left below; on the right is the equivalent circuit. Potentiometer Position Sensor The three potentiometer leads are used when the pot is to be used in a voltage divider circuit as shown in the figures below, a linear pot on the left and a rotary pot on the right. In the voltage divider configuration, one lead is to be attached to +v s , one lead is to be attached to ground, and the other lead is connected to the wiper (or pick-off point), v o .

© ECE3710, School of Electrical and Computer Engineering, Georgia Tech 3 v s v o + y (m) v o  v s + Linear potentiometer Rotary potentiometer Wheatstone Bridge A Wheatstone Bridge is used commonly to measure small voltage resistance changes from a nominal value. In the figure below, - + v s R 2 R 1 R 3 R x b a When balanced, V ba = 0v and 2 1 3 R R R R x = . When R x increases, then V ba increases. When R x decreases, V ba decreases (becoming more negative). Lab Procedures To help build and troubleshoot circuits, lay out a circuit on the breadboard the same way it is drawn in the schematic. An example schematic and breadboard layout is shown below to emphasize this tactic. Do not build this circuit. The groups along the side rails are all connected in a long row to make a giant node.* Wider gap

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