me104_lab3

me104_lab3 - ME 104 Sensors and Actuators Fall 2002...

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ME 104 Sensors and Actuators Fall 2002 Laboratory #3 Strain Gage Sensors Department of Mechanical and Environmental Engineering, University of California, Santa Barbara October 15, 2002 Revision By Aruna Ranaweera 1
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Introduction In this laboratory, you will build an analog circuit that will enable you to use a strain gage 1 to measure the deflection of a metal ruler. You will then add a noninverting op-amp to amplify the voltage output from your circuit and an analog low-pass filter to remove voltage fluctuations caused by high- frequency noise. As an extra credit exercise, you will write a LabVIEW program to compute the Power Spectrum of the output from your strain gage circuit before and after the low-pass filter. Background Reading Please read the following material prior to this lab: 1. Histand and Alciatore, Introduction to Mechatronics , Pages 330-331 and Section 9.3.2. 2. Data Sheet , LMC6484 CMOS Quad Rail-to-Rail Input and Output Operational Amplifier , National Semiconductor Corporation. Available online at http://www.national.com/ds/LM/LMC6484.pdf. 1 Also spelled strain gauge . 2 Sensor Circuit Noninverting amplifier Circuit Low-pass Filter Oscilloscope PC DAQ board Strain gage Ruler deflection Figure 1: Strain gage sensor system
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Experiment #1: Build an Analog Circuit for Obtaining Deflection Measurements Using a Strain Gage In this experiment, you will build an analog circuit for using a 350 strain gage to measure the deflection of a metal ruler. You will then observe the voltage output from your deflection sensor circuit using an oscilloscope. The strain gage, which includes two wire leads, has already been attached (glued) to a bendable ruler. 1. Build the analog circuit shown in Figure 3 on an electronic breadboard. Remember to use red wire for positive power connections and black wire for ground connections. Since the strain gage has a resistance of (approximately) R SG = 350 , the resistors 1 on the remaining three arms of the Wheatstone bridge should be matched such that R B1 = R B2 = R B3 = 350 . 1 The R B resistors are known as “bridge completion resistors”. 3 Sensor Circuit Oscilloscope Strain gage Ruler deflection Figure 2: Strain gage sensor V OUT
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Figure 3: Analog sensor circuit for using a strain gage as a deflection sensor You will amplify the voltage output from the Wheatstone bridge using an LMC6484 operational amplifier. Although the LMC6484 chip contains four op-amps with identical capabilities (see Figure 4), you will use only op-amp number one at this time (LMC6484 pins 1, 2, and 3). Figure 4: LMC6484 op-amp connection diagram Choose the op-amp resistors such that R 1 = R 3 = 1 M R 2 = R 4 = 100 k . Then, the voltage gain A V of your op-amp circuit will be 4
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A V = 2 1 R R = 10. Provide power (V CC = +5 volts) and ground (GND) to your circuit board using the “5 V FIXED 3 A” output from your Tektronix PS280 DC Power Supply.
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This note was uploaded on 12/29/2011 for the course ME 104 taught by Professor Staff during the Fall '08 term at UCSB.

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me104_lab3 - ME 104 Sensors and Actuators Fall 2002...

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