1、Appendix C Introduction to Arduino8.1 Overview of sensor technology8.2 Resistive sensor8.3 Inductive sensor8.4 Capacitance sensor8.5 Magnetoelectric tranducer8.6 Piezoelectric transducer8.7 Hall sensorChapter 8 Principles of sensorsFundamentals of Measurement and Signal Analysis8.8 Photoelectric sen
2、sor8.9 Image sensor8.10 Thermocouple8.11 Fiberoptic sensor8.12 Grating8.13 Biosensor8.14 How to select a sensor8.2 Resistive sensor - strain gaugeWorking principle: when the metal conductor is mechanically deformed under external forces, its resistance value changes with the mechanical deformation (
3、elongation or shortening).Metal wire resistance： AlR a. Metal wire strain gauge8.2 Resistive sensor - strain gaugeMetal wire resistance： AlR Take the derivative of the resistance： dAldAAldlAdR 2 dRAdARldlR : length induced resistance change: area induced resistance change: resistivity induced resist
4、ance change8.2 Resistive sensor - strain gaugeAdAldlRdR For constant resistivity：2rA rdrldlRdR 2The area：Volume of the wire remains unchanged: ldlrdr - Poissons ratio - strainFinally： )21(2 RdR The change of resistance is proportional to the strain8.2 Resistive sensor - strain gaugeMeasuring princip
5、le：Input a strain Output a resistancekRdR Commonly measured parameters：strain, force, displacement, acceleration, torque.(k = 2 + 1)8.2 Resistive sensor - strain gaugeStrain gauge structures:8.2 Resistive sensor - strain gaugeb. Semiconductor strain gaugeWhen the semiconductor material itself is pul
6、led or compressed due to mechanical stress, its conductive properties will change, which is called the piezoresistive effect.Semiconductor strain gauge structuredRAdARldlR dR dRdR E8.2 Resistive sensor - strain gaugeMain parameters of the strain gauge:d) Other parameters indicating the performance o
7、f the strain gauge (Working temperature, hysteresis, zero drift, fatigue life, etc.).a）Geometrical parameters: length L and width b, commonly represented as b L by manufacturers.b) Resistance value: the original resistance of the strain gauge.c) Sensitivity coefficient: an important parameter indica
8、ting the performance of the strain gauge.8.2 Resistive sensor - strain gaugeStrain gauge measurement circuit: ERRRR RRRRV )( 4231 3142 VE R1 R2R3 R4Wheatstone bridge8.2 Resistive sensor - strain gaugeAssume： kRdR ；RRR 321R dRRR 4RdREdRRdRV 4E24Strain gauge：Thus：k4EV Strain can be measured by bridge
9、voltage8.2 Resistive sensor - strain gaugeSingle arm Half bridge Full bridgeUsing multiple strain gauges to improve sensitivityFR1R2 R3R48.2 Resistive sensor - strain gaugeInstallation techniques for strain gauge1. The strain gauge has no defects such as creases or broken wires.2. Use a multimeter t
10、o measure the resistance value of the strain gauges. The difference in resistance between the strain gauges in the same bridge should be less than 0.5 ohms.3. The surface of the test piece is polished with fine sandpaper, and the paste is repeatedly scrubbed with an alcohol cotton ball until the cot
11、ton ball is black.4. Squeeze a small drop of super glue on the base of the strain gauge, gently apply it evenly, and immediately place it on the position of the strain patch.5. Use a soldering iron to weld a wire to the lead of the strain gauge.6. Use a megohmmeter to check the insulation between th
12、e strain gauge and the test piece, which should be greater than 500M ohm.7. Cover the strain gauge with 704 silicone rubber to prevent moisture.8.2 Resistive sensor - strain gaugeSensors using strain gauge8.2 Resistive sensor - strain gaugeElectronic scale application:8.2 Resistive sensor - strain g
13、augeExample: METTLER TOLEDOs SLP85xD automatic loading sensorhttps:/ Resistive sensor - strain gaugeExample: Vibration detectorIt is used to find destructive actions such as digging walls, drilling holes, and blasting in vaults, warehouses, and ancient buildings. 8.2 Resistive sensor - strain gaugeA
14、nti-theft alarm for electric bikes / cars:8.1 Overview of sensor technologyHomework1. Briefly describe the working principle of resistive strain gauge and its measuring circuit.2. Which are the physical quantities that can be measured by a strain gauge? Briefly describe its working principle.3. Design an automatic weighing system with Arduino and strain beam.
