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bp_tension_sensor [2016/03/23 20:20]
mr.octopus
bp_tension_sensor [2016/03/24 11:27] (当前版本)
mr.octopus
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Method III:Measuring through strain gages Method III:Measuring through strain gages
-Most of the commercial strain gages utilize the fact that the resistance of a colume-shape resistor depends on its resistivity, cross section and length, namely //R// = //ρl// / //S//. Commercial strain gages have copper wires inside to serve as detectors (Fig 5). By definition 1% strain will cause 1% change on the length, besides, there will also be 1% change on the cross section due to the unchanged total volume. So the precentage of resisance change will be twice of the strain when strain is small.(1×(1 + //x//)/(1 - //x//) ≈ 1 + 2//x//, when //x//<<1)+Most of the commercial strain gages utilize the fact that the resistance of a colume-shape resistor depends on its resistivity, cross section and length, namely //R// = //ρl// / //S//. Commercial strain gages have copper wires inside to serve as detectors (Fig 5). By definition 1% strain will cause 1% change on the length, besides, there will also be 1% change on the cross section due to the unchanged total volume. So the precentage of resisance change will be twice of the strain when strain is small.(1×(1 + //x//)/(1 - //x//) ≈ 1 + 2//x//, where //x//<<1)
{{:zy:commercial_gauge.png|}} {{:zy:commercial_gauge.png|}}
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Figure6: Commercial gage Figure6: Commercial gage
-To achieve a high sensibility, the standard setup is to attach 4 strain gages on the substrate, 2 on one side and 2 on the other and using them to form a wheatstone bridge and measure the voltage difference between two midpoints as shown in figure7 .As //Vout// = [//R//1/(//R//1+//R//2)-//R//4/(//R//4+//R//3))]//Vin//+To achieve a high sensibility, the standard setup is to attach 4 strain gages on the substrate, 2 on one side and 2 on the other and using them to form a wheatstone bridge and measure the voltage difference between two midpoints as shown in figure7 . 
 + 
 + //Vout// = [//R//1/(//R//1+//R//2)-//R//4/(//R//4+//R//3))]//Vin// 
 + 
 +Combining with //R//1 = //R//3 = //R// + //ΔR//, //R//2 = //R//4 = //R// - //ΔR//, we have  
 + 
 + 
 + //Vout// = [//ΔR// / //R//]//Vin//
{{:zy:bridge_compressed.png|}} {{:zy:bridge_compressed.png|}}
-figure7 configuration of + 
 +figure7: configuration of bridge circuit 
 + 
 +{{:zy:setup_of_the_bridge.jpg|}} 
 + 
 +figure8: photos of the bridge circuit 
For detailed information please refer to the attached {{:report_on_strain_project.pdf|experimental report}}. For detailed information please refer to the attached {{:report_on_strain_project.pdf|experimental report}}.
 
bp_tension_sensor.txt · 最后更改: 2016/03/24 11:27 由 mr.octopus
 
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