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Strain Measurement
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What is strain?
When we applied a force on object or material at rest, the the deformation occurs and the length of the material will change(∆L).the strain is noted by
Foil type strain gauge In Foil type strain gauge we use thin sheets or foils of 5 micro metre thick. by photo etching or masked vacuum deposition process , based on our requirement or application we can shaped the strain gauge. The end turns are made fat so as to reduce the contribution from the transverse strain which is a superiors input. Metal Foil Strain Gauge The arrangement consists of the following; The metal foil of 0.02mm thick is produced using the printed circuit technique. This metal foil is produced on one side of the plastic backing. Leads are soldered to the metal foil for electrically connecting the strain gauge to a measuring instrument (wheat stone bridge). Operations of Metal foil Strain gauge With the help of an adhesive material, the strain gauge is pasted/bonded on the structure under study. Now the structure is subjected to a force (tensile or compressive). Due to the force, the structure will change the dimension. As the strain gauge is bonded to the structure, ...
Hair hygrometer In the hair hygrometer, horse hair is used to sense the relative humidity because of horse hair is sensitive to humidity. so as the humidity increase or decrease also the length of the horse hair is increase or decrease. by using this property of horse hair we can measure the humidity. Construction and working As we can see in above figure, there is a number of horse hair connected as shown in the figure. One end of the Pointer is connected to pivot and other end of the pointer is move on the calibrated scale. this scale is calibrated in terms of relative humidity. now as humidity is increase or decrease the length of the hair hygrometer is also increase and decrease. So the pointer is move accordingly on the calibrated scale due to mechanical connection as show in figure. This pointer indicate the relative humidity.
Wirewound strain gauge There are two types of wirewound strain gauge bonded and unbonded. Bonded strain gauge It consists of specimen surface Gauge is directly bonded with the surface of the specimen surface being tested. The thin layer of adhesive cement is also there this cement is not only serve to transmit the strain from the specimen to the gauge wire but also act as an insulator. Depending upon the application the bonded strain gauge have various structure so we can use this structure as our application. Unbonded strain gauge These strain gauges are not directly bonded onto the surface of the structure under study. Hence they are termed as unbounded strain gauges. Description of the Unbonded Strain gauges: The arrangement of an unbonded strain gauges consists of the following. Two frames P and Q carrying rigidly fixed insulated pins as shown in diagram. these two frames can move relative with respect to each other and they are ...
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