2 INTRODUCTIONTRANSDUCERS THAT MEASURE FORCE AND TORQUE USUALLYCONTAIN AN ELASTIC MEMBER THAT CONVERTS THE MECHANICALQUANTITY TO A DEFLECTION OR STRAIN (IS CALLED LOAD CELL)A DEFLECTION SENSOR (FOR EXAMPLE, STRAIN GAGE) IS THEN USEDTO GIVE AN ELECTRICAL SIGNAL PROPORTIONAL TO THE QUANTITYOF INTEREST (FORCE OR TORQUE)RANGE, LINEARITY AND SENSITIVITY ARE DETERMINED BY THE SIZEAND SHAPE OF THE ELASTIC MEMBER, THE MATERIAL USED ANDTHE SENSOR
3 LOAD CELLSThe elastic members commonly used in load cells are links, beam, rings,and shear web
4 For full bridge arrangement LINK TYPE LOAD CELLPWheatstone bridgestrain gage 3(axial) on the back facestrain gage 4 (transverse)strain gage 2 (transverse)For full bridge arrangementstrain gage 1 (axial)If R1=R2=R3=R4P
5 EXAMPLEA strip of high strength steel has a length of 30 cm and a cross section of20 mm by 20 mm. The modulus of elasticity is 200 GPa, and Poisson’s ratiois It is subjected to an axial load of N and it is instrumented withfull bridge arrangement of strain gage with R=120 W and gage factor of 2.10.Determine output voltage if a supply voltage of 2.5 V is applied.Solution :Use equation
6 where the link type load cell is too stiff to be effective BEAM TYPE LOAD CELLBeam type load cells are commonly employed for measuring low-level loadswhere the link type load cell is too stiff to be effectivePx13hbaxial gage 1 and 3axial gage 2 and 4 on thebottom surfaceIf all strain gage are identical
8 TORQUE MEASUREMENT (TORQUE CELLS) Torque cells are transducers that convert an applied torque to an electricaloutput signal.For circular shaft subjected to pure torsion,all normal stress are 0, the principal stress s1=s2=txzPrincipal strain
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