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## FORCE MEASUREMENT

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**INTRODUCTION**• TRANSDUCERS THAT MEASURE FORCE AND TORQUE USUALLY • CONTAIN AN ELASTIC MEMBER THAT CONVERTS THE MECHANICAL • QUANTITY TO A DEFLECTION OR STRAIN (IS CALLED LOAD CELL) • A DEFLECTION SENSOR (FOR EXAMPLE, STRAIN GAGE) IS THEN USED • TO GIVE AN ELECTRICAL SIGNAL PROPORTIONAL TO THE QUANTITY • OF INTEREST (FORCE OR TORQUE) • RANGE, LINEARITY AND SENSITIVITY ARE DETERMINED BY THE SIZE • AND SHAPE OF THE ELASTIC MEMBER, THE MATERIAL USED AND • THE SENSOR**LOAD CELLS**The elastic members commonly used in load cells are links, beam, rings, and shear web**LINK TYPE LOAD CELL**P Wheatstone bridge strain gage 3(axial) on the back face strain gage 4 (transverse) strain gage 2 (transverse) For full bridge arrangement strain gage 1 (axial) If R1=R2=R3=R4 P**EXAMPLE**A strip of high strength steel has a length of 30 cm and a cross section of 20 mm by 20 mm. The modulus of elasticity is 200 GPa, and Poisson’s ratio is 0.27. It is subjected to an axial load of 15000 N and it is instrumented with full 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**BEAM TYPE LOAD CELL**Beam type load cells are commonly employed for measuring low-level loads where the link type load cell is too stiff to be effective P x 1 h 3 b axial gage 1 and 3 If all strain gage are identical axial gage 2 and 4 on the bottom surface**TORQUE MEASUREMENT (TORQUE CELLS)**Torque cells are transducers that convert an applied torque to an electrical output signal. For circular shaft subjected to pure torsion, all normal stress are 0, the principal stress s1=s2=txz Principal strain**MECHANICAL POWER MEASUREMENT**(DYNAMOMETER)