1. FORCE MEASUREMENT

2. 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

3. LOAD CELLS
The elastic members commonly used in load cells are links, beam, rings,
and shear web

4. For full bridge arrangement
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

5. 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 It is subjected to an axial load of 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

6. where the link type load cell is too stiff to be effective
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 3 h b
axial gage 1 and 3
axial gage 2 and 4 on the
bottom surface
If all strain gage are identical

8. 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

9. MECHANICAL POWER MEASUREMENT
(DYNAMOMETER)

11. END OF LECTURE