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Measurement of Force, Torque, and Other Mechanical Variables With Strain Gages

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Page 38 of 46
Separate Measurement of Combined Loads
 
In the treatment of the D-I-Y transducers described up to this point, techniques were illustrated not only for canceling the strain gage thermal output, but also for canceling load components other than the primary one which is the object of measurement. In each case, the cancellation of undesired signal components was achieved by taking advantage of Wheatstone bridge arithmetic -- the addition and subtraction of resistance changes in opposite and adjacent bridge arms, respectively. Sometimes, however, there is the need to simultaneously measure two mechanical variables, such as the axial force and bending moment on a shaft. This can be accomplished with multiple strain gages mounted on the shaft; but the strains must be measured individually for each gage (in a separate bridge circuit), and the load components obtained by subsequent data reduction.