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Interactive Guide
Technical Articles
Measurement of Force, Torque, and other
Variables
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Measurement of Force, Torque,
and Other Mechanical Variables With Strain
Gages
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A representative direct-stress spring element is illustrated schematically (shown above). It can be noted that the physical arrangement of the strain gages on the spring, and their locations within the bridge circuit, are different from those for the bending beam. This is done to take advantage of the algebraic addition and subtraction characteristics of the bridge circuit relative to the strain distribution in the spring. For uniformly distributed uniaxial stress in the spring, there are no locations where the strains are equal in magnitude and opposite in sign. Thus, if the two axially oriented gages on the spring were connected in adjacent bridge arms (such as 1 and 2), their resistance changes would be subtracted, and there would be no bridge output under load. Instead, these two gages are connected in opposite bridge arms (1 and 3), causing their resistance changes to be added, and doubling the bridge output compared to a single gage. Moreover, if the transducer is subjected to an off-axis or transverse component of force, the resultant bending strains at the gage site, which should be the same in magnitude and opposite in sign, will be canceled due to algebraic addition of the resistance changes.
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Tension/Compression (Direct-Stress) Force
Transducer
A representative direct-stress spring element is illustrated schematically (shown above). It can be noted that the physical arrangement of the strain gages on the spring, and their locations within the bridge circuit, are different from those for the bending beam. This is done to take advantage of the algebraic addition and subtraction characteristics of the bridge circuit relative to the strain distribution in the spring. For uniformly distributed uniaxial stress in the spring, there are no locations where the strains are equal in magnitude and opposite in sign. Thus, if the two axially oriented gages on the spring were connected in adjacent bridge arms (such as 1 and 2), their resistance changes would be subtracted, and there would be no bridge output under load. Instead, these two gages are connected in opposite bridge arms (1 and 3), causing their resistance changes to be added, and doubling the bridge output compared to a single gage. Moreover, if the transducer is subjected to an off-axis or transverse component of force, the resultant bending strains at the gage site, which should be the same in magnitude and opposite in sign, will be canceled due to algebraic addition of the resistance changes.
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