Differential optical strain gauge for torsion measurements.
An optical strain gauge has been built to measure extremely small torsion strains in cylindrical specimens. Moiré fringe techniques are used to measure the differential angular changes between two sensing mirrors supported on two rings attached to the specimen. The present instrument has a useable linear range of about 0.5 mrad with a sensitivity of 500 mV/mrad. Angular changes as small as 2 microrad are easily detected. Risley prisms are used to extend the range to 10 mrad as well as to verify the calibration procedure.
Palmer
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