Methodology for the measurement of deformation in rods by means of a capacitance strain gage

The operation of a capacitance strain gage in measuring deformation in cylindrical rods is examined. The capacitance is formed in a system which consists of the specimen surface, a conducting ring with a thin dielectric layer which is applied to the surface and an air gap between the two contact surfaces. As the specimen surface is deformed, the capacitance of the sensor changes, producing a corresponding change in potential at the electrodes of the sensor. The change in capacitance of the sensor is found to be dependent on the change of the air gap with constant thickness of the dielectric layer. Comparisons between resistance gages and capacitance gages show that the capacitance gage produces higher signal amplitude and has higher noise immunity.