Mechanical impedance gauge based on measurement of strains on a vibrating rod

Abstract An impedance gauge based on measurement of strains at two different cross-sections of a vibrating rod is analyzed and tested. The gauge rod, which may have variable characteristic impedance, is in contact with the object at one end and is driven by a harmonic vibrator at the other end. For conical and cylindrical rods explicit relations between point impedance and measured strains are derived. For a cylindrical gauge rod of steel with length 800 mm, diameter 10 mm, and distance between strain gauges 250 mm a fair agreement was generally obtained between experimental and theoretical point impedances of cylindrical test objects in the frequency range 50 Hz to 1·7 kHz. Significant improvements in accuracy over that of the tested prototype are expected to be feasible.