Method and apparatus for resonant sensing device

摘要

A resonant sensing device for measuring the hardness of a workpiece to be tested includes a diamond tipped rod adapted to be resonant and for determining the hardness of a workpiece to be tested is brought into forced contact with such workpiece. The difference in resonant frequency of the rod between its not-constrained condition and its constrained condition (forced contact) is a measure of the hardness of the workpiece. The present invention describes a circuit wherein during a first time interval an up/down counter accumulates the counts arising from the oscillations of the not-constrained rod. During the ensuing interval of the same duration, the counter counts down the accumulated count responsive to the oscillations of the constrained rod. As the counter reaches the zero count condition, which condition is reached before the expiration of the time interval, the counter becomes coupled to an adjustable frequency calibration oscillator and for the remainder of the interval the counter accumulates counts from the oscillations of the calibration oscillator. At the end of the interval, the accumulated count is a measure of the hardness of the workpiece.