REJECTING NOISE IN MAGNETOSTRICTIVE POSITION DETECTOR BY DETERMINING VALID TIME RANGE FOR PROPAGATION OF REFERENCE SONIC PULSES

摘要

A position detection probe (1) having a magnetostrictive wire (22) stretched between a head (12) and a reflective foot end termination (28), and a magnet (20) movable along the probe (1) uses the sonic pulse propagation time from the magnet (20) to the head (12) as one parameter and the time from the magnet (20) to the foot and reflected back to the head as another parameter for determining the magnet position. The sum of the propagation times is a constant which is used as a reference value. Upon receipt of the first two pulses the propagation times are summed and compared to the reference value, and the data is accepted if the sum is within a prescribed window around the reference value. When noise occurs, it creates a false measure of propagation time so that the sum of the propagation times is no longer equal to the reference value and the data is rejected.