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) stretchedbetween a head (12) and a reflective foot endtermination (28), and a magnet (20) movable along the probe (1) uses the sonicpulse propagation time from the magnet (20) tothe head (12) as one parameter and the time from the magnet (20) to the footand reflected back to the head as another parameterfor determining the magnet position. The sum of the propagation times is aconstant which is used as a reference value. Upon re-ceipt of the first two pulses the propagation times are summed and compared tothe reference value, and the data is accepted ifthe sum is within a prescribed window around the reference value. When noiseoccurs, it creates a false measure of propagationtime so that the sum of the propagation times is no longer equal to thereference value and the data is rejected.