Detection of damped sine waves in a magnestostrictive displacement transducer using pretrigger and detection thresholds of opposite polarity

A magnetostrictive linear displacement detector comprising:

• a magnetostrictive wire having opposite head and a foot ends defining a measurement interval therebetween;
• a return wire having a foot end electrically coupled to said foot end of said magnetorestrictive wire and a head end;
• a magnet disposed for displacement along the said magnetostrictive wire within said measurement interval, the position of said magnet within said measurement interval being the linear displacement detected;
• an electrical excitation means electrically coupled to said head end of said magnetostrictive wire and said head end of said return wire for producing a predetermined electrical excitation through said magnetostrictive wire and said return wire;
• a torsional motion sensor disposed proximate to said head end of said magnetostrictive wire for generating an electrical indication of torsional motion within said magnetostrictive wire;
• and
• a displacement determination means connected to said electrical excitation means and said torsional motion sensor for detecting the position of said magnet within said measurement interval of said magnetostrictive wire from the interval of time between producing said predetermined electrical excitation and the detection of the torsional motion within said magnetostrictive wire induced by said electrical excitation traveling, said displacement determination means including
• a first comparator having a non-inverting input connected to the input line, an inverting input connected to a predetermined negative threshold voltage, and an output generating a first output signal when the level of the signal on the input line falls below said predetermined negative threshold voltage;
• a first latch circuit having a data input connected to a first predetermined positive voltage, a clock input connected to said output of said first comparator and an output for generating a first latch signal upon receipt of said first output signal;
• a second comparator having an inverting input connected to the input line, a non-inverting input connected to a second predetermined positive threshold voltage, and an output generating a second output signal when the level of the signal on the input line rises above said second predetermined positive threshold voltage;
• a second latch circuit having a data input connected to said output of said first latch circuit, a clock input connected to said output of said second comparator and an output for generating a second latch signal if said data input receives said first latch signal upon receipt of said second output signal, said second latch signal indicating detection of the damped sine wave.

A method for detecting a damped sine wave signal having an expected duration of a plurality of periods comprising the steps of:

• detecting when the level of the signal falls below a predetermined negative threshold;
• detecting when the level of the signal rises above a predetermined positive threshold;
• generating a detection signal when the signal is detected rising above said predetermined positive threshold following being detected falling below said predetermined negative threshold;
• preventing more than one detection signal in the duration of a given damped sine wave signal by maintaining said detection signal a first predetermined interval of time following initial generation of said detection signal wherein said first predetermined interval of time is longer than the maximum expected duration of the damped sine wave signal.