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Caliper

  • US 4,226,024 A
  • Filed: 01/24/1979
  • Issued: 10/07/1980
  • Est. Priority Date: 01/30/1978
  • Status: Expired due to Term
First Claim
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1. A caliper for measuring the diameter of tree stems comprising:

  • (1) a stationary leg fixed with a bar having a length and a movable leg slidably mounted on said bar by a support member and movable along the length thereof in two opposite directions;

    (2) a plurality of grooves located in the bar for a length of the bar along which the movable leg is movable, the bar being of a magnetic material at least in a portion containing the grooves and the grooves being uniformly spaced from each other and directed perpendicular to the directions of movement of the movable leg; and

    (3) electronic means for measuring the distance the movable leg is moved from the stationary leg, said means comprising;

    (a) two field plates rigidly attached to the support member of the movable leg adjacent said grooves, each field plate magnetically sensing each groove and producing an electrical signal in response thereto, the plates being located relative to each other so that the electrical signals produced thereby in response to the sensed grooves are out of phase from each other, and the phase difference between the produced electrical signals indicating the direction of movement of the movable leg relative to the stationary leg;

    (b) means for converting said electrical signals from the field plates to pulses substantially in phase with said electrical signals;

    (c) comparison and scaling means for comparing the phase relationship of the pulses to determine the direction of travel of the movable leg along the bar and for counting the number of pulses to determine the distance the movable leg is moved from the stationary leg;

    (d) converter means for converting the number of pulses to readable measurement values; and

    (e) portable data terminal means for storing the measurement values.

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