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Apparatus for measuring the length of pipe and other hollow members

  • US 4,234,942 A
  • Filed: 07/24/1978
  • Issued: 11/18/1980
  • Est. Priority Date: 07/24/1978
  • Status: Expired due to Term
First Claim
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1. A distance measuring apparatus comprising:

  • an electromagnetic wave transmitter including a frequency modulator, for sending a start timing signal in the form of a frequency modulated electromagnetic wave, disposed at a first location;

    an electromagnetic energy sensor disposed at a second location, for detecting said frequency modulated start timing signal, where the difference between said first and second locations equals the distance to be measured;

    an acoustic transmitter for sending an acoustic stop timing signal over said distance to be measured, located at said first location;

    an acoustic receiver for detecting said stop timing signal, located at said second location;

    a reference signal generator for initiating both of said start and stop timing signals; and

    circuit means for calculating the time delay response between the detection of said start time signal and said stop timing signal.

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