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Amplitude and phase measurement in electromagnetic logging

  • US 4,547,733 A
  • Filed: 12/18/1981
  • Issued: 10/15/1985
  • Est. Priority Date: 12/31/1980
  • Status: Expired due to Fees
First Claim
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1. An electromagnetic logging apparatus for investigating properties of an earth formation surrounding a borehole, comprising:

  • a support member movable through said borehole;

    a transmitter supported by said support member for transmitting electromagnetic energy toward said formation;

    a receiver supported on said support member a predetermined distance from said transmitter for receiving electromagnetic energy from said formation to provide a received signal;

    means for amplifying with high gain stability said received signal;

    means for amplifying with high phase stability said received signal;

    means for controlling the gain of said gain stabilized amplifying means, the output thereof further being provided to said phase stabilized amplifying means for controlling the gain thereof;

    means coupled to said gain stabilized amplifying means for detecting the amplitude of said received signal;

    means coupled to said phase stabilized amplifying means for detecting a zero crossing of said received signal;

    means for measuring said amplitude; and

    means for determining a value of the phase of said received signal relative to the phase of the electromagnetic energy transmitted by said transmitter comprising;

    a rising edge detector coupled to said zero crossing detecting means and responsive to a reference signal indicative of the electromagnetic energy transmitted by said transmitter;

    a falling edge detector coupled to said zero crossing detecting means and responsive to said reference signal; and

    a counter coupled to said rising edge detector and said falling edge detector for determining an offset-compensated phase value.

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