Apparatus for measuring resistivity of an earth formation using delta-sigma digital signal generation and sigma-delta digital detection system
First Claim
1. An apparatus for measuring resistivity of an earth formation penetrated by a borehole, comprising:
- a sonde adapted to traverse said borehole;
at least one source of measuring current including a delta-sigma modulator and a serial bit source coupled to said modulator, said bit source providing a digital representation of a magnitude of said measuring current sampled at spaced apart time intervals, said source of measuring current coupled to an emitter disposed on said sonde;
at least one sensor disposed on said sonde, said sensor generating a signal in response to formation current resulting from interaction of said measuring current with said earth formation; and
a sigma-delta modulator coupled to said at least one sensor, said modulator coupled to a digital mixer, said digital mixer coupled to a digital filter, an output of said filter comprising digital words corresponding to amplitude of said signal generated by said at least one sensor, said words sampled at spaced apart time intervals.
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Abstract
An apparatus for measuring resistivity of an earth formation. The apparatus includes at least one source of measuring current. The source includes a delta-sigma modulator and a serial bit source coupled to the modulator. The serial bit source represents the magnitude of the measuring current at spaced apart time intervals. The apparatus includes a sensor responsive to formation current resulting from interaction of the measure current with the earth formation. The sensor is coupled to a sigma-delta modulator. The modulator is coupled to a digital mixer and a digital filter. The output of the digital filter corresponds to the magnitude of the measure current detected by the sensor sampled at spaced apart time intervals. In a preferred embodiment, the apparatus includes a plurality of current sources each having a different frequency. The sigma-delta modulator is coupled to a plurality of mixers each for demodulating one of the different source frequencies.
31 Citations
21 Claims
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1. An apparatus for measuring resistivity of an earth formation penetrated by a borehole, comprising:
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a sonde adapted to traverse said borehole; at least one source of measuring current including a delta-sigma modulator and a serial bit source coupled to said modulator, said bit source providing a digital representation of a magnitude of said measuring current sampled at spaced apart time intervals, said source of measuring current coupled to an emitter disposed on said sonde; at least one sensor disposed on said sonde, said sensor generating a signal in response to formation current resulting from interaction of said measuring current with said earth formation; and a sigma-delta modulator coupled to said at least one sensor, said modulator coupled to a digital mixer, said digital mixer coupled to a digital filter, an output of said filter comprising digital words corresponding to amplitude of said signal generated by said at least one sensor, said words sampled at spaced apart time intervals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An apparatus for measuring resistivity of an earth formation penetrated by a borehole, comprising:
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a sonde adapted to traverse said borehole; at least one source of measuring current including a modulator and a serial bit source coupled to said modulator, said bit source providing a digital representation of a magnitude of said measuring current sampled at spaced apart time intervals, said source of measuring current coupled to an emitter disposed on said sonde; at least one sensor disposed on said sonde, said sensor generating a signal in response to a current resulting from interaction of said measuring current with said earth formation; and means for measuring a magnitude of said signal coupled to said at least one sensor, said means for measuring including a sigma-delta modulator coupled to said sensor;
a digital mixer coupled to said sigma-delta modulator and a digital filter coupled to said mixer. - View Dependent Claims (12, 13, 14, 15)
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16. An apparatus for measuring resistivity of an earth formation penetrated by a borehole, comprising:
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a sonde adapted to traverse said borehole; at least one source of measuring current coupled to an emitter disposed on said sonde, said source comprising a substantially monochromatic sinusoidal alternating current, said source including a delta-sigma modulator and a delta-sigma modulator and a serial bit source coupled to said modulator, said bit source providing a digital representation of a magnitude of said measuring current sampled at spaced apart time intervals, said source of measuring current coupled to an emitter disposed on said sonde; at least one sensor disposed on said sonde, said sensor generating a signal in response to a current resulting from interaction of said measuring current with said formation; and a sigma-delta modulator coupled to said at least one sensor, an output of said modulator coupled to a digital mixer, an output of said mixer coupled to a digital filter, an output of said filter comprising digital words corresponding to amplitude of said signal sampled at spaced apart time intervals. - View Dependent Claims (17)
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18. An apparatus for measuring resistivity of an earth formation penetrated by a borehole, comprising:
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a sonde adapted to traverse said borehole; at least one source of measuring current including a delta-sigma modulator and a serial bit source coupled to said modulator, said bit source providing a digital representation of a magnitude of said measuring current sampled at spaced apart time intervals, said source of measuring current coupled to source electrodes disposed on said sonde; sensor electrodes disposed on said sonde, said sensor electrodes responsive to formation current resulting from interaction of said measure current with said earth formation; and a sigma-delta modulator coupled to said sensor electrodes, said sigma-delta modulator coupled to a digital mixer, said mixer coupled to a digital filter, an output of said filter comprising digital words corresponding to amplitude of formation current detected by said sensor electrodes, said words sampled at spaced apart time intervals. - View Dependent Claims (19)
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20. An apparatus for measuring resistivity of an earth formation penetrated by a borehole, comprising:
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a sonde adapted to traverse said borehole; at least one source of measuring current including a delta-sigma modulator and a serial bit source coupled to said modulator, said bit source providing a digital representation of a magnitude of said measuring current sampled at spaced apart time intervals, said source of measuring current coupled to an induction transmitter disposed on said sonde; an induction receiver disposed on said sonde, said receiver responsive to current resulting from interaction of said measure current with said earth formation; and a sigma-delta modulator coupled to said induction receiver, said sigma-delta modulator coupled to a digital mixer, said mixer coupled to a digital filter, an output of said filter comprising digital words corresponding to amplitude of electrical voltage detected by said induction receiver, said words sampled at spaced apart time intervals. - View Dependent Claims (21)
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Specification