Borehole acoustic telemetry system synchronous detector
First Claim
1. In a borehole telemetry system for passing acoustic signals in the form of a data stream over an elongated column acting as an acoustic path in the borehole, such acoustic signals having a data component embedded in a high level of noise, circuit means for filtering noise from the signal to provide a useable data component, which means comprises:
- first commutative filter means for filtering noise components of the data stream which occur at frequencies outside a narrow frequency band;
second commutative filter means for sequentially measuring the amplitude of a discrete portion of the data stream after the frequency filtering, said first commutative filter means further providing means for phase shifting noise components of the data stream before passage of the data stream into the second commutative filter means;
means for operating the sequential measuring means in timed relation to the occurrence in the data stream of a switching signal occurring at a selected frequency; and
means for outputting the average value of discrete portions of the data stream.
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Accused Products
Abstract
In a borehole telemetry system for acoustically transmitting data over a pipe suspended in a borehole, the level of noise in the data stream is inherently high, making the use of discrete frequencies advantageous to provide useful data. Any drift in electrical circuits which might affect or be affected by the use of precise frequencies is undesirable. A synchronous detector facilitates the removal of noise components from the data stream by comparing in a commutative filter the phase difference between a switching signal taken from the incoming data signal path, after the second stage of commutative filtering, with the data signal emerging from the last stage of filtering. The synchronous detector also compares a data signal having two stages of filtering with another data signal having six stages of filtering with the additional filtering, causing a phase shift in frequencies outside the precise frequency window, which the synchronous detector also rejects.
102 Citations
19 Claims
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1. In a borehole telemetry system for passing acoustic signals in the form of a data stream over an elongated column acting as an acoustic path in the borehole, such acoustic signals having a data component embedded in a high level of noise, circuit means for filtering noise from the signal to provide a useable data component, which means comprises:
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first commutative filter means for filtering noise components of the data stream which occur at frequencies outside a narrow frequency band; second commutative filter means for sequentially measuring the amplitude of a discrete portion of the data stream after the frequency filtering, said first commutative filter means further providing means for phase shifting noise components of the data stream before passage of the data stream into the second commutative filter means; means for operating the sequential measuring means in timed relation to the occurrence in the data stream of a switching signal occurring at a selected frequency; and means for outputting the average value of discrete portions of the data stream. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. In apparatus including a synchronous detector for use in a borehole telemetry system to detect a phase shift in acoustic signals being passed at a precise frequency over an elongated column acting as an acoustic signal path in a borehole, such acoustic signal having a data component embedded in a high level of noise, circuit means for filtering noise from the signal to provide a useable data component, which means comprises:
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first commutative filter means having a plurality of filter stage for eliminating noise components from the acoustic signal occurring at frequencies other than at a discrete center frequency of said first commutative filter means; second commutative filter means for sequentially measuring a parameter of discrete portions of the acoustic signal after it has passed through n stages of first commutative filter means; clock means for operating said sequential measuring means; said sequentially measured signal having been phase shifted by said first commutative filter means with respect to said clock means; and means for outputting the average value of the discrete portions of the measured parameter. - View Dependent Claims (12)
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13. A method for synchronously detecting a noise component in an acoustic telemetry data stream to transmit a useable data component of the data stream over an elongated column in a borehole, including the steps of:
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passing the data stream through a phase shifting network of a plurality of stages of commutative filters for phase shifting the noise component of the data stream; operating another commutative filter as a synchronous detector to charge a sequence of capacitors to the average value of a discrete portion of the data stream occurring at a precise frequency; clocking the operation of the another commutative filter by means of detecting a parameter of the data stream before it has passed through all of the stages of the commutative filter phase shifting network. - View Dependent Claims (14, 15)
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16. In a borehole telemetry system for passing acoustic signals in the form of a data stream over an elongated column acting as an acoustic path in the borehole, such acoustic signals having a data component embedded in a high level of noise, circuit means for filtering noise from the signal to provide a useable data component, which means comprises:
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means for sequentially measuring the amplitude of a discrete portion of the data stream; commutative filter means for phase shifting noise components of the data stream before passage of the data stream into the sequential measuring means, said phase shifting commutative filter means having a plurality of stages comprised of a series of commutative filters; means for operating the sequential measuring means in timed relation to the occurrence in the data stream of a switching signal occurring at a selected frequency, said switching signal being taken from the data stream after the data stream has passed through only a portion of the plurality of phase shifting stages; and means for outputting the average value of discrete portions of the waveform of the signal path.
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17. In a borehole telemetry system for transmitting acoustic signals over an elongated column acting as an acoustic path in the borehole, said acoustic signals having a data component embedded in a noise background, circuit means forming a circuit path to receive and retransmit said acoustic signal and for maintaining a precise frequency for said acoustic signal transmission, which means comprises:
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means for detecting an acoustic signal in the elongated column; means for amplifying the data component of the detected signal, said amplifier means having a feedback control; means receiving the amplified signal for filtering noise from the acoustic signal, which noise is at a frequency other than the precise frequency of the data component, said filtering means being comprised of a plurality of commutative filters in series; means in the circuit path for passing a feedback control signal to said amplifying means, said control signal being derived from the signal path after filtering has taken place; means in the circuit path receiving the filtered signal for detecting a phase shift in frequencies outside the precise frequency, said phase shift detecting means being clocked by the acoustic signal after it has passed through less than all of said commutative filters; and means for retransmitting the data component of the acoustic signal at a precise frequency. - View Dependent Claims (18, 19)
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Specification