Gas Research Institute

Intelligent Modem Corporation

Donald L Chaffee

Karl F Kiefer

Gerard T Pittard

Terry P Clifton

Mark P Mallory

W Kurt Dobson

Graham H Brand

C Grissom Steele

An ultrasonic scan assembly is adapted to efficiently and accurately scan a surface and cross-section of a wall of an underground gas pipe with ultrasonic energy transmitted and received by an ultrasonic transducer provided therein. The input pulse applied to the ultrasonic transducer is calibrated so that its width matches the natural mechanical resonant frequency of the ultrasonic transducer. As a result, the energy efficiency of the transducer is maximized and the accuracy of the scan is improved.

Scan assembly and method for calibrating the width of an input pulse to

Apparatus is disclosed for providing one hundred percent inspection of natural gas mains under operating flow conditions. The apparatus includes a scan unit assembly which is inserted into the gas main to collect data for the production of graphic images of the wall of the gas main. The scan unit includes a plurality of scan rollers, each containing an ultrasonic transducer, which traverse the surface of the wall defining the inner diameter of the gas main. The ultrasonic transducers transmit interrogating pulses into the wall of the gas main at a pre-determined spaced apart interval resulting in a helical scan pattern of interrogating pulses. The return pulses from the surfaces defining the inner diameter and outer diameter of the gas main and any imperfections and/or flaws within the wall of the main are received by the transducer and transmitted to a display unit for a visual indication (a tomograph) of the wall of the gas main.

Scan assembly structure

A system and method for reducing echoes on a duplex communication channel having both transmitted and received signals carried thereon, particularly a telephone channel having digital data transmitted thereon by way of a modem. The transmitted signal is converted from a time domain signal to a frequency domain transmitted signal by a fast fourier transform process. The frequency domain transmitted signal is multiplied by a set of filter coefficients to generate estimated echo coefficients. The estimated echo coefficients are converted from the frequency domain to the time domain by an inverse fast fourier transform process and then subtracted from the received signal to generate a residual echo signal. The residual echo signal is converted to a frequency domain residual echo signal by a fast fourier transform process and then multiplied by the complex conjugate of the frequency domain transmitted signal to generate correlation frequency components. The correlation frequency components are then used to update the filter coefficients so as to minimize the residual echo and at least partially cancel the echo present on the communication channel.

Frequency domain adaptive echo canceller for full-duplex data

A modem system includes a transmitter section having generators for successively generating sets of carrier signals where each carrier signal of a set has a different frequency and a modulator for modulating each carrier signal of a set with a different portion of digital data to be transmitted where all such portions used to modulate a set of carrier signals comprise a frame of digital data. Also included are an adder for successively combining together the modulated carrier signals of each set to produce a frame waveform, an inverse Fast Fourier Transform circuit for transforming each waveform from a frequency domain signal to a time domain signal, a rotate and match buffer circuit for rotating each transform waveform so that its beginning point amplitude and slope substantially match the ending point amplitude and slope of the immediately preceding transformed waveform, and a transmitter for successively and continuously transmitting the transformed and rotated waveforms over a telephone channel. The modem system also includes a receiver section having a circuit for receiving from the telephone channel transmitted signals, a rerotate circuit for rerotating each received waveform substantially to its original condition before rotating, a Fast Fourier Transform circuit for transforming each received, rerotated waveform from a time domain signal back to a frequency domain signal, and a demodulator for demodulating each received and rerotated waveform to recover the digital data transmitted.

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Park City, UT, United States of America

Donald L Chaffee