Abstract: A system and method use magnetic field sensing to detect underground objects for strike avoidance. The system detects magnetic field components for both passive distortions in the magnetic field indicative of a ferromagnetic object and active magnetic fields that are impressed on an object by a signal generator. A detection module has a magnetic sensor assembly that detects the magnetic field components. The magnetic field component data is transferred through a multiplexer to an analog/digital converter to a processor. Pitch angle data from a pitch sensor and roll angle data from a roll sensor also may be transferred to the processor. The data is processed by the processor to determine the orientation of the detection module with respect to the object. The detection module may be installed in an underground boring tool or a trenching assembly.

Abstract: A system and method use magnetic field sensing to detect underground objects for strike avoidance. The system detects magnetic field components for both passive distortions in the magnetic field indicative of a ferromagnetic object and active magnetic fields that are impressed on an object by a signal generator. A detection module has a magnetic sensor assembly that detects the magnetic field components. The magnetic field component data is transferred through a multiplexer to an analog/digital converter to a processor. Pitch angle data from a pitch sensor and roll angle data from a roll sensor also may be transferred to the processor. The data is processed by the processor to determine the orientation of the detection module with respect to the object. The detection module may be installed in an underground boring tool or a trenching assembly.

Abstract: A balanced bandpass preamplifier assembly (23) is disclosed for use in a locator (10) for locating a beacon transmitter (18) housed within an underground boring device (12). The bandpass preamplifier assembly (23) includes a balanced bandpass filter (28) of the Butterworth type with second order filter characteristics. The preamplifier assembly (23) provides reception of beacon frequencies at two distinct frequencies, preferably 29.430 KHz and 32.768 KHz. The antenna (14) of the . locator (10) forms the series inductance in the bandpass filter (28).

Abstract: An electronic compass (10) for use in a boring tool (12) which will provide an orientation of the boring tool relative to the earth's magnetic field. In addition, a more straightforward left or right deviation from an initial bearing can be determined. The invention can correct for pitch angle and roll angle variation as well. The magnetic field is sensed by an axial magnetic field (12), a radial magnetic field sensor (18) and a plane-normal magnetic sensor (24) which are preferably magnetoresistive sensors.

Abstract: An apparatus and method is provided for determining if the signal received from an underground beacon (10) at a locator (22) is a true signal or a ghost signal. Orthogonal horizontal antenna (38) and vertical antenna (40) are used and a ratio is computed of the signal strengths measured by the two antennas. At the true location, the signal strength in the horizontal antenna (38) will be maximum and the signal strength of the vertical antenna (40) will be a null. If the ratio of the signal strength sensed by the horizontal antenna and vertical antenna is large, exceeding a predetermined value, the locator is receiving a valid signal from the beacon and a display of this fact is made on a display on the locator and the depth of the beacon is calculated. If the ratio is less than the predetermined value, a ghost signal is being received and this fact is displayed on the display on the locator (22).

Abstract: Precise alignment of the focal spot position on an x-ray CT system is achieved using a deflection coil that produces a magnetic field which acts on the electron beam path in the x-ray tube. A variable current power supply drives the deflection coil and is controlled by input signals to align the focal spot at a static reference position, to correct for focal spot drift between scans, and to wobble the focal spot position during a scan or between scans.

Abstract: A CT system includes a pair of detectors in its detector array which measure x-ray intensity from a source after passing through a differential x-ray filter. The ratio of the signals produced by these two detector elements are input to a KV calculator which produces a signal indicative of x-ray tube voltage.

Abstract: An imaging system includes a linear detector array which measures x-rays passing through a patient from an x-ray source. A mask disposed over the detector array has staggered segments that block x-rays and divide the detector array into a pair of slice planes. Signals from the detector elements receiving x-rays in respective ones of the two slice planes are used to separately reconstruct a slice image for each of the two slice planes.

Abstract: A CT system includes a pair of detectors in its detector array which measure x-ray intensity from a source after passing through a differential x-ray filter. The ratio of the signals produced by these two detector elements are input to a KV calculator which produces a signal indicative of x-ray tube voltage.

Abstract: A medical imaging system has a source of X-rays and a detector which produces an electrical signal in response to X-rays. A signal generated by the detector, during an acquisition interval, is used to construct an image of a medical patient, which may contain artifacts due to motion of patient. A signal is produced indicative of the motion, which has a quiescent period of minimum movement. A first portion of the signal is selected such that if image acquisition commenced at the end of the first portion, the acquisition interval would occur during a quiescent period. This first portion is initially used as a reference signal portion. Then subsequent portions of the signal are compared to the reference signal portion to produce a descriptor of the degree of similarity. An image acquisition is commenced when the descriptor indicates a given degree of similarity that is above a defined threshold.

Abstract: A medical imaging system has a source of X-rays and a detector which produces an electrical signal in response to X-rays from said source. A circuit amplifies the electrical signal by a gain factor that varies in response to a number received from a gain control circuit. A converter transforms an analog output signal from the amplifier into digital data. An error compensation circuit stores an offset correction value and a gain correction value for each value of the number from the gain control circuit. A pair of correction values is selected based on the gain of the amplifier for a given item of digital data. The selected offset correction value is summed with the item of digital data and the result is multiplied by the selected gain correction value. A circuit is provided to numerically integrate the corrected data.

Abstract: A detector for detecting z-axis position in the plane of the fan beam of a computed tomography machine with respect to the detector array employs a pair of slotted masks over independent detector cells, the slots creating exposed widths that decrease and increase along their length. The intensity signals from the two detector cells so masked are subtracted to produce a z-axis position signal eliminating the effect of dark currents. Multiple cells may be ganged to reduce the effects of sensitivity variations among pairs of detector cells. The z-axis position signal may be used to control the z-axis position of the fan beam with respect to the detector array and to reduce the effect of the detector cell's variations in sensitivity.

Abstract: A modulator (14) and a demodulator (30) cooperate in a system (10) to communicate data at a high data rate using a pulse frequency modulation scheme (PFM). The modulator (14) receives data symbols in a FIFO memory (72) and applies the data symbols, after an adjustable delay, to a variable frequency oscillator (74) to control the frequency of a carrier waveform (16) generated by the oscillator (74). Circuits (76, 78, 98) monitor the carrier waveform (16) and couple to the FIFO memory (72) to control the advancing of data to the oscillator (74). Consequently, the carrir waveform (16) is capable of changing frequency at each half-cycle of the carrier waveform (16), and such changes occur only at zero-crossings of the carrier waveform (16). The carrier waveform (16) is applied through a transmission channel (22) to the demodulator (30). The demodulator (30) includes a comparison circuit (36-42) which produces bipolar signals describing positive and negative half-cycles of the carrier waveform (16).

Abstract: A logging tool (22) for use in measuring underground parameters and transmitting electromagnetic energy (38) through the lithosphere (16) is disclosed. The logging tool (22) includes a CPU-controlled data acquisition circuit (44-56) to measure down-hole parameters. A modulator (58) generates an output signal modulated to describe the measured parameters, and the modulator drives a power amplifier (66). In the power amplifier (66), DC current from a positive terminal of a battery (30) is routed through a semiconductor switching device (74) and an inductor (78) to an electrode (34), which directly contacts a well casing (18). A ground terminal (80) couples to a negative terminal of the battery (30) and another electrode (36), which also directly contacts the well casing (18). A diode (76) couples between the switch (74) and inductor (78) at a cathode and ground (80) at an anode. A capacitor (82) couples between the electrodes (34-36).

Abstract: A coiled tubing injection unit for injecting a continuous length of coiled steel tubing into a wellbore for performing well operations includes an x-ray inspection apparatus arranged to continuously monitor the wall section of the tubing as it is inserted into or withdrawn from the well to detect structural defects in the tubing. An x-ray source and detector unit are mounted in a housing which is supported for rotation about the longitudinal axis of the tubing for projecting an x-ray image through suitable processing and display apparatus. The x-ray detection unit may be mounted on a level wind mechanism of the coiled tubing storgage spool or at another point between the storage spool and the wellhead into which the tubing is being injected.

Abstract: An FM discriminator (34) which independently recovers modulating information from each half-cycle of a modulated waveform (16) is disclosed. The discriminator (34) includes a comparison circuit (36-42, 80-82) which produces bipolar signals describing positive and negative half-cycles of the modulated waveform (16). These bipolar signals are de-glitched (80, 82, 52, 54) for respective positive and negative counter circuits (44p, 44n). Each of the counter circuits (44) includes a counter (58) which counts a high speed clock signal supplied by a clock generator (46) during one of the half-cycles to produce a period count that describes the duration of the half-cycle. During a subsequent half-cycle, a translation circuit (60) converts the period count into an amplitude value that describes the information modulated onto the modulated waveform (16), and a resetting circuit (64-68) presets the counter (58) to an initial value.

Abstract: An ultrasonic logging apparatus is provided with a receiver for receiving acoustic returns of varying amplitudes and a digitizer for digitizing the acoustic returns. The receiver utilizes the same transducer as the transmitter, and has input switching protection to protect the amplifiers from the transmitter signal. The receiver amplifiers have gain switching, utilizing junction field-effect transistors to produce rapid gain switching during an acoustic return. The gain switching allows the digitizer to digitize with satisfactory resolution.

Abstract: A transient electromagnetic apparatus for use in detecting irregularities on conductive walls of containers forms a multichannel distributed system and includes at least one transmitting antenna, at least one transmitter unit, plural receiving antennas, plural receiver units, and a computer for controlling the transmitter and receiver units. The receiver units each include elements that suppress noise in the received signals. Each receiver unit has a preamplifier, first and second low pass Bessel type filters, a gain ranging amplifier, and an A/D converter. The gain ranging amplifier receives feedback from the output of the A/D converter and provides increased small signal resolution. Each receiver unit also rejects common mode noise with a choke and balanced input impedances in the preamplifier. The apparatus allows an arbitrary number of receiving antennas, receiver units, and even transmitting antennas, and transmitting units, so that the apparatus can be configured to a variety of containers.

Abstract: A circuit for physical placement within an underground well to amplify low level differential DC voltage signals measured at a well casing is disclosed. The circuit incorporates an instrument amplifier with a first switching device before the amplifier and an inverter after the amplifier in the signal path. A second switching device selectively connects one of the amplifier and inverter outputs to a low-pass filter. The switching devices operate synchronously under control of an operating clock signal so that DC error terms associated with the amplifier are converted into a substantially AC error signal while maintaining the signal being amplified as a DC signal. The duty cycle of the operating clock signal is established to cause the substantially AC error signal to include a DC component of appropriate polarity and magnitude to compensate for DC error terms associated with the inverter and low-pass filter.

Abstract: The present invention provides an improved method for transmitting logging data from a logging apparatus operating in a well borehole to surface equipment over a logging cable. The logging data has variations in amplitude, which are converted to a frequency-modulated signal. The center frequency of the frequency-modulated signal is relocated to a lower frequency, which is within the bandwidth of the logging cable. The frequency-modulated signal is transmitted over the logging cable and received by the surface equipment, where the logging data is reconstructed.