Abstract: A method is described for providing an estimate of the state of a moving contact. The method comprises providing a device for estimating the state of the contact, inputting information about a location of an observer platform at particular time intervals and information from at least one sensor about a position of the moving contact relative to the observer platform at each time interval into the device, transforming the inputted information into a series of geographical grids with one grid being formed for each reading of the at least one sensor; combining grids corresponding to similar time intervals into a series of consolidated grid representations; and analyzing the series of consolidated grid representations to produce an estimate of the state of the contact at a final point in time where an observation was made.

Abstract: A system and method for determining the position of an automatically guided vehicle within a workspace is disclosed which operates by detecting sounds generated by beacons placed within the workspace. The time for the beacon sounds to reach the vehicle is measured and a distance to each beacon is determined. From these measured distances and the known positions of the beacons, the vehicle can determine its relative position.

Abstract: A trajectory estimation system for estimating a trajectory of a target in sponse to a series of data items which generated in response to motion of the target. The trajectory estimation system includes a data segmentation means and a trajectory selection means. The data segmentation means processes the series of data items in accordance with a regression/multiple-hypothesis methodology to generate a plurality of segments, each having associated data items which have similar features. The trajectory selection means for processing said segments in accordance with a multiple-model hypothesis methodology to generate a corresponding statistically-supportable candidate trajectory motion estimate of target motion thereby to provide indicia of an overall trajectory of the target.

Abstract: An object locating system, especially for use in locating a gaming ball in the game of football, utilizes a series of three sensors positioned on one side of a football playing field and a calibration source positioned on the other side. The calibration source emits an ultrasonic signal which is received by the sensors in order to provide a calibration signal. A ball marking unit is positionable on the field at a location of the ball and emits an ultrasonic signal which is received by the sensors and an RF signal which is received by the calibration source in order to turn the calibration source off. The sensors provide signals in which a processing unit calculates time delays by a time acquisition process in order to determine the position of the ball. In an alternate embodiment, the ball marking unit emits only an RF signal which is received by the sensors. The sensors again provide signals which are analyzed by the processing unit to determine delay between receipt of the signals at the sensors.

Abstract: A variable depth sonar is disclosed which is adapted to provide passive multipath target ranging and depth estimates. The sonar employs a novel estimation procedure which is adapted to sonars with relatively small sensors and limited computing power. A novel feature of the invention is the introduction of a change of depth of the sonar receiver, mounted on a mobile platform, into the estimation process. Measurements at the two different depths are combined to provide target range and depth.Other features and improvements are disclosed.

Abstract: An acoustic tracking system designed to allow scientists and fishermen to follow dolphins and whales without harming or harassing them. The system utilizes six flow shielded hydrophones mounted on the bottom of a vessel in two arrays of three hydrophones in each array. Acoustic signals of interest (dolphin calls) which strike the hydrophone piezo-electric elements are transmitted to a receiver-display device which determines and displays both the bearing to the signal of interest and the relative range from the vessel to that signal. The receiver-display device utilizes digital microprocessors to determine the difference in signal arrival time of an incoming signal at pairs of hydrophones. The resulting computed bearing to the dolphin call is displayed as a lighted indicator on an electronic heading display.

Abstract: An apparatus is disclosed for determining the position of a moveable element over the surface of a solid medium. First and second transducer devices are provided and are moveable for placement at selected respective first and second locations on the surface for coupling with said surface. A third transducer device, for coupling with said surface, is mounted with the moveable element. Ultrasonic energy is transmitted, in either direction, between the third transducer device and the first and second transducer devices, the ultrasonic energy travelling through said solid medium. The transit times of the ultrasonic energy propagating, in either direction, between the third transducer device and the first and second transducer devices are determined, the transit times being indicative of the position of the third transducer device with respect to the first and second transducer devices.

Abstract: A real time passive trajectography device comprises at least three pairs of ensors. Each pair of sensers is separated from the other pairs of sensors by a distance which is greater than the distance separating each of the sensors of the pair. One of the pairs of sensors is roughly aligned with the currently determined trajectory while other pairs of the sensors are aligned at 0.degree. to 30.degree. from the perpendicular to the current trajectory. Of each pair of sensors, the output signal from a first sensor is used as a reference signal. The output signal from a second sensor is compared to the output signal of the first signal based on a presumed speed of the object being tracked. The presumed speed is continually updated until a maximum correlation between the first and second output signals is obtained. The measurement and correlation operation is repeated at predetermined intervals, with the initial presumed speed extrapolated from the trajectory previously computed during previous intervals.

Abstract: Apparatus and methods for improving signal detection and tracking in underwater acoustic devices receiving a set of acoustic pulses propagated in response to repetitive synchronizing events. Each of the set of pulses is correlated with a replica of each pulse in a receiver in the underwater devices during an associated time window. The correlated output of the receiver is compared to an adjustable threshold characteristic in a detector for selection of the actual pulse according to predetermined criteria for each of the set of pulses. An actual time of reception relative to the synchronizing event is assigned to the selected pulse. Previous actual times of reception are used to estimate the expected time of reception of the associated pulse relative to the next synchronizing event. The estimate is used to adjust the associated time window to encompass the expected time of reception.

Abstract: The transit time of acoustic waves between a generator and a receiver positioned across a fluid chamber is determined by generating acoustic waves using a self-purging pneumatic sound generator, a transducer adjacent the outlet of the sound generator, and a receiving transducer positioned away from the sound generator outlet so that the acoustic waves received by the receiving transducer pass through a portion of the fluid. The electrical signals generated by the transmitting transducer and the receiving transducer are processed to obtain the impulse response of these electrical signals, and the point of maximum value is determined. This point of maximum value corresponds to the arrival time of the acoustic waves at the receiving location. The transit time determination may be used to calculate the fluid temperature or other parameters.

Abstract: The positions of one or more underwater divers or vehicles are determined through an underwater acoustic communication link and at least a base buoy and one remote buoy with acoustic transponders and GPS position locating equipment. The location of the buoys is determined by the GPS equipment. The underwater diver or vehicle each carries an acoustic tracking unit transponder which emits a tracking unit message specifying its identity and its last known position at an assigned time slot. Upon reception of the tracking unit message by the base buoy, an acoustic base buoy message is emitted which includes the buoy position. The tracking unit receives the base buoy message, and marks the time of arrival to determine the propagation delay between the tracking unit and the base buoy. A predetermined delay after the receipt of the tracking unit message by the remote buoy, it sends an acoustic remote buoy message specifying its location.

Abstract: Method for determining the ranges between pairs of transceivers deployed underwater. According to a preferred embodiment, the transceivers transmit acoustic pulses to and receive acoustic pulses from other of such transceivers according to a coordinated schedule of individual transmission times and reception windows stored in each transceiver. Timers in each transceiver sequence the transceiver through its scheduled events. Periodic synchronization of all deployed transceivers keeps the transceivers synchronized. One- or two-way ranging between pairs of receivers is possible, with two-way ranging requiring only loose synchronization of transceivers. The preferred method of range determination includes a two-way range between pairs of transceivers, each transceiver transmitting pulses having preselected characteristics to the other on a different frequency channel.

Abstract: A microphone 13 is provided upon the ceiling 4 of an elevator hoistway 3 and a loudspeaker 8 upon the top of an elevator car 1. A 9-16 kHz up-sweep is provided to the loudspeaker 8 and a sound signal is transmitted from the loudspeaker 8 to the microphone 13. The travel time of the sound signal is obtained by cross-correlating 53 the sound signal received by the microphone 13 with a reference signal. The reference signal is a received signal in a relatively noiseless environment. By multiplying the travel time of the signal by its velocity, the distance between microphone and loudspeaker is calculated 59. The hoistway temperature is measured 26 and used 57 in the absolute position calculation 59.

Abstract: The invention provides a method and apparatus for determining the combination of distance and relative direction between two locations in a fluid medium.

Abstract: A detecting system and method of determining the position of a mobile point of interest in a m dimensional coordinate system having an ultrasonic transmitter mounted on the point of interest, and a plurality of stationary ultrasonic receivers, the number being at least m plus 2. The location of the receivers are determined optimally by using a linear matrix formulation. Alternatively, the location of the receivers can be determined during installation or self-calibration of the system. The system also includes receiver controlling means for processing the received signal to generate time of flight measurements which are used to eliminate the speed of sound as a variable and to compute the location of the point of interest. The controlling means also generates phase measurements when prompted by an outside source by comparing the transmitted signal with a 40kHz pulse sync to refine the accuracy of the location of the point of interest.

Abstract: An apparatus for locating a source of acoustic emission in a material comprises four spaced transducers coupled to the material. Each transducer produces an output signal corresponding to a detected acoustic emission activity, and each output signal is amplified, rectified and enveloped before being supplied to a processor. Artificially induced acoustic emission events, of known location, are generated in the material. The processor measures the times taken for each output signal corresponding to artificially induced acoustic emission events, to exceed two predetermined amplitudes from a datum time. A neural network analyzes the measured times to exceed the predetermined amplitudes for the output signals corresponding to the artificially induced acoustic emission events and infers the mathematical relationship between values of time and location of acoustic emission event.

Abstract: This invention is concerned with an indicator apparatus for determination of the trajectory or the trajectory direction of a projectile travelling at supersonic speed. It comprises pressure sensitive transducers (T.sub.1 -T.sub.4), which have fixed positions relative to each other or move relative to each other in a defined way, and which are devised to measure the pressure wave generated by the projectile. Also, there are means to produce electrical signals from the transducers, which represent the pressure values sensed by the transducers. Using said signals from each pressure transducer the computing circuits determine a value for a time instance when the pressure wave pass the transducer. From these time values and the geometrical quantities, which specify the position of each transducer in relation to a spatial coordinate system, the computing circuits evaluate the direction of the projectile trajectory more or less accurately.

Abstract: A digital range measuring system utilizes a digital signal processing prosor in connection with a precision time standard to generate a unique, characterizing frequency signal for transmission through a medium such as a body of water, at precisely known time intervals wherein a received signal at a second, different DRMS performs a predetermined number of frequency domain analyzations on the received signal to detect the presence of a known, unique frequency signal representative of at least one originating DRMS. Each of the frequency domain analyzations are time identified so that the one frequency domain analyzation during which the presence of the known frequency is detected is used to determine the time of detection. A personal computer is coupled to the digital signal processing processor and uses the time of detection in calculating the range between the receiver and the originating transmission.

Abstract: Apparatus and method for determining the trajectory of a supersonic projectile of unknown velocity and direction having at least three spaced-apart sensors capable of encountering a shock wave generated by a supersonic projectile passing in the vicinity of the sensors and capable of generating signals in response to the shock wave, which signals are related to an azimuth and elevation angle of a unit sighting vector from each sensor to an origin of the shock wave. Means are provided for calculating from the signals the azimuth and elevation angle of the unit sighting vector from each sensor to the origin of the shock wave. Means are provided for calculating from the unit sighting vector of each of the three sensors, the azimuth and elevation angle of the local trajectory of the projectile.

Abstract: The present invention is a method and apparatus for monitoring the linear displacement of a body using a pair of ultrasonic transducers, one for transmitting an ultrasonic signal and one for receiving the ultrasonic signal. For example, the present invention may be used for monitoring the position of a stapling device relative to a set of copy sheets. The position monitoring system senses the linear position of the stapling device by measuring the time delay required for the ultrasonic signal to propagate from the transmitting transducer, located on a stationary reference, and the receiving transducer, operatively attached to the movable stapling device. The time delay is determined as a function of both a partial signal period and an integral number of complete signal periods for the ultrasonic signal.

Abstract: Two ultrasonic transducers are provided, one upon the ceiling of an elevator hoistway and the other one the top of an elevator car for measuring the time for an ultrasonic signal to travel from one transducer to another and return for treasuring elevator position.

Abstract: An ultrasonic transducer is provided with an ultrasonic transmitter; an ultrasonic receiver; and a propagation-delay-time calculating device for calculating a propagation delay time from the time when an ultrasonic wave is transmitted by the transmitter until the time when the ultrasonic wave is received by the receiver.

Abstract: A trailer hitching aid includes a dual transmitter mounted on the forward end of a trailer or other vehicle to be towed and arranged to transmit pulses of infrared light and pulses of ultrasonic sound. A towing vehicle mounts on its rear end an infrared light detector and a pair of laterally spaced ultrasonic sound detectors. The detectors are incorporated in an electrical circuit which includes a computer the program of which operates to measure the time difference between the detection of a light burst and the detection of sound bursts. The time differences then are utilizes to calculate the distance from each detector to the transmitter, and the distances and angles between the detectors and transmitter are displayed on the computer screen as visual indications to direct the operator of the towing vehicle to maneuver the vehicle to back it up and bring the hitch components on the vehicles into coupling registry.

Abstract: An ultrasonic measuring apparatus comprising a master unit and a slave unit each having a respective transmitter circuit for transmitting towards the other unit a burst of ultrasound and each having a respective receiver circuit to detect the burst of ultrasound transmitted by the other unit. The slave unit is responsive to the detection of a burst transmitted by the master unit to transmit a return burst back to the master unit. The master unit includes control means for disabling its receiver circuit during transmission of the said burst to the slave unit and thereafter until the end of a first period of time which is sufficiently long to permit all echoes from the said burst to decay to a level where the master unit receiver circuit is not sensitive enough to detect them.

Abstract: A positional locating method and apparatus (10) for measuring distances by accurately determining the transit time of ultrasonic wave bursts (22) between two or more points is disclosed. Timer clocks (60), (62), (64) and (66) are started when each of the bursts (22) is triggered to be emitted from a transmission point (14), and are stopped when a highly defined point (56) in the burst (22) is received at a corresponding receiving point (32), (34), (36) and (38). The highly defined point (56) is determined by first analyzing the burst (22) to identify a particular cycle (54) within the burst (22). That particular cycle (54) is then analyzed to detect the specific point (56) within the cycle (54). Use of multiple transmitters (9312), (9314) and (9316) or receivers (932), (934) and (936) permits the dimensions using ordinary trigonometric calculations.

Abstract: A method is disclosed for determining the separation between a seismic energy source and a seismic sensor, the location of which is known imperfectly. After the source emits a wavefield, the first-arriving impulse at the sensor is statistically processed to form a range statistic that is related to the true travel time between the source and the sensor. A set of range statistics from a plurality of source positions are filtered and converted to range loci, the intersection of which marks the location of the sensor.

Abstract: A distance measuring apparatus and method using an acoustic signal. It includes a transmitting probe for transmitting an acoustic signal from a transmitter, a plurality of receiving probes having resonance frequencies different from the central frequency of the signal transmitted from the transmitting probe, and a control circuit for controlling the functions of those probes. The acoustic signal is received by a receiving probe having a resonance frequency which provides the maximum received-signal sensitivity at the central frequency of the received acoustic signal under the control of the control circuit to thereby measure a long distance accurately.

Abstract: A passive surveillance system provides ranging and location capability of a signal source. A single receiver in a multipath environment or alternatively a plurality of receivers receive the signal from the source having different propagation delays along different paths. Selection of corresponding frequency components from different paths and mixing of the corresponding selected frequency components from each of the paths generates complex pseudo-noise signals that are suitable for correlation processing. Correlation processing of the mixed signals yields the time difference between the multiple paths. The maximum time difference parameters for each path are used to generate a locus line, either explicitly or implicitly. Range and location processing of the locus information identifies range and location of the signal source.

Abstract: Aquatic animal finder apparatus and method include one or more passive transducers for converting sounds, including bio-soundwaves from a living aquatic animal source traveling in a body of water, to electrical signals, the transducer is caused to scan about a selected axis, the electrical signals are filtered to eliminate all man-made signals of a periodic character and pass bio-sound electrical signals. A discriminator is connected to the filter and programmed to pass a predetermined pattern of the bio-soundwave electrical signals constituting a sonic profile, signature or imprint of a selected aquatic animal. The direction of a selected aquatic animal is detected and presented to the user and range, depth and direction of movement of the selected aquatic animal are determined solely from the biosound signals received from the aquatic animal.

Abstract: A coin tube monitor and control device for monitoring and controlling the number of coins in a coin tube by determining the time between when a coin enters a coin tube and when it strikes the stack of coins that has accumulated therein. The device includes an acoustic sensor for responding to certain movements of the coins.

Abstract: The miss distance of a projectile aimed towards a target is determined by a line of pressure transducers other than microphones which through response to a sudden pressure change together establish a cone section through a passing Mach cone; and the time space analogies of that cone permits reconstruction of the projectile path being in effect the axis of that cone.

Abstract: An acoustic touch position sensor is shown wherein a transducer coupled to a side of a substrate imparts a shear wave into the substrate that propagates along a first axis. A shear to Lamb wave converting array disposed along the first axis converts the shear wave to Lamb waves propagating along a plurality of parallel paths where each path is associated with a different axial position on the substrate relative to the first axis. The Lamb waves are converted back to shear waves by a Lamb to shear wave converting array disposed along an axis parallel to the first axis, the second converting array being spaced across a touch surface of the substrate from the first array. The shear wave from the second converting propagate to a receiving transducer that provides a signal representative of the waves.

Abstract: A magnetostrictive linear position transducer generating a 4-20 ma output in response to the position of a position indicating magnet. System resolution is enhanced by averaging in the analogue domain, a digitally developed position location signal.

Abstract: Apparatus for sensing distances between two objects by using multiple pulses from the detector and from the object to be detected by using a transmitter and not using any reflected waves the reliability and the ability to reject clutter is improved. The periods between transmission are accurately controlled so that there is no signal returned until the object to be detected generates such a signal. As a result it is possible to accurately measure the distance between two objects and indeed the system may be used between two objects when both are in motion.

Abstract: An ultrasonic linear measurement system uses the travel time of surface waves along the perimeter of a three-dimensional curvilinear body to determine the perimeter of the curvilinear body. The system can also be used piece-wise to measure distances along plane surfaces. The system can be used to measure perimeters where use of laser light, optical means or steel tape would be extremely difficult, time consuming or impossible. It can also be used to determine discontinuities in surfaces of known perimeter or dimension.

Abstract: The disclosure is directed to a method and apparatus for more accurately determining the transit time of acoustic energy travel between a transmitter location and a receiver location. An electrode pair spark gap is provided at the transmitter location, and an acoustic receiver is provided at the receiver location. The spark-gap is energized to produce a spark by coupling an electrical potential across the electrode pair. The generation of a spark at the spark gap is sensed, and an initializing signal is generated in response thereto. A timer is initialized in response to the initializing signal. The receipt of acoustic energy from the spark is detected at the receiver location and a terminating signal is generated in response thereto. The timer is terminated in response to the terminating signal, and the time measured by the timer is indicative of the transit time of acoustic energy travel between the transmitter and receiver locations.

Abstract: A position monitoring device for accurately determining a plurality of distances, velocity or acceleration along a line using a plurality of electromagnets. The position monitoring device includes an ultrasound transducer disposed along a line, an ultrasound generator to provide an ultrasound wave pulse along the ultrasound transducer and a plurality of electromagnets disposed along the line at selected positions. The electromagnets generate a magnetic field which interacts with the ultrasound pulse to generate a reflected pulse. A sensor measures the time lapse between generation of the initial pulse and receipt of the reflected pulse, and electronic components convert the time lapse interval to a position measurement.

Abstract: An acoustic signal receiving and processing circuit provides an output signal that enables a distance to be determined between a transmitter and a sensor. The circuit comprises a sensor which receives both noise and acoustic position signals, the acoustic signals arriving after a time delay indicative of distance between the signal's transmitter and a sensor. A level control circuit provides a plurality of output potentials, one of which is a ramp signal and another is a neutral voltage, the ramp signal produced in response to a start signal manifestation. A comparator circuit, has a pair of inputs connected to the level control and sensor circuits, respectively. The comparator circuit produces a first output signal in response to a potential on one of its inputs exceeding a potential on another of its inputs, i.e. when a voltage transition of a received acoustic signal initially passes a voltage manifested by the ramp signal.

Abstract: A method is disclosed for ultrasonically detecting creep swelling in tubular members such as fossil utility steam lines and headers. Ultrasonic surface waves (34) are propagated around the pipe (10) in a circumferential direction. The transit time (.DELTA.T) is measured by using the pulse overlap technique with an oscilloscope (24). Circumferential dimension is obtained by multiplying the transit time (.DELTA.T) by the known Raleigh velocity of sound in the tubular member.

Abstract: Apparatus located aboard a platform situated in an acoustic environment for racking a moving body when the body is proximate to the platform. The apparatus includes a selected number of acoustic sensor elements at selected locations around the platform, each of the elements for detecting acoustic information arriving at its selected location. The apparatus further includes signal conditioners coupled to the sensor elements, a given one of the signal conditioners providing a conditioned signal representing acoustic information which is emitted by the moving body when the body is proximate to the platform, and which arrives at the location of the acoustic sensor element to which the given signal conditioner is coupled.

Abstract: This invention is an automatic gunnery system, responsive to airborne acoustic shock waves produced by a projectile passing through a target area. Curved elongated acoustic energy conductors are located adjacent to one side of said target area with acoustic transducers attached to the end portions thereof. Said transducers produce an electrical signal when a shock wave from the projectile reaches them through said energy conductors. Electrical signal from the transducers is connected to electronic circuitry which determines the location of each "hit" on or near the target which is registered on display means.

Abstract: The ultrasound detector for a thin film includes an ultrasound transmitter and an ultrasound receiver. It is generally known that a plastic film introduced into a sound field attenuates the field to a greater or lesser degree. A sound wave of a frequency of e.g. 40 kHz has a wave length of approximately 9 mm in air. When a plastic film of a thickness of, e.g., 0.50-0.10 mm is introduced, the sound field is typically attenuated with 6-20 dB. The the ultrasound detector is formed as a resonator, and the distance between the transmitter and the receiver corresponds substantially to an integral multiple of one half of a wave length. As a result, the obtained sound field is stronger than previously and the attenuation caused by a plastic film between the transmitter and the receiver is higher than previously. Furthermore, the ultrasound frequency is scanned for taking tolerances, such as changes in temperature and humidity of air into account.

Abstract: Hydrophones are installed in each tank of a liquid cargo tanker ship. In the unfortunate event that the tanker collides with an obstacle in the water, the hydrophones detect the shock wave due to the collision. The relative first arrival times of the shock wave at the respective hydrophones are measured and the arrival-time differences between two hydrophones of any two different selected pairs of hydrophones is calculated. Hyperbolic lines of constant time difference are projected on a map of the locations of the hydrophones on the ship. The intersection of the lines of position representing the calculated first arrival time differences marks the location of the impact of the ship with the obstacle.

Abstract: A technique for the non-intrusive position determination of one or more natural or artificial acoustic transmitters (S1, S2, S3) in marine or terrestrial environments by processing data from five or more receivers (R1, R2, R3, R4, R5) distributed in the area. The data processing includes cross correlation (24) of receiver data to determine differences in acoustic data travel times (MTTD) and tomographic reconstruction (16) to determine transmitter position as well as receiver position (42), wind or current (40) and sound speed or temperature fields (44) and errors (41) associated with all of the above. Accuracy can be greatly enhanced by use of calibration transmissions at receiver or other known or unknown position locations. Position and wind, sound speed and error fields may conveniently be displayed by computer generated maps (18, 20, 22, 43).

Abstract: Apparatus and method for sonar or radar target tracking. Digital apparatus nd techniques are employed. A variable delay is used for beam steering.

Abstract: An ultrasonic tracking system comprising a transmitting unit and a drive unit. The transmitting unit is carried by the subject to be tracked and produces brief, periodic ultrasonic bursts. The drive unit has an ultrasonic receiver and a motorized assembly capable of tilting and panning an attached camera in response to control signals from the receiver. This receiver employs three ultrasonic microphones located at three of the four corners of an imaginary square centered on and perpendicular to the axis of the camera lens. The receiver measures the relative arrival times of signals received by the microphones, determines the direction and degree to which the camera is not pointed directly at the subject, and supplies control signals to the motorized assembly, to drive motors to re-orient the camera (and receiver) to point toward the subject.

Abstract: An apparatus for determining the length of an open or closed-end pipe by measuring the propagation delay of a sound pulse transmitted down the pipe bore. The apparatus includes an acoustic transducer, an acoustic detector and associated circuitry for computing the time required for an acoustic pulse to travel and return the length of a pipe. Electronic circuitry, including a microprocessor, is employed to provide the apparatus with an automatic gain adjustment feature. The gain circuitry increases the amplification until a return pulse of desired amplitude is obtained. The gain is time varying to make the last-to-return signals strongest thereby avoiding false readings from pipe discontinuities. Compensation is made for speed-of-sound variations due to temperature, humidity, and barometric pressure by direct measurement of speed of sound during each length measurement. The open or closed endedness of a pipe is determined by return signal charateristics and a correction factor applied for open-ended pipe.

Abstract: In a method of indicating the time of an acoustic pulse at the transmission or reception of the same, the acoustic pulse is a wave package, the amplitude envelope of which having an ascending and a descending flank. The method is characterized in that the beginning of the descending flank of the amplitude is detected for determining of a reference time in the wave package, that a predetermined zero crossing in the wave package is identified from the reference time and that the time of the identified zero crossing is determined.

Abstract: A method and apparatus for automaticlly controlling the position of a tool carried by a machine, which in the preferred embodiment may be the blade of a grader or paver for leveling a surface at a chosen depth. The method includes determination of time taken for an acoustic pulse to travel from a transducer to a reference surface and back, with this value being used to calibrate a microprocessor-controlled distance-measuring device. As the grader moves over a surface to be graded, the distance to the reference surface is constantly detected by a repeated emission and detection of such acoustic pulses. The timing of the echoed pulses is converted to addresses in a look-up table which contains control words symbolizing commands to be given to hydraulic rams carried by the grader. By implementing these commands, the depth of the blade relative to the reference surface is constantly updated, compensating for variations with the height of the reference surface.

Abstract: In order to locate a source of acoustic emissions, two multi-element transducers are employed. The elements of each transducer are subjected to an impinging acoustic wave at different moment in time depending upon the angle of the wave. Outputs from the elements of each transducer are compared with a look-up table to determine the angle. Then, another look-up table is used to determine the X-Y intersection of impinging wave angles from both transducers which locates the source.