Abstract: A portable testing apparatus to detect air leaks across large sealed gaps comprising an elastomeric, air impervious sheet sized and shaped to overlap a gap between an opening in a structure and an insert, a vacuum plenum extending through and sealing with said sheet, means for attaching the plenum to a vacuum source, channels, with openings therein for uniformly distributing and drawing a vacuum between a sheet and the structure, extending from the plenum along the inside surface of said sheet. The testing apparatus also comprising means for detecting the passage of air through the sealed gap when a vacuum is drawn therethrough.

Abstract: A pipeline inspection apparatus includes a pipeline pig which has a shaker for causing the pig to vibrate in one or more of the vertical, longitudinal, lateral, bending and torsional senses. The vibrations are transmitted into the wall of a pipeline through which the pig is moved and the vibration response of the pipeline is measured by accelerometers in the pig for detecting one or more of the vertical, longitudinal, lateral, bending and torsional motions of the pig. A data acquisition system and computer are used. For displaying and/or recording the measured data in a form which can be used to identify variations in the structural condition of the pipeline.

Abstract: An accelerometer is attached to a pipe wall to measure the acoustic pressure waves generated in a fluid within the pipe as a result of a leak in a valve in the pipeline. Calibrating the accelerometer and tuning it to particular wave frequencies allows a determination of the magnitude of the leak through the valve.

Abstract: A process and an apparatus for the ultrasonic testing of welds between plastic packaging like food trays and cover foils. The welded joint between the tray and cover foil is periodically exposed to pulses of ultrasonic radiation. The pulses pass through the weld and are picked up or received by a receiver. The amplitude of the received pulses is evaluated. The cross-section of the beam of ultrasonic radiation is so small that the radiation only passes through the weld itself. The packages and the ultrasonic tester are moved relative to each other in order to examine the whole circuit of the weld. The pulse rate is such that the weld areas covered by successive pulses overlap.

Abstract: A method for locating leak from a tank containing a fluid using acoustic signals by adaptively correlating the phase of the acoustic signals to determine a first set of possible leak locations and subsequently correlating acoustic signals from a second set of locations on the tank to determine a second set of possible leak locations and converging the first and second set of possible leak locations to determine the location of the leak.

Abstract: In an abnormality monitoring apparatus of the present invention, a plurality of detectors (13, 14) are arranged at a plurality of positions in the axial direction of a pipeline (11) to detect respective sound waves (37) propagating from a position (B) of occurrence of abnormality. The aforementioned position is calculated from a sound wave detection time difference between the detectors (13, 14) and position between the detectors (13, 14). The apparatus further includes an abnormal waveform memory unit (28) for storing the waveforms of a plurality of kinds of typical abnormal sound waves generated from abnormality on the pipeline (11). A display device (19) displays, on the same image screen, the abnormal waveform stored in the abnormal waveform memory unit and that of the sound wave detected. It is, therefore, possible for a monitoring personnel to readily identify a kind of abnormality occurred.

Abstract: An acoustic leak detection system comprises a sensor array, data acquisition unit, and computer analysis of detected leak signals. Sensors are arranged in a small array about the base of the storage tank and provide signals to the data acquisition module which are digitized and analyzed to compute spherical coordinates of detected signals for all permutations of sensor positions and signal arrival times for forming a vector indicative of the signal path.

Abstract: An improved method and apparatus for detecting leaks in pipelines using cross-correlation techniques including improved correlating circuitry featuring a pair of circulating delay lines for respectively receiving, temporarily storing and processing in a revolving sequence samples of input data obtained from a pair of remotely positioned sensors, a multiplying circuit for causing samples input to each channel to be multiplied by each sample stored in the circulating delay line associated with the other channel, an adder and accumulator memory for accumulating the multiplication results, and a display for displaying the correlation results.

Abstract: An apparatus and method for the rapid detection and location of a gas leak. A collimated beam of light is scanned across the component under test which has been pressurized with a tracer gas that strongly absorbs the light. When the light passes through the gas emerging from the source of the leak, the light energy absorbed by the gas produces an acoustic emission which is detected by a microphone. The resulting signal may be processed either as an alarm to notify the operator that a leak is present, or, it may be processed in coordination with the beam scanning mechanism to indicate exactly where the leak is located on the component.

Abstract: An apparatus and process for controlling a high pressure fluid leak, such as a combustible gas, by determining the leak rate of the fluid from the leak source utilizing sound sensors wherein the step of determining the leak rate includes the step of comparing the signals from the sound sensors with a known standard curve, and activating a controller for controlling the fluid to prevent the fluid from spreading in the atmosphere.

Abstract: An acoustic emission leak simulator (10) for a nondestructive simulation of a leak in a structure employs a fluid supply with variable orifice (18) for controllably releasing the fluid to create a simulated leak source (20). An acoustic waveguide (22) acoustically coupled to the variable orifice (18) couples the sound waves into the structure (12) for simulation of a leak signal. Transducer (30) positioned at a predetermined distance from the simulated leak source (20) characterize the leak signals for a leak detection system.

Abstract: An improved apparatus and method for ultrasonic inspection of materials through barriers such as gaps in manufactured parts is disclosed. The improvement herein is directed to enabling such ultrasonic testing to bridge ambient gaps such as intentionally formed gaps in composite structures having a first structure for originally receiving and transmitting sound separated by the gap from another structure to be inspected. Preferably, the gap is flooded with a gas having a predictable and optimum speed of sound relative to the material of the first and second structures. Sound is propagated to the first structure in a wave packet that is transmitted through the couplant fluid. The sound is generated in a wave packet having a spatial width at least twice the dimension of the gap to be bridged. The wave packet has a contained frequency having a wavelength (relative to the speed of sound of the gas flooding the gap) to create a constructively interfering standing wave node within the gap.

Abstract: A simple acoustic detection system is described for measuring leaks from long gas pipelines. Microphones are strung along (and attached to) the pipeline exterior. The outputs of the microphones are spectrally analyzed. A peak at a frequency f.congruent.V.sub.s /(2d) and its harmonics indicates a leak in the vicinity of the recording microphone, where V.sub.s is the velocity of sound in the gas and d is the thickness of the pipe wall.

Abstract: A method and apparatus for detecting a blockage in a cored passage of a hydraulic valve casting includes a sound generating device disposed within the spool bore and communicating with the passageway so that a sound wave may be introduced into the passageway and a sound detecting device disposed within the spool bore and communicating with an opposite end of the passageway so that the level of sound transmitted through the passageway may be detected.

Abstract: A signal detector and signal detection methodology is provided to monitor oscillatory signals, such as sound signals, to produce detector output in response to the presence of target signals having a frequency within a selected frequency range, such as ultrasonic sound signals. The detector has input processing circuitry that receives the oscillatory signals and filters out those which do not fall within the selected frequency range to produce an input signal. The input signal is split into two components, a primary input component and a control component. The primary input component is amplified proportionally to the amplitude of the control component. Preferably, the primary input component is processed to produce a clean, stable intermediate signal.

Abstract: An apparatus and method for determining the location of a pipe leak detects the pipe leak sound at a first remote location and at a second remote location, and generates first and second signals indicative of the sound. A time lay between the first and second signals is calculated at each of a plurality of frequencies. Integer multiplies of an associated period are added to each time lag to form a plurality of potential time delays at each of the plurality of frequencies. The plurality of potential time delays at all of the plurality of frequencies are stored in a memory. The time delay value which occurs most frequently is selected from the memory and is utilized to calculate the location of the sound source relative to the first and second locations. The invention can also be employed to determined the location of a sound source other than a pipe leak.

Abstract: An acoustic sensor and associated electronic circuitry are used to determine when a catastrophic leak (as e.g. may be caused by a sprinkler nozzle being broken off a pipe) occurs in a sprinkling system. When a catastrophic leak is detected, an alarm signal is generated and a shutoff valve may be actuated in order to prevent loss of fluid and possible damage that can occur due to localized high flow of the fluid that is being sprayed. The acoustic sensor responds to a frequency range of acoustic signals that encompasses the generally low frequency signals generated by the relatively unconstrained flow of fluid through a pipe, as well as the higher frequency signals generated by flow of fluid through one or more nozzles. Electronic signal processing means are employed to form a ratio of the acoustic power in two different frequency regions and to generate an alarm signal when flow generates an excess of low frequency acoustic power.

Abstract: Fluid leakage from a crack or other leakage point and other vibration-generating events in pipes and conduits may be located and analyzed by sensing axial and torsional vibrations and pressure fluctuations created by such events by placing accelerometers and/or strain gauges and pressure sensors on the conduit at selected points. The location of the event may be determined by comparing the travel time of selected pairs of signals such as axial propagated signals as compared with torsional propagated signals as a result in the difference of the acoustic wave speed of axial versus torsional waves. Cross correlation and deconvolution processes are carried out on the measured signals to determine differential signal arrival times at the sensors and to eliminate pipe response signals.

Abstract: The present invention provides a method of detecting a void-related fault in a metal or metal alloy component. The method comprising filling the fault with a fluid, preferably liquid; treating the component and fluid so as to produce thermal-excitation in the component and fluid; and thereby cause a detectable acoustic signal. The detection of the signal detects the presence of a void-related fault. The invention also provides a method of locating and characterizing a void-related fault which comprises detection of the fault as described, measuring the parameters of the acoustic signal and the conditions for producing the signal, and correlating the parameters and conditions with the location and characteristics of the fault. The invention is particularly useful for the detection of microbiologically induced corrosion (MIC). The invention also concerns a method of evaluating a component for the severity of a void-related damage.

Abstract: A method and apparatus for generating and introducing an acoustic signal into a piping system, such as a natural gas distribution system. A first case is sealably secured to a second case to form a diaphragm case. A diaphragm is sealably positioned within the diaphragm case between the first case and the second case. The first case and the diaphragm define a first chamber and the second case and the diaphragm define a second chamber. The first chamber is preferably in communication with the ambient atmosphere and operates at atmospheric pressure. The diaphragm case is one component of a pressure regulator that has an inlet and an outlet for connecting the pressure regulator within a piping system. The pressure regulator regulates fluid pressure within the piping system, downstream from the pressure regulator. The pressure regulator has a valve plug and a valve stem connected to the valve plug. An opposite end of the valve stem is connected to the diaphragm.

Abstract: A method and apparatus detect a noise disappearance of instruments, etc. in various instrumentations in a chemical plant or the like. Detection values which are outputs from a detector (1) are input into a data store (3) via a data collector (2). Inputs to a processor (4) are a detection value (Sold) at a previous point and time from the data storer (3) and further a current detection value serving as a newest value (Snew) from the data collector (2). In the processor (4), an absolute difference between the newest value (Snew) and the previous value (Sold) is calculated. When this difference is smaller than a preset value, a count number (C) of a counter (5) is incremented, whereas when this difference is larger than the preset value, the count number (C) is cleared. When the count number from the counter (5) exceeds a predetermined threshold value, this is regarded the occurrence of a noise disappearance, and a trigger signal (T) for actuating a notifier (7) is output from a limiter (6).

Abstract: Acoustic leak detection systems for boilers use wave guide tubes to conduct sound waves through the boiler wall for an environmentally safe location of microphones or transducers. To protect such wave guides from soot plugging, the boiler wall penetrating end of a wave guide is reciprocationally mounted within a soot shield. Linear motors mounted between the wave guide and soot shield base stroke the wave guide axially within the shield to dislodge accumulated soot upon command signal. Compressed air released from within the wave guide, also upon command signal, ejects loose soot particles from interior wave guide surfaces.

Abstract: A subsea pipeline leak is located by: (1) introducing sonic energy into the line; (2) deploying an array of hydrophones in the vicinity of the line; (3) knowing the orientation of the array; processing the signals from the array so as to identify the location of the sonic anomaly at the pipe rupture created by the sonic energy introduced into the pipe.

Abstract: Method and apparatus for testing leak integrity of a workpiece such as a wheel rim in which the rim is positioned within an air-tight housing with the axial rim edges is sealing engagement with opposed wall portions of the housing so as to form first and second chambers within the housing internally and externally of the rim. One of such chambers is supplied with air under pressure. Microphones are positioned in the other chamber for detecting leakage of air through the rim as a function of intensity of ultrasonic radiation emitted thereby. The test apparatus is calibrated to detect air leakage that exceeds a pre-specified maximum allowable air flow rate by removably mounting a calibration orifice on a test workpiece, with the orifice being sized to provide the pre-specified maximum allowable leakage flow rate for a satisfactory workpiece at the operating pressure of the apparatus.

Abstract: To permit ultrasonic leak detection, especially in internal combustion engines, an ultrasonic source is housed in a tubular body adapted for attachment to a sparking plug aperture in an engine and ultrasonic signals may thereby be injected into engine cylinders, there being an ultrasonic detector having a body with a tapered end to ensure directional limitation is used.

Abstract: Two laser beams derived from a laser pass through a furnace and are superposed in a laser spot to produce interference fringes having the same pitch as that of a Ronchi grating printed on a retroreflecting screen. Minute fluctuations of the laser beams caused by sound waves from leaks result in intensity fluctuations of the laser spot when the laser fringes move past the fixed grating. A telescope and photocell arrangement detects the light variations to produce an electrical signal which is amplified and filtered to detect the sound of leaks. This non-contact laser Schlieren microphone is sensitive to sounds all along the path of the beams.

Abstract: A sensor detects a vibration generated due to water leakage. An integration circuit integrates time intervals for which a signal obtained by absolute-value amplifying an output signal from the sensor exceeds a predetermined level within a predetermined period of time. The integration circuit performs the integration a plurality of times. A detection circuit selects a minimum value of a plurality of integration values obtained by the plurality of measurements as an integration value obtained when the influence of unrelated noise is at a minimum and compares the minimum value with a preset reference value. When the minimum value exceeds the reference value, the detection circuit determines the presence of water leakage, and when the minimum value is smaller than the reference value, determines the absence of water leakage.

Abstract: A method for electromagnetic ultrasonic conversion includes exerting dynamic-mechanical forces upon particles of an electrically conductive material of a test sample by superimposing quasi-static magnetic and electromagnetic high-frequency fields of a transmission converter for generating ultrasonic vibrations when transmitting. Electrical fields are induced by waves arriving in the test sample resulting in vibrations of the particles of material inductively affecting the fields of a receiver converter when receiving. The excitation of the vibrations when transmitting and the induction of electrical fields when receiving are effected by Lorentz and magnetic forces as well as by magnetostriction forces if the test sample is ferromagnetic. Fill level and bubble formation are monitored in enclosures in the form of containers and pipelines for liquid, by coupling a transmission converter and a receiver converter to an enclosure wall.

Abstract: A system for analyzing containment integrity of a containment system includes data storage for inspection data and characteristic data and a data evaluation processor for evaluating the inspection data. A data acquisition system is used for periodically obtaining wall thicknesses of selected components in the containment system. After data validation, the actual wall thicknesses are stored as the inspection data in the data storage. The data evaluation processor analyzes the present pipe wall integrity in light of stress calculated from the characteristic data including operational conditions and material properties. In addition, the data evaluation processor analyzes the trend in change of wall thickness to forecast future wall thicknesses.

Abstract: A method and an apparatus for the detection of corrosion, pitting or the like in pipelines is proposed and measured results produced in an appropriate manner are digitally converted, linked with measured values concerning the place and azimuth of the individual sensors to form individual blocks, which are intermediately stored to form larger units and are finally stored in a mass store.

Abstract: Leak detector arrangement for the detection of small openings in car bodies or other enclosures or containers which may permit undesired passage of water, fumes, or other fluids in which phase coded or linearly frequency modulated sound waves are directed towards potential leak areas. The portion of these waves which pass through the leak openings is received, and these signals are processed so as to discriminate these leak signals from other sound waves normally entering the receiver from other parts or from other sources. The discriminated signals are compared with a threshold so as to determine the absence or presence of a leak.

Abstract: A steam trap operation detector provided with a vibration detecting section and a arithmetric section. The detecting section includes a probe, a diaphragm for generating ultrasonic vibration in response to mechanical vibrations sensed by the probe and a vibration sensor for converting the ultrasonic vibration into an electrical signal. The detector also includes an arthimetric section for receiving an amplified signal from the vibration sensor and processing the same into information indicative of the operation of the steam trap.

Abstract: Nuclear fuel rods are checked for the presence of water in their interior by injecting bursts of ultrasound radially into the wall of each tube, producing echoing back and forth between the inner and outer surfaces of the tube. The rate of decay of this echoing indicates whether or not water is present.

Abstract: A method for evaluating the extent of deterioration of pipes whereby an inspection instrument is passed through a length of casing to determine the extent of corrosive deterioration. The resulting measurements generated by the inspection instrument are processed to exclude those responses caused by the structural configuration of the casing length under inspection. The remaining responses are then analyzed to compile a detailed interpretation of the measurements including specific information regarding the state of deterioration of the length of casing under inspection.

Abstract: A method and apparatus for locating a leak which produces a continuous acoustic emission having background noise and spikes, comprises continuously monitoring the acoustic emissions using spaced apart detectors which produce signals having background noise and spikes corresponding to those of the continuous acoustic emissions. The spikes of one signal are offset in time with respect to the spikes of the other signal, which corresponds to the difference in travel time of the acoustic signals to each of the detectors. By measuring the offset between the spikes, the relative position of the acoustic emission, and thus the relative position of the leak, can be determined with respect to the position of the detectors. To facilitate separating the spikes from the background noise, a floating detection threshold value is applied to the signals for eliminating the background noise.

Abstract: Ultrasonic vibrations indicating trouble at remote locations are detected by sensors spaced in the vinicity of expected trouble. These sensors have weather resistant transducers that convert ultrasonic vibrations from a leak in a conduit, electrical arc, bearing vibration or the like, into an electrical signal. In the sensor there are circuits that amplify the electrical signal and transmit it with a current loop transmission system over a twisted pair of wires to a central control and analysis computer. The amplification of the signal at the sensor is controlled by a signal from the center computer which changes the gain increments until the sensor circuits are not saturated by the ultrasonic signal. This gain control signal is also delivered to the sensors over a twisted pair of wires by current loop transmission system.

Abstract: A method and apparatus for monitoring operation of a valve is disclosed in which a signal, such as an alternating current electrical signal, is propagated through a fluid path defined by the valve. The occlusion of the fluid path is indicated by monitoring the propagation of the signal. The system is highly immune to electrical noise and to variations in fluid conductivity. The system is also well adapted for monitoring operation of valves having a plurality of ports. In installations employing a plurality of valves, as plurality of valve monitors can be used without mutual interference.

Abstract: A pipe flow detector for activating a solenoid to automatically close a pipe shutoff valve in the event of a leak. The detector comprises a piezoelectric film transducer attached to the pipe, the transducer producing a fluctuating electrical signal in response to pipe vibration. An amplifier amplifies the signal, which is then passed to a tunable low-pass filter. The output from the filter is passed to an averaging circuit to produce an electrical signal representative of the total voltage changes of the fluctuating electrical signals. An LED is connected to the output of the averaging circuit to provide a means to tune the filter.

Abstract: A steam leakage measuring device particularly for use in a steam trap having a detector member which includes a vibration sensor and a temperature sensor which are connected separately to a signal processing or arithmetic unit receiving and processing the temperature and vibration signals from the detector member. The temperature sensed by the temperature sensor is converted into a saturated pressure measurement and a true steam leakage measurement is developed in the signal processing unit based upon a predetermined relationship between the sensed vibration level and a leakage measurement for a particular developed pressure level.

Abstract: Seals in an automotive body are inspected for leaks by sensing ultrasonic energy passing through a seal. Either of an ultrasonic emitter or detector is scanned along a seal outside the body by a robot and the other is inside the body. The emitter operates at frequencies of 65 to 80 kHz and repetitively sweeps through a range of 6 kHz. The body may be either open or closed.

Abstract: A method for detecting leakage from an in-ground liquid containment having a nominally impermeable floor, wherein a source emits a burst and a row of sensors are placed on an opposing side of the containment to receive boundary wave energy transmitted along the containment floor. Traces from the sensors show a regular pattern of boundary wave amplitude or arrival time, with irregularities indicative of regions of floor defects. The sensors each receive energy propagated along a strip radiating from the source. To locate leakage, the method is repeated with source and sensors oriented across a second direction. Irregularities in first and second crossing strips indicate a defect located in the region of intersection of the two strips. Power spectrum analysis of the traces identifies particular types of floor defects, and baseline measurements correct for natural subterranean features.

Abstract: A moisture intrusion detection system is provided, wherein a plurality of independent and insular moisture detecting units are placed in a predetermined spaced apart relationship across the surface of a roof structure, or other system incorporating a water impermeable membrane, beneath the water impermeable membrane thereof. Each of the detecting units includes a moisture detecting and power supply unit and signalling unit. When moisture penetrates the water impermeable membrane of the roof structure, a leak condition exists and a water activated battery is activated. Each detecting unit in contact with water is activated. In combination with the detecting units, position and direction locator apparatus are used in combination with the detecting units to localize the source of the leak and the extent of any water damage caused thereby.

Abstract: A method and apparatus for detecting the presence of a gaseous substance within a space bounded by an enclosure utilizes the fact that sound is not transmitted through a vacuum and is transmitted through the material of the enclosure. A sonic wave transmitter and a sonic wave receiver are engaged with the material of the enclosure and separated by the space. Using the calculated arrival times and/or amplitudes for the soundwave portions through the space and through the material of the enclosure, it can be determined whether a soundwave portion has passed through the space and thus a leakage of gaseous substance into the space above a threshold amount has taken place.

Abstract: The invention provides a sensing device and method to determine irregularities of a pipeline wall arising from corrosion, pitting, gouges, scale and deposits, and dents causing out of round conditions. This sensing device may be carried through a pipeline by a pipeline pig and comprises radial, movable spring-loaded sensing fingers adapted to continuously contact the pipeline inner surface, said sensing fingers preferably being secured to a fluid-tight drum. The sensing fingers are acoustically connected to one or more microphones, which may be confined within the interior chamber of the fluid-tight drum. The microphones, in turn, are electrically connected to a recording device for recording the audio signal the sensing fingers make as they move through the pipeline.

Abstract: An ultrasonic method and apparatus are described for determining the depth of cracks 12 in a pipe or conduit 14. The apparatus 10 includes a transmitting transducer 30 and a receiving transducer 40 that are placed on the outside surface of the pipe to one side of the pipe. The transmit transducer 30 is energized to direct a shear wave beam 34 of ultrasonic energy at the crack to generate a complex reflected wave front from the crack 12 which contains information as to the size of the crack in relation to the wall thickness. The recovery transducer 40 is moved relative to the transmit transducer until a peak or maximum amplitude reading is found. When the maximum amplitude is found, the distance between the transducers is measured. The measured distance is then correlated with information obtained from specimens 80 of the same material and wall thickness as the on-site pipe to determine the depth of the crack 12.

Abstract: A method of detecting inadequately supported sections or overloaded points in a pipeline including the steps of traversing the interior of the pipeline with an instrumentation pig, sequentially striking or vibrating the wall of the pipeline by means carried by the pig to introduce vibratory signals into the pipeline, receiving said signals from within the pipeline by listening to the sounds generated as a consequence of the striking of the interior wall, and detecting preselected characteristics of received sound which are indicative of unsupported sections or of points of load and stress concentration in the pipeline.

Abstract: A method and apparatus are disclosed for inspecting and testing tires under high pressure in excess of 50 p.s.i. The apparatus includes a base, a pair of flanges on the shaft which support the tire, means for moving the flanges together to insure a seal between the flanges and the tire beads and means for introducing air under pressure into the interior of the tire. High frequency sound wave sensing means and indication means are also provided.

Abstract: A method and apparatus for detecting perforations in an underground fuel storage tank, employs the creation of a partial vacuum in the tank and a pressure difference across the tank wall, to cause air to pass through the perforation, and a hydrophone to sense the acoustic waves produced by the formation of air bubbles in the fuel. The acoustic waves of the bubbles caused by the air passage are sensed by a hydrophone and processed to provide an electrical signal indicative of the presence of the perforation. A water level sensor is also used to detect the level of water beneath hydrocarbon fuel in the tank. The method and apparatus can also be used with above ground fuel storage tanks and other types of above and below ground storage tanks.

Abstract: An apparatus and method for detecting the presence of liquid in pipes or tubes using ultrasonic techniques A first piezoelectric crystal is coupled to the outside of the pipe or tube at the location where liquid in the tube is to be detected. A second piezoelectric crystal is coupled to the outside of the pipe or tube at the same location along the tube but circumferentially displaced from the first crystal by an angle around the pipe or tube of less than 180.degree.. Liquid in the pipe or tube is detected by measuring the attenuation of an ultrasonic signal sent by the first piezoelectric crystal and received by the second piezoelectric crystal.

Abstract: Leaks or thin spots in containers, as well as mechanical faults, e.g. worn bearings, are detected by an ultrasonic energy indicator that includes a modulator that heterodynes ultrasonic signals received by a transducer and creates an audio signal related thereto. The transducer includes a series arrangement of piezoelectric crystals feeding a field-effect transistor amplifier and the modulator operates in an amplitude modulation, suppressed-carrier mode which can be stabilized by a feedback loop. For indicating the presence of the audio signal, either headphones or a meter or both are employed. When leaks in a container are being detected, an ultrasonic generator is used which varies its output frequency slowly over a band of frequencies. The leak detection technique can be improved by applying a thin layer of a liquid to the container surface so that pressure introduced into the container causes the formation and bursting of bubbles in the liquid that results in the production of ultrasonic energy.