Ultrasonic leak detecting method and apparatus
First Claim
1. Apparatus for indicating the presence of ultrasonic energy comprising:
- an ultrasonic transducer means for converting ultrasonic energy into electrical energy having a related ultrasonic frequency;
an amplifier means for amplifying the electrical energy produced by said transducer means to produce an amplified ultrasonic signal;
a heterodyne means for translating the frequency of the amplified ultrasonic sound into the audio frequency range by modulating it with a carrier frequency signal whose frequency differs from the ultrasonic frequency by a frequency within the audio range, said heterodyne means including a carrier frequency signal generator and a suppressed-carrier amplitude modulator means for modulating said amplified ultrasonic signal with said carrier signal to produce an output audio frequency signal related to the amplified ultrasonic signal; and
an indicator means responsive to the amplitude of the audio frequency signal for indicating an output level related to the level of the ultrasonic energy.
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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.
46 Citations
36 Claims
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1. Apparatus for indicating the presence of ultrasonic energy comprising:
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an ultrasonic transducer means for converting ultrasonic energy into electrical energy having a related ultrasonic frequency; an amplifier means for amplifying the electrical energy produced by said transducer means to produce an amplified ultrasonic signal; a heterodyne means for translating the frequency of the amplified ultrasonic sound into the audio frequency range by modulating it with a carrier frequency signal whose frequency differs from the ultrasonic frequency by a frequency within the audio range, said heterodyne means including a carrier frequency signal generator and a suppressed-carrier amplitude modulator means for modulating said amplified ultrasonic signal with said carrier signal to produce an output audio frequency signal related to the amplified ultrasonic signal; and an indicator means responsive to the amplitude of the audio frequency signal for indicating an output level related to the level of the ultrasonic energy. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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- 19. In a method of detecting small openings or thin spots in an otherwise closed container, involving the steps of positioning a source of ultrasonic energy within said container, detecting the existence of ultrasonic energy outside the container with an ultrasonic detector that converts ultrasonic energy into energy in the audio range, and locating the origin of the ultrasonic energy outside the container by passing the ultrasonic detector over the outer surface of the container to locate the position at which the largest audio energy signal is obtained, the improvement comprising the step of sweeping the frequencies of the ultrasonic source over a band of frequencies at a rate below the upper limit of the audio range so that no standing wave node continuously exists at one location on the surface of the container.
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22. In a method of detecting small openings in an otherwise closed container, involving the steps of pressurizing the container with a gas, detecting the existence of ultrasonic energy outside the container due to the pressure of the gas through the opening with an ultrasonic detector that converts the ultrasonic energy into energy in the audio range, and locating the origin of the ultrasonic energy outside the container by passing the ultrasonic detector over the outer surface of the container to locate the position at with the largest audio energy signal is obtained, the improvement comprising the step of covering the outer surface of the container with a layer of a liquid having a surface tension such that the pressure of the gas through small openings in the container causes the formation and bursting of bubbles in the layer of liquid at that location, said bubbles having a size such that their bursting generates ultrasonic energy.
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25. An ultrasonic energy generator comprising:
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an oscillator circuit means for producing an electrical oscillation in a narrow ultrasonic band of frequencies, said oscillator circuit including a feedback path with a piezoelectric crystal, said crystal having a resonant frequency in said narrow band of frequencies and converting the electrical oscillation signals in the feedback path into ultrasonic energy; and sweep means for causing the output of said oscillator to vary within said narrow band of frequencies at a periodic frequency rate that is no higher than the upper limit of the audio range. - View Dependent Claims (26, 27, 28)
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29. An ultrasonic transducer for converting ultrasonic energy into electrical energy having a selected ultrasonic frequency comprising:
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at least two piezoelectric crystals electrically connected in series and spaced adjacent each other on a generally planar surface such that both are exposed to the ultrasonic energy, the degree of curvature of said planar surface being related to the distance from said surface for which said transistor means is focused to received ultrasonic energy; and an amplifier means including an input field-effect transistor, said crystals being connected in series between a gate terminal of said field-effect transistor and a common reference level, said input field-effect transistor being biased to have a high impedance between the gate terminal and the common reference level sufficient to avoid loading the series arrangement of crystals. - View Dependent Claims (30, 31)
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32. The method of detecting leaks in a container, comprising the steps of:
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irradiating the inside of the container with ultrasonic energy, repetitively sweeping the ultrasonic energy through a frequency range on the order of 2 KHz to 5 KHz bandwidth so that no standing wave node continuously exists at one location on the surface of the container, sensing the energy passed through the container in a frequency range above 20 KHz, whereby the sensed energy is low in the absence of a leak and measurably higher in the presence of a leak, and determining the location of a leak by correlating the detection of high energy to a leak location by means of a receiver including a detector that converts ultrasonic energy into energy in the audio range. .Iaddend. .Iadd.
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33. The method of detecting leaks in a container, comprising the steps of:
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irradiating the inside of the container with ultrasonic energy; repetitively sweeping the ultrasonic energy through a frequency range on the order of about 2 KHz to 5 KHz bandwidth at a repetition rate in the range of 5 to 20 Hz so that no standing wave node continuously exists at one location on the surface of the container; sensing with an ultrasonic detector the energy passed through the container that is in a frequency range above 20 KHz by passing the detector over the surface of the container, converting the ultrasonic energy into energy in the audio range, whereby the sensed energy is low in the absence of a leak and measurably higher in the pressure of a leak; and determining the location of a leak by locating the position at which the largest audio energy signal is obtained, and correlating the detection of said high energy to a leak location. .Iaddend. .Iadd.
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34. In a method of detecting leaks in a container defined by enclosing surfaces, involving the steps of:
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positioning a source of ultrasonic energy to produce ultrasonic energy in said container, detecting the existence within said container of ultrasonic energy with an ultrasonic detector; converting the detected ultrasonic energy into energy in the audio range in a receiver operating in a frequency range above 20 KHz; locating the origin of the detected ultrasonic energy by passing the ultrasonic detector over said container surface to locate the position at which the largest audio energy signal is obtained, the improvement comprising the step of sweeping the frequencies of the ultrasonic source over a band of frequencies at a rate below the upper limit of the audio range so that no standing wave node continuously exists at one location on the surface of the container. .Iaddend. .Iadd.
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35. An apparatus for inspecting a container for leaks comprising:
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a source of ultrasonic energy comprising a first transducer acting as an ultrasonic emitter, means for driving the emitter to repetitively sweep the emitted energy through a frequency range so that no standing wave node continuously exists at one location on the surface of the container, said source of ultrasonic energy being located within the container, means for detecting the existence of ultrasonic energy outside the container comprising an ultrasonic receiver including a second transducer, said receiver operating in a range above 20 KHz and being responsive to the emitted energy, and converting the ultrasonic energy into energy in the audio range, the first transducer inside the container being positioned so that the ultrasonic energy is received by the receiver at a low level if no leak is present and an increase in received energy is detected if a leak is present, and circuit means coupled to the means for detecting for responding to the detection of a leak and identifying the location of the leak. .Iaddend. .Iadd. - View Dependent Claims (36)
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Specification