System and method for heterodyning an ultrasonic signal
First Claim
1. An apparatus for processing an ultrasonic signal, comprising:
- a pre-amplifier stage for amplifying a signal from an ultrasonic detector to produce an output;
a first heterodyning stage operatively coupled to receive the amplified output signal of the pre-amplifier stage, said first heterodyning stage converting the amplified output signal of the pre-amplifier stage into a first lower frequency signal suitable for driving a meter, said first lower frequency signal having a certain dynamic range and bandwidth;
a second heterodyning stage operatively coupled to receive the output of the pre-amplifier stage, said second heterodyning stage converting the amplified output signal of the pre-amplifier stage into a second lower frequency signal which is in the audible range; and
a feedback loop from the output to the input of the second heterodyning stage, said feedback loop acting to lower the dynamic range and broaden the bandwidth of the output of the second heterodyning stage with respect to the first heterodyning stage.
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Abstract
A method and apparatus for detecting leaks and mechanical faults by way of an ultrasonic device. An output from a variable gain amplifier is supplied to a pair of heterodyning circuits, i.e., a dual heterodyning circuit. At each respective heterodyning circuit, the output signal from the variable gain amplifier is multiplied by a local oscillator that is internal to each circuit. The dual heterodyning circuit is used to provide an enhanced input transducer signal for spectral analysis. This permits the capture of low level frequency components for extraction during spectral analysis. The dual heterodyning circuit of the present invention to provide the enhanced spectrum to thereby permit an easy determination of whether the resonance is mechanical or electrical becomes clear. In addition, fault frequencies are also more easily discernable. In other words, the enhanced signal output provides a lower signal to noise ratio such that the ease with which frequency components are analyzed is increased.
46 Citations
47 Claims
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1. An apparatus for processing an ultrasonic signal, comprising:
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a pre-amplifier stage for amplifying a signal from an ultrasonic detector to produce an output;
a first heterodyning stage operatively coupled to receive the amplified output signal of the pre-amplifier stage, said first heterodyning stage converting the amplified output signal of the pre-amplifier stage into a first lower frequency signal suitable for driving a meter, said first lower frequency signal having a certain dynamic range and bandwidth;
a second heterodyning stage operatively coupled to receive the output of the pre-amplifier stage, said second heterodyning stage converting the amplified output signal of the pre-amplifier stage into a second lower frequency signal which is in the audible range; and
a feedback loop from the output to the input of the second heterodyning stage, said feedback loop acting to lower the dynamic range and broaden the bandwidth of the output of the second heterodyning stage with respect to the first heterodyning stage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
a battery level detection circuit located in the apparatus for indicating a battery charge level.
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8. The apparatus of claim 7, wherein the battery level detection circuit comprises a plurality of differential amplifiers arranged in series to indicate that the battery is adequately charged at a first voltage level and to indicate that the battery is inadequately charged at a second voltage level.
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9. The apparatus of claim 8, wherein the first voltage level is 0 volts and the second voltage level is in a range of 3.5 volts to 4 volts.
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10. The apparatus of claim 1, further comprising:
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an audio amplifier stage located between the second heterodyne stage and a transformer;
wherein the audio amplifier provides an audio output through headphones.
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11. The apparatus of claim 1, further comprising:
a signal level converter for converting meter signals from said first heterodyne stage into root mean square signals and dB units for display on a liquid crystal display.
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12. The apparatus of claim 1, wherein said pre-amplifier and gain stage comprises
a buffer amplifier receiving an input transducer signal and providing an amplified output signal; -
a voltage controller coupled to the buffer amplifier for receiving the amplified output signal and providing a regulated output signal; and
a variable gain amplifier coupled to the voltage controller for receiving the regulated output signal.
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13. The apparatus of claim 12, wherein the buffer amplifier is a unity gain amplifier, the voltage controller is a voltage controlled amplifier that has a fixed gain, and the variable gain amplifier is switchable between two fixed levels.
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14. The apparatus of claim 12, wherein the voltage controlled amplifier has a fixed gain of approximately 20 dB, and the variable gain amplifier is switchable between approximately 0 dB and 20 dB.
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15. The apparatus of claim 1, wherein each of said heterodyning stages comprises
a local oscillator that is set at a respective predetermined frequency to provide, a mixer circuit for receiving the pre-amplifier output and the local oscillator signal and producing said lower frequency signal representing the difference signal. -
16. The apparatus of claim 10, wherein the oscillating frequency is 38 kHz, the second output of the pre-amplifier is in a range about 40 kHz and the difference frequency is in a range up to 2 kHz.
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17. The apparatus of claim 15, wherein an output signal from said heterodyning circuits stage is divided into multiple signal paths.
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18. The apparatus of claim 17, wherein the multiple signals paths comprise a first signal path connected to a headphone by way of an amplifier and a second signal path.
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19. The apparatus of claim 15, each of s aid heterodyning circuits further comprising tuning resistors for modifying a respective oscillator carrier frequency within each heterodyning circuit.
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20. The apparatus of claim 16, wherein the frequency of the oscillator signal is 42 kHz, and output of the second pre-amplifier is about 40 kHz, so the difference frequency is up to 2 kHz.
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21. The apparatus of claim 1, further comprising a camera operatively coupled to the apparatus for recording an image of the item under test.
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22. The apparatus of claim 21, wherein the camera is a digital camera that stores image files for transmittal to a printer.
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23. The apparatus of claim 1, further comprising a printer operatively coupled thereto.
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24. The apparatus of claim 23, wherein the printer receives and prints digital information generated by the second heterodyne stage, spectral information and pictures of a device under test.
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25. A method for processing an ultrasonic signal, comprising the steps of:
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amplifying a signal in a preamplifier stage to produce an output;
receiving the amplified output signal of the pre-amplifier stage at a first heterodyning stage, said first heterodyning stage converting the amplified output signal of the pre-amplifier stage into a first lower frequency signal suitable for driving a meter, said first lower frequency signal having a certain dynamic range and bandwidth;
receiving the output of the pre-amplifier stage at a second heterodyning stage, converting the amplified output signal of the pre-amplifier stage into a second lower frequency signal at said second heterodyning stage;
said second lower frequency signal being in an audible range;
lowering a dynamic range and broadening a bandwidth of an output of the second heterodyning stage with respect to the first heterodyning stage using a feedback loop from the output to the input of the second heterodyning stage; and
storing the output of the second heterodyning stage for subsequent conversion to a digital file. - View Dependent Claims (26, 27, 28, 29, 30, 31, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47)
forming a line output using a first transformer which is coupled to receive the second lower frequency signal.
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28. The method of claim 25, further comprising the step of:
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receiving the lower second lower frequency signal at a second transformer; and
producing a headphone output which can drive audio headphones.
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29. The method of claim 25, further comprising the steps of:
setting a level of a signal applied to the heterodyne circuits using a gain/sensitivity stage that is located between the pre-amplifier stage and either of the first and second heterodyning stages to prevent saturation of a meter signal and the output of the second heterodyne stage.
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30. The method of claim 25, further comprising:
displaying a battery level using a battery level detection circuit to indicate a battery charge level.
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31. The method of claim 30, further comprising the steps of:
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indicating that the battery is adequately charged at a first voltage level; and
indicating the battery is inadequately charged at a second voltage level;
wherein the battery level detection circuit comprises a plurality of differential amplifiers arranged in series to indicate that the battery is adequately or inadequately charged at the first voltage level and at the second voltage level, respectively.
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33. The method of claim 25, further comprising the step of:
providing an audio output through headphones using an audio amplifier stage located between the second heterodyne stage and a transformer.
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34. The method of claim 25, further comprising the step of:
converting meter signal levels from said first heterodyne stage into root mean square signals and dB units for display on a liquid crystal display using a signal level converter.
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35. The method of claim 25, wherein said amplifying step comprises the step of:
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receiving an input transducer signal at a buffer amplifier to providing an amplified output signal;
regulating the amplified output signal at voltage controller coupled to provide a regulated output signal; and
providing the regulated output signal to a variable gain amplifier.
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36. The method of claim 35, wherein the buffer amplifier is a unity gain amplifier, the voltage controller is a voltage controlled amplifier that has a fixed gain, and the variable gain amplifier is switchable between two fixed levels.
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37. The method of claim 35, wherein the voltage controlled amplifier has a fixed gain of approximately 20 dB, and the variable gain amplifier is switchable between approximately 0 dB and 20 dB.
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38. The method of claim 25, wherein each of said heterodyning stages comprises:
a local oscillator that is set at a respective predetermined frequency to provide, a mixer circuit for receiving the pre-amplifier output and the local oscillator signal and producing said lower frequency signal representing a difference signal.
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39. The method of claim 33, wherein the oscillating frequency is 38 kHz, the second output of the pre-amplifier is in a range about 40 kHz and the difference frequency is in a range up to 2 kHz.
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40. The method of claim 38, further comprising the step of:
dividing an output signal from said heterodyning circuits into multiple signal paths.
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41. The method of claim 40, wherein the multiple signals paths comprise a first signal path connected to a headphone by way of an amplifier and a second signal path.
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42. The method of claim 38, further comprising the step of:
modifying a respective oscillator carrier frequency within each heterodyning circuit by way of tuning resistors.
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43. The method of claim 39, wherein the frequency of the oscillator signal is 42 kHz, and output of the second pre-amplifier is about 40 kHz, so the difference frequency is up to 2 kHz.
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44. The method of claim 25, further comprising the step of:
recording an image of an item under test using a camera.
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45. The method of claim 44, wherein the camera is a digital camera that stores image files for transmittal to a printer.
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46. The method of claim 25, further comprising the steps of:
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receiving at least one of digital information generated by the second heterodyne stage at a printer; and
printing the digital information generated by the second heterodyne stage, spectral information and pictures of a device under test.
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47. The method of claim 25, further comprising the step of:
processing the digital file using a software application.
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32. The method of claim 32, wherein the first voltage level is 0 volts and the second voltage level is in a range of 3.5 volts to 4 volts.
Specification