Ultrasonic leak detection system

• US 5,710,377 A
• Filed: 10/17/1995
• Issued: 01/20/1998
• Est. Priority Date: 10/17/1995
• Status: Expired due to Term

• Current Assignee: Department of Health and Human Services (State of Victoria), The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Youngquist, Robert C., Moerk, J. Steven
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): Kwok, Helen C.
• Application Number:
  US08/540,616
• Time in Patent Office: 826 Days
• Field of Search: 73/584, 73/585, 73/587, 73/588, 73/592, 73/593, 73/661, 73/40.5 A, 367/118, 367/129, 367/140, 367/178, 367/191
• US Class Current: 73/584
• CPC Class Codes: G01H 3/00 Measuring characteristics of vibrations by using a detector in a fluid G01H7/00, G01H9/00, G01H11/00 take precedence
• CPC Class Codes: G01M 3/24 using infrasonic, sonic, or ultrasonic vibrations
• CPC Class Codes: G01V 1/001 Acoustic presence detection
• CPC Class Codes: G10K 11/28 using reflection, e.g. parabolic reflectors

Abstract

A system for detecting ultrasonic vibrations, such as those generated by a small leak in a pressurized container, vessel, pipe, or the like, comprises an ultrasonic transducer assembly and a processing circuit for converting transducer signals into an audio frequency range signal. The audio frequency range signal can be used to drive a pair of headphones worn by an operator. A diode rectifier based mixing circuit provides a simple, inexpensive way to mix the transducer signal with a square wave signal generated by an oscillator, and thereby generate the audio frequency signal. The sensitivity of the system is greatly increased through proper selection and matching of the system components, and the use of noise rejection filters and elements. In addition, a parabolic collecting horn is preferably employed which is mounted on the transducer assembly housing. The collecting horn increases sensitivity of the system by amplifying the received signals, and provides directionality which facilitates easier location of an ultrasonic vibration source.

Claims

1. A system for detecting ultrasonic vibrations comprising:

a) a first housing;

b) an ultrasonic transducer disposed in said housing for detecting ultrasonic vibrations and generating an electrical signal in response thereto, said transducer including an output for transmitting a transducer signal generated thereby;

c) a parabolic collecting horn attached to said housing and positioned for collecting and focusing said ultrasonic vibrations onto said transducer; and

d) a processing circuit electrically connected to said output of said transducer for converting said transducer signal into an audio frequency signal having a magnitude proportional to a magnitude of said transducer signal.

2. The system of claim 1, wherein said processing circuit comprises:

i) an oscillator for generating an oscillating signal;

ii) means for forming a weighted sum of said oscillating signal and said transducer signal; and

iii) a mixing circuit for multiplying an oscillating signal component of the weighted sum and a transducer signal component of the weighted sum, and thereby generating said audio frequency signal having a frequency equal to a difference between a frequency of said transducer signal and a frequency of said oscillating signal, said mixing circuit comprising a diode bridge rectifier generating first and second complimentary outputs, and a differential amplifier having a first, positive input connected to the first output of said diode bridge rectifier, and a second, negative input connected to the second output of said diode bridge rectifier, said differential amplifier generating said audio frequency signal.

3. The system of claim 2, wherein said processing circuit further comprises:

iv) an audio amplifier for amplifying said audio frequency signal generated by said differential amplifier.

4. The system of claim 3, wherein said processing circuit further comprises:

v) first and second filters disposed in series between an output of said differential amplifier and an input of said audio amplifier, said first filter being a low pass filter, and said second filter being a high pass filter.

5. The system of claim 3, wherein said processing circuit further comprises:

v) means for converting the audio frequency signal generated by said differential amplifier into a DC voltage having a magnitude proportional to a magnitude of ultrasonic vibrations detected by said ultrasonic transducer; and

vi) means for applying said DC voltage to a multimeter for providing a visual indication of the magnitude of the detected ultrasonic vibrations.

6. The system of claim 1, wherein said processing circuit further comprises:

i) means for converting said audio frequency signal into a DC voltage having a magnitude proportional to a magnitude of ultrasonic vibrations detected by said transducer; and

ii) means for applying said DC voltage to a multimeter for providing a visual representation of said ultrasonic vibrations detected by said transducer.

7. The system of claim 1, further comprising:

e) a high sensitivity, low noise preamp contained in said first housing, said preamp having an input connected to said output of said ultrasonic transducer, and an output connected to said processing circuit.

8. The system of claim 7, further comprising:

f) an electrical cable for connecting said preamp to said processing circuit, said electrical cable including first and second wires, said first wire carrying said transducer signal and said second wire being connected to ground; and

g) means connected to said first and second wires for subtracting a noise signal on said second wire from a signal on said first wire, to thereby form a noise filtered signal to be converted by said processing circuit.

9. The system of claim 1, further comprising:

e) a second housing containing said processing circuit; and

f) an electrical cable connected between said first housing and said second housing for electrically connecting said output of said transducer to said processing circuit.

10. The system of claim 1, wherein the transducer is positioned at the focal point of the parabolic collecting horn.

11. A system for detecting ultrasonic vibrations comprising:

a) an ultrasonic transducer for detecting ultrasonic vibrations and generating an electrical signal in response thereto, said transducer including an output for transmitting a transducer signal generated thereby; and

b) a processing circuit electrically connected to said output for converting said transducer signal into an audio frequency signal, said processing circuit comprising;

i) an oscillator for generating an oscillating signal;

ii) means for forming a weighted sum of said oscillating signal and said transducer signal; and

iii) a mixing circuit for multiplying an oscillating signal component of the weighted sum and a transducer signal component of the weighted sum, and thereby generating said audio frequency signal having a frequency equal to a difference between a frequency of said transducer signal and a frequency of said oscillating signal, said mixing circuit comprising a diode bridge rectifier generating first and second complimentary outputs, and a differential amplifier having a first, positive input connected to the first output of said diode bridge rectifier, and a second, negative input connected to the second output of said diode bridge rectifier, said differential amplifier generating said audio frequency signal.

12. The system of claim 11, further comprising:

c) a high sensitivity, low noise preamp having an input connected directly to said output of said ultrasonic transducer, and having an output connected to said processing circuit.

13. The system of claim 12, further comprising:

d) a first housing containing said ultrasonic transducer and said preamp;

e) a second housing containing said processing circuit; and

f) an electrical cable connecting said output of such preamp to said processing circuit.

14. The system of claim 13, wherein said electrical cable includes first and second wires, said first wire carrying said transducer signal and said second wire being connected to ground, and said processing circuit further includes means connected to said first and second wires for subtracting a noise signal on said second wire from said transducer signal on said first wire, to thereby form a noise filtered signal to be converted by said processing circuit.

15. The system of claim 11, wherein said processing circuit further comprises:

iv) an audio amplifier for amplifying said audio frequency signal generated by said differential amplifier.

16. The system of claim 15, wherein said processing circuit further comprises:

v) first and second filters disposed in series between an output of said differential amplifier and an input of said audio amplifier, said first filter being a low pass filter, and said second filter being a high pass filter.

17. The system of claim 15, wherein said processing circuit further comprises:

v) means for converting the audio frequency signal generated by said differential amplifier into a DC voltage having a magnitude proportional to a magnitude of ultrasonic vibrations detected by said ultrasonic transducer; and

vi) means for applying said DC voltage to a multimeter for providing a visual indication of the magnitude of the detected ultrasonic vibrations.

18. The system of claim 11, wherein said processing circuit further comprises:

iv) means for converting said audio frequency signal into a DC voltage having a magnitude proportional to a magnitude of ultrasonic vibrations detected by said transducer; and

v) means for applying said DC voltage to a multimeter for providing a visual representation of said ultrasonic vibrations detected by said transducer.

19. The system of claim 11, wherein said ultrasonic transducer further includes a parabolic collecting horn for focusing said ultrasonic vibrations onto said ultrasonic transducer.

20. The system of claim 19, wherein the ultrasonic transducer is positioned at the focal point of the parabolic collecting horn.