Abstract:
A system for ultrasonic leak detection employs a number of ultrasonic signal generators, each of which include an ultrasonic transducer generating an ultrasonic signal and an audio transducer generating an audio signal in the frequency range of human hearing that is a replica of the ultrasonic waveform. The ultrasonic signal generators are activated and placed at selected locations within the enclosure to be tested. The operator can listen for the audio signal to verify operation and the output waveform type of the ultrasonic signal generators. A mobile ultrasonic leak detector can then be employed outside the enclosure to detect any leakage of the ultrasonic signal through the enclosure wall to identify any leak paths.

Description:
RELATED APPLICATION 
     The present application is based on and claims priority to the Applicants&#39; U.S. Provisional Patent Application 61/928,108, entitled “Multi-Function Ultrasonic Sound Generator With An Audio Transducer For Human Hearing,” filed on Jan. 16, 2014. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates generally to the field of ultrasonic sound generators. More specifically, the present invention discloses a multi-function ultrasonic sound generator with an audio transducer that enables a human operator to hear a frequency-shifted version of the ultrasonic signal. 
     Statement of the Problem 
     Ultrasonic sound generators (USGs) producing airborne ultrasound are used for artificially pressurizing with sound waves volumes such as tanks, rooms, automobiles, cabins and enclosures that cannot be pressurized with compressed air or other means for leak testing. One conventional method of use is to place the USG in a room (tank or enclosure), seal it, and from the outside using an ultrasonic leak detector (ULD) try to find where sound is coming through the wall or the seals of the enclosure. The points where this sound is detected are leak points. 
     Currently some manufacturers offer models that produce a constant sound wave (CW) which when detected by an ultrasonic leak detector or translator sounds like a constant pitch tone. Others produce devices that generate two waveforms, a CW or a burst wave, which is a rhythmic on-and-off cycling of the CW wave. Yet others make simple sweeps that repeat or sweeps that the sound increases in pitch up to a maximum then decreases to a minimum and repeats. With the exception of one device on the market that offers CW and burst wave selectable by the user, all others are either only CW or only sweep. 
     Conventional USG devices are inaudible when operating and, depending on their sophistication, communicate with the operator via lights (if they are so equipped) to indicate which mode they are in. However since the sound produced by the USG is inaudible, it is typically necessary to use an ULD to verify that the USG is actually producing an ultrasonic signal. 
     Also, it can be difficult to find an USG that has been placed in a large dark enclosure after the completion of a leak detection job without the use of a ULD, especially if the USG has fallen from its initial position. This is another area in which an audible signal from the USG would be helpful. 
     Finally, large enclosures such as the hull of a bulk carrier or commercial ship often cannot be adequately covered with one USG, and therefore require multiple USGs placed in different regions within the enclosure. The operation of multiple USGs can cause standing waves especially in symmetrical spaces, which can result in constructive or destructive interference if the devices are tuned to the same frequency. Here also, a need exists for means to enable the operator to verify proper operation and placement of multiple USGs within a large enclosure. 
     Solution to the Problem 
     The present invention addresses these shortcomings in the prior art by providing an ultrasonic sound generator that generates both an ultrasonic signal and an audio signal that is replica of the ultrasonic waveform. This enables the operator to verify proper operation and placement of the USG simply by listening to the audio signal before proceeding with ultrasonic leak detection outside the enclosure with an ULD. 
     SUMMARY OF THE INVENTION 
     This invention provides a system for ultrasonic leak detection that employs a number of ultrasonic signal generators, each of which include an ultrasonic transducer generating an ultrasonic signal and an audio transducer generating an audio signal in the frequency range of human hearing that is a replica of the ultrasonic waveform. The ultrasonic signal generators are activated and placed at selected locations within the enclosure to be tested. The operator can listen for the audio signal to verify operation and the waveform output of the ultrasonic signal generators. A mobile ultrasonic leak detector can then be employed outside the enclosure to detect any leakage of the ultrasonic signal through the enclosure wall to identify any leak paths. 
     These and other advantages, features, and objects of the present invention will be more readily understood in view of the following detailed description and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be more readily understood in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic block diagram of an ultrasonic sound generator (USG)  10  embodying the present invention. 
         FIG. 2  is a diagram illustrating use of the ultrasonic sound generator  10  and an ultrasonic leak detector (ULD)  20  to detect a leak  32  through the wall of an enclosure  30 . 
         FIG. 3  is a diagram illustrating use of multiple ultrasonic sound generators  10   a ,  10   b  with distinctive signal waveforms to detect a leak  32  in an enclosure  30 . 
         FIGS. 4 a -4 d    show examples of various ultrasonic signal waveforms that can be selected as outputs for the ultrasonic sound generator  10 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A block diagram of an ultrasonic sound generator (USG)  20  embodying the present invention is shown in  FIG. 1 . The present invention uses a processor  11  (e.g., microcontroller) that generates multiple waveforms via software and drives an ultrasonic transducer  12  and an audio transducer  14  to generate two output signals: one ultrasonic and the other sonic (or audible). The audible signal  15  mimics the waveform of the ultrasonic signal  13  and is output to an audio speaker or audio transducer  14 . For example, the audio output signal  15  can be a mapped replica of the ultrasonic signal  13  waveform that has been transformed or translated into the frequency range for human hearing. The audio sound  15  produced is similar to the audible output signal produced by a conventional ultrasonic leak detector (ULD) depending on how the ULD transforms or translates the ultrasonic signal into the audible frequency range for human hearing. 
     For example, the audio signal  15  can be a replica of the ultrasonic signal  13  that has been frequency-shifted by a fixed amount in the frequency domain to translate the ultrasonic signal  13  into the audible frequency range. In this embodiment, if the ultrasonic waveform of the USG  10  is a constant 40 kHz wave and the ULD&#39;s local oscillator is tuned to 38 kHz, the difference is 2 kHz and this is the audible frequency that the ULD will produce and the operator will hear. Similarly, if the ultrasonic generator waveform is a 40 kHz burst with a repetition rate of 1 Hz, the audio signal output will be a series of 2 kHz bursts with a repetition rate of 1 Hz. 
     It should be noted that other types of frequency-shifting or translation could be employed. For example, frequency division can also be used to reduce the frequency of the ultrasonic signal  13  into the audible range. In this embodiment, if the USG  10  generates an ultrasonic chirp (burst of a frequency sweep), the audio signal  15  will be a chirp of a fixed reduction ratio of the frequency content of the sweep. If the ratio is 20:1, a 40 kHz ultrasonic signal will be reduced to 2 kHz. 
     In other words, the present invention generates an audio sound  15  at the ultrasonic sound generator  10  to mimic the sound a ULD would produce after translating or frequency-shifting the detected ultrasonic wave into the audible range for human hearing. The USG operator can select a variety of waveforms via an appropriate user interface  16 , and can select if he wants to hear what the generator produces. Furthermore, the ultrasonic sound generator  10  is capable of generating a range of ultrasonic signal intensities, and the operator can select a desired intensity via the user interface  16 . For example, the user interface  16  can be a touch screen offering a number of waveform options, or a selector switch to allow the operator to select a desired waveform. The embodiment shown in  FIG. 1  uses an on/off button, a “mode selection” button and an array of indicator lights as the user interface  16 . The ability to hear the USG  10  offers many advantages such as confirmation that the USG  10  is on and knowledge of what is expected to be heard with the ULD  20  during testing. Additionally, it helps the user find and retrieve the USG  10  within a large space using his ears without the need to use an ULD  20 . 
     In the preferred embodiment of the present invention, the USG  10  is based on a processor  11  (or microcontroller) that drives both the ultrasonic transducer  12  and audio transducer  14 . This architecture allows great flexibility in selecting signal waveforms, since the processor  11  can be used to generate virtually any software-defined ultrasonic and sonic (audio) waveform alone or simultaneously, such as carrier waves (CW or single tone), burst tones, ascending or descending frequency (triangle) sweeps, saw tooth sweeps, chirps, double chirps, ascending or descending chirp-sweeps, linear or nonlinear sweeps and other arbitrary waveforms. The ultrasonic waveform and the corresponding sonic replica can be time-synchronized or randomly linked between them. Several such examples of ultrasonic signal waveforms  13  are illustrated in  FIGS. 4 a   - 4   d.    
     As shown in  FIG. 1 , the processor  11  can be powered by a conventional battery  18  via battery voltage regulation circuitry  19 . This can include reverse polarity protection, and a battery voltage sensor to warn the user if the battery needs to be replaced or recharged. 
       FIG. 2  is a diagram illustrating use of an USG  10  and an ultrasonic leak detector (ULD)  20  to detect a leak  32  through the wall of an enclosure  30 . The USG  10  is initially placed within the enclosure  30  and activated. The operator can employ the user interface  16  to select a desired ultrasonic waveform  13  and intensity. The replica audio waveform  15  produced by the USG  10  offers confirmation that the device is properly functioning, and that the desired waveform has been selected. The ultrasonic signal  13  from the USG  10  propagates throughout the interior of the enclosure  30  and escapes through any leak paths  32  in the enclosure wall. The operator can use an ULD  20  outside the enclosure  30  to identify and localize these leak points  32  by searching and maximizing the strength of the ultrasonic signal  13  detected by the ULD  20 . 
     Placing multiple USGs  10   a ,  10   b  within an enclosure  30 , as shown in  FIG. 3 , increases the resulting sound pressure and the possibility of detecting a leak  32 . Having the ability to place multiple USGs  10   a ,  10   b  with different, distinctive waveforms helps the operator of the ultrasonic leak detector  20  by providing information as to where the leak path is. For example, a first USG  10   a  generating a burst-tone ultrasonic signal  13   a  and replica audio signal  15   a  can be placed in a first region of the enclosure under test, and a second USG  10   b  generating a sweep ultrasonic signal  13   b  and replica audio signal  15   b  can be placed in a second region of the enclosure. If the operator of the ULD  20  hears a burst versus a sweep, the operator will know merely by listening that the leak  32  is located closer to the USG  10   a  that generates bursts and thus, will be able to localize the area to search for the leak  32  with the ULD  20 . 
     The present instrument can be used with a tripod for support. For example, placing an USG  10  in a refrigerated super-market show case may be a problem if the location and orientation of the ultrasound producing transducer is not easily aligned with the door or other test point within the show case. The present instrument can be equipped with a threaded insert (e.g., on the bottom of instrument) to enable the USG  10  to be removably secured onto a tripod (rigid or flexible) and placed anywhere the tripod can be supported. In this manner, multiple USGs producing distinctive sound patterns can be placed in multiple show cases to test their door seals. Again, this configuration of multiple USGs maximizes the sound pressure within the enclosure and makes it easier to localize any leaks by distinguishing the audio waveform. 
     The above disclosure sets forth a number of embodiments of the present invention described in detail with respect to the accompanying drawings. Those skilled in this art will appreciate that various changes, modifications, other structural arrangements, and other embodiments could be practiced under the teachings of the present invention without departing from the scope of this invention as set forth in the following claims.