Abstract:
A contaminant sensor is provided which has an ultrasonic guided wave transducer that is bonded to a wall in which the ultrasonic energy is transmitted. A detector reflector is provided at a selected distance from the transducer, which will reflect signals that are affected or changed by contaminants collecting on an exposed surface of the wall. A self test reflector is positioned closely adjacent to the transducer and provides a reflected signal that is substantially unaffected by contaminants on the exposed surface of the wall, but which reflects signals only when the transducer assembly is functioning properly, and is properly bonded to the wall. The signal that is reflected by the self test reflector changes when the bond loosens. The receiver is activated right after transmission ceases to determine if the transmitter is operating.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a self test system for use with an ultrasonic transducer mounted on a wave guide plate assembly or wall and which is used for contaminant detection. The ultrasonic transducer is bonded to the wave guide wall or plate, or other wave guide, and the self test procedure determines that the tranducer is working and whether the transducer is acoustically bonded or coupled to the wall or plate.  
           [0002]    In the prior art, acoustic channels or wave guides that have ultrasonic transducers bonded to one location, that transmit signals that are reflected from a reflector positioned at a spaced location have been known. The wave guide generally comprises a plate or sheet that has a surface exposed to ambient conditions. Snow, ice, or other contaminants that adhere to the exposed surface will cause changes (attenuation) in the reflected wave that is sensed by the transducer. The changes in the reflected wave indicate the presence of ice, as well as other contaminants.  
           [0003]    U.S. Pat. No. 5,922,958 to Schugt shows such a detector device. The weakening or loosening of the bond between the transducer or transmitter and the plate can occur and some way of checking for adequate ultrasonic vibration coupling to the plate is desired. When a sensor disbonds or in some way the bond fails the ultrasonic sensors will give spurious or no signals and a shortened sensor life. If there is heavy plate contamination, the guided wave signature or reflected signal received from the reflector near the end of the plate disappears, which can indicate that either the plate is truly contaminated, the transducer is not working, or a disbond occurred. The present invertion provides a simple self test procedure that will provide information about the integrity and performance of the bond of the transducer, as well as its ability to function for determining contaminants on a surface of a wall or plate . Contaminant detection systems are also shown in Rose et al. U.S. Pat. Nos. 5,629,485 and 5,932,806.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention relates to an ultrasonic vibration sensor, preferably formed as a wall or plate with a surface exposed to ambient elements, and which has an ultrasonic transducer, including a transmitter bonded to the wall or plate. The transmitter and a receiver for reflected or returned ultrasonic vibration can be combined and placed at one location, generally adjacent one end of a plate. An ultrasonic or acoustic vibration reflector is placed at a location spaced from the transmitter. Preferably, the reflector has a surface extending transversely to the direction of transmission of the ultrasonic energy at the opposite end of the sensor wall. The reflector, as shown may be a block bonded to the wall or plate.  
           [0005]    A self test procedure is provided by placing a second known discontinuity, as shown a waveguide, in the plate or wall adjacent the ultrasonic vibration transmitter. The second discontinuity forms an ultrasonic wave reflector that will reflect any wave transmitted from the transducer. The preferred construction is a small waveguide bonded to the under surface of the wall or plate. Wave displacements normal to the plate surface would transfer into the waveguide, hit the end of the waveguide and reflect back toward the transducer. Other known reflectors close to the transmitter or transducer can be used. The second ultrasonic wave reflector that is positioned close to the transmitter is of less a disruption than the contaminate signal generating reflector near the end of the sensor wall. Because the test reflector is close to the transmitter, the signal received from the self test reflector is not attenuated by ice or other contaminants adhering to the opposite side of the wall or plate. The receiver circuit provides a signal indicating receipt of the signal reflected from the second discontinuity.  
           [0006]    A processor circuit is connected to receive the signal related to the reflected wave from the second discontinuity. The process converts the signal that is received from the self test reflector into a readout indicating the transmitter is operating. If the transmitter has a failure or it has disbanded, there will be no signal.  
           [0007]    Again, the self test reflector is close enough to the transmitter portion to the transducer so even with contaminants adhering to the exposed surface of the transmission wall or plate there will be a signal shape that will not change unless there is a disbond or other problem with the ultrasonic transducer itself. The length of the self test waveguide forming a reflector that is in contact with and bonded to the plate or wall is related to the wavelength of the ultrasonic energy in the plate to insure that the ultrasonic energy is transferred to the waveguide. Also, the overall length of the self test waveguide forming the self test reflector is selected to provide a time before having a return signal from the self test reflector so that any disturbances from internal reflection in the transducer or transducer mounting are abated. This insures that the internal reflections are not confused with or thought to be signals from the self test waveguide.  
           [0008]    The self test reflector arrangement is easily formed or installed, and serves as a integrity check each time the transducer transmits an ultrasonic signal toward the contaminant detector.  
           [0009]    It should be noted that while the preferred embodiment illustrates a bonded on waveguide for the self test and a bonded on block for the main contaminant detection, other types of reflectors can be utilized. For example, the surface on the plate opposite from the surface exposed to ambient conditions can have a groove or other known type formed in the plate. A rivet array in the wall can serve as the self test reflector as well. Further, the wall of a structure can transmit the ultrasonic signal, so a separate plate is not always necessary. The first reflector used for detecting contaminates can be replaced by a separate receiver positioned on the wall or plate at the location disclosed for the reflector. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a plan view of a typical acoustic guided wave plate forming an ultrasonic path, and including a self test construction made according to the present invention;  
         [0011]    [0011]FIG. 2 is a sectional view of the sensor plate of FIG. 1;  
         [0012]    [0012]FIG. 3 is a bottom plan view of the plate of FIG. 1;  
         [0013]    [0013]FIG. 4 is a schematic representation of a timing diagram illustrating the operation of the present invention;  
         [0014]    [0014]FIG. 5 is an enlarged fragmentary sectional view of a waveguide used as part of the self test construction shown in FIG. 2;  
         [0015]    [0015]FIG. 6 is a side sectional view of a modified waveguide usable in the self test construction; and  
         [0016]    [0016]FIG. 7 is a further modified waveguide usable in the self test construction. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    Referring to FIG. 1, an acoustic (ultrasonic frequency range) contaminant sensor assembly  10  is shown schematically in position along the upper skin or wall  12  of an aircraft wing. As shown, the acoustic sensor assembly  10  extends essentially in a direction parallel to the airflow across the wing, which is shown by the arrows  14 . The wing can be constructed in any desired manner, and the acoustic sensor assembly  10  is made to sense contaminants, such as ice illustrated in FIG. 2 at  16 , on the exterior surface of the wall or plate that is ultrasonically vibrated. The acoustic sensor assembly  10  comprises a wall or plate  20  that has a length that is parallel to the direction of airflow, and as shown parallel to the chord of the wing or aircraft wall  12 . The sensor wall or plate  20  is fastened in place with suitable fasteners such as flush rivets or by bonding the parts. The wall or plate  20  may be the structural wall, such as the skin or wall  12  of an aircraft. Various configurations of contaminant detection systems are shown and discussed in Rose et al. U.S. Pat. Nos. 5,629,485 and 5,932,806. For illustrative purposes, the plate or wall  20  is shown as a uniform thickness plate. The wall or plate  20  has an interior surface  22 , as well as an exterior surface  24  on which the ice shown at  16  accumulates.  
         [0018]    Ultrasonic or acoustic energy that causes acoustic vibration in the wall or plate  20  is provided by a transducer assembly indicated generally at  26 . The transducer assembly can be of any desired type, for example the type shown in U.S. Pat. No. 5,922,958, and is the transmitter preferably is a well known piezoelectric sensor element  25 A . As illustrated, there is one transducer  25 , mounted onto a housing  27 . The housing  27  is supported with a wedge  32  so that the plane of the piezoelectric element  25 A that sends acoustic energy and receives the reflected acoustic energy is at an angle relative to the general plane  28  of the wall or plate  20 .  
         [0019]    The transducer support wedge  32  is bonded with a bonding layer shown illustratively at  34  to the inner surface  22  of the wall or plate  20 . The transducer  25  is at a first location on the wall or plate  20 , as indicated, near one end of the sensor wall or plate.  
         [0020]    When the transducer  25  is energized by suitable processor circuitry  30 , the transmitter section  25 A will provide a desired vibration pattern (in the form of a Lamb wave) on the outer surface  24  of the wall or plate  20 . This is discussed in the Rose et al. U.S. Pat. No. 5,629,485.  
         [0021]    The processor circuit  30  is of known design and is connected to the transducer  25  for providing excitation for the transducer  25  to create an acoustic wave in the wall or plate  20  during a first time period, and for receiving and processing a return signal, typically a frequency vs. amplitude signal, during one or more second time periods, in a known manner. In other words, the transmitter section of transducer  25  transmits the ultrasonic signal forming an acoustic energy wave, and then the transmitter portion turns off.  
         [0022]    The transducer  25  then has a section that acts as a receiver to receive a reflected wave at certain times or time windows. The transducer thus determines presence of a reflected or return ultrasonic vibration. A separate receiver also can be used for such detection of return signals As shown, the plate  20  has a contaminate detecting first ultrasonic wave reflector, shown as a bonded on bar reflector  40  defined adjacent an opposite end of the plate, and extending transversely to the direction, indicated by the arrow  42 , of transmission of the ultrasonic wave. The direction of reflected waves is indicated generally at  44 . The reflector  40  forms a wave reflecting surface for the ultrasonic vibration signal to be echoed back to the transducer assembly  26  and sensed by the transducer  25 . The reflector  40  can be formed to reduce bouncing of the ultrasonic wave in the reflector. The reflector can be replaced with a groove formed in either the top or bottom surface of wall or plate  20 , if desired.  
         [0023]    The transducer support wedge  32  is bonded securely to the inner surface  22 , but it is known that this bonding can become loose or fail. Also, ultrasonic transmitters can fail. As stated, this disbanding is a serious problem with ultrasonic sensors, since poor bonds resulted in spurious signals and shortened sensor life. During the occurrence of neavy plate contamination such as a buildup of a thick layer of ice  16 , the guided wave signature received from the reflector  40  near the end of the plate or wall  20  disappears, and this indicates that the plate is truly contaminated, or the sensor is dead, or a disbond occurred. With the present invention, the plate or wall is provided with a self test reflector, as shown a waveguide  50  which extends laterally across the plate or wall generally parallel to the reflector  40 , but positioned closely adjacent to the transducer  25 . Preferably the waveguide  50  is secured to the plate or wall within the first ultrasonic wave length determined by the frequency and ultrasonic velocity in the plate.  
         [0024]    In FIG. 5, an enlarged view of the waveguide  50  is illustrated. The dimension of the reflector indicated by the double arrow W, is the length of the waveguide that is in contact with and bonded to the plate or wall  20 , and the overall length of the travel path is indicated at L. This path follows the curve of the waveguide  50  as shown. The dimension W of the waveguide contacting the plate or wall should be greater than one wavelength of ultrasonic energy in the contaminate detection plate or wall  20 . By satisfying this requirement, it is insured that the ultrasonic energy is transferred to the waveguide. The length L, which is the overall travel path of the waveguide is preferably designed such that the ultrasonic energy received back from the end of the waveguide indicated at  50 A in FIG. 5, is of sufficient length so that the time between transmission of a signal and receipt of a reflected vibration signal by the transducer  25  will be sufficient to avoid mistaking disturbances or false signals from internal reflections for the self test signal. Such internal disturbances may occur in the transducer  25  or in the wedge or mounting block  32  between the transducer and the wall or plate  20 .  
         [0025]    Thus, selection or parameters for the waveguide insure that the correct reflected self test signal will be recognized.  
         [0026]    [0026]FIG. 6 shows an alternate form of the self test waveguide mounted relative to the transducer  25  and wedge  32 , and in this case, the waveguide  70  is a wall that is formed to have offset sections. The length W again is the length that is in contact with and bonded to the plate or wall  20 , and the overall travel length of the ultrasonic wave or vibration is the length following the offset sections to the outer end  70 A of the waveguide  70 .  
         [0027]    [0027]FIG. 7 is a further modified form of a self test waveguide that is in the shape of an angle iron. The length W is one leg that is in contact with and bonded to the plate or wall  20 , and the overall length of the waveguide shown at  76  is from the end adjacent the wedge  32  at transducer  25 , to the outer end  76 A of the waveguide  76 .  
         [0028]    Other configurations of waveguides can also be used, within the parameters outlined.  
         [0029]    In FIG. 3, the waveguide  50  is illustrated in the preferred form as a curved member. The dimension D, or the transverse width of the waveguide is kept to a minimum so that while insuring that the disturbance that it creates is enough to detect. In other words, the dimension D is selected to be minimized, but based upon the output of the transducer  25 .  
         [0030]    Instead of having the discontinuities or reflectors for reflecting ultrasonic vibrations, a separate receiver close to the transmitter at the position of waveguide  50 , and another receiver adjacent the position of reflector  40  can be used to provide the self test procedure and the contaminate detection.  
         [0031]    The operation of the self test is illustrated in the timing diagram of FIG. 4. A transmitted signal shown in FIG. 4 at  52  is transmitted between times t 0  and t 1 , by the transmitter portion of transducer  25 . Immediately after time t 1 , up to time t 2  the receiver portion of transducer  25  is turned on, and if a signal  53  is received, it is known that the transmitter  25 A is operable.  
         [0032]    From time t 2  to time t 3 , the receiver section of the transducer  25  is burned off.  
         [0033]    At time t 3  the receiver section of the transducer again is turned on to “look for” a signal reflected from the self test reflector  50 . A reflected signal indicated at  54  between times t 3  and t 4  is from the self test reflector, and if received, it is known that the transducer is operable, and the bond needed to couple the ultrasonic energy or acoustic wave to the wall or plate  20  has not loosened or become non functional. It is then also known that the reflected signal from the main contaminant detection reflector  40 , can be relied upon. The reflected signal from discontinuity is expected at a later time, as shown, between times t 5  and t 6 , and indicated at  58  in FIG. 4, can be relied upon as representing a signature that indicates either no contaminants on the surface, or the presence of such contaminants.  
         [0034]    The transducer  25  will provide an output electrical signal from the piezoelectric sensor element  25 A that is part of the transducer  25 . The techniques of transmitting and receiving ultrasonic vibrations are well known.  
         [0035]    The time periods shown in FIG. 4 typically can be as follows: from t 0  to t 1 , 150 μseconds; to t 2 , 100 μseconds; to t 3   , 150 μseconds; to t   4 , 200 μseconds; to t 5 , 350 μseconds and to t 6 , 500 μseconds. The times for transmitting and for tuning on the receiver depend on the overall length between the transmitter and main reflector, the wall material and power needed.  
         [0036]    If a response is present between time t 1  and t 2 , the transducer is functional, and if there is a response from the self test reflector between time t 3  and t 4 , it is known that ultrasonic wave energy is coupled into the wall.  
         [0037]    If responses are received between time t 1  and t 2  and between t 3  and t 4 , then the receiver looks at responses between t 5  and t 6  to determine if ice is on the surface  24 . No response would mean heavy ice and a large amplitude response would mean no ice. Amplitudes between the extremes would be a function of ice or other contaminant build up.  
         [0038]    Again, typically, the first or self test reflector is designed to give a minimal reflection, and consecutive reflected signals from reflector  50  would be attenuated before time t 5 , so the self test reflector will not affect the response from the main or detector reflector.  
         [0039]    The processor is set up so that each time it energizes the transducer  25  to transmit a pulse, which is done at regular time intervals, the self test reflector, shown as waveguide  50  will reflect a signal that is substantially unaffected by contaminants because of its close proximity to the transducer assembly  26 . The initial response between times t 1  and t 2  is a “ringing” of the transmitter rather than a reflected signal. The return signal from the self test reflector, which as shown, is not as severe a discontinuity as the main sensor reflector  40 , will always indicate whether the transducer assembly is operable, or whether disbonding has occurred. The processor circuit is used for indicating when contaminants are present because of changes in the return signal received between times t 5  and t 6 . The processor circuit  30  also is used for each transmission for the self test by setting the receiver portion to look for a return signal at the time (t 3  to t 4 ) when a return can be expected, based on the spacing of the waveguide  50  from the transducer  25  and the path length L of the waveguide.  
         [0040]    While the reflectors  40  and  50  have been illustrated, it is to be understood that other types of reflectors can be utilized, such as grooves formed on the inner (or outer) surface  22  of the wall or plate  20 , or, if the application of the sensor assembly is one that will permit it, reflectors on the exterior surface also can be used for providing a disruption of the transmitted acoustic signal that will provide a reflection adequate for the transducer  25  to sense it. It is common to have a bar on the interior surface, or some other discontinuity that will perform the same function as the reflectors The reflectors thus encompass grooves, bars, arid other irregularities, such as a rivet assembly, which can be used for the self test reflector. An interface between different materials at the location of the reflector, also can serve as a reflector.  
         [0041]    It also should be noted that tna reflector  50  can be curved as shown or in other words made to form an arc to provide a reflector that will tend to focus the reflected waves back toward the transducer  25 . The wall or plate material also can be of any desired type, and while a piezoelectric element  25 A is commonly used, other types of ultrasonic generators can be utilized as well. As stated, separate transmitters and receivers can be used, and bonded to the interior surface  22  of the plate. The wall acting as the ultrasonic or acoustic energy transmitting wall can be the actual structural wall.  
         [0042]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.