Patent Publication Number: US-2007107488-A1

Title: System and method for enabling calibration of sensors used for detecting leaks in compartments

Description:
CROSS REFERENCE TO RELATED APPLICATION  
      This application claims priority to U.S. Provisional Application No. 60/730,429, entitled “Sensor Calibrating System and Method,” and filed on Oct. 26, 2005, which is incorporated herein by reference. 
    
    
     RELATED ART  
      In the manufacture or repair of products that include a sealed compartment, various methods have been used to determine how well the compartment is sealed, and where water or air intrusion (or extrusion) might occur. In the case of vehicles, for example, it is important to verify that water will not leak into the passenger compartment. Since visual inspection can be highly unreliable, certain vehicle manufacturers utilize spray booths for subjecting fully assembled vehicles to an intense water spray to ensure that vehicles shipped from the factory will not leak due to faulty or damaged seals. While this type of testing can be fairly reliable, it requires a worker to check for the presence of water in the compartment, and it is destructive in the sense that it can cause significant water intrusion in poorly sealed vehicles, or in vehicles where a window or door has been inadvertently left partially open, requiring significant expenditure of time and material for repairs due to water damage. Additionally, the spray booths are expensive to install and maintain, and cannot be easily duplicated at vehicle service and repair facilities.  
      In attempts to alleviate some of the problems associated with spray booths, some leak detection systems employ ultrasonic sensors to non-destructively detect leaks within vehicles. U.S. Pat. No. 6,983,642 entitled “System and Method for Automatically Judging the Sealing Effectiveness of a Sealed Compartment,” which is incorporated herein by reference, describes one such leak detection system. In this regard, at least one ultrasonic transmitter is placed within the passenger compartment of a vehicle and emits ultrasonic energy. Ultrasonic sensors on the outside of the vehicle are used to determine the levels of ultrasonic energy within a close proximity of the vehicle. Ultrasonic energy may escape from the vehicle through a leak causing an increased amount of ultrasonic energy external to the vehicle at or close to the location of the leak. Thus, by detecting the increased ultrasonic energy, a sensor can detect the presence of the leak.  
      Unfortunately, manufacturing an efficient and reliable leak detection system that utilizes non-destructive ultrasonic sensing capabilities can be difficult and expensive. Further, it is contemplated that a convenient location for a leak detection system is on or close to an assembly line of a vehicle manufacturer. Such an environment can be extremely noisy and, therefore, adversely affect the performance of the leak detection system. Moreover, better and less expensive leak detection systems and methods capable of non-destructively detecting leaks of sealed compartments, such as passenger compartments of vehicles, are generally desirable. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention can be better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale relative to each other, emphasis instead being placed upon clearly illustrating the principles of the disclosure. Furthermore, like reference numerals designate corresponding parts throughout the several views.  
       FIG. 1A  depicts an exemplary leak detection system.  
       FIG. 1B  depicts a front view of an exemplary leak detection system, such as is depicted in  FIG. 1A .  
       FIG. 2  depicts an exemplary embodiment of a sensor for the leak detection system of  FIG. 2 .  
       FIG. 3  depicts an exemplary calibrator for calibrating the sensor of  FIG. 2 .  
       FIG. 4  depicts a side view of a calibrator port depicted n  FIG. 2 .  
       FIG. 5  depicts a side view of a calibrator connector depicted in  FIG. 3 .  
       FIG. 6  depicts the sensor of  FIG. 2  and the calibrator of  FIG. 3  positioned for sensor calibration in accordance with one embodiment of the present disclosure.  
       FIG. 7  is a block diagram illustrating an exemplary arrangement of circuit elements for sensor calibration, such as may be performed by elements from the sensor of  FIG. 2  and the calibrator of  FIG. 3 .  
       FIG. 8  is a flow chart illustrating an exemplary method for sensor calibration.  
       FIG. 9  depicts an exemplary sensor and calibrator positioned for sensor calibration in accordance with one embodiment of the present disclosure.  
       FIG. 10  is a block diagram illustrating portions of the sensor and calibrator depicted in  FIG. 9 .  
    
    
     DETAILED DESCRIPTION  
      The present disclosure generally pertains to sensor calibrating systems and methods for enabling calibration of sensors, which may be used in a variety of applications including reliably detecting leaks in sealed compartments, such as compartments within vehicles. In several embodiments of the present disclosure, an apparatus having a sealed compartment, such as a vehicle (e.g., automobile, airplane, etc.), is moved past at least one ultrasonic sensor. An ultrasonic transmitter is placed in the sealed compartment and emits acoustic energy as the apparatus is moved past the ultrasonic sensors. A leak can be automatically and non-destructively detected by analyzing data from the ultrasonic sensors.  
      For purposes of illustration, the calibration systems and methods of the present disclosure will be described hereafter as calibrating sensors for detecting leaks within sealed compartments, such as passenger compartments or trunks, of vehicles (e.g., automobiles, aircraft, boats, etc.). It is to be understood, however, that the calibration systems and methods of the present disclosure may be similarly used to calibrate other sensors.  
       FIGS. 1A and 1B  depict an exemplary leak detection system  30  that tests for abnormal compartment leaks. The system  30  comprises an ultrasonic transmitter  33  that is placed within a compartment  36 , such as a passenger compartment of a vehicle  59 . The compartment  36  is moved past ultrasonic sensors  45  tuned to the frequency of the transmitter  33 . For example, ultrasonic sensors  45   a - p  ( FIG. 1B ) may be mounted on an arch-shaped support structure  52 , and the vehicle  59  may be passed through the arch formed by the structure  52 . The structure  52  may have other shapes in other embodiments.  
      In one exemplary embodiment, the transmitter  33  emits ultrasonic energy at approximately 40 kilo-Hertz (kHz), although other frequencies are possible in other embodiments. An object sensing system  46  detects a location of the vehicle  59  during the test, and ultrasonic sensors  45  detect ultrasonic energy, if any, that escapes from the compartment  36  as it is moved past the sensors  45 . Based on the ultrasonic energy detected by the sensors  45 , a test manager  50  determines whether the compartment  36  has any abnormal leaks. Further, by analyzing the data from the sensors  45  relative to the position of the vehicle compartment  36  during the test, the test manager  50  identifies a location of each abnormal leak detected by the system  30 . The test manager  50  displays data indicative of the identifier location and/or other information about the detected leak via an output device  52 , such as a printer or monitor. Exemplary embodiments of the system  30  are described in commonly-assigned U.S. Patent Application (attorney docket no. 731701-1050) entitled, “System and Method for Detecting Leaks in Sealed Compartments,” and filed on Oct. 25, 2006, which is incorporated herein by reference.  
      In order for the leak detection system  30  to more consistently and accurately detect leaks, it is desirable for the sensors  45  to be calibrated. In general, the components of an ultrasonic sensor, such as sensors  45 , have parameters that vary with time thereby causing undesirable variations in measurements. Conventional techniques for calibrating electronic devices, similar to the sensors  45 , include removing the sensors and using calibration instruments within an equipment servicing laboratory. However, due to the time and effort required to remove the sensors and the possible undesirable amount of downtime for the test line, as well as other factors, there is a need for improved calibration techniques.  
      An exemplary embodiment of a sensor  45  is depicted in  FIG. 2 . The sensor  45  has a housing  302  mounted on a structure  315 . When the sensor  45  is implemented in the leak detection system  30  depicted by  FIG. 1B , the structure  315  depicted by  FIG. 2  may be a portion of the structure  52  depicted by  FIG. 1B . The sensor  45  has a calibrator port  335  attached to the housing  302 . Note that the housing  302  can be any shape, such as rectangular. In addition, an exposed transducer  320  is attached to the housing  302 . The transducer  320  can be shock mounted, if desired. The housing  302  houses a sensor circuit  310  and possibly other components not specifically shown in  FIG. 2 . A calibrator  400  adapted to connect with the calibrator port  335  is illustrated in  FIG. 3 .  FIG. 6  shows the sensor  45  connected with the calibrator  400  to enable calibration of the sensor  45 , as will be described in more detail hereinbelow.  
      Referring now to  FIG. 2 , the sensor  45 , when used to test leakage from compartments in the system  30 , senses ultrasonic energy from the transmitter  33 . The sensor  45  has a sensor transducer  320  that converts ultrasonic energy from the transmitter  33  into a sensor signal, s(t). The sensor signal is received by a sensor circuit  310  that processes the signal so that the relative amount of ultrasonic energy detected by the sensor transducer  320  may be indicated (e.g., transmitted to a computer and/or displayed via an output device, such as a printer or monitor). The processing by the sensor circuit  310  may include amplifying, filtering and converting the signal to a digital format. In particular, an amplifier of the circuit  310  adjusts the amplitude of the sensor signal, and a filter of the circuit  310  removes out of band undesirable sound energy. Because the transmitter  33  typically provides an ultrasonic signal having a center frequency of around 40 kHz, the sensor transducer  320  selected preferably has a flat response at around 40 kHz and is responsive to any frequencies the transmitter  33  may emit. In one exemplary embodiment, a bandpass filter with a center frequency of about 40 kHz and a bandwidth of around 3 kHz equalized to the characteristics of the sensor transducer  320  helps to assure that undesirable sound noise is minimized. In the instant example, the output ultrasonic signal from the transmitter  33  may have frequencies in a range of approximately 39-41 kHz, although other frequency ranges are possible in other examples. Thus, the bandpass filter preferably has a flat shape for that frequency range. The amplifier gain, providing amplification in the sensor circuit  310 , is a design parameter dependent on the expected strength of the sensor signal and the interface requirements for coupling information to output devices.  
      When the leak detection system  30  is checking for leaks, the sensor circuit  310  processes the sensor signal and a processed signal is forwarded to the test manager  50  to determine if an abnormal leak is detected. As previously indicated, in order for the leak detection system  30  to operate reliably, it is desirable for the sensor  45  to operate reliably during testing. Because the electronic and electrical components of the sensor  45  have parameters that can change with time (a normal occurrence with aging), the calibrator  400  is preferably used to periodically evaluate and adjust the sensor  45 . A sensor port  335  ( FIG. 2 ) is comprised of a sensor connector  330  with a sensor electrical plug  332  as shown on one side of the sensor  45 . The sensor connector  330  and sensor plug  332  are adapted to receive the calibrator  400  ( FIG. 3 ), as depicted by  FIG. 6 .  
      The calibrator  400  has an arm  410  that, as shown in  FIG. 3 , is generally “L-shaped,” although other shapes are possible in other embodiments. One end of the arm  410  forms a calibrator connector  430  having a calibrator plug  432 , also shown in  FIG. 5 . The calibrator connector  430  and calibrator plug  432  are adapted to make a secure but detachable mechanical and electrical coupling to the sensor connector  330  and sensor plug  332 , although having separate mechanical and electrical connections are possible in other embodiments. In this regard, as shown by  FIGS. 2 and 4 , the sensor connector  330  has a hollow region  333  in which the calibrator plug  432  fits. Further, the electrical plug  332  is exposed through this hollow region  333 . When the plug  432  is inserted into the hollow region  333 , the inner walls of the connector  335  defining the hollow region  333  counteract gravity forces and hold the calibrator  400 . To detach the calibrator  400  from the sensor  45 , the calibrator  400  can be pulled in the x-direction so that the plug  432  slides out of the connector  330 . In other embodiments, other configurations of the connectors  330  and  430  are possible, and other techniques may be used to connect the calibrator  400  to the sensor  45 . However, as described herein, it is generally desirable for the distance y to be precisely maintained. Thus, it is desirable for the connectors  330  and  430  to be configured, as is described herein, so that, if a secure connection is made, the transducer  422  is ensured to be precisely at the distance y from the transducer  320 .  
      The electrical connection provided by plugs  332 ,  432  provides a power connection to the calibrator  400  from the sensor  45 . In addition, the plugs  332 ,  432  provide at least for signal transfer from the sensor  45  to the calibrator  400  and may also provide an information loop for sending information to a central computer or system manager from the calibrator  400 . For example, the calibrator  400  may communicate through the sensor  45  to the test manager  50 . A calibrator circuit  412  is contained within an enclosure that forms the shape of the calibrator  400 . In one embodiment, the calibrator circuit  412  has a signal generator, a driver (to excite a calibrator transducer  422 ), a comparator and evaluation logic. In other embodiments the calibrator may also have a processor, a display module, an input device, and other interface components, as well as other combinations of components. Note that the body of arm  410  can have any of a variety of cross-sectional shapes, such as circular, rectangular, etc.  
      In an exemplary embodiment, the signal generator of the calibrator circuit  412  provides a signal having a plurality of tones at different frequencies. For example, in one embodiment the signal has three tones of around 39 kHz, 40 kHz and 41 kHz, respectively, although other frequencies and numbers of tones are possible in other embodiments. Further, the tones may be transmitted simultaneously or in succession. The signal generator sends the tones to the driver of the calibrator circuit  412 , which sends electrical energy to the calibrator transducer  422 . Upon receiving the electrical energy from the driver, the transducer  422  emits ultrasonic energy  470  that is directed towards the sensor transducer  320 . Because the transmitted ultrasonic energy  470  diverges, as illustrated by the conical shape, not all the transmitted ultrasonic energy is received and converted to electrical energy by the sensor transducer  320 . The strength of the transmitted ultrasonic signal from transducer  422  is selected based on the dynamic range of energy expected at the sensor  45  when sensing energy leaks from the transmitter  33  of the leak detection system  30 .  
       FIG. 6  shows the calibrator  400  electrically and mechanically coupled to the sensor  45 . A distance y between the calibrator transducer  422  and the sensor transducer  320  is selected to limit the effect of noise (unwanted sound energy) on the calibration process. In this regard, placing the calibrator transducer  422  too close to the sensor transducer  320  may cause undesirable interference or feedback. Further, placing the transmitter too far from the sensor transducer  320  may reduce the strength of energy received by sensor transducer  320  to undesirable levels. Thus, the distance y is selected to optimize these considerations. For example, the calibrator  400  may be arranged such that the calibrator transducer  422  is positioned approximately as close as possible to the sensor calibrator  320  without causing feedback that significantly distorts the measurements of the calibration test. In one embodiment, the calibrator  400  is adapted such that the sensor transducer  320  is placed at a distance of about 20 centimeters from the calibrator transducer  422  when the calibrator  400  is coupled to the sensor  45 , as shown by  FIG. 6 , although other distances are possible in other embodiments.  
      A circuit diagram illustrating exemplary functional elements of the calibrator system is shown in  FIG. 7 . As indicated above, power is supplied to the calibrator  400  by the sensor  45 . For example, the sensor  45  may include a power source (not shown), such as a battery, and electrical power from this source may be provided to the calibrator components. In another embodiment, the power source may be external to the sensor  45 , and a cable may be used to supply power from the power source to the sensor  45  and/or calibrator  400 . In other embodiments, power may be supplied by a battery or other power supply of the calibrator  400 .  
      As shown by  FIG. 7 , the calibrator circuit  412  comprises control logic  414 , which may be implemented in hardware, software, or a combination thereof. When implemented in software, the circuit  412  may comprise an instruction execution device, such as a microprocessor, for executing instructions defined by the control logic  414 .  
      After the calibrator circuit  412  receives power, control logic  414  in calibrator  400  directs the signal generator  416  to send three tones, as discussed above, to the driver  418 . For each tone, electrical energy from the driver  418  excites the calibrator transducer (TRSD)  422  and ultrasonic energy  470  is transmitted. The frequency of the ultrasonic energy for each tone is different than the frequencies of the ultrasonic energy for the other two tones. The sensor transducer  320  receives a portion of the transmitted ultrasonic energy and converts that portion into a sensor signal, s(t). The sensor signal is processed by the sensor circuit  310  wherein the processing includes at least amplifying and filtering. The output of the sensor circuit  310  returns to the calibrator  400  and is received by the control logic  414 . The control logic  414  has a monitoring and evaluation function that determines the energy level of each of the three tones coming from the sensor  45 . If the ratio of the received values to the transmitted values for each tone is within a desired range, then the sensor  45  has passed the calibration test. However, if the ratios are outside a desired range, then the sensor  45  has failed the calibration test. Note that the desired range can be a function of the distance y. Moreover, connecting the calibrator  400  to the sensor  45 , as shown by  FIG. 6 , ensures that the sensor transducer  320  is precisely at the expected distance, y, from the calibrator transducer  422 . Thus, the desired range for the ratio of the received and transmitted values can be pre-computed and stored in the calibrator  400 , or other location, prior to testing.  
      If the sensor  45  fails the calibration test, corrective action can be performed. For example, if the calibration test is failed, the control logic  414  can be configured to provide an output indicating that the test has been failed. As a mere example, one or more light indicators (not shown), such as light emitting diodes (LEDs), may be used to indicate whether the test has been passed or failed. Such indicators may be mounted on the arm  410  or elsewhere. Further, the corrective action may include tuning (an on-site action) the filter portion of the sensor circuit  310 , replacing the sensor  45 , or performing other actions. Corrective action may be done manually or automatically. For example, the sensor processing circuits  310  may include a component that, based on sample values indicating the measured level of acoustic energy, automatically adjusts the taps of one or more filters in an effort to tune the sensor  45  to the desired frequency or frequency range.  
      An exemplary method for sensor calibration is illustrated in  FIG. 8 . After the calibrator  400  is plugged into the sensor port  335 , ultrasonic energy  470  is transmitted from the calibrator  400  towards the sensor  45 , step  610 . Because energy from the calibrator transducer  422  diverges, not all the transmitted ultrasonic energy arrives at the sensor transducer  320 . The energy received by the sensor transducer  320  is converted to electrical energy as a sensor signal, step  620 . The sensor signal is processed, step  630 , by the sensor circuit  310  and returned to the calibrator  400 . The processed signal is compared with the electrical signal transmitted from the calibrator  400  and logic in the control logic  414  determines if the sensor  45  has passed or failed, step  640 . Corrective action is taken, step  650 , if the sensor  45  fails the calibration test.  
      The corrective action taken may include adjusting a filter, such as an 8 th  order filter, in the sensor  45  to change the frequency response of the filter. In a sensor system having a digital signal process, where a digital filter is used for processing, the characteristics of the filter may be changed by adjusting the values of the filter taps. Various other types of adjustments may be made in other embodiments. In this regard, the filter may be adjusted manually or logic in the calibrator  400  or sensor  45  may automatically determine and adjust the tap coefficients.  
      It should be noted that the embodiments described above are exemplary, and various modifications may be made to the described embodiments without departing form the principles of the present disclosure. As an example,  FIG. 9  depicts an exemplary embodiment in which the calibrator circuit  412 , including the control logic  414 , signal generator  416 , and driver  418 , reside within the housing  302 . Further, an electrical connection  702  is connected to the transducer  422  and an electrical interface  705 , and this connection  702  provides a communication link with between the sensor  45  and the transducer  422 . Yet other configurations are possible.  
       FIG. 10  depicts an exemplary block diagram for an embodiment in which the control logic  414 , the signal generator  416 , and the driver  418 , reside within the housing  302 . In the embodiment depicted by  FIG. 10 , the control logic  414  is implemented in software and stored within memory  725 . In other embodiments, the control logic  414  can be implemented in hardware or a combination of hardware and software.  
      The exemplary embodiment depicted by  FIG. 10  comprises at least one conventional processing element  733 , such as a digital signal processor (DSP) or a central processing unit (CPU), that communicates to and drives the other elements the housing  302  via a local interface  736 , which can include at least one bus. Furthermore, a data interface  738  is coupled to the interface  736  and used for communicating with the test manager  50  ( FIG. 1B ) of the leak detection system  30 . As shown by  FIG. 10 , the signal generator  416  is also coupled to the interface  736 , and the driver  418  is coupled to the signal generator  416 , as well as the electrical interface  705 . The transducer  320  is coupled to signal processing circuits  310 , which processes signals from the transducer  320 , such as performing filtering and amplification of such signals. Sensor logic  745  is shown as implemented in software and stored in memory  725 , although the logic  745  can be implemented in hardware or a combination of hardware and software in other embodiments. The sensor logic  745  can perform various functions, such as communicating sample values from the transducer  320  to the test manager  50  when the sensor  45  is being used for testing a compartment for leaks.  
      In one exemplary embodiment, the control logic  414  is configured to use the data interface  738  to transmit data indicative of the calibration test results to the test manager  50 . The test manager  50  then provides an output indicative of the test results.  
      For example, as described above, the test manager  50  may be configured to provide outputs indicative of leakage test results via an output device  52 . This same output device  52  could be used to report calibration test results as well. Further, the reported test results could include more information than just whether the sensor  45  under test passed or failed the calibration test. For example, a value indicative of the extent of acoustic energy detected in the calibration test could be reported so that a user can be more informed about the calibration.  
      For illustrative purposes, assume that the desired transmit frequency of the transmitter  33  is about 40 kHz. In one exemplary embodiment, threshold data  766  defining at least one threshold for the calibration test is stored in memory  725 . For example, in one embodiment, the threshold data  766  a threshold (TH). The threshold is based on the distance y, and is set to establish a minimum amount of acoustic energy that should be detected by the sensor  45  if a source of the energy is positioned a distance of y from the transducer  320 . For example, if the transducer  320  detects acoustic energy from a source transmitting at a distance of y and a frequency of about 40 kHz, then the measured value of acoustic energy should exceed TH. If so, the sensor  45  is deemed to pass the calibration test for that frequency (i.e., 40 kHz). If not, the sensor  45  is deemed to fail the calibration test.  
      During calibration, the control logic  414  instructs the signal generator  416  to generate a signal for causing the transducer  422  to emit acoustic energy at about 40 kHz. The generated signal is amplified by driver  418  and transmitted to the transducer  422  via the electrical interface  705 . In response, the transducer  422  emits acoustic energy at about 40 kHz. The transducer  320  senses the acoustic energy and generates an electrical signal, which is processed by the circuits  310  to produce a sample value indicative of the amount of acoustic energy detected by the transducer  320 . The sample value is compared to the threshold (TH). If the sample value exceeds the threshold, the control logic  414  determines that the sensor  45  passes the calibration test. If the sample value is below the threshold, the control logic  414  determines that the sensor  45  fails the calibration test.  
      The control logic  414  transmits data indicative of the calibration test to the test manager  50 , which then displays the data via output device  52 . As an example, the displayed information may indicate the sample value from the test and/or an indication whether the sensor  45  passed the test. Further, the displayed information may indicate the difference between sample value and the threshold (TH). Other types of information are possible in other embodiments.  
      Moreover, other configurations of the calibrating system would be apparent to one of ordinary skill in the art upon reading this disclosure. For example, the arm  410  could be detachably coupled to the structure  52  or some, if desired, provided that the distance between the transducers  320  and  422  can be precisely controlled such that the transducer  422  is at the expected distance y from the transducer  320  when the arm  410  is secured to the structure  52 .