Abstract:
The present invention relates to a system for acquisition of at least one physical variable, in particular for a critical on-board avionics system, comprising a sensor for measuring the physical variable; an acquisition channel receiving an analog signal corresponding to the physical variable measured by the sensor and transforming this analog signal into a corresponding digital signal, at least some of these transformations being able to be carried out with loss of accuracy; self-test unit for checking the integrity of the acquisition channel and generating a self-test result. The system further comprises an analyzer analyzing the self-test result in order to determine an operating mode of the acquisition channel, and for activating the operation of means for correcting the signal delivered by the channel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a U.S. national phase application under 35 U.S.C. §371 of International Patent Application No. PCT/EP2015/062396, filed Jun. 3, 2015, and claims benefit of priority to French Patent Application No. 1401273, filed Jun. 3, 2014. The entire contents of these applications are hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a system for acquisition of at least one physical variable, in particular for a critical on-board avionics system. 
         [0003]    More specifically, the invention relates to such an acquisition system, of the type including:
       at least one sensor for measuring the physical variable;   at least one acquisition channel receiving an analog signal corresponding to the physical variable measured by the sensor and transforming this analog signal into a corresponding digital signal, at least some of these transformations being able to be carried out with loss of accuracy;   self-test means for checking the integrity of the acquisition channel and generating a self-test result.       
 
         [0007]    The present invention also relates to an acquisition method associated with this acquisition system. 
       BACKGROUND 
       [0008]    Such an acquisition system for example includes a sensor for measuring at least one physical variable, for example the position, speed, ambient temperature, pressure or humidity. 
         [0009]    The measured physical variable is transmitted to the acquisition system for example in the form of an electrical resistance, or more generally in the form of an analog signal. 
         [0010]    The acquisition system then makes it possible to transform this analog signal into a digital signal that can next be processed by a suitable digital processing means and optionally be communicated to an operator. 
         [0011]    Thus, the acquisition systems are usable in many technical fields. 
         [0012]    This is particularly the case for on-board avionics systems for example making it possible to measure the temperature outside the aircraft using a suitable sensor. 
         [0013]    The operation of such acquisition systems must therefore meet a certain level of criticality or safety generally imposed by aeronautics standards based on the significance of the applied physical variable and/or its influence on the piloting of the aircraft. 
         [0014]    Thus, for example, aeronautics standards ARP 4754A, ED-12C and DO-178C define five levels of criticality (from A to E) or DAL (Design Assurance Level) for avionics systems. The DAL A level has the highest criticality level and is assigned to avionics systems whereof an operating defect may cause a catastrophic event in the aeronautics sense of the term (loss of human life). 
         [0015]    The DAL A level is for example assigned to various acquisition systems usable in DAL A avionics systems. This requires many constraints regarding the operating safety of these systems. One can then see that development, production and operating costs for the systems become increasingly high with the increase in the number of these constraints. 
         [0016]    Thus, to decrease these costs while retaining the overall DAL A criticality level of the avionics system, it is known to use several redundant acquisition systems with a lower criticality level, for example DAL B. Different voting systems may next be applied by the avionics system to choose the majority value from among all of the values delivered by these redundant acquisition systems. 
         [0017]    Furthermore, to avoid aging of these systems, their criticality level is often oversized in production, which makes it possible to ensure their proper operation over the entire operating period despite any aging. 
         [0018]    One can then see that this results in a certain number of drawbacks, which include electricity consumption, bulk, complexity, weight and high costs of these acquisition systems. 
         [0019]    Furthermore, the existing acquisition systems often have limited abilities to detect flaws in their operation and make it possible to detect only sudden flaws of the straightforward failure type. 
       SUMMARY 
       [0020]    The present invention aims to provide an acquisition system resolving these drawbacks and having higher capacities for detecting flaws in its operation. 
         [0021]    To that end, the present invention relates to an acquisition system of the aforementioned type, further including means for analyzing the self-test result in order to determine a normal, downgraded or failure operating mode of the acquisition channel, and for activating the operation of means for correcting the digital signal delivered by the channel when the latter is in the downgraded operating mode. 
         [0022]    According to other advantageous aspects of the invention, the acquisition system comprises one or more of the following features, considered alone or according to all technically possible combinations:
       in the normal operating mode, the values of the accuracy losses of the acquisition channel belong to a first predetermined value range;   in the downgraded operating mode, the values of the accuracy losses of the acquisition channel belong to a second predetermined value range, each value of the second range being greater than each value of the first range and less than each value of a third predetermined value range;   in the failure operating mode, the values of the accuracy losses of the acquisition channel belong to the third value range;   the self-test means include a computing unit able to dynamically execute a reverse operating model of the acquisition channel, the reverse operating model being defined by a plurality of parameters and allowing the correction means to correct the digital signal delivered by the acquisition channel when the latter is in the downgraded operating mode;   it is able to deliver at least one original digital signal corresponding to the digital signal delivered by the acquisition channel, a status signal generated by the analysis means and indicating the current operating mode of the acquisition channel, and a digital signal with compensation generated by the correction means and corresponding to the digital signal delivered by the acquisition channel and corrected by these correction means;   the self-test means further include a storage unit able to store a database including the parameters of the reverse operating model;   the parameters of the reverse operating model are computed dynamically;   the reverse operating model further makes it possible to compute, for a reference digital signal, a reference analog signal, to inject it into the acquisition channel;   the self-test means include a storage unit able to store a database including digital reference signals and analog reference signals, each digital reference signal being associated with an analog reference signal able to be injected into the acquisition channel;   the self-test means further include a unit for comparing a digital test signal delivered by the acquisition channel and corresponding to said analog reference signal injected into the acquisition channel, with said digital reference signal;   it further includes learning means able to calibrate the parameters of the reverse operating model, in the downgraded operating mode of the acquisition channel;   the correction means are able to correct the delivered digital signal, from parameters of the reverse operating model calibrated by the learning means;   the self-test means, the analysis means, the correction means and the learning means are integrated at least partially into a single component; and   the single component is situated near the sensor.       
 
         [0037]    The present invention also relates to a method for the acquisition of at least one physical variable, implemented by the acquisition system as defined, comprising an acquisition phase including the following steps:
       the sensor measures a physical variable;   an analog signal corresponding to the measured physical variable is injected into the acquisition channel;   the acquisition channel converts the analog signal into a digital signal;   the digital signal is delivered.       
 
         [0042]    According to other advantageous aspects of the invention, the acquisition method comprises one or more of the following features, considered alone or according to all technically possible combinations:
       it further comprises a self-test phase including the following steps: a digital reference signal is developed; the reverse operation model converts the digital reference signal into an analog reference signal; this analog reference signal is injected into the acquisition channel; the acquisition channel converts this analog reference signal into a digital test signal; the comparison unit compares the additional test signal to the digital reference signal; and an operating mode of the acquisition channel is determined from among the normal, downgraded or failure operating modes;   it further comprises a learning phase including the following steps: the self-test phase is applied for a minimal digital reference signal and for a maximal digital reference signal to determine the losses of accuracy on each of these digital reference signals, and the learning means calibrate a new set of parameters for the reverse operating model of the acquisition channel;   it further comprises a compensation phase including the following steps: the digital signal delivered by the acquisition channel is converted into an analog signal with compensation by the reverse operating model calibrated with the new set of parameters, and the analog signal with compensation is converted into a digital signal with compensation by the correction means.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0046]    These features and advantages of the invention will appear more clearly upon reading the following description, provided solely as a non-limiting example, and done in reference to the appended drawings, in which: 
           [0047]      FIG. 1  is a diagrammatic view of an acquisition system according to the invention; 
           [0048]      FIG. 2  is a flowchart of a phase for the acquisition of a physical variable implemented in an acquisition method according to the invention; 
           [0049]      FIG. 3  is a flowchart of a self-test phase implemented in the method of  FIG. 2 ; 
           [0050]      FIG. 4  is a flowchart of a learning phase implemented in the method of  FIG. 2 ; 
           [0051]      FIG. 5  is a flowchart of a compensation phase implemented in the method of  FIG. 2 ; and 
           [0052]      FIG. 6  is a diagram illustrating different operating modes of the system of  FIG. 1  based on its aging. 
       
    
    
     DETAILED DESCRIPTION 
       [0053]      FIG. 1  indeed shows a system for the acquisition of at least one physical variable according to the invention. In this  FIG. 1 , the acquisition system is designated by general reference  10 . 
         [0054]    This acquisition system  10  is for example usable in on-board avionics systems in an aircraft. The acquisition system  10  thus meets a certain criticality level, for example criticality level DAL A. 
         [0055]    Of course, the acquisition system  10  can be used in many other technical fields, which include the automobile, railroad, aerospace, etc. fields. 
         [0056]    The system  10  for example includes a sensor for measuring the physical variable and able to emit an analog signal SA corresponding to the physical variable. In  FIG. 1 , this sensor is designated by general reference  12 . 
         [0057]    The measured physical variable is for example the temperature outside the aircraft or the position of a flight control surface. Thus, in this case, the analog signal SA for example corresponds to a resistance value emitted by the sensor  12 . 
         [0058]    The system  10  further includes an acquisition channel connected to the sensor  12  and able to receive the analog signal SA emitted by the sensor  12  to convert it into a digital signal SN. In  FIG. 1 , the acquisition channel is designated by general reference  14 . 
         [0059]    Thus, this digital signal SN is for example delivered to an onboard computer connected to the acquisition channel  14  and allowing suitable processing of this signal. In  FIG. 1 , this computer is then designated by general reference  16 . 
         [0060]    As is known in itself in the state of the art, the conversions of the analog signal SA into a digital signal SN can be done with potential losses of accuracy. 
         [0061]    The system  10  further includes self-test means for checking the integrity of the acquisition channel  14 , means for analyzing the results of this verification, means for correcting the digital signal delivered by the acquisition channel  14  and means for calibrating the self-test means. 
         [0062]    In  FIG. 1 , these means are respectively designated by general references  18 ,  20 ,  22  and  24 . 
         [0063]    Furthermore, these means  18 ,  20 ,  22  and  24  are at least partially integrated into a single component designated by general reference  26  in  FIG. 1 . 
         [0064]    The single component  26  is for example situated in the immediate vicinity of the sensor  12 . 
         [0065]    The self-test means  18  make it possible to verify the integrity of the acquisition channel  14  by injecting an analog reference signal SA R  therein and comparing a digital test signal SN T  delivered by the acquisition channel  14  and corresponding to this analog reference signal SA R , with the original signal. 
         [0066]    To that end, the self-test means  18  includes a storage unit, a computing unit and a comparison unit respectively designated by general references  30 ,  32  and  34  in  FIG. 1 . 
         [0067]    A computing unit  32  is able to dynamically execute a reverse operating model of the acquisition channel  14  making it possible to model the operation of the acquisition channel  14  to check its integrity. 
         [0068]    The reverse operating model is defined by a plurality of parameters from a database provided to that end and stored in the storage unit  30 . 
         [0069]    These parameters are computed dynamically by the computing unit  30  and at least partially describe the operation of the acquisition channel  14 . 
         [0070]    Thus, the reverse operating model further makes it possible to compute, from a reference digital signal SN R , a reference analog signal SA R , to inject this analog signal into the acquisition channel  14 . 
         [0071]    According to another alternative embodiment, the digital reference signal SN R  and analog reference signal SA R  pair for example comes from a database stored in the storage unit  30 . 
         [0072]    According to still another alternative embodiment, the digital reference signal SN R  corresponds to a digital signal SN previously acquired by the acquisition channel  14 . 
         [0073]    The comparison unit  34  then makes it possible to compare the digital test signal SN T  delivered by the acquisition channel  14  with the original digital reference signal SNR of this test signal. 
         [0074]    The comparison unit  34  further makes it possible to generate a result of this comparison and deliver it to the analysis means  20 . 
         [0075]    This comparison result for example corresponds to losses of accuracy between the digital test signal SN T  and the original digital reference signal SN R  of this test signal. 
         [0076]    Based on the result of the comparison, the analysis means  20  make it possible to determine an operating mode for the acquisition channel  14  between a normal, downgraded or failure operating mode. 
         [0077]    Thus, in the normal operating mode, the values of the accuracy losses of the acquisition channel  14  belong to a first predetermined value range [V 1 , V 2 ]. 
         [0078]    In this operating mode, the losses of accuracy in the acquisition channel  14  do not affect the operation of the system  10 . 
         [0079]    In the downgraded operating mode, the values of the accuracy losses of the acquisition channel  14  belong to a second predetermined value range ]V 2 , V 3 ]. 
         [0080]    Each value of the second range ]V 2 , V 3 ] is greater than each value of the first range [V 1 , V 2 ] and less than each value of a third predetermined value range ]V 3 , V 4 ]. 
         [0081]    Thus, in this operating mode, the losses of accuracy in the acquisition channel  14  affect the operation of the system  10 , but are tolerated. 
         [0082]    Lastly, in the failure operating mode, the values of the accuracy losses of the acquisition channel  14  belong to the third value range ]V 3 , V 4 ]. 
         [0083]    This means that in the failure mode, the losses of accuracy in the acquisition channel  14  are not tolerated and the acquisition system  10  is fully recognized as having failed. 
         [0084]    The analysis means  20  are also able to send a status signal SE to the computer  16 , indicating the current operating mode of the acquisition channel  14 . 
         [0085]    When the acquisition channel  14  is in the downgraded or failure operating mode, the reverse operating model allows the correction means  22  to correct the digital signal SN delivered by the acquisition channel  14 . 
         [0086]    Furthermore, in the downgraded or failure operating mode, the learning means  24  are able to calibrate the parameters of the reverse operating model by minimizing the accuracy losses between the digital test signals SN T  and the digital reference signals SN R  corresponding to these test signals. 
         [0087]    Thus, the correction means  22  are able to generate a digital signal with compensation SN C  corresponding to an analog signal with compensation SA C  computed from the digital signal SN delivered by the acquisition channel  14  and corrected using the recalibrated reverse operating model. This digital signal with compensation SN C  is for example delivered to the computer  16 . 
         [0088]    This more particularly makes it possible to adapt these parameters to the aging of the acquisition channel  14 . 
         [0089]    One can then see that based on the results of this calibration, the analysis means  20  can change the downgraded operating mode to the normal operating mode or the failure operating mode to the downgraded operating mode. 
         [0090]    It is also clear that the correction means  22  can correct the delivered digital signal, from parameters of the reverse operating model calibrated by the learning means  24 . 
         [0091]    A method  50  for the acquisition of at least one physical variable, implemented by the acquisition system  10 , will now be explained in reference to  FIGS. 2 to 5 . 
         [0092]    This method  50  comprises an acquisition phase P 1 , a self-test phase P 2 , a learning phase P 3  and a compensation phase P 4 . 
         [0093]    A flowchart of the acquisition phase P 1  of the method  50  is shown in  FIG. 2 . 
         [0094]    Thus, according to this flowchart, during an initial step  51  of the phase P 1 , the sensor  12  measures the physical variable and generates an analog signal SA corresponding to the measured value. 
         [0095]    During a following step  53 , the sensor  12  injects the generated analog signal SA into the acquisition channel  14 . 
         [0096]    During a following step  55 , the acquisition channel  14  converts this analog signal SA into a digital signal SN. 
         [0097]    Lastly, during a final step  57 , the acquisition channel  14  delivers the converted digital signal SN to the computer  16 . 
         [0098]    A flowchart of the self-test phase P 2  of the method  50  is shown in  FIG. 3 . 
         [0099]    Thus, according to this flowchart, during an initial step  61  of the phase P 2 , the self-test means  18  develop a digital reference signal SN R  as previously indicated. 
         [0100]    During a following step  63 , the self-test means  18  convert this digital reference signal SN R  into an analog reference signal SA R  by applying the reverse operating model. 
         [0101]    During a following step  65 , the self-test means  18  inject this analog reference signal SA R  into the acquisition channel  14 . 
         [0102]    During a following step  67 , the acquisition channel  14  converts this analog reference signal SA R  into a digital test signal SN T  and delivers this test signal to the self-test means  18 . 
         [0103]    During a following step  69 , the self-test means  18 , and in particular the comparison unit  34 , compare the digital test signal SN T  with the corresponding digital reference signal SN R  and communicate the result of this comparison to the analysis means  20 . This result for example corresponds to losses of accuracy between the two signals. 
         [0104]    During a following step  71 , the analysis means  20  determine an operating mode for the acquisition channel  14  from among the normal, downgraded or failure operating modes. 
         [0105]    Lastly, during a final step  73 , the analysis means  20  send a status signal SE indicating the current operating mode of the acquisition channel  10  to the computer  16 . 
         [0106]    The learning phase P 3  of the method  50  can be launched after the self-test phase P 2 . 
         [0107]    A flowchart of the learning phase P 3  of the method  50  is shown in  FIG. 4 . 
         [0108]    Thus, according to this flowchart, during an initial step  81  of the phase P 3 , the learning means  24  develop a minimal digital reference signal SN R  min and a maximal digital reference signal SN R  max. 
         [0109]    During a following step  83 , a self-test sequence repeating steps  63  to  69  of the self-test phase P 2  is launched to determine the losses of accuracy on each digital reference signal SN R  min and SN R  max. 
         [0110]    During a final step  85 , the learning means  24  calibrate the parameters of the reverse operating model of the acquisition channel  14  to minimize the accuracy losses. 
         [0111]    The compensation phase P 4  of the method  50  can be launched after the learning phase P 3 . 
         [0112]    A flowchart of the compensation phase P 4  of the method  50  is shown in  FIG. 5 . 
         [0113]    Thus, according to this flowchart, during an initial step  91  of phase P 4 , the correction means  22  convert the digital signal SN delivered by the acquisition channel  14  into an analog signal with compensation SA C  by the reverse operating model calibrated with the new parameters. 
         [0114]    During a following step  93 , the correction means  22  convert the analog signal with compensation SA C  into a digital signal with compensation SN C  by applying a normal operating model of the acquisition system with the initial parameters. 
         [0115]    Lastly, during a final step  95 , the correction means  22  deliver the digital signal with compensation SN C  to the computer  16 . 
         [0116]    A diagram illustrating the accuracy losses in the acquisition channel  14  based on the aging of the acquisition system  10  is shown in  FIG. 6 . 
         [0117]    Thus, as illustrated in this  FIG. 6 , initially the accuracy losses are minimal and the acquisition channel  14  is in the normal operating mode. 
         [0118]    In this operating mode, the self-test phase P 2  follows the acquisition phase P 1  to evaluate the accuracy losses. 
         [0119]    When these losses exceed the threshold V 2 , the analysis means  20  activate the downgraded operating mode. 
         [0120]    In this operating mode, the learning P 3  and compensation P 4  phases are respectively launched to calibrate the parameters of the reverse operating model of the acquisition channel  14  and to correct the delivered digital signal. 
         [0121]    If, after the learning phase P 3 , the accuracy losses are below the threshold V 2 , the analysis means  20  activate the normal operating mode. Otherwise, the acquisition channel  14  continues to operate in the downgraded operating mode. 
         [0122]    When the accuracy losses exceed the threshold V 3 , the analysis means  20  activate the failure operating mode and the learning P 3  and compensation P 4  phases are launched again. 
         [0123]    If, after the learning phase P 3 , the accuracy losses are below the threshold V 3 , the analysis means  20  activate the downgraded operating mode. Otherwise, the acquisition channel  14  continues to operate in the failure operating mode and the entire system  10  is therefore recognized by the computer  16  as having failed. 
         [0124]    Of course, other embodiments and examples of the acquisition system and the associated method can also be considered. 
         [0125]    One can then see that the present invention has a certain number of advantages. 
         [0126]    The acquisition system according to the invention takes into account the aging of the acquisition channel and thus adapt its self-test means. 
         [0127]    This then makes it possible to model this acquisition system based on its actual criticality level at the beginning of its lifetime without needing to oversize it. 
         [0128]    Thus, the acquisition system according to the invention is less bulky, simpler and more compact to operate relative to the acquisition systems of the state of the art. 
         [0129]    Furthermore, the acquisition system according to the invention makes it possible to detect flaws in its operation effectively.