(19)
(11)EP 2 619 528 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
10.06.2020 Bulletin 2020/24

(21)Application number: 11767802.9

(22)Date of filing:  13.09.2011
(51)International Patent Classification (IPC): 
G01D 3/032(2006.01)
G01D 5/244(2006.01)
(86)International application number:
PCT/IT2011/000319
(87)International publication number:
WO 2012/038995 (29.03.2012 Gazette  2012/13)

(54)

SYSTEM AND PROCESS FOR DETERMINING OFFSETS OF MEASURING INSTRUMENTS

SYSTEM UND VERFAHREN ZUR BESTIMMUNG VON MESSINSTRUMENTFEHLERN

SYSTÈME ET PROCÉDÉ DÉTERMINATION DE DÉCALAGES D'INSTRUMENTS DE MESURES


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 20.09.2010 IT TO20100764

(43)Date of publication of application:
31.07.2013 Bulletin 2013/31

(73)Proprietor: PSC Engineering S.r.l.
10146 Torino (IT)

(72)Inventor:
  • CRUPI SANTINO
    I-10146 TORINO (IT)

(74)Representative: Garavelli, Paolo 
A.BRE.MAR. S.R.L. Consulenza in Proprietà Industriale Via Servais 27
10146 Torino
10146 Torino (IT)


(56)References cited: : 
US-A1- 2004 210 411
US-A1- 2010 164 425
US-A1- 2009 121 769
US-B1- 6 498 409
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description


    [0001] The present invention refers to a system for determining offsets (bias) of measuring instruments (included electronic adaptation and interface), with measures with null or constant mean value. The present invention is applicable to all sensors, complete of electronic interfacing, used to measure variations of one physical phenomenon: there is a steady state condition and a variation respect to this condition. When the interest is the real value of physical phenomena, it is necessary to use a sensor with adequate absolute precision; it is not possible to subtract bias (offsets). If the interest is the variation respect to the steady state value, it is possible to estimate offsets and to apply the present invention. It is known that the physical phenomena moves with respect to a constant mean value allow the estimation of offsets (bias) and the measure, with the presented method, of physical phenomena with very high precision (higher sensors used). The present invention further refers to a process for determining offsets of measuring instruments through a system according to the present invention. It is applicable to the following sensors: linear or angular position, speed and acceleration sensors, pressure, temperature, rate of flow, heading, etc. to measure the variation with very high resolution or with a precision better than the original physical sensor. The method allows estimating total bias (due to sensor, its physical arrangement and its conditioning and adapting electronic circuits)
    As known, any measuring instrument or sensor is substantially affected by an offset composed of two types of errors:
    • systematic measuring errors, constant and dependent from the physical principle used and the sensibility of the instrument or sensor itself;
    • slowly-varying errors, dependent from environmental and use conditions in which the instrument or sensor has to operate, such as for example temperature, pressure, humidity, instrument and electronic ageing, height variation on sea level (for accelerometers measure), etc.


    [0002] When measures performed by the measuring instrument have a null or constant mean value, or point out the difference with respect to a fixed position, it is possible to determine the measuring error rather accurately, and thereby clean the measure itself from the global error, as sum of fixed and slowly-varying errors with respect to the dynamics of the system to which it is applied.

    [0003] In particular, for example, it is also known in the art that angular speed sensors have a particularly important role in stabilisation systems for roll and pitch in boats and other different systems, since the rolling speed has a major weight on the efficiency of adjustments through fins. In order to be able to use sensors with acceptable costs, currently angular speed sensors are used with a ±50°/s full scale, while the working range for measures is on the maximum order of magnitude of 2 or 3°/s. Every sensor therefore has a systematic error and a slowly-varying error that depends on environmental temperature, ageing, and other above-mentioned conditions: this error is typically on the order of 1%. In this case the measuring error is of the same order of magnitude of the amount that has to be measured, and it would therefore be essential to clean the sensor from fixed and (slowly with respect to the phenomenon that has to be detected) varying errors automatically, and obtain a measure with a better accuracy than the one obtained by the pure sensor. However, without the estimation and subtraction of this error, it is not possible to use the sensor importantly and with relevant efficiency with respect to other measures and, consequently, the regulating systems, in which the sensor is used, cannot have relevant performances.

    [0004] Similar example is the problem of estimation of the vertical movement of an object. To make a good estimation of vertical movement is necessary to extract the bias of accelerometer measure; this is possible, with the present invention, with the estimation and subtraction of the bias. The offset of accelerometers changes with temperature, sensor ageing, height respect the sea level, etc. The present invention allows the correct calculation of bias and its subtraction.

    [0005] Documents US-A1-2004/210411, US-A1-2010/164425, US-B1-6 498 409 and US-A1-2009/121769 disclose systems according to the preamble of claim 1.

    [0006] Therefore, object of the present invention is solving the above prior art problems by providing a system and a process for determining offsets of measuring instruments, with measures with a null or constant mean value, that allow measuring the systematic errors depending from environmental conditions and sensor ageing.

    [0007] Another object of the present invention is providing a system and a process for determining offsets of measuring instruments, with measures with a null or constant mean value, that can be applied to any type of measure, such as linear and angular speed measures, linear and angular acceleration, in which it is necessary to remove the constant error part (gravity acceleration, for accelerometers), and/or the slowly-varying error part (due to temperature variation, pressure, sensor ageing, etc.) in any sensor, including those used on board ships.

    [0008] Moreover, an object of the present invention is providing a system and a process for determining offsets of measuring instruments, with measures with a null or constant mean value, that can be applied in applications in which the sensors are used, as working range of the measure, in the instrument error range (a few percentage units).

    [0009] The above and other objects and advantages of the invention, as will appear from the following description, are obtained with a system for determining offsets of measuring instruments, with measures with a null or constant mean value, as claimed in claim 1.

    [0010] Moreover, the above and other objects and advantages of the invention are obtained with a process for determining offsets of measuring instruments, with measures with a null or constant mean value, as claimed in claim 2.

    [0011] It will be immediately obvious that numerous variations and modifications (for example related to shape, sizes, arrangements and parts with equivalent functionality) can be made to what is described, without departing from the scope of the invention as defined in the enclosed claims.

    [0012] The present invention will be better described by some preferred embodiments thereof, provided as a non-limiting example, with reference to the single enclosed drawing, in which Figure 1 is a block diagram showing a preferred embodiment of the system according to the present invention.

    [0013] With reference to Figure 1, it is possible to note that the system 1 for determining offsets of measuring instruments, in particular of measures with a null or constant mean value, according to the present invention, is composed of:
    • first processing means 3 adapted to compute, from at least one value of a measuring signal S deriving from an instantaneous measure performed by at least one measuring instrument or a sensor (not shown), at least one offset value δ of such signal S; and
    • second processing means 5 adapted to subtract such offset value δ from the value of the instantaneous measuring signal S to obtain a corrected measure value S-δ of such signal S, therefore cleaned from the offset δ, and that can be possibly used for further processing.


    [0014] In the system 1 according to the present invention, the measuring error or the offset value δ is determined by computing a moving, possibly weighted, mean, and with an adequate number of samples, of the value of the measuring signal S: in such case, the first processing means 3 therefore comprise means for computing a moving mean of the measuring signal S value to determine such offset value δ.

    [0015] The first processing means 3 comprise at least any one numeric low-pass filter, of the FIR (Finite Impulse Response) or IIR (Infinite Impulse Response) type or equivalent function implemented by PLC or by analogical circuit, adapted to determine such offset value δ from the measuring signal S value.

    [0016] The first processing means 3 comprise at least any one analogue low-pass filter (of o a more or less high order), made as a circuit or through preset equivalent functions implemented by PLC, adapted to determine such offset value δ from the measuring signal S value.

    [0017] The filter included in the first processing means 3 must have, among possible other components, a strong low-pass component with cutting frequency much lower than the useful band of the signal S. For naval applications to stabilise the roll, the filter cutting frequency is on the order of magnitude of 10 minutes): in particular, it must be noted that if the filter included in the first processing means 3 is applied to a sensor such as an accelerometer without subtracting the gravity acceleration, it is able to estimate and subtract the constant and slowly-varying components, including the gravity acceleration variation depending on the height from the sea level (for aeronautical applications).

    [0018] The present invention further refers to a process for determining offsets of measuring instruments, with measures with a null or constant mean value and using a system 1 as previously described. The process according to the present invention then comprises the steps of:
    1. a) detecting at least one value of a measuring signal S deriving from an instantaneous measure performed by at least one measuring instrument or a sensor (not shown), computing a moving, possibly weighted, mean with an adequate number of samples, of the value of the measuring signal S, for example through the means for computing a moving, possibly weighted, mean, of the first processing means 3 of the system 1 according to the present invention;
    2. b) computing from such measuring signal S value at least one offset value δ of such signal S; and
    3. c) subtracting such offset value δ from the instantaneous measuring signal S value to obtain a corrected measure value S-δ of such signal S: such step is performed through the second processing means 5 of the system 1 according to the present invention.


    [0019] Alternatively, the step of computing can be performed by any numeric low-pass filter, of the FIR (Finite Impulse Response), IIR (Infinite Impulse Response) type or an analogue low-pass filter of with an equivalent function implemented by PLC of the first processing means 3 of the system 1 according to the present invention.

    [0020] Obviously, the system 1 and the process according to the present invention as previously described can be applied to all types of sensors: linear or angular position, speed and acceleration sensors, pressure, temperature, rate of flow, heading, etc. in any application where their use is necessary.


    Claims

    1. System (1) for determining and subtracting offsets (δ) of measuring instruments and instrumentations for naval applications to stabilise roll, said system (1) being composed of:

    - first processing means (3) adapted to compute, from at least one value of a measuring signal (S) deriving from an instantaneous measure performed by at least one of said measuring instruments or a sensor, at least one offset value (δ) of said signal (S); and

    - second processing means (5) adapted to subtract said offset value (δ) from said value of said instantaneous measure signal (S) to obtain a corrected measure value (S-δ) of said signal (S),

    wherein said measuring instruments are adapted to perform measures with a null or constant mean value, measuring the systematic errors depending from environmental conditions and ageing of the measuring sensors, said first processing means (3) comprising means for computing a moving, possibly weighted, mean, of said value of said measuring signal (S) to determine said offset value (δ),
    wherein said first processing means (3) comprise at least one low-pass filter, said low-pass filter being a numeric low-pass filter of the FIR (Finite Impulse Response) or IIR (Infinite Impulse Response) type or an analogue low-pass filter or a filter with equivalent function implemented by a PLC adapted to determine said offset value (δ) from said value of said measuring signal (S), said low-pass filter further having a strong low-pass component with cutting frequency much lower than a useful band of the signal (S), characterized in that a cutting frequency of said filter being on the order of magnitude of 1/600 Hz with time constants on the order of 10 minutes.
     
    2. Process for determining and subtracting offsets (δ) of measuring instruments for naval applications to stabilise roll, adapted to perform measures with a null or constant mean value through a system (1) according to claim 1, characterised in that it comprises the steps of:

    a) detecting at least one value of a measuring signal (S) deriving from an instantaneous measure performed by at least one measuring instrument or a sensor, computing a moving, possibly weighted, mean, of said value of said measuring signal (S), through said means for computing a moving, possibly weighted, mean of said first processing means (3) of said system (1);

    b) computing from said value of said measuring signal (S) at least one offset value (δ) of said signal (S); and

    c) subtracting said offset value (δ) from said value of said instantaneous measure signal (S) to obtain a corrected measure value (S-δ) of said signal (S).


     


    Ansprüche

    1. System (1) zur Bestimmung und Subtraktion der Abdriften (Offset) (δ) mit Messgeräten und einer Instrumentenausrüstung für Anwendungen in der Schifffahrt für die Stabilisierung von Rollbewegungen, das genannte System (1) ist folgendermaßen zusammengesetzt:

    - erste Verarbeitungsgeräte (3), die dazu dienen, aus mindestens einem Wert eines Messsignals (S), der aus einer sofortigen Messung erhalten wird, die durch mindestens eines der Messgeräte oder durch einen Sensor ausgeführt wurde, mindestens einen Abdriftwert (Offset) (δ) des genannten Signals (S) zu berechnen; und

    - zweite Verarbeitungsgeräte (5), die dazu dienen, den genannten Abdriftwert (Offset) (δ) aus dem genannten Wert des genannten sofortigen Messsignals (S) zu subtrahieren, um einen korrekten Messwert (S-δ) des genannten Signals (S) zu erhalten,

    in dem die genannten Messgeräte dazu dienen, Messungen mit einem Durchschnittswert null oder einem konstanten Durchschnittswert auszuführen, indem die systematischen Fehler je nach den Umgebungs- und Alterungsbedingungen der Messsensoren gemessen werden, die genannten ersten Verarbeitungsgeräte (3) enthalten Geräte für die Berechnung eines gleitenden, ggf. gewogenen Durchschnitts des genannten Wertes des genannten Messsignals (S), um den genannten Abdriftwert (Offset) (δ) zu bestimmen,
    in dem die genannten ersten Verarbeitungsgeräte (3) mindestens einen Tiefpassfilter enthalten, der genannte Tiefpassfilter ist ein numerischer FIR- (Finite Impulse Response) oder IIR-Tiefpassfilter (Infinite Impulse Response) oder ein analoger Tiefpassfilter oder ein Filter mit einer gleichwertigen Funktion, die durch PLC implementiert wird, die dazu dient, den genannten Abdriftwert (Offset) (δ) aus dem genannten Wert des genannten Messsignals (S) zu bestimmen, der genannte Tiefpassfilter hat außerdem eine starke Tiefpasskomponente mit sehr viel niedrigerer Schnittfrequenz als das nutzbare Signalband (S), und ist dadurch gekennzeichnet, dass eine Schnittfrequenz des genannten Filters in der Größenordnung von 1/600 Hz mit Zeitkonstanten in Höhe von 10 Minuten liegt.
     
    2. Verfahren zur Bestimmung und Subtraktion der Abdriften (Offset) (δ) von Messgeräten für Anwendungen in der Schifffahrt für die Stabilisierung von Rollbewegungen, das dazu dient, Messungen mit Durchschnittswert null oder mit konstantem Durchschnittswert durch ein System (1) gemäß Patentanspruch 1 auszuführen, das dadurch gekennzeichnet ist, dass es folgende Phasen enthält:

    a) Erfassung von mindestens einem Wert eines Messsignals (S), der aus einer sofortigen Messung erhalten wird, die durch mindestens eines der Messgeräte oder durch einen Sensor ausgeführt wurde, Berechnung eines gleitenden, ggf. gewogenen Durchschnitts des genannten Wertes des genannten Messsignals (S) durch die genannten Geräte für die Berechnung eines gleitenden, ggf. gewogenen Durchschnitts der genannten ersten Verarbeitungsgeräte (3) des genannten Systems (1);

    b) Berechnung des genannten Wertes des genannten Messsignals (S) von mindestens einem Abdriftwert (Offset) (δ) des genannten Signals (S); und

    c) Subtraktion des genannten Abdriftwertes (Offset) (δ) aus dem genannten Wert des genannten sofortigen Messsignals (S), um einen korrekten Messwert (S-δ) des genannten Signals (S) zu erhalten.


     


    Revendications

    1. Système (1) de détermination et soustraction de dérives (offset) (δ) d'instruments et d'appareils de mesure pour des applications navales afin de stabiliser le roulis ; le système (1) est composé de :

    - premiers moyens d'élaboration (3) aptes à calculer, à partir au moins d'une valeur d'un signal de mesure (S) dérivant d'une mesure instantanée effectuée par au moins l'un des instruments de mesure ou un capteur, au moins une valeur de dérive (offset) (δ) du signal (S) ; et

    - seconds moyens d'élaboration (5) aptes à soustraire la valeur de dérive (offset) (δ) à la valeur du signal de mesure (S) instantanée pour obtenir une valeur de mesure correcte (S-δ) du signal (S),

    où les instruments de mesure sont aptes à exécuter des mesures avec une valeur moyenne nulle ou constante, en mesurant les erreurs systématiques selon les conditions environnementales et un vieillissement des capteurs de mesure ; les premiers moyens d'élaboration (3) comprennent des moyens pour calculer une moyenne mobile, éventuellement pesée, de la valeur du signal de mesure (S) pour déterminer la valeur de dérive (offset) (δ),
    où les premiers moyens d'élaboration (3) comprennent au moins un filtre passe-bas numérique de type FIR (Finite Impulse Response) ou IIR (Infinité Impulse Response) ou bien un filtre passe-bas analogique ou un filtre ayant une fonction équivalente implémentée par un Automate (PLC) apte à déterminer la valeur de dérive (offset) (δ) à partir de la valeur du signal de mesure (S) ; le filtre passe-bas possède par ailleurs une forte composante passe-bas à fréquence de coupure très basse de la bande utile du signal (S), caractérisé en ce qu'une fréquence de coupure du filtre est l'ordre de grandeur de 1/600 Hz avec des constantes de temps de l'ordre de 10 minutes.
     
    2. Procédure de détermination et soustraction de dérives (offset) (δ) d'instruments de mesure pour les applications navales afin de stabiliser le roulis, apte à exécuter des mesure en valeur moyenne nulle ou constante à travers un système (1) selon la revendication 1, caractérisé en ce qu'il comprend les phases suivantes :

    a) relever au moins une valeur d'un signal de mesure (S) dérivant d'une mesure instantanée effectuée au moins par un instrument de mesure ou un capteur, en calculant une moyenne mobile, éventuellement pesée, de la valeur du signal de mesure (S), à travers les moyens de calcul d'une moyenne mobile, éventuellement pesée, des premiers moyens d'élaboration (3) du système (1) ;

    b) calculer à partir de la valeur du signal de mesure (S) au moins une valeur de dérive (offset) (δ) du signal (S) ; et

    c) soustraire cette valeur de dérive (offset) (δ) à la valeur du signal de mesure (S) instantanée pour obtenir une valeur de mesure correcte (S-δ) du signal (S).


     




    Drawing








    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description