DE102010029903A1 - Sensor arrangement for detecting e.g. pressure of micro electromechanical system of motor car, has sensor for detecting physical quantity, and device for online monitoring sensitivity of arrangement - Google Patents

Abstract

The arrangement (10) has a sensor (12) for detecting a physical quantity. A converter (14) transforms a physical input into voltage. An analog/digital (A/D) converter (16) produces a digital sensor output signal. A device (18) online monitors sensitivity of the arrangement. A stimulus generator (20) generates sensitivity of a stimulus. A stimulus passport filter (24) provides a stimulus filter output signal. A multiplier (28) multiplies the stimulus filter output signal with a correlation signal. A stimulus band elimination filter is placed between the A/D converter and an evaluation unit. An independent claim is also included for a method for online monitoring of a sensor arrangement.

Description

State of the art

The invention is based on an on-line monitoring sensor arrangement having a sensor for receiving a physical input variable, a converter for converting the physical variable into a voltage, and an A / D converter for generating a digital sensor output signal.

Sensor systems used in safety-critical applications such. B. in a motor vehicle in ESP and ABS, must be monitored to prevent malfunction and the resulting personal and economic damage. This is done with self-tests, which usually take place when the sensor arrangement is switched on with the initialization of the sensor.

The WO2005083449 describes a micromechanical sensor arrangement and a method for a continuous self-test of the sensor arrangement. The sensor detects a parameter to be measured for an excitation and receives an externally generated stimulation in a frequency range higher than the expected measurement signals. The sensor generates a sensor output signal which is a combination of a measurement signal due to the excitation and a test signal due to the stimulation. A low-pass filter separates the measurement signal from the sensor output signal, while an external test device compares the sensor output signal with an expected signal and generates a self-test signal with the result of the comparison. Thus, the function of the sensor arrangement can be monitored.

For digital electronic components, a self-test may occur during operation. The DE 10 2006 050 discloses a delta-sigma data converter arrangement with a delta-sigma modulator and a downstream filter device and a method for checking a delta-sigma data converter. A test signal generator generates an analog test signal, which can be given instead of an analog input signal by means of multiplexer to the input of the test signal generator. The test signal generator also generates a digital test signal which, instead of an output signal of the delta-sigma modulator, can be added thereto or given solely to the input of the filter device. The output signal of the delta-sigma data converter arrangement to the test signal is compared with a generated expected signal. Thus, the function of individual components of the delta-sigma data converter arrangement can be monitored during operation.

The described prior art devices and methods qualitatively monitor the function of the devices, but not sensitivity of the measurement system.

Disclosure of the invention

In contrast, a sensor arrangement and a method for online monitoring of a sensor arrangement according to the present invention have the advantage that even with a sensor during operation, a self-test can be carried out, without the intended measurement of the sensor is interrupted by a multiplexer. Thus transient errors generated by cosmic radiation, tip-over bits, are detectable. Another advantage of the invention is the recognizability of temperature-dependent permanent errors in the sensor, both in the analog operating electronic sensor front end and in the digital electronics of the evaluation. Another advantage of the present invention is the ability to monitor the sensitivity of the measuring system, i. H. What is the ratio between the output value and the input quantity in the sensor system at zero frequency. Changes in the frequency response of the system affect the sensitivity measurement only if the frequency response at zero frequency, the sensitivity, actually changes. Another advantage of the present invention is the utility of almost any test signal. The correlation function is not explicitly calculated, but the measured value of the sensitivity of the sensor arrangement is calculated directly from a combination of the sensor output signal with a reference sequence. Another advantage of the invention is the use of special filters that pass the relevant frequency components of the stimulus without change, but other frequencies, such. B. disturbances from the outside, suppress as well as possible.

Embodiments of the invention will be explained with reference to the drawings, in which

1 a schematic representation of a sensor arrangement according to an embodiment of the present invention;

2 a schematic representation of a sensor arrangement according to another embodiment of the present invention; and

3 a flowchart of the method according to an embodiment of the present invention;

1 shows a sensor arrangement 10 with on-line monitoring according to an embodiment of the present invention. A sensor 12 serves to detect a physical quantity e, z. B. way, pressure, force, acceleration. One from the sensor 12 Detected physical input is in an analog front end of a converter 14 converted into an electrical voltage. The converter 14 is with an A / D converter 16 connected, which converts the analog voltage into a digital signal y. This signal represents the physical input and can be output and processed externally.

The A / D converter 16 can be realized by a sigma-delta converter. In this case, the A / D conversion is followed by a digital decimation filter for bandwidth limitation and the decimation or sampling rate reduction, which in the A / D converter 16 can be integrated.

The sensor arrangement 10 also has a facility 18 continue to online for the sensitivity monitoring. The device 18 For online monitoring of sensitivity includes a stimulus generator 20 for generating a stimulus signal s with stimulus frequencies and one with the stimulus generator 20 connected coupling device 22 for coupling the stimulus signal s with the physical quantity e to be detected. The device 18 for on-line sensitivity monitoring further includes one with the A / D converter 16 connected stimulus-pass filter 24 for providing a stimulus-filter output passing stimulus frequencies, a stimulus-correlation reference signal generator 26 for providing a stimulus correlation reference signal r, a multiplier 28 which multiplies the stimulus filter output by the stimulus correlation reference signal and provides a correlation signal, and a mean value image 30 which averages the correlation signal and outputs as a sensitivity reading v _DC .

The sensor system can, for. B. represent a MEMS (micro electromechanical system) acceleration sensor; However, online monitoring can also be used for other sensor systems.

Online monitoring works with the stimulus generator 20 as follows. The stimulus generator 20 generates a periodic signal s. This can be done for example by calculating a digital signal or by reading a permanently stored in a memory signal. The periodic signal s is the measured variable to be measured in the coupling device 22 superimposed additively after D / A conversion. For example, in a micromechanical acceleration sensor, a structure of capacitor plates with an applied voltage can ensure that not only an external acceleration force F _b = a · m acts on a test mass m of the acceleration sensor, but that an electrostatic force F _{el is} superimposed on this force depicts the desired time course of s. Here a is the acceleration acting on the sensor. The sensor 12 detects a physical input in the form of a superposition of the physical quantity e and the stimulus signal s. This physical input is in an analog front end of a converter 14 converted into an electrical voltage. The converter 14 is with an A / D converter 16 connected, which converts the analog voltage into a digital signal y. After the A / D conversion, the signal y is available, which represents the response of the sensor system to the sum of the stimulus and the physical quantity e to be measured. The signal y represents the physical quantity e and can be output and further processed externally. The signal y also goes through a signal path for online monitoring, and first the stimulus pass filter 24 , which is sized to allow the stimulus-containing frequencies needed for online monitoring to pass without amplitude or phase change, but suppress other frequencies as well as possible.

The stimulus signal s is generated digitally; the output of the stimulus values is at the sampling rate f _{a of} the A / D converter 16 , The stimulus signal s has a stimulus length of N clocks and is repeated after the N clocks. As a rule, the stimulus signal s is chosen so that its frequency components do not disturb the actual measurement signal. The frequencies included in the periodic stimulus signal s are selected from a set of frequencies for which f _i = f _a * i / N where i = 0, ..., N / 2, where f _{a is} the sampling rate of the sensor array and N is the stimulus length in a number of measures. However, not every one of these theoretically possible frequencies has to be included. In general, one will want to avoid a permanent deflection of the sensor by the stimulus; this means that the stimulus should not contain the frequency 0 Hz (i = 0) and the stimulus signal s should be free of equal components.

The stimulus correlation reference signal generator 26 provides a stimulus correlation reference signal r corresponding to the output of a FIR filter into which a stimulus signal s is input. However, in this embodiment, the stimulus correlation reference signal r becomes the stimulus correlation reference signal generator 26 read from a memory in which it is stored permanently. At the output of the stimulus correlation reference signal generator 26 is the reference signal r available, which also has a period of N clocks.

The output signal yf of the stimulus-pass filter 24 is connected to the reference signal r in the multiplier 28 multiplied. The multiplier 28 provides a correlation signal as a result of the multiplication. This correlation signal forms the input signal of the mean value generator 30 which averages the correlation signal over an integer number p of periods and outputs as the sensitivity measurement value v _DC . The sensitivity reading v _DC can be used for monitoring purposes, e.g. B. is compared with limits. Is there an error in the sensor system, eg. B. Partial or total failure of a component, the measured value V _DC violate the specified limits and an alarm can be triggered.

2 shows a sensor arrangement 40 according to another embodiment of the present invention. Out 1 known elements of the sensor arrangement 10 have the same reference numbers and work as described there. The sensor arrangement 40 indicates in addition to the sensor arrangement 10 out 1 in the regular evaluation path on with the output of the A / D converter 16 connected stimulus-lock filter 42 and an evaluation unit connected to its output 44 on. The stimulus-lock filter 42 is dimensioned so that it does not transmit the frequencies present in the stimulus. It is used if otherwise a subsequent evaluation algorithm would be disturbed by the stimulus frequency components. In applications where the stimulus frequency components do not interfere, the stimulus-lock filter may be used 42 omitted. The evaluation unit 44 contains an evaluation algorithm, which evaluates the signal y and provides a measurement signal ya.

The sensor arrangement 40 indicates in addition to the sensor arrangement 10 out 1 still a changed facility 46 for online monitoring of sensitivity. The stimulus correlation reference signal generator 48 is now running as a FIR filter that works with the stimulus generator 20 is connected and in that of the stimulus generator 20 generated stimulus signal s is input. It also provides a stimulus correlation reference signal r having a period of N clocks.

The inventive dimensioning of the various filters will now be described in connection with the method according to the invention with reference to the sensor arrangements 1 and 2 ,

• a) Bereitstellen eines Stimulus-Signals mit Stimulus-Frequenzen. Dies geschieht mittels dem Stimulus-Generator 20. Die Stimulus-Frequenzen sind aus einer Menge Frequenzen gewählt, für die gilt f_i = f_a·i/N mit i = 1, ..., N/2, wobei f_a die Abtastrate der Sensoranordnung ist und N die Stimuluslänge in einer Anzahl Takte ist. Vorzugsweise beträgt die Anzahl der Stimulus-Frequenzen, die mit endlicher Amplitude im Stimulus-Signal vorhanden sind mindestens k/2, aufgerundet, wobei k die maximale Länge der Impulsantwort der Signalkette der Sensoranordnung ist. Für die Dimensionierung ist zunächst die Signalkette Sensor-Frontend-A/D-Wandler zu betrachten. Die Datenrate des A/D-Wandler-Ausgangs beträgt ebenso wie die Stimulus-Taktrate f_a. Die Signalkette besitzt eine Impulsantwort, deren Betrag nach k Takten der Abtastfrequenz f_a auf einen sehr kleinen Wert, z. B. 10^–5 abgeklungen ist. Dies gilt auch für den Fall, dass der A/D-Wandler aus einem Sigma-Delta-Wandler mit Dezimationsfilter und nachfolgender Dezimation der Abtastrate auf den Wert f_a aufgebaut ist. Der Wert k sollte so groß gewählt werden, dass auch zu erwartende Veränderungen der Impulsantwort der Signalkette mit einer Länge von k Takten mit abgedeckt sind. Somit hat die Impulsantwort der Signalkette eine Länge von maximal k Takten. Die Stimulus-Länge N wird so gewählt, dass die im Stimulus enthaltenen Frequenzen, insbesondere die Grundwelle f_a/N, die Funktion des regulären Auswertepfades nicht stört. Der zeitliche Verlauf des Stimulussignals s ist bei der beschriebenen Anordnung nahezu beliebig wählbar; es muss nur darauf geachtet werden, dass im Stimulus mindestens k/2, aufgerundet, Frequenzen vorhanden sind. Eine aufwandsarme Realisierung sieht einen binären Stimulus mit Werten +a bzw. –a vor. Obwohl beliebige Verläufe des Stimulus möglich sind, liefert ein einfaches Rechtecksignal mit N/2 Werten +a, gefolgt von N/2 Werten –a, besonders gute, rauscharme Ergebnisse.

3 shows a flowchart 50 the method according to the invention for the online monitoring of a sensor arrangement. The method is based on a sensor arrangement such as sensor arrangement 10 or 40 with a sensor 12 for receiving a physical input quantity, a converter 14 and an A / D converter 16 , The method for online monitoring of the sensitivity of the sensor arrangement begins with method step

• a) Provide a stimulus signal with stimulus frequencies. This is done by means of the stimulus generator 20 , The stimulus frequencies are selected from a set of frequencies for which f _i = f _a * i / N where i = 1, ..., N / 2, where f _{a is} the sampling rate of the sensor array and N is the stimulus length in one Number of bars is. Preferably, the number of stimulus frequencies present in finite amplitude in the stimulus signal is at least k / 2, rounded up, where k is the maximum length of the impulse response of the signal chain of the sensor array. For dimensioning, the signal chain sensor front-end A / D converter is to be considered first. The data rate of the A / D converter output is the same as the stimulus clock rate f _a . The signal chain has an impulse response whose magnitude after k clocking the sampling frequency f _a to a very small value, z. B. 10 ^{-5 has} subsided. This also applies to the case where the A / D converter is constructed from a sigma-delta converter with decimation filter and subsequent decimation of the sampling rate to the value f _a . The value k should be chosen so large that also expected changes in the impulse response of the signal chain with a length of k cycles are covered. Thus, the impulse response of the signal chain has a maximum length of k clocks. The stimulus length N is chosen so that the frequencies contained in the stimulus, in particular the fundamental wave f _a / N, does not interfere with the function of the regular evaluation path. The time profile of the stimulus signal s is almost arbitrary in the described arrangement; care must be taken that at least k / 2, rounded up, frequencies are present in the stimulus. A low-effort realization provides for a binary stimulus with values + a or -a. Although any waveforms of the stimulus are possible, a simple square-wave signal with N / 2 values + a, followed by N / 2 values -a, gives particularly good, low-noise results.

• b) Kopplung des Stimulus-Signals mit der physikalischen Eingangs-Größe. Das periodische Signal s wird der zu messenden Messgröße e in der Koppeleinrichtung 22 nach D/A-Wandlung additiv überlagert. Nun geschieht in Verfahrensschritt
• c) die Wandlung der physikalischen Größe in eine Spannung in dem Umformer 14. Es folgt Verfahrensschritt
• d) Erzeugung eines digitalen Sensor-Ausgangssignals y in dem A/D-Wandler 16. Das digitalen Sensor-Ausgangssignals y kann nun wie in Sensoranordnung 10 direkt oder wie in Sensoranordnung 40 über ein mit dem Ausgang des A/D-Wandlers 16 verbundenes Stimulus-Sperr-Filter 42 und/oder eine Auswerteeinheit 44 ausgegeben werden.

Now follows process step

• b) Coupling of the Stimulus Signal to the Physical Input Size. The periodic signal s becomes the measurand e to be measured in the coupling device 22 superimposed additively after D / A conversion. Now happens in process step
• c) the conversion of the physical quantity into a voltage in the converter 14 , It follows process step
• d) Generation of a digital sensor output signal y in the A / D converter 16 , The digital sensor output signal y can now be as in sensor arrangement 10 directly or as in sensor arrangement 40 via a to the output of the A / D converter 16 connected stimulus-lock filter 42 and / or an evaluation unit 44 be issued.

• f) Entfernen von Frequenzen die keine Stimulus-Frequenzen sind aus dem digitalen Sensor-Ausgangssignal und Bereitstellen eines gefilterten Sensor-Ausgangssignals in dem Stimulus-Pass-Filter 24. Das Stimulus-Pass-Filter 24 ist in der erfindungsgemäßen Anordnung so dimensioniert, dass es die im periodischen Referenzsignal r enthaltenen Frequenzen ohne Amplituden- oder Phasenänderung exakt durchlässt, und dass die Summe der Quadrate seiner Impulsantwort-Abtastwerte minimal wird. Dies bedeutet, dass ein Referenzsignal unverändert durchgelassen, andere Frequenzen jedoch maximal gedämpft werden. Die erreichbare Dämpfung hängt vom gewählten Grad des Filters ab.

In the facility 46 For online monitoring of the sensitivity is now process step

• f) removing frequencies that are not stimulus frequencies from the digital sensor output signal and providing a filtered sensor output signal in the stimulus pass filter 24 , The stimulus pass filter 24 is dimensioned in the arrangement according to the invention so that it accurately passes the frequencies contained in the periodic reference signal r without amplitude or phase change, and that the sum of the squares of its impulse response samples is minimal. This means that a reference signal is passed through unchanged, but other frequencies are maximally attenuated. The achievable damping depends on the selected degree of the filter.

• g) die Bereitstellung eines Stimulus-Korrelations-Referenzsignals im Stimulus-Korrelations-Referenzsignal-Generator 26 bzw. 48. Ist der Stimulusverlauf s_i, i = 0 ... (N – 1) ausgewählt, können die Koeffizienten des Filters G(z) berechnet werden. Zunächst wird die periodische Autokorrelationsfunktion ACF(n) des Stimulus berechnet
  
  und daraus eine Autokorrelationsmatrix gebildet, und diese invertiert:
  

It takes place in process step

• g) the provision of a stimulus correlation reference signal in the stimulus correlation reference signal generator 26 respectively. 48 , If the stimulus course s _i , i = 0 ... (N-1) is selected, the coefficients of the filter G (z) can be calculated. First, the periodic autocorrelation function ACF (n) of the stimulus is calculated
  
  and from this an autocorrelation matrix is formed and inverted:
  

The coefficient vector g of the filter G (z), consisting of k values g ₀ to g _k-1 , is obtained by adding the elements of B over one column each: g = (1 1 ... 1) · B

This special choice of filter coefficients ensures that the V _DC sensitivity is measured with high accuracy at the output of the system monitor.

• h) Multiplizieren des gefilterten Sensor-Ausgangssignals mit dem Stimulus-Korrelations-Referenzsignals und Bereitstellen eines Korrelationssignals im Multiplizierer 28. Schließlich folgt Verfahrensschritt
• i) Bilden eines Mittelwerts des Korrelationssignals und Ausgeben als Empfindlichkeitsmesswert in dem Mittelwert-Bilder 30.

Now follows process step

• h) multiplying the filtered sensor output signal with the stimulus correlation reference signal and providing a correlation signal in the multiplier 28 , Finally, procedural step follows
• i) forming an average value of the correlation signal and outputting as a sensitivity measurement value in the mean value images 30 ,

was einer Mittelwertbildung über N Takte entspricht. Für symmetrische Stimuli mit der Eigenschaft s_i = –s_i-N/2, die z. B. bei dem oben erwähnten Rechtecksignal erfüllt ist, wird ein einfacheres Sperrfilter eingesetzt: H_r(z) = 1/2·(1 + z^–N/2) The optional stimulus cut filter 42 has the transfer function for any stimuli

which corresponds to averaging over N bars. For symmetric stimuli with the property s _i = -s _{iN / 2} , the z. B. is satisfied in the above-mentioned rectangular signal, a simpler notch filter is used: H _r (z) = 1/2 · (1 + z ^{-N / 2} )

The sensor arrangement is preferably an acceleration sensor.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2005083449 [0003]
• DE 102006050 [0004]

Claims (15)

Sensor arrangement ( 10 . 40 ) with online monitoring with a sensor ( 12 ) for detecting a physical quantity e, a converter ( 14 ) for converting a physical input variable into a voltage, and an A / D converter ( 16 ) for generating a digital sensor output signal, characterized in that the sensor arrangement ( 10 . 40 ) An institution ( 18 ) for online monitoring of the sensitivity of the sensor arrangement. Sensor arrangement ( 10 . 40 ) according to claim 1, characterized in that the device ( 18 ) for online monitoring of sensitivity has a stimulus generator ( 20 ) for generating a stimulus signal, a coupling device ( 22 ) for coupling the stimulus signal with the physical quantity e, a stimulus pass filter ( 24 ) to provide a stimulus-filter output signal that passes stimulus frequencies, a stimulus-correlation reference signal generator ( 26 . 48 ) for providing a stimulus correlation reference signal, a multiplier ( 28 ) which multiplies the stimulus filter output signal with the stimulus correlation reference signal and provides a correlation signal, and averages images ( 30 ) which averages the correlation signal and outputs as a sensitivity measurement. Sensor arrangement ( 40 ) according to claim 2, characterized in that the stimulus correlation reference signal generator ( 48 ) is a FIR filter connected to the stimulus signal generator. Sensor arrangement ( 10 ) according to claim 2, characterized in that the stimulus correlation reference signal generator ( 26 ) has a memory from which the stimulus correlation reference signal is read out. Sensor arrangement ( 40 ) according to one of claims 2 to 4, characterized in that the sensor arrangement ( 40 ) an evaluation unit ( 44 ) for evaluating the digital sensor output signal and generating a measurement signal. Sensor arrangement ( 40 ) according to claim 5, characterized in that the sensor arrangement ( 40 ) a stimulus-lock filter ( 42 ) between the A / D converter ( 16 ) and the evaluation unit ( 44 ) having. Sensor arrangement ( 10 . 40 ) according to one of claims 2 to 6, characterized in that the stimulus generator ( 20 ) generates a stimulus signal periodically with N clocks. Sensor arrangement ( 10 . 40 ) according to one of claims 2 to 7, characterized in that the stimulus generator ( 20 ) generates a DC-free stimulus signal. Sensor arrangement ( 10 . 40 ) according to one of claims 2 to 8, characterized in that the stimulus generator ( 20 ) generates a symmetrical square wave signal. Sensor arrangement ( 10 . 40 ) according to one of claims 2 to 9, characterized in that the stimulus pass filter ( 24 ) is designed such that the sum of the squares of its impulse response samples becomes minimal. Method for online monitoring of a sensor arrangement with a sensor for detecting a physical quantity e, a converter and an A / D converter, the method for online monitoring of the sensitivity of the sensor arrangement comprising the method steps: a) providing a stimulus signal with stimulus frequencies; b) coupling the stimulus signal to the physical physical quantity e; c) conversion of a physical input variable into a voltage; d) generating a digital sensor output signal; f) removing frequencies that are not stimulus frequencies from the digital sensor output signal and providing a filtered sensor output signal; g) providing a stimulus correlation reference signal; h) multiplying the filtered sensor output signal with the stimulus correlation reference signal and providing a correlation signal; i) forming an average of the correlation signal and outputting as a sensitivity measurement. A method according to claim 11, characterized in that the stimulus frequencies are selected from a set of frequencies for which f _i = f _a * i / N where i = 1, ..., N / 2, where f _{a is} the sampling rate the sensor array is and N is the stimulus length in a number of bars. A method according to claim 12, characterized in that the number of stimulus frequencies present in finite amplitude in the stimulus signal is at least k / 2, rounded up, where k is the maximum length of the impulse response of the signal chain of the sensor array. Method according to one of Claims 11 to 13, characterized in that the stimulus correlation reference signal corresponds to a filtered stimulation signal, the filter being defined by a coefficient vector whose elements g ₀ ... g _k are calculated as the sum of the elements of a column a matrix B g = (1 1 ... 1) · B which is the inverse of an autocorrelation matrix

with the elements

with the stimulus curve s _i , i = 0 ... (N - 1). Method according to one of claims 11 to 14, characterized in that the removal of frequencies from the digital sensor output signal with a stimulus-lock filter is carried out with the transfer function

Images