Resonator measuring device and method involving same

Translation of description of equivalent WO 2006069937 A1

p0001Measuring device resonator and method implementing the device

p0002The invention relates to a device and method for detecting failure of a measuring device comprising a resonator and means for measuring a of the resonator resonance frequency. The measuring device comprises for example a fluid pressure sensor. The invention finds particular utility in aeronautics where pressure measurements are essential to the conduct of flight of an aircraft. Indeed, elevation of a flight level required for an aircraft is determined by the static pressure of the air surrounding the aircraft. Furthermore, air traffic increases, the traffic control authorities are seeking to reduce the gap between levels of theft neighbors. The detection of a failure of a pressure sensor is essential to ensure the safety of air traffic.

p0003The invention can also be implemented for other devices implementing a resonator such as in an accelerometer as described in the French patent application FR 2848298, a gyroscope as described in the French patent application FR 2,834,055 or yet in time base. The following description will be made in reference to an air pressure sensor without of course limiting.

p0004For measuring the pressure of the ambient air are commonly used pressure sensors having a chamber maintained at a reference pressure usually close vacuum. An example of this type of sensor is described in the French patent application FR 2 687 783. The pressure sensor measures the pressure difference between the chamber and the air. The guarantee of accuracy in pressure measurement basically depends on maintaining the vacuum prevailing inside the chamber during the lifetime of a sensor, or at least between two calibrations of the pressure sensor. Several phenomena can degrade the vacuum in the room, especially as leaks can occur at the junctions of different components of the walls of the chamber or the vent walls or components in the room.

p0005The pressure sensor described in the French patent application FR 2687783 comprises a resonator of which one end is subjected to a force based on the pressure difference between the interior of the chamber and the ambient air. The principle of pressure measurement is to measure the resonator resonance frequency.

p0006It was found also that at a constant air pressure, ambient temperature affected the value of the resonant frequency. It is possible to add to the pressure sensor a temperature sensor. During a calibration phase is established a function combining the measured temperature and the resonance frequency to determine the pressure. This function can be established empirically. This correction does not take into account any change in the pressure in the chamber. To date, only a recalibration of the pressure measuring device used to find such an amendment.

p0007The invention aims to improve knowledge of the level of accuracy of the pressure sensor during use and avoid the requirement to periodically recalibrate the sensor preventatively. Another object of the invention is to maintain a level of accuracy of the order of 0.1 hPa.

p0008To this end, the invention relates to a measuring device comprising a resonator and means for measuring a resonance frequency of the resonator, characterized in that it comprises means for delivering information representative of the resonator quality factor at the resonant frequency.

p0009The invention also relates to a method of using an air pressure measurement device comprising a pressure sensor and a chamber maintained at a reference pressure, the pressure sensor measuring a pressure difference between the chamber and air, the sensor comprising a resonator excited by an oscillation controlled by automatic amplitude control means characterized in that the device comprises means for detecting a variation of pressure in the chamber and in that the method consists in comparing a first gain of the automatic control of the amplitude of the driver measured during the measurement of pressure with a second gain of the automatic control of the amplitude of the excitation calculating the excitation frequency measured from parameters defined during a calibration of a defect detecting device to the device when the difference between the two gains is greater than a given value. The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given as an example, description illustrated by the attached drawing in which: - Figure 1 shows diagram form block an example device according to the invention;

p0010- Figure 2 shows an embodiment of part of the diagram of Figure 1.

p00111 shows an air pressure measurement device comprising a pressure sensor 1 and a chamber 2 maintained at a reference pressure, as a near vacuum. 1 measure the pressure sensor a pressure difference between the chamber 2 and the air surrounding the pressure sensor 1. Advantageously, the device includes a resonator 3 and means for measuring a resonance frequency of the resonator 3. The resonator 3 is for example achieved by means of a silicon plate 4 which may come into resonance under the effect of an electrical excitation signal E. the silicon plate 4 is located in the chamber 2. the silicon plate 4 is fixed at one of its ends 5 in a body 6 of the resonator 3 and at the other of its ends 7 on a thinned wall 8 of the chamber 2. the wall 8 is subjected on one of its faces to the pressure of the air, pressure to be measured, and on the other of its faces to the pressure of the chamber 2. the wall 8 is deformed depending on the pressure difference between the chamber 2 and the air. This deformation of the wall 8 causes a stress in the silicon plate 4. The stress changes according to the pressure difference between the air and the chamber 2. The resonance frequency of the silicon blade 4 is thus also a function of the pressure difference between the air and the chamber 2. a more detailed explanation of achieving this example of a resonator can be obtained by reading the french patent application FR 2 687 783. It is of course possible to use another type pressure sensor by implementing a resonator and wherein the resonator is located outside of a chamber maintained at a reference pressure.

p0012Detecting the resonance is performed by capacitive effect between the silicon blade 4 and the body 6 of the resonator 3 by means of a signal D Electric taken at the body of the resonator 6 3. D electric signal is amplified by an amplifier 9 and then filtered through a bandpass filter 10 to retain only the resonant frequency and be issued to automatic control means the amplitude of the excitation signal E, means commonly known as automatic gain control AGC and bearing the reference 1 in FIG. Automatic gain control is controlled by a set C. The AGC delivers the excitation signal E. the excitation signal E as the Fp signal used by a computer 14 to determine the pressure of the air. The device further comprises means 15 for measuring the temperature of the air. The means 15 comprise for example a negative temperature coefficient resistor. The means 15 outputs a signal St to the computer 14 to correct the air pressure measurement. This correction is for example calculated based on the signal St and the signal Fp by means of a polynomial function defined during a calibration of the device. This calibration is performed using a pressure measuring campaign carried out at different temperatures. The polynomial function is for example of the form:

p0013P = AO + A1 + .fp A2.St A3.Fp.St + + A4. fp².st A5 + Fp.St² ... Where P is the pressure of the air and where Ai are constants. It was found that a polynomial of the fifth order provides sufficient accuracy to the pressure value P.

p0014According to the invention, the device comprises means for detecting a variation of pressure in the chamber 2. These means advantageously deliver information representative of the quality coefficient of the resonator at the resonant frequency, for example as a gain S3 AGC delivered to computer 14 to detect a fault of the device. Furthermore, during the calibration, the measured signal S3 for each pressure measurement. Measurements made during calibration can calculate, for future pressure measurement, a value that should take the S3 signal if the chamber pressure remained unchanged. As before, it was found that the signal S3 is a function of the signals Fp and St and that this function can be approximated by a polynomial function. To detect a defect of the device, a method of comparing a first signal S3 measured when measuring pressure with a second signal S3 calculated from parameters defined in the calibration of the device and according to Fp and St measured signals. The device is then declared faulty if the difference between the measured and the calculated signal S3 S3 signal is higher than a given value. The comparison and the various calculations are performed by the computer 14.

p0015Advantageously, it is possible to correct the measurement of pressure difference between the chamber 2 and the air in function of the difference between the two signals S3. Pressure example P is calculated based on Fp signals St and S3 measured. This calculation can be done using a function with parameters set during the calibration phase. The function is again eg polynomial. Thus, even if the pressure sensor 1 was derived, due to a pressure derived from the chamber 2, it is possible to compensate for this drift using the S3 gain of the automatic control of the amplitude of the excitation signal E of the resonator 3.

p00162 shows an embodiment of part of the diagram of Figure 1. To avoid overloading the figure 2, the computer 14 and the means 15 for measuring the air temperature have not been represented.

p0017The amplifier 9 and the bandpass filter 10 are formed around an operational amplifier 20 at its inverting input attacked by the signal D. The non-inverting input of the operational amplifier 20 is connected to ground. Against a reaction of the operational amplifier is formed by a resistor 21 and a capacitor 22 connected in parallel between the inverting input and the output of the operational amplifier 20. A capacitor 23 is connected to the output of the operational amplifier 20 to deliver a signal to the automatic gain control AGC which can weaken the signal through a 24 resistor and a field effect transistor 25. the signal thus weakened is biased and shaped by passing through a circuit 26. bias voltage is a voltage V₀ supplied to the circuit 26. The output of circuit 26 supplies the excitation signal E. The signal Fp is formed from the signal E through a circuit 27 whose function is to depolarize the signal E by means of a capacitor 28 and to amplify the signal E by means of an operational amplifier 29. Fp signal is then rectified by means a circuit 30 to be issued to the automatic gain control AGC. The AGC AGC is controlled by a set C. The AGC AGC comprises a first integration stage carried around an operational amplifier 31 whose output forms the signal S3 which controls a gate G of the transistor effect field 25.