Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
  • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
  • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
  • G01P15/097—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by vibratory elements
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P21/00—Testing or calibrating of apparatus or devices covered by the preceding groups

Definitions

• the present invention relates to a method of measuring an acceleration by means of a piezoelectric vibrating accelerometer and the corresponding measuring device.
• Acceleration measuring devices comprising a vibrating accelerometer comprising a piezoelectric cell having an excitation electrode connected to an excitation control element and a detection electrode connected to an acceleration computer.
• piezoelectric cell being associated with a control loop of the excitation control at a resonant frequency of the piezoelectric cell.
• the output signal whose amplitude is used to calculate the acceleration is not only an image of the capacitance of the piezoelectric cell but is also influenced by parasitic characteristics, in particular parasitic capacitance resulting from the wiring or a resistance. parasite resulting from an insulation fault. These parasitic electrical characteristics vary not only from one device to another but also vary over time.
• parasitic electrical characteristics are compensated in a standard manner so that neither variations between different devices nor variations in time of these parasitic electrical characteristics for the same device are taken into account.
• An object of the invention is to provide a method and a device for accurately compensating for at least one parasitic electrical characteristic.
• a method of measuring an acceleration by means of a vibrating accelerometer comprising a piezoelectric vibrating cell comprising the steps of exciting the cell. vibrating by means of an excitation signal at a resonant frequency of the vibrating cell, and calculating a value of the acceleration from a detection signal resulting from the excitation signal, and exciting in addition, the vibrating cell with a correction excitation signal at a correction frequency different from the resonance frequency, extracting from the detection signal a correction signal representative of an electrical characteristic to be corrected and combining the signal of correction with the detection signal in a way reducing the electrical characteristic to be corrected.
• the correction signal extracted at a frequency different from the resonant frequency can be considered as representative of the only parasitic electrical characteristics so that the correction can be performed by a simple subtraction of the correction signal.
• the correction frequency is close to the resonance frequency. This ensures that the electrical characteristics to be corrected as detected at the correction frequency are close to those detected at the resonance frequency.
• the correction signal is extracted by demodulating the detection signal at the correction frequency.
• a device for measuring an acceleration comprising a vibrating accelerometer comprising a piezoelectric vibrating cell having an excitation electrode receiving an excitation command signal at a frequency resonant circuit of the vibrating cell, and a detection electrode associated with a control loop for extracting a detection signal representative of an acceleration to which the device is subjected, and at least one correction loop comprising means for extracting at a correction frequency different from the resonant frequency a correction signal representative of an electrical characteristic to be corrected, and means for combining the correction signal with the detection signal at the resonant frequency in a reducing manner. the characteristic to correct.
• the device according to the invention comprises a vibrating accelerometer comprising a piezoelectric vibrating cell 1 on which are fixed an excitation electrode 2 and a detection electrode 3.
• the piezoelectric vibrating cell 1 can be in a manner known per se consisting of two piezoelectric cell elements mounted in opposition to sensitivity to accelerations.
• the detection electrode 3 is connected to the direct input of an addi- 4, the output of which is connected to a bandpass filter 5.
• the output of the bandpass filter 5 is connected on the one hand to an acceleration calculator 6 and on the other hand to a main control loop 7, a first correction loop 8 and a second correction loop 9.
• the main control loop 7 comprises a synchronous demodulator 10 at a resonant frequency f0 of the vibrating cell 1.
• a regulator 11 has an input connected to the demodulator 10 and an input receiving an amplitude command setpoint CA (f0), and an output connected to an integral proportional corrector 12.
• the output of the integral proportional corrector 12 is connected to an input of a modulator 13 whose second input is connected to the output of the bandpass filter 5.
• the output of the modulator 13 is connected to the acceleration calculator 6 and to a direct input of an adder 14, a second direct input receives a comm signal ande of AC amplitude (fl) at a first correction frequency f1 different from the resonance frequency f0, and a third direct input receives a control signal at a second correction frequency f2 different from f0 and f1.
• the output of the adder 14 is connected to the excitation electrode 2.
• the vibrating cell 1 is therefore excited simultaneously by an amplitude control signal at the resonance frequency f0 and amplitude control signals at the frequencies correction fl and f2 different from the resonance frequency f0.
• the first correction loop 8 comprises in parallel a synchronous demodulator 15 at the first correction frequency f1 and a synchronous demodulator 15a at the second correction frequency f2.
• the outputs of demodulators 15 and 15a are connected to the input of an averager 25 which averages the signals received from the demodulators 15 and 15a.
• the output of the averager 25 is connected to the input of a regulator member 16 whose second input receives a regulation setpoint, here a zero regulation.
• the output of the regulator 16 is connected to an integral proportional corrector 17 whose output is connected to the input of a modulator 18, a second input of which is connected to the supply line of the excitation electrode. 2.
• the output of the modulator 18 is connected to an inverting input of the adder 4.
• the second correction loop 9 comprises a ⁇ / 2 phase shifter 19 which can indifferently be a derivative member or an integrating member, connected in parallel with a synchronous demodulator 20 at the correction frequency f1 and with a synchronous demodulator 20a at the second correction frequency f2.
• the outputs of the demodulators 20 and 20a are connected to the input of an averager 26 whose output is connected to a regulator 21 having an input receiving a regulation setpoint, here a zero regulation.
• the output of the regulator 21 is connected to an integral proportional corrector 22 whose output is connected to an input of a modulator 23 having a second input connected to the supply line of the excitation electrode 2 and whose output is connected to a ⁇ / 2 phase shift element 24 which ensures that the correction signal is put back in phase before it is applied to an inverting input of the adder 4.
• the demodulator 10 carries out a signal extraction at the resonance frequency f0 and the regulation loop 7 maintains the main excitation signal at the amplitude control command CA (f0) which is supplied to the excitation electrode 2.
• the regulation loop 8 ensures an extraction at the correction frequencies f1 and f2 of a correction signal which is representative of parasitic resistances.
• the regulation loop 9 performs an extraction at the correction frequencies f1 and f2 of a signal which, because of its phase shift by the phase shifter 19, is representative of parasitic capacitances. Extraction at two different correction frequencies makes it possible to correct even if one of the parasitic parameters (resistance and / or capacitance) can not be corrected at one of the correction frequencies due to insensitivity of the cell to one of the correction frequencies for the parameter considered.
• the averagers have the advantage of returning the correction to the same amplitude as the parasitic signal in the case where the cell is sensitive to the two correction frequencies.
• the correction frequencies f 1 and f 2 are as close as possible to the resonance frequency f 0 while having a sufficient distance for the component of the correction signal resulting from the capacity of the vibrating cell itself to be small compared to this same component in the detection signal at the resonance frequency f0.
• the method gives excellent results with correction signals f1 and f2 having, with f0, frequency deviations of 10 kHz.
• the determination of the correction signals is carried out simultaneously with the determination of the main signal by superimposing an amplitude control at the resonant frequency and amplitude commands at the correction frequencies
• the invention has been illustrated with extractions with two correction frequencies having the same deviation from the resonance frequency f0, extraction can be carried out at correction frequencies having different deviations from the resonance frequency, or still perform an extraction at a single correction frequency.
• the correction loop with ⁇ / 2 phase shift has been illustrated with a common phase shifter 19 upstream of the demodulators 20 and 20a, it is also possible, particularly when the correction is performed at a single frequency, to mount the phase-shifting device downstream of the demodulator 20. Similarly, the phase shifter 24 can be mounted upstream of the modulator 23.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Gyroscopes (AREA)
• Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=39410463

Family Applications (1)

Country Status (4)

Families Citing this family (2)

Family Cites Families (7)

• 2007
  • 2007-07-19 FR FR0705220A patent/FR2919067B1/fr active Active
• 2008
  • 2008-07-16 WO PCT/FR2008/001039 patent/WO2009030829A2/fr active Application Filing
  • 2008-07-16 EP EP08829111A patent/EP2171481A2/de not_active Withdrawn
  • 2008-07-16 US US12/669,319 patent/US8413508B2/en active Active

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events