A quartz tuning fork accelerometer differential measurement system and method of use thereof

Abstract

The application discloses a quartz vibrating beam accelerometer differential measurement system and a use method thereof, which comprises a frequency difference circuit module, a digital frequency synthesis circuit module and a frequency measurement module, the frequency difference circuit module is used for completing subtraction operation of square wave signal frequency; the digital frequency synthesis circuit module is used for synthesizing the minuend frequency and the subtrahend frequency in the frequency difference circuit module; and the frequency measurement module is used for measuring the output frequency in the frequency difference circuit module and controlling the digital frequency synthesis circuit module; according to the synthesized minuend frequency and the subtrahend frequency in the digital frequency synthesis circuit module, the frequency difference circuit module performs difference processing on two square wave signals, and inputs the difference-processed signal into the frequency measurement module, so that the real-time output frequency of the accelerometer is measured, the differential measurement is completed, the frequency and scale factor drift of the quartz vibrating beam accelerometer caused by temperature change can be effectively inhibited, the requirement on the frequency measurement method accuracy can be reduced, and the resolution is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of accelerometer, and relates to a quartz vibrating beam accelerometer, in particular to a differential measurement system of a quartz vibrating beam accelerometer and a use method thereof. BACKGROUND

[0002] With the continuous development of micro-mechanical technology and sensor technology, MEMS sensors are continuously reduced in size, and continuously improved in accuracy, and accordingly, the requirements for temperature characteristics and the accuracy of the frequency measurement system are also continuously improved.

[0003] The quartz vibrating beam accelerometer is an acceleration sensor based on the resonant beam force frequency effect and the piezoelectric and inverse piezoelectric effect of quartz material, which can directly output a square wave frequency signal for transmission and processing, and has the characteristics of high long-term stability, simple structure, easy mass production and the like. However, due to the temperature characteristics of the quartz material itself, the linear expansion of the structure, the temperature characteristics of the elastic coefficient matrix, the temperature characteristics of the density and the like, the resonant frequency of the quartz vibrating beam accelerometer will deviate from the design frequency, that is, the temperature drift will occur, and the frequency drift can even reach several hertz, which is converted into an acceleration value of several hundred mg.

[0004] In addition, the resolution of the quartz vibrating beam accelerometer is usually high, which is in the order of μg, and converted into a frequency value, it can reach 1x10 -4 Hz, and the design oscillation frequency is usually several tens of kilohertz, so in order to achieve the design resolution, the relative accuracy of the frequency measurement system needs to reach 1x10 -9 The above, and a high-precision frequency measurement system will undoubtedly increase the cost, the volume and the power consumption of the measurement system, which is contrary to the trend of sensor miniaturization and low power consumption, therefore, designing a differential measurement system which can reduce the requirements for the frequency measurement system and reduce the cost has become a key to be overcome for the technical personnel in the field. SUMMARY

[0005] The quartz vibrating beam accelerometer differential measurement system of the present application is provided to solve the existing problems, comprising a frequency difference circuit module, a digital frequency synthesis circuit module and a frequency measurement module, the frequency difference circuit module comprises at least a multi-stage D-type flip-flop and a low-pass filter to complete the subtraction operation of the frequency of square wave signals; the digital frequency synthesis circuit module comprises a digital frequency synthesis chip and an oscillator to synthesize the subtracted frequency or the frequency to be subtracted in the frequency difference circuit module; the frequency measurement module is used to measure the output frequency in the frequency difference circuit module and control the digital frequency synthesis circuit module; in the system, according to the synthesized subtracted frequency / frequency to be subtracted in the digital frequency synthesis circuit module, the frequency difference circuit module processes the difference of two square wave signals, and inputs the processed signal into the frequency measurement module to measure the real-time output frequency of the accelerometer, complete the differential measurement, the system and method can effectively suppress the frequency and scale factor drift of the quartz vibrating beam accelerometer caused by temperature change, and can reduce the requirement for the accuracy of the frequency measurement method, and effectively improve the resolution under the condition of using the same frequency measurement method.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: a quartz vibrating beam accelerometer differential measurement system, comprising: a frequency difference circuit module, a digital frequency synthesis circuit module and a frequency measurement module,

[0007] The frequency difference circuit module comprises at least a multi-stage D-type flip-flop and a low-pass filter to complete the subtraction operation of the frequency of square wave signals;

[0008] The digital frequency synthesis circuit module comprises a digital frequency synthesis chip and an oscillator to synthesize the subtracted frequency / frequency to be subtracted in the frequency difference circuit module;

[0009] The frequency measurement module is used to measure the output frequency in the frequency difference circuit module and control the digital frequency synthesis circuit module;

[0010] In the system, according to the synthesized subtracted frequency / frequency to be subtracted in the digital frequency synthesis circuit module, the frequency difference circuit module processes the difference of two square wave signals, and inputs the processed signal into the frequency measurement module to measure the real-time output frequency of the accelerometer, complete the differential measurement.

[0011] As an improvement of the present application, the synthesized subtracted frequency / frequency to be subtracted in the digital frequency synthesis circuit module is not more than 2 times the output frequency of the accelerometer, and is not less than

[0012] As another improvement of the present application, the oscillator in the digital frequency synthesis circuit module is a temperature-compensated crystal oscillator or a constant-temperature crystal oscillator, and the digital frequency synthesis circuit module communicates with the frequency measurement module through a three-wire SPI interface.

[0013] As another improvement of the present application, the frequency measurement module is composed of a single-chip microcomputer minimum system, a power module and an upper computer communication module, wherein the power module supplies power for the frequency measurement module; the upper computer communication module is used for outputting the measured frequency to the upper computer; the single-chip microcomputer minimum system is composed of an SPI bus interface, a frequency measurement interface, a crystal oscillator and an MCU;

[0014] The SPI bus interface is connected to the three-wire SPI communication interface of the digital frequency synthesis chip in the digital frequency synthesis circuit module, and is used for controlling the output square wave frequency of the digital frequency synthesis chip.

[0015] The frequency measurement interface is used for inputting the measured square wave frequency.

[0016] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: a differential measurement method of a quartz beam accelerometer, which comprises the following steps:

[0017] S1, determining the scale factor SF of the quartz beam accelerometer A and B through ±1g rolling experiment and 0g static experiment at normal temperature A and SF B and the 0g output frequency f 0A and f 0B , and determining the range R max , R min ; S2, obtaining the change range f Rmin ~f Rmax of the output frequency of the quartz beam accelerometer in the full range from the parameters SF A , SF B , f 0A , f 0B , R max , R min obtained in step S1 respectively according to the following formulas

[0018] f=f0+SF×R

[0019] In the formula, f represents the output frequency of the accelerometer, f0 represents the 0g output frequency of the accelerometer, SF represents the scale factor, and R represents the range;

[0020] S3, determining the output frequency f dig of the digital frequency synthesis circuit module, so that the output frequency satisfies the condition of being less than 2min{f Rmin , f Rmax} and being greater than max{f Rmin ,f Rmax};

[0021] S4, write the output frequency f into the digital frequency synthesis chip through the SPI bus of the frequency measurement module master chip single-chip microcomputer dig ;

[0022] S5, system power-on work, complete the differential measurement of the quartz vibrating beam accelerometer.

[0023] Compared with the prior art, the beneficial effects of the present application are:

[0024] 1. By differentially arranging the quartz vibrating beam accelerometer, the temperature drift thereof is effectively suppressed.

[0025] 2. By the frequency difference circuit, the measured frequency size is reduced, and the requirement for the frequency measurement method is effectively reduced, and in the case of the same frequency measurement method, higher resolution can be achieved.

[0026] 3. The present application has low cost, can significantly improve the full-temperature performance of the quartz vibrating beam accelerometer, and can reduce the requirement for the frequency measurement method by one to two orders of magnitude, effectively reduce the volume of the frequency measurement module, and meet the trend of sensor miniaturization. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a structural schematic diagram of the system of the present application;

[0028] Figure 2 is a whole process schematic diagram of the method of the present application;

[0029] Figure 3 is a structural block diagram of the frequency measurement module in the system of the present application; DETAILED DESCRIPTION

[0030] The present application will be further illustrated below in conjunction with the drawings and specific embodiments, and it should be understood that the following specific embodiments are only used to illustrate the present application and not to limit the scope of the present application.

[0031] Example 1

[0032] A quartz vibrating beam accelerometer differential measurement system, as shown in Figure 1 , comprises a frequency difference circuit module, a digital frequency synthesis circuit module and a frequency measurement module, the frequency difference circuit module at least comprises a plurality of D-type flip-flops and a low-pass filter, and completes the subtraction operation of the frequency of the square wave signal; the digital frequency synthesis circuit module comprises a digital frequency synthesis chip and an oscillator, and is used for synthesizing the subtracted frequency and the subtracted frequency in the frequency difference circuit module; the frequency measurement module is used for measuring the output frequency in the frequency difference circuit module and controlling the digital frequency synthesis circuit module;

[0033] , wherein Figure 2As shown, the frequency difference circuit module can generate a first-order difference frequency circuit and a second-order difference frequency circuit; the digital frequency synthesis circuit module is composed of a temperature compensated crystal oscillator (TCXO) and a digital frequency synthesis chip, and the temperature compensated crystal oscillator (TCXO) provides a high-stability and high-precision reference clock source for the two digital frequency synthesis chips; a first D-type flip-flop of the first-order difference frequency circuit has a D input end connected to a frequency output end of the quartz beam accelerometer A and an oscillation shaping circuit thereof, a CLK input end connected to a frequency output end of a first digital frequency synthesis chip of the digital frequency synthesis circuit module, and a Q end output to a low-pass filter; a second D-type flip-flop of the first-order difference frequency circuit has a D input end connected to a frequency output end of the quartz beam accelerometer B and an oscillation shaping circuit thereof, a CLK end connected to a frequency output end of a second digital frequency synthesis chip of the digital frequency synthesis circuit module, and a Q end output to a low-pass filter; the two low-pass filters in the first-order difference frequency circuit have output ends connected to D input ends and CLK input ends of D-type flip-flops in the second-order difference frequency circuit, a Q end connected to a low-pass filter, and an output end of the low-pass filter connected to a frequency measurement interface in a frequency measurement module.

[0034] The temperature compensated crystal oscillator (TCXO) in the embodiment can also be replaced by an oven-controlled crystal oscillator (OCXO) with higher precision.

[0035] As shown in the figure, Figure 3 The frequency measurement module is composed of a single-chip microcomputer minimum system, a power module, and an upper computer communication module, wherein the single-chip microcomputer minimum system is composed of an SPI bus interface, a frequency measurement interface, a crystal oscillator, and an MCU, wherein the SPI bus interface is connected to a three-wire SPI communication interface of a digital frequency synthesis chip in the digital frequency synthesis circuit, used for controlling the output square wave frequency of the digital frequency synthesis chip, the frequency measurement interface is used for inputting the measured square wave frequency; the upper computer communication module is used for outputting the measured frequency to the upper computer, and the power module supplies power for the frequency measurement module.

[0036] The frequency difference circuit module is connected to an output stage of the quartz beam accelerometer oscillation shaping circuit and a digital frequency synthesis circuit module, the frequency measurement module is connected to an output stage of the frequency difference circuit module, and the frequency measurement module controls the digital frequency synthesis circuit module through three-wire SPI communication. The subtracted frequency or the frequency to be subtracted in the synthesized frequency difference circuit does not exceed 2 times the output frequency of the quartz beam accelerometer, and is not less than .

[0037] When acceleration measurement units A and B and their respective oscillation shaping circuits are powered on, their output square waves f1 and f2 are input to a first-stage differential frequency circuit. This circuit subtracts the frequency of square wave f1 from the output square wave f3 of the digital frequency synthesis circuit, and subtracts square wave f2 from the output square wave f4 of the digital frequency synthesis circuit, yielding square wave signals f6 and f5 respectively. The frequency of square wave signal f5 is the difference between the frequencies of f4 and f2, and the frequency of square wave signal f6 is the difference between the frequencies of f3 and f1. After passing through a low-pass filter circuit, f5 and f6 are input to a second-stage differential frequency circuit, resulting in square wave signal f7, whose frequency is the difference between the frequencies of f5 and f6. At this point, the quartz beam accelerometers A and B complete differential operation, reducing the measured frequency value and thus lowering the relative accuracy requirements of the frequency measurement module.

[0038] Therefore, in the system of the present invention, based on the subtractive frequency / minimum frequency synthesized in the digital frequency synthesis circuit module, the frequency differential circuit module performs differential processing on the two square wave signals, and inputs the differential processed signal into the frequency measurement module to measure the real-time output frequency of the accelerometer, thereby completing the differential measurement. This effectively suppresses the frequency and scale factor drift of the quartz beam accelerometer caused by temperature changes, and reduces the accuracy requirements of the frequency measurement method, effectively improving the resolution when using the same frequency measurement method.

[0039] Example 2

[0040] A method for using a differential measurement system for a quartz beam accelerometer, comprising the following steps:

[0041] The first step was to determine the 0g output frequency f of quartz vibrating beam accelerometers A and B through ±1g tumbling experiments and 0g static experiments at room temperature. 0A with f 0B and the corresponding scaling factor SF A With SF B And determine the range R max R min For finished quartz vibrating beam accelerometers, the measurement range is usually available in the datasheet provided by the accelerometer designer. In this embodiment, f 0A with f 0B The values ​​are 61987Hz and 62424Hz respectively, SF A With SF B The values ​​are 51.5 Hz / g and 55.9 Hz / g, respectively, with a measurement range R. min R max The values ​​are -50g and +50g respectively. Since accelerometer A is installed in reverse, its scale factor SF A It should be -51.5Hz / g.

[0042] The second step, as Figure 2As shown, by f 0A +R min ×SF A and f 0A +R max ×SF A Calculations show that accelerometer A travels from R... min ~R max The frequency variation range within the measurement range is 64561Hz to 59411Hz, that is, the frequency f1 variation range is 64561Hz to 59411Hz, denoted as f. 1_Rmin =64561Hz, f 1_Rmax =59411Hz; f 0B +R min ×SF B and f 0B +R max ×SF B The frequency variation range of accelerometer B is 59629Hz to 65219Hz, such as Figure 2 As shown, the frequency f2 varies from 59629Hz to 65219Hz, denoted as f 2_Rmin =59629Hz, f 2_Rmax =65219Hz.

[0043] The third step is to calculate f from the second step. 1_Rmin f 1_Rmax f 2_Rmin f 2_Rmax The value of the output frequency f3 of the digital frequency synthesizer chip is set not to exceed the minimum value of the frequency variation range of f1 (i.e., f...). 1_Rmax It is twice the value of f1, and not less than the maximum value of the frequency variation range of f1 (i.e., f). 1_Rmin )of The digital frequency synthesizer chip's output frequency f4 is set to be no greater than the minimum value of the frequency variation range of f2 (i.e., f...). 2_Rmin It is twice the value of f2, and not less than the maximum value of the frequency variation range of f2 (i.e., f). 2_Rmax )of In this embodiment, the frequency f3 is set to 75kHz and the frequency f4 is set to 81kHz. In fact, the values ​​of f3 and f4 can be arbitrarily set under the above conditions.

[0044] The fourth step is from f4-f 2_Rmin and f4-f 2_Rmax Calculations show that the frequency f5 varies from 21371Hz to 15781Hz within the range of -50g to +50g. Let f be the value of f. 5_Rmin =21371Hz, f 5_Rmax =15781Hz, from f3-f 1_Rmin and f3-f1_Rmax It can be calculated that the value of f6 changes in the range of 10439Hz-15589Hz in the frequency range of-50g+50g, denoted as f 6_Rmin =10439Hz, f 6_Rmax =15589Hz.

[0045] In the fifth step, f 5_Rmin -f 6_Rmin and f 5_Rmax -f 6_Rmax It can be calculated that f7 changes in the range of 10932Hz-192Hz in the frequency range of-50g+50g; and the SF A -SF B The scale factor of the differential accelerometer is-107.4Hz / g after the calculation.

[0046] In the sixth step, the single-chip microcomputer writes the set frequencies f3 and f4 into the digital frequency synthesis chip through the SPI bus.

[0047] In the seventh step, the system is powered on, the quartz vibration beam accelerometer is connected, and the system can work normally, that is, the differential measurement of the accelerometer is realized. The frequency of the differential accelerometer changes in the range of 10932Hz-192Hz in the range of-50g+50g, and the scale factor is-107.4Hz / g. The relative accuracy requirement of the frequency measurement module is reduced by one order of magnitude in total, and the common-mode error of the accelerometer caused by temperature can be suppressed.

[0048] It should be noted that the above content only illustrates the technical idea of the present application and cannot limit the protection scope of the present application. For ordinary skilled persons in the technical field, some improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements fall within the protection scope of the claims of the present application.

Claims

1. A differential measurement method for a quartz tuning fork accelerometer, characterized by: The application relates to a differential measurement system of a quartz beam accelerometer, which comprises a frequency difference circuit module, a digital frequency synthesis circuit module and a frequency measurement module. The frequency difference circuit module comprises at least a multi-stage D-type flip-flop and a low-pass filter, and completes the subtraction operation of the frequency of square wave signals. The digital frequency synthesis circuit module comprises a digital frequency synthesis chip and an oscillator, and is used for synthesizing the subtracted frequency and the subtracted frequency in the frequency difference circuit module. The frequency measurement module is used for measuring the output frequency in the frequency difference circuit module and controlling the digital frequency synthesis circuit module. In the system, according to the subtracted frequency and the subtracted frequency synthesized in the digital frequency synthesis circuit module, the frequency difference circuit module processes the difference of two square wave signals, inputs the processed signals into the frequency measurement module, measures the real-time output frequency of the accelerometer, and completes the differential measurement. The method comprises the following steps: S1, determine the scale factor of quartz vibrating beam accelerometers A and B at normal temperature by ±1g rolling experiment and 0g static experiment With and 0g output frequency With and determine the range , ; S2, the parameters obtained in step S1 , , , , The range of variation of the output frequency of the quartz vibrating beam accelerometer over the full range of the range is calculated from the following formula, respectively ~ , ； wherein represents the accelerometer output frequency, represents the accelerometer 0g output frequency, represents the scale factor, represents the range; S3, determining the output frequency of the digital frequency synthesis circuit module such that the output frequency satisfies the condition of being less than } and greater than . S4, write the output frequency into the digital frequency synthesis chip through the SPI bus of the frequency measurement module master control chip MCU ; S5, the system is powered on and works, and the differential measurement of the quartz beam accelerometer is completed.

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