Pressure and temperature dependency correction method of quartz tuning fork sensor

Abstract

The invention discloses a pressure and temperature dependence correction method for a quartz tuning fork sensor, and the method comprises the steps: building a correction algorithm based on the influence of changing pressure and temperature environmental factors in actual external field application on the resonant frequency and quality factors of a quartz tuning fork according to the response characteristics of the quartz tuning fork to environmental pressure and temperature changes, the method effectively solves the problem of reliability of measured parameters of a spectrum system or a gas sensor developed based on the quartz tuning fork in an actual external field environment, is high in precision, makes up for important defects in the prior art, and has wide practical value.

Description

Technical Field

[0001] The invention relates to the technical field of sensors, in particular to a pressure and temperature dependency correction method for a quartz tuning fork sensor. Background Art

[0002] The quartz tuning fork was originally derived from a commercial electronic device - a cylindrical crystal oscillator. Because its internal core device, the quartz wafer, looks like a tuning fork, it is commonly known as a quartz crystal tuning fork (also called a cylindrical crystal oscillator). Quartz tuning forks have many advantages, such as high quality factor (Q value), small size, simple structure, and low cost. By measuring the change of its resonant frequency under different disturbances, it is widely used in the development of various types of high-precision resonant sensors, including pressure, temperature, accelerometers, density, viscosity, gyroscopes, etc. It is used in the measurement of key parameters in the fields of near-field acoustic / optical microscopy, low-temperature physics, and industrial automation, and plays an important supporting role.

[0003] In the field of spectroscopy, in 2002, the research group of Professor Tittel of Rice University in the United States first used quartz tuning forks as photoacoustic signal sensors in photoacoustic spectroscopy, replacing traditional microphone detectors, and proposed quartz-enhanced photoacoustic spectroscopy (QEPAS). The high resonance frequency and high quality factor make it immune to various low-frequency acoustic noises, and achieve higher detection sensitivity than traditional photoacoustic spectroscopy. In response to the important needs of multi-component simultaneous measurement and supercontinuum spectrum response detectors in the field of gas detection, in 2015, Li Jinsong's team at Anhui University first proposed to use quartz tuning forks as photodetectors (ZL201711172585.5), using the resonance effect and piezoelectric effect of quartz tuning forks to successfully achieve continuous and simultaneous measurement of spectral signals in various bands (ultraviolet-terahertz), and compared with the commercial VIGO detectors widely relied on internationally, it has comparable effects, realizing the supercontinuum spectrum response characteristics based on a single quartz tuning fork photodetector and high-sensitivity quartz tuning fork enhanced absorption spectroscopy technology.

[0004] Since the concept of the quartz tuning fork photodetector was proposed, the quartz tuning fork has been further promoted as a high-quality sensor component to be widely used in the fields of photoacoustic spectroscopy and absorption spectroscopy. In particular, the quartz tuning fork photodetector has supercontinuum spectral response characteristics, and is widely favored in the development of spectral analysis systems or gas sensors as a core device to achieve high sensitivity. The essence of quartz tuning fork to achieve spectral signal detection is to use the resonance effect of the continuous signal source modulation frequency (or the repetition rate of the pulse signal) and the quartz tuning fork intrinsic frequency. Therefore, the frequency stability of the quartz tuning fork is a key factor affecting the final detection sensitivity and measurement accuracy. However, the resistance and frequency of the quartz tuning fork are mainly affected by factors such as material purity, crystal structure, ambient pressure and temperature, manufacturing process and mechanical stress. Whether it is a commercial 32.768kHz quartz tuning fork or a customized quartz tuning fork of other frequencies, detecting changes in ambient pressure and temperature in practical applications is an important factor affecting the frequency stability of the quartz tuning fork.

[0005] In existing research, although photoacoustic / photothermal spectroscopy and absorption / modulation spectroscopy based on quartz tuning forks can achieve high-sensitivity detection of various trace gases, such as the authorized Chinese patents: ZL202210569759.6, ZL201910202212.0, ZL202110865290.6, etc., all such related public technologies are currently limited to the stable environment of the laboratory, and have not yet considered and solved the impact of changing environmental factors (pressure and temperature) in the final actual field application on the key parameters (resonance frequency and quality factor) of the quartz tuning fork and the problem of effective correction methods. Summary of the invention

[0006] The object of the present invention is to provide a method for correcting the pressure and temperature dependence of a quartz tuning fork sensor to solve the above defects.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for correcting the pressure and temperature dependence of a quartz tuning fork sensor comprises the following steps:

[0009] S1. Environmental pressure dependence correction:

[0010] S11, using an excitation source to excite the quartz tuning fork sensor to resonate near its resonance frequency f, combining the fast Fourier transform algorithm to perform spectrum analysis on the quartz tuning fork sensor signal, and using the Lorentz function to fit the optimal center frequency f of its resonance profile 0 and quality factor Q u value;

[0011] S12, optimal center frequency f 0Generate analog modulation signals and modulate the laser used in the spectral system. The specific wavelength light beam output by the laser and the gas molecules to be measured in the gas sample generate spectral signals through the absorption process.

[0012] S13, select the second harmonic 2F signal in the spectrum signal generated by the laser output, detect it with a quartz tuning fork sensor and realize photoelectric conversion, and then calculate the 2F signal peak value S through the peak extraction algorithm u ;

[0013] S14, fitted quality factor Q u The values ​​are input into the quality factor correction matrix function, and the corresponding concentration values ​​are fitted using a linear fitting algorithm;

[0014] S15, the 2F signal peak value S calculated in step S13 u , input into the concentration correction formula; then the concentration value fitted in step S14 is fed back to the concentration correction formula, thereby reversing the true concentration value C(S) of the gas molecules to be measured. u );

[0015] S2. Ambient temperature dependence correction:

[0016] The temperature dependence of the quartz tuning fork sensor is corrected using the temperature correction formula of the quartz tuning fork under ambient temperature T.

[0017] In step S11, the excitation source is a mixed single-frequency signal based on the superposition of multiple single-frequency signals, and excites the quartz tuning fork sensor at its resonant frequency f by means of an optical signal, an acoustic signal or an electrical signal. 0 Nearby resonance.

[0018] In step S14, the quality factor correction matrix function is specifically:

[0019]

[0020] In formula (1), S 1 , S 2 ,……,S n , are the measured values ​​of the molecular absorption spectrum signal amplitude under n known concentrations of the gas to be detected; Q is the quality factor value of the quartz tuning fork sensor; a 1 、a 2 ,……,a n and b 1 、b 2 ,……,b n They are the coefficients of the linear relationship satisfied between the absorption spectrum signal amplitude of the corresponding molecule at the above n known concentrations and the quality factor value of the quartz tuning fork sensor: slope and intercept.

[0021] In step S15, the concentration correction formula is specifically:

[0022] C(S)=k u ·S+b u (2)

[0023] In formula (2), S is the molecular absorption spectrum signal amplitude; C(S) is the concentration of the absorbing gas molecules when the molecular absorption spectrum signal amplitude is S; k u and b u The quality factor is Q u The slope and intercept of the linear relationship between the molecular absorption spectrum signal amplitude and the concentration of the absorbing gas molecules when .

[0024] In step S2, the quartz tuning fork temperature correction formula is specifically:

[0025] f(T)=f(T 0 )*[1-k*(T- T 0 ) 2 ] (3),

[0026] In formula (3), T 0 and f(T 0 ) are the center temperature corresponding to the quadratic parabola equation obtained under laboratory test conditions and the center frequency of the quartz tuning fork corresponding to the center temperature; k is the coefficient of the quadratic term of the parabola equation, usually around 10 -8 magnitude; T represents the ambient temperature in the experiment; f(T) represents the central frequency of the quartz tuning fork at temperature T.

[0027] The quadratic parabola equation is specifically f(T)=32.760*[1-3.0*10 -8 *(T-25) 2 ].

[0028] The beneficial effects of the present invention are:

[0029] The pressure and temperature dependence correction method of the quartz tuning fork sensor of the present invention establishes a set of effective correction algorithms based on the response characteristics of the quartz tuning fork to environmental pressure and temperature changes explored in experiments, effectively solves the reliability problem of measurement results of spectral analysis systems or gas sensors developed based on quartz tuning forks in actual field environments, makes up for important defects of existing technologies, and has broad practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The figure is a flow chart of the environmental pressure dependence calibration of the quartz tuning fork sensor of the present invention;

[0031] Figure 2The graph is a temperature dependence graph of the resonant frequency of the quartz tuning fork sensor of the present invention. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with the embodiments. It should be noted that these are merely examples and illustrations of the concept of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should be deemed to fall within the protection scope of the present invention.

[0033] Embodiment 1:

[0034] A method for correcting the pressure and temperature dependence of a quartz tuning fork sensor comprises the following steps:

[0035] S1. Environmental pressure dependence correction:

[0036] Figure 1 FIG. 1 is a flow chart of the environmental pressure dependence calibration of the quartz tuning fork sensor of the present invention. Figure 1 As shown, the specific steps are as follows:

[0037] S11. Use an excitation source to excite the quartz tuning fork sensor to resonate near its resonance frequency f, use the fast Fourier transform algorithm to perform spectrum analysis on the quartz tuning fork sensor signal, and use the Lorentz function to fit the optimal center frequency f of the resonance profile. 0 and quality factor Q u value.

[0038] The excitation source is a mixed single-frequency signal based on the superposition of multiple single-frequency signals, and can excite the quartz tuning fork sensor to resonate near its resonance frequency f by means of an optical signal, an acoustic signal or an electrical signal.

[0039] S12, the best center frequency f fitted by S11 process 0 It is used to generate analog modulation signals and modulate the laser used in the spectral system. The specific wavelength light beam output by the laser and the gas molecules to be measured in the gas sample generate spectral signals through the absorption process.

[0040] S13, select the second harmonic 2F signal in the spectrum signal generated by the laser output, detect it with a quartz tuning fork sensor and realize photoelectric conversion, and then calculate the 2F signal peak value S through the peak extraction algorithm u .

[0041] S14, the quality factor Q fitted by S11 process u The values ​​are input into the quality factor correction matrix function, and the corresponding concentration values ​​are fitted using a linear fitting algorithm.

[0042] Quality factor correction algorithm: In theory, the amplitude S of the molecular absorption spectrum signal is directly proportional to the concentration C of the absorbing molecules, and in harmonic detection, the amplitude of the quartz tuning fork sensor detection signal is also directly proportional to its quality factor Q value. Based on these two linear relationships, within the concentration detection range of the known gas spectrometer or sensor system, firstly, a linear relationship between S and Q under a series of known concentrations of the gas to be detected is established through experiments. Assuming that n linear correction functions are established, the linear relationship between S and Q is measured under n known concentrations, and the following quality factor correction matrix function can be determined, specifically:

[0043]

[0044] In formula (1), S 1 , S 2 ,……,S n , are the measured values ​​of the molecular absorption spectrum signal amplitude under n known concentrations of the gas to be detected; Q is the quality factor value of the quartz tuning fork sensor; a 1 、a 2 ,……,a n and b 1 , b 2 ,……,b n are respectively the coefficients of the linear relationship between the amplitude of the absorption spectrum signal of the corresponding molecule at the above n known concentrations and the quality factor value of the quartz tuning fork sensor.

[0045] In practical applications, for target gases of unknown concentration, the spectral signal amplitude S is first measured by a spectral system or sensor based on a quartz tuning fork sensor. u And the quality factor Q of the quartz tuning fork under experimental conditions u , then Q u Substituting into the above formula, we can get the quality factor Q u The signal amplitudes of the lower quartz tuning fork are S 1 (Q u ),S 2 (Q u ),…,S n (Q u ). Based on the linear relationship between the signal amplitude S and the gas concentration C, S can be 1 (Q u ),S 2 (Q u ),…,S n (Q u ) and C 1 , C 2 , …, C n By performing linear fitting, we can obtain the conversion formula between the signal amplitude of the quartz tuning fork sensor and the concentration of the gas to be measured, that is, the concentration correction formula, which is specifically:

[0046] C(S)=k u ·S+b u (2)

[0047] In formula (2), S is the molecular absorption spectrum signal amplitude; C(S) is the concentration of absorbing gas molecules when the molecular absorption spectrum signal amplitude is S; k u and b u The quality factor is Q u The slope and intercept of the linear relationship between the molecular absorption spectrum signal amplitude and the concentration of the absorbing molecule when .

[0048] S15, the 2F signal peak value S calculated in step S13 u , input into the concentration correction formula; then the concentration value fitted in step S14 is fed back to the concentration correction formula, thereby reversing the true concentration value C(S) of the gas molecules to be measured. u ).

[0049] S2. Ambient temperature dependence correction:

[0050] Figure 2 : is a temperature dependence curve of the resonant frequency of the quartz tuning fork sensor of the present invention. Figure 2 As shown in Figure 2, a large number of experimental studies have shown that the temperature response curve of a quartz tuning fork sensor exposed to the atmosphere is nonlinear, has a negative quadratic curve characteristic, and exhibits a temperature response curve that is approximately equal to room temperature T. 0 The downward parabola with an opening as the center will cause the resonant frequency to drift when the temperature is too low or too high.

[0051] Therefore, the temperature dependence of the quartz tuning fork sensor can be corrected using the quartz tuning fork temperature correction formula under ambient temperature T.

[0052] Among them, the quartz tuning fork temperature correction formula is specifically:

[0053] f(T)=f(T 0 )*[1-k*(T- T 0 ) 2 ] (3),

[0054] In formula (3), T 0 and f(T 0 ) are the center temperature corresponding to the quadratic parabola equation obtained under laboratory test conditions and the center frequency of the quartz tuning fork corresponding to the center temperature; k is the coefficient of the quadratic term of the parabola equation, usually around 10 -8 magnitude; T represents the ambient temperature in the experiment.

[0055] The equation of the quadratic parabola is f(T)=32.760*[1-3.0*10 -8 *(T-25) 2 ].

[0056] In view of the technical limitations of quartz tuning forks in the detection of signal sources such as sound signals and light signals, the present invention proposes a pressure and temperature dependence correction method for quartz tuning fork sensors. Based on the response characteristics of quartz tuning forks to changes in environmental pressure and temperature explored experimentally, a set of effective correction algorithms is established, which effectively solves the reliability problem of measurement results of spectral systems or gas sensors developed based on quartz tuning forks in actual field environments, makes up for the important defects of existing technologies, and has broad practical value.

[0057] The above is an exemplary description of the invention. Obviously, the specific implementation of the present invention is not limited to the above-mentioned method. As long as such non-substantial improvements are made by adopting the method concept and technical solution of the present invention, or the concept and technical solution of the invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method for correcting the pressure and temperature dependence of a quartz tuning fork sensor, characterized in that: The following steps are involved: S1. Environmental pressure dependence correction: S11. Use the excitation source to excite the quartz tuning fork sensor to resonate near its resonance frequency f, combine the fast Fourier transform algorithm to perform spectrum analysis on the quartz tuning fork sensor signal, and combine the Lorentz function to fit the optimal center frequency f0 and quality factor Q of the resonance profile. u value; S12, the optimal center frequency f0 generates an analog modulation signal, and modulates the laser used in the spectral system, and the specific wavelength light beam output by the laser and the gas molecules to be measured in the gas sample generate a spectral signal through an absorption process; S13, select the second harmonic 2F signal in the spectrum signal generated by the laser output, detect it with a quartz tuning fork sensor and realize photoelectric conversion, and then calculate the 2F signal peak value A through the peak extraction algorithm u ; S14, fitted quality factor Q u The values ​​are input into the quality factor correction matrix function, and the corresponding concentration values ​​are fitted using a linear fitting algorithm; S15, the 2F signal peak value S calculated in step S13 u , input into the concentration correction formula; then the concentration value fitted in step S14 is fed back to the concentration correction formula, thereby reversing the true concentration value C(S) of the gas molecules to be measured. u ); S2. Ambient temperature dependence correction: The temperature dependence of the quartz tuning fork sensor is corrected using the temperature correction formula of the quartz tuning fork under ambient temperature T.

2. The method for correcting the pressure and temperature dependence of a quartz tuning fork sensor according to claim 1, characterized in that: In step S11, the excitation source is a mixed single-frequency signal based on the superposition of multiple single-frequency signals, and excites the quartz tuning fork sensor to resonate near its resonance frequency f0 by means of an optical signal, an acoustic signal or an electrical signal.

3. The pressure and temperature dependence correction method of the quartz tuning fork sensor according to claim 1, characterized in that: In step S14, the quality factor correction matrix function is specifically: In formula (1), S1, S2, ..., S n , respectively, are the measured values ​​of the molecular absorption spectrum signal amplitude under n known concentrations of the gases to be detected; Q is the quality factor value of the quartz tuning fork sensor; a1, a2, ..., a n and b1, b2, ..., b n They are respectively the coefficients of the linear relationship between the amplitude of the absorption spectrum signal of the corresponding molecule at the above n known concentrations and the quality factor value of the quartz tuning fork sensor: slope and intercept.

4. The method for correcting the pressure and temperature dependence of a quartz tuning fork sensor according to claim 3, characterized in that: In step S15, the concentration correction formula is specifically: C(S)=k u ·S+b u (2), In formula (2), S is the molecular absorption spectrum signal amplitude; C(S) is the concentration of the absorbing molecule when the molecular absorption spectrum signal amplitude is S; k u and b u The quality factor is Q u The slope and intercept of the linear relationship between the molecular absorption spectrum signal amplitude S and the concentration C of the absorbing molecules.

5. The method for correcting the pressure and temperature dependence of a quartz tuning fork sensor according to claim 1, characterized in that: In step S2, the quartz tuning fork temperature correction formula is specifically: f(T)=f(T0)*[1-k*(T- T0) 2 ] (3), In formula (3), T0 and f(T0) are the center temperature and the center frequency of the quartz tuning fork corresponding to the quadratic parabola equation obtained under laboratory test conditions, respectively; k is the coefficient of the quadratic term of the parabola equation, which is usually around 10 -8 magnitude; T represents the ambient temperature in the experiment; f(T) represents the central frequency of the quartz tuning fork at temperature T.

6. The method for calibrating the pressure and temperature dependence of a quartz tuning fork sensor according to claim 1, characterized in that: The quadratic parabola equation is specifically f(T)=32.760*[1-3.0*10 -8 *(T-25) 2 ].

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