Low humidity detection method and system based on phase detection high resolution QCM sensor

Abstract

The present invention relates to the field of sensor technology and humidity detection, and in particular to a low-humidity detection method and system of a QCM sensor based on high-resolution phase detection. The optimized miniaturized structure is particularly suitable for high-precision QCM applications, enhancing the resolution of humidity detection and the overall stability of the system; in order to ensure the high precision of phase detection, a phase shift circuit is introduced at the signal source end to solve the binary and nonlinear problems of traditional phase output. The high-precision DDS frequency source and conditioning circuit adopted ensure the stability of the amplitude of the driving signal, avoid the oscillation pause phenomenon of the sensor, and improve the working stability and signal quality of the system; an adaptive frequency stepping strategy based on phase voltage feedback is adopted to achieve rapid locking and fine adjustment of the resonant frequency of the quartz crystal. When far away from the resonance point, a large step length is used for rapid approximation, and when close to the resonant frequency, it switches to a small step length mode to balance the detection speed and accuracy, greatly improving the detection efficiency and real-time response capability.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology and humidity, and in particular to a low humidity detection method and system of a QCM sensor based on phase detection and high resolution. Background Art

[0002] As an important type of sensor, humidity sensors are widely used in meteorology, agriculture, industrial control and other fields. With the continuous development of science and technology, people's demand for high-performance humidity sensors is increasing. Traditional hair humidity sensors and dry-bulb humidity sensors have long been unable to meet the requirements of the industry, so many types of electronic humidity sensors have emerged. In the 1960s, a quartz crystal microbalance (QCM) humidity sensor appeared.

[0003] The quartz crystal microbalance (QCM) humidity sensor consists of a quartz crystal resonator and a metal electrode; the water molecules deposited on the metal electrode cause the surface mass of the quartz crystal resonator to increase, thereby generating a frequency shift related to the molecular weight of the adsorbed water ( ) Since the amount of water molecules adsorbed is related to the humidity to be measured in the environment, the humidity in the environment can be obtained by measuring the resonant frequency offset.

[0004] There are relatively few studies on the signal acquisition circuit of quartz crystal microbalance (QCM) sensors in China. However, several research groups have conducted in-depth research on the signal acquisition method of quartz crystal microbalance (QCM) sensors. Harbin Institute of Technology has made public the development of a QCM humidity sensor measurement system. The oscillation circuit uses a series oscillation circuit based on a voltage comparator, and a D-type trigger is used to build a difference frequency circuit to eliminate the frequency shift caused by temperature. The frequency acquisition module is completed by a single-chip microcomputer, and the software design method is the equal-precision measurement method. However, the signal source part of the design uses a series oscillation circuit, and the accuracy of the measurement system cannot be guaranteed.

[0005] Chinese invention patent application CN207779519U discloses an 8-channel QCM test system based on STM32. It achieves the effect of monitoring multiple groups of signals at the same time and comparing them. However, the signal source part adopts an oscillation circuit solution, and the signal acquisition part adopts a frequency counter. The measurement method using this method will have the problem of decreasing the quartz crystal quality factor, which will cause the circuit to stop oscillating and the measurement system to be unstable.

[0006] Chinese patent application CN115165656A discloses a high-frequency quartz chip microbalance small humidity sensor and humidity measurement device. The designed QCM humidity sensor is small in size and high in sensitivity. However, a network analyzer is used in the entire measurement system, which makes the measurement system closer to the laboratory environment and is not conducive to portable operation.

[0007] Chinese invention patent application CN220473287U discloses a QCM dual-channel oscillation acquisition device. It uses a dual-channel detection module and supports the advantage of multi-device interaction. However, the signal source part also uses an oscillation circuit solution, which may cause unstable signal acquisition in the application of biological immune sensors.

[0008] It can be seen from the above documents and patents that the signal source construction part of most QCM sensor-based measurement systems adopts the oscillation circuit method. This method will cause large damping caused by the load, causing the circuit to stop oscillating and the system resolution to be low. In addition, the system is expensive and not portable because it uses expensive instruments such as frequency meters or impedance analyzers for testing. Summary of the invention

[0009] In view of the above problems existing in the prior art, the present invention is proposed.

[0010] Therefore, the present invention provides a low humidity detection method based on phase detection high-resolution QCM sensor, which can solve the problem that traditional piezoelectric quartz crystal sensors are difficult to meet the requirements of high resolution and high sensitivity of humidity detection due to the limitations of their processing and packaging processes.

[0011] In order to solve the above technical problems, the present invention provides the following technical solutions, a low-humidity detection method of a QCM sensor with high resolution based on phase detection, including: utilizing the relationship between load mass and phase response, when the ambient humidity changes, monitoring the change in phase, reflecting the resonant frequency of the quartz crystal under different ambient humidity conditions, and designing a signal processing amplitude and phase detection circuit module based on the principle of phase measurement; and designing a phase shifting circuit at the signal driving circuit module to solve the binary and nonlinear problems of the phase output signal; adopting a variable step control algorithm at the single-chip microcomputer control unit module, and feeding back the collected phase information to the single-chip microcomputer in real time to control the phase frequency register in the frequency source; the signal driving circuit module adopts a DDS frequency source, and by adding a signal conditioning circuit control, ensures the output stability of the driving signal.

[0012] As a preferred solution of the low humidity detection method of the QCM sensor based on phase detection high resolution of the present invention, wherein: the resonant frequency of the quartz crystal under different environmental humidity conditions includes, Martin equation combined with Sauerbrey mass effect and Kanazawa liquid effect, calculate the frequency shift , Martin equation is expressed as,

[0013] ,

[0014] in, Expressed as the acoustic impedance of the quartz crystal, Expressed as surface coating quality, Expressed as the mass of the surface solution, Indicates the fundamental frequency of the quartz crystal;

[0015] The relationship between the load mass and the phase response includes the phase shift related to the amount of material in contact with the quartz crystal surface. The phase signal changes with the mass, achieving continuous measurement, which is expressed as,

[0016] ,

[0017] in, Expressed as a phase shift, Expressed as phase, Indicates the phase detected when the system is in state 1, Indicates the phase detected when the system is in state 2. is the change in surface solution mass, is the density of the substance, is the penetration depth of the wave in the liquid, is the viscosity of the substance, is the angular frequency, is the mass of the quartz crystal.

[0018] As a preferred solution of the low humidity detection method of the QCM sensor based on phase detection high resolution of the present invention, wherein: the designed phase detection part includes a mixer and a low-pass filter;

[0019] The QCM sensor module is divided into two channels, where channel one is the original signal, and channel two is obtained based on the phase shift of the source signal. The amplitude and frequency of the two signals are the same, and the low-pass filtering effect in the phase detection part is added to filter out the high-frequency component. The phase detection part provides a voltage proportional to the phase shift. The range of change is within 30 degrees, and the sinusoidal signal output is linearly related to the input phase. The final output voltage is expressed as:

[0020] ,

[0021] in, Represented as the original signal of channel one, It is represented as the channel 2 signal obtained by phase shifting the original signal. It is expressed as the amplitude of the channel 1 signal, It is expressed as the amplitude of the channel 2 signal. is the frequency of the signal, It is expressed as the offset of the channel 2 signal after the phase shift is 90 degrees. Expressed as time, Expressed as voltage-phase coefficient;

[0022] The mixer and low-pass filter are connected in series to the original signal of channel one. and channel 2 signal Later, the AD8302 module was used.

[0023] As a preferred solution of the low humidity detection method of the QCM sensor based on phase detection high resolution described in the present invention, the AD8302 module has two-channel output, the amplitude channel provides an output signal of the amplitude ratio of the two input signals, the phase detection channel identifies the phase difference between the two input signals, the sensor response is mixed with the source signal and passes through the low-pass filtering effect to generate a DC output proportional to the resonator phase shift, and the combination of the output phase voltage and the output amplitude voltage measurement obtains the complete characteristics of the sensor.

[0024] As a preferred solution of the low humidity detection method of the QCM sensor based on phase detection high resolution described in the present invention, wherein: the phase shift circuit includes shifting the test signal by 90° in the signal driving circuit module, and including a phase shift network composed of R and C at the input end of the sensor, the phase shift network composed of R and C is used to obtain two signals with a phase shift of 90° and the same amplitude, and the two channels are sent to the phase detection part for processing, so that the phase difference signals of the two signals are calibrated with each other;

[0025] Among them, R represents resistance and C represents capacitance.

[0026] As a preferred solution of the low humidity detection method of the QCM sensor based on phase detection high resolution described in the present invention, the variable step length control algorithm includes the frequency control of the signal driving part using AD9834, there is a 16-bit control register inside the AD9834, the working mode is selected by writing the control word, and different frequency control words are written to the phase accumulation register to realize the frequency sweep output. When the output phase voltage When the output is greater than 200mv, the frequency is adjusted to coarse adjustment, close to the resonant frequency, and the efficiency of the detection system is improved; when the output When it is less than 200mv, the frequency adjustment should be fine-tuned to improve the resolution of the detection system. Due to the phase noise in the system circuit and the nonlinearity of the circuit elements, the output voltage approaches 0v. When the voltage is collected, when it is judged that the voltage is around 20mv, it is determined that the resonant frequency of the quartz crystal in different humidity environments is measured;

[0027] The frequency resolution is obtained by dividing the Allan deviation of the output voltage of the QCM sensor module under test by the voltage sensitivity of the QCM sensor module under test, expressed as,

[0028] ,

[0029] in, Expressed as the frequency resolution of the system, Expressed as voltage sensitivity, Expressed as the Allan deviation of the output voltage;

[0030] The single-chip control unit module is controlled by STM32 single-chip microcomputer, and the phase voltage is collected and amplitude voltage , continuous monitoring signal and Through the signal processing and control based on the STM32 microcontroller system, real-time and The feedback adjustment signal drives the frequency output of the circuit module.

[0031] As a preferred solution of the low humidity detection method of the QCM sensor based on phase detection high resolution described in the present invention, wherein: the conditioning circuit ensures the output stability of the driving signal, and due to the structural characteristics of the DDS frequency source, the output end has noise and stray components. The present invention adds a signal conditioning circuit after the phase shift circuit to improve the detection level of the system.

[0032] Another object of the present invention is to provide a low humidity detection system of a QCM sensor with high resolution based on phase detection. The key point of using a quartz crystal sensor to build a humidity measurement system is how to lock the resonant frequency of the QCM. The original intention of the system is to accurately measure the resonant frequency of the quartz crystal during the change of environmental humidity, so as to accurately reflect the change of environmental humidity. The traditional solution improves the sensitivity of the quartz crystal microbalance (QCM) application by increasing the fundamental frequency of the sensor. However, this improvement in sensitivity has not been completely transferred to the resolution. Due to the influence of phase noise in the circuit, the frequency stability cannot be controlled, so that the system cannot achieve the expected resolution. Therefore, when considering the humidity measurement system, the detection capability of the QCM sensor must be considered from different angles. In order to improve the resolution of the quartz crystal humidity sensor, the system establishes a relationship between the phase and the moisture content. A quartz crystal humidity sensor measurement system based on phase measurement is designed. Compared with the traditional frequency response, the phase signal measurement method is not easy to stop the phase response system, the performance is stable, and the resolution is higher. Starting from the phase angle, the present invention establishes a phase quality relationship, improves the stability of the phase, improves the frequency stability, and indirectly improves the sensitivity. The signal driving circuit uses a DDS module to ensure the stability of the output frequency, and the sensor will not stop vibrating during the humidity measurement process. The signal acquisition part uses a phase detector to collect phase and amplitude voltage, ensuring the high resolution and high sensitivity of the system. In addition, the designed system has the advantages of miniaturization and convenience.

[0033] As a preferred solution of the low humidity detection method of the QCM sensor based on phase detection high resolution of the present invention, it includes: a signal driving circuit module, a QCM sensor module, a signal processing amplitude and phase detection circuit module, a signal acquisition module and a single chip control unit module;

[0034] The signal driving circuit module controls the output signals of different frequencies by controlling the DDS, and outputs two signals through the phase shift circuit and the signal conditioning circuit. The reference branch and the sensing branch in the QCM sensor module have the same output and are shifted by 90 degrees. The output signal of the QCM sensor module is sent to the signal processing amplitude detection and phase detection circuit module, where the signal processing amplitude detection and phase detection circuit module is composed of a mixer and a filter. The signal acquisition module converts the amplitude ratio and phase difference of the output signal of AD8302 into a voltage output signal, and sends it to the single-chip microcomputer control unit for processing. The single-chip microcomputer control unit module then controls the DDS frequency source in real time according to the received phase signal by changing the step size to ensure that the resonant frequency of the quartz crystal is detected in real time.

[0035] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and is characterized in that when the processor executes the computer program, the steps of any one of the methods for low-humidity detection of a QCM sensor based on phase detection high resolution are implemented.

[0036] A computer-readable storage medium having a computer program stored thereon, characterized in that when the computer program is executed by a processor, the steps of any one of the methods for low-humidity detection of a QCM sensor based on phase detection high resolution are implemented.

[0037] Beneficial effects of the present invention: The method of the present invention utilizes the concept of phase signal detection, designs a phase signal acquisition module, and designs a QCM humidity sensor system based on phase detection. The measurement system is miniaturized and is particularly suitable for high-resolution QCM applications, which improves the resolution of the humidity detection system and the stability of the entire system. In order to improve the accuracy of phase detection, a phase shift circuit is used at the signal source to solve the binary and nonlinear problems of the phase output signal, adopt a higher-precision DDS frequency source, and increase the signal conditioning circuit control to make the drive signal amplitude output stable. The sensor will not stop vibrating. Based on the output of the phase voltage, when the quartz crystal resonant frequency is locked, the frequency step size is controlled according to the size of the output voltage. This method can quickly approach the resonance point when the frequency source excitation frequency is far from the resonant frequency, thereby improving the detection efficiency. When the frequency source frequency is near the resonant frequency, the step size is reduced to improve the real-time detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0039] Figure 1 A flow chart of a low humidity detection method using a QCM sensor with high resolution based on phase detection provided by an embodiment of the present invention.

[0040] Figure 2 A schematic diagram of a quartz crystal (QCM) humidity detection system based on phase detection, which is a low humidity detection system based on a phase detection high-resolution QCM sensor provided by an embodiment of the present invention.

[0041] Figure 3 The invention provides a result obtained by phase discrimination between a reference signal before phase shift and a reference signal after phase shift and a measurement signal of a low humidity detection method based on a phase detection high-resolution QCM sensor provided by an embodiment of the present invention.

[0042] Figure 4 An environmental humidity sensitivity curve of a humidity sensor based on a quartz crystal microbalance according to a low humidity detection method of a QCM sensor based on phase detection high resolution provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0043] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0044] Example 1

[0045] Reference Figure 1 , which is the first embodiment of the present invention, provides a low humidity detection method of a QCM sensor based on phase detection high resolution, comprising:

[0046] S1: By utilizing the relationship between load mass and phase response, when the ambient humidity changes, the slight change in phase is monitored to accurately reflect the resonant frequency of the quartz crystal under different ambient humidity conditions, and a signal acquisition module is designed based on the principle of phase measurement.

[0047] It should be noted that Sauerbrey discovered the linear relationship between the change in the resonant frequency of a quartz crystal (QCM) and the mass deposited on it, and established the fact that the decrease in the resonant frequency of the resonator is proportional to the increase in the mass density on the sensor surface. The Sauerbrey equation is described as follows.

[0048] ,

[0049] in, Expressed as the fundamental frequency of the quartz crystal, Expressed as the effective area of ​​the electrode, Expressed as density, Expressed as the elastic stiffness coefficient of the quartz crystal, Expressed as frequency offset;

[0050] In the past, most measurement systems based on quartz crystal (QCM) sensors were based on the Sauerbrey equation, but they all ignored the properties of the material being measured by the sensor and the resolution of the system was subject to certain limitations. For the application of quartz crystal (QCM) in humidity detection, the present invention starts with the Martin equation, which combines the Sauerbrey mass effect and the Kanazawa liquid effect. Martin's equation is described as follows.

[0051] ,

[0052] in, Expressed as the acoustic impedance of the quartz crystal, Expressed as surface coating quality, Expressed as the mass of the surface solution, Indicates the fundamental frequency of the quartz crystal;

[0053] The relationship between the load mass and the phase response is shown in the following formula. As can be seen from the following formula, the phase shift is related to the amount of material in contact with the surface of the quartz crystal. The phase signal changes with the change of mass, which can achieve continuous measurement.

[0054] ,

[0055] in, Expressed as a phase shift, Expressed as phase, Indicates the phase detected when the system is in state 1, Indicates the phase detected when the system is in state 2. is the change in surface solution mass, is the density of the substance, is the penetration depth of the wave in the liquid, is the viscosity of the substance, is the angular frequency, is the mass of the quartz crystal.

[0056] The QCM sensor module can be divided into two channels, where channel one is the original signal and channel two is obtained based on the phase shift of the source signal. The amplitude and frequency of the two signals are the same, and the low-pass filtering effect in the phase-locked part filters out the high-frequency component. The phase-locked part based on the mixer provides a voltage proportional to the phase shift. The change in the amount of change is small and the range of change is within 30 degrees. Within a certain range, the sinusoidal signal output is linearly related to the input phase. The final output voltage can be shown as follows, where is the phase change around 90 degrees.

[0057] ,

[0058] The specific signal processing amplitude and phase detection circuit module construction process, the starting point of the present invention is that the system can detect very small phase shifts in the sensor response, so the construction of the phase detection part is extremely important. The mixer and the low-pass filter are connected in series to the input signal and Later, as part of the phase detector, the AD8302 module is used in the design of this system. The module has two channels of output, one of which provides an output signal of the amplitude ratio of the two input signals, and the other is used to identify the phase difference of the two input signals. The sensor response is mixed with the source signal and low-pass filtered to produce a DC output proportional to the resonator phase shift. The combination of output phase voltage and output amplitude voltage measurement obtains the complete characteristics of the sensor.

[0059] It should be noted that an additional amplifier is added to the signal acquisition module to enhance the phase detection signal. Both reference voltages are set to 900mv to center their biases, which is used to properly fix the output of the amplifier in the reference state to compensate for any offset. The gain of the differential amplifier can be increased to provide the maximum resolution of phase shift monitoring. At the same time, it helps to input the phase voltage signal to the microcontroller in real time for negative feedback variable step adjustment of the frequency.

[0060] S2: In order to improve the accuracy of phase detection, the signal processing amplitude and phase detection circuit module is designed, which includes a mixer and a low-pass filter, and a phase shift circuit is designed in the signal driving circuit module to solve the binary and nonlinear problems of the phase output signal.

[0061] It should be noted that how to accurately lock the frequency of the maximum conductance of the quartz crystal sensor under different ambient humidity has always been a puzzling problem. On the one hand, when the driving frequency is close to the crystal resonant frequency, the conductivity change rate weakens, increasing the requirements for ADC resolution and increasing the measurement error. On the other hand, the conductivity response obtained by the measurement circuit cannot help determine whether the current driving frequency is higher or lower than the resonant frequency.

[0062] Therefore, in order to solve the above problem, the test signal is shifted 90° in advance in the signal driving circuit module. For this purpose, a phase shift network composed of R and C is included at the input end of the sensor circuit. The phase shift network composed of R and C obtains two signals with a phase shift of 90° and the same amplitude. Finally, the two channels are sent to the phase detection part for processing. This method calibrates the phase difference signals of the two signals with each other. Among them, R represents resistance and C represents capacitance.

[0063] S3: In order to improve the real-time performance of phase detection, a variable step-size control algorithm is used at the frequency source. The phase information collected by the system is fed back to the microcontroller in real time to control the phase frequency register in the frequency source.

[0064] It should be noted that in order to improve the real-time performance of phase acquisition, the frequency control program is optimized and a variable step control algorithm is adopted. The signal drive part uses the frequency control of AD9834. AD9834 has a 16-bit control register inside, and its working mode is selected by writing a control word to it. Write different frequency control words to the phase accumulation register to achieve frequency sweep output. If the frequency scanning range is too small, it may be that the resonant frequency is not within the scanning range and the resonant frequency cannot be obtained. If the scanning range is too large, a longer scanning time is required and real-time performance cannot be guaranteed. In order to improve the phase sampling efficiency, the frequency control program is optimized. That is, when the output phase voltage When the output is greater than 200mv, the frequency is adjusted to coarse adjustment to quickly approach the resonant frequency and improve the efficiency of the detection system; When it is smaller than 200mv, the frequency adjustment should be fine-tuned to improve the resolution of the detection system. Due to the phase noise in the entire system circuit and the nonlinearity of the circuit elements, the output voltage approaches 0v but is not 0v. Therefore, when collecting voltage, when the output phase voltage is judged to be around 20mv, it is judged to be within a certain set limit, and it can be considered that the resonant frequency of the quartz crystal in different humidity environments is measured.

[0065] Allan deviation is applied to study the actual frequency resolution of the developed system. The Allan deviation value varies with the averaging time. Since the system developed in this work determines the resonant frequency of the quartz crystal sensor according to the phase voltage output by the measured system, the frequency resolution of the developed system can be obtained by dividing the Allan deviation of the measured system output voltage by the voltage sensitivity of the measured system. The relationship is as follows:

[0066] ,

[0067] in, Expressed as the frequency resolution of the system, Expressed as voltage sensitivity, Expressed as the Allan deviation of the output voltage;

[0068] The single-chip control unit module is controlled by STM32 single-chip microcomputer. and , continuous monitoring signal and Through signal processing and control based on STM32 microcontroller, real-time and Feedback adjusts the frequency output of the DDS driver module.

[0069] S4: In order to improve the stability of the phase signal, a higher-precision DDS frequency source is used in the signal driving circuit, and a signal conditioning circuit is added to ensure the output stability of the driving signal.

[0070] It should be noted that due to the structural characteristics of the DDS frequency source, its output end inevitably has noise and spurious components, which are mainly caused by phase truncation, amplitude quantization and DAC conversion. Therefore, the present invention adds a signal conditioning circuit.

[0071] The frequency source part uses a sweeping frequency source to drive the quartz crystal sensor. The frequency and amplitude of the excitation source commonly used are not stable enough and the output power is low. The present invention uses a higher-precision DDS frequency source. Due to the composition and structural characteristics of the DDS frequency source, its output end inevitably has noise and stray components, which are mainly errors caused by phase truncation, amplitude quantization and DAC conversion. Therefore, the present invention adds a signal conditioning circuit, and the function of the signal conditioning circuit is to ensure that the peak value of the sinusoidal signal remains constant in the working frequency range. The reference frequency signal is set by the conditioning circuit of the input signal, and has a very stable frequency output and minimal phase noise to improve the detection level of the system.

[0072] Example 2

[0073] refer to Figure 2-Figure 4, which is the second embodiment of the present invention, provides a low humidity detection system based on phase detection high resolution QCM sensor, characterized by: comprising a signal driving circuit module, a QCM sensor module, a signal processing amplitude and phase detection circuit module, a signal acquisition module and a single chip control unit module;

[0074] The signal driving circuit module controls the output signals of different frequencies by controlling the DDS, and outputs two signals through the phase shift circuit and the signal conditioning circuit. The reference branch and the sensing branch in the QCM sensor module have the same output and are shifted by 90 degrees. The output signal of the QCM sensor module is sent to the signal processing amplitude detection and phase detection circuit module, wherein the signal processing amplitude detection and phase detection circuit module is composed of a mixer and a filter. The signal acquisition module converts the amplitude ratio and phase difference of the output signal of AD8302 into a voltage output signal, and sends it to the single-chip microcomputer control unit for processing. The single-chip microcomputer control unit module then controls the DDS frequency source in real time according to the received phase signal by changing the step size to ensure that the resonant frequency of the quartz crystal is detected in real time.

[0075] Depend on Figure 2 It can be seen that the system construction is mainly composed of five modules, including signal driving circuit module, QCM sensor module, signal processing amplitude and phase detection circuit module, signal acquisition module and single chip control unit module. Among them, the signal driving circuit module controls the output signals of different frequencies by DDS, and outputs two signals through the phase shift circuit and signal conditioning circuit. The QCM sensor module contains channel one signal , Channel 2 signal The output signals INPA and INPB of the QCM sensor module are sent to the signal processing amplitude detection and phase detection circuit module, where the signal processing amplitude detection and phase detection circuit module is mainly composed of a mixer and a filter. The signal acquisition module contains two amplifiers for enhancing the phase detection signal and setting the reference voltage. The signal acquisition module converts the amplitude ratio and phase difference of the output signal of the signal processing amplitude detection and phase detection circuit module into a phase voltage. and amplitude voltage , and sent to the single-chip control unit for processing, and the single-chip control unit module then changes the step size in real time to control the DDS frequency source according to the received phase signal, ensuring that the resonant frequency of the quartz crystal is detected in real time.

[0076] Depend on Figure 3It can be seen that the reference signal before phase shift and the reference signal after phase shift are phase-compared with the measured signal. It can be seen from the figure that the measurement result has an obvious translation after phase shift. When the phase difference is about 0°, the actual response part of the phase-comparison part cannot determine whether the phase difference is positive or negative, and there is a large error and nonlinearity. For example, the level values ​​of point A and point B in the figure are the same, but the phases of the two are opposite to each other. Therefore, if the level value of the actual small phase is measured, there will be a problem of phase binary judgment. By adding a phase shift circuit, A and B will become points A1 and B1 at this time. At this time, the positive and negative phase difference can be judged by the measured voltage value. If the measured voltage value is the voltage value of A1, then the phase difference between the measured signal and the reference signal can be judged to be A. Since the two reference voltages of the signal sampling part are set to 900 mv, they are used to properly fix the output of the amplifier in the reference state. Figure 3 The results are obtained by phase discrimination between the reference signal before phase shift and the reference signal after phase shift and the measurement signal. The final designed system can achieve a minimum frequency resolution of about 0.22 Hz within a measurement time of 0.1 s. The system voltage sensitivity is 1.6mv / Hz, which is in line with the expected design, improves the system resolution, and improves the system stability.

[0077] Figure 4 To plot the frequency offset versus humidity, the rate of change of the frequency offset at different ambient humidity can be intuitively displayed. The frequency offset gradually increases with the increase of humidity. As the humidity increases, the offset changes faster, while the frequency offset changes slowly at low humidity. The proposed QCM sensor humidity detection system based on phase detection has a humidity sensitivity of 10.8Hz / %RH in a low humidity environment and when the ambient humidity is between 0%RH-30%RH.

[0078] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

[0079] Example 3

[0080] The third embodiment of the present invention is different from the first two embodiments in that:

[0081] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions to enable a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program codes.

[0082] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0083] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering or, if necessary, processing in another suitable manner, and then stored in a computer memory.

[0084] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

Claims

1. A low humidity detection method based on a phase detection high-resolution QCM sensor, characterized in that: include, By using the relationship between load mass and phase response, when the ambient humidity changes, the change in phase is monitored to reflect the resonant frequency of the quartz crystal under different ambient humidity conditions, and a signal acquisition module is designed based on the principle of phase measurement; Design the signal processing amplitude and phase detection circuit module, and design the phase shift circuit in the signal driving circuit module to solve the binary and nonlinear problems of the phase output signal; A variable step length control algorithm is used in the single-chip control unit module, and the collected phase information is fed back to the STM32 single-chip microcomputer in real time to control the phase frequency register in the frequency source; The signal driving circuit module adopts a high-precision DDS frequency source. By adding signal conditioning circuit control, the driving signal amplitude output is stabilized, thus improving the detection level of the system. The designed signal processing amplitude and phase detection circuit module includes a mixer and a low-pass filter; The input part of the QCM sensor module has two channels, channel one is the original signal, and channel two is obtained based on the phase shift of the original signal. The amplitude and frequency of the two signals are the same. The low-pass filter in the phase detection part filters out the high-frequency component. The phase detection part provides The phase shift is proportional to the voltage, due to The range of change is within 30 degrees, and the sinusoidal signal output is linearly related to the input phase. The final output voltage is expressed as: Among them, u1 represents the original signal of channel one, u2 represents the signal of channel two obtained by phase shifting based on the original signal, U1 represents the amplitude of the signal of channel one, U2 represents the amplitude of the signal of channel two, and ω represents the frequency of the signal. It is expressed as the offset of the channel 2 signal after the phase shift is 90 degrees, t is expressed as time, and K is expressed as the voltage-phase coefficient; The mixer and low-pass filter are connected in series behind the original signal u1 of channel one and the signal u2 of channel two, using the AD8302 module; The phase shift circuit includes shifting the test signal by 90° in the signal driving circuit module, and including a phase shift network composed of R and C at the input end of the sensor circuit, the phase shift network composed of R and C is used to obtain two signals with a phase shift of 90° and the same amplitude, and the two-channel signals are sent to the signal processing amplitude and phase detection circuit module for processing, so that the phase difference signals of the two channels are calibrated with each other; Among them, R represents resistance and C represents capacitance; The variable step length control algorithm includes the frequency control of the signal driving part using AD9834. There is a 16-bit control register inside the AD9834. The working mode is selected by writing the control word, and different frequency control words are written to the phase accumulation register to realize the frequency sweep output. When the output phase voltage is greater than 200mv, the frequency is adjusted to coarse adjustment, close to the resonant frequency, and the efficiency of the detection system is improved; when the output phase voltage is When the voltage is less than 200mv, the frequency adjustment should be fine-tuned to improve the resolution of the detection system. Due to the phase noise in the detection system circuit and the nonlinearity of the circuit elements, when the voltage is 20mv, it is determined to be the resonant frequency of the quartz crystal in different humidity environments. The frequency resolution is obtained by dividing the Allan deviation of the output phase voltage of the QCM sensor module under test by the voltage sensitivity of the QCM sensor module under test, expressed as, Where Δf(t) represents the frequency resolution of the system, S represents the voltage sensitivity, and σ o (t) is expressed as the Allan deviation of the output voltage; The single-chip control unit module is controlled by STM32 single-chip microcomputer, and the phase voltage is collected And amplitude voltage uA, continuous monitoring signals u1 and u2, signal processing and control through STM32 microcontroller, real-time according to And uA feedback adjusts the frequency output of the signal driving the circuit module.

2. The low humidity detection method of the QCM sensor based on phase detection high resolution as claimed in claim 1, characterized in that: The resonant frequency of the quartz crystal under different ambient humidity conditions includes the Martin equation combined with the Sauerbrey mass effect and the Kanazawa liquid effect to calculate the frequency shift Δf. The Martin equation is expressed as: Among them, Z cq Expressed as the acoustic impedance of the quartz crystal, m c Expressed as surface coating mass, m l It is expressed as the mass of the surface liquid, and f0 is the fundamental frequency of the quartz crystal; The relationship between the load mass and the phase response includes the phase shift related to the amount of material in contact with the quartz crystal surface. The phase signal changes with the mass, achieving continuous measurement, which is expressed as, in, Expressed as a phase shift, Expressed as phase, Indicates the phase detected when the system is in state 1, Indicates the phase detected at system state 2, Δm l =ρ l δ l is the surface mass change, ρ l Expressed as the density of the substance, δ l =(2η l / ω l ρ l ) 1 / 2 is the penetration depth of the wave in the liquid, η l is the viscosity of the substance, m l is the angular frequency, m q is the mass of the quartz crystal.

3. The low humidity detection method of the QCM sensor based on phase detection high resolution as claimed in claim 2, characterized in that: The AD8302 module has two-channel output. The amplitude channel provides an output signal of the amplitude ratio of the two input signals, and the phase detection channel identifies the phase difference between the two input signals. The sensor response is mixed with the source signal and passes through a low-pass filtering effect to produce a DC output proportional to the resonator phase shift. The combination of output phase voltage and output amplitude voltage measurement obtains the complete characteristics of the sensor.

4. The low humidity detection method based on phase detection high resolution QCM sensor as claimed in claim 3, characterized in that: Due to the structural characteristics of the DDS frequency source in the signal driving circuit module, there are noise and stray components at the output end. Therefore, a signal conditioning circuit is added after the phase shift circuit to improve the detection level of the system.

5. A system based on the low humidity detection method of the QCM sensor based on phase detection high resolution according to any one of claims 1 to 4, characterized in that: It includes a signal driving circuit module, a QCM sensor module, a signal processing amplitude and phase detection circuit module, a signal acquisition module and a single-chip microcomputer control unit module; The signal driving circuit module controls the output signals of different frequencies by controlling the DDS, and outputs two signals through the phase shift circuit and the signal conditioning circuit. The reference branch and the sensing branch in the QCM sensor module have the same output and are shifted by 90 degrees. The output signal of the QCM sensor module is sent to the signal processing amplitude detection and phase detection circuit module, wherein the signal processing amplitude detection and phase detection circuit module is composed of a mixer and a filter. The signal acquisition module converts the amplitude ratio and phase difference of the output signal of AD8302 into a voltage output signal, and sends it to the single-chip microcomputer control unit for processing. The single-chip microcomputer control unit module then controls the DDS frequency source in real time according to the received phase signal by changing the step size to ensure that the resonant frequency of the quartz crystal is detected in real time.

6. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 4 are implemented.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 4 are implemented.

Images