Double-QCM difference frequency type humidity sensor measuring method and double-QCM difference frequency type humidity sensor measuring device

Abstract

The invention discloses a double-QCM difference frequency type humidity sensor measuring method and device, is applied to the technical field of electronics and circuits, and aims to solve the problem of low humidity measuring precision in the prior art. The characteristic that the output frequencies of the double QCMs are different in the humidity environment is utilized, the output frequencies of the double-QCM humidity sensor are measured respectively, difference frequency calculation is carried out, the influence of QCM output frequency drift is reduced, frequency difference-humidity data fitting is carried out through frequency difference data, then the frequency difference of the double QCMs is converted into humidity data through a fitting relational expression, and humidity measurement is achieved. The error of a humidity measurement result is further reduced by introducing a dual-channel measurement scheme and a fitting algorithm.

Description

Technical Field

[0001] The invention belongs to the field of electronics and circuit technology, and in particular relates to a humidity measurement technology and device. Background Art

[0002] The QCM humidity sensor is a sensor that uses the humidity-sensitive film on the surface of the quartz crystal resonator electrode as a sensitive element and the quartz crystal resonator as a transducer element. It uses the inverse piezoelectric effect and surface mass sensitive effect of the quartz crystal to achieve sensing measurement. Its characteristics are that when an electric field is applied to the quartz crystal, the crystal surface will produce mechanical deformation; if the electric field is an alternating electric field, mechanical oscillations will occur in the lattice, and the quartz crystal will vibrate mechanically at a certain frequency. When the frequency of the alternating voltage is the same as the natural frequency of the crystal, resonance will occur, and the mechanical vibration will reach the maximum. This frequency is also called the resonant frequency. Under certain conditions, when the electrode surface on the quartz crystal adsorbs the substance to be measured, its natural frequency will change, and the change in frequency is related to the adsorbed mass. According to the Sauerbrey equation, since the fundamental frequency and electrode area of ​​a specific quartz crystal are fixed values, the change in the frequency of the quartz crystal is in a simple linear relationship with the change in the mass attached to the electrode on the crystal surface.

[0003] Therefore, a layer of humidity-sensitive material film is plated on the electrode surface of the quartz crystal to make a QCM humidity sensor. The sensor is placed in a humid environment. When the humidity-sensitive film adsorbs water vapor molecules in the air, the surface quality of the sensor changes. The output frequency change of the QCM is measured, and the humidity of the environment to be measured can be obtained by processing and converting the resonant frequency.

[0004] Existing humidity measurement methods include: weight method, electrolysis method, capacitance method, cold mirror method and vibration frequency method. Among them, the weight method has the characteristics of high precision, but the operation is more complicated and must absorb enough water, so it is especially difficult for low-humidity gas to be measured; the electrolysis method has good measurement accuracy and low price, but the electrolytic cell must be dried for a long time before use, and has poor anti-pollution ability. The measurement range of the capacitance method can reach a very low level and the response speed is very fast, but most of them have serious problems of aging and drift; although the cold mirror method has the advantages of wide measurement range, small drift and high precision, it responds slowly in low humidity environment and is complicated to operate. In addition, it has high requirements on the cleanliness and corrosiveness of the gas, so it is generally only used as a humidity benchmark in the laboratory. The typical representative of the vibration frequency method is the QCM humidity sensor, which has the potential advantages of high sensitivity, good stability, high accuracy, wide measurement range, low cost, and easy to achieve on-site continuous detection. Regarding the QCM humidity sensor, it is necessary to select a suitable humidity-sensitive film to prepare a high-performance QCM humidity sensor to achieve high-precision humidity measurement; but the QCM humidity sensor also generally has the problem of frequency drift, especially in an environment with high relative humidity (greater than 75% RH). The oscillation circuit method is usually used to measure the resonant frequency of the QCM. The principle is to connect a quartz crystal as a frequency-selective element to a positive feedback circuit to form an oscillation circuit. The oscillation frequency of the circuit is the resonant frequency of the quartz crystal. The output end of the circuit is connected to a digital frequency meter to measure the signal, and the resonant frequency of the quartz crystal can be obtained. The oscillation circuit method has the advantages of simple structure and fast speed, and is one of the commonly used methods for measuring the resonant frequency of quartz crystals. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a dual-QCM difference frequency humidity sensor measurement method and device. By utilizing the characteristic that the dual QCM has different output frequencies in a humidity environment, the output frequencies of the dual QCM humidity sensors are measured respectively, and the difference frequency calculation is performed. The frequency difference data is used to fit the frequency difference-humidity data. Then, the frequency difference of the dual QCM is converted into humidity data through the fitting relationship to achieve humidity measurement.

[0006] One of the technical solutions adopted by the present invention is: a dual QCM difference frequency humidity sensor measurement method, comprising: respectively measuring the output frequencies of two humidity sensors with different sensitivities in a known humidity environment, and calculating the frequency difference in the known humidity environment; fitting the frequency differences corresponding to the obtained multiple different known humidity environments with frequency difference-humidity data through a fitting algorithm to obtain a frequency-humidity relationship; then measuring the output frequencies of the two humidity sensors with different sensitivities in the humidity environment to be measured, and calculating the frequency difference in the humidity environment to be measured, and using the fitted frequency-humidity relationship to convert the frequency difference in the humidity environment to be measured into humidity data, thereby realizing humidity measurement of the humidity environment to be measured.

[0007] The second technical solution adopted by the present invention is: a dual QCM difference frequency humidity sensor measuring device; comprising: two QCM humidity sensors with different humidity sensitivities, respectively named QS1 and QS2, and also comprising: an FPGA core board;

[0008] The FPGA module mainly includes two parts: a digital frequency meter and an embedded soft core;

[0009] The digital frequency meter includes: a multiplexer module, a clock signal generating module, a pulse counting module, and an operation module; the frequency measurement process of QS1 is:

[0010] The multiplexer first connects the clock frequency signal clk_fx to be measured to the input port of the digital frequency meter; generates a reference clock signal CLK_FS of equal precision frequency through the clock signal generation module; the pulse counting module uses its internal register to generate a gating signal for counting the signal to be measured under the clock frequency signal clk_fx to be measured; and simultaneously captures the rising and falling edges of the reference clock signal CLK_FS and the clock signal clk_fx to be measured to ensure that the counting is triggered and terminated within the gating signal; within the gating signal, the pulse counting module counts the clock signal clk_fx to be measured and the reference clock signal CLK_FS respectively; finally, the operation module converts the frequency measurement value of the clock signal clk_fx to be measured according to the pulse counting results of the reference clock signal CLK_FS and the clock signal clk_fx to be measured, and stores the result in the first register reg_1 in the operation module;

[0011] After completing the frequency measurement of QS1, the multiplexer switches the input signal of the digital frequency meter, connects the output frequency signal of QS2 to the digital frequency meter, performs the same frequency measurement process as QS1, obtains the frequency measurement value of QS2, and stores the result in the second register reg_2 in the operation module, and then switches the input signal of the digital frequency meter again through the multiplexer, connects the output frequency of QS1 to the digital frequency meter, and repeats the cycle to realize the frequency measurement of the dual-channel QCM humidity sensor; at the same time, after each frequency measurement of the dual-channel QCM humidity sensor is completed, the operation module will also read the frequency measurement values ​​of QS1 and QS2 stored in its internal first register reg_1 and second register reg_2, perform difference frequency calculation, and obtain frequency difference data;

[0012] The embedded soft core includes: a Nios II processor and an Avalon bus module; the Nios II processor reads the frequency difference data output by the operation module through the Avalon bus module; then the Nios II processor fits the frequency difference-humidity data through a fitting algorithm to obtain a frequency-humidity relationship as shown in formula (1):

[0013] f(x)=ax 2+bx+c (1)

[0014] Where x is the frequency, f(x) is the humidity conversion result corresponding to the current frequency, and a, b, and c are correlation coefficients.

[0015] When measuring humidity, the Nios II processor will convert the frequency difference to humidity using the frequency-humidity relationship.

[0016] The embedded soft core also includes a UART serial port module, through which the frequency measurement result and the frequency-humidity relationship and the influence of humidity measurement are displayed on the PC side.

[0017] Beneficial effects of the present invention: The present invention uses the frequency difference value output by the dual QCM humidity sensor to fit the frequency difference-humidity data, and the determination coefficient of the obtained fitting relationship is higher; the fitting algorithm is introduced, and the correlation coefficients a, b, and c in the obtained frequency-humidity relationship are saved as double-precision floating-point types. When performing frequency-to-humidity data conversion operations, the correlation coefficient can participate in the operation with up to 16 decimal digits (15 decimal places) , The humidity value finally obtained is more accurate, and it also further simplifies the data calibration process before starting humidity measurement. The introduction of the dual-channel measurement scheme and the fitting algorithm further reduces the error of the humidity measurement results. The present invention has the following advantages:

[0018] (1) The present invention makes full use of the inverse piezoelectric effect and surface mass sensitivity effect of QCM, and can obtain humidity information by measuring the output frequency change of the QCM humidity sensor. Compared with the traditional humidity sensor, the structure is simpler and the measurement error is smaller;

[0019] (2) The present invention adopts a dual-channel measurement scheme, uses two QCM humidity sensors, performs frequency difference processing on the output frequency of the dual QCM humidity sensors, and uses the frequency difference between the two to perform frequency difference-humidity conversion. Through experimental verification, the influence of the output frequency drift of the QCM humidity sensor is suppressed to a certain extent, further reducing the humidity measurement error;

[0020] (3) The present invention introduces a fitting algorithm to simplify the data calibration process. In the frequency difference-humidity conversion operation process, the correlation coefficient of the fitting relationship is directly involved in the operation with double-precision floating point numbers, avoiding the situation where the humidity conversion result has large errors or even errors due to insufficient coefficient precision;

[0021] (4) The digital frequency meter designed by the present invention uses FPGA as the core measurement device, which can accurately measure high-frequency signals. Compared with other microprocessors, it has more advantages in measuring high-frequency signals and other complex numerical calculations;

[0022] (5) The present invention designs a multiplexer that allows multiple QCM output frequency signals to be simultaneously connected to the digital frequency meter, so that the digital frequency meter can be effectively reused, promoting multi-channel measurement and sensor arrays with minimal logic resource overhead, and eliminating the need to call multiple digital frequency meters to consume additional resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the QCM humidity sensor measurement method provided by the present invention.

[0024] Figure 2 This is a structural block diagram of the QCM humidity sensor measurement device provided by the present invention.

[0025] Figure 3 This is a measurement timing diagram of a digital frequency meter in a measuring device according to an embodiment of the present invention.

[0026] Figure 4 This is a diagram of humidity measurement results achieved by an embodiment of the present invention. DETAILED DESCRIPTION

[0027] To facilitate those skilled in the art to understand the technical content of the present invention, the present invention is further explained below with reference to the accompanying drawings.

[0028] like Figure 1 As shown, the measurement method of the present invention, the specific steps are as follows:

[0029] (1) Before the measurement begins, two QCM humidity sensors with different humidity sensitivities are prepared, which are named QS1 and QS2, respectively. QS1 has a higher humidity-frequency response sensitivity. In this embodiment, the sensitivity is at least greater than 20 Hz / % RH, which is considered to be higher. QS2 has a lower humidity-frequency response sensitivity. In this embodiment, the sensitivity is less than 10 Hz / % RH, which is considered to be lower.

[0030] (2) Measure the RH of QS1 and QS2 respectively under a known humidity environment i The output frequency of QS1 and QS2 is calculated and the difference frequency is calculated. By setting the waiting time, the stable frequency difference data DF of QS1 and QS2 is obtained. i In this embodiment, the waiting time is set to 10s;

[0031] (3) Change the humidity environment, i.e. RH i+1 ≠RH i Repeat step (2) at least once to obtain new frequency difference data DF i+1 ;

[0032] (4) Obtain frequency difference-humidity data, which are arrays DF[x] and RH[x], respectively, where x ≥ 2;

[0033] (5) Based on the frequency difference-humidity data obtained in step (4), the frequency difference-humidity data is fitted by a fitting algorithm to obtain a frequency-humidity relationship; the correlation coefficient of the fitting relationship is saved as a double-precision floating-point number type, which can be directly used in the frequency difference-humidity conversion operation later;

[0034] (6) Start measuring and place QS1 and QS2 in the humidity environment to be measured;

[0035] (7) By measuring the frequency difference between QS1 and QS2 and using the frequency-humidity relationship fitted in step (5), the frequency difference data of QS1 and QS2 are converted into humidity data to achieve humidity measurement.

[0036] The process of preparing two QCM humidity sensors with different humidity sensitivities in this embodiment is as follows:

[0037] Before film formation, the QCM sensor is cleaned and then placed in a clean container to dry at room temperature for standby use. Deionized water and graphene oxide mother liquor are used to prepare a graphene oxide solution of the required concentration, and a humidity-sensitive film is deposited on the QCM electrode in many ways, such as drop coating, spin coating, self-assembly, spraying, etc. The drop coating method has the advantages of low cost, simple operation, high flexibility, and short preparation time. Therefore, in this embodiment, a layer of graphene oxide film is formed on the QCM electrode using a drop coating method. The specific operation is: use a micro-syringe to take 0.2 μL, 2.5 mg / mL of graphene oxide solution, and drop the solution on the surface of the QCM sensor electrode. After that, the graphene oxide film-modified QCM sensor is placed in a drying container and dried at room temperature for 6 hours. After the water is completely evaporated, the graphene oxide film-modified QCM humidity sensor (QS1) is prepared. In the same way, 0.1 μL, 0.5 mg / mL of graphene oxide film is deposited on the surface of another QCM sensor electrode to complete the preparation of QS2.

[0038] Graphene oxide has the advantages of strong hydrophilicity, large specific surface area, excellent electrical properties, good stability and easy preparation and processing. It is widely used in QCM humidity sensors for humidity detection. The concentration of graphene oxide will directly affect the sensitivity and hysteresis of the sensor. Within a certain range, with the increase of graphene oxide concentration, the sensitivity of the sensor tends to increase, and the hysteresis of the sensor also tends to decrease. The coating amount directly affects the thickness of the sensor surface and the distribution of thicker humidity-sensitive layers. It may take longer to adsorb or desorb water molecules, thereby increasing the response and recovery time of the sensor. On the contrary, a thinner humidity-sensitive layer may have a faster response and recovery speed.

[0039] When designing and manufacturing QCM humidity sensors, it is necessary to select appropriate humidity-sensitive material concentrations and coating amounts according to specific application requirements in order to obtain optimal sensor performance. At the same time, experimental verification and optimization are also required to ensure that the sensor can meet performance requirements in actual use. According to the results of current experimental tests, the concentration of graphene oxide film is in the range of 2mg / mL to 5mg / mL, and the coating amount is in the range of 0.1μL to 0.3μL. The QCM humidity sensor can exhibit good performance, and humidity measurement can be achieved in combination with the dual-channel measurement scheme of the present invention. The output frequencies of QS1 and QS2 are subtracted and frequency-reduced. In this embodiment, in the range of 0%RH-97%RH, the fitting determination coefficient R of QS1 is 2 =0.99, the fitting determination coefficient of QS2 R 2 =0.97, QS1 and QS2 both have good linearity, but the sensitivities of QS1 and QS2 are different, the frequency difference value also shows a trend of gradual increase, and the frequency difference value is also linearly related to humidity, which can realize dual-channel humidity measurement; because the output frequencies of the two sensors tend to decrease with the increase of humidity, the frequency drift is reduced and thus the humidity measurement error is reduced.

[0040] For the reference sensor (QS2) in the dual-channel measurement, this embodiment has tried to use a sensor without a humidity-sensitive film as the reference sensor, but the frequency shift of the sensor in the entire 0%RH-97%RH range is very small, and the output frequency is not regular, which will have a certain impact on the humidity measurement results. The core idea of ​​the measurement scheme of the present invention is to perform frequency reduction processing and frequency drift compensation on the output frequency. If the frequency shift of the reference sensor is too large, or even close to that of the measurement sensor (that is, the output frequency response curves of the reference sensor and the measurement sensor are close to parallel), then the dual-channel difference is used for frequency reduction processing, and the obtained frequency difference value will always be a constant value, and the subsequent frequency-humidity conversion cannot be achieved. The present invention prepares QS2 by coating 0.1μL of a graphene oxide solution with a concentration of 0.5mg / mL on the reference sensor, so that its frequency shift in the range of 0%RH-97%RH is small but has good linearity, and has a regularity that the output frequency gradually decreases with increasing humidity.

[0041] Explanation on the sensitivity of two QCM humidity sensors with different humidity sensitivity:

[0042] The sensitivity of a QCM humidity sensor is defined as the frequency change (Hz / %RH) caused by a one percent relative humidity (%RH) change. Under this standard, if a sensor can produce a large frequency change when the humidity changes, then we can consider it to have a high sensitivity. Generally speaking, if the sensitivity of the QCM humidity sensor can reach tens of Hz / %RH or even higher, then it can usually be considered to have a high sensitivity. In the present invention, the sensitivity of QS1 is about 42.8Hz / %RH, and the sensitivity of QS2 is about 6.2Hz / %RH.

[0043] Figure 2 The present invention is a block diagram of a QCM humidity sensor measuring device based on which the QCM humidity sensor measuring method of the present invention is implemented. The measuring device can be used for humidity measurement in different humidity environments, and mainly includes: two QCM humidity sensors with different humidity sensitivity, named QS1 and QS2, respectively, wherein QS1 has a higher humidity-frequency response sensitivity, and QS2 has a lower humidity-frequency response sensitivity, and also includes: an FPGA core board and an OLED display screen.

[0044] Frequency measurement, data fitting and frequency difference-humidity data conversion are completed through FPGA. The FPGA module mainly includes two parts: a digital frequency meter and an embedded soft core. The digital frequency meter designed based on the equal-precision measurement method processes the frequency signals from QS1 and QS2, measures the output frequencies of QS1 and QS2 and calculates the difference frequency. The waiting time is set, and the frequency difference-humidity data is fitted after the frequency difference data is stable. The embedded soft-core processor can convert the output frequency difference of QS1 and QS2 into humidity data by fitting the relationship, and drive the OLED display to display information.

[0045] The response time of the QCM humidity sensor is the time it takes for the output frequency to stabilize when the QCM humidity sensor is placed in a new humidity environment. The response time of the QCM humidity sensor used in the present invention is about 5s (±1s). Therefore, after completing the frequency measurement and frequency difference calculation, the waiting time is theoretically set to be greater than 5s, and the stable frequency difference value corresponding to the current humidity environment can be read to perform frequency difference-humidity data fitting.

[0046] The FPGA module is mainly composed of a digital frequency meter and an embedded soft core; the digital frequency meter, as a coprocessor, mainly includes a multiplexer module, a clock signal generation module, a pulse counting module, and an operation module, wherein the operation module is mainly composed of a multiplier and a divider; the embedded soft core mainly includes a Nios II processor, an Avalon bus module, a data fitting module, a humidity conversion module, a UART serial port module, and an SPI driver module.

[0047] In the frequency measurement stage, the digital frequency meter will measure the output frequencies of QS1 and QS2 respectively and perform difference frequency calculation. First, the output frequency of QS1 is measured. After the measurement is completed, the input port signal of the digital frequency meter will be switched through the multiplexer, and the output frequency of QS2 will be measured in the same way. After that, the multiplexer will connect the output frequency of QS1 to the digital frequency meter again, and the dual-channel QCM frequency measurement will be realized in a cycle. Nios II completes the frequency difference-data fitting through the fitting algorithm, and completes the frequency difference-humidity conversion using the frequency-humidity relationship. Through the SPI driver module, the frequency measurement value and humidity measurement results during humidity measurement and other information are displayed on the OLED display.

[0048] The working principle of the digital frequency meter is:

[0049] The output frequencies of QS1 and QS2 are simultaneously connected to the multiplexer, and the multiplexer first connects the output frequency of QS1 to the input port of the digital frequency meter; the reference clock signal CLK_FS of equal precision frequency is generated through the clock signal generation module; the pulse counting module uses its internal register to generate a gating signal for counting the signal to be measured under the clock frequency clk_fx to be measured (i.e., the output frequency of QS1); the rising and falling edges of the reference clock signal CLK_FS and the clock signal to be measured clk_fx are captured at the same time to ensure that the counting is triggered and terminated within the gating signal; within the gating signal, the pulse counting module counts the clock signal clk_fx to be measured and the reference clock signal CLK_FS respectively; the frequency measurement value of the clock signal to be measured clk_fx (i.e., the output frequency of QS1) is obtained by conversion through the operation module, and The result is stored in the first register reg_1 in the operation module; at this time, the multiplexer switches the input signal of the digital frequency meter, connects the output frequency of QS2 to the digital frequency meter, uses the same measurement method to measure the frequency, obtains the output frequency of QS2, and stores the result in the second register reg_2 in the operation module; after each frequency measurement of the dual-channel QCM humidity sensor is completed, the operation module will also read the frequency measurement values ​​of QS1 and QS2 stored in its internal first register reg_1 and second register reg_2 to complete the difference frequency calculation, that is, calculate the difference between the output frequency of QS2 and the output frequency of QS1, and obtain the final frequency difference value; at the same time, the multiplexer connects the output frequency of QS1 to the digital frequency meter again, and repeats the cycle to realize the real-time measurement of the output frequency of the dual-channel QCM humidity sensor.

[0050] If the gated signal time in the digital frequency meter is set too short, it will affect the measurement accuracy, and if the setting time is too long, it will affect the measurement efficiency. It is necessary to set an appropriate gated signal time to ensure accurate and efficient frequency measurement. The gated signal time set in the present invention is 1000000 cycles of the signal to be measured, and the frequency clk_fx of the clock signal to be measured is about 16MHz, that is, the time required to complete a frequency measurement is about 0.063s, which can ensure that the digital frequency meter can achieve accurate and efficient measurement.

[0051] The working principle of the embedded soft core is:

[0052] The Nios II processor reads the output frequency difference data of QS1 and QS2 through the Avalon bus module; then the Nios II fits the frequency difference-humidity data through the data fitting module to obtain a frequency-humidity relationship; the corresponding frequency measurement results and frequency-humidity relationship during the fitting process are displayed on the PC side through the UART serial port module. When performing humidity measurement, the Nios II processor also includes a humidity conversion module, which performs frequency difference-humidity conversion through the frequency-humidity relationship; the frequency and humidity results and other information are displayed on the OLED display screen through the SPI driver module.

[0053] Figure 3 This is a measurement timing diagram of a digital frequency meter based on the equal-precision measurement principle in the embodiment. The digital frequency meter is designed using the equal-precision measurement method. The biggest feature of this method is that the time of the gating signal is related to the clock signal to be measured and is exactly an integer multiple of the signal to be measured. Set a suitable counting time, count the pulses of the reference clock signal and the clock signal to be measured respectively, and the frequency signal to be measured can be obtained through mathematical conversion; the gating signal is controlled by the clock signal to be measured, so the gating signal is exactly an integer multiple of the clock signal to be measured. For the pulse counting of the reference clock signal, ±1 clock error will be generated, but because the frequency of the reference clock signal is much greater than the clock signal to be measured, the final error is also very small.

[0054] The gating signal time needs to be set in advance. In the clock domain of the signal to be measured, the gating signal is generated by counting the pulses of the signal to be measured, ensuring that the gating signal is controlled by the clock signal to be measured and is an integer multiple of the signal to be measured. In the gating time, the pulse counting module counts the pulses of the clock signal to be measured and the reference clock signal in different clock domains respectively. The multiplier and divider in the operation module complete the mathematical operation of formula (2) based on the pulse counting result to obtain the frequency measurement value of the clock signal to be measured.

[0055]

[0056] Where clk_fx is the measured value of the clock frequency to be measured, fx_cnt is the pulse count of the clock signal to be measured, CLK_FS is the reference clock signal frequency, and fs_cnt is the pulse count of the reference clock signal.

[0057] Using the above example, the QCM humidity sensor can be used for humidity measurement. Two QCM humidity sensors with different humidity sensitivity and a base frequency of 16MHz are used, named QS1 and QS2 respectively. 0.2μL, 2.5mg / mL graphene oxide solution is coated on the surface of QS1, and 0.1μL, 0.5mg / mL graphene oxide solution is coated on the surface of QS2, so that the humidity-frequency response sensitivity of QS1 is higher and the humidity-frequency response sensitivity of QS2 is lower. In a closed container, a saturated salt solution is configured to simulate a closed humidity environment. A total of 7 salt solutions are configured to simulate 0%RH, 11%RH, 33%RH, 54%RH, 75%RH, 84%RH, and 97%RH humidity environments. Data calibration is performed before humidity measurement. The measuring device is set to data calibration mode. QS1 and QS2 are placed in 7 different relative humidity environments. The measuring device will automatically complete the frequency measurement and data fitting process. After completing the data calibration, switch the measuring device to the humidity measurement mode, start the humidity measurement, put QS1 and QS2 into the humidity environment to be measured, and finally display the humidity measurement results on the OLED display. Repeat the humidity measurement experiment many times to get the following Figure 4 The humidity measurement results shown are Figure 4 The reference line in is a straight line with a slope of 1 and passing through the origin, which can indicate the degree of deviation of each measurement result relative to the accurate value. Experimental data show that the method and device proposed in the present invention can achieve humidity measurement and the maximum error of the measurement result is less than ±3%RH.

[0058] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. For those skilled in the art, the present invention may have various changes and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A dual QCM difference frequency humidity sensor measurement method, characterized in that: include: The output frequencies of two humidity sensors with different sensitivities in a known humidity environment are measured respectively, and the frequency difference in the known humidity environment is calculated; the frequency differences corresponding to the obtained multiple different known humidity environments are fitted with frequency difference-humidity data through a fitting algorithm to obtain a frequency-humidity relationship; the output frequencies of the two humidity sensors with different sensitivities in the humidity environment to be measured are measured, and the frequency difference in the humidity environment to be measured is calculated; the frequency difference in the humidity environment to be measured is converted into humidity data using the fitted frequency-humidity relationship, thereby realizing humidity measurement of the humidity environment to be measured.

2. A dual QCM difference frequency humidity sensor measuring device, characterized in that: include: Two QCM humidity sensors with different humidity sensitivities, named QS1 and QS2, also include: FPGA core board; The FPGA core board mainly includes two parts: a digital frequency meter and an embedded soft core; The digital frequency meter includes: a multiplexer module, a clock signal generating module, a pulse counting module, and an operation module; the frequency measurement process of QS1 is: The multiplexer first connects the clock frequency signal clk_fx to be measured to the input port of the digital frequency meter; generates a reference clock signal CLK_FS of equal precision frequency through the clock signal generation module; the pulse counting module uses its internal register to generate a gating signal for counting the signal to be measured under the clock frequency signal clk_fx to be measured; and simultaneously captures the rising and falling edges of the reference clock signal CLK_FS and the clock signal clk_fx to be measured to ensure that the counting is triggered and terminated within the gating signal; within the gating signal, the pulse counting module counts the clock signal clk_fx to be measured and the reference clock signal CLK_FS respectively; finally, the operation module converts the frequency measurement value of the clock signal clk_fx to be measured according to the pulse counting results of the reference clock signal CLK_FS and the clock signal clk_fx to be measured, and stores the result in the first register reg_1 in the operation module; After completing the frequency measurement of QS1, the multiplexer switches the input signal of the digital frequency meter, connects the output frequency signal of QS2 to the digital frequency meter, performs the same frequency measurement process as QS1, obtains the frequency measurement value of QS2, and stores the result in the second register reg_2 in the operation module, and then switches the input signal of the digital frequency meter again through the multiplexer, connects the output frequency of QS1 to the digital frequency meter, and repeats the cycle to realize the frequency measurement of the dual-channel QCM humidity sensor; at the same time, after each frequency measurement of the dual-channel QCM humidity sensor is completed, the operation module will also read the frequency measurement values ​​of QS1 and QS2 stored in its internal first register reg_1 and second register reg_2, perform difference frequency calculation, and obtain frequency difference data; The embedded soft core includes: a Nios II processor and an Avalon bus module; the Nios II processor reads the frequency difference data output by the operation module through the Avalon bus module; then the Nios II processor fits the frequency difference-humidity data through a fitting algorithm to obtain a frequency-humidity relationship; when performing humidity measurement, the Nios II processor will perform frequency difference-humidity conversion through the frequency-humidity relationship.

3. A dual QCM difference frequency humidity sensor measuring device according to claim 2, characterized in that: The resulting frequency-humidity relationship is: f(x)=ax 2 +bx+c Where x is the frequency, f(x) is the humidity conversion result corresponding to the current frequency, and a, b, and c are correlation coefficients.

4. A dual-QCM difference frequency humidity sensor measuring device according to claim 3, characterized in that: The correlation coefficients a, b, and c are saved as double-precision floating-point numbers.

5. A dual QCM difference frequency humidity sensor measuring device according to claim 4, characterized in that: The humidity-sensitive material used in QS1 and QS2 is graphene oxide.

6. A dual-QCM difference frequency humidity sensor measuring device according to claim 5, characterized in that: QS1 and QS2 deposit graphene oxide films on the surface of QCM sensor electrodes by drop coating.

7. A dual-QCM difference frequency humidity sensor measuring device according to claim 6, characterized in that: The concentration of the graphene oxide film drop-coated on QS1 and QS2 was 2 mg / mL to 5 mg / mL, and the coating amount was 0.1 μL to 0.3 μL.

8. A dual QCM difference frequency humidity sensor measuring device according to claim 7, characterized in that: The embedded soft core also includes a UART serial port module, which displays the corresponding frequency measurement value and frequency-humidity relationship during fitting, as well as the frequency measurement value and humidity measurement result during humidity measurement on the PC side through the UART serial port module.

9. A dual-QCM difference frequency humidity sensor measuring device according to claim 8, characterized in that: The embedded soft core also includes: an SPI driver module and an OLED display screen; the Nios II processor displays the frequency measurement value and the humidity measurement result during humidity measurement on the OLED display screen through the SPI driver module.

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