A PM2.5 detection device based on amplitude characteristic measurement

Abstract

The application discloses a PM2.5 detection device based on amplitude characteristic measurement. The device comprises a micro flow pump, a PM2.5 detection pool, a quartz crystal vibrator driving circuit, an envelope detection circuit, a low-pass filter, an AD sampling unit, a control unit and a data transmission unit. The application can acquire mapping information of the mass concentration of the liquid to be measured in real time and upload the mapping information to an upper computer. The application maps the mass change on the surface of the QCM into the change of the amplitude by establishing the linear relationship between the amplitude of the quartz crystal vibrator driving circuit and the mass, and compared with the traditional method, the application has the advantages of low cost, fast response speed and good portability. The application is different from the previous method of reflecting the mass change by the change of the resonant frequency. The resonant frequency has small frequency response value for the measurement of the mass of the tiny liquid drops, is difficult to distinguish and is easily affected by the environment. The measurement precision and stability can be improved by measuring the amplitude.

Description

Technical Field

[0001] This invention relates to the field of PM2.5 detection, and more specifically to a PM2.5 detection device based on amplitude characteristic measurement. Background Technology

[0002] In recent years, as health and environmental issues have received increasing attention from the government and the public, PM2.5 has become a major focus of concern. PM2.5 particles are small in size, allowing them to penetrate deep into the respiratory tract and lungs. They are also rich in toxic and harmful substances, can remain in the atmosphere for extended periods, and have a long transmission distance, thus having a significant impact on human health and air quality. Therefore, monitoring PM2.5 concentrations, controlling and reducing emissions, and taking measures to improve air quality are crucial for protecting public health and the environment.

[0003] Currently, common devices for detecting PM2.5 concentrations include the Dylos DC1100 Pro series particulate air quality concentration meter from Dylos Corporation in the United States, the indoor environmental comprehensive detector from TSI Instruments in the United States, the Hills S601 compressed air quality analyzer from Germany, and air quality detectors from domestic brands such as Sainawei, Hanwang Haze Meter, and GreenTech.

[0004] The methods used in the above devices are mostly light scattering, turbidity, beta-ray, and oscillating balance methods. However, these methods have some problems. For example, light scattering is easily affected by the size and shape of particles and by relative humidity; beta-ray method is expensive and has a slow response speed; gravimetric method cannot be measured online and is time-consuming to operate.

[0005] The Quartz Crystal Microbalance (QCM) method is a resonant mass sensor with extremely high resolution and sensitivity, using an AT-cut quartz crystal wafer as its core. The change in mass adsorbed on the surface of the quartz crystal wafer electrode is directly proportional to the change in its resonant frequency; therefore, changes in its oscillation frequency can reflect changes in the mass adsorbed on the crystal electrode surface. However, the change in its resonant frequency is easily affected by air temperature and humidity, resulting in unstable results and causing errors in the measurement.

[0006] Existing PM2.5 detection methods, such as the beta-ray absorption method, are costly and have a slow response speed. The gravimetric method cannot be used for online measurement, is time-consuming to operate, has a long detection time, or the measurement accuracy cannot reach μg / m3 (beta-ray particulate matter monitoring equipment CN202211149712.0).

[0007] The existing quartz crystal microbalance method uses the resonant frequency to reflect the mass change of the liquid being measured. On the one hand, the change of the resonant frequency is easily affected by the air temperature and humidity, and the change is unstable, which causes the measurement result to be incorrect. On the other hand, for the measurement of the mass of tiny droplets, the frequency response value is small and difficult to distinguish (Zhang Yanyan. Research progress of PM2.5 detection technology [J]. Sensor World, 2019, 25(03)). Summary of the Invention

[0008] The present invention aims to provide a PM2.5 detection device based on amplitude feature measurement, which solves the problems of high cost, poor portability and poor stability of existing detection devices.

[0009] The objective of this invention is achieved by at least one of the following technical solutions.

[0010] A PM2.5 detection device based on amplitude characteristic measurement includes a microfluidic pump, a PM2.5 detection cell, a quartz crystal oscillator driving circuit, an envelope detection circuit, a low-pass filter, an AD sampling unit, a control unit, and a data transmission unit.

[0011] The microfluidic pump is used to receive the liquid to be detected and inject the liquid to be detected into the PM2.5 detection pool;

[0012] The PM2.5 detection cell is equipped with a quartz crystal oscillator, and the two poles of the quartz crystal oscillator are connected to the quartz crystal oscillator driving circuit.

[0013] The principle of the quartz crystal oscillator driving circuit is that the quartz crystal oscillator is connected to the positive feedback loop of the quartz crystal oscillator driving circuit as a frequency selection element. It satisfies the phase condition. If the parameters of the quartz crystal oscillator driving circuit are appropriate, that is, the amplitude condition is satisfied, the quartz crystal oscillator driving circuit can work normally and continuously generate a sine wave signal.

[0014] The quartz crystal oscillator driving circuit includes a parallel quartz crystal oscillator oscillation circuit. The quartz crystal oscillator driving circuit is connected to the envelope detection circuit and transmits the generated sine wave signal to the envelope detection circuit.

[0015] The envelope detector circuit is used to rectify the sinusoidal signal to measure the peak value, obtain an analog signal whose amplitude changes with time, and transmit the analog signal to the low-pass filter;

[0016] The low-pass filter is used to remove high-frequency noise or unwanted high-frequency oscillations from the analog signal, thereby obtaining a more stable and smoother envelope, improving signal quality, and finally transmitting the smoothed analog signal to the AD sampling unit.

[0017] The AD sampling unit is used to convert the smoothed analog signal into a digital signal to obtain the digital signal of the amplitude of the quartz crystal oscillator driving circuit.

[0018] The control unit is used to control the AD sampling unit, set the AD sampling rate, control the sampling timing, and receive digital signals from the AD sampling unit. These digital signals are the voltage amplitude data required for measurement by this device. The control unit serially outputs the voltage amplitude data to the data transmission unit.

[0019] The data transmission unit is used to upload the voltage amplitude data to the host computer.

[0020] Since the change in voltage amplitude is positively correlated with PM2.5 concentration, voltage amplitude data can be used to represent PM2.5 concentration. To know the specific PM2.5 concentration, it is necessary to prepare standard solutions of different concentrations from 0.1% to 10% and measure their voltage amplitudes to obtain the voltage amplitude and the change curve of different concentrations. When it is necessary to measure an unknown solution, the concentration can be obtained by referring to this curve based on the obtained voltage amplitude data of the unknown solution.

[0021] Furthermore, the envelope detection circuit includes a detection element; the low-pass filter includes a filtering element and an analog signal output terminal Vol_amp_out;

[0022] The AD sampling unit includes an analog signal input terminal An_Vol_in, an ADC control signal input terminal Din_in, an ADC working status input terminal ADC_state, an ADC acquisition signal output terminal ADC_Data_out, and a conversion completion flag output terminal Flag_done_out.

[0023] The control unit includes an ADC acquisition signal input terminal ADC_data_in, a read data flag signal input terminal Read_done_in, an ADC conversion channel selection input terminal channel, a voltage amplitude data output terminal Di_Vol_Data, a data completion signal output terminal Flag_out, and an ADC control signal output terminal din_out.

[0024] The data transmission unit includes a voltage amplitude data input terminal Vol_Data_in, a voltage amplitude data output terminal Vol_Data_out, and a data preparation signal input terminal Data_ready;

[0025] The analog signal output terminal Vol_amp_out of the low-pass filter is connected to the analog signal input terminal An_Vol_in of the AD sampling unit;

[0026] The analog signal input terminal An_Vol_in of the AD sampling unit is connected to the analog signal output terminal Vol_amp_out of the low-pass filter; the ADC control signal input terminal Din_in of the AD sampling unit is connected to the ADC control signal output terminal din_out of the control unit; the ADC acquisition signal output terminal ADC_Data_out of the AD sampling unit is connected to the ADC acquisition signal input terminal ADC_data_in of the control unit; and the conversion completion flag output terminal Flag_done_out of the AD sampling unit is connected to the read data flag signal input terminal Read_done_in of the control unit.

[0027] The ADC acquisition signal input terminal ADC_data_in of the control unit is connected to the ADC acquisition signal output terminal ADC_Data_out of the AD sampling unit; the read data flag signal input terminal of the control unit is connected to the conversion completion flag output terminal Flag_done_out of the AD sampling unit; the ADC control signal output terminal din_out of the control unit is connected to the ADC control signal input terminal Din_in of the AD sampling unit; the voltage amplitude data output terminal Di_Vol_Data of the control unit is connected to the voltage amplitude data input terminal Vol_Data_in of the data transmission unit; and the data completion signal output terminal Flag_out of the control unit is connected to the data preparation signal input terminal Data_ready of the data transmission unit.

[0028] The voltage amplitude data input terminal Vol_Data_in of the data transmission unit is connected to the voltage amplitude data output terminal Di_Vol_Data of the control unit, and the data preparation signal input terminal Data_ready of the data transmission unit is connected to the data completion signal output terminal Flag_out of the control unit.

[0029] Furthermore, the principle of the quartz crystal oscillator driving circuit is that the quartz crystal oscillator is connected to the positive feedback loop of the quartz crystal oscillator driving circuit as a frequency selection element. When the quartz crystal oscillator driving circuit is in normal working condition, it can generate self-excited oscillation. At this time, when the surface of the quartz crystal oscillator is subjected to pressure, that is, when the liquid to be tested is placed, due to the increase in impedance value, the output signal will be attenuated in amplitude accordingly, and as the amount of liquid increases, the amplitude signal will continue to attenuate.

[0030] The working process of the quartz crystal oscillator driving circuit is that the change in the surface mass of the quartz crystal oscillator leads to a change in the amplitude of the quartz crystal oscillator driving circuit. By measuring the change in amplitude, the change in the mass of the liquid added to the surface of the quartz crystal oscillator can be obtained.

[0031] Furthermore, the envelope detection circuit operates by using the sinusoidal signal of the quartz crystal oscillator driving circuit as the input signal of the envelope detection circuit. Through the continuous switching of the diodes in the envelope detection circuit, an analog signal showing the amplitude of the quartz crystal oscillator driving circuit changing with time is obtained at the output of the envelope detection circuit.

[0032] Furthermore, the operation of the AD sampling unit includes:

[0033] When the device is powered on, the AD sampling unit receives the ADC control signal Din and the ADC working status signal ADC_state sent by the control module. When ADC_state = 0, the AD sampling unit switches to the data input state and accepts the analog signal from the low-pass filter. When ADC_state = 1, the AD sampling unit switches to the waiting data state. After the conversion is completed, the AD sampling unit outputs the ADC acquisition signal at the ADC_Data_out terminal and sets the conversion completion flag signal output terminal Flag_done to 1.

[0034] Furthermore, the operation of the control unit includes:

[0035] When the device is powered on, if the Read_done_in input terminal is 1, the control unit switches to data input mode, and the ADC acquisition signal input terminal ADC_data_in of the control unit receives data from the ADC acquisition signal output terminal ADC_Data_out of the AD sampling unit; if the Read_done_in input terminal is 0, the control unit switches to waiting for data preparation mode; when the measurement is completed, the voltage amplitude data is output through the voltage amplitude data output terminal Di_Vol_Data, and the data completion signal output terminal Flag_out is set to 1.

[0036] Furthermore, the operation of the data transmission unit includes: when the device is powered on or Rst_n = 0, the data transmission unit switches to an initialization state; when Rst_n is not 0, the data transmission unit switches to a waiting-for-data-write state; when the data preparation signal Data_ready = 1, the data transmission unit switches to a write-data state, and the data transmission unit receives data from the voltage amplitude data output terminal Di_Vol_Data of the control unit, and transmits the voltage amplitude data to the host computer via serial port.

[0037] Once data transmission is complete, if the data readiness signal Data_ready = 1, the data transmission unit switches to the write data state; if the data readiness signal Data_ready = 0, the data transmission unit switches to the wait-to-write-data state.

[0038] Furthermore, the data transmission unit transmits the voltage amplitude data of the PM2.5 detection cell to the host computer via a serial port.

[0039] Furthermore, in the serial port transmission mode, the data transmission module also includes a serial port data output terminal Uart_tx (Vol_Data_out), which is connected to the UART controller.

[0040] Furthermore, since PM2.5 particles are relatively small, a high-precision AD sampling unit is needed to obtain amplitude data in order to distinguish the mass of PM2.5 particles in the solution. The AD sampling unit must be able to distinguish 1mV; that is, it can analyze changes greater than 1mV.

[0041] Compared with the prior art, the advantages of the present invention are:

[0042] This invention can acquire the mapping information of the mass concentration of the liquid to be tested in real time and upload it to the host computer.

[0043] This invention establishes a linear relationship between the amplitude and mass of the quartz crystal oscillator driving circuit, mapping the mass change of the QCM surface to the amplitude change. Compared with traditional methods, it has lower cost, faster response speed, and better portability.

[0044] Unlike previous methods that used changes in resonant frequency to reflect changes in mass, this invention provides a different approach. Resonant frequency has a small frequency response value for measuring the mass of tiny droplets, making it difficult to distinguish and easily affected by the environment. By measuring the amplitude, the measurement accuracy and stability can be improved. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of a PM2.5 detection device based on amplitude feature measurement in an embodiment of the present invention;

[0046] Figure 2 This is an illustration of the quartz crystal oscillator driving circuit in an embodiment of the present invention;

[0047] Figure 3 This is a schematic diagram of the structure of the AD sampling unit in an embodiment of the present invention;

[0048] Figure 4 This is a schematic diagram of the control unit in an embodiment of the present invention;

[0049] Figure 5 This is a schematic diagram of the data transmission unit in an embodiment of the present invention;

[0050] Figure 6 This is a mapping diagram of amplitude change versus volume change of the standard solution in an embodiment of the present invention;

[0051] Figure 7 This is a frequency offset-volume change mapping diagram of the standard solution in an embodiment of the present invention;

[0052] Figure 8 This is a comparison chart of the amplitude changes of the sampled solution and the PM2.5 concentration changes at the monitoring station in an embodiment of the present invention. Detailed Implementation

[0053] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0054] Example:

[0055] A PM2.5 detection device based on amplitude characteristic measurement, such as Figure 1 As shown, it includes a microfluidic pump, a PM2.5 detection cell, a quartz crystal oscillator driving circuit, an envelope detection circuit, a low-pass filter, an AD sampling unit, a control unit, and a data transmission unit;

[0056] The microfluidic pump is used to receive the liquid to be detected and inject the liquid to be detected into the PM2.5 detection pool;

[0057] The PM2.5 detection cell is equipped with a quartz crystal oscillator, and the two poles of the quartz crystal oscillator are connected to the quartz crystal oscillator driving circuit.

[0058] The principle of the quartz crystal oscillator driving circuit is that the quartz crystal oscillator is connected to the positive feedback loop of the quartz crystal oscillator driving circuit as a frequency selection element. It satisfies the phase condition. If the parameters of the quartz crystal oscillator driving circuit are appropriate, that is, if the amplitude condition is satisfied, the quartz crystal oscillator driving circuit can work normally and continuously generate a sine wave signal. The quartz crystal microbalance (QCM) is a resonant mass sensor with extremely high resolution and sensitivity, based on an AT-cut quartz crystal wafer.

[0059] In one embodiment, in actual testing, such as Figure 6 As shown, the amplitude change versus volume change curves were plotted using continuously varying volumes of the same standard solution.

[0060] In a comparative example, such as Figure 7 As shown, a calibration curve of frequency shift versus volume change was prepared using consecutively different volumes of the same standard solution.

[0061] Figure 6 and Figure 7 Compared to the frequency offset-volume change curve, it also has better linearity than traditional frequency measurement, and its measurement stability is also higher under the same volume.

[0062] according to Figure 6 and Figure 7 The comparative results show that, unlike previous methods that used changes in resonant frequency to reflect mass changes, this invention has better linearity and higher measurement stability. On the other hand, the resonant frequency has a small frequency response value for measuring the mass of tiny droplets, making it difficult to distinguish. By measuring the amplitude, the frequency response can be increased from 1ul / 37Hz to 1ul / 77mv. For low-concentration PM2.5 solutions, the frequency change will be very small, while the amplitude change will be slightly larger, resulting in higher resolution. This can improve measurement accuracy and the lower limit of measurement, achieving high precision and a wide measurement range.

[0063] like Figure 2 As shown, the quartz crystal oscillator driving circuit includes a parallel quartz crystal oscillator oscillation circuit. The quartz crystal oscillator driving circuit is connected to the envelope detection circuit and transmits the generated sine wave signal to the envelope detection circuit.

[0064] The envelope detector circuit is used to rectify the sinusoidal signal to measure the peak value, obtain an analog signal whose amplitude changes with time, and transmit the analog signal to the low-pass filter;

[0065] The low-pass filter is used to remove high-frequency noise or unwanted high-frequency oscillations from the analog signal, thereby obtaining a more stable and smoother envelope, improving signal quality, and finally transmitting the smoothed analog signal to the AD sampling unit.

[0066] The AD sampling unit is used to convert the smoothed analog signal into a digital signal to obtain the digital signal of the amplitude of the quartz crystal oscillator driving circuit.

[0067] The control unit is used to control the AD sampling unit, set the AD sampling rate, control the sampling timing, and receive digital signals from the AD sampling unit. These digital signals are the voltage amplitude data required for measurement by this device. The control unit serially outputs the voltage amplitude data to the data transmission unit.

[0068] The data transmission unit is used to upload the voltage amplitude data to the host computer.

[0069] Since the change in voltage amplitude is positively correlated with PM2.5 concentration, voltage amplitude data can be used to represent PM2.5 concentration. To know the specific PM2.5 concentration, it is necessary to prepare standard solutions of different concentrations from 0.1% to 10% and measure their voltage amplitudes to obtain the voltage amplitude and the change curve of different concentrations. When it is necessary to measure an unknown solution, the concentration can be obtained by referring to this curve based on the obtained voltage amplitude data of the unknown solution.

[0070] like Figure 2As shown, the envelope detection circuit includes a detection element; the low-pass filter includes a filtering element and an analog signal output terminal Vol_amp_out;

[0071] like Figure 3 As shown, the AD sampling unit includes an analog signal input terminal An_Vol_in, an ADC control signal input terminal Din_in, an ADC working state input terminal ADC_state, an ADC acquisition signal output terminal ADC_Data_out, and a conversion completion flag output terminal Flag_done_out;

[0072] like Figure 4 As shown, the control unit includes an ADC acquisition signal input terminal ADC_data_in, a read data flag signal input terminal Read_done_in, an ADC conversion channel selection input terminal channel, a voltage amplitude data output terminal Di_Vol_Data, a data completion signal output terminal Flag_out, and an ADC control signal output terminal din_out.

[0073] like Figure 5 As shown, the data transmission unit includes a voltage amplitude data input terminal Vol_Data_in, a voltage amplitude data output terminal Vol_Data_out, and a data preparation signal input terminal Data_ready;

[0074] The analog signal output terminal Vol_amp_out of the low-pass filter is connected to the analog signal input terminal An_Vol_in of the AD sampling unit;

[0075] The analog signal input terminal An_Vol_in of the AD sampling unit is connected to the analog signal output terminal Vol_amp_out of the low-pass filter; the ADC control signal input terminal Din_in of the AD sampling unit is connected to the ADC control signal output terminal din_out of the control unit; the ADC acquisition signal output terminal ADC_Data_out of the AD sampling unit is connected to the ADC acquisition signal input terminal ADC_data_in of the control unit; and the conversion completion flag output terminal Flag_done_out of the AD sampling unit is connected to the read data flag signal input terminal Read_done_in of the control unit.

[0076] The ADC acquisition signal input terminal ADC_data_in of the control unit is connected to the ADC acquisition signal output terminal ADC_Data_out of the AD sampling unit; the read data flag signal input terminal of the control unit is connected to the conversion completion flag output terminal Flag_done_out of the AD sampling unit; the ADC control signal output terminal din_out of the control unit is connected to the ADC control signal input terminal Din_in of the AD sampling unit; the voltage amplitude data output terminal Di_Vol_Data of the control unit is connected to the voltage amplitude data input terminal Vol_Data_in of the data transmission unit; and the data completion signal output terminal Flag_out of the control unit is connected to the data preparation signal input terminal Data_ready of the data transmission unit.

[0077] The voltage amplitude data input terminal Vol_Data_in of the data transmission unit is connected to the voltage amplitude data output terminal Di_Vol_Data of the control unit, and the data preparation signal input terminal Data_ready of the data transmission unit is connected to the data completion signal output terminal Flag_out of the control unit.

[0078] Furthermore, the principle of the quartz crystal oscillator driving circuit is that the quartz crystal oscillator is connected to the positive feedback loop of the quartz crystal oscillator driving circuit as a frequency selection element. When the quartz crystal oscillator driving circuit is in normal working condition, it can generate self-excited oscillation. At this time, when the surface of the quartz crystal oscillator is subjected to pressure, that is, when the liquid to be tested is placed, due to the increase in impedance value, the output signal will be attenuated in amplitude accordingly, and as the amount of liquid increases, the amplitude signal will continue to attenuate.

[0079] The working process of the quartz crystal oscillator driving circuit is that the change in the surface mass of the quartz crystal oscillator leads to a change in the amplitude of the quartz crystal oscillator driving circuit. By measuring the change in amplitude, the change in the mass of the liquid added to the surface of the quartz crystal oscillator can be obtained.

[0080] Furthermore, the envelope detection circuit operates by using the sinusoidal signal of the quartz crystal oscillator driving circuit as the input signal of the envelope detection circuit. Through the continuous switching of the diodes in the envelope detection circuit, an analog signal showing the amplitude of the quartz crystal oscillator driving circuit changing with time is obtained at the output of the envelope detection circuit.

[0081] In one embodiment, the AD sampling unit is an ADC sampling module, and its operation includes:

[0082] When the device is powered on, the AD sampling unit receives the ADC control signal Din and the ADC working status signal ADC_state sent by the control module. When ADC_state = 0, the AD sampling unit switches to the data input state and accepts the analog signal from the low-pass filter. When ADC_state = 1, the AD sampling unit switches to the waiting data state. After the conversion is completed, the AD sampling unit outputs the ADC acquisition signal at the ADC_Data_out terminal and sets the conversion completion flag signal output terminal Flag_done to 1.

[0083] In one embodiment, the control unit is an FPGA, and its operation includes:

[0084] When the device is powered on, if the Read_done_in input terminal is 1, the control unit switches to data input mode, and the ADC acquisition signal input terminal ADC_data_in of the control unit receives data from the ADC acquisition signal output terminal ADC_Data_out of the AD sampling unit; if the Read_done_in input terminal is 0, the control unit switches to waiting for data preparation mode; when the measurement is completed, the voltage amplitude data is output through the voltage amplitude data output terminal Di_Vol_Data, and the data completion signal output terminal Flag_out is set to 1.

[0085] In another embodiment, the control unit is a microcontroller.

[0086] Furthermore, the operation of the data transmission unit includes: when the device is powered on or Rst_n = 0, the data transmission unit switches to an initialization state; when Rst_n is not 0, the data transmission unit switches to a waiting-for-data-write state; when the data preparation signal Data_ready = 1, the data transmission unit switches to a write-data state, and the data transmission unit receives data from the voltage amplitude data output terminal Di_Vol_Data of the control unit, and transmits the voltage amplitude data to the host computer via serial port.

[0087] Once data transmission is complete, if the data readiness signal Data_ready = 1, the data transmission unit switches to the write data state; if the data readiness signal Data_ready = 0, the data transmission unit switches to the wait-to-write-data state.

[0088] In one embodiment, the data transmission unit transmits the voltage amplitude data of the PM2.5 detection cell to the host computer via a serial port.

[0089] In one embodiment, in the serial port transmission mode, the data transmission module further includes a serial port data output terminal Uart_tx (Vol_Data_out), which is connected to the UART controller.

[0090] In another embodiment, the data transmission module transmits data using a USB 3.0 or USB 2.0 interface.

[0091] Furthermore,

[0092] Because PM2.5 particles are relatively small, distinguishing their mass in a solution requires a high-precision analog-to-digital (AD) sampling unit to obtain amplitude data. Experiments show that this AD sampling unit should be able to resolve changes of 1 mV or more.

[0093] In one embodiment, the procedure for measuring the concentration of a specific PM2.5 solution is as follows:

[0094] Initialization: Pour pure water into the system and keep it running for one minute to clean the system.

[0095] Settle: Stop the water supply and let it stand for 2 minutes to ensure the system is stable. Record the change in amplitude at this time.

[0096] Test liquid injection: Introduce the PM2.5 test liquid into the system and maintain it for 60 seconds to enter the experimental stage.

[0097] Let it stand again: Stop the flow of suspension, let it stand for 2 minutes again, and record the change in amplitude at this time.

[0098] Data recording: Recording data and observations during the experiment.

[0099] The difference in amplitude change when pure water and PM2.5 suspension are introduced is taken as Δv, which is the mass mapping of PM2.5 in the PM2.5 solution. Using this method, three measurements are performed on the same group of samples to obtain the average amplitude change of the group of samples.

[0100] PM2.5 samples were measured at different time periods on the same day, and the results were obtained. Figure 8 The measurement results are shown.

[0101] The monitoring station generally uses the most accurate and currently recognized benchmark method – the gravimetric method, and its standard results are as follows: Figure 8 As shown.

[0102] In a comparative example, the traditional gravimetric method proceeds as follows:

[0103] Place the filter membrane to be used in a constant temperature and humidity chamber for 24 hours and weigh it using a balance.

[0104] Prepare a collector with a filter membrane to capture airborne particulate matter.

[0105] Place the data logger in the air where you want to measure the air, and use an air pump or other air extraction device to draw in the air.

[0106] The collector collects particulate matter in the air over a certain period of time (usually 24 hours).

[0107] After the collection is completed, remove the filter membrane.

[0108] The collected filter membrane was placed in a constant temperature and humidity chamber for 24 hours and then weighed using a balance.

[0109] The mass of captured PM2.5 can be obtained by subtracting the initial mass and the mass after sampling.

[0110] Based on the above comparison, compared with the traditional gravimetric method, the present invention has a faster response speed and can obtain the trend of PM2.5 mass concentration change in a short time, achieving online real-time measurement; and on the same day, the standard data obtained by the Guangzhou Panyu University Town monitoring station and the data obtained by this device were compared, and their trends were basically consistent.

[0111] It should be noted that in a specific example of PM2.5 solution concentration measurement, the time for introducing PM2.5 suspension, pure water, and the settling time are not fixed and can be adjusted according to the actual situation.

Claims

1. A PM2.5 detection device based on amplitude characteristic measurement, characterized in that, It includes a microfluidic pump, a PM2.5 detection cell, a quartz crystal oscillator driving circuit, an envelope detection circuit, a low-pass filter, an AD sampling unit, a control unit, and a data transmission unit; The microfluidic pump is used to receive the liquid to be detected and inject the liquid to be detected into the PM2.5 detection pool; The PM2.5 detection cell is equipped with a quartz crystal oscillator, and the two poles of the quartz crystal oscillator are connected to the quartz crystal oscillator driving circuit. The principle of the quartz crystal oscillator driving circuit is that the quartz crystal oscillator is used as a frequency selection element and connected to the positive feedback loop of the quartz crystal oscillator driving circuit so that the positive feedback loop satisfies the phase condition; when the quartz crystal oscillator driving circuit satisfies the amplitude condition, the quartz crystal oscillator driving circuit continuously generates a sine wave signal. The quartz crystal oscillator driving circuit includes a parallel quartz crystal oscillator oscillation circuit. The quartz crystal oscillator driving circuit is connected to the envelope detection circuit and transmits the generated sine wave signal to the envelope detection circuit. The envelope detector circuit is used to rectify the sinusoidal signal to measure the peak value, obtain an analog signal whose amplitude changes with time, and transmit the analog signal to the low-pass filter; The low-pass filter is used to remove high-frequency noise or unwanted high-frequency oscillations from the analog signal, and finally the smoothed analog signal is transmitted to the AD sampling unit. The AD sampling unit is used to convert the smoothed analog signal into a digital signal to obtain the digital signal of the amplitude of the quartz crystal oscillator driving circuit. The control unit is used to control the AD sampling unit, set the AD sampling rate, control the sampling timing, and receive digital signals from the AD sampling unit. These digital signals are the voltage amplitude data required for measurement by this device. The control unit serially outputs the voltage amplitude data to the data transmission unit. The data transmission unit is used to upload the voltage amplitude data to the host computer; Voltage amplitude data is used to represent the concentration of PM2.5 in the liquid being tested; the change in voltage amplitude is positively correlated with the PM2.5 concentration.

2. The PM2.5 detection device based on amplitude characteristic measurement according to claim 1, characterized in that, The envelope detection circuit includes a detection element; the low-pass filter includes a filtering element and an analog signal output terminal Vol_amp_out; The AD sampling unit includes an analog signal input terminal An_Vol_in, an ADC control signal input terminal Din_in, an ADC working status input terminal ADC_state, an ADC acquisition signal output terminal ADC_Data_out, and a conversion completion flag output terminal Flag_done_out. The control unit includes an ADC acquisition signal input terminal ADC_data_in, a read data flag signal input terminal Read_done_in, an ADC conversion channel selection input terminal channel, a voltage amplitude data output terminal Di_Vol_Data, a data completion signal output terminal Flag_out, and an ADC control signal output terminal din_out. The data transmission unit includes a voltage amplitude data input terminal Vol_Data_in, a voltage amplitude data output terminal Vol_Data_out, and a data preparation signal input terminal Data_ready; The analog signal output terminal Vol_amp_out of the low-pass filter is connected to the analog signal input terminal An_Vol_in of the AD sampling unit; The analog signal input terminal An_Vol_in of the AD sampling unit is connected to the analog signal output terminal Vol_amp_out of the low-pass filter; the ADC control signal input terminal Din_in of the AD sampling unit is connected to the ADC control signal output terminal din_out of the control unit; the ADC acquisition signal output terminal ADC_Data_out of the AD sampling unit is connected to the ADC acquisition signal input terminal ADC_data_in of the control unit; and the conversion completion flag output terminal Flag_done_out of the AD sampling unit is connected to the read data flag signal input terminal Read_done_in of the control unit. The ADC acquisition signal input terminal ADC_data_in of the control unit is connected to the ADC acquisition signal output terminal ADC_Data_out of the AD sampling unit; the read data flag signal input terminal of the control unit is connected to the conversion completion flag output terminal Flag_done_out of the AD sampling unit; the ADC control signal output terminal din_out of the control unit is connected to the ADC control signal input terminal Din_in of the AD sampling unit; the voltage amplitude data output terminal Di_Vol_Data of the control unit is connected to the voltage amplitude data input terminal Vol_Data_in of the data transmission unit; and the data completion signal output terminal Flag_out of the control unit is connected to the data preparation signal input terminal Data_ready of the data transmission unit. The voltage amplitude data input terminal Vol_Data_in of the data transmission unit is connected to the voltage amplitude data output terminal Di_Vol_Data of the control unit, and the data preparation signal input terminal Data_ready of the data transmission unit is connected to the data completion signal output terminal Flag_out of the control unit.

3. The PM2.5 detection device based on amplitude characteristic measurement according to claim 1, characterized in that, The principle of the quartz crystal oscillator driving circuit is that the quartz crystal oscillator is connected to the positive feedback loop of the quartz crystal oscillator driving circuit as a frequency selection element. When the quartz crystal oscillator driving circuit is in normal working condition, it can generate self-excited oscillation. At this time, when the surface of the quartz crystal oscillator is subjected to pressure, that is, when the liquid to be tested is placed, the output signal will be attenuated in amplitude due to the increase in impedance value, and the amplitude signal will continue to attenuate as the amount of liquid increases. The quartz crystal oscillator driving circuit operates by changing the surface mass of the quartz crystal oscillator, which in turn causes a change in the amplitude of the quartz crystal oscillator driving circuit. By measuring the change in amplitude, the change in the mass of the liquid added to the surface of the quartz crystal oscillator can be obtained.

4. The PM2.5 detection device based on amplitude characteristic measurement according to claim 1, characterized in that, The envelope detection circuit operates by using the sinusoidal signal from the quartz crystal oscillator driving circuit as the input signal. Through the continuous switching on and off process of the diodes in the envelope detection circuit, an analog signal showing the amplitude of the quartz crystal oscillator driving circuit changing with time is obtained at the output of the envelope detection circuit.

5. A PM2.5 detection device based on amplitude characteristic measurement according to claim 1, characterized in that, The operation of the AD sampling unit includes: When the device is powered on, the AD sampling unit receives the ADC control signal Din and the ADC working status signal ADC_state sent by the control module. When ADC_state=0, the AD sampling unit switches to the data input state and receives the analog signal from the low-pass filter. When ADC_state=1, the AD sampling unit switches to the waiting data state. After the conversion is completed, the AD sampling unit outputs the ADC acquisition signal at the ADC_Data_out terminal and sets the conversion completion flag signal output terminal Flag_done to 1.

6. A PM2.5 detection device based on amplitude characteristic measurement according to claim 1, characterized in that, The operation of the control unit includes: When the device is powered on, when the Read_done_in input terminal is 1, the control unit switches to the data input state, and the ADC acquisition signal input terminal ADC_data_in of the control unit receives data from the ADC acquisition signal output terminal ADC_Data_out of the AD sampling unit; when the Read_done_in input terminal is 0, the control unit switches to the waiting data preparation state; when the measurement is completed, the voltage amplitude data is output through the voltage amplitude data output terminal Di_Vol_Data, and the data completion signal output terminal Flag_out is set to 1.

7. A PM2.5 detection device based on amplitude characteristic measurement according to claim 1, characterized in that, The data transmission unit operates as follows: when the device is powered on or Rst_n=0, the data transmission unit switches to an initialization state; when Rst_n is not 0, the data transmission unit switches to a waiting-for-data-write state; when the data ready signal Data_ready=1, the data transmission unit switches to a write-data state. The data transmission unit receives data from the voltage amplitude data output terminal Di_Vol_Data of the control unit and transmits the voltage amplitude data to the host computer via a serial port. Once data transmission is complete, if the data readiness signal Data_ready=1, the data transmission unit switches to the write data state; if the data readiness signal Data_ready=0, the data transmission unit switches to the wait-to-write-data state.

8. A PM2.5 detection device based on amplitude characteristic measurement according to claim 1, characterized in that, The data transmission unit transmits the voltage amplitude data of the PM2.5 detection cell to the host computer via a serial port.

9. A PM2.5 detection device based on amplitude characteristic measurement according to claim 8, characterized in that, In the serial port transmission mode, the data transmission module also includes a serial port data output terminal Uart_tx, which is connected to the UART controller.

10. A PM2.5 detection device based on amplitude characteristic measurement according to claim 1, characterized in that, Because PM2.5 particles are relatively small, a high-precision AD sampling unit is needed to obtain amplitude data in order to distinguish the mass of PM2.5 particles in a solution. The AD sampling unit must be able to distinguish 1 mV; that is, it can resolve changes greater than 1 mV.

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