A high-precision light scattering particle concentration monitor and monitoring method

Abstract

The present invention provides a high-precision light scattering particle concentration monitor and monitoring method, the method comprising: step 1, the single-chip microcomputer adjusts the operating speed of the exhaust device through the pulse width to control the air to flow into the monitor at a constant flow rate; step 2, the single-chip microcomputer obtains the current air humidity value, and controls the air humidity in the instrument to within the humidity threshold through the heating and dehumidification device; step 3, the pulse width is set by the single-chip microcomputer to control the laser emission frequency, the light signal collected is converted into an electrical signal by the photosensitive sensor, the scattered light pulse signal is calculated, and the concentration of PM2.5 is obtained by the inversion formula; step 4, the self-calibration function is started regularly, and the concentration monitor is calibrated by turning on the calibration light source. The monitor and monitoring method in the present invention can improve the monitoring accuracy of the instrument while increasing the service life of the instrument and reducing the maintenance cost.

Description

Technical Field

[0001] The present invention relates to the field of environmental monitoring technology, and in particular to a high-precision light scattering particle concentration monitor and a monitoring method. Background Art

[0002] Atmospheric particulate matter is an important pollutant that affects human health, atmospheric visibility and the earth's radiation balance. Among them, fine particulate matter (PM2.5) has the greatest impact on human health. Fine particulate matter (PM2.5) refers to particulate matter suspended in the atmosphere with an aerodynamic diameter of less than or equal to 2.5μm. It mainly comes from motor vehicle emissions, coal dust, road dust, construction dust and industrial dust. At present, fine particulate matter (PM2.5) is a problem of great concern to our society. In 2012, the state revised the "Ambient Air Quality Standards", added the monitoring and control requirements of PM2.5, and monitored and released it in major cities across the country.

[0003] At present, there are four main methods for monitoring fine particulate matter (PM2.5): weight method, micro-oscillating balance method, beta ray method and particle light scattering method. Although the first three methods have high measurement accuracy, they are all bulky, noisy, inconvenient to carry and expensive, which to a certain extent limits the widespread use of PM2.5 monitoring. The particle light scattering method is based on the Mie scattering theory. Air is passed through a closed measurement space at a constant flow rate. The laser beam irradiates the particles to produce scattered light proportional to their particle size and concentration. The collected light signal is converted into an electrical signal by the sensor to calculate the concentration of PM2.5. Due to the advantages of fast measurement speed, high sensitivity, online non-contact measurement, strong applicability, etc., the particle light scattering method has become another common method for PM2.5 measurement and is widely used. However, the traditional PM2.5 monitor uses an infrared light source or a laser source as the transmitting light source, a photosensitive sensor as the receiving unit, and a diaphragm pump or a fan as the air flow power source. Although this solution has many advantages such as high integration, fast measurement speed, high sensitivity, fast response, and low cost. However, the traditional monitoring instruments using light scattering still have the following shortcomings:

[0004] (1) It is easily affected by the ambient humidity. When the air humidity is high, water droplets will be mistaken for particles, and small-sized particles that stick together with water vapor in the air will also be mistaken for large particles, increasing the measurement error;

[0005] (2) As the monitoring instrument is used for a longer time, its components age and cannot perform the corresponding functions according to the preset parameters, resulting in reduced measurement accuracy. For example, the use of an infrared light source or a laser source working continuously will cause the light source power to decay rapidly, resulting in a decrease in the measured value of the particle mass concentration. For example, after the motor of a diaphragm pump (or fan) ages after long-term operation, the resistance increases, causing the gas flow rate to be lower than the preset constant flow rate, resulting in a smaller measured value.

[0006] (3) Since environmental monitoring instruments are generally installed in remote places such as construction sites and suburbs, the commonly used information networking methods for transmission (such as any combination of Zigbee, 433 and GPRS) have the problems of high power consumption, narrow range and unstable transmission. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a high-precision light scattering particle concentration monitor and a monitoring method, which improves the monitoring accuracy of the instrument while increasing the service life of the instrument and reducing maintenance costs.

[0008] In a first aspect, the present invention provides a high-precision light scattering particle concentration monitor, comprising a single-chip microcomputer, a heating and dehumidifying device, a concentration monitoring device, a flow monitoring device and an exhaust device, wherein the heating and dehumidifying device, the concentration monitoring device, the flow monitoring device and the exhaust device are respectively connected to the single-chip microcomputer;

[0009] The heating and dehumidifying device, concentration monitoring device, flow monitoring device and air extraction device are arranged along the air flow direction;

[0010] The concentration monitoring device comprises a particle measurement cavity, and a laser and a photosensitive sensor arranged in the particle measurement cavity. The laser and the photosensitive sensor are respectively connected to a single chip microcomputer, and the light emission frequency of the laser is controlled by the single chip microcomputer.

[0011] Furthermore, the heating and dehumidifying device includes a temperature and humidity sensor arranged at the air inlet, a heating cavity, and a heating wire and a temperature sensor arranged in the heating cavity, wherein the temperature sensor is attached to the surface of the heating wire, and the heating wire is connected to the single-chip microcomputer through a solid-state relay. The temperature sensor is a K-type thermocouple.

[0012] Furthermore, a calibration light source is also provided in the particle measurement chamber, and the calibration light source is connected to the single chip microcomputer and is controlled by the single chip microcomputer to perform timing calibration.

[0013] Furthermore, the flow monitoring unit includes an ultrasonic flow monitoring sensor.

[0014] Furthermore, the air extraction device is a vacuum pump or a diaphragm pump, and a filter is provided at the input end of the air extraction device.

[0015] Furthermore, the monitoring instrument also includes a data storage module, a display module and an NB-IOT module. The single chip microcomputer displays the measurement data and the measurement time through the display module, and the single chip microcomputer remotely transmits the data to the remote terminal through the NB-IOT module.

[0016] Furthermore, the monitor also includes an atmospheric pressure monitoring device for monitoring the atmospheric pressure in the external environment.

[0017] In a second aspect, the present invention provides a high-precision light scattering particle concentration monitoring method, which requires providing a monitoring instrument as described in the first aspect, and the method comprises the following steps:

[0018] Step 1, the single chip microcomputer adjusts the operating speed of the air extraction device through pulse width to control the air to flow into the monitor at a constant flow rate;

[0019] Step 2, the single chip microcomputer obtains the current air humidity value, and controls the air humidity in the instrument to within the humidity threshold through the heating and dehumidification device;

[0020] Step 3: Set the pulse width to control the laser emission frequency through the single chip microcomputer, convert the collected light signal into an electrical signal using a photosensor, calculate the scattered light pulse signal, and use the inversion formula to obtain the PM2.5 concentration;

[0021] Step 4: Start the self-calibration function regularly and calibrate the concentration monitor by turning on the calibration light source.

[0022] Furthermore, the step 2 specifically includes:

[0023] Step 21, monitoring the current air humidity value through the humidity sensor in the heating and dehumidification device and transmitting it to the single chip microcomputer;

[0024] Step 22, the single chip computer determines whether the current air humidity value is higher than the humidity threshold value, if so, proceeds to step 23, otherwise, does not perform the dehumidification operation;

[0025] Step 23, start the PID control program, obtain the current temperature value, target temperature value, current air humidity value and humidity threshold value, calculate the heating time and heating stop time required for the corresponding heating wire according to the current temperature value and the target temperature value, generate PWM pulses through the microcontroller IO and control the operation of the heating wire through the solid-state relay, and continuously adjust the heating and heating stop time through the PID control program to make the gas humidity in the monitor lower than the humidity threshold value and ensure that the temperature is not higher than the target temperature value.

[0026] Furthermore, the inversion formula is Where C is the PM2.5 particle concentration, n is the number of pulse signal channels of the optical monitoring device, N(v i) is the amplitude distribution of discrete voltage pulse signal, v i is the amplitude information, β is the particle morphology information parameter, and k is the proportional coefficient corresponding to the photosensitive sensor, which is set according to the calibration result.

[0027] Furthermore, the step 4 further comprises:

[0028] Step 41, regularly start the calibration light source through the single chip microcomputer to obtain the concentration measurement value under the calibration light source;

[0029] Step 42, calculating the difference between the measured concentration value in step 41 and the actual concentration value, and recording it as an error value;

[0030] Step 43: If the error value is greater than a preset error range, proceed to step 54 to calibrate the concentration monitor; otherwise, no calibration is performed;

[0031] Step 44, according to the size of the error value, correspondingly adjust the pulse width modulation to increase the light emission frequency of the laser until the error value is reduced to within the error range;

[0032] Or adjusting the proportional coefficient value in the inversion formula according to the size of the error value until the error value is reduced to within the error range;

[0033] Alternatively, the pulse width modulation is adjusted to change the light emission frequency of the laser and the coefficient value in the inversion formula at the same time until the error value is reduced to within the error range.

[0034] The advantages of the present invention are:

[0035] 1. The PWM flashing frequency is generated by controlling and adjusting the laser's light emission frequency through a single-chip microcomputer, which reduces the loss of the laser, prolongs the laser's working life, and meets the monitoring accuracy requirements;

[0036] 2. By adding a timed calibration module, the accuracy of the instrument is regularly self-checked and calibrated to form a feedback mechanism to ensure that the instrument remains within a certain accuracy range for a long time;

[0037] 3. Use the laser frequency and photosensitive element parameter adjustment for calibration to reduce the cost of parts replacement and maintenance costs;

[0038] 4. Set up heating and dehumidification devices and flow stabilization control to improve monitoring accuracy from the input end. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention will be further described below in conjunction with embodiments with reference to the accompanying drawings.

[0040] Figure 1 The figure is a schematic diagram of the gas path connection of a high-precision light scattering particle concentration monitor of the present invention.

[0041] Figure 2 The figure is a schematic diagram of the principle of a high-precision light scattering particle concentration monitor of the present invention.

[0042] Figure 3 The figure is a schematic diagram of the structure of a heating and dehumidification device of a high-precision light scattering particle concentration monitor of the present invention.

[0043] Figure 4 The present invention is a flowchart of a method for monitoring the concentration of light-scattering particles with high precision. DETAILED DESCRIPTION

[0044] See also Figures 1 to 3 A high-precision light scattering particle concentration monitor of the present invention comprises a single-chip microcomputer, a heating and dehumidifying device, a concentration monitoring device, a flow monitoring device and an exhaust device, wherein the heating and dehumidifying device, the concentration monitoring device, the flow monitoring device and the exhaust device are respectively connected to the single-chip microcomputer;

[0045] The heating and dehumidifying device, concentration monitoring device, flow monitoring device and air extraction device are arranged along the air flow direction;

[0046] The concentration monitoring device comprises a particle measurement cavity and a laser and a photosensitive sensor arranged in the particle measurement cavity, wherein the laser and the photosensitive sensor are respectively connected to a single chip microcomputer, and the light emission frequency of the laser is controlled by the single chip microcomputer. The particle measurement cavity is a dark box.

[0047] Preferably, the heating and dehumidifying device comprises a temperature and humidity sensor arranged at the air inlet, a heating cavity, and a heating wire and a temperature sensor arranged in the heating cavity, wherein the temperature sensor is attached to the surface of the heating wire, and the heating wire is connected to the single-chip microcomputer through a solid-state relay. The temperature sensor is a K-type thermocouple for measuring the temperature of the heating wire, and the temperature and humidity sensor is used to measure the temperature and humidity of the air in the external environment.

[0048] Preferably, a calibration light source is also provided in the particle measurement chamber, and the calibration light source is connected to the single chip microcomputer and controlled by the single chip microcomputer for timing calibration. The calibration light source is only enabled during calibration and used to temporarily replace the laser light emission.

[0049] Preferably, the flow monitoring unit includes an ultrasonic flow monitoring sensor, and the flow range is (0-20) L / min, level 1.5.

[0050] Preferably, the air extraction device is a vacuum pump or a diaphragm pump, and a filter is provided at the input end of the air extraction device. Adding a dust removal filter at the front end of the vacuum pump or diaphragm pump can prevent a large amount of dust in the air from being sucked into the pump, reduce the wear of the particulate matter on the pump rotor and parts in the pump cavity, and extend the service life of the pump.

[0051] Preferably, the monitor also includes a data storage module, a display module and an NB-IOT module. The single-chip microcomputer displays the measurement data and measurement time through the display module, and the single-chip microcomputer transmits the data remotely to the remote terminal through the NB-IOT module, so as to realize remote data viewing, real-time early warning, alarm, data storage, query and other functions. The use of NB-IoT has a 20dB gain over the existing network, and improves the coverage area by 100 times, supports low latency sensitivity, ultra-low equipment cost, low equipment power consumption and optimized network architecture, and ensures the normal use of the instrument in different environments.

[0052] Preferably, the monitor also includes an atmospheric pressure monitoring device for monitoring the atmospheric pressure in the external environment.

[0053] like Figures 1 to 4 As shown, the present invention provides a high-precision light scattering particle concentration monitoring method, which requires providing the above-mentioned monitoring instrument, and the method comprises the following steps:

[0054] Step 1, the single chip microcomputer adjusts the operating speed of the exhaust device through pulse width to control the air to flow into the monitor at a constant flow rate; in order to obtain the flow value more accurately, the weighted average value is used to measure the flow value. When the flow value exceeds the predetermined range, the single chip microcomputer adjusts the motor speed of the vacuum pump or diaphragm pump in the exhaust device through pulse width modulation technology. When the flow rate is stable and within the predetermined range, the control data at this time is recorded for the next startup to ensure that the gas enters the particle measurement chamber of the monitor at a relatively constant flow rate, thereby ensuring the accuracy of the calculation; for example, a constant flow rate of 1.0L / min is set, and the flow rate stability control is better than ±3%. Assuming that the flow rate is set to 1.0L / min and the flow sensor measures 1.2L / min, the motor speed is reduced according to the PID control pulse width adjustment (PWM adjustment) to achieve a flow rate equal to 1.0L / min. Due to the instability of the pump, the flow rate cannot be kept stable at 1.0L / min, and there will be insufficient or overloaded conditions. Therefore, it is necessary to continuously adjust the control pump flow rate to fluctuate in a smaller range.

[0055] Step 2, the single chip microcomputer obtains the current air humidity value, and controls the air humidity in the instrument to within the humidity threshold through the heating and dehumidification device;

[0056] Step 3, setting the pulse width by the single chip microcomputer to control the laser emission frequency, using the photosensitive sensor to convert the collected light signal into an electrical signal, calculating the scattered light pulse signal, and using the inversion formula to obtain the PM2.5 concentration; preferably, the inversion formula is Where C is the PM2.5 particle concentration, n is the number of pulse signal channels of the optical monitoring device, N(v i ) is the amplitude distribution of discrete voltage pulse signal, v i is the amplitude information, β is the particle morphology information parameter, and k is the proportional coefficient corresponding to the photosensitive sensor, which is set according to the calibration result;

[0057] Step 4: Start the self-calibration function regularly and calibrate the concentration monitor by turning on the calibration light source.

[0058] Preferably, the step 2 specifically includes:

[0059] Step 21, monitoring the current air humidity value through the humidity sensor in the heating and dehumidification device and transmitting it to the single chip microcomputer;

[0060] Step 22, the single chip computer determines whether the current air humidity value is higher than the humidity threshold value, if so, proceeds to step 23, otherwise, does not perform the dehumidification operation;

[0061] Step 23, start the PID control program, obtain the current temperature value (data from the temperature sensor on the heating wire), the target temperature value (manually set based on experience), the current air humidity value (data from the temperature and humidity sensor) and the humidity threshold (pre-defined), calculate the heating time and heating stop time required for the corresponding heating wire according to the current temperature value and the target temperature value, generate PWM pulses through the microcontroller IO and control the operation of the heating wire through the solid-state relay, and continuously adjust the heating and heating stop time through the PID control program to make the gas humidity in the monitor lower than the humidity threshold and ensure that the temperature is not higher than the target temperature value.

[0062] Preferably, the step 4 further comprises:

[0063] Step 41, regularly start the calibration light source through the single chip microcomputer to obtain the concentration measurement value under the calibration light source;

[0064] Step 42, calculating the difference between the measured concentration value in step 41 and the actual concentration value, and recording it as an error value;

[0065] Step 43: If the error value is greater than a preset error range, proceed to step 54 to calibrate the concentration monitor; otherwise, no calibration is performed;

[0066] Step 44, according to the size of the error value, the pulse width modulation is adjusted accordingly to increase the light emission frequency of the laser until the error value is reduced to within the error range; as the use time increases, the brightness of the laser will decay at the original light emission frequency, so by increasing the pulse width (PWM modulation) to increase the laser light emission frequency, the problem of insufficient light can be compensated, so that the brightness at this time is equivalent to the original brightness, ensuring that the pulse height generated by the corresponding particle size is consistent;

[0067] Alternatively, the proportional coefficient value in the inversion formula is adjusted according to the size of the error value until the error value is reduced to within the error range; since there is a proportional coefficient related to the photosensor in the inversion formula used to calculate the concentration, after the intensity of the photosensor decays after a period of use, the proportional coefficient can be adjusted to make the calculation result close to the actual concentration, thereby improving the calculation accuracy.

[0068] Alternatively, the pulse width modulation is adjusted to change the light emission frequency of the laser and the coefficient value in the inversion formula at the same time until the error value is reduced to within the error range.

[0069] In the present invention, the mass concentration of aerosol particles is obtained by calculating the distribution of particle size by obtaining a voltage pulse signal through particle scattering. When the laser and the photosensitive sensor are attenuated, the intensity of the pulse signal generated by the corresponding particle size will be affected, and the mass concentration of the measured aerosol particles will be low. In the present invention, the measurement deviation is corrected by using the relationship between the different signals of the laser light source and the coefficient value and the measured particle concentration value, thereby realizing the calibration of the instrument.

[0070] The advantages of the present invention are that the PWM flickering frequency is generated by controlling and adjusting the light-emitting frequency of the laser through a single-chip microcomputer. A lower frequency that meets the needs can be set at the beginning. After using it for a period of time, the light-emitting frequency of the laser is increased to avoid rapid aging of the laser due to long-term work. With PWM modulation, the laser will work intermittently and dissipate heat effectively, thereby extending the working life of the laser and meeting the monitoring accuracy requirements at the same time. The present invention adds a timing calibration module to regularly self-check and calibrate the accuracy of the instrument to form a feedback mechanism to ensure that the instrument remains within a certain accuracy range for a long time, and uses PWM modulation to adjust the frequency of the laser or / and adjusts the coefficients in the calculation formula to calibrate the instrument, thereby reducing frequent replacement of parts and reducing maintenance costs. The present invention also provides a heating and dehumidification device and a flow stabilization control to control the gas source and improve monitoring accuracy.

[0071] Although the specific implementation modes of the present invention are described above, those skilled in the art should understand that the specific implementation modes described are only illustrative and are not intended to limit the scope of the present invention. Equivalent modifications and changes made by those skilled in the art in accordance with the spirit of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A high-precision light scattering particle concentration monitor, characterized in that: It includes a single chip microcomputer, a heating and dehumidifying device, a concentration monitoring device, a flow monitoring device and an air extraction device, wherein the heating and dehumidifying device, the concentration monitoring device, the flow monitoring device and the air extraction device are respectively connected to the single chip microcomputer; The heating and dehumidifying device, concentration monitoring device, flow monitoring device and air extraction device are arranged along the air flow direction; The concentration monitoring device includes a particle measurement cavity, and a laser and a photosensitive sensor arranged in the particle measurement cavity, wherein the laser and the photosensitive sensor are respectively connected to a single-chip microcomputer, and the light emission frequency of the laser is controlled by the single-chip microcomputer, and the PWM flashing frequency of the laser is controlled and adjusted by the single-chip microcomputer; The particle measurement chamber is also provided with a calibration light source, which is connected to the single-chip microcomputer and controlled by the single-chip microcomputer for timed calibration. The calibration light source is only enabled during calibration and is used to temporarily replace the laser light emission.

2. A high-precision light scattering particle concentration monitor as claimed in claim 1, characterized in that: The heating and dehumidification device includes a temperature and humidity sensor arranged at the air inlet, a heating cavity, and a heating wire and a temperature sensor arranged in the heating cavity. The temperature sensor is attached to the surface of the heating wire, and the heating wire is connected to the single-chip microcomputer through a solid-state relay.

3. A high-precision light scattering particle concentration monitor as claimed in claim 1, characterized in that: The flow monitoring device includes an ultrasonic flow monitoring sensor.

4. A high-precision light scattering particle concentration monitor as claimed in claim 1, characterized in that: The air extraction device is a vacuum pump or a diaphragm pump, and a filter is provided at the input end of the air extraction device.

5. A high-precision light scattering particle concentration monitor as claimed in claim 1, characterized in that: The monitoring instrument also includes a data storage module, a display module and an NB-IOT module. The single-chip microcomputer displays the measurement data and the measurement time through the display module, and the single-chip microcomputer remotely transmits the data to the remote terminal through the NB-IOT module.

6. A high-precision light scattering particle concentration monitoring method, characterized in that: A monitoring device according to any one of claims 1 to 5 is provided, wherein the method comprises the following steps: Step 1, the single chip microcomputer adjusts the operating speed of the air extraction device through pulse width to control the air to flow into the monitor at a constant flow rate; Step 2, the single chip microcomputer obtains the current air humidity value, and controls the air humidity in the instrument to within the humidity threshold through the heating and dehumidification device; Step 3: Set the pulse width to control the laser emission frequency through the single chip microcomputer, use the photosensor to convert the collected light signal into an electrical signal, calculate the scattered light pulse signal, and use the inversion formula to obtain the PM2.5 concentration; Step 4: regularly start the self-calibration function and calibrate the concentration monitor by turning on the calibration light source; the step 4 further includes: Step 41, regularly start the calibration light source through the single chip microcomputer to obtain the concentration measurement value under the calibration light source; Step 42, calculating the difference between the measured concentration value in step 41 and the actual concentration value, and recording it as an error value; Step 43: If the error value is greater than a preset error range, proceed to step 54 to calibrate the concentration monitor; otherwise, no calibration is performed; Step 44, according to the size of the error value, correspondingly adjust the pulse width modulation to increase the light emission frequency of the laser until the error value is reduced to within the error range; Or adjusting the coefficient value in the inversion formula according to the size of the error value until the error value is reduced to within the error range; Alternatively, the pulse width modulation is adjusted to change the light emission frequency of the laser and the coefficient value in the inversion formula at the same time until the error value is reduced to within the error range.

7. A high-precision light scattering particle concentration monitoring method as claimed in claim 6, characterized in that: The step 2 specifically includes: Step 21, monitoring the current air humidity value through the humidity sensor in the heating and dehumidification device and transmitting it to the single chip microcomputer; Step 22, the single chip computer determines whether the current air humidity value is higher than the humidity threshold value, if so, proceeds to step 23, otherwise, does not perform the dehumidification operation; Step 23, start the PID control program, obtain the current temperature value, target temperature value, current air humidity value and humidity threshold value, calculate the heating time and heating stop time required for the corresponding heating wire according to the current temperature value and the target temperature value, generate PWM pulses through the microcontroller IO and control the operation of the heating wire through the solid-state relay, and continuously adjust the heating and heating stop time through the PID control program to make the gas humidity in the monitor lower than the humidity threshold value and ensure that the temperature is not higher than the target temperature value.

8. A high-precision light scattering particle concentration monitoring method as claimed in claim 6, characterized in that: The inversion formula is Where C is the PM2.5 particle concentration, n is the number of pulse signal channels of the optical monitoring device, and N(v i ) is the amplitude distribution of discrete voltage pulse signal, v i is the amplitude information, β is the particle morphology information parameter, and k is the proportional coefficient corresponding to the photosensitive sensor, which is set according to the calibration result.

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