CN104198348A - System and method for PM2.5 concentration detection based on photoelectric integration - Google Patents

Abstract

The invention belongs to the technical field of PM2.5 concentration detection and particularly relates to a system and a method for PM2.5 concentration detection based on photoelectric integration. The system consists of a ventilation chamber, a measurement chamber and a detection part, wherein the ventilation chamber is separated from the measurement chamber by a gas cutter, and the other end of the measurement chamber is connected with a detection channel; the detection part is arranged at the periphery of the detection channel and consists of an optical detection part, a power detection part and a data processing part; the optical detection part and the power detection part are respectively connected with the data processing part. The concentration of PM2.5 particles is respectively detected through optical detection and power detection, and then, fusion calculation is carried out on two detection signals by a kalman filtering algorithm. As no laser generator is used in the invention, the cost of the system is greatly reduced. Meanwhile, detection data is obtained by the detection method adopting two different principles, and the actual value is obtained through fusion calculation, so that the detection precision of the system can be ensured.

Description

The PM2.5 concentration detection system and the detection method that based on photoelectricity, merge

Technical field

The invention belongs to PM2.5 Concentration Detection field, particularly a kind of PM2.5 concentration detection system and detection method merging based on photoelectricity.

Background technology

PM2.5 also cries and can enter lung particle, refer to that aerodynamic diameter is less than or equal to the particle of 2.5 microns, its atmospheric aerosol forming in air has larger extinction coefficient than the gasoloid of the particle formation of all the other particle size range, is the major pollutants of common " haze " phenomenon in this year.Because the specific surface area of PM2.5 is large, easily adsorb poisonous and harmful substances, and the reaction bed of atmospheric reaction thing is provided, generate secondary pollution, therefore very big to environmental hazard.

When illumination is mapped to after PM2.5 gasoloid, due to particle to scattering of light, absorb and disperse, make light distribution and the particle concentration of light in space have correlationship.Based on this principle, the product of the market mainstream is the diffuse transmission type PM2.5 concentration meter based on laser mostly, although accuracy of detection is high, reproducible, equipment manufacturing cost is high, is difficult to popularize.

Summary of the invention

For overcoming the above problems, the object of the invention is to design the PM2.5 concentration detection system and the detection method that merge based on photoelectricity that a kind of precision is suitable with laser scattering type detector, cost performance is high, to meet the demand of market to this series products.

For reaching above object, the technical scheme of employing of the present invention is:

This detection system is comprised of breather chamber, measuring chamber, test section; Described measuring chamber is front wide and rear narrow infundibulate, between the wide end of breather chamber and measuring chamber, by gas cutter, is separated; The narrow end of measuring chamber is connected with sense channel;

Described test section is arranged on around sense channel, by optical detection part divide, electro-detection part and data processing division be grouped into; Optical detection part divides with electro-detection part and is connected with data processing section respectively;

Described optical detection part divides by photodetector and nonconducting optical glass and forms; The optical glass of annular is arranged on sense channel wall, optical glass arranged outside photodetector;

Capacitor and small capacitance testing circuit that described electro-detection part consists of conductive plate form; Capacitor is arranged on the sense channel wall at optical glass rear, and small capacitance testing circuit is connected with capacitor.

The xsect of described breather chamber and measuring chamber junction is rectangle; Described gas cutter is sealing installation.

The xsect of described sense channel is the rectangle that length and width are 5～10mm.

Described data processing division is divided into treatment circuit and display.

In described system, except optical glass, remainder is opaque material.

Detection method based on said detecting system, comprises the following steps:

(1) obtain an air containing PM2.5 to be detected:

Normal air enters detection system from the entrance of breather chamber, by gas cutter by airborne PM2.5 particle and non-PM2.5 particulate separation; The air that contains PM2.5 enters measuring chamber, starts to detect after standing indoor PM2.5 concentration stabilize to be measured;

(2) test section work, obtains detection signal, and it is processed:

First open photodetector, the white light that light source sends is through after the air that contains PM2.5, because PM2.5 particle is to the refraction of light, scattering and absorption, the light intensity of the air by containing PM2.5 is relevant to the concentration of PM2.5 particle, the probe that is positioned at light source opposite side is converted into electric signal by light intensity signal, forms first via light detecting signal;

Then open electro-detection part, the capacitance of capacitor is relevant with the concentration of PM2.5 particle, by small capacitance testing circuit, the capacitance of capacitor is converted into electric signal, forms the second road power detection signal;

Obtained two paths of signals is carried out respectively to signal processing, by filtering, shaping, be converted to the standard voltage signal of 0-5V, through analog to digital conversion, send into data processing section;

(3) use Kalman filtering algorithm, two-way detection signal carried out to fusion calculation:

Data processing section receives after signal, the light detecting signal of sending into of synchronization and power detection signal are stored in to the same row of two-dimensional array, light detecting signal is stored in the first row of two-dimensional array according to time order and function, power detection signal is the second row at two-dimensional array according to time order and function sequential storage; Data processing section carries out fusion calculation according to Kalman filtering algorithm to two paths of signals, and result of calculation is stored in another one-dimension array, carries out output display while needing.

Beneficial effect of the present invention is:

Optical detection part of the present invention divides with now conventional laser scattering type detector based on same physical process, but the physical quantity that the present invention detects is the light intensity through aerosol particle thing, compare with the equipment that detects scattered light intensity, maximum advantage is to utilize white light also can obtain good detection characteristic, can greatly reduce system cost.

Meanwhile, by the detection method of two kinds of different principle, obtain detection data, and obtain actual value by fusion calculation, can guarantee the accuracy of detection of system.

In addition, by adjusting blending algorithm parameter, can realize any mapping relations, to change the result of fusion calculation, therefore system reduces the degree of dependence of hardware precision, can to testing result, revise by the mode of software compensation, reduce hardware production precision, also can reduce system cost.

Accompanying drawing explanation

Fig. 1 is workflow schematic diagram of the present invention.

Fig. 2 is system architecture schematic diagram of the present invention.

Fig. 3 is while adopting circle cutter, the system architecture schematic diagram of seeing from air intake direction.

Fig. 4 is the structural drawing of small capacitance testing circuit.

Fig. 5 is the process flow diagram of blending algorithm.

Fig. 6 is the result of blending algorithm.

Number in the figure:

1-breather chamber, 2-cutting head, 3-measuring chamber, 4-treatment circuit and display, 5-photodetector, 6-optical glass, 7-capacitor.

Embodiment

The invention provides a kind of PM2.5 concentration detection system and detection method merging based on photoelectricity, below in conjunction with the drawings and specific embodiments, the present invention will be further described.

As shown in Figure 1, as shown in Figure 2, label Cx represents to measure electric capacity to system architecture for detection principle of the present invention and flow process, and D represents air intake direction.

This system is comprised of breather chamber 1, measuring chamber 3, test section; Described measuring chamber 3 is front wide and rear narrow infundibulate, between breather chamber 1 and the wide end of measuring chamber 3, by gas cutter 2, is separated; The narrow end of measuring chamber 3 is connected with sense channel.Breather chamber 1 is rectangle with the xsect of measuring chamber 3 junctions; Described gas cutter 2 is circle or rectangle, adopts sealing to install, and its function is that normal air is divided into part and the remainder that only contains PM2.5 particle, when adopting circular gas cutter 2, from air intake direction, sees gas cutter 2 as shown in Figure 3.

For reducing sensor cost, measuring chamber 3 detections place are highly unsuitable excessive, otherwise can cause measuring, capacitance is too small, transmitted intensity is too small, thereby require system to select the higher sensor of sensitivity, and then raise the cost, detection place is simultaneously highly unsuitable too small, otherwise detection place wind speed increment is crossed conference and is caused actual wind speed fluctuation larger, affect measuring accuracy, it is proper that the xsect of sense channel is that length and width are the rectangle of 5～10mm.

Test section is arranged on around sense channel, by optical detection part divide, electro-detection part and data processing division be grouped into; Optical detection part divides with electro-detection part and is connected with data processing section respectively.Data processing division is divided into treatment circuit and display 4, is arranged on the outer wall of measuring chamber 3.

Described optical detection part divides by photodetector 5 and nonconducting optical glass 6 and forms; The optical glass 6 of annular is arranged on sense channel wall, optical glass 6 arranged outside photodetectors 5.Optical detection part divides with now conventional laser scattering type detector based on same physical process, but the physical quantity that the present invention detects is the light intensity through aerosol particle thing, compare with the equipment that detects scattered light intensity, maximum advantage is to utilize white light also can obtain good detection characteristic, can greatly reduce system cost.

Capacitor 7 and small capacitance testing circuit that described electro-detection part consists of conductive plate form; Capacitor 7 is arranged on the sense channel wall at optical glass 6 rears, and small capacitance testing circuit is connected with capacitor 7.The principle of electro-detection part is that the electrology characteristic of PM2.5 particle is different from air, the specific inductive capacity that the air of the PM2.5 particle that contains variable concentrations has is different, and then cause measuring electric capacity difference, by demarcating, can obtain the corresponding relation of measuring capacitance and PM2.5 granule density.

The structure of small capacitance testing circuit as shown in Figure 4.

Label i indication circuit input in circuit, Cx represents testing capacitance, and Cr represents reference capacitance, and U is an operational amplifier, and R1, R2, R3 and Rf represent resistance.

The principle of this circuit working is: first closed two switches, and now two electric capacity all discharge, and connect two electronic switches simultaneously, by the identical current source of size, charge to testing capacitance and reference capacitance simultaneously, according to the definition of electric capacity:

C＝Q/U＝i·Δt/U，

In capacitor charging process, capacitor voltage at both ends meets:

U＝i·Δt/C，

After operational amplifier carries out subtraction, the voltage difference of the two ends of operational amplifier input has following relation:

$U_o=\frac{\mathrm{Rf}}{R1}(i\·\mathrm{\Δt}/\mathrm{Cx}-i\·\mathrm{\Δt}/\mathrm{Cr}),$

Obviously, output voltage U ₀be proportional to the duration of charging, its scale-up factor has reflected C _xvalue.

Because capacitor charging time is shorter, for avoiding relaxation phenomena, said process should not continue the long period simultaneously.

For avoiding interference optical detection part minute accuracy of detection, this system is except nonconducting optical glass 6, and remainder all adopts opaque material, and when signal is processed, the method for employing difference is removed the interference of surround lighting simultaneously.

The step that this detection system is carried out the detection of PM2.5 concentration is:

(1) obtain an air containing PM2.5 to be detected:

Normal air enters detection system from the entrance of breather chamber 1, by gas cutter 2 by airborne PM2.5 particle and non-PM2.5 particulate separation; The air that contains PM2.5 enters measuring chamber 3, starts to detect after the interior PM2.5 concentration stabilize in standing chamber 3 to be measured;

(2) test section work, obtains detection signal, and it is processed:

First open photodetector 5, the white light that light source sends is through after the air that contains PM2.5, because PM2.5 particle is to the refraction of light, scattering and absorption, the light intensity of the air by containing PM2.5 is relevant to the concentration of PM2.5 particle, the probe that is positioned at light source opposite side is converted into electric signal by light intensity signal, forms first via light detecting signal;

Then open electro-detection part, the capacitance of capacitor 7 is relevant with the concentration of PM2.5 particle, by small capacitance testing circuit, the capacitance of capacitor 7 is converted into electric signal, forms the second road power detection signal;

Obtained two paths of signals is carried out respectively to signal processing, by filtering, shaping, be converted to the standard voltage signal of 0-5V, through analog to digital conversion, send into data processing section;

(3) use Kalman filtering algorithm, two-way detection signal carried out to fusion calculation:

The essence of data fusion is according to a plurality of detected values that contain actual concentration, searches out the mapping relations of detected value and actual value, adopts Kalman filtering algorithm.Kalman filtering algorithm is the optimum solution under classical linear regression hypothesis, can farthest avoid random noise to detecting the interference of effect.Fig. 5 is the process of Kalman filtering algorithm, and in figure, region I represents to predict link, and region II represents to revise link.

The mathematical model of algorithm supposing the system is comprised of formula (1), formula (2).

S(k)＝A·S(k-1)+w(k-1) (1)

Z(k)＝C·S(k)+v(k) (2)

Wherein, k represents to merge for the k time, and S represents actual value, and w represents the noise of introducing in model, and Z represents detected value, the noise of introducing when v represents to detect, and A, C are known coefficient.All parameters can be scalar forms above, can be also matrix forms.

The implication of formula (1) is that in the situation that there is no outside input, the virtual condition of system can fluctuate within the specific limits due to some unkownable factors, if macroscopic view consideration can be ignored latter one.In this example, although the concentration of PM2.5 can be subject to the impact of the factors such as discharge, weather in air, Kalman filtering algorithm is the filtering algorithm based on detected value, so do not affect filter effect.

The implication of formula (2) is that current detected value, except relevant with actual value, also can be introduced some not eliminable random noise, i.e. stochastic errors in testing process.

When filtering starts, first the light detecting signal of sending into of synchronization and power detection signal are stored in to the same row of two-dimensional array, light detecting signal is stored in the first row of two-dimensional array according to time order and function, power detection signal is the second row at two-dimensional array according to time order and function sequential storage, forms the matrix of the some row of 2 row.Then start filtering algorithm, according to the order of formula, every calculating once, can obtain the actual value with the current corresponding moment of detected value.

E′(k)＝A·E(k-1)·A ^T+Q (3)

H(k)＝E′(k)·C ^T／(C·E′(k)·C ^T+R) (4)

E(k)＝(I-H(k)·C)·E′(k) (5)

$\hat{S}\left(k\right)=A\·\hat{S}(k-1)+H\left(k\right)(Z\left(k\right)-C\·A\·\hat{S}(k-1))---\left(6\right)$

Wherein, the result of fusion calculation, I representation unit matrix, exponent number is identical with other parts in formula, and all the other are the pilot process value in computation process.The conjugate transpose of subscript " T " representing matrix, does not occur that in the situation of imaginary number be exactly transpose of a matrix, if be all scalar operation, can ignore.

Q and R are the parameter informations of aforementioned adjustment filtering algorithm effect, and when covariance matrix, the R that equals the random perturbation w in model as Q equals the covariance matrix of the random perturbation v in measuring process, the result of calculation of filtering algorithm is best.In practice, can adjust by changing the value of Q and R the performance of filtering algorithm.

Fig. 6 is the result of blending algorithm, the corresponding actual value of solid line in figure, the result of the corresponding fusion calculation of dotted line, the respectively corresponding measured value of all the other two curves.Can see, but the measured value that contain actual value information large according to two-way error, result and the actual value of fusion calculation are more or less the same.

Claims (6)

1. the PM2.5 concentration detection system merging based on photoelectricity, by breather chamber (1), measuring chamber (3), test section, formed, it is characterized in that, described measuring chamber (3) is front wide and rear narrow infundibulate, between breather chamber (1) and the wide end of measuring chamber (3), by gas cutter (2), is separated; The narrow end of measuring chamber (3) is connected with sense channel;

Described test section is arranged on around sense channel, by optical detection part divide, electro-detection part and data processing division be grouped into; Optical detection part divides with electro-detection part and is connected with data processing section respectively;

Described optical detection part divides by photodetector (5) and nonconducting optical glass (6) and forms; The optical glass (6) of annular is arranged on sense channel wall, optical glass (6) arranged outside photodetector (5);

Capacitor (7) and small capacitance testing circuit that described electro-detection part consists of conductive plate form; Capacitor (7) is arranged on the sense channel wall at optical glass (6) rear, and small capacitance testing circuit is connected with capacitor (7).

2. the PM2.5 concentration detection system merging based on photoelectricity according to claim 1, is characterized in that, described breather chamber (1) is rectangle with the xsect of measuring chamber (3) junction; Described gas cutter (2) is sealing installation.

3. the PM2.5 concentration detection system merging based on photoelectricity according to claim 1, is characterized in that, the xsect of described sense channel is the rectangle that length and width are 5～10mm.

4. the PM2.5 concentration detection system merging based on photoelectricity according to claim 1, is characterized in that, described data processing division is divided into treatment circuit and display (4).

5. the PM2.5 concentration detection system merging based on photoelectricity according to claim 1, is characterized in that, in described system, except optical glass (6), remainder is opaque material.

6. the detection method based on detection system described in claim 1, is characterized in that, comprises the following steps:

(1) obtain an air containing PM2.5 to be detected:

Normal air enters detection system from the entrance of breather chamber (1), by gas cutter (2) by airborne PM2.5 particle and non-PM2.5 particulate separation; The air that contains PM2.5 enters measuring chamber (3), starts to detect after the interior PM2.5 concentration stabilize in standing chamber to be measured (3);

(2) test section work, obtains detection signal, and it is processed:

First open photodetector (5), the white light that light source sends is through after the air that contains PM2.5, because PM2.5 particle is to the refraction of light, scattering and absorption, the light intensity of the air by containing PM2.5 is relevant to the concentration of PM2.5 particle, the probe that is positioned at light source opposite side is converted into electric signal by light intensity signal, forms first via light detecting signal;

Then open electro-detection part, the capacitance of capacitor (7) is relevant with the concentration of PM2.5 particle, by small capacitance testing circuit, the capacitance of capacitor (7) is converted into electric signal, forms the second road power detection signal;

Obtained two paths of signals is carried out respectively to signal processing, by filtering, shaping, be converted to the standard voltage signal of 0-5V, through analog to digital conversion, send into data processing section;

(3) use Kalman filtering algorithm, two-way detection signal carried out to fusion calculation:

Data processing section receives after signal, the light detecting signal of sending into of synchronization and power detection signal are stored in to the same row of two-dimensional array, light detecting signal is stored in the first row of two-dimensional array according to time order and function, power detection signal is the second row at two-dimensional array according to time order and function sequential storage; Data processing section carries out fusion calculation according to Kalman filtering algorithm to two paths of signals, and result of calculation is stored in another one-dimension array, carries out output display while needing.