CN103575695A - Detection device for nitrogen oxide content of gas - Google Patents

Abstract

The invention discloses a detection device for the nitrogen oxide content of a gas, which is used for detecting the concentration of nitrogen oxides contained in the gas. The detection device comprises a treater, a program-controlled current source, a laser, a gas absorption pool, a detector and a signal conditioner. By applying the detection device disclosed by the invention, a high-temperature conversion process is not needed, thus reducing power consumption and energy consumption; and moreover, because the content of the nitrogen oxides in the gas is directly measured, the influence of the existence of other substances on a content detection for the to-be-detected gas is avoided, so that the detection result is more accurate. Furthermore, because a ZrO2 sensor does not need to be used, the problem of poisoning of the ZrO2 sensor due to the compounds of P, S and Si, such as H2S is avoided. Meanwhile, because a ZrO2 sensor technology is a technology monopolized by foreign companies, and the ZrO2 sensor does not need to be used in the detection device disclosed by the invention, the existing technical barrier is broken.

Description

A kind of the GN 2 oxide content pick-up unit

Technical field

The present invention relates to gas content detection technique field, particularly a kind of the GN 2 oxide content pick-up unit.

Background technology

The high speed development of China's automobile industry, demand will break through 1,000 ten thousand.When facilitating the people to go on a journey, pull the aspects such as GDP growth to obtain remarkable result, also caused serious environmental issue.Automotive emission has become the important source of atmospheric pollution, and the sustainable development of body health of people and national society is produced and had a strong impact on.Therefore, countries in the world constantly propose more and more higher requirement to motor-driven vehicle gas disposal.China has executed state 3 (Europe 3) standard, estimates on July 1st, 2012 and will execute state IV (Europe IV) standard, this means solar obligation oxides of nitrogen (NOx) pick-up unit to control discharge content.

At present, common way is to use zirconia (ZrO ₂) lambda sensor of system carries out oxides of nitrogen detection, it detects principle and is specially: in the first air chamber,, then by catalytic reaction, nitrogen oxide NOx is converted into N by oxygen pump to 1ppb once ₂and O ₂, N after transforming ₂and O ₂enter the second air chamber, in the second air chamber, pass through again ZrO ₂lambda sensor is measured the oxygen content generating, thereby indirectly measures the content of nitrogen oxide NOx.

Although said method can record the content of oxides of nitrogen, at least there is following problem:

1, by catalytic reaction, NO is being converted into O ₂process in need to make the temperature of conversion environment to reach the high temperature of 300 degrees Celsius, power consumption is high, energy consumption is large;

2, due to the temperature of conversion environment, need to reach the high temperature of 300 degrees Celsius, thereby be subject to inflammable gas as H ₂, CH ₄, the impact of CO equal size, makes testing result be subject to the impact of inflammable gas content very large, and the accuracy of testing result is low;

3, P, S, the compound of Si, for example H ₂s, can cause ZrO ₂sensor Poisoning, causes ZrO ₂sensor failure.

Summary of the invention

The embodiment of the present invention provides a kind of the GN 2 oxide content pick-up unit, both can avoid sensor poisoning because of some compound so that testing result is not subject to the impact of inflammable gas content, has also reduced power consumption.

The invention discloses a kind of the GN 2 oxide content pick-up unit, for the concentration of gas institute nitrogen-containing oxide is detected, described pick-up unit comprises: processor (100), programmable current source (200), laser instrument (300), gas absorption cell (400), detector (500) and signal conditioner (600), wherein, described gas absorption cell (400) has broken line type air chamber, on described broken line type air chamber, there is air admission hole (415) and venthole (416), gas to be measured enters described broken line type air chamber from described air admission hole (415), along fold-line-shaped air chamber, flow, from venthole (416), flow out described broken line type air chamber, on described broken line type air chamber, also there is incident light hole and light perforation hole, incident laser enters described broken line type air chamber from described incident light hole, along the reflection of broken line type air chamber, from light perforation hole, penetrates,

Described programmable current source (200) is directly adjusted laser instrument under the control of processor, makes laser instrument (300) export the laser that a road light intensity and wavelength are sinusoidal fluctuation; A described road laser enters the broken line type air chamber in gas absorption cell 400 by described incident light hole, from light perforation hole, penetrates, and enters detector;

Described detector (500), is converted to electric signal by a described road light signal, sends the electric signal after conversion to signal conditioning circuit;

Signal conditioning circuit (600), to sending processor to after described electric signal conditioning;

Processor (100) according to the instruction receiving, detects second harmonic and base wave intensity in shoot laser from the signal the conditioning receiving, and obtains the concentration of the middle oxides of nitrogen of gas to be measured according to described two kinds of humorous wave intensity.

Wherein, described signal conditioning circuit comprises:

Wave filter, carries out filtering processing by the electric signal from detector;

AD converter, sends processor to after described filtered analog electrical signal is converted to digital signal.

Wherein, described processor comprises:

Memory storage, when the concentration that is kept at oxides of nitrogen gas in the gas that comprises oxides of nitrogen surpasses the first preset value, the nox adsorption peak measuring and reference absorption peak center be the difference DELTA D of corresponding laser diode current value respectively; Be kept at the corresponding current value D of reference absorption peak center institute measuring in the gas of nitrogenfree oxide gas ₂₀, and preserve current value D ₂₀the amplitude A of the first harmonic of the reference absorption peak at place ₀, and under equal conditions, current value is (D ₂₀-Δ D) the second harmonic value I locating _2f0;

Humorous intensity of wave acquisition device, first measures the corresponding current value D in reference absorption peak center in gas to be measured ₂, and measure current value D ₂the first harmonic amplitude A at place; Measuring laser diode current value is D again ₁=D ₂the second harmonic value I of-Δ D position _{2f surveys}; The amplitude A of the first harmonic of the reference absorption peak measuring under the condition without gas to be measured from described memory storage acquisition ₀, and electric current is (D ₂₀-Δ D) the second harmonic value I locating _2f0, calculate background f (A)=I _2f0* A/A ₀, making laser diode current is D ₁nox adsorption peak second harmonic intensity I _2f=I _{2f surveys}-f (A);

Concentration calculation element, according to the intensity I of the second harmonic at institute's corresponding current value place, described nox adsorption peak _2fobtain the concentration of the middle oxides of nitrogen of gas to be measured with the intensity A of the first-harmonic at reference absorption peak institute corresponding current value place.

Wherein, described signal conditioning circuit comprises:

Wave filter, carries out filtering processing by the electric signal from detector;

Phase-locked amplifying circuit, detects after described filtering the intensity I of the second harmonic of shoot laser in signal _{2f surveys}.

Wherein, described processor comprises:

Memory storage, when the concentration that is kept at oxides of nitrogen gas in the gas that comprises oxides of nitrogen surpasses the first preset value, the nox adsorption peak measuring and reference absorption peak center be the difference DELTA D of corresponding laser diode current value respectively; Be kept at the corresponding current value D of reference absorption peak center institute measuring in the gas of nitrogenfree oxide gas ₂₀, and preserve current value D ₂₀the amplitude A of the first harmonic of the reference absorption peak at place ₀, and under equal conditions, current value is (D ₂₀-Δ D) the second harmonic value I locating _2f0;

Humorous intensity of wave acquisition device, first measures the corresponding current value D in reference absorption peak center in gas to be measured ₂, and measure current value D ₂the first harmonic amplitude A at place; The amplitude A of the first harmonic of the reference absorption peak measuring under the condition without gas to be measured from described memory storage acquisition ₀, and electric current is (D ₂₀-Δ D) the second harmonic value I locating _2f0, calculate background f (A)=I _2f0* A/A ₀, making laser diode current is D ₁nox adsorption peak second harmonic intensity I _2f=I _{2f surveys}-f (A);

Concentration calculation element, according to the intensity I of the second harmonic at institute's corresponding current value place, described nox adsorption peak _2fobtain the concentration of the middle oxides of nitrogen of gas to be measured with the intensity A of the first-harmonic at reference absorption peak institute corresponding current value place.

Wherein, described gas to be measured is vehicle exhaust; Described reference gas is aqueous vapor.

Wherein, described gas absorption cell (400) comprising: pond body (401), the first plane mirror (402), the peaceful surface cover of the second plane mirror (403) (404), described the first plane mirror (402) and the second plane mirror (403) are close to respectively described pond body (401) pond body the first side wall (406) and pond body the second sidewall (407), wherein, described pond body the first side wall (406) is vertical with pond body upper surface (405) with pond body the second sidewall (407), and described pond body the first side wall (406) and pond body the second sidewall (407) are parallel to each other; On described pond body upper surface (405), be provided with broken line type raceway groove (410), described plane cover plate (404) covers on the broken line type raceway groove of described pond body (401) and forms broken line type air chamber, described broken line type air chamber is positioned between described the first plane mirror (402) and described the second plane mirror (403), at pond body the first side wall (406) and pond body the second sidewall (407), above along the direction perpendicular to pond body the first side wall (406) and pond body the second sidewall (407), have a plurality of smooth reflection holes (412), light reflection hole (412) communicates with fold-line-shaped raceway groove (410);

On described pond body upper surface (405), offer air admission hole (415) and venthole (416), gas to be measured enters described broken line type air chamber from described air admission hole (415), along fold-line-shaped raceway groove (410), flow, from venthole (416), flow out described broken line type air chamber;

Described gas absorption cell (400) also has pond body the 3rd sidewall (408) and pond body the 4th sidewall (409), wherein, body the 3rd sidewall (408) in described pond becomes to preset respectively the angle that adds of the number of degrees with pond body the 4th sidewall (409) with pond body the second sidewall (407); Direction on the upper edge of pond body the 3rd sidewall (408) perpendicular to pond body the 3rd sidewall has incident light hole (411), described incident light hole (411) communicates with fold-line-shaped raceway groove (410): the direction on the upper edge of pond body the 4th sidewall (409) perpendicular to pond body the 4th sidewall (409) has light perforation hole (413), and described smooth perforation hole (413) communicates with fold-line-shaped raceway groove (410); Incident laser enters described broken line type air chamber from described incident light hole (411), along the reflection of broken line type air chamber, from light perforation hole (413), penetrates.

Wherein, described pick-up unit also comprises: cooling line, is connected between the air admission hole (415) of broken line type air chamber of gas purging to be measured outlet and described gas absorption cell, with by cooled to be measured being sent in described gas absorption cell.

Wherein, described pick-up unit also comprises: filtrator and gas-liquid separator, be connected between the end of cooling line and the air admission hole (415) of the broken line type air chamber of described gas absorption cell, to filter impurity and the liquid in gas to be measured.

The pick-up unit that the application embodiment of the present invention provides, use spectrum test method, do not need pyrolytic conversion process, therefore power consumption and energy consumption have been reduced, and, owing to being the content of oxides of nitrogen in direct measurement gas, the impact that the existence of having avoided other materials detects gas content to be measured, makes check result more accurate.Have again, owing to not needing to use ZrO ₂, therefore, there is not P, S, the compound of Si, for example H in sensor yet ₂s, can cause ZrO ₂the problem of Sensor Poisoning.Meanwhile, due to ZrO ₂the technology of sensor technology Shi Bei offshore company monopolization, and the application does not need to use ZrO ₂sensor, has therefore broken prior art barrier.

Have again, in the scheme of application, only need laser instrument to export a road detecting light beam, the intensity of the second harmonic by final shoot laser is carried out the concentration of the middle oxides of nitrogen of gas to be measured, do not need standard air chamber, do not need reference arm, thereby avoided the spectrum test method of existing two-way balance can not be applied to the problem of industry spot, the industry spot application that can in officely what is the need for and want yet.

Have again, gas absorption cell in application the embodiment of the present application, make concentration equiblibrium mass distribution in gas absorption cell of gas to be measured, not only can in a less area of space, extend effective light path, and can realize the quick turnover of gas to be measured in gas absorption cell.

Accompanying drawing explanation

In order to be illustrated more clearly in the embodiment of the present invention or technical scheme of the prior art, to the accompanying drawing of required use in embodiment or description of the Prior Art be briefly described below, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skills, do not paying under the prerequisite of creative work, can also obtain according to these accompanying drawings other accompanying drawing.

Fig. 1 is the structural drawing of the GN 2 oxide content pick-up unit according to an embodiment of the invention;

Fig. 2 is according to the structural representation of a kind of gas absorption cell of the embodiment of the present invention, and wherein Fig. 2 A is front view, and Fig. 2 B is left view, and Fig. 2 C is vertical view;

Fig. 3 is pond body inner structure and the light transmission path schematic diagram according to gas absorption cell embodiment illustrated in fig. 2;

Fig. 4 is according to one of the embodiment of the present invention concrete application example schematic diagram.

Embodiment

Below in conjunction with the accompanying drawing in the embodiment of the present invention, the technical scheme in the embodiment of the present invention is clearly and completely described, obviously, described embodiment is only the present invention's part embodiment, rather than whole embodiment.Embodiment based in the present invention, those of ordinary skills, not making the every other embodiment obtaining under creative work prerequisite, belong to the scope of protection of the invention.

Referring to Fig. 1, it is the structural drawing of the GN 2 oxide content pick-up unit according to an embodiment of the invention, in the present embodiment, this pick-up unit is for detecting the concentration of gas institute nitrogen-containing oxide, it specifically comprises: processor 100, programmable current source 200, laser instrument 300, gas absorption cell 400, detector 500 and signal conditioner 600, wherein, gas absorption cell 400 has broken line type air chamber, on described broken line type air chamber, there is air admission hole 415 and venthole 416, gas to be measured enters described broken line type air chamber from described air admission hole 415, along fold-line-shaped air chamber, flow, from venthole 416, flow out described broken line type air chamber, on described broken line type air chamber, also there is incident light hole and light perforation hole, incident laser enters described broken line type air chamber from described incident light hole, along the reflection of broken line type air chamber, from light perforation hole, penetrates,

Programmable current source 200 is directly adjusted laser instrument under the control of processor 100, makes laser instrument export the laser that a road light intensity and wavelength are sinusoidal fluctuation; A described road laser enters the broken line type air chamber in gas absorption cell 400 by described incident light hole, from light perforation hole, penetrates, and enters detector;

Detector 500, is converted to electric signal by a described road light signal, sends the electric signal after conversion to signal conditioning circuit;

Signal conditioning circuit 600, to sending processor to after described electric signal conditioning;

Processor 100 according to the instruction receiving, detects second harmonic and base wave intensity in shoot laser from the signal the conditioning receiving, and obtains the concentration of the middle oxides of nitrogen of gas to be measured according to described two kinds of humorous wave intensity.

In a kind of possible embodiment, above-mentioned signal conditioning circuit 600 can comprise:

Wave filter (not shown), carries out filtering processing by the electric signal from detector; And

Modulus (AD) converter (not shown), sends processor to after described filtered analog electrical signal is converted to digital signal.

Now, described processor 100, according to the instruction receiving, detects second harmonic and base wave intensity in shoot laser, obtains the concentration of oxides of nitrogen in gas to be measured according to described second harmonic and base wave intensity.In this embodiment, the second harmonic of shoot laser and base wave intensity are detected by processor.

Concrete, described processor 100 can comprise:

Memory storage, the concentration that is kept at oxides of nitrogen gas in the gas that comprises oxides of nitrogen surpasses the first preset value as 10% time, and the nox adsorption peak measuring and reference absorption peak center be the difference DELTA D of corresponding laser diode current value respectively; Be kept at the corresponding current value D of reference absorption peak center institute measuring in the gas of nitrogenfree oxide gas ₂₀, and preserve current value D ₂₀the amplitude A of the first harmonic of the reference absorption peak at place ₀, and under equal conditions, current value is (D ₂₀-Δ D) the second harmonic value I locating _2f0;

Humorous intensity of wave acquisition device, first measures the corresponding current value D in reference absorption peak center in gas to be measured ₂, and measure current value D ₂the first harmonic amplitude A at place; Measuring laser diode current value is D again ₁=D ₂the second harmonic value I of-Δ D position _{2f surveys}; The amplitude A of the first harmonic of the reference absorption peak measuring under the condition without gas to be measured from described memory storage acquisition ₀, and electric current is (D ₂₀-Δ D) the second harmonic value I locating _2f0, calculate background f (A)=I _2f0* A/A ₀, making laser diode current is D ₁nox adsorption peak second harmonic intensity I _2f=I _{2f surveys}-f (A);

Concentration calculation element, according to the intensity I of the second harmonic at nox adsorption peak institute corresponding current value place _2fobtain the concentration of the middle oxides of nitrogen of gas to be measured with the intensity A of the first-harmonic at reference absorption peak institute corresponding current value place.

Here, the above-mentioned concept relating to is done to a simple declaration.

Background, non-linear due to the P-I curve of laser instrument, and the other system existing is non-linear, and even in the situation that there is no gas to be measured, the second harmonic value of the gas to be measured measuring can not be 0 yet, this non-zero value is called background;

Oxides of nitrogen gas, it has been generally acknowledged that it is weak absorption gas, and the absorption peak of oxides of nitrogen gas is because second harmonic intensity level and background that absorption causes are substantially suitable.

Reference absorption peak: if the second harmonic intensity level that the absorption peak of certain gas causes due to absorption is much larger than background, this absorption peak is called as strong absorption peak, this strong absorption peak is usually used as reference absorption peak, and the corresponding gas of this reference absorption peak is called reference gas.For example, the background values that the second harmonic intensity level that certain absorption peak causes due to absorption is greater than 10 times, this absorption peak can be used as reference absorption peak; Here, if the product value of absorption intensity and concentration is larger, but this gas dense under a kind of possible situation lower environment to be measured that is absorption intensity, but another kind of possible situation is that the lower absorption intensity of concentration is high.

Conventionally, nox adsorption peak and reference absorb peak-to-peak distance range, are the scopes that current-modulation can reach, generally in several nanometers at zero point, however again can not be too approaching, in order to avoid overlapping, absorption cross section influences each other.

Wherein, the principle that concentration is calculated is same as the prior art, only does simple declaration here.

First, when light is by after certain gas, it will be subject to the absorption of gas, and its output intensity is determined by Bill-Lambert (Beer-Lambert) formula

I(υ)＝I ₀(υ)exp[-α(υ)CL] (4.1)

Wherein, I (υ) is emergent light light intensity, and υ is this light frequency; I ₀by the initial light intensity before air chamber; C is the concentration of gas; L is that passed through air chamber is long; α is the absorption coefficient of gas, and the absorption frequency that gas with various is corresponding is also different; For same gas, also there are a plurality of absorption peaks.

Utilize this character, select the wavelength of incident laser, make it the center of certain absorption peak in gas to be measured.Then allow this laser by gas to be measured.By detecting outgoing light intensity, can obtain it by the absorption intensity of gas, thereby indirectly obtain the concentration of gas to be measured.Concrete,

The drive current of light source is added to a low frequency (k hertz rank) small signal modulation, laser instrument is directly adjusted, thereby laser output wavelength is produced to a modulation, simultaneously an additional intensity modulation

$\mathrm{\υ}=\stackrel{\‾}{\mathrm{\υ}}+a\sin \mathrm{\ωt}$

(4.2)

I ₀(t)＝I ₀(1+ηsin ωt)

Wherein, υ is light wavelength, I ₀(t) the time dependent light intensity value of light intensity of laser instrument output, ω is the angular frequency of add modulation, for the centre frequency of laser, a is frequency modulation (PFM) amplitude, the intensity modulation degree of depth of η for causing due to frequency modulation (PFM), and t is time parameter.

Because now gas concentration is very low, so have-α (υ) CL < < 1

(4.1) formula can be rewritten as so:

I(υ)＝I ₀(υ)e ^-α(υ)CL≈I ₀(υ)[1-α(υ)CL] (4.3)

The absorption peak of general gas flow is Lorentz line shape,

$\mathrm{\&alpha;}\left(\mathrm{\&upsi;}\right)=\frac{{\mathrm{\&alpha;}}_0}{1+{\left(\frac{{\mathrm{\&upsi;}-\mathrm{\&upsi;}}_0}{\mathrm{\&Delta;\&upsi;}}\right)}^2}---\left(4.4\right)$

υ in formula ₀for the center of absorption peak, α ₀for υ ₀the absorption coefficient at place; Δ ν is the halfwidth of absorption peak.

By (4.2), (4.4) bring (4.3) into, and the output intensity (arriving the light intensity of detector) after absorbing is

$I\left(t\right)=I_0(1+\mathrm{\&eta;}\sin \mathrm{\&omega;t})[1-\frac{{\mathrm{\&alpha;}}_0\mathrm{CL}}{1+{\left(\frac{\stackrel{\&OverBar;}{\mathrm{\&upsi;}}-{\mathrm{\&upsi;}}_0+a\sin \mathrm{\&omega;t}}{\mathrm{\&Delta;\&upsi;}}\right)}^2}]---\left(4.5\right)$

The drive current of adjusting laser instrument makes the center of output light wavelength overlap with the center at gas absorption peak,

have

$I\left(t\right)=I_0(1+\mathrm{\&eta;}\sin \mathrm{\&omega;t})(1-\frac{{\mathrm{\&alpha;}}_0\mathrm{CL}}{1+m^2{\sin }^2\mathrm{\&omega;t}})$

(4.6)

$=I\left(t\right)=I_0+I_0\mathrm{\&eta;}\sin \mathrm{\&omega;t}-\frac{I_0{\mathrm{\&alpha;}}_0\mathrm{CL}}{1+m^2{\sin }^2\mathrm{\&omega;t}}-\frac{{\mathrm{\&alpha;}}_0\mathrm{\&eta;}\sin \mathrm{\&omega;tCL}}{1+m^2{\sin }^2\mathrm{\&omega;t}}$

In formula, $m=\frac{a}{\mathrm{\&Delta;\&nu;}}.$

Owing to being small signal modulation, η < < 1, therefore can ignore second order in a small amount

obtain:

$I\left(t\right)=I_0+I_0\mathrm{\&eta;}\sin \mathrm{\&omega;t}-\frac{I_0{\mathrm{\&alpha;}}_0\mathrm{CL}}{1+m^2{\sin }^2\mathrm{\&omega;t}}---\left(4.7\right)$

(4.7) are done to Fourier expansion according to ω, can obtain the wherein fundametal compoment I of ω _fwith second harmonic component I _2fintensity be respectively:

I _f＝I _Oη

$I_{2f}=-I_0\frac{2({2+m}^2-2\sqrt{1+m^2})}{m^2\sqrt{1+m^2}}{\mathrm{\&alpha;}}_0\mathrm{CL}---\left(4.8\right)$

$=-I_{0}k\left(m\right){\mathrm{\&alpha;}}_0\mathrm{CL}$

In formula, $k\left(m\right)=\frac{2(2+m^2-2\sqrt{1+m^2})}{m^2\sqrt{1+m^2}}.$

Visible, the intensity of fundametal compoment is proportional to the depth of modulation of light intensity and intensity modulated; And for second harmonic, k (m) only with

relevant, can regulate by changing warbled amplitude.For a definite system, m is definite value, and k (m) is just also a definite value; Meanwhile, α ₀l is also definite value.Therefore the intensity of second harmonic component is proportional to light intensity and gas concentration, utilizes the intensity I of second harmonic _2fcan obtain gas concentration C.

Utilize above-mentioned formula (4.8) although can calculate gas concentration C theoretically, but, if only detect vapour concentration by the intensity of second harmonic, to introduce unnecessary common-mode noise, this is that the decay causing due to reasons such as airborne dust scatterings during by reference to air chamber at laser causes.

In order to eliminate above-mentioned impact, can be by second harmonic component I _2fwith fundametal compoment I _fcompare, obtain

$\frac{I_{2f}}{I_f}=-\frac{2(2+m^2-2\sqrt{1+m^2})}{\mathrm{\&eta;}{m}^2\sqrt{1+m^2}}{\mathrm{\&alpha;}}_0\mathrm{CL}---\left(4.9\right)$

Therefore second harmonic and first-harmonic are actually the different frequency component of same light beam, owing to only there being light beam, are subject to dust scattering or other non-pneumatics to absorb the impact of the light intensity decreasing causing identical in communication process.The ratio I of the two _2f/ I _firrelevant with equivalent power.So just eliminate common-mode noise, made the concentration of gas detect more accurate.

Therefore, measure I _fobject actual be the impact of eliminating equivalent power, eliminate common-mode noise, and first harmonic amplitude A in abovementioned steps 203 be exactly reference absorption peak place first harmonic intensity I ' _f=I ₀η ', can first calculate I so _2fwith the ratio of A, wherein, I _2fbe the second harmonic intensity at target absorption peak institute corresponding current value place, A is the first harmonic width intensity at reference absorption peak institute corresponding current value place; Again according to described I _2fobtain the concentration of the middle object gas of gas to be measured with the ratio of A.

Concrete, I _2fwith the ratio of A be

$\frac{I_{2f}}{A}=\frac{I_{2f}}{{I^{\&prime;}}_f}=-\frac{2(2+m^2-2\sqrt{1+m^2})}{{\mathrm{\&eta;}}^{\&prime;}{m}^2\sqrt{1+m^2}}{\mathrm{\&alpha;}}_0\mathrm{CL}---(4.10)$

It is visible,

be directly proportional to concentration equally.Wherein, I ' _fthe first harmonic amplitude at the corresponding current value of reference absorption peak place, the intensity modulation degree of depth that η ' causes due to frequency modulation (PFM) for the corresponding current value of reference absorption peak place.

, due to I _2f=I _{2f surveys}-f (A), so have

By above-mentioned formula (4.10) and formula (4.11), can be calculated the concentration of gas to be measured.

In the possible embodiment of another kind, described signal conditioning circuit 600 can comprise:

Wave filter, carries out filtering processing by the electric signal from detector;

Phase-locked amplifying circuit, detects after described filtering the intensity I of the second harmonic of shoot laser in signal _{2f surveys}.

Now, described processor extracts intensity and the base wave intensity of described second harmonic from the signal the modulation receiving, and obtains the concentration of oxides of nitrogen in gas to be measured according to described second harmonic and base wave intensity.In this embodiment, the second harmonic of shoot laser and base wave intensity are detected by phase-locked amplifying circuit, and processor carries out concentration calculating.

In this case, processor comprises:

Memory storage, when the concentration that is kept at oxides of nitrogen gas in the gas that comprises oxides of nitrogen surpasses the first preset value, the nox adsorption peak measuring and reference absorption peak center be the difference DELTA D of corresponding laser diode current value respectively; Be kept at the corresponding current value D of reference absorption peak center institute measuring in the gas of nitrogenfree oxide gas ₂₀, and preserve current value D ₂₀the amplitude A of the first harmonic of the reference absorption peak at place ₀, and under equal conditions, current value is (D ₂₀-Δ D) the second harmonic value I locating _2f0;

Humorous intensity of wave acquisition device, first measures the corresponding current value D in reference absorption peak center in gas to be measured ₂, and measure current value D ₂the first harmonic amplitude A at place; The amplitude A of the first harmonic of the reference absorption peak measuring under the condition without gas to be measured from described memory storage acquisition ₀, and electric current is (D ₂₀-Δ D) the second harmonic value I locating _2f0, calculate background f (A)=I _2f0* A/A ₀, making laser diode current is D ₁nox adsorption peak second harmonic intensity I _2f=I _{2f surveys}-f (A);

Concentration calculation element, according to the intensity I of the second harmonic at nox adsorption peak institute corresponding current value place _2fobtain the concentration of the middle oxides of nitrogen of gas to be measured with the intensity A of the first-harmonic at reference absorption peak institute corresponding current value place.

It should be noted that, aforementioned gas to be measured can be vehicle exhaust, can be also other gas of nitrogen-containing oxide, such as waste gas discharging from chimney etc.; Aforementioned reference gas is aqueous vapor H ₂o can be also other gas with strong receptivity, as carbon dioxide CO ₂deng.

The pick-up unit that the application embodiment of the present invention provides, use spectrum test method, do not need pyrolytic conversion process, therefore power consumption and energy consumption have been reduced, and, owing to being the content of oxides of nitrogen in direct measurement gas, the impact that the existence of having avoided other materials detects gas content to be measured, makes check result more accurate.Have again, owing to not needing to use ZrO ₂, therefore, there is not P, S, the compound of Si, for example H in sensor yet ₂s, can cause ZrO ₂the problem of Sensor Poisoning.Meanwhile, due to ZrO ₂the technology of sensor technology Shi Bei offshore company monopolization, and the application does not need to use ZrO ₂sensor, has therefore broken prior art barrier.

Having, is all to use two-way balancing method ，Ji mono-reference path ，Yi road, tunnel to survey light path in existing spectrum test method again, by adjusting direct current flow point, makes first harmonic that two-way records equate to lock the position of absorption peak.This scheme is feasible in laboratory, but in commercial Application, has obvious problem.This is that its residing environment is different from branch road to be measured because reference arm is generally standard air chamber, and in real commercial Application owing to cannot eliminating airborne dust scattering, the factors such as the imbalance that is coupled cannot provide satisfactory reference arm at all.Therefore, two-way balancing method can only can not be for practical application for laboratory examination.And in the application's scheme, only need laser instrument to export a road detecting light beam, the intensity of the second harmonic by final shoot laser is carried out the concentration of the middle oxides of nitrogen of gas to be measured, do not need standard air chamber, do not need reference arm yet, thereby the spectrum test method of having avoided existing two-way balance can not be applied to the problem of industry spot, the industry spot application that can in officely what is the need for and want.

The ground gas concentration portion causing due to gas turbulence and circulation in gas absorption cell for fear of gas to be measured is balanced, need the long period just can complete the problem that in air chamber, gaseous sample upgrades, the embodiment of the present application also provides a kind of gas absorption cell of special structure, make concentration equiblibrium mass distribution in gas absorption cell of gas to be measured, not only can in a less area of space, extend effective light path, and can realize the quick turnover of gas to be measured in gas absorption cell.

Fig. 2 is according to the structural representation of a kind of gas absorption cell of the embodiment of the present invention, and wherein Fig. 2 A is front view, and Fig. 2 B is left view, and Fig. 2 C is vertical view.Fig. 3 is pond body inner structure and the light transmission path schematic diagram according to gas absorption cell embodiment illustrated in fig. 2.

Referring to Fig. 2 and Fig. 3, gas absorption cell shown in the present embodiment comprises: pond body 401, the first plane mirror 402, the peaceful surface cover 404 of the second plane mirror 403, described the first plane mirror 402 and the second plane mirror 403 are close to respectively described pond body 401 pond body the first side walls 406 and pond body the second sidewall 407, wherein, described pond body the first side wall 406 is vertical with pond body upper surface 405 with pond body the second sidewall 407, and described pond body the first side wall 406 and pond body the second sidewall 407 are parallel to each other; On described pond body upper surface 405, be provided with broken line type raceway groove 410, described plane cover plate 404 covers on the broken line type raceway groove of described pond body 401 and forms broken line type air chamber, described broken line type air chamber is between described the first plane mirror 402 and described the second plane mirror 403, on pond body the first side wall 406 and pond body the second sidewall 407, along the direction perpendicular to pond body the first side wall 406 and pond body the second sidewall 407, have a plurality of smooth reflection holes 412, light reflection hole 412 communicates with fold-line-shaped raceway groove 410;

On described pond body upper surface 405, offer air admission hole 415 and venthole 416, gas to be measured enters described broken line type air chamber from described air admission hole 415, along fold-line-shaped raceway groove 410, flows, and from venthole 416, flows out described broken line type air chamber;

Described gas absorption cell 400 also has pond body the 3rd sidewall 408 and pond body the 4th sidewall 409, wherein, described pond body the 3rd sidewall 408 and pond body the 4th sidewall 409 respectively with the angles of 407 one-tenth default number of degrees of pond body the second sidewall, for example, can be 3 °～10 °, can be preferably 4 °, 5 °, 6 ° or 7 °; On pond body the 3rd sidewall 408, along the direction perpendicular to pond body the 3rd sidewall, have incident light hole 411, described incident light hole 411 communicates with fold-line-shaped raceway groove 410; On pond body the 4th sidewall 409, along the direction perpendicular to pond body the 4th sidewall 409, have light perforation hole 413, described smooth perforation hole 413 communicates with fold-line-shaped raceway groove 410; Incident laser enters described broken line type air chamber from described incident light hole 411, along the reflection of broken line type air chamber, from light perforation hole 413, penetrates.

It should be noted that, the angle α of fold-line-shaped raceway groove can adjust according to the length of the angle of incident laser and needed light path, and the application does not strictly limit the size of angle α, and it can decide according to practical application.

It should be noted that, the angle of pond body the 3rd sidewall 408 and the default number of degrees of body the 4th sidewall 409 in pond respectively and between pond body the second sidewall 407 is also determined according to practical application, installation site for example, the laser incident angle of requirement etc., the application does not do strict restriction to this.

In a preferred embodiment, plane cover plate 404 is identical with size with pond body upper surface 405 shapes, and by impressed pressure and flexible member, as the cooperation lower seal of O type circle covers fold-line-shaped raceway groove 410, sealing forms the broken line type air chamber of gas absorption cell.407 one-tenth 5 ° of angles of pond body the 3rd sidewall 408 and pond body the 4th sidewall 409 and pond body the second sidewall, body the 3rd sidewall 408 in pond is plane and vertical with pond body upper surface 405 with pond body the 4th sidewall 409.The broken line direction of fold-line-shaped raceway groove 410 is vertical with pond body the 4th sidewall 409 with pond body the 3rd sidewall 408 respectively.On pond body the 3rd sidewall 408, along having incident light hole 411 in the direction perpendicular to the 3rd sidewall 408, incident light hole 411 communicates with fold-line-shaped raceway groove 410.On pond body the first side wall 406 and pond body the second sidewall 407, along having a plurality of smooth reflection holes 412 perpendicular to pond body the first side wall 406 and pond body the second sidewall 407 directions, the plurality of smooth reflection hole 412 communicates with fold-line-shaped raceway groove 410.On pond body the 4th sidewall 409, along the direction perpendicular to pond body the 4th sidewall 409, have a light perforation hole 413, light perforation hole 413 communicates with fold-line-shaped raceway groove 410.Incident light hole 411 and light perforation hole 413 are sealed by translucent element.

Gas absorption cell described in application drawing 2 and Fig. 3, is conducive to the detection real-time of continually varying gaseous sample, has effectively improved low concentration, has changed continuously the detection sensitivity of gaseous sample; And above-mentioned air chamber structure is simple, be easy to carry.

It should be noted that, for pick-up unit described in Fig. 1, can also comprise: cooling line, this cooling line is connected between the air admission hole (415) of broken line type air chamber of gas purging to be measured outlet and described gas absorption cell, with by cooled to be measured being sent in described gas absorption cell.By cooling line, can avoid high temperature gas to be measured to enter gas absorption cell, with the serviceable life of extension detection device.

It should be noted that, for pick-up unit described in Fig. 1, can also comprise: filtrator and gas-liquid separator, be connected between the end of cooling line and the air admission hole (415) of the broken line type air chamber of described gas absorption cell, to filter impurity and the liquid in gas to be measured.Impurity in gas to be measured and liquid are leached, can improve final accuracy of detection, the serviceable life of all right extension detection device.

It should be noted that, for pick-up unit described in Fig. 1, can also comprise: display device, is connected with processor, for showing the concentration of the oxides of nitrogen of gas to be measured.The physical location of this display device can from processor very close to for example just on processor side, be convenient to like this field observation, can also, apart from processor more for example at point of presence, be convenient to like this operations such as follow-up statistical study.

Referring to Fig. 4, it is according to one of the embodiment of the present invention concrete application example schematic diagram.In this example, tail gas to be measured is vehicle exhaust, and the vehicle exhaust of drawing from three-element catalytic tank 640 is introduced into cooling line 610, then enters sensor 630 by filtrator gas-liquid separator 620, thereby detects easily the content of oxides of nitrogen in vehicle exhaust.Sensor 630 has comprised processor, programmable current source, laser instrument, gas absorption cell, detector and signal conditioner.

Pick-up unit shown in application drawing 4, does not need pyrolytic conversion process, has therefore reduced power consumption and energy consumption, and, owing to being the content of oxides of nitrogen in direct measurement gas, the impact that the existence of having avoided other materials detects gas content to be measured, makes check result more accurate.Have again, owing to not needing to use ZrO ₂, therefore, there is not P, S, the compound of Si, for example H in sensor yet ₂s, can cause ZrO ₂the problem of Sensor Poisoning.Meanwhile, due to ZrO ₂the technology of sensor technology Shi Bei offshore company monopolization, and the present embodiment does not need to use ZrO ₂sensor, has therefore broken prior art barrier.

It should be noted that, in this article, term " comprises ", " comprising " or its any other variant are intended to contain comprising of nonexcludability, thereby the process, method, article or the equipment that make to comprise a series of key elements not only comprise those key elements, but also comprise other key elements of clearly not listing, or be also included as the intrinsic key element of this process, method, article or equipment.The in the situation that of more restrictions not, the key element being limited by statement " comprising ... ", and be not precluded within process, method, article or the equipment that comprises described key element and also have other identical element.

The foregoing is only preferred embodiment of the present invention, be not intended to limit protection scope of the present invention.All any modifications of doing within the spirit and principles in the present invention, be equal to replacement, improvement etc., be all included in protection scope of the present invention.

Claims (9)

1. the GN 2 oxide content pick-up unit, for the concentration of gas institute nitrogen-containing oxide is detected, it is characterized in that, described pick-up unit comprises: processor (100), programmable current source (200), laser instrument (300), gas absorption cell (400), detector (500) and signal conditioner (600), wherein, described gas absorption cell (400) has broken line type air chamber, on described broken line type air chamber, there is air admission hole (415) and venthole (416), gas to be measured enters described broken line type air chamber from described air admission hole (415), along fold-line-shaped air chamber, flow, from venthole (416), flow out described broken line type air chamber, on described broken line type air chamber, also there is incident light hole and light perforation hole, incident laser enters described broken line type air chamber from described incident light hole, along the reflection of broken line type air chamber, from light perforation hole, penetrates,

Described programmable current source (200) is directly adjusted laser instrument under the control of processor, makes laser instrument (300) export the laser that a road light intensity and wavelength are sinusoidal fluctuation; A described road laser enters the broken line type air chamber in gas absorption cell 400 by described incident light hole, from light perforation hole, penetrates, and enters detector;

Described detector (500), is converted to electric signal by a described road light signal, sends the electric signal after conversion to signal conditioning circuit;

Signal conditioning circuit (600), to sending processor to after described electric signal conditioning;

Processor (100) according to the instruction receiving, detects second harmonic and base wave intensity in shoot laser from the signal the conditioning receiving, and obtains the concentration of the middle oxides of nitrogen of gas to be measured according to described two kinds of humorous wave intensity.

2. pick-up unit according to claim 1, is characterized in that, described signal conditioning circuit comprises:

Wave filter, carries out filtering processing by the electric signal from detector;

AD converter, sends processor to after described filtered analog electrical signal is converted to digital signal.

3. pick-up unit according to claim 2, is characterized in that, described processor comprises:

Memory storage, when the concentration that is kept at oxides of nitrogen gas in the gas that comprises oxides of nitrogen surpasses the first preset value, the nox adsorption peak measuring and reference absorption peak center be the difference DELTA D of corresponding laser diode current value respectively; Be kept at the corresponding current value D of reference absorption peak center institute measuring in the gas of nitrogenfree oxide gas ₂₀, and preserve current value D ₂₀the amplitude A of the first harmonic of the reference absorption peak at place ₀, and under equal conditions, current value is (D ₂₀-Δ D) the second harmonic value I locating _2f0;

Humorous intensity of wave acquisition device, first measures the corresponding current value D in reference absorption peak center in gas to be measured ₂, and measure current value D ₂the first harmonic amplitude A at place; Measuring laser diode current value is D again ₁=D ₂the second harmonic value I of-Δ D position _{2f surveys}; The amplitude A of the first harmonic of the reference absorption peak measuring under the condition without gas to be measured from described memory storage acquisition ₀, and electric current is (D ₂₀-Δ D) the second harmonic value I locating _2f0, calculate background f (A)=I _2f0* A/A ₀, making laser diode current is D ₁nox adsorption peak second harmonic intensity I _2f=I _{2f surveys}-f (A);

Concentration calculation element, according to the intensity I of the second harmonic at institute's corresponding current value place, described nox adsorption peak _2fobtain the concentration of the middle oxides of nitrogen of gas to be measured with the intensity A of the first-harmonic at reference absorption peak institute corresponding current value place.

4. pick-up unit according to claim 1, is characterized in that, described signal conditioning circuit comprises:

Wave filter, carries out filtering processing by the electric signal from detector;

Phase-locked amplifying circuit, detects after described filtering the intensity I of the second harmonic of shoot laser in signal _{2f surveys}.

5. pick-up unit according to claim 4, is characterized in that, described processor comprises:

Memory storage, when the concentration that is kept at oxides of nitrogen gas in the gas that comprises oxides of nitrogen surpasses the first preset value, the nox adsorption peak measuring and reference absorption peak center be the difference DELTA D of corresponding laser diode current value respectively; Be kept at the corresponding current value D of reference absorption peak center institute measuring in the gas of nitrogenfree oxide gas ₂₀, and preserve current value D ₂₀the amplitude A of the first harmonic of the reference absorption peak at place ₀, and under equal conditions, current value is (D ₂₀-Δ D) the second harmonic value I locating _2f0;

Humorous intensity of wave acquisition device, first measures the corresponding current value D in reference absorption peak center in gas to be measured ₂, and measure current value D ₂the first harmonic amplitude A at place; The amplitude A of the first harmonic of the reference absorption peak measuring under the condition without gas to be measured from described memory storage acquisition ₀, and electric current is (D ₂₀-Δ D) the second harmonic value I locating _2f0, calculate background f (A)=I _2f0* A/A ₀, making laser diode current is D ₁nox adsorption peak second harmonic intensity I _2f=I _{2f surveys}-f (A);

Concentration calculation element, according to the intensity I of the second harmonic at institute's corresponding current value place, described nox adsorption peak _2fobtain the concentration of the middle oxides of nitrogen of gas to be measured with the intensity A of the first-harmonic at reference absorption peak institute corresponding current value place.

6. according to the pick-up unit described in claim 3 or 5, it is characterized in that,

Described gas to be measured is vehicle exhaust;

Described reference gas is aqueous vapor.

7. pick-up unit according to claim 1, it is characterized in that, described gas absorption cell (400) comprising: pond body (401), the first plane mirror (402), the peaceful surface cover of the second plane mirror (403) (404), described the first plane mirror (402) and the second plane mirror (403) are close to respectively described pond body (401) pond body the first side wall (406) and pond body the second sidewall (407), wherein, described pond body the first side wall (406) is vertical with pond body upper surface (405) with pond body the second sidewall (407), and described pond body the first side wall (406) and pond body the second sidewall (407) are parallel to each other, on described pond body upper surface (405), be provided with broken line type raceway groove (410), described plane cover plate (404) covers on the broken line type raceway groove of described pond body (401) and forms broken line type air chamber, described broken line type air chamber is positioned between described the first plane mirror (402) and described the second plane mirror (403), at pond body the first side wall (406) and pond body the second sidewall (407), above along the direction perpendicular to pond body the first side wall (406) and pond body the second sidewall (407), have a plurality of smooth reflection holes (412), light reflection hole (412) communicates with fold-line-shaped raceway groove (410),

On described pond body upper surface (405), offer air admission hole (415) and venthole (416), gas to be measured enters described broken line type air chamber from described air admission hole (415), along fold-line-shaped raceway groove (410), flow, from venthole (416), flow out described broken line type air chamber;

Described gas absorption cell (400) also has pond body the 3rd sidewall (408) and pond body the 4th sidewall (409), wherein, body the 3rd sidewall (408) in described pond becomes to preset respectively the angle that adds of the number of degrees with pond body the 4th sidewall (409) with pond body the second sidewall (407); Direction on the upper edge of pond body the 3rd sidewall (408) perpendicular to pond body the 3rd sidewall has incident light hole (411), and described incident light hole (411) communicates with fold-line-shaped raceway groove (410); Direction on the upper edge of pond body the 4th sidewall (409) perpendicular to pond body the 4th sidewall (409) has light perforation hole (413), and described smooth perforation hole (413) communicates with fold-line-shaped raceway groove (410); Incident laser enters described broken line type air chamber from described incident light hole (411), along the reflection of broken line type air chamber, from light perforation hole (413), penetrates.

8. pick-up unit according to claim 1, it is characterized in that, described pick-up unit also comprises: cooling line, be connected between the air admission hole (415) of broken line type air chamber of gas purging to be measured outlet and described gas absorption cell, with by cooled to be measured being sent in described gas absorption cell.

9. pick-up unit according to claim 8, it is characterized in that, described pick-up unit also comprises: filtrator and gas-liquid separator, be connected between the end of cooling line and the air admission hole (415) of the broken line type air chamber of described gas absorption cell, to filter impurity and the liquid in gas to be measured.

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