CN103940776A - Humidity detection device and humidity detection method using humidity detection device - Google Patents

Abstract

The invention discloses a humidity detection device and a humidity detection method using the humidity detection device. The humidity detection device is used for the detection of the water vapor concentration in a gas, and the detection device comprises: a processor (100), a program-controlled current source (200), a laser (300), a gas chamber (400), a detector (500), a DC conditioning circuit (600), an AC regulator (700) and a bus interface 1200. The humidity detection device of the embodiment uses an absorption spectrum to measure the water vapor concentration without a humidity return process, fundamentally solves the problems of slow humidity return, moreover, is high in degree of accuracy, furthermore, is fast in response time and wide in measuring range. In addition, by the application of the humidity detection device, not only the absolute humidity of the gas to be detected can be detected, the relative humidity of the gas to be detected also can be detected.

Description

A kind of humidity detector and apply the humidity detection method of described device

Technical field

The present invention relates to gas content detection technique field, particularly a kind of humidity detector and apply the humidity detection method of described device.

Background technology

Humidity, the physical quantity of expression air drying degree.The steam containing in the air of certain volume is at a certain temperature fewer, and air is drier; Steam is more, and air is moister.The dry wet degree of air is called " humidity ".In departments such as industrial and agricultural production, meteorology, national defence, environmental protection, scientific research, space flight, often need to the humidity of environment be measured and be controlled.Along with modern realization, be difficult to find out one and come with the irrelevant field of humidity.But as like this important environmental parameter, humidity is the most difficult Measurement accuracies than other environmental parameters.

At present, traditional measuring method has several lower several:

Method one: measurement with wet measuring moisture

Wet and dry bulb is again psychrometer.It is the humidity sensor that a kind of history is very long.Utilize water evaporation to want absorbing and cooling temperature, and the speed of evaporation (i.e. cooling number) is to make with relevant this principle of relative humidity of air at that time.

Because wet bulb below 0 DEG C can freeze, thereby greatly reduce the resolution characteristic of wet-bulb temperature for surveyed relative humidity, cause error very large.So wet and dry bulb mensuration can only use more than 0 DEG C.If impurity is more in air in addition, also will pollutes wet bulb, thereby affect the accuracy of moisture measurement.

Method two: humicap formula Integrated Humidity Sensor

Humicap is generally made with macromolecule membrane electric capacity, and conventional macromolecular material has polystyrene, polyimide, cruel sour acetate fiber etc.In the time that ambient humidity changes, the specific inductive capacity of humicap changes, and its electric capacity is also changed, and its capacitance change is directly proportional to relative humidity.

This measuring method is poor-performing under high humidity environment, and especially, when for a long time in super-humid conditions, humicap tends to damage or needs could recover normal for a long time.Situation about often occurring is, in the time that weather continues two to three days high humidity under field conditions (factors), while being reduced to below 50%RH Deng weather humidity, the indicating value of humicap still there will be maintain 90% or its above relative humidity exceed the situation of 24 hours (h), measuring error now can reach 30%～40%RH.And this kind of humicap be under DEG C condition of low temperature-30, moisture measurement error is also more than 10%RH.

Chilled-mirror type dew point instrument

Chilled-mirror type dew point instrument is 0 DEG C of following and 0 DEG C of spendable moisture instruments all above, its dew point (can cause the maximum temperature of dewfall under current vapour concentration, vapour concentration value is corresponding one by one with dew point) measurement range of temperature can reach-70 DEG C～60 DEG C, and principle of work schematic diagram is as shown in Figure 1.

Tested gas is sucked by air pump by conduit, enter sensor and skim over minute surface 101 with certain flow velocity, if minute surface 101 temperature are higher than the dewpoint temperature of this gas, steam can not condense at minute surface, and dry minute surface 101 is by the equal angular optical receiver 103 that reflexes to of incident light of following reflection law laser generator 102 being produced.Pass through temperature-control circuit, semiconductor cooler 104 is lowered the temperature to minute surface, in the time that mirror temperature reaches the dewpoint temperature of sample gas, minute surface dewfall (frost), incident light is diffuse reflection state on minute surface 101, and optical receiver 103 receives signal and reduces, and makes original minute surface is freezed and becomes heating by the monitoring of photo eye, through repeatedly automatically adjusting, finally make mirror temperature self-poise suck in the dewpoint temperature of gas.This temperature is detected by temperature element, and this temperature value also just in time meets the definition of dewpoint temperature.

Owing to must emit more heats in refrigeration, this heat must be derived from temperature sensor 105, in order to avoid cause that mirror temperature is unstable or burn near components and parts, especially, in the time that dewpoint temperature is lower, conventionally with water-cooling pattern, semiconductor cooler 104 is lowered the temperature.

Chilled-mirror type dew point instrument is that system accurately can be traced to the source and measure to one.But the problem of dew point hygrometer maximum be exactly stabilization time longer, common dew point testing needs several minutes even longer time.And the method cannot carry out dynamic test, can only carry out static single-spot testing.The all dew point value that show before stable are all process variables, and only having the dew point value after last stablizing is accurately.

Summary of the invention

The embodiment of the present invention provides a kind of humidity detector and applies the humidity detection method of described device, and the temperature range that not only can survey is large, and has avoided moving back wet slow-footed problem, and the fast response time of measuring, and accuracy of measurement is high.

The embodiment of the present invention provides a kind of humidity detector, for the vapour concentration of gas is detected, described pick-up unit comprises: processor 100, programmable current source 200, laser instrument 300, air chamber 400, detector 500, direct current modulate circuit 600, interchange conditioner 700 and bus interface 1200;

Described programmable current source 200 is directly adjusted laser instrument under the control of processor 100;

Described laser instrument 300 is exported a road light intensity and wavelength and is the laser of sinusoidal fluctuation under the control of described programmable current source 200;

Described air chamber 400, receives from the laser of described laser instrument 300 as incident light, penetrates emergent light after reflection-absorption;

Described detector 500, receives described emergent light, and described emergent light is converted to electric signal, and the electric signal after conversion is sent respectively to direct current modulate circuit 600 and exchanges modulate circuit 700;

Direct current modulate circuit 600, to obtaining the first conditioned signal after described electric signal rectification and analog to digital conversion, sends described the first conditioned signal to processor;

Exchange modulate circuit 700, to obtaining the second conditioned signal after described electric signal rectification and analog to digital conversion, send described the second conditioned signal to processor;

Processor 100, exports for controlling the steering order of programmable current source according to the electric current regulating command from bus interface 1200 receiving, and the absolute concentration value of the steam calculating is transferred to external unit by described bus interface 1200; Receive from the first conditioned signal of described direct current modulate circuit 600 and from the second conditioned signal that exchanges modulate circuit 700, calculate first value of considering according to described the first conditioned signal, calculate second value of considering according to described the second conditioned signal, in the time that described first value of considering is greater than first threshold, adopt described first value of considering to utilize direct measurement pattern to calculate the absolute concentration value of steam, in the time that described second value of considering is less than Second Threshold, adopt described second value of considering to utilize the absolute concentration value of harmonic measure mode computation steam.

Wherein, described first value of considering is-ln (T), the transmissivity that T is laser; Described second value of considering is i _ffor the fundametal compoment of emergent light, I _2fthe second harmonic component of emergent light; Described first threshold is greater than Second Threshold.

Wherein, described device also comprises:

Low-pass filter 800, is connected between processor 100 and programmable current source 200, and the signal of self processor 100 carries out sending to programmable current source 200 after low-pass filtering in the future.

Wherein, described device also comprises:

Baroceptor 900, is connected with processor 100, sends the current barometric information detecting to processor 100;

Temperature sensor 1000, is connected with AD conversion unit 1100, sends the current temperature data detecting to AD conversion unit 1100;

AD conversion unit 1100, is connected with processor 100, and current temperature data is carried out sending processor 100 to after analog to digital conversion;

Processor 100, according to the relative concentration value of the absolute concentration value calculating steam of the temperature data after described barometric information, analog to digital conversion and steam.

Wherein, described baroceptor 900 is piezoresistive silicon sensors; Described temperature sensor 1000 is platinum resistance temperature sensor or thermocouple temperature sensor.

Wherein, described laser instrument 300 is distributed feedback structure laser instruments.

The embodiment of the present invention also provides a kind of humidity detection method of applying above-mentioned humidity detector, comprising:

A) calculate first value of considering, described first value of considering is-ln (T), the transmissivity that T is laser;

B) judge whether described first value of considering is greater than first threshold, if so, adopt direct measurement pattern to calculate the absolute concentration value of steam; Otherwise, execution step C);

C) calculate second value of considering, described second value of considering is i _ffor the fundametal compoment of emergent light, I _2fthe second harmonic component of emergent light;

D) judge that whether described second value of considering is less than Second Threshold, if so, adopts the absolute concentration value of harmonic measure mode computation steam; Otherwise, execution step A);

Wherein, described first threshold is greater than Second Threshold.

Wherein, the step of described calculating first value of considering comprises:

After laser is penetrated by air chamber, gather actual P-I curve, obtain the signal I that direct-detection arrives _signal,

The signal I arriving according to described direct-detection _signalsimulate the signal I of original P-I curve _fIT;

Calculate the signal I that direct-detection arrives _signalsignal I with the original P-I curve simulating _fITa series of differences, obtain this difference corresponding current value when maximum; Calculate the transmissivity T at this current value place, wherein, T=I _signal/ I _fIT;

According to described transmissivity T, obtain first value of considering-ln (T).

Wherein, the step of described calculating second value of considering comprises:

After laser is penetrated by air chamber, gather actual P-I curve, obtain the signal I that direct-detection arrives _signal, and, record different current offsets and put corresponding signal;

Calculate the first-harmonic value I of each current offset point institute respective signal _fand second harmonic value I _2f;

Obtain second harmonic value I _2fcorresponding current value when value is maximum;

Calculate the corresponding second harmonic value I of this current value place _2fwith first-harmonic value I _fratio, obtain second value of considering.

Wherein, described method also comprises:

Obtain current barometric information value and temperature data value by sensor;

According to the absolute concentration value of described steam, current barometric information value and current temperature data value, calculate the relative concentration value of steam.

Humidity detector and method that the application embodiment of the present invention provides, utilize absorption spectra to measure the concentration of steam, do not have the wet process of moving back, and fundamentally solved the wet slow problem of moving back; And, utilize absorption spectra can select accurately the wavelength needing, can not be subject to the interference of other gases, accuracy is high; Have, the instantaneous absorption reaction of light and gas is fast again, and this response time is lower than 10ms, thereby the fast response time of moisture measurement is also very fast, only needs a few tens of milliseconds.

Have again, the environment that is applicable to high humidity due to the direct method of measurement calculates vapour concentration, and Resonance measuring method is applicable to the environment measurement vapour concentration of low humidity, and this device adopts the mode that two algorithm switches to make the temperature range that can survey large, can cover the scope of low humidity (1ppm) to high humidity (room temperature 100% relative humidity).

In addition, application the present invention, not only can measure the absolute humidity in gas to be measured, can also measure the relative humidity in gas to be measured.

Brief description of the drawings

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 skill in the art, do not paying under the prerequisite of creative work, can also obtain according to these accompanying drawings other accompanying drawing.

Fig. 1 is the minute surface part principle schematic of the chilled-mirror type dew point instrument of prior art;

Fig. 2 is according to the structural drawing of a kind of humidity detector of the embodiment of the present invention;

Fig. 3 is according to the structural drawing of the another kind of humidity detector of the embodiment of the present invention;

Fig. 4 is according to the process flow diagram of the humidity detection method of the embodiment of the present invention;

Fig. 5 is according to the process flow diagram of calculating first value of considering of the embodiment of the present invention;

Fig. 6 is the schematic diagram of the original P-I curve of matching;

Fig. 7 is according to the process flow diagram of calculating second value of considering of the embodiment of the present invention;

Fig. 8 a is first harmonic schematic diagram;

Fig. 8 b is second harmonic value I _2fschematic 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, instead of whole embodiment.Based on the embodiment in the present invention, those of ordinary skill in the art, not making the every other embodiment obtaining under creative work prerequisite, belong to the scope of protection of the invention.

Referring to Fig. 2, it is according to the structural drawing of a kind of humidity detector of the embodiment of the present invention; This device is for detecting the vapour concentration of gas, and described pick-up unit comprises: processor 100, programmable current source 200, laser instrument 300, air chamber 400, detector 500, direct current modulate circuit 600, interchange conditioner 700, and bus interface 1200.Wherein, processor 100, programmable current source 200, laser instrument 300, air chamber 400, detector 500 are directly connected successively, direct current modulate circuit 600 with exchange conditioner 700 and be connected with processor 100 with detector 500 respectively, described processor 100 is also connected with bus interface 1200.Each device specifically describes as follows:

Described programmable current source 200 is directly adjusted laser instrument under the control of processor 100; Concrete, the voltage signal of self processor is converted to current signal in the future, thereby laser instrument is directly adjusted;

Described laser instrument 300 is exported a road light intensity and wavelength and is the laser of sinusoidal fluctuation under the control of described programmable current source 200; This laser instrument 300 can be distributed feedback structure (DFB) laser instrument or extends perpendicular cavity surface emitting laser (VECSEL);

Described air chamber 400, receives from the laser of described laser instrument 300 as incident light, penetrates emergent light after reflection-absorption;

Described detector 500, with direct current modulate circuit 600 DC coupling, and exchange modulate circuit 700 AC coupling, receive described emergent light, described emergent light is converted to electric signal, the electric signal after conversion is sent respectively to direct current modulate circuit 600 and exchanges modulate circuit 700; For example, this detector uses the FC type photodiode of Hai Te;

Direct current modulate circuit 600, to obtaining the first conditioned signal after described electric signal rectification and analog to digital conversion, sends described the first conditioned signal to processor;

Exchange modulate circuit 700, to obtaining the second conditioned signal after described electric signal rectification and analog to digital conversion, send described the second conditioned signal to processor;

Processor 100, exports for controlling the steering order of programmable current source according to the electric current regulating command from bus interface 1200 receiving, and the absolute concentration value of the steam calculating is transferred to external unit by described bus interface 1200; Receive from the first conditioned signal of described direct current modulate circuit 600 and from the second conditioned signal that exchanges modulate circuit 700, calculate first value of considering according to described the first conditioned signal, calculate second value of considering according to described the second conditioned signal, in the time that described first value of considering is greater than first threshold, adopt described first value of considering to utilize direct measurement pattern to calculate the absolute concentration value of steam, in the time that described second value of considering is less than Second Threshold, adopt described second value of considering to utilize the absolute concentration value of harmonic measure mode computation steam;

Wherein, described first value of considering is-ln (T), the transmissivity that T is laser; Described second value of considering is i _ffor the fundametal compoment of emergent light, I _2fthe second harmonic component of emergent light; Described first threshold is greater than Second Threshold.

What above-mentioned processor 100 was exported is the steering order after digital to analog converter (DAC) modulation for controlling the steering order of programmable current source.

The humidity detector that the application embodiment of the present invention provides, utilizes absorption spectra to measure the concentration of steam, does not have the wet process of moving back, and has fundamentally solved the wet slow problem of moving back; And, utilize absorption spectra can select accurately the wavelength needing, can not be subject to the interference of other gases, accuracy is high; Have, the instantaneous absorption reaction of light and gas is fast again, and this response time is lower than 10ms, thereby the fast response time of moisture measurement is also very fast, only needs a few tens of milliseconds.

Have again, the environment that is applicable to high humidity due to the direct method of measurement calculates vapour concentration, and Resonance measuring method is applicable to the environment measurement vapour concentration of low humidity, and this device adopts the mode that two algorithm switches to make the temperature range that can survey large, can cover the scope of low humidity (1ppm) to high humidity (room temperature 100% relative humidity).

Referring to Fig. 3, install for described in Fig. 1, can also comprise: low-pass filter 800, this low-pass filter 800 is connected between processor (100) and programmable current source (200), the signal of self processor (100) carries out sending to programmable current source (200) after low-pass filtering in the future, the clutter in being signaled with filtering processor.

Referring to Fig. 3, install for described in Fig. 2, can also comprise:

Baroceptor (900), is connected with processor (100), sends the current barometric information detecting to processor (100); This baroceptor (900) can be piezoresistive silicon sensor;

Temperature sensor (1000), is connected with AD conversion unit (1100), sends the current temperature data detecting to AD conversion unit (1100); This temperature sensor (1000) can be platinum resistance temperature sensor or thermocouple temperature sensor.

AD conversion unit (1100), is connected with processor (100), and current temperature data is carried out sending processor (100) to after analog to digital conversion;

Processor (100), according to the relative concentration value of the absolute concentration value calculating steam of the temperature data after described barometric information, analog to digital conversion and steam.

Like this, the humidity detector that the application embodiment of the present invention provides, not only can measure the absolute humidity in gas to be measured, can also measure the relative humidity in gas to be measured.

Illustrate the humidity detection method of the above-mentioned humidity detector of application below.

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

I(υ)＝I ₀(υ)exp[-α(υ)CL] （1-1）

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 for passed through air chamber 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.

Based on above-mentioned theory, utilize the aforementioned humidity detector embodiment of the present invention that a kind of humidity detection method is provided, referring to Fig. 4, specifically comprise:

Step 401, calculates first value of considering, and described first value of considering is-ln (T), the transmissivity that T is laser;

Wherein, calculate the flow process of first value of considering as shown in Figure 5, be specially:

Step 501, after laser is penetrated by air chamber, gathers real power-electric current (P-I) curve, obtains the signal I that direct-detection arrives _signal, this signal I _signalsend processor to as the first conditioned signal;

Step 502, the signal I that processor arrives according to described direct-detection _signalsimulate the signal I of original P-I curve _fIT;

Concrete, due in the time not absorbing, the P-I curve of laser instrument has good linearity in the range of linearity, therefore can select the several points away from from absorption peak center, determine original P-I curve by linear fit, as shown in Figure 6, the solid wire in figure is the signal I that direct-detection arrives _signal; The initial point away from absorption peak on solid wire is the point for the original P-I curve of matching of selecting, and dotted line is the signal I of the original P-I curve that simulates _fIT; Dot-and-dash line is noise level I _noise; Article two, between dotted line, be actual scanning scope.

Step 503, calculates the signal I that direct-detection arrives _signalsignal I with the original P-I curve simulating _fITa series of differences, obtain this difference corresponding current value when maximum; Calculate the transmissivity T at this current value place, wherein, T=I _signal/ I _fIT;

Step 504, according to described transmissivity T, obtains first value of considering-ln (T).

So far, calculated first value of considering.

Step 402, judges whether described first value of considering is greater than first threshold, if so, performs step 403, otherwise execution step 404;

Step 403, adopts direct measurement pattern to calculate the absolute concentration value of steam;

Wherein, the mode that adopts direct measurement pattern to calculate the absolute concentration value of steam is to utilize formula (1-2) to calculate:

$C=-\frac{1}{\mathrm{\α}\left({\mathrm{\υ}}_0\right)L}\ln \frac{I\left({\mathrm{\υ}}_0\right)}{I_0\left({\mathrm{\υ}}_0\right)}=-\frac{1}{\mathrm{\α}\left({\mathrm{\υ}}_0\right)L}\ln T---(1-2)$

Wherein, I (υ ₀) be emergent light light intensity, υ ₀it is this light frequency; I ₀(υ ₀) be by the initial light intensity before air chamber; C is the concentration of gas; L for passed through air chamber long; α is the absorption coefficient of gas, the transmissivity that T is laser.

Here, first threshold obtains according to practical experience.

Step 404, calculates second value of considering, and described second value of considering is i _ffor the fundametal compoment of emergent light, I _2fthe second harmonic component of emergent light;

Wherein, calculate the flow process of second value of considering as shown in Figure 7, be specially:

Step 701, after laser is penetrated by air chamber, gathers actual P-I curve, obtains the signal I that direct-detection arrives _signal, and, record different current offsets and put corresponding signal;

Step 702, calculates the first-harmonic value I of each current offset point institute respective signal _fand second harmonic value I _2f;

Wherein, concrete computation process is same as the prior art, no longer describes in detail here.Referring to Fig. 8 a, it is first harmonic value I _fschematic diagram; Fig. 8 b is second harmonic value I _2fschematic diagram; Horizontal stroke in Fig. 8 a and Fig. 8 b is as being current value, and ordinate is harmonic value.Every line in Fig. 8 a, 8b is all the harmonic curve that sweep current bias point obtains, different concentration corresponding to curve.In Fig. 8 b, the line the darkest by color is the process that concentration increases successively to the highest line in position.

Step 703, obtains second harmonic value I _2fcorresponding current value when value is maximum;

Step 704, calculates the corresponding second harmonic value I of this current value place _2fwith first-harmonic value I _fratio obtain second value of considering.

So far, calculated second value of considering.

Step 405, judges whether described second value of considering is less than Second Threshold, if so, performs step 406, otherwise execution step 401; Wherein, described first threshold is greater than Second Threshold.

Here, Second Threshold obtains according to practical experience.

Step 406, the absolute concentration value of employing harmonic measure mode computation steam;

In the description of the mode of the absolute concentration value of employing harmonic measure mode computation steam below, illustrate.

It should be noted that, for method shown in Fig. 4, can also comprise: obtain current atmospheric pressure value and temperature value by sensor; According to the absolute concentration value of described steam, current atmospheric pressure value and current temperature value, calculate the relative concentration value of steam.

Apply method provided by the invention, utilize absorption spectra to measure the concentration of steam, do not have the wet process of moving back, fundamentally solved the wet slow problem of moving back; And, utilize absorption spectra can select accurately the wavelength needing, can not be subject to the interference of other gases, accuracy is high; Have, the instantaneous absorption reaction of light and gas is fast again, and this response time is lower than 10ms, thereby the fast response time of moisture measurement is also very fast, only needs a few tens of milliseconds.

Have again, the environment that is applicable to high humidity due to the direct method of measurement calculates vapour concentration, and Resonance measuring method is applicable to the environment measurement vapour concentration of low humidity, and this device adopts the mode that two algorithm switches to make the temperature range that can survey large, can cover the scope of low humidity (1ppm) to high humidity (room temperature 100% relative humidity).

In addition, application the present invention, not only can measure the absolute humidity in gas to be measured, can also measure the relative humidity in gas to be measured.

Adopt the absolute concentration value of harmonic measure mode computation steam itself same as the prior art, it is done to simple declaration here.

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

$\mathrm{\υ}=\stackrel{\‾}{\mathrm{\υ}}+a\sin \mathrm{\ωt}$ （1-3）

$I_0\left(t\right)=I_0(1+\mathrm{\η}\sin \mathrm{\ωt})$

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

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

(1-1) formula can be rewritten as so:

I(υ)＝I ₀(υ)e ^-α(υ)CL≈I ₀(υ)[1-α(υ)CL] （1-4）

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

$\mathrm{\&alpha;}\left(\mathrm{\&upsi;}\right)=\frac{{\mathrm{\&alpha;}}_0}{1+{\left(\frac{\mathrm{\&upsi;}-{\mathrm{\&upsi;}}_0}{\mathrm{\&Delta;\&upsi;}}\right)}^2}---(1-5)$

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

By (1-3), (1-5) bring (1-4) into, the output intensity (arriving the light intensity of detector) after absorbing is

$I\left(t\right)=I_0(1+\mathrm{\&eta;}\sin \mathrm{\&omega;t})[1-\frac{{\mathrm{\&alpha;}}_0\mathrm{CL}}{1+{\left(\frac{\stackrel{\&OverBar;}{\mathrm{\&upsi;}}-{\mathrm{\&upsi;}}_0+a\sin \mathrm{\&omega;t}}{\mathrm{\&Delta;\&upsi;}}\right)}^2}]---(1-6)$

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

$I\left(t\right)=I_0(1+\mathrm{\&eta;}\sin \mathrm{\&omega;t})(1-\frac{{\mathrm{\&alpha;}}_0\mathrm{CL}}{1+m^2{\sin }^2\mathrm{\&omega;t}})$ （1-7）

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

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

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

$I\left(t\right)=I_0+I_0\mathrm{\&eta;}\sin \mathrm{\&omega;t}-\frac{I_0{\mathrm{\&alpha;}}_0\mathrm{CL}}{1+m^2{\sin }^2\mathrm{\&omega;t}}---(1-8)$

(1-8) 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 ₀η

$I_{2f}=-I_0\frac{2(2+m^2-2\sqrt{1+m^2})}{m^2\sqrt{1+m^2}}{\mathrm{\&alpha;}}_0\mathrm{CL}---(1-9)$

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

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 (1-9) although can calculate theoretically gas concentration C, 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

$\frac{I_{2f}}{I_f}=-\frac{2(2+m^2-2\sqrt{1+m^2})}{{\mathrm{\&eta;m}}^2\sqrt{1+m^2}}{\mathrm{\&alpha;}}_0\mathrm{CL}---(1-10)$

Second harmonic and first-harmonic are actually the different frequency component of same light beam, owing to only there is light beam, therefore in communication process, are subject to dust scattering or other non-pneumatics to absorb the impact of the light intensity decreasing causing identical.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.

It should be noted that, in this article, relational terms such as the first and second grades is only used for an entity or operation to separate with another entity or operational zone, and not necessarily requires or imply and between these entities or operation, have the relation of any this reality or sequentially.And, 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.

One of ordinary skill in the art will appreciate that all or part of step realizing in said method embodiment is can carry out the hardware that instruction is relevant by program to complete, described program can be stored in computer read/write memory medium, here the alleged storage medium obtaining, as: ROM/RAM, magnetic disc, CD etc.

The foregoing is only preferred embodiment of the present invention, be not intended to limit protection scope of the present invention.All any amendments 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 (10)

1. a humidity detector, for the vapour concentration of gas is detected, it is characterized in that, described pick-up unit comprises: processor (100), programmable current source (200), laser instrument (300), air chamber (400), detector (500), direct current modulate circuit (600), interchange conditioner (700) and bus interface (1200);

Described programmable current source (200) is directly adjusted laser instrument under the control of processor (100);

Described laser instrument (300) is exported a road light intensity and wavelength and is the laser of sinusoidal fluctuation under the control of described programmable current source (200);

Described air chamber (400), receives from the laser of described laser instrument (300) as incident light, penetrates emergent light after reflection-absorption;

Described detector (500), receives described emergent light, and described emergent light is converted to electric signal, and the electric signal after conversion is sent respectively to direct current modulate circuit (600) and exchanges modulate circuit (700);

Direct current modulate circuit (600), to obtaining the first conditioned signal after described electric signal rectification and analog to digital conversion, sends described the first conditioned signal to processor;

Exchange modulate circuit (700), to obtaining the second conditioned signal after described electric signal rectification and analog to digital conversion, send described the second conditioned signal to processor;

Processor (100), for controlling the steering order of programmable current source, is transferred to external unit by the absolute concentration value of the steam calculating by described bus interface (1200) according to the output of the electric current regulating command from bus interface (1200) receiving; Receive from the first conditioned signal of described direct current modulate circuit (600) and from the second conditioned signal that exchanges modulate circuit (700), calculate first value of considering according to described the first conditioned signal, calculate second value of considering according to described the second conditioned signal, in the time that described first value of considering is greater than first threshold, adopt described first value of considering to utilize direct measurement pattern to calculate the absolute concentration value of steam, in the time that described second value of considering is less than Second Threshold, adopt described second value of considering to utilize the absolute concentration value of harmonic measure mode computation steam.

2. humidity detector according to claim 1, is characterized in that, described first value of considering is-ln (T), the transmissivity that T is laser; Described second value of considering is i _ffor the fundametal compoment of emergent light, I _2fthe second harmonic component of emergent light; Described first threshold is greater than Second Threshold.

3. humidity detector according to claim 1, is characterized in that, described device also comprises:

Low-pass filter (800), is connected between processor (100) and programmable current source (200), and the signal of self processor (100) carries out sending to programmable current source (200) after low-pass filtering in the future.

4. according to the arbitrary described humidity detector of claim 1-3, it is characterized in that, described device also comprises:

Baroceptor (900), is connected with processor (100), sends the current barometric information detecting to processor (100);

Temperature sensor (1000), is connected with AD conversion unit (1100), sends the current temperature data detecting to AD conversion unit (1100);

AD conversion unit (1100), is connected with processor (100), and current temperature data is carried out sending processor (100) to after analog to digital conversion;

Processor (100), according to the relative concentration value of the absolute concentration value calculating steam of the temperature data after described barometric information, analog to digital conversion and steam.

5. humidity detector according to claim 4, is characterized in that,

Described baroceptor (900) is piezoresistive silicon sensor;

Described temperature sensor (1000) is platinum resistance temperature sensor or thermocouple temperature sensor.

6. humidity detector according to claim 1, is characterized in that,

Described laser instrument (300) is distributed feedback structure laser instrument.

7. apply a humidity detection method for humidity detector as claimed in claim 1, it is characterized in that, comprising:

A) calculate first value of considering, described first value of considering is-ln (T), the transmissivity that T is laser;

B) judge whether described first value of considering is greater than first threshold, if so, adopt direct measurement pattern to calculate the absolute concentration value of steam; Otherwise, execution step C);

C) calculate second value of considering, described second value of considering is i _ffor the fundametal compoment of emergent light, I _2fthe second harmonic component of emergent light;

D) judge that whether described second value of considering is less than Second Threshold, if so, adopts the absolute concentration value of harmonic measure mode computation steam; Otherwise, execution step A);

Wherein, described first threshold is greater than Second Threshold.

8. method according to claim 7, is characterized in that, the step of described calculating first value of considering comprises:

After laser is penetrated by air chamber, gather actual P-I curve, obtain the signal I that direct-detection arrives _signal,

The signal I arriving according to described direct-detection _signalsimulate the signal I of original P-I curve _fIT;

Calculate the signal I that direct-detection arrives _signalsignal I with the original P-I curve simulating _fITa series of differences, obtain this difference corresponding current value when maximum; Calculate the transmissivity T at this current value place, wherein, T=I _signal/ I _fIT;

According to described transmissivity T, obtain first value of considering-ln (T).

9. method according to claim 7, is characterized in that, the step of described calculating second value of considering comprises:

After laser is penetrated by air chamber, gather actual P-I curve, obtain the signal I that direct-detection arrives _signal, and, record different current offsets and put corresponding signal;

Calculate the first-harmonic value I of each current offset point institute respective signal _fand second harmonic value I _2f;

Obtain second harmonic value I _2fcorresponding current value when value is maximum;

Calculate the corresponding second harmonic value I of this current value place _2fwith first-harmonic value I _fratio, obtain second value of considering.

10. method according to claim 7, is characterized in that, described method also comprises:

Obtain current barometric information value and temperature data value by sensor;

According to the absolute concentration value of described steam, current barometric information value and current temperature data value, calculate the relative concentration value of steam.