CN100543457C - A kind of semi-conductor laser absorption spectrum gas analyzing method - Google Patents

Abstract

The invention discloses a kind of semi-conductor laser absorption spectrum gas analyzing method, said method comprising the steps of: a. determines the operating temperature range and the current margin of semiconductor laser; B. in the operating temperature range of described semiconductor laser, mark off interval and at least one the no absorption line temperature range of at least two working temperatures, make at least one absorption line of the interval corresponding tested gas of arbitrary working temperature; C. record the operating ambient temperature T of described semiconductor laser, determine the absorption line of the tested gas that plan is used according to described operating ambient temperature T; D. according to the work temperature of semiconductor laser _WorkThe working current of semiconductor laser is determined and adjusted to the centre frequency of the absorption line of determining with step c; E. the light that sends of semiconductor laser passes tested gas and is received; The light signal that receives is carried out absorption spectroanalysis, obtain the measured parameter and the demonstration of tested gas.

Description

A kind of semi-conductor laser absorption spectrum gas analyzing method

Technical field

The present invention relates to a kind of gas parameter analytical approach, more particularly, relate to a kind of method of utilizing semiconductor laser gas absorption spectroanalysis gas parameter.

Background technology

The semi-conductor laser absorption spectrum gas analyzing technology is a kind of gas analysis technology of widespread use.This technology is used single mode semiconductor laser usually, when the light beam that the frequency that single mode semiconductor laser is launched is identical with a certain absorption line centre frequency of tested gas passed tested gas, this absorption line of tested gas caused the decay of measured light intensity to the absorption of measuring beam energy.Semiconductor laser passes the light intensity attenuation of tested gas and can accurately explain with the Beer-Lambert relation:

I _v＝I _v，0T(v)＝I _v，0exp[-S(T)g(v-v ₀)PXL]

I _V.0And I _vWhen representing respectively that frequency is the laser incident of v and through the light intensity behind the gas of pressure P, concentration X and light path L, line strength of S (T) expression gas absorption spectrum line, line shape function g (v-v ₀) characterize the shape of this absorption line.By the Beer-Lambert relation as can be known, the decay of light intensity is relevant with tested gas content, temperature, pressure etc., therefore, just can analyze the correlation parameter that obtains tested gas by the measured light intensity dampening information.

For example, when line strength S (T) of pressure P, temperature T, light path L and a certain gas absorption spectrum line of known tested gas, can utilize above-mentioned Beer-Lambert to concern to come the concentration of measurement gas then by measuring the absorption spectrum of this gas absorption spectrum line.Again for example, utilize above-mentioned Beer-Lambert relation to measure the absorption spectrum of two tested gas absorption spectrum lines of same gas componant, obtain the right strong ratio of line of this spectral line thereby measure.This spectral line to the strong ratio of the line when temperature is T is:

$R=\frac{S_1\left(T_0\right)}{S_2\left(T_0\right)}\exp [-\left(\frac{\mathrm{hc}}{k}\right)(E_1^{\′\′}-E_2^{\′\′})(\frac{1}{T}-\frac{1}{T_0})]$

Wherein, S (T ₀) be reference temperature T ₀The line of tested absorption line is strong down, and h is a Planck's constant, and c is the light velocity, and k is a Boltzmann constant,

Be the low-lying level energy of absorption line transition correspondence, subscript 1,2 is two spectral lines of corresponding spectral line centering respectively.By following formula as seen, the strong ratio R of line is the function of temperature T.Therefore, just can the measurement gas temperature T by measuring ratio R.The right following energy level difference of this ratio and spectral line is relevant, and therefore, the right selection meeting of spectral line directly influences the measuring accuracy of gas temperature, selects rational spectral line most important for gas thermometry.

In order to measure the absorption spectrum signal that obtains gas absorption spectrum line, the frequency of semiconductor laser need be transferred to the centre frequency place (fixed frequency analytical technology) or the scanned tested gas absorption spectrum line (frequency sweeping analytical technology) of tested gas absorption spectrum line.As shown in Figure 1, dullness reduces the output frequency of single mode semiconductor laser such as DFB, DBR, VCSEL etc. with the temperature increase, reduces with electric current increase also dullness.Therefore, the method that changes semiconductor laser output light frequency has two kinds, and the one, the working temperature by changing semiconductor laser (be often referred to the temperature of laser socket, rather than junction temperature), another kind is by changing the working current of semiconductor laser.Usually, the time response of first method is slow, but frequency adjustment range is big, and the time response of second method is fast, but frequency adjustment range is smaller.Usually, the semi-conductor laser absorption spectrum gas analyzing technology is positioned at the centre frequency place of tested gas absorption spectrum line by the light frequency that suitable semiconductor laser working temperature and working current are set make semiconductor laser.If adopt the frequency sweeping measuring technique, then sawtooth wave or the triangular current that injects certain frequency to semiconductor laser simultaneously makes the scanned whole piece absorption line of light frequency obtain complete high resolving power absorption spectrum signal.

Work under stable working temperature for the assurance semiconductor laser, above-mentioned absorption spectrum gas analysis technology is generally used semiconductor thermoelectric refrigeration device (TEC), by controlling the working temperature that its working current comes the stabilization of semiconductor laser instrument.It can heat semiconductor laser or cooling with 0.001 degree centigrade precision, and its dynamic range can reach 60 ℃.

The semiconductor thermoelectric refrigeration device is to utilize amber ear card (Peltier) viewed in 1834, and electric current can be realized the so-called peltier effect of object refrigeration contacted with it or heating during by knot that bimetallic strip was constituted with different directions.Present semiconductor thermoelectric refrigeration device is to utilize the semiconductor of two heavily doped dissimilar impurity to make it the thermopair that is constituted in parallel on series connection, calorifics on the electricity.In the time of need lowering the temperature to laser instrument, its cold junction is put in the surrounding environment from semiconductor laser seat absorption heat and with hot type; In the time of need heating laser instrument, TEC absorbs heat and transfers heat to the semiconductor laser seat from surrounding environment.

From the speed of heat load pumping heat depend on the quantity of the contained thermopair of TEC module, by electric current size, module medial temperature with and the temperature difference at two ends.Can be expressed as from the general power that the hot junction shed:

$Q_H=Q_C+I_{\mathrm{TEC}}V=Q_C(1+\frac{1}{E})$

In the following formula, Q _CBe thermal power from the pumping of semiconductor thermoelectric refrigeration device cold junction; I _TECBe respectively electric current and the pressure drop that is added on the semiconductor thermoelectric refrigeration device with V; E is the coefficient of performance of semiconductor thermoelectric refrigeration device.

As shown in Figure 2, a kind of pumping thermal power Q of typical semiconductor thermoelectric refrigerating unit _CWith coefficient of performance E, drive current I _TECRelation.As seen from the figure, if need to produce 40 ℃ the temperature difference in the cold-peace hot junction, need could be from the thermal power of pumping 5W in the heat load at the electric current that adds 3A on the semiconductor thermoelectric refrigeration device.The pairing coefficient of performance has only 35% in the working point, and by following formula as can be known, the total heat dissipated power is 19W, as seen, realizes that the refrigeration work consumption of 5w needs additive decrementation circuit energy 14W.

Although adopt the semiconductor thermoelectric refrigeration device can more accurately control the working temperature of semiconductor laser, this scheme has following shortcoming: 1) need to use TEC and custom-designed control and driving circuit, cost is higher; 2) working current of TEC and power consumption are bigger, and the efficient of refrigeration is low, are using when power autonomous the working time shorter, and the big heat that sends has simultaneously increased the complicacy and the difficulty of thermal design, thus difficult miniaturization and the portability that realizes gas analysis system; 3) a lot of application scenarios need analytic system to have explosion prevention function, and big working current causes and can't or difficultly realize the intrinsic safe explosion-proof design, and in addition, TEC and control and driving circuit cause bigger volume, and this also can increase the complicacy of flame proof design.Above-mentioned drawbacks limit use the application of the semi-conductor laser absorption spectrum gas analyzing system of TEC.

Summary of the invention

In order to solve above-mentioned deficiency of the prior art, the invention provides a kind of low cost, low-power consumption, the small size of TEC and semi-conductor laser absorption spectrum gas analyzing method that is easy to realize explosion prevention functions such as intrinsic safety and flame proof of not needing.

The objective of the invention is to be achieved by following technical proposals:

A kind of semi-conductor laser absorption spectrum gas analyzing method said method comprising the steps of:

A. determine the operating temperature range and the current margin of semiconductor laser;

B. according to the absorption line characteristic of tested gas, and the current margin of described semiconductor laser and operating temperature range, in the operating temperature range of described semiconductor laser, mark off interval and at least one the no absorption line temperature range of at least two working temperatures, make at least one absorption line of the interval corresponding tested gas of arbitrary working temperature;

C. record the operating ambient temperature T of described semiconductor laser, in the time of in described operating ambient temperature T is in a working temperature interval that marks off among the step b, determine and the interval corresponding absorption line of absorption line of this working temperature that this operating ambient temperature T is as work temperature simultaneously for intending using _WorkAs described operating ambient temperature T _WorkWhen being in the described one no absorption line temperature range, make the work temperature of described semiconductor laser by heating _WorkEnter in the working temperature interval that marks off among the step b, determine and the interval corresponding absorption line of absorption line of this working temperature for intending using;

D. according to the work temperature of described semiconductor laser _WorkThe working current of described semiconductor laser is determined and adjusted to the centre frequency of the absorption line of determining with step c;

E. the light that described semiconductor laser sends passes tested gas and is received; The light signal that receives is carried out absorption spectroanalysis, obtain the measured parameter and the demonstration of tested gas.

In the gas analysis process, repeating said steps c, d and e.

Among the described step a, determine the operating ambient temperature range [T of described semiconductor laser ₁, T ₂], the nominal operation temperature range of the semiconductor laser of selection is [T ₃, T ₄], should make T ₄〉=T ₂T ₃Work as T ₃≤ T ₁The time, the operating temperature range of described semiconductor laser is [T ₁, T ₄]; Work as T ₃T ₁The time, the operating temperature range of described semiconductor laser is [T ₃, T ₄].

Described step b is: determine the maximum output light frequency scope of described semiconductor laser, and select the absorption line of at least two tested gases in described maximum output light frequency scope; Determine the laser instrument maximum operation temperature interval corresponding respectively with described selection spectral line; In described operating temperature range, mark off interval and at least one the no absorption line temperature range of at least two working temperatures, make at least one absorption line of the interval corresponding tested gas of arbitrary working temperature.

When measured parameter is concentration, also the tested gas concentration value that records is compensated: X _Mend=K _InK _OutwardX _Survey, in the K gas concentration penalty coefficient in the same working temperature interval, K _OutwardFor striding the gas concentration penalty coefficient in working temperature interval, X _SurveyBe the gas concentration value that records.

Gas concentration penalty coefficient K in the described same working temperature interval _InDetermine by experiment: record the gas concentration value under the different operating temperature of described semiconductor laser in same working temperature interval, with the concentration value under the reference work temperature is reference value, determine the concentration value of other working temperature correspondence in this working temperature interval is compensated to the coefficient of reference value, obtain in this working temperature interval and the corresponding penalty coefficient K of working temperature _In

The described gas concentration penalty coefficient K that strides the working temperature interval _OutwardDetermine by experiment: record the gas concentration value under the reference work temperature of described semiconductor laser in the different operating temperature range, with the concentration value under the reference work temperature in the working temperature interval is reference value, determine the concentration value that records under the interval internal reference working temperature of other working temperature is compensated to the coefficient of reference value, obtain and the interval corresponding penalty coefficient K of working temperature _Outward

Know-why of the present invention is: because the discreteness of tested gas absorption spectrum line, in a few thing ambient temperature range of semiconductor laser, by regulate working current be can the output light frequency of laser instrument be tuned to some absorption line places of tested gas, in other operating ambient temperature ranges, then can not; Have, absorption line that neither be all can both be applied in the measurement environment again.So in the operating temperature range of semiconductor laser, mark off absorption line corresponding the working temperature interval and no absorption line temperature range suitable with tested gas, when the operating ambient temperature of the semiconductor laser that records is in the described working temperature interval, the interval corresponding absorption line of absorption line of this working temperature for intending using; In the time of in being in described no absorption line temperature range, the working temperature of semiconductor laser is entered in the described working temperature interval, the interval corresponding absorption line of absorption line of this working temperature for intending using by heating.So, arbitrary temperature in the operating ambient temperature range of semiconductor laser, by determining and adjust the absorption line that working current makes the corresponding tested gas of output light frequency of semiconductor laser, thereby receive and analyze the light that passes tested gas, calculate measured parameter and show.

Compared with prior art, the present invention has following advantage: 1) owing to be to utilize the operating ambient temperature that records to go to determine the working temperature of semiconductor laser, and then can use the interval corresponding absorption line of different working temperatures, avoid using all the time absorption line corresponding between the high-temperature region, prolonged the serviceable life of laser instrument.2) semiconductor laser does not need refrigeration, therefore need not to use TEC, can adopt power resistor as heater element simply, and control is compared simpler with driving circuit, has reduced the cost of corresponding analysis system.3) different with use TEC refrigeration, power resistor heats does not have excessive power drain, therefore efficient is higher, the working current of the analytic system of adopting said method and power consumption are all littler, use when power autonomous the working time longer, and the heat that sends is less, easily realize thermal design, and then realized the miniaturization and the portability of analytic system, as exploitation hand-held gas analyzing apparatus, expand the application of gas analysis system.4) need not to use TEC and special TEC control and driving circuit after, reduced the volume of analytic system, the while working current of analytic system is less, is easy to realize intrinsic safe explosion-proof and flame proof.

Description of drawings

Fig. 1 is the output frequency of semiconductor laser instrument and working temperature, working current graph of a relation;

Fig. 2 is that the running parameter of a TEC concerns synoptic diagram;

Fig. 3 is a structural representation of using the gas concentration analytic system of the inventive method;

Fig. 4 is the schematic flow sheet of the inventive method;

Fig. 5 is that semiconductor laser works temperature range is divided synoptic diagram;

Fig. 6 is that the serviceable life and the working temperature of semiconductor laser instrument concerns synoptic diagram;

Fig. 7 is penalty coefficient and the working temperature graph of a relation in the same working temperature interval;

Fig. 8 is a structural representation of using the gas flow rate analytic system of the inventive method;

Fig. 9 is the Doppler shift synoptic diagram.

Embodiment

Below in conjunction with drawings and Examples, the present invention is described in further detail.

Embodiment 1:

As shown in Figure 3, a kind of semi-conductor laser absorption spectrum methane concentration analytic system comprises Optical Transmit Unit, light receiving unit 11 and analytic unit 12.This analytic system adopts laser frequency scanning absorption spectroanalysis technology.

Described Optical Transmit Unit comprises semiconductor laser 1, laser socket 2, thermistor 3 and 5, current source 9, driving circuit 8, control device 7, heat block 4 and driving circuit 6 thereof.Semiconductor laser 1 is installed on the laser socket 2, thermistor 3 is installed on the laser socket 2 position near semiconductor laser 1, the working temperature of monitoring semiconductor laser 1, the signal of thermistor 3 is sent into control device 7, goes to control the working current and the temperature of semiconductor laser 1 after control device 7 is handled.Control device 7 judges according to thermistor 3 signals of input whether laser instrument works in assigned temperature.Thermistor 5 is used to record the temperature of semiconductor laser working environment of living in.The working current of semiconductor laser 1 is provided by current source 9, and the driving circuit 8 of current source 9 is made up of dc bias circuit 81 and ac signal circuit 82.Dc bias circuit 81 produces a direct current signal, is used to control the average working current of semiconductor laser 1, adjusts the output center frequency of semiconductor laser 1; Ac signal circuit 82 produces a triangular current, and (peak-to-peak value is 0.21mA, frequency is 1Hz), make the absorption line of the inswept tested methane of output frequency of semiconductor laser 1, this circuit also superposes on above-mentioned triangular current simultaneously, and (peak-to-peak value is 0.17mA to a sine-wave current, frequency is 1kHz), be used to realize the second order modulated optical absorption spectra.

A kind of semi-conductor laser absorption spectrum methane concentration analytical approach also is the course of work of above-mentioned methane concentration analytic system, as shown in Figure 4, said method comprising the steps of:

A. determine the operating temperature range and the current margin of semiconductor laser.

At the application of this methane concentration analytic system, the operating ambient temperature range of described semiconductor laser is [T ₁, T ₂], present embodiment is [5 ℃, 55 ℃].Though because the electronic unit in the analytic system can produce heat, cause the residing operating ambient temperature of semiconductor laser 1 can be slightly higher, can be approximated to be identical than the operating ambient temperature of analytic system.

The nominal operation temperature range of the semiconductor laser of selecting is [T ₃, T ₄], should make T ₄〉=T ₂T ₃Work as T ₃≤ T ₁The time, the operating temperature range of described semiconductor laser is [T ₁, T ₄].Work as T ₃T ₁The time, the operating temperature range of described semiconductor laser is [T ₃, T ₄], at this moment, when the operating ambient temperature of semiconductor laser be lower than the nominal operation temperature range following in limited time, make the working temperature of semiconductor laser 1 be positioned at the nominal operation temperature range by described heat block.Present embodiment is selected a VCSEL N-type semiconductor N laser instrument, and the nominal operation temperature range is [0 a ℃, 65 ℃].By the definition of aforementioned operating temperature range as can be known, the operating temperature range of semiconductor laser is [5 ℃, 65 ℃].

The current margin of described semiconductor laser 1 is [3mA, 7mA], and wherein 3mA is the threshold current of semiconductor laser work, and 7mA is specified maximum operating currenbt.

B. determine the maximum output light frequency scope of semiconductor laser in described working temperature and range of current,, in described maximum output light frequency scope, select at least two suitable tested gas absorption spectrum lines according to the absorption line characteristic of tested gas; Current margin according to semiconductor laser, determine the semiconductor laser maximum operation temperature interval corresponding, can make the output light frequency of semiconductor laser corresponding to described absorption line by the working current of regulating semiconductor laser when making in described maximum operation temperature interval with arbitrary absorption line of described selection; In described semiconductor laser operating temperature range, mark off interval and at least one the no absorption line temperature range of at least two working temperatures, make the absorption line of the interval corresponding at least one tested gas of arbitrary working temperature, and the working temperature interval corresponding with described absorption line covered with the corresponding maximum operation temperature interval of this absorption line; Spectroscopic data, the no absorption line temperature range of the interval and corresponding absorption line of the described working temperature that marks off are stored in the described control device.

As shown in Figure 6, the serviceable life of semiconductor laser is relevant with its working temperature, and along with the rising of semiconductor laser working temperature, descend serviceable life gradually.Therefore, in order to prolong the serviceable life of semiconductor laser, should avoid making described semiconductor laser to be operated between the high-temperature region always.So, in the operating temperature range of semiconductor laser, mark off at least two temperature range and at least one no absorption line temperature ranges that absorption line is arranged according to the absorption line characteristic of tested gas.

Above-mentioned suitable spectral line refers to the application scenario at this methane analytic system, the spectral line of better performances for the methane concentration analytic function of needs, as do not have that background gas disturbs, the spectral line line is strong enough strong etc.Above-mentioned spectral line also can be the set of close some spectral lines, or the spectral line family that forms of overlapping some spectral lines.

Frequency-the electric current of described semiconductor laser 1 and frequency-temperature characterisitic all are non-linear, and electric current, the temperature characterisitic of its output light frequency can be described with following formula:

v＝v ₀-k ₁I-k ₂I ²-k ₃T-k ₄T ²…

Be approximately: v ≈ v ₀-k ₁I-k _TT

The concrete parameter of described semiconductor laser 1 is: v ₀=6055.2cm ^-1k ₁=1.295cm ^-1/ mA, k _T=0.478cm ^-1/ ℃.In the operating temperature range [5 ℃, 65 ℃] and current margin [3mA, 7mA] of semiconductor laser 1, the maximum of semiconductor laser 1 output light frequency scope is: [6014.98cm ^-1, 6048.93cm ^-1].

As shown in Figure 5, at [6014.98cm ^-1, 6048.93cm ^-1] in the frequency range, the suitable spectral line of methane has 4, at each spectral line, according to the current margin [3mA, 7mA] of semiconductor laser 1, determines the maximum operation temperature interval corresponding with this spectral line, sees Table one.

Table one

Spectral line	Centre frequency (cm -1)	The maximum operation temperature interval (℃)	The working temperature interval (℃)	The reference work temperature (℃)	Reference work electric current (mA)
						1	6015.67	63.7-65	63.7-65	65	6.53
2	6026.24	41.6-52.5	41.6-52.5	45	5.75
						3	6036.61	19.9-30.8	19.9-30.8	25	5.14
4	6046.91	5-9.2	5-9.2	5	4.56

As seen, [63.7 ℃ in working temperature interval, 65 ℃] not [5 ℃ of the operating ambient temperature ranges of semiconductor laser, 55 ℃] in, but in order to make (52.5 ℃ of temperature ranges in the semiconductor laser operating ambient temperature range, 55 ℃] in the absorption line of spendable tested gas is arranged, so keep absorption line 1.

[5 ℃ of the operating temperature ranges of semiconductor laser 1,65 ℃] in mark off and (9.2 ℃ of corresponding respectively four the working temperatures intervals of above-mentioned 4 absorption lines and three no absorption line temperature ranges, 19.9 ℃), (30.8 ℃, 41.6 ℃), (52.5 ℃, 55 ℃].Temperature range (55 ℃, 63.7 ℃) need not to consider not in the operating ambient temperature range of semiconductor laser.

If the operating ambient temperature range of described semiconductor laser is [5 ℃, 52 ℃], though [5 ℃ of the operating temperature ranges of semiconductor laser, 65 ℃] interior to the absorption line of four methane should be arranged, but as shown in Table 1, the working temperature interval of absorption line 2 correspondences has comprised 52 ℃ of the maximal values of operating ambient temperature, so only select for use absorption line 2,3,4 to get final product.

To consider also that when selecting spectral line interference that whether other gas spectral lines are arranged etc. is all multifactor in test environment.In addition, in order to reduce the complexity of measurement, the spectral line number of choosing usually is also unsuitable too many.For example, the absorption line of four methane is arranged in the operating temperature range of above-mentioned semiconductor laser, but absorption line 4 there is bigger background gas cross interference, therefore, can only selects spectral line 1,2 and 3, and absorption line 4 is weeded out.Like this, originally corresponding in [5 ℃, 9.2 ℃] in the working temperature interval is absorption line 4, but because other reasons has weeded out absorption line 4, so temperature range [5 ℃, 9.2 ℃] has also become no absorption line temperature range.

C. record the operating ambient temperature T of described semiconductor laser, in the time of in described operating ambient temperature T is in a working temperature interval that marks off among the step b, determine the absorption line of absorption line for intending using of the tested gas corresponding with this working temperature interval, described operating ambient temperature T is as the work temperature of semiconductor laser simultaneously _WorkIn the time of in described operating ambient temperature T is in described no absorption line temperature range, make the work temperature of described semiconductor laser by heating _WorkEnter in the working temperature interval that marks off among the step b, determine the absorption line of absorption line for intending using of the tested gas corresponding with this working temperature interval.

The operating ambient temperature that records described semiconductor laser 1 according to thermistor 5 is 18 ℃, and from the above, corresponding with 18 ℃ of operating ambient temperatures is no absorption line temperature range (9.2 ℃, 19.9 ℃).At this moment, described heat block 4 work of control device 7 controls, simultaneously by thermistor 3 monitoring, thereby the working temperature of described semiconductor laser 1 is raise,, enter into the working temperature interval that step b marks off as to 24 ℃, as [19.9 ℃, 30.8 ℃], this working temperature is interval corresponding with absorption line 3, i.e. the absorption line of absorption line 3 for intending using.

The temperature of semiconductor laser 1 environment of living in is 53 ℃ as described in recording as thermistor 5, this temperature be in no absorption line temperature range (52.5 ℃, 55 ℃] in, but can utilize heat block 4 to make the work temperature of semiconductor laser _WorkRaise, as to 65 ℃ (these temperature exceeded as described in the operating ambient temperature range of semiconductor laser), heated temperatures enters in the working temperature interval [63.7 ℃, 65 ℃] for 65 ℃, this working temperature is interval corresponding with absorption line 1, i.e. the absorption line of absorption line 1 for intending using.

As seen, arbitrary temperature in the operating ambient temperature range [5 ℃, 55 ℃] of semiconductor laser can be determined the absorption line of intending use.

Present embodiment is the temperature range according to semiconductor laser operating ambient temperature place, determine the absorption line of the tested gas of intending use, rather than the working temperature of semiconductor laser is set in [63.7 ℃ in hot operation interval all the time, 65 ℃], only utilize the interval pairing tested gas absorption spectrum line 1 of this hot operation.Like this, just avoided semiconductor laser is always worked between the high-temperature region, thereby prolonged the serviceable life of semiconductor laser.

D. according to the work temperature of semiconductor laser _WorkThe working current of semiconductor laser is determined and adjusted to the centre frequency of the absorption line of determining with step c, the absorption line that the output light frequency of semiconductor laser is used corresponding to the plan of being determined by step b.

Work temperature after being heated according to the semiconductor laser among the step c 1 _WorkBe 24 ℃, the working temperature interval at place is [19.9 ℃ 30.8 ℃], and table one has provided and the interval corresponding reference work temperature of this working temperature _RefWith the reference work electric current I _RefBe respectively 25 ℃ and 5.14mA; The output light frequency of the semiconductor laser 1 under above-mentioned reference work temperature and current conditions is positioned at the centre frequency place of absorption line 2.

When the working temperature after semiconductor laser 1 is heated is 24 ℃,, determine and adjust the working direct current of semiconductor laser 1 according to the output frequency-temperature and the output frequency-current characteristics of semiconductor laser 1:

$I_{\mathrm{work}}=I_{\mathrm{ref}}-\frac{k_T}{k_I}\·(T_{\mathrm{work}}-T_{\mathrm{ref}})=5.51\mathrm{mA}$

Thereby the scanned absorption line 2 of the output light frequency that makes described semiconductor laser 1.Said process all is to finish in control device 7.

E. the light that sends of semiconductor laser passes tested gas and is received; The light signal that receives is carried out absorption spectroanalysis, obtain the measured parameter and the demonstration of tested gas.

The laser that described semiconductor laser 1 sends passes tested methane 10 backs and is received by light receiving unit 11; Send the light signal that receives analytic unit 12 to obtain the second order modulated optical absorption spectras and analyze, utilize conventional method to obtain the concentration of tested methane 10.

Control semiconductor laser actuator temperature for routine is the second order modulated optical absorption spectra analytical technology of normal temperature, and its measurement of concetration formula is:

X _Survey=K (S _2f/ I ₀) (B (P _Ref, T _Ref, S _Ref)/B (P, T, S)),

S wherein _2fBe the second harmonic signal peak-to-peak value, I ₀DC component for light intensity signal, B parameter (P, T, S) be used to revise the second harmonic signal peak-to-peak value with the variation of tested gas temperature T, pressure P and the strong S of line (comprised gas temperature change the line that causes strong change and different spectral line between line change by force), can obtain by basic spectrum data computation, also can record according to experiment, COEFFICIENT K is the calibration coefficient relevant with instrument, and it is demarcated by the gas that feeds concentration known and obtains.

The noise spectra of semiconductor lasers working temperature by stages that proposes for the present invention but not be controlled to be the technical scheme of normal temperature also needs compensate the tested gas concentration value that records, and concrete formula is:

X _Mend=K _{I, in}K _{I, outer}K (S _2f/ I ₀) (B _i(P _Ref, T _Ref, S _Ref)/B _i(P, T, S))=K _{I, in}(T _Work) K _{I, outer}X _Survey, wherein the subscript i working temperature that provides semiconductor laser drops in i the working temperature interval B _i(P, T S) are used to revise second harmonic signal peak-to-peak value and the strong variation relation of tested gas temperature, pressure and line when adopting the absorption line corresponding with i working temperature interval, K _{I, in}Be the gas concentration penalty coefficient in the same working temperature interval, be used for compensate semi-conductor's laser instrument in i working temperature interval arbitrarily record concentration value and the working temperature during working temperature be reference work temperature T in this temperature range _{I, ref}The time the relative variation of concentration value; K _{I, outer}Be the gas concentration penalty coefficient of striding the working temperature interval, be used to compensate and adopt the relative variation that records concentration value that causes with the corresponding different absorption lines of different operating temperature range.

As shown in Table 2, in a working temperature interval of described semiconductor laser 1, change the semiconductor laser working temperature, between 19.9 ℃ to 30.8 ℃, is benchmark with a certain temperature as 25 ℃, under the record different operating temperature analytic system record concentration value, concentration error was less than ± 2% before experimental result showed compensation.As shown in Table 3, in the different operating temperature range of described semiconductor laser 1, between 5 ℃ to 65 ℃, with 25 ℃ be benchmark, also be the measurement of concetration error of different spectral line correspondences before compensation less than ± 3%.Concentration error is by due to the fine difference of the duty of semiconductor laser such as working current etc.In order to obtain higher measuring accuracy, need the described concentration value that records to be compensated according to above-mentioned concentration compensation formula.

Penalty coefficient K in the described same working temperature interval _{I, in}Determined by following method: it is interval as [19.9 ℃ in a certain working temperature that experiment records semiconductor laser 1,30.8 ℃] in the reference work temperature as 25 ℃ and some other working temperature the tested gas concentration value X during as 23 ℃, 24 ℃, 29 ℃ and 30 ℃, the penalty coefficient K when these working temperatures _{I, in}For recording the ratio that records concentration under concentration and these working temperatures under the reference work temperature; Penalty coefficient under these discrete working temperatures is carried out linearity or high-order match (as shown in Figure 7), just can obtain the penalty function K in this working temperature interval _{I, in}(T _Work), the described penalty function that obtains is stored into described analytic unit 12.When the work temperature that records described semiconductor laser _Work, just can be according to described penalty function K _{I, in}(T _Work) obtain and described T _WorkCorresponding penalty coefficient.Experimental result shows, according to above-mentioned concentration compensation method, adopts three rank matches, and the concentration error under the different operating temperature is less than 0.1%.

The described gas concentration penalty coefficient K that strides the working temperature interval _{I, outer}Can obtain by the following method: the tested gas concentration X when experiment records reference work temperature in the different operating temperature range of semiconductor laser 1 as 5 ℃, 25 ℃ and 45 ℃, the gas concentration penalty coefficient K in corresponding these working temperature intervals _{I, outer}Record concentration and the ratio that under above-mentioned different reference work temperature, records concentration when being 25 ℃, the described penalty coefficient that obtains is stored into described analytic unit 12.

Table two: the measurement of concetration compensation in the same working temperature interval

Electric current (mA)	Working temperature (℃)	Record concentration (%)	Concentration error (%)	Penalty coefficient K I, in
					6.62	21	1.274	1.839	0.982
6.25	22	1.268	1.359	0.987
					5.87	23	1.262	0.879	0.991
5.50	24	1.257	0.480	0.995
					5.14	25	1.251	0	1
4.77	26	1.246	-0.400	1.004
					4.40	27	1.241	-0.800	1.008
4.03	28	1.237	-1.119	1.011
					3.66	29	1.232	-1.518	1.015
3.29	30	1.23	-1.679	1.017

Table three: the measurement of concetration compensation of different operating temperature range

The reference work temperature (℃)	Record concentration (%)	Error (%)	Penalty coefficient K I, outer
				65	1.216	-2.798％	1.0288
45	1.225	-2.078	1.0212
				25	1.251	0	1
5	1.282	2.478	0.9758

Working temperature according to semiconductor laser among the step b is heated to be 24 ℃, and the concentration value that records methane according to conventional method is: X _Survey=2.11%.Also need the concentration value that records is compensated: X _Mend=K _{I, in}(T _Work) K _{I, outer}X _Survey, working temperature is in the working temperature interval [19.9 ℃, 30.8 ℃] for 24 ℃, and analytic unit 12 calls the penalty function in this working temperature interval, obtains the gas concentration penalty coefficient K with 24 ℃ of corresponding same working temperature intervals of working temperature _In=0.995, stride the gas concentration penalty coefficient K in working temperature interval _Outward=1, be X so be compensated concentration value _Mend=2.10%, the compensation concentration value that obtains is presented on the display screen of described analytic unit 12.

In the analytical gas process, repeat above-mentioned steps c, d and e.As, after last time, measurement was finished, also to utilize thermistor 5 to record the operating ambient temperature of laser instrument, and determine whether needs work of described heat block 4 according to the temperature that records.As record operating ambient temperature and drop to 8 ℃, being in the working temperature interval [5 ℃, 9.2 ℃], this moment, heat block 4 quit work, and the working temperature of semiconductor laser is cooled to 8 ℃ from 24 ℃, and then utilizes absorption line 4.As to record operating ambient temperature be 35 ℃, corresponding with this temperature is (30.8 ℃ of no absorption line temperature ranges, 41.6 ℃), then strengthen the heating power of described heat block 4, the working temperature of described semiconductor laser 1 is elevated to from 24 ℃ enters [41.6 ℃ in working temperature interval, 52.5 ℃] in, as 45 ℃, with the interval corresponding absorption line of this working temperature is spectral line 2, according to 45 ℃ of working temperatures after the heating and absorption line 2, and then determine and adjust the working current of described semiconductor laser 1, thereby obtain the concentration of tested methane.

Described control device 7 also writes down the working temperature of the semiconductor laser 1 that thermistor 3 records, and is used to compensate follow-up concentration result of calculation.

Embodiment 2:

A kind of semi-conductor laser absorption spectrum gas analyzing method is applied in the fluid-velocity survey of methane in the pipeline.As shown in Figure 8, what described flow velocity measuring system was different with methane concentration analytic system among the embodiment 1 is: the light scioptics 14 that semiconductor laser 1 sends are injected in the tested pipeline 13, the angle of laser beam and tested gas flow is α=45 °, and laser beam is passed lens 15 backs and received by light receiving unit 11.Concrete flow velocity analytical approach may further comprise the steps:

A. detailed process is identical with step a among the embodiment 1;

B. detailed process is identical with step b among the embodiment 1;

C. the operating ambient temperature that records semiconductor laser 1 is 35 ℃, be positioned at (30.8 ℃ of no absorption line temperature ranges, 41.6 ℃), the described semiconductor laser 1 of described heat block 4 heating of these timed unit 7 controls, making the working temperature rising of described semiconductor laser 1 is 46 ℃, and working temperature is in the working temperature interval [41.6 ℃, 50 ℃] for 46 ℃, corresponding absorption line is a spectral line 1, and its centre frequency is 6026.24cm ^-1Absorption line 1 is the absorption line of intending use;

D. the working current of determining semiconductor laser 1 is 5.38mA, and detailed process is identical with steps d among the embodiment 1;

E. the light that sends of semiconductor laser 1 passes tested methane and is received by light receiving unit 11; The light signal that receives is carried out absorption spectroanalysis, and then obtain the flow velocity and the demonstration of tested methane.

When output frequency is v ₀Laser beam pass the methane that flow velocity is V, methane molecule absorption line centre frequency produces Doppler shift (Doppler-shift), the Doppler shift amount is described by following formula:

$\mathrm{\Δ}{v}_{\mathrm{Doppler}}=\frac{V}{c}\·v_0\·\cos \mathrm{\α}$

Av _DopplerBe the Doppler shift amount, α be laser beam and methane stream to angle, v ₀Be the centre frequency of methane adsorption spectral line, c is the light velocity.

The Doppler shift amount of measuring absorption line just can calculate the flow velocity V of methane:

$V=\frac{\mathrm{\Δ}{v}_{\mathrm{Doppler}}}{v_0}\·\frac{c}{\cos \mathrm{\α}}$

As shown in Figure 9, solid line is represented the preceding waveform of frequency displacement among the figure, and dotted line is the waveform after the frequency displacement; Record Doppler shift amount Δ v _Doppler=2.573 * 10 ^-3Cm ^-1, and then to obtain flow velocity be 83.34m/s and show.

In measuring channel in the process of methane flow rate, repeating said steps c, d and step e.Each operating ambient temperature that all records semiconductor laser again, and remove the absorption line of the tested gas that determine to intend uses according to operating ambient temperature, and then according to the working temperature of semiconductor laser and the absorption line of intending using determine and adjust the working current of laser instrument, thereby obtain the flow velocity of tested methane.

It is pointed out that above-mentioned embodiment should not be construed as limiting the scope of the invention.Such as, among the step c of the foregoing description, when the operating ambient temperature of described semiconductor laser is in a certain working temperature interval, although this working temperature interval is to there being absorption line, if but the characteristic of this absorption line in this measurement moment is not fine, for example background gas disturbs bigger, also can be by the heating semiconductor laser, make the working temperature of laser instrument enter corresponding working temperature interval of disturbing less absorption line, at this moment, this disturbs the absorption line of less spectral line for intending using.Key of the present invention is, marks off interval and at least one the no absorption line temperature range of at least two working temperatures in the operating temperature range of semiconductor laser, makes at least one absorption line of the corresponding tested gas in arbitrary working temperature interval; Select measuring gas absorption spectrum line according to the operating ambient temperature of the semiconductor laser that records, and then utilize this absorption line to obtain the parameter of tested gas, as concentration, flow velocity, temperature etc.Under the situation that does not break away from spirit of the present invention, any type of change that the present invention is made all should fall within protection scope of the present invention.

Claims (7)

1, a kind of semi-conductor laser absorption spectrum gas analyzing method said method comprising the steps of:

A. according to the operating ambient temperature range and the nominal operation temperature range of semiconductor laser, determine the operating temperature range of semiconductor laser, go to determine the current margin of semiconductor laser according to the rated operational current scope of semiconductor laser;

B. determine maximum output light frequency scope according to the operating temperature range and the current margin of semiconductor laser, in described maximum output light frequency scope, select the absorption line of at least two tested gases; In described operating temperature range, mark off interval and at least one the no absorption line temperature range of at least two working temperatures, in arbitrary working temperature interval, can make the tested gas absorption spectrum line of corresponding at least one selection of output light frequency of semiconductor laser by the working current of regulating semiconductor laser;

C. record the operating ambient temperature T of described semiconductor laser, in the time of in described operating ambient temperature T is in a working temperature interval that marks off among the step b, determine and the interval corresponding absorption line of absorption line of this working temperature that this operating ambient temperature T is as the work temperature of semiconductor laser simultaneously for intending using _WorkIn the time of in described operating ambient temperature T is in described one no absorption line temperature range, make the work temperature of described semiconductor laser by heating _WorkEnter in the working temperature interval that marks off among the step b, determine and the interval corresponding absorption line of absorption line of this working temperature for intending using;

D. according to the work temperature of described semiconductor laser _WorkThe working current of described semiconductor laser is determined and adjusted to the centre frequency of the absorption line of determining with step c;

The light that e, described semiconductor laser send passes tested gas and is received; The light signal that receives is carried out absorption spectroanalysis, obtain the measured parameter and the demonstration of tested gas.

2, analytical approach according to claim 1 is characterized in that: in the gas analysis process, and repeating said steps c, d and e.

3, analytical approach according to claim 1 and 2 is characterized in that: among the described step a, determine the operating ambient temperature range [T of described semiconductor laser ₁, T ₂], the nominal operation temperature range of the semiconductor laser of selection is [T ₃, T ₄], should make T ₄〉=T ₂T ₃Work as T ₃≤ T ₁The time, the operating temperature range of described semiconductor laser is [T ₁, T ₄]; Work as T ₃T ₁The time, the operating temperature range of described semiconductor laser is [T ₃, T ₄].

4, analytical approach according to claim 3, it is characterized in that: among the described step b, according to the absorption line of selecting and the current margin of laser instrument, determine the laser instrument maximum operation temperature interval corresponding respectively with the absorption line of selecting, in the maximum operation temperature interval, can make the output light frequency of laser instrument corresponding to the absorption line of selecting by the working current of regulating laser instrument, in described operating temperature range, mark off interval and at least one the no absorption line temperature range of at least two working temperatures, make at least one absorption line of the interval corresponding tested gas of arbitrary working temperature, the working temperature interval corresponding with described absorption line covered with the corresponding maximum operation temperature interval of absorption line.

5, analytical approach according to claim 1 and 2 is characterized in that: when measured parameter is concentration, and tested gas concentration value X also to recording _SurveyCompensate the tested gas concentration X after the compensation _MendFor: X _Mend=K _InK _OutwardX _Survey, K _InBe the gas concentration penalty coefficient in the same working temperature interval, be used for compensate semi-conductor's laser instrument in a working temperature interval arbitrarily during working temperature record concentration value and working temperature for this working temperature interval internal reference working temperature the time the relative variation of concentration value; K _OutwardFor striding the gas concentration penalty coefficient in working temperature interval, the relative variation that records concentration value when being used for the reference work temperature of compensate semi-conductor's laser instrument in the different operating temperature range.

6, analytical approach according to claim 5 is characterized in that: the gas concentration penalty coefficient K in the described same working temperature interval _InDetermine by experiment: record the gas concentration value under the different operating temperature of described semiconductor laser in a working temperature interval, with the concentration value under the reference work temperature is reference value, determine the concentration value of other working temperature correspondence in this working temperature interval is compensated to the coefficient of reference value, obtain in this working temperature interval and the corresponding penalty coefficient K of working temperature _In

7, analytical approach according to claim 5 is characterized in that: the described gas concentration penalty coefficient K that strides the working temperature interval _OutwardDetermine by experiment: record the gas concentration value under the reference work temperature of described semiconductor laser in the different operating temperature range, with the concentration value under the reference work temperature in the working temperature interval is reference value, determine the concentration value that records under the interval internal reference working temperature of other working temperature is compensated to the coefficient of reference value, obtain and the interval corresponding penalty coefficient K of working temperature _Outward

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