CN102589815A - Calculation method for detection limit in gas-leakage infrared imaging - Google Patents

Abstract

The invention relates to a calculation method for detection limit in gas-leakage infrared imaging, and belongs to the field of gas leakage detection. The calculation method comprises the following steps of: firstly calculating the background radiant exitance when no gas leaks, and taking the background radiant exitance as background radiant exitance for imaging detection; calculating equivalent blackbody temperature of the imaging detection background by the background radiant exitance for imaging detection; secondly, when gas leaks, calculating the radiant exitance after the background radiation is absorbed by gas according to a gas parameter in the background radiant exitance for imaging detection, namely a target radiant exitance for imaging detection; calculating target equivalent blackbody temperature for imaging detection by the target radiant exitance for imaging detection; then calculating an absolute value of the difference between the imaging detection background and the target equivalent blackbody temperature, and defining the absolute value as a gas equivalent blackbody temperature difference; and finally comparing gas equivalent temperature difference with a noise equivalent temperature difference of comprehensive performance parameters of an infrared detector and an optical system, and determining gas-leakage detection limit value, namely, a minimum flow of leaked gas.

Description

A kind of gas leaks infrared imaging detection Calculation of Limit method

Technical field

The present invention relates to a kind of gas and leak infrared imaging detection Calculation of Limit method, belong to gas leak detection field.

Background technology

According to the statistics of China's tank/tank car carrier, up to the present, kind surplus the hazardous chemical that China had transported has 130, wherein the transportation of poisonous and harmful, flammable explosive gas is the most important thing.For example, except that liquefied petroleum gas (LPG), only the annual production of chlorine China surpasses 6,000,000 tons, and 0.1 milligram chlorine just is enough to environment and personnel are damaged in every cubic metres of air.According to country " chlorine safety regulations GB 11984-89 " regulation, the workshop (operation place) that produces, uses chlorine, chlorine content maximum permissible concentration 1mg/m in the air ³In the transportation of hazardous chemical, in a single day the leakage meeting takes place road resident, ecologic environment on every side along the line is caused very big harm in poisonous and harmful, flammable explosive gas.After leakage accident took place, some gas colorless and odorless was not easy to come to light, and gas as easy as rolling off a log rapid diffusion in air, confirmed that in time gas leakage source, the gas space distribute to taking effective accident treatment measure to seem particularly important.

Traditional gas detection method is that gas sensor is placed on the tank body valve place that easy generation is leaked, and through the measurement of concentration, carries out gas Leak Detection and warning, detects time and effort consuming.And passive type gas leaks infrared imagery technique and is to use medium wave or the visual gas molecule of long wave thermal imaging system that the infrared radiation of 3～14 mu m wavebands is absorbed; Make naked eyes can not observed gas leakage high-visible on infrared video; The technology of a kind of quick identification source of leaks and gas space distribution is provided for the testing staff through visual image; Adopt image processing techniques to improve picture quality simultaneously, be convenient to eye-observation and judgement.This technology has good application prospects in a lot of fields, such as the detection that chemistry, electric power, industrial circle gas leak, and the detection of the biochemical toxic agent gas of military affairs and public safety field etc.With other detection of gas compared with techniques, gas leak infrared imagery technique have portable, fast, plurality of advantages such as remote measurement on a large scale.

It is ultimate principle: I with Bill-bouguer's law (Beer-LaEbert Absorption Law) that passive type gas leaks infrared imagery technique ₁=I ₀Exp [τ (λ, c, L)], I in the formula ₀Expression gets into the background radiation before the gas cloud cluster, I ₁Remaining radiation behind the gas cloud cluster is passed in expression, and τ (λ, c, the L) transmitance of expression gas, λ is a wavelength, and c is the concentration of gas, and L is an optical path.I ₀And I ₁Difference reflected what of infrared radiation that gas absorbs, also be simultaneously the key that on thermal imaging system, forms the gas image, I ₀And I ₁Difference is big more, and the picture contrast between gas and the background is high more, is arrived by eye-observation more easily.Find out that according to above formula four factor affecting gas imagings are arranged: the size of gas concentration, background radiation, optical path, gas permeation rate.In addition, be used for receiving the optical system of infrared radiation and the performance of infrared eye also can influence final imaging effect.

Though gas leak infrared imagery technique have portable, fast, plurality of advantages such as remote measurement on a large scale; But present passive type gas leaks infrared imagery technique belongs to the qualitative Detection Techniques that a kind of eye-observation fast is the master, can't realize that quantitative minimum gas concentration detects.When the gas leakage flow is very little, cause gas cloud cluster concentration very low, thus I ₀And I ₁Difference is very little, and the gas cloud cluster just can not form images, and can't realize the gas concentration detection by quantitative because passive type gas leaks infrared imagery technique, and then the Performance Evaluation of gas imaging system design and system is made troubles.

Summary of the invention

Leak the application need of infrared imagery technique to passive type gas; Definition and infrared imaging system according to infrared imaging system performance parameter NETD are surveyed required condition; The invention provides a kind of gas and leak imaging detection Calculation of Limit method; Can be under certain background environment condition, use the minimum flow of gas leakage of the infrared detector array institute ability imaging detection of certain performance.

The present invention realizes through following technical scheme:

A kind of gas leaks infrared imaging detection Calculation of Limit method, specifically comprises the steps:

The first step: the background radiation emittance when calculating no gas and leaking, and with it as imaging detection background radiation emittance E _b

Second step: by imaging detection background radiation emittance E _bCalculate imaging detection background equivalence blackbody temperature T _Bb

The 3rd step: when gas leaks, calculate the radiant exitance of background radiation after gas absorption, be imaging detection target emanation emittance E according to the gas parameter in the imaging detection background radiation emittance _p

The 4th step: by imaging detection target emanation emittance E _pBe calculated to be picture detection of a target equivalence blackbody temperature T _t

The 5th step: the absolute value of second step and the difference of the 4th imaging detection background that calculate of step and target Equivalent blackbody temperature is defined as the equivalent black matrix temperature difference of gas GEBTD;

The 6th step: the combination property parameter-noise equivalent temperature difference NETD of comparison gas equivalence black matrix temperature difference GEBTD and infrared eye and optical system, confirm gas leak detection ultimate value, i.e. the minimum flow of gas leakage.

The described background radiation emittance of the above-mentioned first step is through calculating context parameter substitution planck formula; Context parameter is background emission rate and background surface temperature; The background emission rate determines according to background material; The background surface temperature is through measuring.

The equivalent blackbody temperature T of above-mentioned described imaging detection background of second step _BbAdopt following method to calculate: according to Planck law, the radiant quantity E of background _bWith equivalent blackbody temperature T _BbExpression is with the background radiation emittance E in the first step _bBring the Planck law formula into, obtain the equivalent blackbody temperature T of background _Bb

Described imaging detection target emanation emittance E of above-mentioned the 3rd step _pAdopt following method to calculate: with the background radiation emittance E in the first step _bAnd gas leakage cloud cluster parameter substitution Bill lambert's law formula, calculate background radiation remaining radiant exitance after gas absorption, i.e. target emanation emittance E _pWherein gas cloud cluster parameter comprises: gas concentration, gas temperature, gas absorption path, gas infrared absorption coefficient, and gas infrared absorption coefficient obtains in the infrared absorption spectrum storehouse; Gas temperature is according to measuring; Gas flow is set at certain initial value; Gas concentration and absorption path root Model Calculation according to estimates draw: the flow of setting the gas leakage is certain initial value; It is 0.1m that the space distribution of leaking the gas that comes out is approximately a bottom surface radius; Height is the cone of 0.3m, and then the gas absorption path proximity is the bottom surface radius of cone; Gas concentration is that leakage flow multiply by the infrared imaging system time shutter again divided by the cone volume.

The imaging detection target Equivalent blackbody temperature T in above-mentioned the 4th step _tAdopt following method to calculate: according to Planck law, the radiant exitance M of target _tWith equivalent blackbody temperature T _tExpression is with the radiant quantity E of the imaging detection target in the 3rd step _pBring the Planck law formula into, obtain the equivalent blackbody temperature T of target _t

Confirm that gas leak detection ultimate value adopts following method in above-mentioned the 6th step: compare GEBTD and NETD, if the two equates or approximately equal that the gas stream value of this moment is gas leak detection ultimate value so; If GEBTD is less than NETD; Show infrared eye can't imaging detection the gas flow of this moment; Then improve gas flow recomputate the 3rd the step to the 5th step, if GEBTD greater than NETD, but show the quantity of gas leakage that the infrared eye imaging detection is littler; Reduce gas flow, recomputated for the 3rd step to the 5th step.

Principle of work of the present invention: at first use medium wave or LONG WAVE INFRARED imaging detector and optical system in certain visual field, to observe position to be detected, the scene content when no gas is leaked in the visual field is called background; When gas leak to take place, gas concentration become very thin because of diffusion so that the zone that can't form images and gaseous diffusion less than but still zone in the visual field is called no gas zones; Because of radiant quantity is identical, the no gas zones when background when therefore will not have the gas leakage and gas leak is referred to as the background of imaging detection; The finite space scope of diffusion was called the gas leaking area when gas was leaked, and look be the target of imaging detection.Calculate the radiant exitance of the target and background of imaging detection according to background, gas parameter; Then; By Planck law, obtain the equivalent blackbody temperature of the target and background of imaging detection, further obtain gas equivalence black matrix temperature difference GEBTD; At last; The NETD value of GEBTD and infrared imaging system is compared, and when GEBTD equaled the combination property parameter of infrared eye and optical system-noise equivalent temperature difference NETD, the gas that pairing gas flow is under certain background and context condition leaked the imaging detection limit.

The beneficial effect that the present invention produces is:

1. a gas leaks the minimum flow that infrared imaging detection Calculation of Limit method can be confirmed the gas leakage that the imaging of gas cloud cluster is required; Obtain passive type gas and leak the important performance indexes of infrared imaging system in practical application, can make things convenient for the Performance Evaluation of gas imaging system design and system.In practical application, when the flow of gas leakage leaked the infrared imaging detection limit greater than gas, gas can form images, otherwise, then can not.

2. the present invention obtains the influence factor that passive type gas leaks infrared imaging, comprises context parameter and gas parameter, and context parameter mainly refers to background emission rate, background surface temperature; Gas parameter mainly refers to gas temperature, gas concentration, gas absorption path, gas infrared absorption coefficient.In the experimentation of gas leakage infrared imaging, has directive function preferably.

3. the direct Application of Passive formula of the present invention gas leaks the performance parameter noise equivalent temperature difference NETD of infrared imaging system, makes computation process simple, convenient, directly perceived.

Description of drawings

Fig. 1 leaks the flow chart of steps of imaging detection Calculation of Limit method for gas.

Embodiment

Below in conjunction with accompanying drawing the present invention is done a detailed description.

Concrete implementation procedure in the present embodiment comprises six steps as shown in Figure 1:

Step a. calculates imaging detection background radiation emittance E _b

When gas leak to take place, gas concentration become very thin because of diffusion so that the zone that can't form images and gaseous diffusion less than but still zone in the visual field is called no gas zones, and be called the background of imaging detection.Imaging detection background radiation emittance E then _bThe radiant exitance of the background when equaling not have the gas leakage in the visual field is expressed as through atmospheric attenuation rear backdrop radiant exitance

$E_b={\∫}_{{\mathrm{\λ}}_0}\left\{{\mathrm{\τ}}_a(\mathrm{\λ},R)\right[{\mathrm{\ϵ}}_b\left(\mathrm{\λ}\right)M(\mathrm{\λ},T_b)+{\mathrm{\β}}_b\left(\mathrm{\λ}\right)M(\mathrm{\λ},T_b)]+[1-{\mathrm{\τ}}_a(\mathrm{\λ},R)\left]M(\mathrm{\λ},T_a)\right\}\mathrm{d\λ}---\left(1\right)$

Wherein, λ is a wavelength, and R is a detection range, T _bBe background surface true temperature, T _aBe atmospheric temperature in the environment, (λ R) is the spectral transmittance of atmosphere, ε to τ a _b(λ) be the emissivity of background surface, β _b(λ) be the reflectivity of background surface, M (λ, T _b) the expression temperature is T _bThe radiant exitance of black matrix.

Because detection range less than 20 meters, is ignored the attenuation effect of atmosphere; Suppose that background is a grey body, the background reflectance rate is less, ignores the volume reflection of background.Then formula (1) is reduced to

$E_b={\∫}_{{\mathrm{\λ}}_0}{\mathrm{\ϵ}}_b\left(\mathrm{\λ}\right)M(\mathrm{\λ},T_b)\mathrm{d\λ}={\∫}_{{\mathrm{\λ}}_0}{\mathrm{\ϵ}}_b\·\frac{c_1}{{\mathrm{\λ}}^5}\·\frac{1}{\exp (c_2/\mathrm{\λ}{T}_b)-1}\mathrm{d\λ}---\left(2\right)$

With the background surface temperature of actual measurement gained with search in the background surface emissivity substitution formula (2) of data gained, and then obtain the radiant exitance E of background _b

Step b. calculates the equivalent blackbody temperature T of background _Bb

By Planck law, E _bCan direct representation do

$E_b={\∫}_{{\mathrm{\λ}}_0}\frac{c_1}{{\mathrm{\λ}}^5}\·\frac{1}{\exp (c_2/\mathrm{\λ}{T}_{\mathrm{bb}})-1}\mathrm{d\λ}---\left(3\right)$

T wherein _BbEquivalent blackbody temperature for background.

Simultaneous formula (2) (3) can calculate the equivalent blackbody temperature T of background _Bb

Step c is calculated to be the radiant exitance E of the picture detection of a target _p

Strong absorption background radiation when gas leaks, absorption process is followed Bill's lambert's law, the imaging detection target through the gas cloud cluster infrared radiation degree is absorbed and atmospheric attenuation after radiant exitance be expressed as

$E_p={\∫}_{{\mathrm{\λ}}_0}\left\{\begin{array}{c}{\mathrm{\τ}}_a(\mathrm{\λ},R)\left[{\mathrm{\τ}}_g\left(\mathrm{\λ}\right)\right[{\mathrm{\ϵ}}_b\left(\mathrm{\λ}\right)M(\mathrm{\λ},T_b)+{\mathrm{\β}}_b\left(\mathrm{\λ}\right)M(\mathrm{\λ},T_b)]+(1-{\mathrm{\τ}}_g\left(\mathrm{\λ}\right))M(\mathrm{\λ},T_p)]\\ +[1-{\mathrm{\τ}}_a(\mathrm{\λ},R)]M(\mathrm{\λ},T_a)\end{array}\right\}\mathrm{d\λ}---\left(4\right)$

T _pBe the temperature of gas to be measured, τ _g(λ) be the spectral transmittance of gas to be measured, the physical significance of all the other each parameter representatives is identical with the parameter among the step a.Same because detection range is very near, ignore the attenuation effect of atmosphere; The background reflectance rate is less, ignores the volume reflection of background.Then formula (4) is reduced to

$E_p={\∫}_{{\mathrm{\λ}}_0}[{\mathrm{\τ}}_g\left(\mathrm{\λ}\right)\·{\mathrm{\ϵ}}_b\left(\mathrm{\λ}\right)M(\mathrm{\λ},T_b)+(1-{\mathrm{\τ}}_g\left(\mathrm{\λ}\right))M(\mathrm{\λ},T_p)]\mathrm{d\λ}---\left(5\right)$

Wherein, $M(\mathrm{\λ},T_P)=\frac{c_1/{\mathrm{\λ}}^5}{\mathrm{Exp}(c_2/\mathrm{\λ}{T}_p)-1},M(\mathrm{\λ},T_b)=\frac{c_1/{\mathrm{\λ}}^5}{\mathrm{Exp}(c_2/\mathrm{\λ}{T}_b)-1}\mathrm{D\λ},$ τ _g(λ)=exp [α _g(λ) lc], α _g(λ) be the spectral absorptance of gas, c is a gas concentration, and l is the gas absorption path.

With the temperature and the emissivity of background surface, in the spectral absorptance of gas, gas concentration and the gas absorption path substitution formula (5), just can obtain the radiant exitance E of imaging detection target _pIn practical application, the background emission rate can be tabled look-up according to different backgrounds and drawn; The background surface temperature can measure; Gas infrared absorption coefficient in the gas parameter can obtain in the infrared absorption spectrum storehouse; Gas temperature can measure; Gas concentration calculates according to a certain estimation model with the absorption path.It is r=0.1m that the space distribution of leaking the gas that comes out is approximately a bottom surface radius, and height is the cone of h=0.3m, and then gas absorption path l is approximately the bottom surface radius of cone; Gas concentration is that leakage flow multiply by the infrared imaging system time shutter again divided by the cone volume, and computing formula is:

$c_p=\frac{R\·t}{V}$

Wherein R representes the gas leak rate; T representes the time shutter of infrared system, and V representes the volume of cone.Steps d. be calculated to be the equivalent blackbody temperature T of the picture detection of a target _t

By Planck law, the radiant exitance E of target _pCan direct representation do

$E_p={\∫}_{{\mathrm{\λ}}_0}\frac{c_1}{{\mathrm{\λ}}^5}\·\frac{1}{\exp (c_2/\mathrm{\λ}{T}_t)-1}\mathrm{d\λ}---\left(6\right)$

T wherein _tEquivalent blackbody temperature for target.

Simultaneous formula (5) (6) can calculate under certain gas leakage flow the equivalent blackbody temperature Tt of target.

Step e. is calculated to be the equivalent black matrix temperature difference GEBTD of the picture detection of a target and background;

The absolute value of the difference of imaging detection target and background equivalence blackbody temperature is gas equivalence black matrix temperature difference GEBTD.GEBTD is expressed as:

GEBTD＝|T _t-T _bb| (7)

Step f. confirms the minimum detectable concentration of gas cloud cluster imaging;

Noise equivalent temperature difference NETD is meant when the ratio of system's output voltage and noise voltage is 1 (being that system signal noise ratio is 1), the temperature difference of black matrix target and background.So infrared imaging system is surveyed required condition for when the temperature difference of black matrix target and background during greater than NETD, can form images to the gas cloud cluster.At present, all provided the numerical value of NETD in the performance index of most infrared imaging systems,, when GEBTD equals NETD, obtained the minimum detectable concentration of gas so compare with the GEBTD value of gained among the step e and the NETD value of infrared imaging system; When GEBTD less than NETD, show infrared eye can't imaging detection the gas flow of this moment, need to improve gas flow and recomputate step c to e, be approximately equal to NETD up to GEBTD; If GEBTD is greater than NETD, but show the quantity of gas leakage that the infrared eye imaging detection is littler, reduce gas flow, recomputate step c to e, be approximately equal to NETD up to GEBTD.

Above-described specific descriptions; Purpose, technical scheme and beneficial effect to invention have carried out further explain, and institute it should be understood that the above is merely specific embodiment of the present invention; And be not used in qualification protection scope of the present invention; All within spirit of the present invention and principle, any modification of being made, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (6)

1. a gas leaks infrared imaging detection Calculation of Limit method, it is characterized in that, comprises the steps:

The first step: the background radiation emittance when calculating no gas and leaking, and with it as imaging detection background radiation emittance E _b

Second step: by imaging detection background radiation emittance E _bCalculate imaging detection background equivalence blackbody temperature T _Bb

The 3rd step: when gas leaks, calculate the radiant exitance of background radiation after gas absorption, be imaging detection target emanation emittance E according to the gas parameter in the imaging detection background radiation emittance _p

The 4th step: by imaging detection target emanation emittance E _pBe calculated to be picture detection of a target equivalence blackbody temperature T _t

The 5th step: the absolute value of second step and the difference of the 4th imaging detection background that calculate of step and target Equivalent blackbody temperature is defined as the equivalent black matrix temperature difference of gas GEBTD;

The 6th step: the combination property parameter-noise equivalent temperature difference NETD of comparison gas equivalence black matrix temperature difference GEBTD and infrared eye and optical system, confirm gas leak detection ultimate value, i.e. the minimum flow of gas leakage.

2. a kind of gas as claimed in claim 1 leaks infrared imaging detection Calculation of Limit method, it is characterized in that, the described background radiation emittance of the above-mentioned first step is through calculating context parameter substitution planck formula; Context parameter is background emission rate and background surface temperature; The background emission rate determines according to background material; The background surface temperature is through measuring.

3. a kind of gas as claimed in claim 1 leaks infrared imaging detection Calculation of Limit method, it is characterized in that, the equivalent blackbody temperature T of above-mentioned described imaging detection background of second step _BbAdopt following method to calculate: according to Planck law, the radiant quantity E of background _bWith equivalent blackbody temperature T _BbExpression is with the background radiation emittance E in the first step _bBring the Planck law formula into, obtain the equivalent blackbody temperature T of background _Bb

4. leak infrared imaging detection Calculation of Limit method like claim 1 or 2 or 3 described a kind of gases, it is characterized in that, described imaging detection target emanation emittance E of above-mentioned the 3rd step _pAdopt following method to calculate: with the background radiation emittance E in the first step _bAnd gas leakage cloud cluster parameter substitution Bill lambert's law formula, calculate background radiation remaining radiant exitance after gas absorption, i.e. target emanation emittance E _pWherein gas cloud cluster parameter comprises: gas concentration, gas temperature, gas absorption path, gas infrared absorption coefficient, and gas infrared absorption coefficient obtains in the infrared absorption spectrum storehouse; Gas temperature is according to measuring; Gas flow is set at certain initial value; Gas concentration and absorption path root Model Calculation according to estimates draw: the flow of setting the gas leakage is certain initial value; It is 0.1m that the space distribution of leaking the gas that comes out is approximately a bottom surface radius; Height is the cone of 0.3m, and then the gas absorption path proximity is the bottom surface radius of cone; Gas concentration is that leakage flow multiply by the infrared imaging system time shutter again divided by the cone volume.

5. leak infrared imaging detection Calculation of Limit method like claim 1 or 2 or 3 described a kind of gases, it is characterized in that the imaging detection target Equivalent blackbody temperature T in above-mentioned the 4th step _tAdopt following method to calculate: according to Planck law, the radiant exitance M of target _tWith equivalent blackbody temperature T _tExpression is with the radiant quantity E of the imaging detection target in the 3rd step _pBring the Planck law formula into, obtain the equivalent blackbody temperature T of target _t

6. leak infrared imaging detection Calculation of Limit method like claim 1 or 2 or 3 described a kind of gases; It is characterized in that; Confirm that gas leak detection ultimate value adopts following method in above-mentioned the 6th step: compare GEBTD and NETD; If the two equates or approximately equal that the gas stream value of this moment is gas leak detection ultimate value so; If GEBTD is less than NETD; Show infrared eye can't imaging detection the gas flow of this moment; Then improve gas flow recomputate the 3rd the step to the 5th step, if GEBTD greater than NETD, but show the quantity of gas leakage that the infrared eye imaging detection is littler; Reduce gas flow, recomputated for the 3rd step to the 5th step.

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