CN105067567B - A method of it is applied in combination by attenuator and improves calibration accuracy - Google Patents
A method of it is applied in combination by attenuator and improves calibration accuracy Download PDFInfo
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- CN105067567B CN105067567B CN201510557684.XA CN201510557684A CN105067567B CN 105067567 B CN105067567 B CN 105067567B CN 201510557684 A CN201510557684 A CN 201510557684A CN 105067567 B CN105067567 B CN 105067567B
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- 238000000034 method Methods 0.000 title claims abstract description 15
- 238000002834 transmittance Methods 0.000 claims description 65
- 238000011088 calibration curve Methods 0.000 claims description 12
- 238000012360 testing method Methods 0.000 claims description 12
- 230000003287 optical effect Effects 0.000 claims description 5
- 238000010521 absorption reaction Methods 0.000 claims description 4
- 238000012937 correction Methods 0.000 claims description 2
- 238000002310 reflectometry Methods 0.000 claims description 2
- 238000005259 measurement Methods 0.000 abstract description 3
- 230000005540 biological transmission Effects 0.000 description 7
- 238000010586 diagram Methods 0.000 description 3
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 3
- 239000000779 smoke Substances 0.000 description 3
- 239000000443 aerosol Substances 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000004520 agglutination Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000003344 environmental pollutant Substances 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 239000003595 mist Substances 0.000 description 1
- 230000007935 neutral effect Effects 0.000 description 1
- 231100000719 pollutant Toxicity 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
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Abstract
The method for improving calibration accuracy is applied in combination by attenuator the invention discloses a kind of.Rule of thumb: multiple attenuators are applied in combination, and transmitance is approximately equal to the product of single attenuator transmitance, but actual measurement transmitance can and empirical value there are deviations.It is analyzed it using the method for geometric optics, obtains the relative deviation of theoretical value and empirical value.Combined attenuator transmitance is measured, the transmitance of " combination unit " is used to be demarcated.More nonlinear inflexion point parameters can be obtained in the case where attenuator limited amount, by way of being applied in combination in this way, to draw out more accurate non-liner revision curve.
Description
Technical Field
The invention belongs to the field of transmittance testing, and particularly relates to a method for improving calibration accuracy through combined use of attenuation sheets.
Background
Smog aerosol and artificial aerosol generally refer to mist produced by solid dust agglutination, and secondary pollutants generated by chemical reaction of nitrogen oxides or hydrocarbons. The smoke light transmittance is widely applied to the fields of fire detection, industrial environmental protection and military affairs.
The increasingly strict safety requirements and rapid development of technologies make smoke light transmittance testing methods need to be enriched and improved. The calibration before the test is the basis of transmittance test and the basis of obtaining accurate transmittance values, and is an important link for improving the test accuracy. In the fields of smoke transmittance test and the like, transmittance calibration is an essential link for testing and is one of the most important links influencing the testing precision. The common method is to use a measured single attenuation sheet for calibration to obtain a corresponding relation node of transmittance and relative light intensity.
Disclosure of Invention
The invention discloses a method for improving calibration accuracy through combined use of attenuation sheets. The test system usually adopts three test channels of laser, visible light and infrared. The transmittance calibration is an essential important link in the test, and the calibration by using the attenuation sheet is a universal reliable method. According to the invention, a plurality of attenuation sheets are combined for use, more new transmittances are obtained by combination under the condition that the number of the attenuation sheets is not changed, and the relative deviation between the theoretical value and the empirical value of the transmittance obtained by combination is analyzed by using geometrical optics. The transmittance calibration can be performed in sequence according to the sequence of laser, infrared and visible light. In addition, the transmittance calibration curve is corrected and calibrated by calibrating the new transmittance obtained by combination, so that the transmittance calibration curve with higher precision can be obtained. During calibration, the following transmittances are generally selected in sequence: the attenuation sheet with the transmittance of 1%, 10%, 20%, 30%. 90% (the actual transmittance is based on the measurement result) is placed in the light path for calibration, and the detector can adopt a photoresistor and the like.
Drawings
FIG. 1 is a schematic diagram of a calibration optical path of the present invention;
FIG. 2 is a schematic illustration of the transmission component of a single attenuation sheet of the present invention;
FIG. 3 is a schematic diagram of the first order transmission components of two attenuation sheets of the present invention;
FIG. 4 is a schematic view of the coupling of the bezel of the present invention;
FIG. 5 is a schematic diagram of transmittance calibration for a single attenuator of the present invention;
FIG. 6 is a transmittance calibration curve interpolated by attenuator combination segments according to the present invention;
fig. 7 is a transmittance fitting curve obtained by using the attenuation sheet combination of the present invention.
Detailed Description
When the number of attenuation sheets is determined, a new transmittance can be obtained by combining the attenuation sheets in order to obtain more calibration data.
1. Analysis of relative deviation between empirical transmittance value and theoretical transmittance value of combined attenuation sheet
According to the definition of the transmittance, the transmittance of the attenuation sheet is equal to the ratio of the transmitted light intensity to the incident light intensity of the attenuation sheet.
IoThe transmission intensity, I, and T are the incident intensity and transmittance, respectively.
Empirically, the transmittance T of N attenuation sheets combinedeEqual to the product of the transmittance of each attenuation sheet, namely:
however, considering the existence of light reflection between the attenuation sheets, the actual transmittance does not completely satisfy the formula (2). Theoretical analysis can be carried out on the light reflection between the attenuation sheets, and the relative deviation between the empirical value and the theoretical value is calculated quantitatively.
Firstly, analyzing a single attenuation sheet, wherein the reflectivity rho and the absorptivity g of the attenuation sheet meet the following conditions under the condition of vertical incidence:
wherein n is1Is the refractive index of the environment, n2Is the refractive index of the attenuation sheet.
g＝e-αL (4)
Wherein L is in the optical attenuation sheetα is the absorption coefficient for simplicity of analysis, k may be α l, if the incident light intensity is I, τ0...τTFrom 0 to T order transmission components. The light intensity component of the ith-order transmitted light is:
τi＝ρ2i(1-ρ)2e-(2i+1)kI (5)
therefore, the transmittance T of a single attenuator can be expressed as:
since the transmitted light intensity decreases rapidly as its order increases, neglecting the effect of the light components of order 2 and above, the transmittance can be expressed as:
case where two attenuation sheets are used in combination:
the attenuation sheets X and Y have the same refractive index and the respective transmittances of T1And T2. It can be seen that there are 4 interfaces along the incident direction of light, and analysis shows that: there are i-1 first order light components caused by the reflection of incident light at the ith interface.
Therefore, when two attenuation sheets are combined, the transmission rate after the combination is known as follows according to the formula (1), wherein the transmission rate of the zero order and the first order transmission components is 7:
in the formula,according to experience, throughEmpirical values of rate are:
the ratio of the empirical transmittance to the theoretical value is:
neglecting ρ because ρ is smallN(N.gtoreq.3)) and (1-p)N1, obtainable from the above formula:
the formula shows that: the combined transmittance theoretical value is larger than the empirical value due to light reflection between the attenuation sheets.
Further calculate TeRelative error from T, let k1＝k2＝k：
Equation (12) gives an expression for the relative deviation, where:from this, it is understood that the larger the refractive index of the attenuation sheet, the larger ρ is, and the larger the deviation is.
Further, k is α L, and when k → ∞, there are:
that is, the relative deviation tends to a constant value as the transmittance decreases (the attenuation rate increases).
2. Attenuation sheet combination mode
The measured neutral attenuation pieces are arranged on lens rings which have the same size and are provided with threads at two ends and can be mutually coupled together. In addition, one end of the lens ring can be directly screwed on the detector lens.
In practical use, two measured attenuation pieces are generally selected to be mounted on the lens ring according to the target transmittance to be combined, and then are coupled and connected together in series. Considering the factors of increasing relative error and other uncertain factors, only a combination mode of connecting two attenuation sheets together in series is generally selected. Any two of the N attenuation sheets are combined together to obtain the productAnd (4) a combination mode. Before use, the transmittance of the two attenuation sheets combined is also generally measured. And then calibrating by taking the measured transmittance as a standard.
3. Calibration and correction using attenuator combination
When the single attenuation sheet is used for calibration, a group of nodes of the corresponding relation between the transmittance and the light intensity can be obtained through measurement. And then, carrying out piecewise linear interpolation to obtain a transmittance calibration curve. Due to the nonlinear influence of the photoresistor and the existence of ambient background light (especially visible light wave band), and the data obtained by the calibration of the single attenuation sheet, the obtained transmittance calibration curve has low precision, and particularly at the nonlinear inflection point, the calibration curve hardly reflects the change relationship between the transmittance and the relative light intensity.
In order to improve the precision of the transmittance calibration curve, more calibration data are provided for the places where the nodes are too sparse, and particularly, the nonlinear inflection points are corrected. By using the attenuation sheet combination method, under the condition that the number of attenuation sheets is limited, more calibration parameters are obtained by calibration, and then a new transmittance calibration curve is obtained by piecewise linear interpolation.
In order to further analyze the change rule of the transmittance calibration curve, the transmittance calibration curve is compared with the transmittance calibration curve obtained by segmented interpolation, and all parameters obtained by using a mode of combining a single attenuation sheet and an attenuation sheet can be further fitted by using a least square method to obtain a transmittance fitting curve.
Claims (5)
1. A method for improving calibration accuracy through attenuation sheet combination is characterized in that a plurality of attenuation sheets are combined for use, new transmittance is not completely equal to an empirical value, namely the transmittance after combination is not equal to the product of the transmittances of the attenuation sheets, the transmittance after combination is measured before use, and the actual transmittance value is approximately equal to the empirical value;
wherein, the ratio of the transmittance empirical value to the theoretical value is:
wherein,
wherein Te is an empirical transmittance value of the attenuation sheet, T is a theoretical transmittance value of the attenuation sheet, and rho is the reflectivity of the attenuation sheet;
where L is the optical path length in the attenuation sheet and α is the absorption coefficient, for the sake of simplicity, k may be α L, and since a plurality of attenuation sheets are used in combination, 2 attenuation sheets are used, k1 is the product of the optical path length and the absorption coefficient of the first attenuation sheet, and k2 is the product of the optical path length and the absorption coefficient of the second attenuation sheet.
2. The method of claim 1, wherein the transmittance obtained by combining the plurality of attenuation sheets is not completely equal to the product of the transmittances of the attenuation sheets, and the theoretical expression of the transmittance obtained by combining the plurality of attenuation sheets can be calculated by geometric optics, so as to calculate the relative deviation between the empirical value and the theoretical value.
3. The method of claim 1, wherein the "attenuator assembly" is assembled by mounting a single, metered, geometrically identical attenuator pad on "mirror rings" that can be connected in series with each other, and then connecting in series with each other.
4. The method of claim 3, wherein the transmittance of the combined attenuator sheets is measured before the calibration test using the attenuator sheet assembly, and the calibration is performed based on the measured transmittance or, if the accuracy allows, using the transmittance empirical value of the attenuator sheet assembly.
5. The method as claimed in claim 3, wherein when the attenuation sheet combination device is used for calibration, the target transmittance obtained after combination is made to have typicality, and aiming at the characteristic of poor nonlinearity of the calibration curve, the target transmittance value obtained after attenuation sheet combination is placed near the nonlinear inflection point region, so as to obtain more nonlinear inflection point parameters through calibration, and accordingly, a more accurate nonlinear correction curve is drawn.
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| CN114486654A (en) * | 2021-12-29 | 2022-05-13 | 聚光科技(杭州)股份有限公司 | Dust meter and working method thereof |
| CN115015184A (en) * | 2022-07-07 | 2022-09-06 | 中国烟草总公司郑州烟草研究院 | Light transmission method aerosol concentration detection calibration system, calibration method and measurement method |
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