CN105067567A - Method for increasing calibration accuracy by combined use of attenuation slices - Google Patents

Abstract

The invention discloses a method for increasing calibration accuracy by combined use of attenuation slices. As a matter of experiment, in the combined use of multiple attenuation slices, the transmittance is approximately equal to the product of the transmittance of single attenuation slices, but an error exists between the actually measured transmittance and an empirical value. By analyzing with a geometrical optics method, the relative deviation between a theoretical value and the empirical value can be obtained. The transmittance of the combined attenuation slices is measured and can be calibrated by the transmittance of the combined device. Therefore, under the condition that the number of the attenuation slices is limited, by a manner of combined use, more nonlinear inflection points can be obtained, so as to draw a relatively accurate nonlinear correction curve.

Description

A kind of method being combinationally used raising calibration accuracy by attenuator

Technical field

The invention belongs to transmission measurement field, particularly relate to a kind of method being combinationally used raising calibration accuracy by attenuator.

Background technology

The spray that solid dust aggegation is produced made a general reference by smog aerosol and artificial gasoloid, the secondary pollution that oxides of nitrogen or hydrocarbons generate through chemical reaction.Smog light transmission rate is widely used in fire detection, industry environmental protection and military field.

Increasingly strict safety requirements and scientific and technological developing rapidly, make smog light transmission rate method of testing need to enrich constantly, improve.Demarcation before test is through the basis of rate test, is also the basis obtaining accurate transmitance numerical value, is the important step improving test accuracy.In fields such as smog transmission measurements, it is the requisite link of test that transmitance is demarcated, and is also one of most important link affecting measuring accuracy.Usual way uses the monolithic attenuator measured to demarcate, and obtains the corresponding relation node of transmitance and relative light intensity.

Summary of the invention

The invention discloses a kind of method being combinationally used raising calibration accuracy by attenuator.Test macro adopts laser, visible ray, infrared three test channel usually.It is requisite important step in test that transmitance is demarcated, and uses attenuator demarcation to be general reliable way.The present invention is by combinationally using multiple attenuator, and when attenuator quantity is constant, combination obtains how new transmitance, utilizes Geometric Optics Analysis to combine the relative deviation of transmitance theoretical value and the empirical value obtained.Transmitance is demarcated and can be demarcated successively according to laser, order that is infrared, visible ray.In addition, the new transmitance utilizing combination to obtain, carries out demarcating and revises transmitance calibration curve, calibrate, can obtain the transmitance calibration curve that precision is higher.Timing signal, generally choosing transmitance is successively: 1%, the attenuator of 10%, 20%, 30%...90% (actual transmitance is as the criterion with metric results) is placed in light path and demarcates, and detector can adopt photoresistance etc.

Accompanying drawing explanation

Fig. 1 is demarcation light path schematic diagram of the present invention;

Fig. 2 is the transmitted component schematic diagram of single attenuator of the present invention;

Fig. 3 is the single order transmitted component schematic diagram of two attenuators of the present invention;

Fig. 4 is Jing Quan of the present invention coupling schematic diagram;

Fig. 5 is that single attenuator transmitance of the present invention demarcates schematic diagram;

Fig. 6 is the transmitance calibration curve utilizing attenuator combined section interpolation to go out of the present invention;

Fig. 7 is the transmitance matched curve utilizing attenuator to combinationally use acquisition of the present invention.

Embodiment

When attenuator number is determined, in order to obtain more nominal data, the mode that attenuator can be utilized to combine obtains new transmitance.

1. the transmitance empirical value and the theoretical value relative deviation that combine attenuator are analyzed

According to the definition of transmitance, the transmitance of attenuator equals the transmitted light intensity of attenuator and the ratio of incident intensity.

$T=\frac{I_o}{I}---\left(1\right)$

I _ofor transmitted light intensity, I is incident intensity, and T is transmitance.

Rule of thumb, the transmitance T after the combination of N sheet attenuator _eequal each attenuator transmitance long-pending, that is:

$T_e=\underset{i=1}{\overset{N}{\Π}}{T}_i---\left(2\right)$

But consider that the light that exists between attenuator reflects, actual transmitance is not in full conformity with formula (2).Theoretical analysis can be done to the light reflection between attenuator, quantitatively calculate the relative deviation between empirical value and theoretical value.

First analyze single attenuator, when vertical incidence, the reflectivity ρ of attenuator and absorptivity g meets the following conditions:

$\mathrm{\ρ}={\left(\frac{n_2-n_1}{n_2+n_1}\right)}^2---\left(3\right)$

Wherein, n ₁for the refractive index of environment, n ₂for the refractive index of attenuator.

g＝e ^-αL(4)

Wherein, L is the light path in optical attenuation sheet, and α is absorption coefficient.To simplify the analysis, k=α L can be made.If incident intensity is I, τ ₀... τ _tbe 0 to T rank transmitted component.Then the i-th rank transmitted light light intensity component is:

τ _i＝ρ ²ⁱ(1-ρ) ²e ^-(2i+1)kI(5)

Therefore the transmitance T of single attenuator can be expressed as:

$T=\frac{\underset{i=0}{\overset{\mathrm{\∞}}{\Σ}}{\mathrm{\τ}}_i}{I}=\underset{i=0}{\overset{\mathrm{\∞}}{\Σ}}{\mathrm{\ρ}}^{2i}{(1-\mathrm{\ρ})}^2{e}^{-(2i+1)k}---\left(6\right)$

Reduce rapidly because transmitted light intensity raises along with its order, ignore 2 rank and the impact of above order light component thereof, then transmitance can be expressed as:

$T\≈\frac{\underset{i=0}{\overset{1}{\Σ}}{\mathrm{\τ}}_i}{I}=\frac{{(1-\mathrm{\ρ})}^2(e^{2k}+{\mathrm{\ρ}}^2)}{e^{3k}}---\left(7\right)$

The situation that two attenuators combinationally use:

Attenuator X and Y, refractive index is identical, if transmitance is respectively T ₁and T ₂.Can see, the incident direction along light has 4 interfaces, analyzes known: incident light has i-1 at the single order light component that i-th boundary reflection causes.

So when two attenuator combinations, zeroth order and single order transmitted component one have 7, according to transmitance after formula (1) known combination are:

$T=\frac{\underset{i=0}{\overset{6}{\Σ}}{\mathrm{\τ}}_i}{I}=e^{-(k_1+k_2)}{(1-\mathrm{\ρ})}^{4}F---\left(8\right)$

In formula, $F=1+{\mathrm{\ρ}}^2+{\mathrm{\ρ}}^2\mathrm{\[1+(1-}\mathrm{\ρ}{)}^2{\mathrm{\](e}}^{-2k_1}{\mathrm{+e}}^{-2k_2}\mathrm{)+}{\mathrm{\ρ}}^2{(1-\mathrm{\ρ})}^4{e}^{-2\left(k_1+k_2\right)},$ And rule of thumb, the empirical value of transmitance is:

$T_e=T_1{T}_2=e^{-(k_1+k_2)}{(1-\mathrm{\ρ})}^4\underset{i=1}{\overset{2}{\Π}}(1+{\mathrm{\ρ}}^2{e}^{-2k_i})---\left(9\right)$

Transmitance empirical value with the ratio of theoretical value is:

$\frac{T_e}{T}=\frac{\underset{i=1}{\overset{2}{\Π}}(1+{\mathrm{\ρ}}^2{e}^{-2k_i})}{F}=\frac{1+{\mathrm{\ρ}}^2{e}^{-2k_1}+{\mathrm{\ρ}}^2{e}^{-2k_2}+{\mathrm{\ρ}}^4{e}^{-2(k_1+k_2)}}{F}---\left(10\right)$

Because ρ is very little, ignore ρ ⁿ((N>=3)) item, and make (1-ρ) ⁿ=1, can be obtained fom the above equation:

$\frac{T_e}{T}\≈\frac{1+{\mathrm{\ρ}}^2(e^{-2k_1}+e^{-2k_2})}{1+{\mathrm{\ρ}}^2(e^{-2k_1}+e^{-2k_2})+{\mathrm{\ρ}}^2(1+e^{-2k_1}+e^{-2k_2}+e^{-2(k_1+k_2)})}\≤1---\left(11\right)$

From above formula: the transmitance theoretical value reflected after the combination made due to the light between attenuator is larger than empirical value.

Further calculating T _ewith the relative error of T, suppose k ₁=k ₂=k:

$\frac{T-T_e}{T}=\frac{{\mathrm{\ρ}}^2{(1+e^{-2k})}^2}{1+2{\mathrm{\ρ}}^2{e}^{-2k}+{\mathrm{\ρ}}^2{(1+e^{-2k})}^2}=\frac{1}{1+\frac{1+2{\mathrm{\ρ}}^2{e}^{-2k}}{{\mathrm{\ρ}}^2+2{\mathrm{\ρ}}^2{e}^{-2k}+2{\mathrm{\ρ}}^2{e}^{-4k}}}---\left(12\right)$

Formula (12) gives the expression formula of relative deviation, in formula: it can thus be appreciated that attenuator refractive index is larger, ρ is larger, and deviation is larger.

In addition, k=α L, as k → ∞, has:

$\underset{k\→\mathrm{\∞}}{\lim }\frac{1}{1+\frac{1+2{\mathrm{\ρ}}^2{e}^{-2k}}{{\mathrm{\ρ}}^2+2{\mathrm{\ρ}}^2{e}^{-2k}+{\mathrm{\ρ}}^2{e}^{-4k}}}=\frac{1}{1+\frac{1}{{\mathrm{\ρ}}^2}}---\left(13\right)$

That is, along with reduction (increase of the attenuation rate) relative deviation of transmitance tends to a steady state value.

2. attenuator array mode

The neutral filter measured is installed on equal and opposite in direction, and all there is screw thread at two ends, on the Jing Quan that can intercouple together.In addition, one end of Jing Quan can directly be screwed on detector camera lens.

During actual use, generally only need the target transmitance according to combining, the attenuator selecting two panels to measure is installed on Jing Quan, then their couplings is concatenated into together.Consider that relative error increases and the factor such as other uncertain factor increases, general only select two attenuators to be concatenated into together combinationally use mode.Get any two in N number of attenuator, combine, can obtain individual array mode.Before using, generally to the transmitance after two attenuator combinations also be measured.Then be as the criterion with the transmitance after metering and demarcate.

3. use attenuator combination unit carry out demarcating and revise

Monolithic attenuator is used to carry out timing signal, first by measuring the node that can obtain one group of transmitance and light intensity corresponding relation.Then piecewise linear interpolation goes out transmitance calibration curve.Due to the non-linear effects of photoresistance, and the existence of environmental background light (particularly visible light wave range), in addition it is limited that the monolithic attenuator used demarcates the data obtained, the transmitance calibration curve precision obtained is not high, particularly nonlinear inflexion point place, calibration curve is difficult to the variation relation reflecting transmitance and relative light intensity.

In order to improve the precision of transmitance calibration curve, for the place that node is too sparse provides more nominal datas, particularly nonlinear inflexion point place is revised.Use the method for attenuator combination, in a limited number of situation of attenuator, demarcate and obtain more calibrating parameters, then the transmitance calibration curve that makes new advances of piecewise linear interpolation.

In order to analyze the Changing Pattern of transmitance calibration curve further, the transmitance calibration curve gone out with piecewise interpolation contrasts, least square method can be utilized to carry out matching to all parameters using the mode of monolithic attenuator and attenuator combination to obtain further, obtain transmitance matched curve.

Claims (5)

1. one kind combinationally uses the method improving calibration accuracy by attenuator, it is characterized in that, multiple attenuator is combinationally used, new transmitance is not equal to empirical value, namely the transmitance after combination to be not equal to each attenuator transmitance long-pending, attenuator transmitance after combination to be measured before using, actual transmitance value and empirical value approximately equal can be found.

2. method according to claim 1, it is long-pending that the transmitance that multiple attenuator combinationally uses acquisition not exclusively equals each attenuator transmitance, utilize the method for geometrical optics, the transmitance theoretical expression after the combination of multiple attenuator can be calculated, and calculate the relative deviation of empirical value and theoretical value with this.

3. method according to claim 1, is characterized in that, " attenuator combination unit " by by monolithic, measured, attenuator that physical dimension is identical is arranged on " Jing Quan " that can mutually be connected in series, be then mutually connected in series, combine.

4. method according to claim 1, it is characterized in that, before using attenuator combination unit to carry out demarcation test, transmitance metering to be carried out to the attenuator of combination, timing signal is as the criterion with variable, or uses the transmitance empirical value of attenuator combination unit to demarcate when precision allows.

5. method according to claim 1, it is characterized in that, attenuator combination unit is used to carry out timing signal, the target transmitance that combination is obtained afterwards has typicalness, for the feature of the non-linear difference of calibration curve, the target transmitance value after attenuator combines by emphasis is placed in nonlinear inflexion point areas adjacent, demarcates with this, obtain more nonlinear inflexion point parameter, thus draw out more accurate non-liner revision curve.