CN102967444A - Measuring and self-calibration method for xenon lamp light source - Google Patents

Abstract

The invention discloses a measuring and self-calibration method for a xenon lamp light source. The measuring and self-calibration method comprises (1) measuring a new light pipe of a xenon lamp, obtaining a spectrogram, a total irradiation amount and irradiation intensity of a characteristic wavelength section of the new light pipe, and simultaneously calibrating a xenon lamp measuring system; (2) when the xenon lamp light pipe works for a period of time and needs measuring and calibration, adopting a measuring method which is the same as the step (1) to measure the xenon lamp light pipe working for a period of time, obtaining a spectrogram, a total irradiation amount and irradiation intensity at the position of the characteristic wavelength section of the xenon lamp light pipe, comparing the spectrograms and the irradiation intensity at the position of the characteristic wavelength section of the new xenon lamp light pipe and the xenon lamp light pipe working for a period of time, and obtaining attenuation conditions of the xenon lamp light pipe; and (3) analyzing consistency of the spectrograms of the new light pipe and the light pipe working for a period of time so as to determine whether to adjust power of the xenon lamp or replace a new light pipe. According to the method, the aim of self-calibration of the xenon lamp is achieved through a spectrum technology.

Description

A kind of measurement of xenon source and method for self-calibrating

Technical field

The present invention relates to a kind of measuring technique of xenon source, specifically refer to a kind of measurement and method for self-calibrating of xenon source.

Background technology

As everyone knows, macromolecular material use or storage process in owing to be subject to the impact of environment, such as light, heat, oxygen, humidity, stress, chemical etching etc., its performance can deteriorated or forfeiture, this phenomenon is known as the aging of macromolecular material.Only affect the key factor of macromolecule material aging.Developed in the world at present the light aging behavior that a series of light aging equipment are studied macromolecular material.The xenon lamp aging chamber is one of research macromolecule material aging behavior accelerated test equipment the most commonly used.The xenon lamp aging chamber is to utilize xenon arc lamp as artificial light sources, macromolecular material is shone the ageing process of simulation macromolecular material in physical environment; By the adjustment of test parameters, realize certain accelerated deterioration effect simultaneously.Measurement, analysis to xenon arc lamp spectrum all are very important to aging behavior, modified test method and the testing equipment of research macromolecular material.

Xenon arc lamp is as artificial light sources, and spectrum and intensity of illumination can change along with the prolongation of test period.When material carries out in the process of light aging test in Xenon weather-ometer, total irradiation intensity of xenon lamp can be decayed gradually along with the prolongation of test period, just need to calibrate the xenon lamp light pipe after reaching certain test period, come the stable of warranty test parameter by the mode of regulating xenon lamp power or changing light pipe.The current calibration steps of xenon lamp mainly is divided into two parts, the one, by the calibration light pipe measuring system of xenon lamp itself is calibrated, namely by the calibration light pipe is measured at the irradiation intensity of the characteristic wavelength section (340nm or 420nm) of standard code, by regulating xenon lamp power, the irradiation intensity of adjustment feature wavelength period reaches standard-required; Optical correction is carried out to the xenon lamp light pipe exactly in second aspect.

At present, China there is no producer can produce the calibration light pipe, therefore if realization to the first step of xenon lamp calibration, needs to buy the measuring system that external calibration light pipe is calibrated xenon lamp.China does not also carry out the unified standard of optical correction at present to the xenon lamp light pipe, optical correction can be carried out to the xenon lamp light pipe in the domestic laboratory that there is no at present.Finish the second step of xenon lamp calibration, then need to entrust laboratory overseas to finish, not only whole calibration cycle is long, and the calibration expense is also very expensive.In addition, at present external calibration laboratory needs the proprietary equipment of a cover when the xenon lamp light pipe is carried out optical correction, and this complete equipment China does not produce, and needs import.In sum, the xenon lamp collimation technique of China is limited by abroad always.

In addition, along with increasing research is found, the spectrum of xenon lamp has important impact to the ageing process impact of macromolecular material.Therefore understand the situation of change of xenon lamp light pipe spectrum in the process of the test, keep relatively stable also being very important of xenon lamp light pipe spectrum in the process of the test.

In order to shorten the calibration flow process, reduce the calibration cost, analyse in depth the agine mechaism of macromolecular material, develop a kind of simple xenon lamp method for self-calibrating and just seem very necessary.

Summary of the invention

The measurement and the method for self-calibrating that the purpose of this invention is to provide a kind of xenon source, the method is by using spectrometer and with the optical fiber of cosine corrector the spectrum of light pipe before and after the xenon lamp use being measured, relatively the irradiation intensity of both spectrum and characteristic wavelength is judged the attenuation of light pipe, consistance by judging spectrogram and by regulating the power of xenon lamp is increased to the irradiation intensity of light pipe to satisfy standard-required to reach and finishes the self-alignment purpose of xenon lamp.

Above-mentioned purpose of the present invention realizes by the following technical solutions: a kind of measurement of xenon source and method for self-calibrating, the method comprises the steps:

(1) the new light pipe of xenon lamp is measured, obtain the irradiation intensity of the spectrogram of new light pipe, total irradiation and characteristic wavelength section, described characteristic wavelength section refers to the xenon lamp characteristic wavelength of international standard regulation, be 340nm or 420nm, to measure simultaneously the irradiation intensity of characteristic wavelength section of gained and the irradiation intensity data of the characteristic wavelength section that the xenon lamp instrument panel shows compares, accurately whether can determine data that instrument shows, thereby the measuring system of xenon lamp is calibrated;

(2) after doing a period of time, the xenon lamp plumber needs to measure and when calibrating, adopt the measuring method identical with step (1) that the xenon lamp light pipe of a period of time of having worked is measured, obtain the spectrogram of this xenon lamp light pipe, the irradiation intensity of total irradiation and characteristic wave long section position, compare the new light pipe of xenon lamp and total irradiation of the xenon lamp light pipe of work a period of time and the irradiation intensity of characteristic wave long section position, when the xenon lamp light pipe is reduced to new light pipe at below 90% of irradiation intensity of characteristic wavelength section at the irradiation intensity of characteristic wavelength section, perhaps total irradiation of xenon lamp light pipe is reduced to 90% when following of total irradiation of new light pipe, think that the irradiation of xenon lamp light pipe has decay, namely needs xenon lamp is calibrated.

Be formulated and be:

$\frac{{\mathrm{Ee}}_{\mathrm{\&lambda;}=340}}{{\mathrm{Ee}}_{\mathrm{\&lambda;}=340}^0}\&times;100\%<90\%$ ①

Perhaps:

$\frac{{\mathrm{Ee}}_{\mathrm{\&lambda;}=420}}{{\mathrm{Ee}}_{\mathrm{\&lambda;}=420}^0}\&times;100\%<90\%$ ②

Also or:

$\frac{\mathrm{Ee}}{{\mathrm{Ee}}^0}\&times;100\%<90\%$ ③

In the formula:

Ee _λ=340---used the light pipe of a period of time at the irradiation intensity at 340nm wavelength period place, the W/m of unit ²

Ee _λ=420---used the light pipe of a period of time at the irradiation intensity at 420nm wavelength period place, the W/m of unit ²

---new light pipe is at the irradiation intensity at 340nm wavelength period place, the W/m of unit ²

---new light pipe is at the irradiation intensity at 420nm wavelength period place, the W/m of unit ²

He---used total irradiation of the light pipe measurement gained of a period of time, the J/m of unit ²

He ⁰---new light pipe is measured total irradiation of gained, the J/m of unit ²

Among the present invention, the concrete grammar of in the described step (1) the new light pipe of xenon lamp being measured employing is: use fiber spectrometer and with the optical fiber of cosine corrector, after the new light pipe of xenon lamp vertically installs, the light sensor that fibre-optical probe and xenon lamp carry all is positioned at the xenon lamp cavity inner wall, and be in the same level position, by optical fiber and fiber spectrometer the new light pipe of xenon lamp is measured, the data communication device of the light sensor collection that the while xenon lamp carries is crossed the xenon lamp instrument and is shown.

As a further improvement on the present invention, the method also comprises the steps:

(3) consistance of the spectrogram of the new light pipe of analysis and the light pipe of work a period of time.When the similarity of 95% spectral intensity data of new light pipe and the light pipe of a period of time of having worked reaches 95% when above, think that namely both have reached consistent.

That is: $\frac{{\mathrm{Ee}}_{\mathrm{\&lambda;}}/\mathrm{He}}{{\mathrm{Ee}}_{\mathrm{\&lambda;}}^0/{\mathrm{He}}^0}\&times;100\%>95\%$ ④

In the formula:

Ee _λ---used the light pipe of a period of time at the irradiation intensity at a certain wavelength period place, the W/m of unit ²

---new light pipe is at the irradiation intensity at Same Wavelength section place, the W/m of unit ²

He---used total irradiation of the light pipe measurement gained of a period of time, the J/m of unit ²

He ⁰---new light pipe is measured total irradiation of gained, the J/m of unit ²

(4) if the two spectrogram is consistent, be total irradiation variant (with reference to formula 3.), can by regulating the power of xenon lamp, the light pipe irradiation be increased.When the light pipe of a period of time of having worked is increased to unanimously at the irradiation intensity of same characteristic wavelength section with new light pipe at the irradiation intensity of characteristic wavelength section, namely finished the self calibration to the xenon lamp light pipe.

(5) if 95% spectral intensity data of the light pipe of a period of time of having worked do not reach consistent with the spectral intensity data of new light pipe, and also can not make the two irradiation intensity in the characteristic wavelength section reach consistent by power adjustments, then light pipe has reached mission life, the light pipe that need to more renew.

That is: $\frac{{\mathrm{Ee}}_{\mathrm{\&lambda;}}/\mathrm{He}}{{\mathrm{Ee}}_{\mathrm{\&lambda;}}^0/{\mathrm{He}}^0}\&times;100\%>95\%$

In the formula:

Ee _λ---used the light pipe of a period of time at the irradiation intensity at a certain wavelength period place, the W/m of unit ²

---new light pipe is at the irradiation intensity at Same Wavelength section place, the W/m of unit ²

He---used total irradiation of the light pipe measurement gained of a period of time, the J/m of unit ²

He ⁰---new light pipe is measured total irradiation of gained, the J/m of unit ²

Method of the present invention needs to adopt standard sources that whole measuring system is calibrated before each spectral measurement before use, guarantees the accuracy of measuring.

At present general calibration steps is that irradiation intensity according to the characteristic wave strong point that shows on the xenon lamp panel carries out measurement and calibration, and this kind calibration steps is accurate not.And this method is to calibrate according to the total irradiation of spectrogram, light pipe of light pipe itself and the irradiation intensity of special wavelength section, can not be subject to the impact of xenon lamp structure itself, so calibration steps is more accurate.Compared with prior art, the present invention has following remarkable result:

(1) foundation of this xenon source Measurement and calibration is the irradiation intensity of the spectrogram of light pipe itself, total irradiation and special wavelength section (340nm or 420nm), and this will be so that calibration be more accurate.

(2) xenon lamp light pipe behaviour worker light source, the stability of himself spectrum better, this has just guaranteed that the spectrogram reappearance that measures is better, has also avoided the impact of human factor simultaneously, thereby can guarantee the accuracy of calibration result.

(3) can calibrate xenon lamp in working order, needn't under specific calibration procedure, carry out, simplify the calibration flow process.With new light pipe calibration measurement system, can not use the calibration light pipe, provide cost savings.

(4) fibre ribbon that uses has the cosine corrector, and the scope that makes the radiation (light) that optical fiber collects is consistent with the interior light sensor of xenon lamp, has guaranteed the comparability of measurement result.

(5) fibre-optical probe is in same equivalent position with light sensor in the xenon lamp, this irradiation that special wavelength section (340nm or 420nm) of spectrometer measurement is located has comparability with the data that show on the instrument panel, thereby can calibrate the optical measuring system of xenon lamp itself.

(6) before the measurement, use the standard energy lamp that whole measuring system is calibrated, guaranteed that the benchmark of each measurement result is consistent, namely guaranteed reappearance and the comparability of measurement result.

Description of drawings

The present invention is described in further detail below in conjunction with the drawings and specific embodiments.

Fig. 1 is the spectrogram that adopts the new light pipe that method of the present invention measures;

Fig. 2 is the spectrogram of light pipe a period of time of after that adopted use that method of the present invention measures;

Fig. 3 be Fig. 1 and Fig. 2 in conjunction with figure, the attenuation of light pipe spectrum is compared, wherein, the spectrogram of new light pipe up, the spectrogram that has used light pipe a period of time of after below.

Embodiment

The measurement of a kind of xenon source of the present invention and method for self-calibrating are before use, according to the calibration needs, after whole measuring system connected, the Application standard energy lamp was calibrated whole measuring system, the benchmark of guaranteeing each measurement result is consistent, and this measurement and method for self-calibrating comprise the steps:

(1) use measuring system that the new light pipe of xenon lamp is measured, the concrete grammar of the new light pipe of xenon lamp being measured employing is: use fiber spectrometer and with the optical fiber of cosine corrector, after the new light pipe of xenon lamp vertically installs, the light sensor that fibre-optical probe and xenon lamp carry all is positioned at the xenon lamp cavity inner wall, and be in the same level position, by optical fiber and fiber spectrometer the new light pipe of xenon lamp is measured, the data communication device of the light sensor collection that the while xenon lamp carries is crossed the xenon lamp instrument and is shown.Can directly record the irradiation intensity of the spectrogram of new light pipe, total irradiation and characteristic wavelength section by optical fiber and fiber spectrometer, wherein, the spectrogram of new light pipe as shown in Figure 1, total irradiation intensity of light pipe is that fiber spectrometer calculates automatically by integration, directly is presented in the measurement result.Described characteristic wavelength section refers to the xenon lamp characteristic wavelength of international standard regulation, be 340nm or 420nm, to measure simultaneously the irradiation intensity of characteristic wavelength section of gained and the irradiation intensity data of the characteristic wavelength section that the xenon lamp instrument panel shows compares, accurately whether can determine data that instrument shows, thereby the measuring system of xenon lamp is calibrated;

(2) after doing a period of time, the xenon lamp plumber needs to measure and when calibrating, adopt the measuring method identical with step (1) that the xenon lamp light pipe of a period of time of having worked is measured, obtain the irradiation intensity of the spectrogram of this xenon lamp light pipe, total irradiation and characteristic wave long section position, spectrogram as shown in Figure 2.Compare the new light pipe of xenon lamp and total irradiation of the xenon lamp light pipe of work a period of time and the irradiation intensity of characteristic wave long section position, such as Fig. 3.When the xenon lamp light pipe is reduced to new light pipe at below 90% of irradiation intensity of characteristic wavelength section at the irradiation intensity of characteristic wavelength section, perhaps total irradiation of xenon lamp light pipe is reduced to 90% when following of total irradiation of new light pipe, think that the irradiation of xenon lamp light pipe has decay, namely needs xenon lamp is calibrated.

That is:

$\frac{{\mathrm{Ee}}_{\mathrm{\&lambda;}=340}}{{\mathrm{Ee}}_{\mathrm{\&lambda;}=340}^0}\&times;100\%<90\%$ ①

Perhaps:

$\frac{{\mathrm{Ee}}_{\mathrm{\&lambda;}=420}}{{\mathrm{Ee}}_{\mathrm{\&lambda;}=420}^0}\&times;100\%<90\%$ ②

Also or:

$\frac{\mathrm{<figure-callout\; id="0"\; label="Ee\; Ee"\; filenames="HDA00002376072300012.png,HDA00002376072300021.png"\; state="\{\{state\}\}">Ee</figure-callout>}}{{\mathrm{Ee}}^{}}\&times;100\%<90\%$ ③

In the formula:

Ee _λ=340---used the light pipe of a period of time at the irradiation intensity at 340nm wavelength period place, the W/m of unit ²

Ee _λ=420---used the light pipe of a period of time at the irradiation intensity at 420nm wavelength period place, the W/m of unit ²

---new light pipe is at the irradiation intensity at 340nm wavelength period place, the W/m of unit ²

---new light pipe is at the irradiation intensity at 420nm wavelength period place, the W/m of unit ²

He---used total irradiation of the light pipe measurement gained of a period of time, the J/m of unit ²

He ⁰---new light pipe is measured total irradiation of gained, the J/m of unit ²

(3) consistance of the spectrogram of the new light pipe of analysis and the light pipe of work a period of time.When the similarity of 95% spectral intensity data of new light pipe and the light pipe of a period of time of having worked reaches 95% when above, think that namely both have reached consistent.That is to say, satisfy formula data 4. and accounted for 95% when above of all measurement data, think that namely both have reached consistent.

That is: $\frac{{\mathrm{Ee}}_{\mathrm{\&lambda;}}/\mathrm{He}}{{\mathrm{Ee}}_{\mathrm{\&lambda;}}^0/{\mathrm{<figure-callout\; id="0"\; label="He"\; filenames="HDA00002376072300012.png,HDA00002376072300021.png"\; state="\{\{state\}\}">He</figure-callout>}}^0}\&times;100\%>95\%$ ④

In the formula:

Ee _λ---used the light pipe of a period of time at the irradiation intensity at a certain wavelength period place, the W/m of unit ²

---new light pipe is at the irradiation intensity at Same Wavelength section place, the W/m of unit ²

He---used total irradiation of the light pipe measurement gained of a period of time, the J/m of unit ²

He ⁰---new light pipe is measured total irradiation of gained, the J/m of unit ²

(4) if the two spectrogram is consistent, be total irradiation variant (with reference to formula 3.), can by regulating the power of xenon lamp, the light pipe irradiation be increased.When the light pipe of a period of time of having worked is increased to unanimously at the irradiation intensity of same characteristic wavelength section with new light pipe at the irradiation intensity of characteristic wavelength section, namely finished the self calibration to the xenon lamp light pipe.

(5) if 95% spectral intensity data of the light pipe of a period of time of having worked do not reach consistent with the spectral intensity data of new light pipe, and also can not make the two irradiation intensity in the characteristic wavelength section reach consistent by power adjustments, then light pipe has reached mission life, the light pipe that need to more renew.

That is: $\frac{{\mathrm{Ee}}_{\mathrm{\&lambda;}}/\mathrm{He}}{{\mathrm{Ee}}_{\mathrm{\&lambda;}}^0/{\mathrm{<figure-callout\; id="0"\; label="He"\; filenames="HDA00002376072300012.png,HDA00002376072300021.png"\; state="\{\{state\}\}">He</figure-callout>}}^0}\&times;100\%>95\%$

In the formula:

Ee _λ---used the light pipe of a period of time at the irradiation intensity at a certain wavelength period place, the W/m of unit ²

---new light pipe is at the irradiation intensity at Same Wavelength section place, the W/m of unit ²

He---used total irradiation of the light pipe measurement gained of a period of time, the J/m of unit ²

He ⁰---new light pipe is measured total irradiation of gained, the J/m of unit ²

The above embodiment of the present invention is not the restriction to protection domain of the present invention; embodiments of the present invention are not limited to this; all this kind is according to foregoing of the present invention; ordinary skill knowledge and customary means according to this area; do not breaking away under the above-mentioned basic fundamental thought of the present invention prerequisite; modification, replacement or the change of other various ways that said structure of the present invention is made all should drop within protection scope of the present invention.

Claims (4)

1. the measurement of an xenon source and method for self-calibrating, the method comprises the steps:

(1) the new light pipe of xenon lamp is measured, obtain the irradiation intensity of the spectrogram of new light pipe, total irradiation and characteristic wavelength section, described characteristic wavelength section refers to the xenon lamp characteristic wavelength of international standard regulation, be 340nm or 420nm, to measure simultaneously the irradiation intensity of characteristic wavelength section of gained and the irradiation intensity data of the characteristic wavelength section that the xenon lamp instrument panel shows compares, accurately whether can determine data that instrument shows, thereby the measuring system of xenon lamp is calibrated;

(2) after doing a period of time, the xenon lamp plumber needs to measure and when calibrating, adopt the measuring method identical with step (1) that the xenon lamp light pipe of a period of time of having worked is measured, obtain the spectrogram of this xenon lamp light pipe, the irradiation intensity of total irradiation and characteristic wave long section position, compare the new light pipe of xenon lamp and total irradiation of the xenon lamp light pipe of work a period of time and the irradiation intensity of characteristic wave long section position, when the xenon lamp light pipe is reduced to new light pipe at below 90% of irradiation intensity of characteristic wavelength section at the irradiation intensity of characteristic wavelength section, perhaps total irradiation of xenon lamp light pipe is reduced to 90% when following of total irradiation of new light pipe, think that the irradiation of xenon lamp light pipe has decay, namely need xenon lamp is calibrated

Be formulated and be:

$\frac{{\mathrm{Ee}}_{\mathrm{\&lambda;}=340}}{{\mathrm{Ee}}_{\mathrm{\&lambda;}=340}^0}\&times;100\%<90\%$ ①

Perhaps:

$\frac{{\mathrm{Ee}}_{\mathrm{\&lambda;}=420}}{{\mathrm{Ee}}_{\mathrm{\&lambda;}=420}^0}\&times;100\%<90\%$ ②

Also or:

$\frac{\mathrm{Ee}}{{\mathrm{Ee}}^0}\&times;100\%<90\%$ ③

In the formula:

Ee _λ=340---used the light pipe of a period of time at the irradiation intensity at 340nm wavelength period place, the W/m of unit ²

Ee _λ=420---used the light pipe of a period of time at the irradiation intensity at 420nm wavelength period place, the W/m of unit ²

---new light pipe is at the irradiation intensity at 340nm wavelength period place, the W/m of unit ²

---new light pipe is at the irradiation intensity at 420nm wavelength period place, the W/m of unit ²

He---used total irradiation of the light pipe measurement gained of a period of time, the J/m of unit ²

He ⁰---new light pipe is measured total irradiation of gained, the J/m of unit ²

2. the measurement of xenon source according to claim 1 and method for self-calibrating, it is characterized in that: the concrete grammar of in the described step (1) the new light pipe of xenon lamp being measured employing is: use fiber spectrometer and with the optical fiber of cosine corrector, after the new light pipe of xenon lamp vertically installs, the light sensor that fibre-optical probe and xenon lamp carry all is positioned at the xenon lamp cavity inner wall, and be in the same level position, by optical fiber and fiber spectrometer the new light pipe of xenon lamp is measured, the data communication device of the light sensor collection that the while xenon lamp carries is crossed the xenon lamp instrument and is shown.

3. the measurement of xenon source according to claim 2 and method for self-calibrating, the method also comprises the steps:

(3) analyze the consistance of the spectrogram of new light pipe and the light pipe of work a period of time, when the similarity of 95% spectral intensity data of new light pipe and the light pipe of a period of time of having worked reaches 95% when above, think that namely both have reached unanimously,

That is: $\frac{{\mathrm{Ee}}_{\mathrm{\&lambda;}}/\mathrm{He}}{{\mathrm{Ee}}_{\mathrm{\&lambda;}}^0/{\mathrm{He}}^0}\&times;100\%>95\%$ ④

In the formula:

Ee _λ---used the light pipe of a period of time at the irradiation intensity at a certain wavelength period place, the W/m of unit ²

---new light pipe is at the irradiation intensity at Same Wavelength section place, the W/m of unit ²

He---used total irradiation of the light pipe measurement gained of a period of time, the J/m of unit ²

He ⁰---new light pipe is measured total irradiation of gained, the J/m of unit ²

(4) if the two spectrogram is consistent, be that total irradiation is variant, with reference to formula 3., by regulating the power of xenon lamp, the light pipe irradiation is increased; When the light pipe of a period of time of having worked is increased to unanimously at the irradiation intensity of same characteristic wavelength section with new light pipe at the irradiation intensity of characteristic wavelength section, namely finished the self calibration to the xenon lamp light pipe;

(5) if 95% spectral intensity data of the light pipe of a period of time of having worked do not reach consistent with the spectral intensity data of new light pipe, and also can not make the two irradiation intensity in the characteristic wavelength section reach consistent by power adjustments, then light pipe has reached mission life, the light pipe that need to more renew;

That is: $\frac{{\mathrm{Ee}}_{\mathrm{\&lambda;}}/\mathrm{He}}{{\mathrm{Ee}}_{\mathrm{\&lambda;}}^0/{\mathrm{He}}^0}\&times;100\%>95\%$

In the formula:

Ee _λ---used the light pipe of a period of time at the irradiation intensity at a certain wavelength period place, the W/m of unit ²

---new light pipe is at the irradiation intensity at Same Wavelength section place, the W/m of unit ²

He---used total irradiation of the light pipe measurement gained of a period of time, the J/m of unit ²

He ⁰---new light pipe is measured total irradiation of gained, the J/m of unit ²

4. according to claim 1 and 2 or the measurement of 3 described xenon sources and method for self-calibrating, it is characterized in that: the method needs to adopt standard sources that whole measuring system is calibrated before each spectral measurement before use, guarantees the accuracy of measuring.

Images