KR101619154B1 - In situ type gas measuring device using tunable laser diode - Google Patents

Abstract

The present invention relates to an in situ gas measuring device using a tunable laser diode which replaces a function corresponding to an optical distribution role with an optical fiber coupler, and uses a small gas cell filled with gas as a method to define a reference wavelength for a wavelength change of a light source (a tunable laser diode) by an intensity of light absorption for standard gas and a change in a surrounding environment. According to an embodiment of the present invention, the in situ gas measuring device using a tunable laser diode comprises: a tunable laser diode to emit light of a tunable wavelength within a prescribed range; a light separation means to separate the light emitted from the tunable laser diode into a first optical path and a second optical path; a gas measuring cell to receive the light through the first optical path to allow gas to pass therethrough; a reference cell to receive the light through the second optical path to compare an intensity of light absorption into the first optical path, and an intensity of light absorption into the second optical path in case of a reference wavelength when measuring gas; and a comparator to output a difference value between the intensity of light absorption into the first optical path and the intensity of light absorption into the second optical path.

Description

TECHNICAL FIELD [0001] The present invention relates to an in situ type gas measuring device using a tunable laser diode,

The present invention relates to an in-situ gas measuring apparatus using a variable-type laser diode, and more particularly, to an analyzer using an in-situ sample extraction method for measuring and analyzing an exhaust gas passing through an industrial stack duct, To an apparatus for analyzing gas utilizing the gas.

The matters described in the background section are intended to enhance the understanding of the background of the invention and may include matters not previously known to those skilled in the art.

In the case of a continuous analyzer for the emission of hazardous gases in industrial stack ducts, quantitative and qualitative analysis with the emission gas to be measured is performed using optical principles. At this time, the method of directly analyzing the measurement sample (gas) without processing in the field is in situ.

All samples (gases) exhibit inherent properties in contact with light. That is, when light such as infrared rays or ultraviolet rays is incident on a gas, a part of a specific wavelength is absorbed or fluoresced by molecules of a gas component. At this time, the concentration of the gas is measured using the characteristic of the absorption.

The optical gas concentration measurement method basically follows the Beer Lambert law. That is, the degree of change in the intensity of the incident light and the intensity of the transmitted light passing through the gas is a relational expression that can define the gas concentration. At this time, the gas may show characteristics depending on the wavelength of light, that is, intensity of the transmitted light according to the wavelength of the gas component is distinguished.

Each measurement gas exhibits absorption characteristics at a specific wavelength. This principle is used to classify the components of the gas. Lamps, lasers, LEDs and the like can be used as the light source. If most of the infrared light sources are used, it can be said that the measurement is possible for the components having the light absorption characteristics within the wavelength range where the light source is emitted. In this case, a method of separating the lamp light source by wavelength and entering the sample gas may be used, or a method of analyzing the light passing through the sample and comparing the intensities of light by the wavelengths of the light before and after the incident light may be used.

When the wavelength of the light source has a predetermined range, the kind and concentration of the gas can be estimated by comparing the intensity of the wavelength with the before and after. Xenon (Xe), black body, or deuterium are mainly used for the lamps using infrared and ultraviolet light sources. Ultimately, the light source to be measured must have a spectroscopic structure before and after the mixed sample, . At this time, many narrow-band optical filters and spectrometers are used. When an optical filter is used, it can be a non dispersive infrared (NDIR) or a non dispersive ultraviolet (NDUV) system. Differential optical absorption spectroscopy (DOAS) It can be said that the spectrometer is used.

On the other hand, due to the nature of the in-situ equipment, it must be operated in a state exposed to external harsh environments, and mechanical vibrations, heat, humidity, and dust are transmitted to the inside, which can affect the measurement signals. It is necessary.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the problems of the prior art described above, and it is an object of the present invention to provide an optical fiber coupler in which a function corresponding to the optical distributing function is replaced by an optical fiber coupler, A tunable diode laser (TDL: tunable diode laser), and a method for defining a reference wavelength of a wavelength change, which is capable of using a small gas cell filled with a gas. That is, since the present invention must operate in a state exposed to external harsh environments due to the nature of the in situ apparatus, mechanical vibrations, heat, humidity, and dust may be transmitted to the inside to affect the measurement signals. The present invention provides an in-situ gas measuring apparatus.

The apparatus for measuring an in-situ gas using a variable-type laser diode according to an embodiment of the present invention includes: a variable-type diode laser that emits light of a variable wavelength within a set range; Optical separation means for separating the light into the light; A gas measurement cell for irradiating light through the first optical path and passing the light through the gas; A reference cell which is irradiated with light through a second optical path and compares an optical intensity of the first optical path with an optical intensity of the second optical path when the gas is measured at a reference wavelength; And a comparator for outputting the difference between the light intensity of the first light path and the light intensity of the second light path.

Here, the optical splitting means is an optical fiber coupler.

The optical fiber connector further includes an optical fiber connector disposed between the variable diode laser and the optical splitting means and connecting the optical fiber connected to the variable diode laser and the optical fiber connected to the optical splitting means.

In addition, the scanning of the variable wavelength coincides with the period of variation of the bias voltage.

In addition, the reference cell can be used as a relative reference of fluctuation and concentration of the variable wavelength due to changes in the environmental factors of the gas measuring device.

According to the present invention, it is possible to safely maintain the measurement performance of the in-situ gas measuring device exposed to the external environment, and to prevent the signal noise due to vibration or dust by using the optical fiber splitter as the light source separation function.

In addition, according to the present invention, a miniaturized standard gas cell can be attached to the inside to detect a change in tunable wavelength according to the ambient temperature, and at the same time to capture a dyestuff gas absorption signal due to wavelength shift, The calibration of the measuring apparatus can be omitted.

Further, according to the present invention, the optical alignment process is also difficult in the production of the in-situ gas analyzer. Since the optical path of the optical fiber is formed, the process can be simplified and the defects can be reduced.

1 is a block diagram of an in-situ gas measuring apparatus using a variable-type laser diode according to an embodiment of the present invention.
2 is a flowchart illustrating a method of measuring an in-situ gas using a variable-type laser diode according to an embodiment of the present invention.

Brief Description of the Drawings The advantages and features of the present invention, and how to accomplish them, will become apparent with reference to the embodiments described hereinafter with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described below, but may be embodied in various forms. It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation only as the invention may make thedetails of the invention rather than limit the scope of the invention to those skilled in the art. Only.

1 is a block diagram of an in-situ gas measuring apparatus using a variable-type laser diode according to an embodiment of the present invention. 1, an in-situ gas analyzer calibration system includes a light source 100, an optical connector 200, an optical isolator 300, a collimation lens 400 for a measurement cell, A reference cell collimation lens 500, a reference cell 600, a gas measurement cell (located in the in-situ probe 700), a first photodiode 810, a second photodiode 820, A first condenser lens 811 for condensing light to the first photodiode, a second condenser lens 821 for condensing light to the second photodiode, a first amplifier 812 for amplifying the optical signal of the first photodiode, A second amplifier 822 for amplifying the optical signal of the second photodiode, a comparator 900 for comparing signals of the first amplifier 812 and the second amplifier 822, and a signal modulation Means 1000 may be included.

일수 있다. 이때, 가변파장의 스캐닝은 바이어스 전압 공급기(30)의 변화주기와 일치한다.The light source 100 emits light of a variable wavelength within a set range. The light source 100 may be a tunable diode laser (TDL), and the light emitted from the light source may be an infrared ray, a visible ray, or an ultraviolet ray. The light source 100 includes a light source power supply 20 for laser driving, a temperature control power supply 10 for temperature control for wavelength stability around the driving circuit of the laser diode, a bias voltage Is connected to the control signal of the feeder (V _bias , 30). The variable wavelength is, for example, 1500 to 1550

Can be. At this time, the scanning of the variable wavelength coincides with the period of change of the bias voltage supply 30.

The optical fiber connector 200 is disposed between the light source 100 and the optical splitting means 300 and connects the optical fiber connected to the light source 100 and the optical fiber connected to the optical splitting means 300.

The optical separating means 300 receives the light emitted from the light source 100 through the optical fiber connector 200 and separates the light into the first and second optical paths. The optical splitting means 300 is an optical fiber coupler. Since the optical isolator 300 is used as an optical fiber coupler, there is an advantage that the gas analyzer can prevent the optical axis from deviating due to external vibration or heat.

The collimating lens 400 for measuring cells is connected to one output end of the optical separating means 300 to form a first optical path, and irradiates the measuring gas inside the measuring cell with light.

The reference cell collimator lens 500 is connected to the other output end of the optical separator 300 to form a second optical path, irradiates the standard gas inside the reference cell 600 with light, So that it can be efficiently received.

The reference cell 600 is for use as a reference relative to the absorption intensity of a single standard gas and includes nitrogen, sulfur dioxide, ammonia, hydrogen chloride, ozone, water vapor (H2O), carbon monoxide, carbon dioxide, hydrogen fluoride It maintains an enclosed or continuous flow, where the gas maintains a certain pressure and concentration. The reference cell 600 is irradiated with light through the second optical path and compares the optical intensity of the first optical path with the optical intensity of the second optical path when the gas is measured at the reference wavelength. The light source 100 internally has a temperature control function, but temporal fluctuation occurs due to the external environment. That is, the change of the wavelength can be moved slightly, which is an object to detect in advance. If a single gas is contained in the reference cell 600, a specific absorption signal is generated, and a point at which the lowest absorption signal is output is designated as a reference wavelength. Based on the first spectral light intensity and the second spectral intensity To compare the light intensity. In addition, the concentration of the gas contained in the reference cell 600 also includes a function for relatively comparing the intensity of light with the gas measurement cell 700 of the first optical path. The reference cell 500 can be used as a relative reference of variation and concentration of the variable wavelength due to changes in the environmental factors of the gas measuring device.

The gas measuring cell 700 is irradiated with light through the first optical path and passes through the gas. The sample (gas) to be measured is a region through which a sample (gas) by natural flow or separate driving passes.

The gas measuring cell 700 is a path for measuring the light intensity of the sample (gas) moving to the first optical path through the optical splitting means 300. The sample (gas) passing through the first optical path is a mixed discharge gas. When ultraviolet, visible or infrared light passes through the gas molecules of a standard gas, the gas molecules absorb and absorb the energy of the light, and light passing through the gas molecules of the gas causes a change in light intensity. Therefore, the concentration of the specific gas containing the reference cell 600 among the measurement sample (gas) can be finely analyzed from the change of the light intensity according to the component concentration of the standard gas by the Beerlambert law to be described later.

On the other hand, the Beer Lambert law relating to the light intensity (light output) is expressed by the following equation. In one embodiment of the present invention, gas is applied as an example of a sample in Equation (1).

[Equation 1]

= 시료를 통과한 후의 광의 세기here,

= Intensity of light after passing through the sample

= 광의 파장

= Wavelength of light

= 시료를 통과하기 전의 초기 광의 세기

= Intensity of initial light before passing through sample

=시료 고유의 흡광계수

= Extinction coefficient inherent to the sample

        C = concentration of sample

        L = distance between samples (path of light)

를 정의하고 L과 제로가스 농도값의

와 스팬가스 농도값의

를 정의함으로써 분석하고자하는 시료의 농도 C를 얻을 수 있다. 위의 수학식 1을 정리하면 수학식 2를 유도할 수 있다.In order to measure the concentration of the sample in the above Equation 1

And the value of L and the zero gas concentration value

And the value of the span gas concentration value

The concentration C of the sample to be analyzed can be obtained. The above equation (1) can be summarized to derive equation (2).

&Quot; (2) "

와 L을 포함한 측정장치의 기계적 상수이다.Where B is

And L is the mechanical constant of the measuring device.

The first photodiode 810 converts the optical signal received through the first condenser lens 811 into an electrical signal through the light passing through the gas measurement cell 700 and the second photodiode 820 converts the optical signal received through the reference cell 600 converts an optical signal received through the second condenser lens 821 into an electrical signal.

The first amplifier 812 amplifies the electrical signal of the first photodiode 810.

The second amplifier 822 amplifies the electrical signal of the second photodiode 820.

The comparator 900 compares the first light intensity and the second light intensity, and calculates and outputs the difference. At this time, the signal modulation unit 1000 frequency-filters the signal based on the periodical electrical reference signal f to output a signal difference generated on the optical path.

The signal modulating means 1000 is means for summing up a signal generated by the periodic signal generator 1100 and a specific frequency f to an input signal of a bias voltage for varying the wavelength of the light source 100. It also includes the role of the reference frequency f in analyzing the measured value of the gas concentration in the signal difference output signal obtained by the comparator 900. For example, a sinusoidal wave of a predetermined period is added to a signal generated by the periodic signal generator 1100 and is input to a bias voltage supplier 30 of the light source 100, and an optical signal having passed through the first optical path and the second optical path, And can be used as a reference signal for the noise removing function.

The periodic signal generator 1100 functions to periodically vary the light source 100. In other words, the light source 100 is a variable diode laser, and the bias voltage and the variable wavelength are mapped on a one-to-one basis under the assumption that the ambient environment (temperature) is stable. By periodically changing the bias voltage, Is converted into a periodic wavelength. For example, a ramp signal or a sawtooth signal.

2 is a flowchart of a method of measuring an in-situ gas using a variable-type laser diode according to an embodiment of the present invention. Referring to FIGS. 1 and 2, it can be seen that the process proceeds to the initial calibration mode and the measurement mode based on the relative difference between the gas measurement cell and the reference cell after passing through the optical separation means.

The measurement device should recognize the electrical signal value by the standard sample measurement in advance and measure the intermediate measurement sample for the minimum and maximum measurement value in order to correct the linearity of the output value of the measurement device, It is common for the measurement device to recognize the value so that the measurement value of the measurement device maintains linearity within the measurement range in the actual measurement mode. FIG. 2 shows the calibration mode and the measurement mode sequentially displayed for the series of processes.

First, the measurement apparatus of the present invention flows standard gas to the gas measurement cell 700 for gas measurement. The definition of a standard gas means a sample (gas) that falls between a single gas component of the measuring device and the maximum gas concentration, 0 and the maximum concentration value. The measurement range refers to the maximum range of the sample (gas) measurement that can be measured by the measuring device.

In the initialization of the measuring apparatus, the measuring apparatus mode selection (S100) may correspond to the calibration mode.

The wavelength of the light is periodically varied by driving the bias voltage supplier 30 by the sum of the signal modulation means 1000 and the periodic signal generator 1100 in the light source 100, And is encountered on the first optical path. At this time, the optical signal received by the measurement cell is measured as an electrical signal value through the first photodiode (S200).

Separately, the other side of the light separating means 300 passes through the second optical path, and an electrical signal is generated through the second photodiode while passing a single gas in the reference cell 600. At this time, the component of the gas to be calibrated indicates the gas contained in the reference cell 600, and the zero gas, the intermediate value gas, and the span value gas are measured, and the values obtained through the comparator 900 and the values A mechanical characteristic constant value B is calculated through Equation (2) (S300). That is, an electrical signal value of an optical signal having passed through a standard gas of a reference cell is measured, and an optical intensity of light passing through a reference gas of the reference cell and a light intensity of light passing through a reference gas of the measurement cell, The difference value is output from the light intensity to calculate the mechanical characteristic constant value.

The measured value of the optical signal passing through the reference cell 600 after S300 can be used as a relative calibration constant and if a physical environmental variable (temperature, pressure) is provided for the optical signal passing through the gas measuring cell 700, (Step S400).

When the flow of the calibration mode is completed and the measurement mode is selected (selected), the measurement sample flows through the gas measurement cell 700. At this time, light emitted from the light source 100 meets the measurement gas through the first optical path, and light passing through the gas outputs an electrical signal through the first photodiode (S500).

The electrical signal obtained from the first photodiode maintains a stable absorption signal value corresponding to the concentration of the sample gas to be measured while passing through the comparator 900 and an optimal value is derived from the predicted value obtained in the calibration mode or the prediction curve S400 The comparison algorithm is performed (S600).

After S600, the optimum value of the final measurement value is displayed on the display device or the terminal (S700).

While the present invention has been described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It is understandable. Accordingly, the true scope of the present invention should be determined by the appended claims.

10: Temperature control power supply
20: Light source power supply
30: Bias voltage supply (including signal summing function)
100: Light source (variable laser diode)
200: Fiber optic connector
300: optical separation means
400: collimation lens for measuring cell
500: collimation lens for reference cell
600: Reference cell
700: gas measuring cell
810: First photodiode
811: first condensing lens
812: First amplifier
820: a second photodiode
821: Second condensing lens
822: Second amplifier
900: comparator
1000: Signal modulation means (Function Generator)
1100: Sawtooth (Ramp signal generator)

Claims (5)

A variable diode laser that emits light of a variable wavelength within a set range;
Optical splitting means for splitting the light emitted from the variable diode laser into first and second optical paths;
A gas measurement cell which is irradiated with light through the first optical path and passes through a gas measurement area of the in situ probe; And
And a single gas reference cell which is irradiated with light through the second optical path and compares an optical intensity of the first optical path with an optical intensity of the second optical path when a gas is measured at a reference wavelength,
Wherein the signal value of the light intensity on the first optical path is extracted on the basis of the signal value of the specific optical intensity of the optical signal obtained on the second optical path. The method according to claim 1,
Wherein the optical isolator is an optical fiber coupler. The method according to claim 1,
Further comprising an optical fiber connector disposed between the variable diode laser and the optical demultiplexer for connecting an optical fiber connected to the variable diode laser and an optical fiber connected to the optical demultiplexer, Gas measuring device. The method according to claim 1,
Wherein the scanning of the variable wavelength coincides with the period of variation of the bias voltage. ≪ RTI ID = 0.0 > 8. < / RTI > The method according to claim 1,
Wherein the reference cell can be used as a relative reference of variation and concentration of a variable wavelength due to a change in environmental factors of the gas measuring device.

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