KR820001025B1 - Infrared analysis equipment for gas - Google Patents

Abstract

A double-beam IR gas analyzer based on the absorption of IR radiation is developed. The chopped radiation from an IR lamp impinges on a semiconductor sensor after passing alternately 2 interference filters and 2 cuvettes: one for the gas to be analyzed, the other for a ref. gas. The alternating component of the signal generated by the difference in the intensities of the 2 IR beams is used as a measure of the gas to be detd., whereas the direct component is used as a feedback signal to control the temp. in the instrument via changing the voltage drop on the heater.

Description

Infrared gas analyzer

1 is an explanatory diagram of a configuration of an infrared gas analyzer according to the present invention.

2 and 3 are explanatory diagrams of the configuration of the interference compensation cell.

4 and 5 are explanatory diagrams of the configuration of the photodetector.

6 is a diagram illustrating the configuration of a signal conversion and temperature conversion circuit.

7 is a diagram showing an example of vibration spectrum with rotation spectrum.

8 is an absorption characteristic diagram.

The present invention relates to an infrared gas analyzer for analyzing a component contained in a gas using infrared absorption, and more particularly, to an infrared gas analyzer for collecting and analyzing a sample gas containing an interference component.

There is often an interference component in the sample gas having an absorption wavelength band overlapping with the absorption wavelength band of the measurement component.

In such a case, a large measurement error occurs, so it is necessary to perform some compensation.

The conventional method performed by the apparatus includes measuring the concentration of the interference component separately and calculating the concentration of the measurement component by calculation.

However, the apparatus using these methods has a problem that the overall configuration becomes complicated.

This invention is made | formed in view of this point.

SUMMARY OF THE INVENTION An object of the present invention is to realize an infrared gas analyzer with a simple configuration that eliminates the influence of the presence of interference components.

A first feature of the present invention is to provide an optical system for measuring light, comprising a first filter that mainly transmits infrared rays of a predetermined wavelength band within an absorption wavelength band of the measuring cell and the measuring component, and a portion of the absorption wavelength band within the transmission wavelength band of the first filter. It consists of a temperature compensating cell which has a gas different from each other in the measurement component and spectrum, and includes infrared rays in the wavelength band including the optical system for reference light, the main part of the transmission wavelength of the interference compensating cell and the first filter. It consists in the interference cell which the 2nd filter which permeate | transmits and the gas containing the measurement component of a constant density | concentration were enclosed.

A second feature of the present invention is that the interfering cells are interleaved with a hermetic structure at one end of the interfering compensation cells, and the length of the interfering compensation cells can be easily changed by moving the interfering cells.

A third feature of the present invention is a photodetector in which an optical sensor and a multilayer film interference filter are installed by processing a metal block, the temperature of the metal block is kept constant, and the influence of the external sensor temperature of the optical sensor and the multilayer film filter is prevented. It is provided.

Hereinafter, the present invention will be described with reference to the drawings.

1 is a block diagram showing an embodiment of the infrared gas analyzer according to the present invention.

In the figure, reference numeral 1 denotes an infrared source, and reference numeral 2 denotes a measurement cell filled with a sample gas.

The measurement cell 2 is provided with windows 21 and 22 that transmit infrared rays, an introduction port 23 and an outlet port 24 for introducing and deriving the sample gas.

Numeral 3 denotes a temperature compensation cell having infrared transmission windows 31 and 32 in which gas is sealed therein.

As the enclosed gas, a part of the absorption wavelength band is the same gas contained in the transmission wavelength band of the filter 74 described later. Furthermore, a gas which differs in the measurement component and spectrum is used.

Since the gas molecules can freely rotate, changes in the vibration state necessarily occur due to changes in the rotation state, and the vibration spectrum appears to be accompanied by the rotation spectrum.

For this reason, as shown in FIG. 7, for example, a spectrum line group called + branch or-branch appears in the spectrum.

Although the spectrum of the gas enclosed in the temperature compensation cell 3 is basically similar to the spectrum of the measurement component, it may differ only in the above-mentioned spectral line group. (For example, when the measured component is NO, C2H₄ It is possible to choose

(4) is an interference cell containing a gas containing a certain concentration of the measurement component, (5) is an interference compensation cell filled with a sample gas. The interference cells 4 are provided with windows 41 and 42 that transmit infrared rays.

In addition, the interference compensation cell 5 is provided with windows 51 and 52 which transmit infrared rays, an introduction port 53 and a discharge port 54 for introducing and deriving sample gas.

In the calibration operation of the apparatus described later, the interference compensating cell 5 is preferably configured so that the adjustment of the length of the cell can be facilitated. For example, the configuration of FIG. 2 or FIG. It may be made to be.

The interference compensation cell 5 of FIG. 2 has a window 52 that transmits infrared rays at one end thereof, and an outer cylinder portion 55 which interpolates the interference cell 4 at the other end thereof.

Then, the interference cell 4 is inserted into the outer cylinder portion 55, the insertion length thereof is adjusted to adjust the length l of the cell of the interference compensation cell 5, and the length screw of the cell with the push screw 56. It can be fixed.

Reference numeral 43 denotes a zero ring embedded with a flaw formed in the outer circumferential surface near the window 42 of the interference cell 4 to prevent leakage of the gas filled in the interference compensation cell 5.

In addition, the interference compensating cell 5 of FIG. 3 constitutes a part of the cylindrical portion of the interference compensating cell 5 by a bellows 57, and fixes the pocket sleeve 58 with a push screw 56 to prevent interference. The length l of the cell of the compensation cell 5 is fixed.

The configuration of the interference compensation cells in FIGS. 2 and 3 is one means for more easily realizing the object of the present invention.

Again, explanation will be given according to FIG.

(6) is an aperture, and the aperture (6), the interference cell (4) and the interference compensation cell (5) are arranged coaxially, while the measurement cell (2) and the temperature compensation cell (3) are arranged coaxially. It is.

(7) is a photodetector and (8) is a signal exchange and temperature control circuit.

The photodetector 7 is disposed near the focal point of the concave reflector 10. Then, intermittent light passing through the measuring cell 2, the interference cell 4, and the like is introduced into the photodetector 7.

The intermittent light is obtained by the sector 11 rotating by the motor 12 using the infrared light 1 as the parallel light with the concave reflector 9.

Next, the photodetector 7 and the signal conversion / temperature control circuit 8 will be described in more detail with reference to FIG. 4, FIG. 5, and FIG.

4 is an explanatory view of the configuration of the photodetector 7 and is a one-side view of the photodetector 7.

5 is a plan view of the photodetector 7.

4 and 5, reference numeral 71 denotes a metal block, and the metal block 71 has a conical light guide hole 711 for guiding measurement light and reference light, and a light guide hole for reference light ( 712 is formed.

An optical sensor attachment hole 713 is formed at the intersection of the light introduction holes 711 and 712 of the metal block 71, and a ring-shaped groove 714 is formed on the outer circumferential surface thereof.

Reference numeral 72 is a substrate inserted into and fixed in the attachment hole 713 of the metal block 71, and a photosensitive element 73 such as a thyme star bolometer is fixed to the substrate 72.

Reference numeral 731 denotes a connecting line for connecting the photosensitive element 73 and the signal conversion / temperature control circuit 8 to each other.

Reference numeral 74 denotes a multi-layer film interference filter attached to the metal block 71 by blocking the light introduction hole 711 for measurement light, and 75 denotes a metal block 71 by blocking the light introduction hole 712 for the reference light. ) Is a multilayer interference filter.

Each interference filter is attached facing each introduced light. The space portions of the light introduction holes 711, 712, and the attachment hole 713 are configured to obtain a completely sealed state, and nitrogen gas N2 is sealed in the space portions.

Reference numeral 76 denotes a heater for heating the metal block 71 attached to the groove 714.

761 denotes a connecting line for supplying the output of the signal conversion / temperature control circuit 8 to the heater 76.

Reference numeral 77 is a member covering the entire metal block 71, and is made of, for example, bakelite resin.

By the covering member 77, the metal block 71 is effectively shielded from the ambient temperature.

771 denotes a window of the measurement light introduction hole 711, and 772 a reference light of the reference light introduction hole 712.

6 shows a circuit configuration of the signal conversion and temperature control circuit 8.

In Fig. 6, r _d denotes a symbol in which the dummy tea bolometer is regarded as a resistance element.

The resistance element r _d constitutes a bridge circuit with resistance elements r 소자, r ₂, r ₃, and a direct current power source E _{0 which} are stable to temperature, and receives intermittent light of the measurement light and the reference light by the sector 11.

Then, the difference between the unbalanced voltage and the set voltage E _S of the bridge circuit is amplified by the amplifier A 'of high input resistance and low noise, and further amplified by the transistor Q', and the heater 76 (resistance element r _h ) is used as the power. At the same time, only the AC component is led to the amplifier A2 through the capacitor C₁, and the measurement signal is obtained at the output terminal OUT.

The operation of the infrared gas analyzer having the above configuration will be described below.

There are two pieces of information in the output signal of the photodetector 7 which is input to the signal conversion / temperature control circuit 8.

One is to use the infrared rays generated by the infrared source 1 as intermittent light by the sector 11, and alternately transmit the measuring cell 2, the interference cell 4, and the like to the photodetector 7. As a measurement signal which is introduced and displays an amount corresponding to the measurement component of the sample gas, the other signal corresponding to the temperature of the dummy star-bloom 73 obtained by heating the metal block 71 with the heater 76. to be.

The former has an alternating current change (short cycle) and the latter has a direct current change (response is slow because the time constant of the heater is large).

Therefore, the output signal of the bridge circuit of the resistance elements rd, r₁, r2, r3 and the power source E ₀ takes a form in which the DC components overlap.

Then, the difference between the superimposition signal and the set voltage E _S is amplified by the amplifier A 'and the transistor Q' to be an excitation signal of the heater 76, and the dummy star bolometer 73 matches the temperature corresponding to the set voltage E _S. To adjust.

In this control system, the alternating current component has a reason that the time constant of the heater 76 or the like is large and does not have an influence.

On the other hand, the AC component of the superimposition signal is amplified again by the amplifier A2 through the capacitor C 'and output as a measurement signal.

The magnitude of this measurement signal is determined in accordance with the properties of the transmitted light path and relates to the basic configuration of the present invention.

In the case of a gas having a measurement component and an indirect component having an absorption characteristic as shown in FIG. 8 (not shown in FIG. 8, the stackel group is omitted) in the apparatus of FIG. This will be described below.

Here, an apparatus in which the wavelength band is selected as the characteristic of FIG. 8a is selected as the filter 74, and the device in which the wavelength band is selected as the characteristic in which the wavelength band is in FIG. 8b is described.

First, the case where the sector 11 is on the interference cell 4 side as shown in FIG. 1 will be described.

In this case, the infrared rays emitted from the infrared ray source 1 are the concave reflector 9 → the temperature compensation cell 3 → the measurement bill 2 → the concave reflector 10 10 → the filter 74? It leads to the path of).

Therefore, the amount of light Lm reaching the dummy star bolometer 73 at this time is

Lm = Lom- (Lxm + Lim + Ltm) (1)

only,

Lom: Assuming that a gas having no absorption wavelength band in the A band enters the measurement cell 2 and the temperature compensation cell 3, these cells 2, 3, and filter 74 The amount of light that passes through and reaches the dummy star bolometer (73).

Lxm: Reduction amount of the light quantity Lom reduced by the measurement component actually present inside the measurement cell 2.

Lim: Reduction amount of light quantity Lom reduced by the indirect component actually present inside the measurement cell 2.

Ltm: The amount of reduction of the light quantity Lom reduced by the gas actually enclosed in the temperature compensation cell 3.

Is displayed.

When the sector 11 rotates 180 degrees from the position of FIG. 1, the infrared rays emitted from the infrared ray source 1 are concave reflectors 9 → apertures 6 → interference cells 4 → interference compensation cells 5 → concave. It passes through the path of the reflector 10 → the filter 75 → the Demister star bolometer 73.

Therefore, the amount of light Lr reaching the dummy star bolometer 73 at this time is

Lr = Lor- (Lxr + Lir + Ltr) (2)

Lor: However, in the case where it is assumed that a gas having no absorption wavelength band in the B band enters the interference cell 4 and the interference compensation cell 5, these cells 4, 5, and a filter ( The amount of light that passes through 75) and reaches the dummy star bolometer (73).

Lxr: The amount of reduction of the light amount Lor reduced by the measurement component actually present inside the interference compensation cell 5.

Lir: The amount of reduction of the light amount Lor reduced by the interference component actually existing inside the interference compensation cell 5.

Lty: The amount of light Lor reduced by the gas actually enclosed inside the interference cell 4.

Is displayed.

In the above formulas (1) and (2), when the difference ΔL of the amount of light reaching the dummy star bolometer 73 is obtained,

ΔL = Lm-Lr

= Lo-Lx-Li-Lt (3)

only,

Lo = Lom-Lor

Lx = Lxm-Lxr

Lr = Lim-Lir

Lt = Ltm-Ltr

Becomes

Lx is an amount indicating the concentration of the measured component in the sample gas, and ΔL is an amount corresponding to the output amplitude (AC component) of the photodetector 7.

In other words, the signal is amplified by the amplifier A2 and output through the capacitor C 콘덴서 of the signal conversion and temperature control circuit 8.

Next, the calibration of the apparatus of the present invention will be described.

First, for the temperature compensation cell 3 provided in order to avoid the temperature error accompanying the addition of the interference cell 4, since Ltr varies with temperature, the temperature compensation is performed so that the variation of Ltm is equal to the variation of this Ltr. The length of the cell 3 and the concentration of enclosed gas are adjusted.

Since the gas inside the interference cell 4 and the temperature compensation cell 3 is invariable, Lt takes a constant value Ca despite the temperature fluctuation.

Next, the procedure of the calibration for removing the influence on the output of the interference component in the sample gas will be described.

First, the diaphragm 6 is adjusted so that the gas which does not have infrared absorption, such as nitrogen as a sample gas, will flow, and the amplitude of the incident light quantity to the photodetector 7 will be 0 or constant value Cb at this time. (This adjustment is not large, so there is no problem such as Lt fluctuating with temperature.)

By this adjustment, Lo-Lt = 0 or Lo-Lt = Cb is realized.

Next, the length of the interference compensation cell 5 is such that a gas containing an interference component as the sample gas and no measurement component is flowed so that the amplitude of the incident light amount to the photodetector 7 is zero or a constant value Cb. Adjust l.

By this adjustment, Li = 0 is realized.

After correction in this way, (DELTA) L is represented by following Formula.

ΔL = Lx or Cb + Lx (4)

Therefore, even if the interference component is contained in the sample gas and its concentration varies, the Lx proportional to the concentration of the measured component can be accurately known from the output amplitude of the photodetector 7.

Moreover, since the effect of the temperature change of the interference cell 4 is removed by providing the temperature compensation cell 3, it is not necessary to take the structure which puts the interference cell 3 etc. in a thermostat.

In addition, by attaching the filters 74 and 75 to the photodetectors 7 of the condensing portion, the filters 74 and 75 can be miniaturized, and the photodetectors 7 and the filters 74 and 75 are made smaller. In the above embodiment, in which the temperature control of the step S) can be performed more easily at the same time, the thermostat is not required at all.

In addition, in the above description, only one kind of arrangement order of the cells and the like is shown, but the same effect is naturally obtained even with another arrangement order.

In addition, although the filter of wavelength band B which includes all the wavelength bands A of a measurement optical axis filter is arrange | positioned at the reference light side is shown, it is the same as superposing | polymerizing in a main part and the effect is the same.

It is also possible to provide an aperture or the like on the measurement cell side depending on the selection of the wavelength bands A, B, and the like.

In the above embodiment, a dummy star bolometer is used as the optical sensor, and a structure in which this is heated and used is used. However, other elements such as photoconductive cells (TIS, PbS, CdS, etc.) are used. What is necessary is just to make it the structure which cools it.

As the cooling means, there is a low temperature stabilization device using a Peltier effect element.

As mentioned above, according to this invention, the infrared gas analyzer which can remove the influence of an interference component automatically can be implement | achieved with a simple structure.

Claims (1)

A measurement cell filled with a sample gas, a first filter mainly transmitting infrared rays of a predetermined wavelength band within the absorption wavelength band of the measurement component, and having a part of the absorption wavelength band within the transmission wavelength band of the first filter and at the same time The temperature compensation cell in which different gases are enclosed in the spectrum and the spectrum, the interference cell in which the gas containing a certain concentration of the measurement component is contained, the interference compensation cell in which the sample gas is filled, and the transmission wavelength band of the first filter And a second filter for transmitting infrared rays in the wavelength band to include a portion, an infrared source for generating infrared rays, and an optical sensor sensitive to the amount of received light, wherein a part of the light emitted from the infrared source is measured in the measurement cell and temperature compensation. The optical system for measuring light is formed to reach the oversensor after passing through the cell and the first filter, and at the same time, other part of the light from the infrared source is interfering with the interference cell and the interference beam. An optical system for reference light is formed so as to reach the optical sensor after passing through the cell and the second filter, and the interference cell has one end forming an infrared transmission window, and the other end interpolates the interference cell in an airtight structure to insert the interference cell. Move in the direction to change the length of the interference compensating cell, and process the optical sensor and the interference filter into a metal block so as to intersect the first and second light introduction holes of the conical shape in the metal block. A light sensor is disposed at the intersection, and the first filter is attached to the first light introduction hole and the second filter is attached to the metal block so as to block the light introduction hole, respectively. An alternating current component of a signal of an optical sensor obtained by alternately introducing a measurement light into the first light introduction hole and a reference light into the second light introduction hole, and a photo detector having a temperature control means for maintaining the metal block at a constant temperature. Measuring signal At the same time, the infrared gas characterized in that the jeungcheop signal of the AC component and DC component to the input of the temperature adjusting means analyzer.

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