JPH10318922A - Infrared gas analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure modulating-type infrared gas analyzer capable of performing stable measurements even when the intensity of infrared light changes, the sensitivity of a detector changes, or stain is present on the inner surface of a cell. SOLUTION: An infrared light source 3 is lighted to irradiate a sample cell 1 with infrared rays from the infrared light source 3, and in the state that a sample gas is in the sample cell 1 by the activation of a pump 9, a control circuit 13 executes the on-off control of a solenoid valve 7 to change the pressure in the sample cell 1. At this time, a motor 12 is driven to rotate in synchronization with the solenoid valve 7 by a.c. signals of the same period as the on-off period of the solenoid valve 7 to repeat the entrance and interruption of infrared rays to be entered into the sample cell 1 in synchronization with the solenoid valve 7. Then, a signal processing unit 5 to which the output of a detector 4 is inputted integrates each area of a positive part of every signal of detector signals in synchronization with the interruption of infrared rays, obtains the ratio of the integrated values, and computes the concentration of a gas from its value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared gas analyzer for measuring the concentration of a specific component contained in a gas by utilizing infrared absorption characteristics, and more particularly to a pressure modulation method for changing the pressure of a sample gas in a sample cell. It relates to an infrared gas analyzer of the type.

[0002]

2. Description of the Related Art In an infrared gas analyzer, a pressure modulation method is well known as a means for extracting an AC signal together with a chopper method and a fluid switching method. It is very practical because it is not necessary to use.

FIG. 4 shows an example of a conventional pressure modulation type infrared gas analyzer. As shown in FIG. 4, an infrared light source 22 is provided on one end face side of a sample cell 21 into which a sample gas is introduced.
And a detector 23 is provided on the other end face side. The sample cell 21 is a cylindrical cell whose inside surface is processed into a mirror surface, and glass windows that transmit infrared light are provided on both end surfaces. The sample cell 21 is provided with a pressure sensor 24, and detects the pressure in the sample cell 21. Sample cell 2
A sample gas is flowed through 1, and an electromagnetic valve 25 is provided in the sample gas introduction path in order to change the pressure of the sample gas.

In this conventional pressure modulation type infrared gas analyzer, infrared light from a light source 22 is projected from one end of a sample cell 21 and passes through a sample gas in the sample cell 21, and then is detected by a detector 23. Received. The detector 23 detects infrared light (transmitted light intensity) in an absorption wavelength band corresponding to the component to be measured contained in the sample gas, and the transmitted light intensity varies depending on the density of the specific component contained in the sample gas. Change. At this time, the pressure in the sample cell 21 is cyclically modulated as shown in FIG. 5A by turning on / off the electromagnetic valve 25 provided in front of the entrance of the sample cell 21, and An AC signal as shown in FIG. 5 (b) can be obtained.

[0005]

The conventional pressure-modulated infrared gas analyzer is constructed as described above, but a condenser microphone type infrared detector is usually used as a detector. When there is a change in light intensity in the differential type, a detection signal is output, and as shown in FIG. 5B, an AC signal having the same cycle as the opening and closing cycle of the solenoid valve is obtained. The concentration of a specific component of the sample gas can be measured from the amplitude of the AC signal.The amplitude of the AC signal is such that the intensity of the infrared light source changes over time, the sensitivity of the detector changes, There is a problem that the stability is lacking because it changes depending on the stain on the inner surface of the cell.

[0006] The present invention has been made in view of such circumstances, and it is intended to stably measure even if there is a change in the intensity of infrared light, a change in the sensitivity of a detector, or a stain on the inner surface of a cell. It is an object of the present invention to provide a pressure modulation type infrared gas analyzer capable of performing the above-mentioned steps.

[0007]

In order to achieve the above object, an infrared gas analyzer according to the present invention is an infrared gas analyzer for measuring the concentration of a specific component contained in a gas by utilizing the infrared absorption characteristics of a sample gas. In a gas analyzer, a sample cell into which a sample gas enters, a light source that projects infrared light onto the sample cell, a detection unit that detects the intensity of light that has passed through the sample cell, and changes the pressure of the sample gas in the sample cell Pressure control means capable of setting two different pressures, light intermittent means for intermittently inputting infrared light in synchronization with a pressure change, and a sample gas based on a ratio of detection values at two different pressures. And a calculating means for calculating the concentration of the specific component contained in.

The infrared gas analyzer of the present invention is configured as described above, and synchronizes the light interrupting means for periodically blocking infrared light with the pressure control means for changing the pressure of the sample gas in the sample cell. By taking infrared light in a pulsed manner at each of the two pressure states, the output is separated and taken out, and the gas concentration is measured from the ratio of these two outputs. Can be.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the infrared gas analyzer of the present invention will be described with reference to FIG.

In FIG. 1, reference numeral 1 denotes a cylindrical sample cell,
The inside of the side surface is processed into a mirror surface, and both ends are sealed with a window material made of an infrared light transmitting material. The sample cell 1 has a gas inlet 1a and a gas outlet 1b, and a pressure sensor 2 for detecting the pressure in the sample cell 1. Reference numeral 3 denotes an infrared light source provided on one side of the sample cell 1, and 4 denotes an infrared detector provided on the other side of the sample cell 1, the output of which is input to the signal processing circuit 5.

Reference numeral 6 denotes a sample gas supply passage connected to the gas inlet 1a via a connecting member, and an electromagnetic valve 7 is provided in the middle thereof. Reference numeral 8 denotes a sample gas discharge passage connected to the gas outlet 1b via a connection member, and a pump 9 and a needle valve 10 are arranged in the middle thereof. Reference numeral 11 denotes a rotating sector as shown in FIG. A control circuit 13 controls the signal processing circuit 5, the solenoid valve 7, and the motor 12.

Next, the operation of the infrared gas analyzer of FIG. 1 will be described. While the infrared light source 3 is turned on to irradiate the sample cell 1 with infrared light from the infrared light source 3, the pump 9 is operated to allow the sample gas to flow through the sample cell 1. Is turned on and off at a cycle of, for example, 1 Hz, fluid modulation is performed, and the pressure in the sample cell 1 changes as shown in FIG. At this time, the motor 12 is rotationally driven by the control circuit 13 in synchronization with the electromagnetic valve 7 by an AC signal having the same cycle as the ON / OFF cycle of the electromagnetic valve 7, so that the infrared light incident on the sample cell 1 is as shown in FIG. As shown, the incidence and cutoff are repeated in synchronization with the electromagnetic valve 7.

On the other hand, the detector 4 for detecting infrared light having an absorption wavelength corresponding to the component to be measured has infrared light (transmitted light) in an absorption wavelength band corresponding to a specific component (component to be measured) contained in the sample gas. 3), an output corresponding to the concentration of the component to be measured at that time is obtained from the output of the detector 4 in synchronization with the intermittent infrared rays, as shown in FIG.
The signal processing circuit 5, to which this signal is input, integrates and calculates the area of the positive portion of each signal of the detector signal in synchronization with the intermittent infrared rays according to the control signal from the control circuit 13, thereby obtaining two pressures. Separate and extract the state signal.
Then, the signal processing circuit 5 calculates the ratio of these signals and calculates the gas concentration from the value.

Here, the transmitted light intensity of the sample cell 1 has a value corresponding to the density of the specific component contained in the sample gas (the amount of the specific component contained in a unit volume). It depends on temperature and pressure, and what is ultimately desired by gas analysis is a volume concentration independent of temperature and pressure. When the intensity of light incident on the sample cell 1 is I ₀ , the cell length is L, the absorbance coefficient determined by the measurement wavelength and the component to be measured is K, and the density of the component to be measured is ρ, the intensity of light transmitted through the cell 1 I is given by the following equation: I = I ₀ · exp (−K · ρ · L) (1)

On the other hand, assuming that the density at a standard temperature and pressure is ρ ₀ , the proportionality constant is k, and the pressure at that time is P, ρ = k · ρ ₀ · P (2) volume concentration c is a pure gas density of (measurement target component only gas consisting of) When _{ρ p c = ρ 0 / ρ} p ··· (3) next to the standard temperature and pressure, (1) formula I = I ₀ · exp (−K · k · ρ _p · c · P · L) (4)

[0016] If the volume concentration of the measurement target component is measured sample gas c _1, the transmitted light intensity I ₁ at pressure P _1, the pressure is transmitted light intensity when the P ₂ was I ₂ Then, from equation (4), I ₁ = I ₀ · exp (−K · k · ρ _P · c ₁ · P ₁ ·
L) I ₂ = I ₀ · exp (−K · k · ρ _P · c ₁ · P ₂ ·
L) Therefore, ln (I ₂ / I ₁ ) = − K · k · ρ _P · c ₁ · L · (P
₂ −P ₁ ), and c ₁ = −ln (I ₂ / I ₁ ) / {K · k · ρ _p · L · (P ₂ −P ₁ )} (5) is obtained. In the equation (5), I ₂ / I _{1 on the} right side
Is the ratio of the output of the detector 4 at a pressure P ₁ and P _2, the pressure P ₁ and P ₂ is a known value, the volume concentration of the measurement target component from the ratio of the detection output of the two pressure conditions c
You can ask for _one .

As described above, by taking the ratio between the outputs in the two pressure states, even if there is a change in the light intensity of the light source, a change in the sensitivity of the detector, or a stain on the inner surface of the cell, the effects thereof are canceled out, so that the stability is maintained. Measurement can be performed.

The pressure sensor 2 monitors the pressure in the sample cell 1, and when the pressure in the two pressure states fluctuates from a predetermined value, the pressure sensor 2 adjusts the opening of the needle valve 10 to thereby control the predetermined degree. A pressure state can be maintained. Also,
The output of the pressure sensor 2 may be constantly taken into the signal processing circuit 5 without adjusting the needle valve 10, and used for the calculation of the equation (5).

Further, in the above-described embodiment, an example in which an electromagnetic valve is used as the pressure control means has been described. However, a diaphragm pump or a reciprocating pump may be used.

In the above embodiment, the rotating sector is used as the light interrupting means. However, the light may be interrupted by shutting off the power to the light source.

[0021]

The infrared gas analyzer of the present invention is constructed as described above, and the two pressure states are obtained by synchronizing a motor for rotating a rotating sector which periodically blocks infrared light and a solenoid valve. Infrared light is incident on each in the form of a pulse, each output is separated and taken out and integrated,
Since the concentration of the sample gas is calculated from the ratio of the integrated values, a stable measurement value can be obtained even if there is a change in the intensity of the infrared light, a change in the sensitivity of the detector, or a stain on the inner surface of the cell.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of an infrared gas analyzer of the present invention.

FIG. 2 is a view showing a shape of a rotating sector used in the infrared gas analyzer of FIG. 1;

FIG. 3 is a diagram for explaining the operation of the infrared gas analyzer of FIG. 1;

FIG. 4 is a diagram showing a conventional infrared gas analyzer.

FIG. 5 is a diagram for explaining the operation of the infrared gas analyzer of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sample cell 2 Pressure sensor 3 Light source 4 Detector 5 Signal processing circuit 6 Gas supply channel 7 Solenoid valve 8 Gas exhaust channel 9 Pump 10 Needle valve 11 Sector 12 Motor 13 Control circuit

Claims (1)

[Claims] 1. An infrared gas analyzer for measuring the concentration of a specific component contained in a gas by utilizing the infrared absorption characteristics of a sample gas, and a sample cell into which a sample gas enters, and infrared light being projected onto the sample cell. A light source, a detecting means for detecting the intensity of light passing through the sample cell, a pressure control means capable of changing the pressure of the sample gas in the sample cell to set two different pressures, and Infrared light characterized by comprising an optical intermittent means for intermittently inputting light in synchronization with a change, and a calculating means for calculating a concentration of a specific component contained in the sample gas based on a ratio of detection values at two different pressures. Gas analyzer.