JPH0134336B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is used as a detector for a non-dispersive infrared gas analyzer, and by measuring the velocity amplitude of Helmholtz resonance using the Doppler effect,
The present invention relates to an infrared detector that detects incident infrared energy. In general, condenser microphones and microflow sensors are conventionally known as detectors used in non-dispersive infrared gas analyzers. The condenser microphone detects the concentration of the component to be measured in the measurement gas by detecting the difference in infrared energy absorbed by the measurement gas and the reference gas as the displacement of the microphone. A flow sensor receives infrared energy absorbed by a measurement gas and a reference gas, respectively, in a detection section filled with a predetermined gas, and detects minute amounts of the predetermined gas by a detection end installed in the detection section. By detecting changes in flow velocity, the concentration of the component to be measured in the measurement gas is detected. However, in the case of the above-mentioned condenser microphone and the above-mentioned microflow sensor, since they are configured to capture the displacement of the capacitor membrane or the change in the flow velocity of a predetermined gas, Coupled with the fact that the infrared energy supplied to the sensor has a frequency of about several Hz, the detected signal is extremely weak, making it difficult to measure the concentration of the component to be measured with high sensitivity. The present invention has been made in view of these drawbacks, and its purpose is to provide an infrared detector that can be used as a detector in a non-dispersive infrared gas analyzer and can measure the concentration of a component to be measured in a measurement gas with high sensitivity. It is about providing. A feature of the present invention is that the velocity amplitude of Helmholtz resonance is measured using the Doppler effect in an infrared detector used as a detector of a non-dispersive infrared gas analyzer to measure the concentration of a component to be measured in a measurement gas. Accordingly, the energy of the infrared rays passing through the measurement gas and the like is detected with high sensitivity. Hereinafter, the present invention will be explained in detail using figures. FIG. 1 is a diagram explaining the principle of a Helmholtz resonator shown to facilitate understanding of the present invention. In the figure, 1 is an airtight cylindrical first container having an internal volume V; 2 is a first container 1 This is a cylindrical second container which is integrally fixed to one side of the container and has an internal space having a cross-sectional area S and a length l. Further, the first container 1 and the second container 2 are usually integrally formed from the same member, and their respective internal spaces are also integrally connected. When the internal space of such a Helmholtz resonator is filled with gas, the gas in the second container 2 becomes a vibrating mass, and the first
The gas inside the container 1 comes to play the role of a spring. Therefore, when the gas in the first container 1 changes adiabatically, the natural frequency fn [c/s] of the gas in the system formed by the internal spaces of the first and second containers 1 and 2
is as shown in equation (1) below. However, P: Pressure of gas [Kg/cm ² ], γ: Adiabatic index (usually 1.4 to 1.7) ρ: Density of gas [Kg・s ² /cm ⁴ ] C: Speed of sound in gas [cm/s] ,

[Formula] Incidentally, V = 2 [cm ³ ], l = 2 [cm], S = 0.2
[cm ² ], C=340x10 ² [cm/s], and find the above natural frequency fn from the above formula (1), fn=
1.21x10 ³ [c/s] = 1.21 [kHz]. Therefore,
When energy is poured into the above system at this 1.21kHz,
The above system absorbs that energy and begins to oscillate. Furthermore, when the above system enters an oscillation state, the vibration amplitude of the gas in the system increases, but due to attenuation due to the viscosity of the gas, it gradually shifts to a steady state. When a certain force is applied to the gas in 1 and 2 by infrared energy etc. supplied from the outside, the speed A of the gas flow caused by thermal expansion of the gas and that force are the trigger. The ratio A/ to the maximum value B of the vibration speed when the gas in the containers 1 and 2 vibrates
B) is given as shown in equation (2) below. However, Vmax: Maximum value of the speed at which the gas vibrates _Vs : Flow velocity of the gas caused by expansion of the gas when constant energy is supplied U: Frequency ratio (i.e., the ratio between 2πf and the resonance frequency ωn) ratio
2πf/ωn) ζ: Damping ratio (0 < ζ < 1, which indicates the ratio of damping in damped vibration. In other words, it can also be said to be a coefficient that indicates the likelihood of vibration between full vibration and non-vibration) Further, FIG. 2 is an explanatory view of an example of use of the embodiment of the present invention, and in the figure, reference numeral 3 denotes a measurement cell into which a measurement gas is introduced from an inlet 3a, flows inside, and is sent out from an outlet 3b; 5 is a reference cell filled with a reference gas; 5a and 5b are light sources such as infrared lamps; 6 is a sector in which the light beams emitted from the light sources 5a and 5b are intermittent light; A rotating motor 8 is a Helmholtz resonator whose interior is filled with a predetermined gas (for example, the same gas as the measurement component gas) and two Helmholtz resonators shown in FIG. 1 are connected; 9a is a Helmholtz resonator 8;
An ultrasonic oscillator 9b, which is fixed to a predetermined part on one side of the resonator 8 and emits an ultrasonic signal, is fixed to a predetermined part on the other side of the resonator 8 (a position opposite to the position where the ultrasonic transmitter 9a is fixed). This is an ultrasonic receiver that receives the ultrasonic signal. Also, a Helmholtz resonator 8, an ultrasonic transmitter 9a, and an ultrasonic receiver 9
b constitutes the infrared detector of the embodiment of the present invention, and the output of the ultrasonic receiver 9b is signal-processed by a predetermined signal processing circuit (not shown) to determine the concentration of the component to be measured in the measurement gas. The concentration is then displayed on a display (not shown). The Helmholtz resonator 8 is a combination of two Helmholtz resonators shown in FIG. 1, and the above equations (1) and (2) hold true as in the case of FIG. Furthermore, FIG. 3 shows the above sector 6.
10 is a plan configuration diagram of parts constituting the
10a ₁ to 10a _o are plural parts having a predetermined width and having one side fixed to the central part 10 while maintaining a distance equal to the width. It is a single feather. Also,
The sector 6 is constructed by combining two parts shown in FIG. 3, one of which is fixed and does not move.
0 is fixed and can be rotated. By the way, the number of the blades 10a ₁ to 10a _o is 200.
When the motor 7 rotates at 360 rpm, the light beams emitted from the light sources 5a and 5b are interrupted at 1.2 kHz. This corresponds to chopping several hundred times faster than sectors used in conventional infrared gas analyzers. Furthermore, by making the frequency of the intermittent light and the resonant frequency ωn of the Helmholtz resonator 8 approximately equal, 2πf≒ωn, that is, u≒1
is established, and μv≒1/2. Therefore, the smaller ζ is, the larger μv becomes, and a larger velocity amplitude of the gas can be obtained.Hereinafter, the operation of the embodiment of the present invention having the above configuration will be explained in detail using FIG. 2. In FIG. 2, a measurement gas containing a component to be measured is introduced into the measurement cell 3 from an inlet 3a as shown by an arrow and is sent out from an outlet 3b, while a predetermined reference gas is contained in a reference cell 4. Filled. Further, the ultrasonic signal emitted from the ultrasonic oscillator 9a propagates through the gas within the Helmholtz resonator 8, reaches the ultrasonic receiver 9b, and is received. Furthermore,
The measurement light and the reference light emitted from the light sources 5a and 5b and made into intermittent light by the sector 6 pass through the measurement gas in the measurement cell 3 and the reference gas in the reference cell 4, respectively, and enter the Helmholtz resonator 8. reach.
Therefore, when the measurement gas in which no component to be measured is present is flowing (hereinafter referred to as the "reference state"), the measurement light and the reference light absorb energy by the measurement gas and the reference gas, respectively. However, when the measurement gas in which the component to be measured is present in the measurement gas is flowing (hereinafter referred to as the "measurement state"), only the measurement light reaches the measurement gas. The Helmholtz resonator 8 is attenuated due to energy absorption by
reach within. Therefore, the Helmholtz resonator 8
(2) above for the reference state and measurement state.
The V _s value in Eq. changes. In order to detect such changes, in the case of a condenser microphone, which is a conventional infrared detector, a rotating chopper is used to extract a signal every cycle of chopping. On the other hand, in the case of the embodiment of the present invention, the resonance state is achieved even if the changing value is small. Therefore, energy is taken in and the value of the velocity multiplier μv increases, and ultimately the velocity amplitude of the gas within the Helmholtz resonator 8 changes greatly. Therefore, when an ultrasonic signal with a frequency fs is emitted from the ultrasonic transmitter 9a, the ultrasonic signal is received by the ultrasonic receiver 9b with a "beat" frequency Δfs due to the Doppler effect. Here, the "beat" frequency Δfs due to the Doppler effect refers to the positive and negative directions of the gas (in the axial direction connecting the ultrasonic transmitter 9a and the ultrasonic receiver 9b in Fig. 2, one direction is the positive direction). and the opposite direction is called the negative direction), and changes periodically from zero to Δfs at the Helmholtz resonance frequency fn. Therefore, the output signal of the ultrasonic receiver 9b is extracted as a frequency difference due to the so-called Doppler effect, is processed by the signal processing circuit, and finally the concentration of the component to be measured is displayed on the display or the like. . Note that the Doppler frequency Δfs is equal to the natural frequency fn of the Helmholtz resonator 8, which is 0.
Since the maximum value of Δfs changes periodically between Δfs and Δfs, the maximum value of Δfs is detected and processed by the signal processing circuit. According to the embodiment of the present invention as described in detail above, the infrared energy taken into the Helmholtz resonator 8 is stored and measured by the ultrasonic signal. Compared to the example, this method has an advantage in that the energy of infrared rays passing through the measurement gas and the like can be detected with high sensitivity. Further, compared to the conventional condenser microphone, etc., there is an advantage that there are fewer moving parts and less chance of failure. In the above embodiment, the case where the infrared energy taken into the Helmholtz resonator 8 is measured using an ultrasonic signal has been described in detail, but the present invention is not limited to this, and for example, the energy can be measured using a laser beam. Alternatively, the sound pressure of the resonance sound may be simply measured using a microphone.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the principle of a Helmholtz resonator, FIG. 2 is an explanatory diagram of an example of use of an embodiment of the present invention, and FIG. 3 is a plan configuration diagram of the constituent parts of a sector. 1, 2... Container, 3... Measurement cell, 3a, 3b
...Derivation/exit entrance, 4...Reference cell, 5a, 5b...
Light source, 6... Sector, 7... Motor, 8... Helmholtz resonator, 9a, 9b... Ultrasonic transmitter/receiver, 10... Central part, 10a ₁ to 10a _o ... Vane.

Claims (1)

[Claims] 1. A reference cell filled with a reference gas and a gas to be measured are supplied by high-speed chopping of infrared light emitted from a light source using a sector provided with a plurality of strip-shaped blades. As a detector for a non-dispersive infrared gas analyzer that irradiates infrared rays alternately and at high speed onto a measuring cell, detects the infrared rays absorbed by the measuring cell, and analyzes the concentration of the gas component to be measured in the gas to be measured. In an infrared detector used to detect the energy of incident infrared rays, a first container part into which the infrared rays that have passed through the reference cell enters, a second container part into which the infrared rays which have passed through the measurement cell enter, and these two containers. A Helmholtz resonator comprising a communication part that communicates the parts and filled with a predetermined gas containing the measurement component gas, and a Helmholtz resonator located on the wall surfaces of the first and second container parts at positions facing each other with the communication part in between. A measuring signal transmitter and a measuring signal receiver are respectively fixed, and the change in the infrared energy incident into the Helmholtz resonator is converted into vibration energy due to gas expansion in the Helmholtz resonator to generate Helmholtz resonance. and detecting the velocity amplitude of the gas in the Helmholtz resonator as a frequency difference due to the Doppler effect of the measurement signal emitted from the measurement signal transmitter, and outputting it from the measurement signal receiver. Infrared detector. 2. The infrared detector according to claim 1, wherein the measurement signal transmitter, measurement signal receiver, and measurement signal are respectively an ultrasonic transmitter, an ultrasonic receiver, and an ultrasonic signal. 3. The infrared detector according to claim 1, wherein the measurement signal transmitter, measurement signal receiver, and measurement signal are respectively a laser transmitter, a laser receiver, and a laser light signal.