KR20010077451A - Apparatus for detecting the concentration of gas using aerometric chamber - Google Patents

Abstract

PURPOSE: A gas density detecting device with a gas reaction chamber is provided to detect density of gas by measuring light absorption of gas with infrared rays, and to output the density of gas with an electrical signal by processing the signal from the gas reaction chamber. CONSTITUTION: A gas density detecting apparatus comprises a gas reaction chamber(1100) having a measuring light source(1110) emitting light including a wavelength reacting on gas by voltage in a case, a reference light source(1120) emitting light to a passage not to react on the specific gas by voltage in the case, and a single sensor(1130) receiving the specific wavelength from the reference light source and the measuring light source; and a sensor signal processing unit(1200) supplying power to the measuring light source and the reference light source, and outputting an electric signal in proportion to the density of gas by sorting the signals reacting on the measuring light source and the reference light source. The density of gas is measured accurately with two light sources, one passage and one sensor regardless of noise.

Description

Apparatus for detecting the concentration of gas using aerometric chamber

The present invention relates to an apparatus for analyzing the concentration of a specific component of a gas, and more particularly, a gas reaction chamber for detecting and analyzing a concentration of a specific gas using infrared light and a sensor, and gas concentration detection using the same. Relates to a device.

Recently, various types of gas concentration analyzers are used to monitor indoor and outdoor air components, to measure concentrations of various gases in medical anesthesia, and to monitor the concentration of carbon dioxide emitted from the human lung.

In general, gases such as carbon dioxide (CO ₂ ), carbon monoxide (CO), HC, and NO ₃ have a property of absorbing light in a specific wavelength band in the infrared region, respectively, and the degree of absorption increases as the gas concentration increases. An apparatus and method for measuring gas concentration using an infrared light source and a sensor using this phenomenon are used.

1 shows an apparatus for detecting a gas concentration by mounting an infrared light source and a sensor in a chamber. In the chamber 100, the infrared light source 110 and the sensor 120 are disposed to face each other, and the desired gas concentration is determined by measuring how far the infrared light from the infrared light source 110 reaches the sensor 120. . The reaction chamber of FIG. 1 is an example of a chamber for measuring carbon dioxide concentration in a room. The indoor air to be measured passes through the porous air filter 130 and is subjected to negative pressure by a weak vacuum pump. Exit to exit 140 above the chamber. Among the components of light emitted from the infrared light source 110 (hereinafter referred to as a lamp), the infrared component of 424 nm wavelength absorbed by carbon dioxide is absorbed by carbon dioxide present in the chamber for a while and the remaining amount reaches the light receiving surface of the sensor 120. . The sensor's infrared filter allows only light at 424nm wavelength to pass through, so the sensor's electrical signal output contains only carbon dioxide concentration information.

2A is a waveform of a voltage applied to the infrared light source 110 of FIG. 1, and FIG. 2B is a sensor output waveform when the sensor in the chamber of FIG. 1 is a photoconductive sensor. The solid and dashed lines represent the state of the sensor output signal at high and low gas concentrations, respectively. As the concentration of the gas to be detected decreases, the amount of infrared absorption decreases, so that the amplitude of the sensor output signal is large. FIG. 2C is a sensor output waveform when the sensor in the chamber of FIG. 1 is a pyroelectric sensor, and the output waveform becomes an exponential waveform because the sensing surface of the pyroelectric sensor responds to heat conduction. Because.

3 shows a structure of a conventional gas concentration detecting apparatus and a signal processing circuit, and processes a gas reaction chamber 300 in which gas concentration is detected and a signal detected therefrom, and outputs the detected gas concentration as an electrical signal. And a signal processing circuit 310. The structure of the gas reaction chamber 300 is the same as that described with reference to FIG. 1, wherein the sensor 302 includes both a photoconductive sensor, a pyroelectric sensor, and a thermopile sensor. Can be used. The signal processing circuit 310 includes a lamp driver circuit 311, a clock pulse generation circuit 312, a preamplifier circuit 313, a band pass circuit 314, a positive peak detection sample / hold circuit 315, and a bulk detection And a sample / hold circuit 316, a phase delay circuit 317, a differential amplifier 318, a temperature compensation amplifier 319, a linearized heavy amplifier 320, a low pass filter and an inverted output amplifier 321. The signal about the concentration of the gas detected from the reaction chamber 300 is processed and its magnitude is output.

FIG. 4 shows waveforms observed in each part shown in FIG. 3. The operation of FIG. 3 will now be described with reference to the block diagram of FIG. 3 and the waveform of FIG. 4.

First, a square wave voltage such as A of FIG. 4 is input to the infrared lamp 301 of the chamber 300 to periodically flash the lamp. The flashing cycle of the lamp can vary depending on the response speed desired by the meter, typically from 0.1Hz to 10Hz. When the concentration of the gas to be measured in the chamber is detected by the flashing of the infrared lamp 301 and output through the sensor 302, the preamplifier 313 amplifies the waveform output from the sensor to produce a waveform as shown in FIG. 4B. Obtained. The reason why the lamp is flickering is because the signal output from the sensor is very weak, so the preamplifier has a high gain, but when using a DC amplifier, the operating point voltage and the amplifier bias voltage of the sensor according to the temperature change are used. The DC voltage drift propagates to the rear end according to the change of, thereby reducing the stability of the measurement. For this reason, intermittent optical chopping is necessary to cut off direct current and amplify only the AC signal. It can be seen that the waveform obtained in B gradually increases in amplitude over time, which is a result of the fact that the concentration of a specific gas entering the chamber gradually decreases. The waveform passed through the bandpass circuit 314, which is a bandpass filter, to remove DC drift and high frequency noise is as shown in C of FIG. 4, and positive and negative, respectively, to generate a DC voltage indicating the magnitude of concentration. Through the negative peak detection sample / hold circuits 315 and 316, waveforms that sample-hold the positive and negative maximums are shown in D and E of FIG. 4, respectively. The phase delay circuit 317 is used to delay the phase of the E signal. To obtain the amplitude signal of the sensor signal, the sample-holded signal is input to the differential amplifier 817 to obtain waveform F, which is the difference between the two signals. In FIG. 4, the linearity amplifier 320 compensates the nonlinearity of the sensor characteristics and passes the low pass filter and the inverted output amplifier 321 to obtain an output signal proportional to the concentration. In this single light source gas concentration sensing method, the signal voltage is severely changed due to the external temperature change. Therefore, when the F signal is input in the figure, the process of compensating with the temperature compensation amplifier is essential.

FIG. 5 illustrates a change in output voltage according to temperature change and disturbance in FIG. 4. The A waveform is an example of a temperature change in the chamber and an external disturbance thermal noise waveform, and the B waveform shows an output signal of the sensor in a steady state without disturbance or temperature change in the chamber. C shows the sensor output signal when there is disturbance and temperature change in the chamber. D shows the output waveform in the F position of FIG.

In the gas concentration detection apparatus as described above, the price of the photoconductive sensor generally used for detecting carbon dioxide and nitrate gas concentration is much higher than the price of the pyroelectric sensor and thermocouple sensor used for the same purpose. As the price of photoconductive infrared sensor is high, it has more stable characteristics against temperature and ambient thermal noise than using pyroelectric sensor and thermocouple sensor. In the future, however, low-cost pyroelectric and thermocouple sensors are expected to be used to reduce the manufacturing cost of products. If the pyroelectric sensor is used in the reaction chamber of FIG. 1 and the circuit of FIG. 3, a change in output voltage of the sensor as shown in FIG. 5 causes a measurement error. The reason is that the base element itself of a pyroelectric sensor without an infrared filter has a wide band so that the response spectral range is theoretically from direct current to infinity frequency, so even if a filter for selecting a specific wavelength is applied, a small amount of indirect penetration through the case of the sensor is required. This is because the noise caused by heat cannot be prevented. Therefore, when the length of the optical path of the reaction chamber is short, the degree of light absorption in the path of light is small. Therefore, the signal signal noise ratio (S / N ratio) is lowered because of the small change in the output signal amplitude. The distinction between cars is not made properly. In the case of the thermocouple sensor, the shape of the sensor output waveform is slightly different from those of FIGS. 4 and 5, and the effect on noise is similar to that of the pyroelectric sensor. Therefore, the conventional gas concentration detection system structure is impossible to implement a small and precise gas concentration meter when using the low-cost sensor described above.

The pyroelectric sensor and thermocouple sensor have a very large amplitude of the output signal and drift of the baseline when the outside air is changed due to ventilation, or when used for a long time. In this case, the temperature sensor 303 and the temperature compensation amplifier attached to the chamber in FIG. The temperature compensation method by 319 does not solve the problem perfectly.

When developing a miniaturized portable gas concentration meter such as a medical or household carbon dioxide gas meter, the shorter the reaction chamber is, the more advantageous it is. Even if a photoconductive sensor is used, the shorter the reaction chamber, the lower the S / N ratio. It is practically difficult to miniaturize the current (about 7 ~ 8cm in the case of carbon dioxide meter for indoor air monitoring).

The technical problem to be achieved by the present invention is to measure the light absorption reaction of the gas in the gas concentration meter using infrared rays and to measure the concentration of the gas to be measured by processing the signal output from the gas reaction chamber for detecting the concentration of the gas to be measured therefrom. The present invention provides a gas concentration detection device that outputs a signal.

1 shows an apparatus for detecting a gas concentration by mounting an infrared light source and a sensor in a chamber.

2A is a waveform of a voltage applied to the infrared light source 110 of FIG. 1.

FIG. 2B is a sensor output waveform when the sensor in the chamber of FIG. 1 is a photoconductive sensor.

2C is a sensor output waveform when the sensor in the chamber of FIG. 1 is a pyroelectric sensor.

3 shows the structure of a conventional gas concentration detection device and a signal processing circuit.

FIG. 4 shows waveforms observed in each part shown in FIG. 3.

FIG. 5 illustrates a change in output voltage according to temperature change and disturbance in FIG. 4.

6 is an embodiment of a gas reaction chamber in accordance with the present invention.

7 is another embodiment of a gas reaction chamber according to the present invention.

8 shows left and right side views of the chamber of FIG. 7, respectively.

9 (A) is another embodiment of a gas reaction chamber according to the present invention.

FIG. 9B is a top view of the gas reaction chamber of FIG. 9A.

FIG. 9C shows both side views of FIG. 9A.

10A illustrates in detail the arrangement of the reference light sources in FIG. 9.

10B illustrates another arrangement of the reference light source in FIG. 9 in detail.

FIG. 10 (C) shows that the reference light source is arranged in parallel with the light receiving portion of the sensor in the Teflon insulation ring as the heat insulating material when FIG. 10 (B).

11 is a block diagram of a gas concentration measuring apparatus according to the present invention.

12 is a waveform diagram of each component part displayed in the sensor signal processor of FIG. 11.

13 is another structural example of the gas concentration measuring apparatus according to the present invention.

FIG. 14 is a waveform diagram for each component part displayed by the sensor signal processor of FIG. 13.

In order to accomplish the above object, a gas concentration detecting device includes a measuring light source that emits light including a wavelength reacting with a predetermined gas to be measured by a predetermined voltage supplied from the outside in a case through which external air can enter and exit, the case A reference light source that emits the same light as the measurement light source by a voltage supplied from the outside, but receives only the specific wavelength from the measurement light source and the reference light source and emits light in a path that cannot react with the specific gas A gas reaction chamber having a single sensor; And supplying a predetermined voltage to the measurement light source and the reference light source, distinguishing a signal reacted by a measurement light source from a signal output from the sensor and a signal reacted by a reference light source, and giving a difference between the two separated signals. It characterized in that it comprises a sensor signal processor for outputting an electrical signal proportional to the gas concentration.

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

6 is an embodiment of a gas reaction chamber according to the present invention, the gas reaction chamber is provided with a case 600, a measurement light source 610, a reference light source 620, a measuring sensor 611, a reference sensor 621. do. For example, the case 600 made of a case made of aluminum has an external air input through the porous air filter 601 at the top of the drawing, and a negative pressure is applied by a weak vacuum pump (not shown). The outlet 602 above the chamber is configured to allow air to escape. The measurement light source 610 is for emitting light including a wavelength having a property of being absorbed in a specific gas (for example, carbon dioxide) to be measured in the external air input into the case 600. Therefore, the measurement light source 610 is positioned to emit a light beam in a passage in which external air exists in the case 600. When measuring the concentration of carbon dioxide, the measurement light source 610 becomes an infrared light source, of which light of wavelength 424nm is absorbed by the carbon dioxide. When the measurement light source 610 emits infrared rays by a predetermined voltage supplied from the outside, when the concentration of carbon dioxide in the measurement light path 630 is high, a wavelength of 424 nm is absorbed by the carbon dioxide and reaches the measurement sensor 611. The signal of? Will be small, and if the concentration of carbon dioxide is lean, the signal of wavelength 424 nm of the infrared rays reaching the measuring sensor 611 will be large. The reference light source 620 is driven by the same external voltage as the measurement light source 610 and outputs the same light beam as the measurement light source 610. Light rays emitted from the reference light source 620 are emitted along the reference light passage 640, which should be a passage in which no outside air exists so as to be independent of an external noise source. The reference light source 620 reaches the reference sensor 621. The measuring sensor 611 and the reference sensor 612 receive only light rays having the same wavelength (for example, 424 nm) and output an electrical signal proportional to the size or intensity of the received light rays.

In FIG. 6, a reference light path 640 and a measurement light path 630 are provided for stable measurement of the gas concentration irrespective of an external noise source, and two light sources 620 and 610 and two sensors flashing simultaneously in each path. (621, 611), the output signals from the two sensors are input to opposite inputs of differential amplifiers (not shown) outside the chamber and the difference is canceled and the noise component is canceled and the signal for the gas concentration to be measured Stable amplification is possible. This can be expressed as in Equation 1.

Here, the light intensity of the measurement light source and the reference light source is I, the amount of light attenuated through the reference passage 640 (The measurement path 630 also has the same amount of light attenuation irrespective of the presence or absence of external air), noise caused by thermal convection or conduction due to thermal noise or temperature difference from the outside, which affects the measuring sensor 611 and the reference sensor 621. N is the same, the response characteristics of the two sensors are the same and the conversion efficiency to the electrical signal is the same. It is called. I_s is an amount of light attenuation due to light absorption of a specific gas (eg, carbon dioxide) on the measurement passage 611. e_0 is a differential output signal from the outputs of the reference sensor 621 and the measurement sensor 611, it can be seen that the reduction value of the amount of light by the gas to be measured can be obtained irrespective of noise. In this example, the characteristics of the reference sensor 621 and the measurement sensor 611 should be the same so that Equation 1 is possible. However, this is very difficult in reality, and even if the sensor characteristics are identical, two sensors are used, which causes a high cost.

FIG. 7 illustrates a configuration of a chamber using only one sensor to compensate for the disadvantages of FIG. 6 as another embodiment of the gas reaction chamber according to the present invention. In the configuration of the chamber shown here for the components that perform the same characteristics and operations as in FIG. In comparison with FIG. 6, in order to use one sensor, the light beam from the measuring light source 610 and the light beam from the reference light source 620 are simultaneously collected on the light receiving surface of the sensor 700 as the light beam approaches the sensor 700. The reflection mirrors 710 and 720 are provided on both walls of the V-shape to solve the gathering of the above-mentioned light beams to the light receiving portion. In addition, there is no air flow between the reference light path 640 and the measurement light path 630, and the transparent diaphragm 730 should be installed so that the light of the reference light path 640 freely reaches the sensor. When two light sources blink at the same time, the light of two stems traveling in different passages simultaneously enters one sensor 700 and the response of the sensors is mixed, so that the intention to obtain the difference between the two responses cannot be executed. Therefore, the flickering of the measurement light source and the reference light source does not occur at the same time, and the flickering waveform of the reference light source is delayed by 180 degrees compared to the flickering of the measurement light source. That is, the difference between the signal received and held by the sensor signal from the reference light source 620 that is turned on when the measurement light source 610 is turned off after receiving and holding the sensor signal when the measurement light source 610 is turned on. Obtain This effectively produces the same result as using two sensors. However, this must be followed by the premise that the amount of noise n is equal immediately before and immediately after the half cycle of the lamp blinking. In general, since the sensor is deeply installed in a material such as aluminum, and the external light is blocked, the external noise on the sensor is only the infrared noise coming through the case surrounding the sensor. In the case of infrared noise, the premise of noise due to external heat is justified given the time taken to heat the case. That is, since the magnitude of the noise does not change rapidly in the half cycle time, it is not practical to drive the measurement light source and the reference light source alternately. However, in the case of FIG. 7, the transparent diaphragm from the reference light source is caused by the surface of the measuring passage side of the transparent diaphragm glass 730 installed between the measuring light path and the reference light path by being clouded or contaminated by air or dust from the outside air. Since the transmission efficiency of light rays through the glass 730 is reduced, there is a possibility of causing a measurement error in the long term use.

FIG. 8 illustrates left and right side views of the chamber of FIG. 7, in which a hole for installing the measurement light source 610 and the reference light source 620 is installed on the left side of the case 600, and one sensor 700 is installed on the right side of the case 600. You can see that there is a hole to be made.

Figure 9 (A) shows another embodiment of the gas reaction chamber according to the present invention, this embodiment is a configuration of a chamber that is a two-light source 1 sensor one passage that improves the problem of Figure 8, which is a case ( 900, a measurement light source 910, a reference light source 920, and a sensor 930. The case 900 is the same case as illustrated in FIGS. 6 to 8. The measurement light source 910 is installed at one end of the case 900 and emits light having a wavelength that reacts with a gas to be measured by an AC voltage transmitted from the outside. Light rays having a specific wavelength among light rays emitted from the measurement light source 910 are absorbed by a specific gas to be measured in the outside air entering and exiting the case 900, and only the rest is transmitted to the light receiving portion of the sensor 930. The central axis and the diverging direction of the light emitted from the measurement light source coincide with the position of the light receiving portion of the sensor 930 located at the other end of the case 900. Therefore, no special reflector 710 or the like needed in FIG. 7 is needed. The reference light source 920 is positioned close to the sensor so that the emitted light does not react with the predetermined air in the case 900 and is directly input to the sensor 930 while the voltage is supplied. The size of the reference light source is drawn smaller than the measurement light source because the attenuation of the amount of light may be as small as it is closer to the sensor. This method uses one channel and one sensor, but alternately cycles the measurement light source and reference light source by half cycle, and in the signal processing circuit at the back stage, flickers the reference light source which is delayed and stored by half cycle and outputs the measurement light source in the signal processing circuit at the rear stage. It is the same as the reaction chamber of FIG. 6 because the sensor response by the reference light source lamp, which is delayed and stored by the output and the half cycle, is used and the difference is used. FIG. 9B is a top view of the gas reaction chamber of FIG. 9A, and FIG. 9C shows both side views of FIG. 9A. The arrangement of the reference light source 920 and the sensor 930 is shown in more detail in FIG. 10A and FIG. 10B shows another arrangement of the reference light source. 10 (A) shows an arrangement in which the reference light source is installed at 90 degrees with the optical axis of the measurement light source on the side wall close to the sensor, and FIG. 10 (B) shows a small light source in a part of the insulating material used when installing the sensor in the case. It is shown that is arranged to have an optical axis shifted by 180 degrees with the optical axis of the measurement light source as a reference light source. FIG. 10 (C) shows that a reference light source is arranged in parallel with the light receiving portion of the sensor in a Teflon insulating ring, which is an insulating material, which is an ellipse portion of FIG. 10 (B).

11 is a configuration diagram of a gas concentration measuring apparatus according to the present invention, wherein the gas concentration measuring apparatus includes a gas reaction chamber 1100 and a sensor signal processor 1200. The gas reaction chamber 1100 includes a measurement light source 1110 that emits light including a wavelength that reacts with a predetermined gas to be measured by a predetermined voltage supplied from the outside in a case through which external air can enter and exit, and the outside in the case. A reference light source 1120 which gives light of the same intensity as the measurement light source to the sensor light-receiving surface by a voltage supplied from the sensor, but emits light in a path that cannot react with the specific gas, and from the measurement light source and the reference light source The sensor 1130 receives only a specific wavelength. The gas reaction chamber 1100 herein may be any of FIG. 7 or FIG. 9. The sensor signal processing unit 1200 supplies a predetermined voltage to the measurement light source and the reference light source, and distinguishes the signal reacted by the measurement light source and the signal reacted by the reference light source among the signals output from the sensor, and compares the two separated signals. To output an electrical signal proportional to the gas concentration to be measured. The sensor signal processor 1200 may include a preamplifier circuit 1210, a band pass filter circuit 1220, a peak detection circuit 1230, a sample hold circuit 1240, an output low pass filter amplifier circuit 1250, and a display circuit 1260. ). When the peak value of the sensor signal output from the gas reaction chamber 1100 at predetermined intervals is P and the peak value of the sensor signal output half a period later is Q, PQ is performed on the same principle as in Equation 1 above to perform differential output. And the value inverted becomes a voltage indicating the concentration of a particular gas. An operation of the sensor signal processor 1200 will be described in detail with reference to the waveform of FIG. 12. A and B are waveforms of voltages for driving the measurement light source 1110 and the reference light source 1120, respectively, and it can be seen that B is supplied with a phase delay for half a period compared to A. Since the light emitted when the measurement light source 1120 is turned on is absorbed by a specific gas to react during the passage in the case, the preamplifier circuit 1210 decreases as the concentration of the specific gas decreases, such as C. The peak value of the output voltage increases. On the other hand, while the voltage of the voltage B after the half cycle drives the reference light source 1120, since a predetermined wavelength of the light source emitted from the reference light source is input to the sensor before reacting to the specific gas, It can be seen from C that an unrelated sensor output is obtained. When the waveform passed through the preamplifier circuit 1210 passes through the band pass filter circuit 1120, the waveform becomes the same as D. Then, the peak value detected by the peak detection circuit 1130 is terminated every half cycle by the clock pulse. It is held and output as E. This signal is again passed through the sample and hold circuit to obtain a stable concentration signal that corresponds to the peak value to obtain the waveform of F. Then, while adjusting the DC level for gain control and calibration, the phase inversion is performed so that the F signal, which is expressed to have a high output voltage when the concentration is low, and the large output signal voltage when the concentration is high, is reversed. The final signal G is obtained. The output voltage G is displayed to the user through the display circuit 1260. G is a voltage that is proportional to the concentration of a particular gas, regardless of ambient thermal noise or temperature changes. Since this method uses a differential reaction chamber based on the measurement light source and the reference light source, a separate temperature sensor and a corresponding temperature compensation circuit are unnecessary in the circuit. However, in order to implement more precise concentration measurement, the temperature in the gas reaction chamber 1100 may be increased. A circuit may be configured to additionally perform temperature compensation in the sensor signal processing unit 1200 by attaching a sensor and using the signal from the excitation signal, which is indicated by a dotted line in FIG. 11.

13 is another example of the gas concentration measuring apparatus according to the present invention, but the gas reaction chamber 1110 is the same, but the sensor signal processing unit 1300 has a different configuration. In the sensor signal processing section, the reference lamp driver circuit, the main lamp driver circuit, the 180-degree phase delay circuit, and the clock pulse generation circuit are the same as those in FIG. However, the process of processing the output signal of the sensor is different from that configured using the analog multiplier 1340 in FIG. 13 so that a stable gas concentration can be detected instead of the peak detection circuit 1230 and the sample hold circuit 1240 of FIG. .

FIG. 14 illustrates waveforms of positions denoted by the letters A, B, C, and D in the configuration diagram of FIG. 13. First, when the gas concentration in the chamber gradually decreases with time, the signal obtained by the infrared sensor 1130 becomes waveform C in FIG. 14 as in the case of waveform C of FIG. 12. After the signal passes through the narrow band bandpass filter 1320, the waveform has a sine wave shape, which is a fundamental wave of the ramp driving voltage, as shown in waveform D, and the amplitude changes in time according to the gas concentration. This is a sine wave which is a fundamental wave of a clock pulse having a constant amplitude obtained by passing a square wave pulse voltage for driving a lamp through a variable phase circuit 1380 to match a phase with a waveform D and then passing through another narrowband bandpass filter 1330. The signal is input to the analog multiplier 1340 together with E. The resultant signal is a product of one sinusoidal signal having the same frequency and phase and having a different amplitude, and a sinusoidal signal having a constant amplitude, thereby obtaining a result as shown in Equation 2 below.

This result shows the signal of sensor signal waveform D. Called the waveform E Is multiplied by two signals. The waveform of this result is the same as the waveform F of FIG. The preferred output signal is the low-frequency component of this waveform, so the first term on the right side of the equation above Which is twice the clock frequency The term is removed from the low pass filter 1350. As such, the signal obtained by filtering the double component of the clock signal and passing the inverting amplifier is the same as the waveform G of FIG. here, Is the frequency of the clock signal and the maximum frequency of the signal component Sig By setting it much higher (more than 4 times), the signal output is filtered and small. Therefore, the cutoff frequency of the lowpass filter Higher than Which is lower than 2 To 3 Decide on the degree. The signal G, which has passed the lowpass filter, is applied to the output amplifier gain circuit 1360 to obtain the amplification degree necessary to supply it to the digital or analog display circuitry 1370.

In this way, the one-pass one-sensor is used, but the influence on external noise can be significantly reduced compared to the conventional one-light-type reaction chamber, thereby enabling accurate gas concentration measurement. In addition, the length of the reaction chamber is the length of the reaction chamber when making a portable measuring instrument. This method is suitable for the manufacture of miniaturized devices because the S / N ratio is higher than the conventional 1-light source method, so the size of the reaction chamber can be reduced. Do. In addition, in the case of pyroelectric and thermocouple sensors, it is difficult to stably measure the concentration of carbon dioxide gas in the air with the length of the reaction chamber of less than 10 cm, but as an improved device, even half of this length is sufficient. Therefore, it can be widely used in gas concentration analyzers using low cost pyroelectric and thermocouple sensors. In addition, by using only one sensor and one optical path, it is possible to achieve the noise removal effect such as using the two-sensor two-path, so that the reaction chamber can be easily processed and manufactured. Finally, since only the difference between the signal from the measurement light source and the reference light source is used, the aging effect of the filament of the lamp according to the long-term use and the amount of light due to the contamination of the light source surface by gas are used. The impact of degradation is reduced.

According to the present invention, the gas concentration can be precisely measured by removing the influence of external noise by using one light path and one path sensor.

Claims (8)

A measurement light source that emits light including a wavelength reacting with a predetermined gas to be measured by a predetermined voltage supplied from the outside in a case through which external air can enter and exit, and the measurement light source by a voltage supplied from the outside in the case; A gas reaction chamber that emits the same light but emits light in a path that cannot react with the specific gas, and a gas reaction chamber having a single sensor that receives only the specific wavelength from the measurement light source and the reference light source; And Supplying a predetermined voltage to the measurement light source and the reference light source, and distinguished between the signal reacted by the measurement light source and the signal reacted by the reference light source among the signals output from the sensor and to measure the difference between the two signals separated And a sensor signal processor for outputting an electrical signal proportional to the gas concentration. The method of claim 1, The measurement light source and the reference light source are each driven by a voltage exhibiting a phase difference of half wavelength, wherein the sensor alternately receives for the wavelength emitted from the measurement light source and the reference light source. The method of claim 2, wherein the sensor, A gas concentration detection device, characterized in that the gas state is shared with only one of the measurement light source and the reference light source, but placed in a position to receive light from both light sources. The method of claim 2, The measuring lamp has a central axis for emitting light and its direction toward the light receiving portion of the sensor, And the reference lamp is positioned close to the sensor so that the emitted light is first input to the sensor before reacting with the predetermined air in the case while the voltage is supplied at a predetermined period. The method of claim 4, wherein the reference lamp A gas concentration detection device, characterized in that placed in a position that emits light in a direction 90 degrees or obliquely shifted with respect to the passage length direction of the measurement chamber. The method of claim 4, wherein the reference lamp And a position at which light is emitted in a direction shifted obliquely at an angle of 180 degrees or a similar angle with respect to a length direction of the passage of the measuring chamber, that is, at a position parallel to the sensor. The method of claim 2, wherein the sensor signal processing unit, A lamp power supply circuit for supplying the measurement light source and the reference light source with a square wave voltage having a predetermined period and a voltage having a phase delay of half a period from the voltage; An amplifier and filter unit for amplifying and filtering the signal output from the sensor; A peak value detector for detecting a peak voltage of the signal output from the amplification and filter unit; A sample and hold unit which samples and holds the voltage output from the peak value detector to obtain a stable signal; A filter and amplifying unit for filtering and amplifying the signal output from the sample and hold unit to a predetermined level; And And a display unit for displaying the signal output from the filter and the amplifier. The method of claim 7, wherein the sensor signal processing unit, A square wave voltage of a predetermined period and a voltage delayed by a half cycle with respect to the voltage are supplied to the measurement light source and the reference light source, respectively, wherein the frequency of the clock pulse driving the lamp is higher than the maximum possible frequency of the gas concentration change signal. Phosphor lamp power supply circuit; A preamplifier circuit for amplifying the signal output from the sensor; A first band pass filter unit configured to band pass filter the signal passing through the preamplifier circuit and output only a fundamental wave signal; A phase varying circuit for varying a phase of a signal output from the lamp power supply circuit to be equal to a signal passing through the preamplifier; A second band pass filter unit outputting only a fundamental wave signal from the signal output from the phase variable circuit; An analog multiplier unit for multiplying two signals from the first and second band pass filter units to generate an output signal including a signal voltage of a low frequency component and a cosine waveform having a frequency twice the clock frequency; A gas concentration signal voltage is output by removing a cosine component having a frequency higher than the maximum frequency that the gas concentration signal has and having a cutoff frequency lower than the clock frequency and having a frequency twice the clock frequency among the signals output from the analog multiplier. Low pass filter unit to make; An output gain amplifier section for amplifying the magnitude of the gas concentration signal voltage output from the low pass filter section to a predetermined level; And And a digital / analog display capable of displaying the output signal of the output gain amplifier unit to a user in digital or analog form or transmitting the output signal to the user.