JP2006038721A - Gas concentration detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct CO<SB>2</SB>concentration that fluctuates by sensor characteristics. <P>SOLUTION: A gas concentration detector comprises a light source 10 for emitting light; first and second IR sensors 21, 22 for receiving light on a light receiving surface and generating an electrical signal at a level corresponding to the intensity of light; a CO<SB>2</SB>concentration-dependent filter 30 that is arranged on the light receiving surface of the second IR sensor 22 and makes the light pass, including the light absorbing wavelength of CO<SB>2</SB>gas; and a comparison section 40 for setting a value obtained, by dividing the electromotive voltage of the second IR sensor 22 by that of the first IR sensor 21 to be the voltage ratio, and for calculating the voltage ratio. Then, the temperature and humidity of the first IR sensor 21 are detected by a temperature sensor 51 and a moisture sensor 52. A correction section 60 has temperature characteristics and moisture characteristics of the electromotive voltage in the first IR sensor 21 as sensor characteristics, and corrects the value of the voltage ratio, based on the electromotive voltage of the first IR sensor 21, temperature, moisture, and the temperature characteristics and moisture characteristics of the electromotive voltage. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a gas concentration detection device that detects the concentration of CO ₂ (carbon dioxide) gas.

2. Description of the Related Art Conventionally, gas concentration detection devices that detect gas concentration in the atmosphere, particularly CO ₂ concentration, are known. FIG. 3 is a block diagram of a conventional gas concentration detection device. The gas concentration detection device generates an electromotive voltage according to the light source 10 that emits light including infrared light and the intensity of incident infrared light, and outputs the electromotive voltage as a voltage signal. , 22, a CO ₂ concentration-dependent filter 30 composed of a band-pass filter that allows only a predetermined wavelength to pass, and a comparison unit 40 that obtains a ratio of voltage signals output from the first and second IR sensors 21, 22 It is configured with.

As shown in FIG. 3, the CO ₂ concentration dependent filter 30 is disposed at a position facing the light receiving surface of the second IR sensor, for example. The CO ₂ concentration dependent filter 30 is configured to pass light having substantially the same wavelength as the light absorption wavelength of the CO ₂ gas.

When CO ₂ is introduced into the gas concentration detection device as described above, the CO ₂ gas absorbs light of a specific wavelength in the light emitted from the light source 10. As a result, the intensity of light passing through the CO ₂ concentration dependent filter 30 decreases. Therefore, the electromotive voltage generated in the second IR sensor 22 is reduced. By monitoring the electromotive voltage of the second IR sensor 22, the concentration of CO ₂ introduced into the apparatus can be detected.

Further, the comparison unit 40 obtains a ratio (hereinafter referred to as a voltage ratio) by dividing the second IR sensor 21 electromotive voltage by the electromotive voltage of the first IR sensor 21 using the electromotive voltage of the first IR sensor 21 as a reference. This makes it possible to obtain a CO ₂ concentration that does not depend on fluctuations in the intensity of light emitted from the light source 10.

However, in the above conventional technique, the influence of the sensor characteristics of the first and second IR sensors 21 and 22, for example, the temperature characteristics of the electromotive voltage is not taken into consideration. That is, there arises a problem that an electromotive voltage generated in each of the sensors 21 and 22 fluctuates with an environment where the sensors 21 and 22 are exposed. As a result, the voltage ratio obtained by the comparison unit 40 also varies, and there is a possibility that an accurate CO ₂ concentration cannot be obtained.

In view of the above points, an object of the present invention is to provide a gas concentration detection device capable of correcting a CO ₂ concentration that varies depending on sensor characteristics.

In order to achieve the above object, according to the first aspect of the present invention, there is provided a gas concentration detection device for detecting the concentration of CO ₂ gas contained in the air, wherein the light source (10) that emits light and the light receiving surface are light sources. A first sensor (21) and a second sensor (22) that receive light at a light receiving surface and generate an electric signal of a level corresponding to the intensity of the light; A filter (30) that is disposed on the light receiving surface of the first sensor and guides the light to the second sensor after passing the light including the light absorption wavelength of the CO ₂ gas; the electrical signal of the first sensor; Based on the electrical signal of the sensor, a comparison unit (40) that calculates a parameter indicating the concentration of CO ₂ gas, a temperature detection unit (51) that detects the temperature of the first sensor, and the parameter and temperature are input And use this temperature to supplement the parameters. It is characterized by having correcting unit to (60), the.

Thus, the parameter indicating the concentration of CO ₂ gas is corrected using the temperature of the first sensor. Thereby, the concentration of the obtained CO ₂ gas can be set to a value independent of temperature. In this way, the CO ₂ gas concentration can be corrected.

  In the second aspect of the invention, the comparison unit calculates a signal ratio that is a value obtained by dividing the electric signal of the second sensor by the electric signal of the first sensor as a parameter, and the correction unit uses the first characteristic as a sensor characteristic. Having a temperature characteristic of an electrical signal in one sensor and inputting an electrical signal, a signal ratio and a temperature of the first sensor, and based on an electrical signal of the first sensor, a temperature, and a temperature characteristic of the electrical signal, It is characterized in that the signal ratio is corrected.

Thus, the voltage signal of the second sensor is divided by the first sensor. This makes it possible to obtain a CO ₂ concentration that does not depend on fluctuations in the intensity of light emitted from the light source. And the temperature of the 1st sensor is measured and this temperature and the electric signal of the 1st sensor are inputted into the amendment part. As a result, the correction unit can correct the signal ratio to a value (that is, CO ₂ concentration) corresponding to the temperature characteristic of the electrical signal of the first sensor. Therefore, a more accurate CO ₂ concentration can be obtained in consideration of the influence of sensor characteristics, particularly temperature characteristics.

According to a third aspect of the present invention, there is provided a gas concentration detection device for detecting the concentration of CO ₂ gas contained in the air, wherein the light source (10) for emitting light and the light receiving surface are arranged to face the light source. The first sensor (21) and the second sensor (22) for receiving light at the light receiving surface and generating an electric signal at a level corresponding to the intensity of the light, and on the light receiving surface of the second sensor A filter (30) that is disposed and transmits light including the light absorption wavelength of CO ₂ gas to the second sensor after passing the light; and an electrical signal of the first sensor and an electrical signal of the second sensor Based on the comparison unit (40) for calculating the parameter indicating the concentration of CO ₂ gas, the humidity detection unit (52) for detecting the humidity in the vicinity of the first sensor, the parameter and the humidity are input, and this humidity is used. Corrector for correcting parameters (60) It is characterized by having a.

Thus, the parameter indicating the concentration of CO ₂ gas is corrected using the humidity in the vicinity of the first sensor. This makes it possible to a value that does not depend the concentration of CO ₂ gas obtained in humidity. In this way, the CO ₂ gas concentration can be corrected.

  In the invention according to claim 4, the comparison unit calculates a signal ratio that is a value obtained by dividing the electric signal of the second sensor by the electric signal of the first sensor, and the correction unit uses the first characteristic as the sensor characteristic. The sensor has an electrical signal humidity characteristic, and inputs the electrical signal, signal ratio, and humidity of the first sensor, and the signal ratio based on the electrical signal, humidity, and humidity characteristics of the electrical signal of the first sensor. It is characterized by the fact that it is designed to correct.

In this way, the humidity to which the first sensor is exposed is detected. Thereby, the signal ratio can be corrected by humidity, and a CO ₂ concentration independent of humidity can be obtained.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In the following, the same components as those shown in FIG. Also, but not limited to, gas concentration detection apparatus according to an embodiment of the present invention is installed in the passenger compartment of the vehicle, the gas concentration in the passenger compartment, and in particular, for detecting a CO ₂ concentration.

FIG. 1 is a block diagram of a gas concentration detection apparatus. As shown in FIG. 1, the gas concentration detection apparatus includes a light source 10, a first IR sensor 21, a second IR sensor 22, a CO ₂ concentration dependent filter 30, a comparison unit 40, a temperature sensor 51, and a humidity sensor. 52 and a correction unit 60.

  The light source 10 emits light, particularly infrared light. The light source 10 only needs to emit infrared light, and for example, a lamp is employed.

  The first and second IR sensors 21 and 22 are well-known optical sensors that detect infrared light. Each of these sensors 21 and 22 is configured by using, for example, a semiconductor element formed on a semiconductor substrate as a light receiving surface. In each of such sensors 21 and 22, the light receiving surface is disposed so as to face the light source 10, and an electromotive voltage is generated according to the intensity of infrared light incident on the light receiving surface. Output as a signal.

  In the present embodiment, the first and second IR sensors 21 and 22 having the same sensor characteristics are used. The first IR sensor 21 corresponds to the first sensor of the present invention, and the second IR sensor 22 corresponds to the second sensor of the present invention.

As described above, in the present embodiment, two IR sensors are used. Among these, the first IR sensor 21 outputs an electromotive voltage as a reference (reference voltage) when calculating the voltage ratio. This is because the intensity of light emitted from the light source 10 is not always constant, so that the voltage ratio value described later is always independent of the light intensity of the light source 10. Further, the 2IR sensor 22 is one responsible for detecting the CO ₂ concentration and generates an electromotive voltage corresponding to the CO ₂ concentration.

The CO ₂ concentration dependent filter 30 is a so-called band-pass filter that allows only light having a predetermined wavelength to pass therethrough. In the present embodiment, the predetermined wavelength is the light absorption wavelength of CO ₂ gas. The CO ₂ concentration dependent filter 30 is disposed at a position facing the light receiving surface of the second IR filter 22 as shown in FIG. The CO ₂ concentration dependent filter 30 corresponds to the filter of the present invention.

The comparison unit 40 calculates a ratio of voltage signals input from the first and second IR filters 21 and 22, that is, a voltage ratio (signal ratio). In the present embodiment, the comparison unit 40 uses the electromotive voltage detected by the first IR filter 21 as a reference (reference). This voltage ratio is a parameter indicating the concentration of CO ₂ gas. As described above, when the CO ₂ concentration increases, the electromotive voltage generated in the second IR sensor 22 decreases. Therefore, it can be said that the closer the voltage ratio is to 1, the lower the CO ₂ concentration is, and the closer the voltage ratio is to 0, the higher the CO ₂ concentration is.

  The temperature sensor 51 measures the temperature to which the first and second IR sensors 21 and 22 are exposed, and includes, for example, a thermistor. That is, the temperature sensor 51 measures an electromotive voltage generated in the thermistor according to the temperature, converts the electromotive voltage into a temperature, and outputs the temperature. The temperature sensor 5 corresponds to a temperature detection unit of the present invention.

  The humidity sensor 52 measures the humidity to which the first and second IR sensors 21 and 22 are exposed, and includes, for example, a capacitor. The humidity sensor 52 utilizes the fact that the capacitance changes when the capacitor absorbs moisture. The humidity sensor 52 detects the change in the capacitance and converts the capacitance into humidity for output. Note that when the capacitor loses moisture, it returns to its original capacity. The humidity sensor 52 corresponds to a humidity detection unit of the present invention.

  The correction unit 60 corrects the voltage ratio input from the comparison unit 40 and outputs it as a sensor output of the present apparatus, and has a configuration including a correction circuit and a memory. In this memory, correction parameters for correcting the voltage ratio according to the sensor characteristics of the first IR sensor 21 are stored. Then, the correction unit 60 determines a correction parameter from the input temperature and humidity values and the electromotive voltage of the first IR sensor 21, and corrects the voltage ratio by the correction circuit using the correction parameter.

  Specifically, the sensor characteristics of the first IR sensor 21, that is, the temperature characteristics and humidity characteristics of the electromotive voltage are examined in advance. Based on the temperature and humidity values detected by the temperature sensor 51 and the humidity sensor 52, correction parameters corresponding to the temperature characteristics and humidity characteristics of the electromotive voltage of the first IR sensor 21 are set. The correction parameters thus set are stored in advance in the memory of the correction unit 60.

FIG. 2 is a diagram showing sensor output with respect to CO ₂ concentration (that is, voltage ratio). As shown in FIG. 2, a proportional relationship is established between the CO ₂ concentration and the sensor output by the correction parameter. As described above, the linear straight line representing the proportional relationship is set based on the correction parameter determined by the temperature and humidity, and is stored in advance in the memory when the apparatus is manufactured.

Therefore, by correcting the voltage ratio (CO ₂ concentration) calculated by the comparison unit 40 with a correction parameter determined by temperature and humidity, the voltage ratio in consideration of sensor characteristics, in other words, voltage independent of temperature and humidity. The ratio can be the sensor output.

  In this manner, the correction unit 60 inputs the signals from the first IR sensor 21, the temperature sensor 51, and the humidity sensor 52, and calculates the voltage ratio input from the comparison unit 40 based on the correction parameters stored in the memory. Correction is performed by the correction circuit.

The above is the configuration of the gas concentration detection device. The gas concentration detection device includes a light source 10, first and second IR sensors 21, 22, a CO ₂ concentration dependent filter 30, a temperature sensor 51, and a humidity sensor 52, for example, in a case provided with a CO ₂ inlet and an outlet. It is installed at a predetermined position, and the comparison unit 40 and the correction unit 60 are arranged outside the case.

  Next, the operation of this apparatus will be described. First, light is emitted from the light source 10 and air is introduced into the apparatus. Then, an electromotive voltage corresponding to the intensity of the infrared light emitted from the light source 10 is generated in each of the first and second IR sensors 21 and 22, and the electromotive voltage is output as a voltage signal.

  Specifically, in the first IR filter 21, an electromotive voltage corresponding to the intensity of light emitted from the light source 10, particularly infrared light, is generated, and this electromotive voltage is applied as a voltage signal to the comparison unit 40 and the correction unit 60. Is output.

Further, when the concentration of CO ₂ in the air introduced into the apparatus rises, light having a specific wavelength in the light emitted from the light source 10 is absorbed by the CO ₂ gas. For this reason, the intensity of light incident on the CO ₂ concentration dependent filter 30 is reduced, and the electromotive voltage generated in the second IR filter 22 is reduced. Therefore, in the second IR filter 22, an electromotive voltage depending on the CO ₂ concentration introduced into the apparatus is generated, and a voltage signal corresponding to the electromotive voltage is output to the comparison unit 40.

When a voltage signal is input from the first and second IR filters 21 and 22 to the comparison unit 40, the comparison unit 40 calculates a voltage ratio. This voltage ratio is calculated by dividing the voltage signal of the second IR sensor 22 by the voltage signal of the first IR sensor 21. Thus, by dividing by the voltage signal of the first IR sensor 21, it is possible to calculate the CO ₂ concentration without depending on fluctuations in the intensity of light emitted from the light source 10. The voltage ratio calculated in this way is output to the correction unit 60.

  Further, the temperature sensor 51 and the humidity sensor 52 detect the temperature and humidity, respectively, and output them to the correction unit 60. Therefore, the voltage ratio is input to the correction unit 60 from the comparison unit 40, and the electromotive voltage, temperature, and humidity are input from the first IR sensor 21, the temperature sensor 51, and the humidity sensor 52, respectively.

  The voltage ratio input to the correction unit 60 is not a value considering the sensor characteristics of the first and second IR sensors 21 and 22. Therefore, the correction unit 60 trims (adjusts) the voltage ratio to a value corresponding to the sensor characteristics. Specifically, the correction parameters stored in the memory of the correction unit 60 are determined from the values of temperature and humidity input to the correction unit 60. In the correction circuit, the correction shown in FIG. 2 is performed, that is, the voltage ratio is corrected by a correction parameter determined by temperature and humidity.

The corrected voltage ratio is output from the correction unit 60 to the outside of the present apparatus, for example, an ECU or the like as a sensor output (that is, CO ₂ concentration) in consideration of sensor characteristics.

As described above, in the present embodiment, the correction unit 60 performs correction to reduce the influence of the sensor characteristics, particularly the temperature characteristics and humidity characteristics of the electromotive voltage. That is, the temperature and humidity of the first IR sensor 21 are measured, and the temperature and humidity and the electromotive voltage of the first IR sensor 21 are input to the correction unit 60. Accordingly, the correction unit 60 can correct the voltage ratio (that is, the CO ₂ concentration) according to the temperature characteristic and the humidity characteristic of the electromotive voltage of the first IR sensor 21. Therefore, it is possible to obtain a more accurate CO ₂ concentration in consideration of the sensor characteristics, particularly the influence of the temperature characteristics and humidity characteristics of the electromotive voltage.

(Other embodiments)
In the first embodiment, the correction is performed based on the temperature characteristic and the humidity characteristic in the first IR sensor 21, but only the temperature characteristic of the electromotive voltage may be corrected. Similarly, only the temperature characteristic of humidity may be corrected. Further, in addition to the correction considering the temperature characteristic and the humidity characteristic of the electromotive voltage in the above embodiment, for example, a correction considering the atmospheric pressure characteristic of the electromotive voltage may be performed. By such correction, a voltage ratio that is not affected by the environment to which the first IR sensor 21 is exposed, that is, a more accurate CO ₂ concentration can be obtained.

  The sensor characteristics are not limited to temperature characteristics, humidity characteristics, and atmospheric pressure characteristics, but refer to all characteristics of the sensors 21 and 22. In the above embodiment, the sensor characteristics include temperature characteristics and The correction is only performed in consideration of humidity characteristics. Therefore, it goes without saying that the correction may be performed using sensor characteristics other than those described above.

  In the first embodiment, the first and second IR sensors 21 and 22 are adopted as the one that detects the light emitted from the light source 10, but is not limited to the sensor that detects infrared light. That is, a sensor that detects light having a wavelength other than infrared light may be used.

  In the first embodiment, the first and second IR sensors 21 and 22 are configured as separate bodies. However, by forming the first and second IR sensors 21 and 22 on a single semiconductor substrate, the first and second IR sensors 21 and 22 are integrated. It is also good.

In the first embodiment, a band-pass filter is used as the CO ₂ concentration-dependent filter 30, but a high-pass filter or a low-pass filter that includes the light absorption wavelength of CO ₂ may be used.

  In the first embodiment, the correction unit 60 includes a correction circuit. However, the correction unit 60 may include a microcomputer or a logic circuit.

In the first embodiment, the concentration of the CO ₂ gas contained in the air is detected, but it is also possible to detect a gas other than the CO ₂ gas. In this case, it can be carried out by adjusting the passing wavelength of the CO ₂ concentration dependent filter 30 to the light absorption wavelength of the gas to be detected.

It is a block block diagram of the gas concentration detection apparatus which concerns on one Embodiment of this invention. It is a diagram showing a sensor output for CO ₂ concentration. It is a block block diagram of the conventional gas concentration detection apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Light source, 21 ... 1st IR sensor, 22 ... 2nd IR sensor,
30 ... CO ₂ concentration dependent filter, 40 ... Comparison section, 51 ... Temperature sensor,
52... Humidity sensor, 60.

Claims (4)

A gas concentration detection device for detecting the concentration of CO ₂ gas contained in air,
A light source (10) that emits light;
A first sensor (21) and a second sensor are disposed so that a light receiving surface faces the light source, and receives the light at the light receiving surface and generates an electric signal of a level corresponding to the intensity of the light. A sensor (22);
A filter (30) disposed on the light-receiving surface of the second sensor and guiding the light to the second sensor after passing light including the light absorption wavelength of the CO ₂ gas;
A comparison unit (40) for calculating a parameter indicating the concentration of the CO ₂ gas based on the electrical signal of the first sensor and the electrical signal of the second sensor;
A temperature detector (51) for detecting the temperature of the first sensor;
A gas concentration detection apparatus comprising: a correction unit (60) for inputting the parameter and the temperature and correcting the parameter using the temperature. The comparison unit calculates a signal ratio that is a value obtained by dividing the electrical signal of the second sensor by the electrical signal of the first sensor as the parameter,
The correction unit has a temperature characteristic of an electric signal in the first sensor as a sensor characteristic, and inputs the electric signal of the first sensor, the signal ratio, and the temperature, and The gas concentration detection device according to claim 1, wherein the signal ratio is corrected based on an electric signal, the temperature, and a temperature characteristic of the electric signal. A gas concentration detection device for detecting the concentration of CO ₂ gas contained in air,
A light source (10) that emits light;
A first sensor (21) and a second sensor are disposed so that a light receiving surface faces the light source, and receives the light at the light receiving surface and generates an electric signal of a level corresponding to the intensity of the light. A sensor (22);
A filter (30) disposed on the light-receiving surface of the second sensor and guiding the light to the second sensor after passing light including the light absorption wavelength of the CO ₂ gas;
A comparison unit (40) for calculating a parameter indicating the concentration of the CO ₂ gas based on the electrical signal of the first sensor and the electrical signal of the second sensor;
A humidity detector (52) for detecting the humidity in the vicinity of the first sensor;
A gas concentration detection apparatus comprising: a correction unit (60) that inputs the parameter and the humidity and corrects the parameter using the humidity. The comparison unit calculates a signal ratio that is a value obtained by dividing the electrical signal of the second sensor by the electrical signal of the first sensor;
The correction unit has a humidity characteristic of an electric signal in the first sensor as a sensor characteristic, and inputs the electric signal, the signal ratio, and the humidity of the first sensor, and the correction signal of the first sensor. The gas concentration detection device according to claim 3, wherein the signal ratio is corrected based on an electric signal, the humidity, and a humidity characteristic of the electric signal.

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