Co2 gas sensor and correction method

Abstract

To facilitate correction of a calibration curve in accordance with reduction in element output.SOLUTION: A CO2 gas sensor 1 includes an exhalation input unit 3 for inputting human body exhalation, a sensor unit 4 for outputting an element output in accordance with CO2 concentration from an infrared sensor when exhalation from the human body is inputted into the exhalation input unit 3, correction coefficient calculation means 7b for setting the CO2 concentration to 1% on the basis of the element output of the sensor unit 4 when the exhalation of the human body at rest is input to the exhalation input unit 3, and calculating a correction coefficient from the ratio between the element output at the CO2 concentration of 1% and the element output at the CO2 concentration of 1% in the calibration curve at the time of shipment, and calibration curve creation means 7c for generating a new calibration curve by multiplying the correction coefficient calculated by the correction coefficient calculation means 7b to the calibration curve at the time of shipment.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a CO2 gas sensor for detecting the concentration of carbon dioxide (hereinafter referred to as CO2) in the atmosphere and a correction method thereof. [Background technology]

[0002] Known refrigeration cycles and air conditioners that use CO2 as a refrigerant are disclosed in, for example, Patent Document 1 and Patent Document 2. Similarly, large freezers and refrigerators installed in convenience stores and supermarkets also use CO2 as a refrigerant, but if the CO2 refrigerant leaks and the CO2 concentration inside the refrigerator increases, it could be harmful to the health of people inside the refrigerator, so a CO2 gas sensor is installed to measure the CO2 concentration.

[0003] According to the Three R Solutions website (see https: / / 3rrr-btob.jp / archives / column / measuring-equipment / 19863#:`:), the Ministry of Economy, Trade and Industry guidelines recommend the following three methods (1) to (3) as ways to check whether this type of CO2 gas sensor is working properly.

[0004] (1) This is a method for measuring carbon dioxide concentration outdoors. When a carbon dioxide concentration meter is used outdoors, if the measured value is close to 415 ppm to 450 ppm, the meter is working properly.

[0005] (2) This method involves blowing your breath into a carbon dioxide concentration meter to check the measurement value. Since your breath contains a lot of carbon dioxide, if the measurement value increases significantly, it is working properly.

[0006] (3) This method involves bringing hands or a cloth that has been coated with disinfectant alcohol close to a carbon dioxide concentration meter. Since optical carbon dioxide concentration meters barely react to alcohol, as long as the measurement value does not change significantly, the meter is operating normally.

[0007] When an NDIR type CO2 gas sensor is used, when infrared light emitted from an infrared light source passes through the gas to be measured, an amount of infrared light corresponding to the concentration of the gas is absorbed, causing a change in the amount of infrared light received by the infrared sensor element.

[0008] In addition, this type of NDIR type CO2 gas sensor requires calibration curve correction because the element output from the gas sensor decreases. Specifically, when the infrared light source deteriorates with age and the light intensity decreases, the element output of the infrared sensor decreases. In addition, the element output of the infrared sensor decreases due to the influence of dirt inside the housing. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2000-320936 A [Patent Document 2] JP 2011-106697 A Summary of the Invention [Problem to be solved by the invention]

[0010] However, in the case of conventional NDIR-type CO2 gas sensors, when correcting the calibration curve of the CO2 gas sensor based on (1), if a CO2 refrigerant refrigeration cycle is used as the refrigeration cycle of a freezer, the CO2 gas sensor must be taken outside the freezer or a reference gas must be brought near the CO2 gas sensor to perform long-term measurements to correct the values ​​when the CO2 concentration is low, making it difficult to correct the calibration curve.

[0011] Therefore, the present invention has been made in consideration of the above problems, and has an object to provide a CO2 gas sensor and a correction method that can easily correct a calibration curve accompanying a decrease in element output. [Means for solving the problem]

[0012] In order to achieve the above object, the CO2 gas sensor according to the present invention comprises: an exhaled breath input unit for inputting exhaled breath of a human body; a sensor unit that outputs an element output corresponding to a CO2 concentration from an infrared sensor when the exhaled air of the human body is input to the exhaled air input unit; A correction coefficient calculation means for calculating a correction coefficient based on a ratio of the element output of the sensor unit when the exhaled breath of the human body at rest is input to the exhaled breath input unit to a CO2 concentration of 1% and the element output of the calibration curve at the time of shipment when the CO2 concentration is 1%; a calibration curve creating means for creating a new calibration curve by multiplying the calibration curve at the time of shipment by the correction coefficient calculated by the correction coefficient calculating means; The present invention is characterized by comprising:

[0013] A method for correcting a CO2 gas sensor according to claim 2 of the present invention includes the steps of inputting exhaled breath of a human body to an exhaled breath input unit; a step of outputting an element output corresponding to a CO2 concentration from an infrared sensor of a sensor unit when the exhaled air of the human body is input to the exhaled air input unit; A step of setting the CO2 concentration by the element output of the sensor unit when the exhaled breath of the human body at rest is input to the exhaled breath input unit to be 1%, and calculating a correction coefficient from the ratio of the element output at this CO2 concentration of 1% to the element output at the CO2 concentration of 1% of the calibration curve at the time of shipment; multiplying the calibration curve at the time of shipment by the correction coefficient to generate a new calibration curve; The present invention is characterized by comprising: Effect of the Invention

[0014] According to the present invention, by using the CO2 concentration in the breath of a human body at rest, it is possible to easily correct the calibration curve of a CO2 gas sensor accompanying a decrease in element output. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a block diagram of a CO2 gas sensor according to the present invention. [Diagram 2]FIG. 4 is a diagram showing an example of a calibration curve showing the relationship between the element output and the CO2 concentration at the time of shipment and after correction in the CO2 gas sensor according to the present invention. [Diagram 3] 4 is a flowchart of a correction method for a CO2 gas sensor according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0017] The CO2 gas sensor of this embodiment is an NDIR type gas sensor that utilizes the characteristic that CO2 gas molecules absorb infrared rays of a specific wavelength. As shown in Fig. 1, the CO2 gas sensor 1 is roughly composed of an operation unit 2, a breath input unit 3, a sensor unit 4, a memory unit 5, a display unit 6, and a control unit 7.

[0018] The operation unit 2 is composed of buttons, switches, keys, etc. that are operated by the user. The operation unit 2 is operated when switching the power ON / OFF, switching between the measurement mode for measuring the gas concentration (CO2 concentration) of the CO2 gas to be measured and the correction mode based on the flowchart in Figure 3 described later (switching between the mode for automatic correction and the mode for manual correction), and issuing instructions to start or stop measurement / correction (automatic correction / manual correction).

[0019] When performing processing based on the flowchart of Figure 3 described later, the breath input unit 3 confirms that the pulse rate is that of a human body at rest, then starts a suction pump provided in the main body of the CO2 gas sensor 1, and inputs the human breath into the sensor unit 4 by suction of the suction pump.

[0020] The sensor unit 4 is configured, for example, with an air inlet and outlet formed in a gold-plated cylindrical housing, and equipped with an infrared light source and an infrared sensor. In the sensor unit 4, infrared light emitted from the infrared light source is absorbed by gas molecules of CO2 gas, which is a measurement target gas contained in the air inside the housing, and reaches the infrared sensor while attenuating. Depending on the amount of infrared light that reaches the sensor, the gas concentration (measured value) of CO2 gas can be calculated from a calibration curve that shows the relationship between the element output of the sensor unit 4 and the CO2 concentration, which is stored in advance in the storage unit 5.

[0021] 2 is an example of a calibration curve showing the relationship between the element output and the CO2 concentration at the time of shipment and after correction of the CO2 gas sensor 1. In FIG. 2, the line connecting multiple black squares is the calibration curve showing the relationship between the element output and the CO2 concentration at the time of shipment, and the line connecting one black star and multiple black circles is the calibration curve showing the relationship between the element output and the CO2 concentration after correction.

[0022] As shown in Figure 2, the behavior of the infrared sensor in the sensor unit 4 with respect to the CO2 concentration is that the higher the CO2 concentration, the more infrared light is absorbed by the CO2 gas molecules, and the smaller the element output of the infrared sensor. In contrast, the lower the CO2 concentration, the less infrared light is absorbed by the CO2 gas molecules, and the larger the element output of the infrared sensor. The reason why the calibration curve after correction is flatter than the calibration curve before correction (at the time of shipment) is that the measurement principle of NDIR type gas sensors is based on the Beer-Lambert law, and the concentration and transmittance (element output of the sensor unit 4) correspond exponentially, which is a well-known fact. In general, the calibration curve is made straight by taking the natural logarithm, making it easier to handle.

[0023] When the infrared light source of the sensor unit 4 deteriorates over time, the amount of infrared light emitted from the infrared light source decreases, and the element output of the infrared sensor also decreases, so that it is necessary to correct the calibration curve at the time of shipment.

[0024] Therefore, in this embodiment, the CO2 concentration (measured value) from the breath of a person at rest is used to execute processing based on the flowchart of Figure 3 described below, thereby correcting the calibration curve of the CO2 gas sensor 1 at the time of shipment and creating a new calibration curve that takes into account deterioration of the light source and dirt inside the casing.

[0025] The storage unit 5 includes a rewritable recording medium, and stores values ​​used in calculations under the control of the control unit 7. The storage unit 5 also stores data on a calibration curve showing the relationship between the element output and the CO2 concentration at the time of shipment and data on the calibration curve after correction.

[0026] The display unit 6 is composed of a display device such as an LCD, a light-emitting diode (LED), or an electroluminescence (EL), and displays the CO2 concentration (measured value) detected by the sensor unit 4 and the status of the equipment (normal state, alarm state, error state, etc.) under the control of the control unit 7.

[0027] In addition, when the element output determination means 7a described later determines that the element output of the infrared sensor of the sensor unit 4 exceeds the allowable range, the display unit 6 displays that correction is not possible (for example, a comment to the effect that correction cannot be performed using the element output of the infrared sensor of the sensor unit 4).

[0028] The control unit 7 controls the operation unit 2, the breath input unit 3, the sensor unit 4, the memory unit 5, and the display unit 6, and is configured with an element output determination means 7a, a correction coefficient calculation means 7b, and a calibration curve creation means 7c to execute processing based on the flowchart of FIG. 3, which will be described later.

[0029] The element output judgment means 7a also assumes the case where the exhaled breath of a human body that is not at rest is input to the exhaled breath input section 3, and judges whether the element output of the infrared sensor of the sensor section 4 when the suction pump of the exhaled breath input section 3 is started and exhaled breath is input does not exceed a preset tolerance range (for example, the fluctuation of the element output is ±αmV, etc.).

[0030] When the element output determination means 7a determines that the element output of the infrared sensor of the sensor unit 4 is within the allowable range and does not exceed it, the correction coefficient calculation means 7b sets the CO2 concentration based on the element output of the infrared sensor of the sensor unit 4 to 1% (black star in Figure 2), and calculates a correction coefficient based on the ratio of the element output at a CO2 concentration of 1% to the element output at a CO2 concentration of 1% on the calibration curve at the time of shipment (element output of black star at CO2 concentration of 1% in Figure 2 / element output of black square).

[0031] The calibration curve creation means 7c multiplies the element output of the calibration curve at the time of shipment by the correction coefficient calculated by the correction coefficient calculation means 7b to correct the calibration curve at the time of shipment, and creates a new calibration curve (the line connecting the black star and black circle in Figure 2) in accordance with the decrease in element output.

[0032] Next, a correction method for the CO2 gas sensor 1 having the above configuration will be described with reference to the flow chart of FIG.

[0033] In performing simple correction of the calibration curve of the CO2 gas sensor 1, after confirming that the pulse rate is that of a human body at rest, the suction pump of the breath input unit 3 is started (ST1), and the state transitions to a breath standby state (ST2) in which the breath is waiting for input of the breath to the breath input unit 3. The pulse rate of the human body at rest is measured and the value is confirmed immediately before the correction.

[0034] Then, the control unit 7 judges whether or not the exhaled breath of the human body has been input to the exhaled breath input unit 3 at the pulse rate at rest from the exhalation standby state (ST3).

[0035] When the control unit 7 determines that the human breath is input to the breath input unit 3 based on the pulse rate at rest (ST3-Yes), it executes an element output determination process by the element output determination means 7a (ST4). In the element output determination process, it is determined whether the element output of the infrared sensor of the sensor unit 4 when the human breath is input to the breath input unit 3 after confirming the pulse rate at rest does not exceed an allowable range (ST5).

[0036] Then, when the control unit 7 determines that the element output of the infrared sensor of the sensor unit 4 does not exceed the allowable range (ST5-Yes), it executes a correction coefficient calculation process by the correction coefficient calculation means 7b (ST6). In the correction coefficient calculation process, the CO2 concentration according to the element output of the infrared sensor of the sensor unit 4 is set to 1% (black star in FIG. 2), and a correction coefficient is calculated by the ratio of the element output at this CO2 concentration of 1% to the element output at the CO2 concentration of 1% of the calibration curve at the time of shipment (element output of black star / element output of black square at CO2 concentration of 1% in FIG. 2).

[0037] Next, the control unit 7 executes a calibration curve preparation process (ST7) and ends the simple correction process. In the calibration curve preparation process, the calibration curve at the time of shipment is corrected by multiplying the element output of the calibration curve at the time of shipment by the correction coefficient calculated in the correction coefficient calculation process, and a new calibration curve is prepared in accordance with the decrease in the element output.

[0038] Here, from the second correction onwards, a method of calculating the correction coefficient based on the ratio between the element output of the infrared sensor of the sensor unit 4 in the current correction (e.g., the second correction) and the element output of the infrared sensor of the sensor unit 4 in the previous correction (e.g., the first correction), or a method of calculating the correction coefficient based on the ratio between the element output of the infrared sensor of the sensor unit 4 in the current correction (e.g., the second correction) and the element output of the calibration curve at the time of shipment can be adopted. In this case, whichever method is adopted, the correction coefficient is calculated based on the element output of the calibration curve at the time of shipment.

[0039] If the control unit 7 determines that the element output of the infrared sensor of the sensor unit 4 exceeds the allowable range (ST5-No), it displays on the display unit 6 that correction is impossible (ST8) and ends the simple correction process.

[0040] As described above, according to the embodiment described above, by using the CO2 concentration (measured value) in the breath of a human body at rest, it is possible to easily correct the calibration curve of the CO2 gas sensor in accordance with a decrease in the element output.

[0041] Incidentally, in the above-described embodiment, a clock function may be added so that the measurement mode and the correction mode are switched according to the time.

[0042] Although the best mode of the CO2 gas sensor and the correction method according to the present invention has been described above, the present invention is not limited to the description and drawings of this mode. In other words, all other modes, examples, and operating techniques made by those skilled in the art based on this mode are naturally included in the scope of the present invention. [Explanation of symbols]

[0043] 1 CO2 gas sensor 2 Control section 3. Exhalation input section 4 Sensor section 5 Storage section 6 Display section 7 Control section 7a Element output determination means 7b Correction coefficient calculation means 7c Calibration curve preparation method

Claims

1. an exhalation input unit for inputting exhaled breath of a human body; a sensor unit that outputs an element output corresponding to a CO2 concentration from an infrared sensor when the exhaled air of the human body is input to the exhaled air input unit; a correction coefficient calculation means for calculating a correction coefficient based on a ratio of the element output of the sensor unit when the exhaled breath of the human body at rest is input to the exhaled breath input unit to a CO2 concentration of 1% and the element output of the calibration curve at the time of shipment when the CO2 concentration is 1%; a calibration curve creating means for creating a new calibration curve by multiplying the calibration curve at the time of shipment by the correction coefficient calculated by the correction coefficient calculating means; A CO2 gas sensor comprising:

2. inputting the exhaled breath of a human body into an exhaled breath input unit; a step of outputting an element output corresponding to a CO2 concentration from an infrared sensor of a sensor unit when the exhaled air of the human body is input to the exhaled air input unit; A step of setting the CO2 concentration by the element output of the sensor unit when the exhaled breath of the human body at rest is input to the exhaled breath input unit to be 1%, and calculating a correction coefficient from the ratio of the element output at this CO2 concentration of 1% to the element output at the CO2 concentration of 1% of the calibration curve at the time of shipment; multiplying the calibration curve at the time of shipment by the correction coefficient to generate a new calibration curve; A method for correcting a CO2 gas sensor, comprising:

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