JP2010175321A - Gas detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas detector capable of precisely performing the correction of sensitivity by a simple method. <P>SOLUTION: In the gas detector equipped with an alcohol sensor 24A having sensitivity to the ethanol concentration and humidity in a detection target gas and a humidity sensor 24B having sensitivity to the humidity of the detection target gas, a value obtained by subjecting the detection value of the alcohol sensor 24A to logarithmic conversion is expressed using the sum of the product of the value which is obtained by subjecting the concentration of ethanol to logarithmic conversion with the coefficient (a) of determination corresponding to sensitivity characteristics and the product of a value which is obtained by subjecting humidity to logarithmic conversion with the coefficient (b) of determination corresponding to sensitivity characteristics and a correction factor α for correcting (a) and (b) corresponding to a change in sensitivity characteristics. The correction factor α is calculated from the ratio of a change in the detection value of the alcohol sensor 24A to a change in the detection value of the humidity sensor 24B, and in a case that the correction factor α is smaller than a predetermined value, the correction factor α is updated to a newly calculated value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a gas detection device, and more particularly to a gas detection device that detects a detection target gas such as ethanol contained in human breath.

  Conventionally, when an ethanol component in an exhalation of a driver is detected by an alcohol sensor and an ethanol component (ethanol concentration) of a predetermined value or more is detected, the engine start is stopped. As an alcohol sensor in such a case, for example, when using a gas sensor whose output changes depending on humidity other than the gas to be detected, such as an oxide semiconductor gas sensor, the output value of the gas sensor is determined according to sensitivity characteristics. In order to express it using a coefficient (the slope and intercept of a calibration curve indicating the output value of the gas sensor with respect to the target gas concentration), at least four reference conditions with a known concentration and a combination of gas concentration 2 levels and humidity 2 levels under four conditions Therefore, it is necessary to determine the quantitative coefficient by measuring the output value of the gas sensor.

  In addition, the detection sensitivity of the gas sensor deteriorates depending on the period of use and usage conditions, and the accuracy of alcohol detection decreases. In order to correct this sensitivity deterioration, the output value of the gas sensor again under the above four conditions. It is necessary to recalculate the quantitative coefficient. However, this method is not practical due to labor and cost.

  Therefore, in a gas sensor that periodically changes the sensor temperature between the high temperature side and the low temperature side, and detects methane on the high temperature side and carbon dioxide on the low temperature side, the temperature on the high temperature side is lowered to an intermediate temperature in the air. Gas detectors that measure resistance values and self-diagnose that the sensitivity of the sensor is high when the ratio between the resistance value at the intermediate temperature and the resistance value at the high temperature side is small have been proposed (for example, patents) Reference 1).

  In addition, the sensor output when the breath of a non-drinking subject is blown is taken as the normal output, and the average value of the sensor output value (initial concentration average value) is measured and stored in units of 100 measurements. Similarly, there has been proposed an alcohol detection system that obtains an average value every 100 times, compares it with an initial concentration average value, and performs sensitivity correction so that the sensor output value becomes the initial concentration average value (for example, patents). Reference 2).

JP 2008-58214 A JP 2005-157599 A

  However, although the gas detection device of Patent Document 1 performs self-diagnosis for increasing the sensitivity of a sensor, correction of sensor sensitivity is not considered. In addition, since the sensor resistance is self-diagnosed by comparing the resistance value of the sensor when the sensor temperature is changed, if the sensor temperature does not need to be changed to detect the target gas, the sensor sensitivity There is a problem in that the process of changing the sensor temperature is necessary for the correction, and the process is complicated and an unnecessary burden is placed on the sensor.

  Further, in the alcohol detection system of Patent Document 2, the sensor output when the breath of a non-drinking subject is blown is taken as the normal output, and the initial concentration average value is taken. Since the output is affected by the humidity of the environment and unspecified substances such as food and drink ingested by the subject before measurement, sufficient accuracy cannot be obtained even if the sensitivity of the sensor is corrected with the average value. There is a problem.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a gas detection device capable of performing sensitivity correction with high accuracy by a simple method.

  In order to achieve the above object, the gas detection device of the present invention is sensitive to the detection target gas contained in the detection target gas and the humidity of the detection target gas, and adjusts the concentration of the detection target gas. A gas detection means for detecting a physical quantity corresponding to a physical quantity related to the humidity and a physical quantity related to the humidity and outputting a detection value; a humidity detection means for detecting and outputting a physical quantity related to the humidity of the gas to be detected; and The detection value of the gas detection means is a product of a physical quantity related to the concentration of the detection target gas and a first coefficient corresponding to the sensitivity characteristic, and a second coefficient corresponding to the physical quantity related to the humidity and the sensitivity characteristic. And a correction coefficient for correcting the first coefficient and the second coefficient in accordance with a change in sensitivity characteristic, and a physical quantity related to the humidity detected by the humidity detecting means. Using the detection target Concentration calculating means for calculating the concentration of gas, correction coefficient calculating means for calculating the correction coefficient from the ratio of the change in the detection value of the gas detection means to the change in the detection value of the humidity detection means, and the correction coefficient calculation means Update means for updating the correction coefficient used in the density calculation means to the correction coefficient calculated by the correction coefficient calculation means when the correction coefficient calculated in step (b) is smaller than a predetermined value. Yes.

  According to the gas detection device of the present invention, the gas detection means is sensitive to the detection target gas contained in the detection target gas and the humidity of the detection target gas, and is a physical quantity related to the concentration of the detection target gas. And a physical quantity corresponding to the physical quantity related to humidity is detected and a detected value is output. The detection value of the gas detection means changes according to the change in sensitivity characteristics. Further, the humidity detecting means detects and outputs a physical quantity related to the humidity of the gas to be detected. Then, the concentration calculation unit determines the detection value of the gas detection unit according to the product of the physical quantity related to the concentration of the detection target gas and the first coefficient corresponding to the sensitivity characteristic, and the physical quantity related to the humidity and the sensitivity characteristic. The sum of the product with the second coefficient and the correction coefficient for correcting the first coefficient and the second coefficient in accordance with the change of the sensitivity characteristic are used, and the humidity is detected by the humidity detecting means. The concentration of the detection target gas is calculated using the physical quantity. This correction coefficient is calculated by the correction coefficient calculation means from the ratio of the change in the detection value of the gas detection means to the change in the detection value of the humidity detection means. Then, the updating means updates the correction coefficient used by the density calculating means to the correction coefficient calculated by the correction coefficient calculating means when the correction coefficient calculated by the correction coefficient calculating means is smaller than a predetermined value.

  As described above, since the correction coefficient can be calculated according to the change in the sensitivity characteristic of the gas detection means from the detection values of the gas detection means and the humidity detection means detected for calculating the concentration of the target gas. Even if the concentration reference gas is not measured and the coefficient is not recalculated, sensitivity correction can be performed with high accuracy by a simple method compared to the case of concentration correction using an average value of a plurality of measurements.

  A value obtained by logarithmically converting the detection value of the gas detection means can be expressed by the following equation (1).

  Where G is a detection value of the gas detection means, α is a correction coefficient, [Gas] is a physical quantity related to the concentration of the gas to be detected, [Humi] is a physical quantity related to humidity, a is the first coefficient, and b is The second coefficient, c, is a constant.

  By expressing in this way, it is possible to set the correction coefficient α by utilizing the property that the sensitivity of the gas detection means regarding the target gas and the sensitivity to humidity change at the same ratio, and the sensitivity correction can be performed by a simple method. It can be performed.

  The correction coefficient can be calculated by the following equation (2).

However, G _peak is the peak value of the detection value of the gas detection means when exhalation is introduced as the gas to be detected, G _base is the detection value of the gas detection means when the exhalation is not introduced, and H _peak is the above The peak value of the detection value of the humidity detection means when exhalation is introduced, H _base is the detection value of the humidity detection means when exhalation is introduced, and d is a constant.

  As described above, based on the equation (2), the correction coefficient can be easily calculated using the detection values of the gas detection means and the humidity detection means.

  As described above, according to the present invention, there is an effect that sensitivity correction can be performed with high accuracy by a simple method.

It is the schematic which shows the state which attached the ethanol concentration detection apparatus of this Embodiment to the steering column of a driver's seat. It is the schematic which shows this Embodiment. It is a block diagram which shows schematic structure of the ethanol concentration detection apparatus of this Embodiment. It is a diagram which shows the relationship between ethanol gas concentration and the detected value of an alcohol sensor. It is a flowchart which shows the content of the correction coefficient in the ethanol concentration detection apparatus of this Embodiment, and an ethanol concentration calculation processing routine.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, a case where the present invention is applied to an ethanol concentration detection device that detects the concentration of ethanol, which is a kind of alcohol, from the breath of a driver will be described as an example.

  As shown in FIG. 1, the ethanol concentration detection device 10 according to the present embodiment is attached to a steering column 12 provided in a driver's seat at a position where the driver's breath can reach. The ethanol concentration detection device 10 includes an elongate cylindrical exhalation introduction tube 20 in which a suction port 20A having an enlarged diameter is formed at the tip, and a sensor group 24 is attached to the inside of the exhalation introduction tube 20 inside. ing.

  As shown in FIG. 2, a suction fan 22 that is driven to suck the breath of the driver from the suction port 20 </ b> A is provided inside the breath introduction tube 20 and on the suction port 20 </ b> A side from the sensor group 24. .

  The sensor group 24 includes an alcohol sensor 24 </ b> A and a humidity sensor 24 </ b> B attached so as to face the inside of the middle part of the exhalation introduction tube 20.

  The alcohol sensor 24 </ b> A is a sensor that detects ethanol gas contained in the gas flowing in the breath introduction pipe 20, and for example, an oxide semiconductor gas sensor can be used. The alcohol sensor 24 </ b> A outputs a detection signal having a higher level as the concentration of ethanol gas contained in the gas flowing in the exhalation introduction tube 20 becomes higher, and the ethanol sensor contained in the gas flowing in the exhalation introduction tube 20. A detection signal with a low level is output as the density decreases. In addition to the ethanol gas, the alcohol sensor 24A has sensitivity to the humidity of the gas flowing in the exhalation introduction tube 20.

  The humidity sensor 24 </ b> B is a sensor that detects the humidity of the gas represented by the concentration of water vapor in the gas flowing through the breath introduction pipe 20. The humidity sensor 24B outputs a detection signal having a higher level as the humidity of the gas flowing in the exhalation introduction tube 20 becomes higher, and outputs a detection signal having a lower level as the humidity of the gas flowing in the exhalation introduction tube 20 becomes lower. Output.

  According to the present embodiment, when the suction fan 22 is driven, the exhaled air exhaled from the driver is sucked into the exhalation introduction tube 20 from the suction port 20A of the exhalation introduction tube 20, and the exhalation is mixed with the air. As a result, the sensor group 24 is arbitrarily diluted and reaches the sensor group 24 at a constant flow rate. The exhaled breath comes into contact with the sensor group 24 and is then discharged out of the exhalation introducing tube 20.

  When the breath comes into contact with the alcohol sensor 24A and the humidity sensor 24B, the alcohol sensor 24A detects a detection value related to the concentration and humidity of ethanol gas in the gas containing the breath, and the humidity sensor 24B detects the gas containing the breath. The detected value related to the humidity of is detected. Based on the detection values detected by the alcohol sensor 24A and the humidity sensor 24B, the concentration of ethanol gas as the detection target gas in the expiration is detected.

  As shown in FIG. 3, the ethanol concentration detection device 10 includes an ethanol concentration detector 30 that is connected to an alcohol sensor 24A, a humidity sensor 24B, and a display device 26 such as a liquid crystal display and detects the concentration of ethanol gas. ing.

  The ethanol concentration detector 30 includes a correction coefficient calculation unit 32 that calculates a correction coefficient for correcting a quantitative coefficient corresponding to the sensitivity characteristic of the alcohol sensor 24A based on detection values of the alcohol sensor 24A and the humidity sensor 24B, and a correction coefficient. Based on the correction coefficient storage unit 34 that stores the correction coefficient calculated by the calculation unit 32, the detection values of the alcohol sensor 24A and the humidity sensor 24B, and the correction coefficient stored in the correction coefficient storage unit 34, the ethanol gas in expiration And a display control unit 38 for controlling the display device 26 to display a calculation result by the ethanol concentration calculation unit 36.

  The ethanol concentration detector 30 is a CPU that controls the entire ethanol concentration detector 10, a ROM as a storage medium that stores various programs such as a correction coefficient and an ethanol concentration calculation processing program that will be described later, and temporarily stores data as a work area. It can be constituted by a microcomputer including a RAM to be connected and a bus connecting them.

  Here, the principle of correction coefficient calculation in the ethanol concentration detection apparatus 10 of the present embodiment will be described.

  Like the oxide semiconductor gas sensor, the value ln (G) obtained by logarithmically converting the detection value G of the alcohol sensor 24A whose detection value changes depending on humidity in addition to the concentration of the ethanol gas that is the detection target gas, and the ethanol concentration [Gas]. The relationship with logarithmically converted value ln [Gas] is as shown in FIG. When this ln (G) is expressed by a logarithmically converted value of the water vapor concentration [Humi], which is a physical quantity related to the ethanol concentration [Gas] and humidity, the equation (3) is obtained.

  However, a is a quantitative coefficient related to the sensitivity of the alcohol sensor 24A to ethanol, b is a quantitative coefficient related to the sensitivity of the alcohol sensor 24A to humidity, and c is a constant. The quantitative coefficients a and b and the constant c are values representing the sensitivity characteristics of the alcohol sensor 24A, and for at least four combinations of ethanol concentration 2 and humidity 2 levels with respect to a gas having a known ethanol concentration and humidity. This is a value calculated by measuring the detection value of the alcohol sensor 24A.

  The sensitivity of the alcohol sensor 24A varies depending on the use state and use period. Usually, the sensitivity of the alcohol sensor 24A with respect to ethanol (quantitative coefficient a in equation (3)) and the sensitivity with respect to humidity (quantitative coefficient b in equation (3)) change in the same way. , B can be assumed to change at the same rate. Therefore, the above equation (3) is expressed as equation (1) using a correction coefficient α indicating the sensitivity deterioration of the alcohol sensor 24A.

  Here, the initial value of the correction coefficient α, that is, the correction coefficient α when the sensitivity of the alcohol sensor 24A is not deteriorated is 1, and in the initial state, the expression (1) is identical to the above expression (3).

  The correction coefficient α is calculated as follows according to the change in the detection value of the alcohol sensor 24A due to the breath blowing.

In the equation (1), the value obtained by logarithmically converting the detected value G _base (base value) of the alcohol sensor 24A before the exhalation and the peak value G _peak of the detected value of the alcohol sensor 24A when the exhalation is applied are (4) and (5)

However, [Gas] _base is the ethanol concentration in the ambient air, [Humi] _base is the water vapor concentration in the ambient air, [Gas] _peak is the peak value of the ethanol concentration changed by the exhalation, and [Humi] _peak is It is the peak value of the water vapor concentration changed by exhalation.

  The correction coefficient α is calculated as in equation (6) using equation (5)-(4).

Here, if the breath does not contain ethanol,
[Gas] _peak − [Gas] _base = 0
Therefore, Expression (6) is expressed as Expression (7).

  Here, the detected value detected by the humidity sensor 24B is used as the water vapor concentration [Humi]. In the case of an oxide semiconductor type humidity sensor, a value ln (H) obtained by logarithmically converting the detected value H of the humidity sensor 24B is expressed by equation (8).

  However, d is a quantitative coefficient related to the sensitivity of the humidity sensor 24B to humidity, and e is a constant.

In the equation (8), the value obtained by logarithmically converting the detected value H _base (base value) of the humidity sensor 24B before exhalation and the peak value H _peak of the detected value of the humidity sensor 24B during exhalation is the water vapor in the ambient atmosphere. Using the concentration [Humi] _base and the peak value [Humi] _peak of the water vapor concentration changed by exhalation, it is expressed by the equations (9) and (10).

  (9) Equation (11) is obtained from Equation (10).

  By substituting equation (11) into equation (7), the correction coefficient α expressed by equation (2) is obtained.

   From the equation (2), the correction coefficient α is expressed as a ratio between the change in the detection value of the humidity sensor 24B before and after the exhalation and the change in the detection value of the alcohol sensor 24A.

  Next, with reference to FIG. 5, the processing routine of the correction coefficient and ethanol concentration calculation processing in the present embodiment will be described. This routine is performed by the CPU executing the correction coefficient and ethanol concentration calculation program stored in the ROM.

  In step 100, the heaters of the alcohol sensor 24A and the humidity sensor 24B are turned on, and acquisition of detection values of the two sensors is started.

  Next, in step 102, it is determined whether or not exhalation is input to the exhalation introduction tube 20. When the detection value of either of the two sensors starts to change, it is determined that exhalation has been input. Further, by providing a flow rate sensor at the introduction port 20A, it may be determined whether or not exhalation has been introduced based on the detection result of the flow rate sensor. If exhalation is input, the process proceeds to step 104. If not, the determination in this step is repeated until it is input.

In step 104, the base value G _base and peak value G _{peak of} the alcohol sensor 24A and the base value H _base and peak value H _{peak of the} humidity sensor 24B are obtained from the acquired detection values of the alcohol sensor 24A and humidity sensor 24B. Then, the correction coefficient α is calculated by substituting into the above equation (2). The correction coefficient α calculated here is α ′.

Next, in step 106, it is determined whether or not the correction coefficient α ′ is larger than a predetermined value. Here, a initial value alpha ₀ of the correction coefficient alpha as a predetermined value. If the exhaled breath does not contain an ethanol component, the detection value of the alcohol sensor 24A changes only due to a change in humidity when the exhaled breath is blown. If change is sensor sensitivity, (2) the correction coefficient alpha is calculated by the equation is from the initial value alpha _0. When the ethanol component is contained in the exhaled breath, the value of ln (G _peak ) in equation (2) is large, and the correction coefficient α is calculated as a value larger than the initial value α ₀ . If the calculated correction coefficient α ′ is larger than the initial value α ₀ , it is determined that the ethanol concentration in the exhalation has changed, not the sensitivity change, and the process proceeds to step 110 as it is.

On the other hand, the correction coefficient α ′ does not normally take a value smaller than the initial value α ₀ for reasons other than sensor sensitivity deterioration. Therefore, if the correction coefficient α ′ is smaller than the initial value α ₀ , step 108 is performed. Proceed to

  In step 108, α in the above equation (1) is changed to the newly calculated correction coefficient α 'and stored. Thereby, the value of α in the equation (1) is updated.

  Next, in step 110, a value ln (G) obtained by logarithmically converting the detection value G of the alcohol sensor 24A and a value obtained by logarithmically converting the water vapor concentration [Humi] obtained from the detection value H of the humidity sensor 24B to the above equation (1). Substitute ln [Humi] to calculate the ethanol concentration [Gas]. Note that ln [Humi] is obtained by substituting the detected value H of the humidity sensor 24B into the equation (8).

  Next, in step 112, the calculation result is displayed on the display device 26, and the process is terminated.

  As described above, according to the ethanol concentration detection apparatus according to the present embodiment, the correction coefficient is set by paying attention to the fact that the sensitivity to the detection target gas and the sensitivity to the humidity change in the same way, and before and after exhalation. In order to calculate the correction coefficient using the detected values of the alcohol sensor and the humidity sensor of the gas sensor, the gas sensor output value is measured under the combined condition of the gas concentration of 2 levels and the humidity of 2 levels as a reference gas of known concentration, and the quantitative coefficient Even if the value is not calculated again, the correction coefficient can be calculated with high accuracy by a simple method as compared with the case where the sensitivity correction is performed using the average value of the detected values.

  In the above embodiment, the base value and the peak value of the alcohol sensor and the humidity sensor are used in the calculation of the correction coefficient α (equation (2)), but the base value and the peak value are not necessarily required. If the exhaled breath introduced into the exhalation introducing tube is a detected value after the point in time when it contacts the alcohol sensor and the humidity sensor, the correction coefficient α can be calculated in the same manner as described above using the change amount or rate of change of the detected value. it can.

  In the above embodiment, the case where the calculated concentration of the ethanol gas in the expiration is displayed has been described. However, the present invention is not limited to this. For example, the calculated ethanol gas concentration and a predetermined threshold value May be determined so that the ethanol concentration is high when the calculated ethanol gas concentration is equal to or greater than the threshold value, and control may be performed so as to prevent fraud such as preventing the engine from starting.

  In the above embodiment, the case where ethanol is detected from the exhalation of the driver has been described. However, the present invention detects ethanol from the exhalation of humans other than the driver by configuring the ethanol concentration detection device to be portable. It can also be applied to cases.

DESCRIPTION OF SYMBOLS 10 Ethanol concentration detection apparatus 24A Alcohol sensor 24B Humidity sensor 26 Display apparatus 30 Ethanol concentration detector 32 Correction coefficient calculation part 34 Correction coefficient memory | storage part 36 Ethanol concentration calculation part 38 Display control part

Claims (3)

It has sensitivity to the detection target gas contained in the detection target gas and the water vapor of the detection target, and detects a physical quantity corresponding to the physical quantity related to the concentration of the detection target gas and the physical quantity related to the humidity. Gas detection means for outputting a detection value;
Humidity detection means for detecting and outputting a physical quantity related to the humidity of the gas to be detected;
The detection value of the gas detection means is a product of a physical quantity related to the concentration of the detection target gas and a first coefficient corresponding to the sensitivity characteristic, and a second coefficient corresponding to the physical quantity related to the humidity and the sensitivity characteristic. And a correction coefficient for correcting the first coefficient and the second coefficient in accordance with a change in sensitivity characteristic, and a physical quantity related to the humidity detected by the humidity detecting means. Concentration calculating means for calculating the concentration of the detection target gas using,
Correction coefficient calculation means for calculating the correction coefficient from the ratio of change in the detection value of the gas detection means to change in the detection value of the humidity detection means;
Updating means for updating the correction coefficient used by the density calculation means to the correction coefficient calculated by the correction coefficient calculation means when the correction coefficient calculated by the correction coefficient calculation means is smaller than a predetermined value;
A gas detection device. The gas detection device according to claim 1, wherein a detection value of the gas detection means is expressed by the following equation (1).

Where G is a detection value of the gas detection means, α is a correction coefficient, [Gas] is a physical quantity related to the concentration of the gas to be detected, [Humi] is a physical quantity related to humidity, a is the first coefficient, and b is The second coefficient, c, is a constant. The gas detection device according to claim 1, wherein the correction coefficient is calculated by the following equation (2).

However, G _peak is the peak value of the detection value of the gas detection means when exhalation is introduced as the gas to be detected, G _base is the detection value of the gas detection means when the exhalation is not introduced, and H _peak is the above The peak value of the detection value of the humidity detection means when exhalation is introduced, H _base is the detection value of the humidity detection means when exhalation is introduced, and d is a constant.

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