Gas sensor and method for correcting gas sensor

Abstract

To appropriately correct an output of a gas sensor in response to change in the output of the gas sensor due to secular deterioration to suppress increase in cost.SOLUTION: A gas sensor 1 includes a MCU 50 for correcting a threshold value for determining a sensor output or detection of a test gas. The MCU 50 acquires an air base output that is the sensor output in environment in which no test gas is present to obtain fluctuations of the air base output or a degree of decrease in a fluctuation range, and corrects a threshold value for determining the sensor output or the detection of the test gas according to the obtained fluctuations of the air base output or a degree of decrease in the fluctuation range.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a gas sensor and a method for correcting the gas sensor. [Background technology]

[0002] Since the output (sensor sensitivity) of a gas sensor changes due to deterioration over time, the sensor sensitivity is corrected in accordance with the change due to the deterioration over time (see, for example, Patent Documents 1 and 2). Patent Document 1 describes a method of using a gas sensor element equipped with a measurement detection section and a correction detection section, and correcting the sensor sensitivity of the measurement detection section in accordance with the comparison result of the outputs of both detection sections. Patent Document 2 describes a method of storing in advance in a ROM (Read Only Memory) the relationship between the air base output, the amount of time elapsed, and the sensitivity of the gas sensor in a catalytic combustion type gas sensor, and acquiring the amount of time elapsed and the sensor sensitivity from the ROM when the difference between the output for a gas to be detected during combustion and the air base output is equal to or less than a certain value to correct the sensor sensitivity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3167798 [Patent Document 2] JP 2008-267810 A Summary of the Invention [Problem to be solved by the invention]

[0004] The correction method described in Patent Document 1 requires multiple detection units for measurement and correction, which increases costs. In addition, trace amounts of flammable gases (VOCs: Volatile Organic Compounds) and water vapor exist in the environment, and the environmental temperature also changes, and slight changes in these (concentration, humidity, temperature) cause fluctuations in the air base output. The correction method described in Patent Document 2 does not take into account fluctuations in the air base output due to environmental influences, and therefore is inferior in detection accuracy of the amount of change due to deterioration of sensor sensitivity over time.

[0005] In view of the above circumstances, an object of the present invention is to provide a gas sensor and a gas sensor correction method that can appropriately correct the output of a gas sensor in response to changes in the output of the gas sensor due to deterioration over time while suppressing increases in costs. [Means for solving the problem]

[0006] The gas sensor of the present invention is a gas sensor equipped with a correction unit that corrects a threshold value for determining the sensor output or the detection of a test gas, and the correction unit acquires an air base output, which is the sensor output in an environment in which the test gas is not present, determines the degree of reduction in the fluctuation or fluctuation range of the air base output, and corrects the sensor output or the threshold value for determining the detection of the test gas in accordance with the determined degree of reduction in the fluctuation or fluctuation range of the air base output.

[0007] The gas sensor correction method of the present invention is a gas sensor correction method that uses a computer to correct the sensor output or a threshold value for determining the detection of a test gas, and involves obtaining an air base output, which is the sensor output in an environment in which the test gas is not present, determining the degree of reduction in the fluctuation or fluctuation range of the air base output, and correcting the sensor output or the threshold value for determining the detection of the test gas according to the determined degree of reduction in the fluctuation or fluctuation range of the air base output. Effect of the Invention

[0008] According to the present invention, it is possible to appropriately correct the output of the gas sensor in response to changes in the output of the gas sensor due to deterioration over time, and to suppress increases in costs. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a gas sensor according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a graph showing the air-based output of a gas sensor. [Diagram 3] FIG. 3 is a graph showing the relationship between the fluctuation of the air base output and the output voltage. [Figure 4] FIG. 4 is a graph showing the relationship between the rate of change of the fluctuation of the air-based output and the rate of deterioration of the output voltage. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will be described below along with preferred embodiments. Note that the present invention is not limited to the embodiments shown below, and can be modified as appropriate within the scope of the present invention. In addition, in the embodiments shown below, some configurations are omitted from illustration and description, but for the details of the omitted technologies, publicly known or well-known technologies are applied as appropriate within the scope of no contradiction with the contents described below.

[0011] 1 is a diagram showing a schematic configuration of a gas sensor 1 according to an embodiment of the present invention. The gas sensor 1 shown in this figure is a catalytic combustion type (or adsorption combustion type) gas sensor equipped with a bridge circuit 40 having a detection element 20 and a compensation element 30 as two sides. Examples of the detection gas detected by this gas sensor 1 include methane, hydrogen, propane, butane, etc. The adsorption combustion type is a gas detection method in which molecules of the detection gas are adsorbed to the catalyst of the detection element 20 while the pulse voltage is OFF or LOW voltage, and the gas molecules are burned on the catalyst of the detection element 20 when the pulse voltage becomes ON or HIGH voltage, thereby obtaining a sensor output.

[0012] The detection element 20 includes a heater 21 and a detection section 22 that covers the heater 21. The compensation element 30 includes a heater 31 and a compensation section 32 that covers the heater 31. The heaters 21 and 31 can be, for example, microheaters patterned on a microchip. The heaters 21 and 31 can be, for example, made of platinum (Pt).

[0013] The detection unit 22 is made of a material having catalytic activity in an oxidation reaction. The detection unit 22 includes a catalyst and a catalyst carrier that supports the catalyst. Examples of the catalyst material of the detection unit 22 include platinum group metals such as platinum, palladium (Pd), iridium (Ir), ruthenium (Ru), and rhodium (Rh), and other metals such as gold (Au), silver (Ag), copper (Cu), nickel (Ni), and cobalt (Co). Examples of the catalyst carrier material of the detection unit 22 include alumina (Al2O3), titanium oxide (TiO2), cerium oxide (CeO2), and tin oxide (SnO2). The compensation unit 32 is made of a material that does not have catalytic activity in an oxidation reaction. The compensation unit 32 is made of the same material as the catalyst carrier of the detection unit 22.

[0014] In the gas sensor 1, when molecules of a combustible test gas come into contact with (or are adsorbed on) the detection section 22 heated to several hundred degrees by the heater 21, a catalytic combustion reaction (or an adsorption combustion reaction) occurs on the detection section 22, and the reaction heat increases the temperature of the heater 21, increasing the resistance value. On the other hand, even if molecules of a combustible test gas come into contact with (or are adsorbed on) the compensation section 32 of the compensation element 30, no catalytic combustion reaction (or an adsorption combustion reaction) occurs. In such a gas sensor 1, the change in the resistance value of the heater 21 is obtained as a sensor output by the bridge circuit 40, and the test gas is detected or the concentration of the test gas is identified.

[0015] The bridge circuit 40 includes a pair of parallel circuits 40A, 40B and a power source 41. The pair of parallel circuits 40A, 40B branch off from a conductor connected to the positive electrode of the power source 41. The pair of branched parallel circuits 40A, 40B are reconnected to a conductor connected to the negative electrode of the power source 41 via a variable resistor VR. In one parallel circuit 40A, a detection element 20 and a compensation element 30 are connected in series. In the other parallel circuit 40B, a pair of fixed resistors R1, R2 are connected in series. In this embodiment, the detection element 20 is disposed on the positive electrode side of the power source 41, and the compensation element 30 is disposed on the negative electrode side of the power source 41.

[0016] The bridge circuit 40 includes a terminal 42 connected between the detection element 20 and the compensation element 30, and a terminal 43 connected between the fixed resistors R1 and R2. The bridge circuit 40 outputs an output voltage V out The MCU 50 pulse-drives the bridge circuit 40 and outputs the output voltage V out As will be described later, the MCU 50 detects the target gas based on the air base output V AB The output voltage V out Correct the following.

[0017] Figure 2 shows the air-based output V of gas sensor 1. AB Graph showing the air base output V [mV] AB is the output voltage V in an environment where the target gas is not present. out Here, since there are traces of flammable gases and water vapor in the environment, and the environmental temperature also changes, the air base output V AB Fluctuations occur in the air base output V AB The "fluctuation" in the air base output V AB does not refer to the long-term variation of the initial value of V, but rather to the air-based output V AB This refers to short-term fluctuations, for example over 600 seconds.

[0018] The MCU50 periodically checks the air base output VAB and obtain the air base output V AB Find the fluctuation of the air base output V AB The acquisition continues for 600 seconds at 10 second intervals, for example. AB The fluctuation of the short-term air base output V AB Examples of such a measure include the standard deviation, root mean square fluctuation, and variance of the time series, which can be calculated from a large number of values ​​taken at 10 second intervals over a period of, for example, 600 seconds.

[0019] The MCU50 has an air base output of V AB The initial value of the fluctuation of the air base output V is calculated and stored in memory (not shown). AB The fluctuation of the air base output V is periodically measured and compared with the initial value stored in memory. AB The degree of decrease in the fluctuation of V from the initial value is calculated. Then, the MCU 50 calculates the air base output V AB Depending on the degree of decrease in the fluctuation of the output voltage V out Correct the following.

[0020] Figure 3 shows the air-based output V AB Fluctuation (μV) and output voltage V out 1 is a graph showing the relationship between the air base output V (mV) when the gas sensor 1 is installed in an environment where the concentration of the detected gas is 1000 ppm. AB Fluctuation (μV) and output voltage V out As shown in this graph, the air base output V AB Fluctuations in and output voltage V out is proportional to the air base output V AB The larger the fluctuation of the output voltage V out will become higher.

[0021] Here, at the beginning of use of the gas sensor 1, the catalyst in the detection portion 22 of the detection element 20 maintains high activity, so that the air-based output V AB is relatively high, and the air-based output V ABOn the other hand, when the gas sensor 1 is used for a long period of time, the fluctuation of the air base output V AB (sensitivity) is relatively low, and the air base output V AB The fluctuation of the air base output V AB The degree of decrease in the fluctuation of the output voltage V out There is a correlation between the degree of deterioration (deterioration rate) and the sensitivity.

[0022] Figure 4 shows the air-based output V AB The degree of fluctuation decrease (rate of change) and the output voltage V out 1 is a graph showing the relationship between the degree of deterioration (deterioration rate) of the air base output V AB The rate of change in the fluctuation of the air base output V is proportional to the rate of deterioration of the sensitivity. AB The larger the rate of change of the fluctuation of the output voltage V out The deterioration rate of

[0023] Therefore, in the gas sensor 1 of the present embodiment, the MCU 50 controls the air base output V AB The rate of change of the fluctuation of the output voltage V is calculated based on the initial value. out By multiplying by , the output voltage V of gas sensor 1 is out Correct the following.

[0024] As described above, in the gas sensor 1 of the present embodiment, the MCU 50 controls the air base output V AB Get the air base output V AB The degree of reduction in the fluctuation of the air base output V AB Depending on the degree of decrease in the fluctuation of the output voltage V out This allows the output voltage V to be calculated without using a sensor element for calibration (only the sensor element for detection), taking into account the effect of deterioration over time of the sensor output (sensitivity) for the detected gas. out Therefore, the output voltage V of the gas sensor 1 can be corrected.out The output voltage V of gas sensor 1 changes according to the change due to deterioration over time. out It is possible to appropriately correct the difference and prevent an increase in the cost of the gas sensor 1.

[0025] In addition, the output voltage V of the gas sensor 1 can be measured without using any calibration gas and without an operator having to go to the installation site of the gas sensor 1. out The output voltage V of gas sensor 1 changes according to the change due to deterioration over time. out can be appropriately corrected.

[0026] The present invention has been described above based on the above embodiment, but the present invention is not limited to the above embodiment, and modifications may be made without departing from the spirit of the present invention, and known or well-known technologies may be appropriately combined.

[0027] For example, in the above embodiment, the air base output V AB Depending on the degree of decrease in the fluctuation of the output voltage V out However, the output voltage V out Instead of correcting the air base output V, the threshold value for determining the presence or absence of the target gas may be corrected. AB The greater the degree of decrease in the fluctuation, the lower the threshold value for determining the presence or absence of the gas to be detected should be.

[0028] In the above embodiment, the air base output V AB The degree of reduction in the fluctuation of the air base output V AB Depending on the degree of decrease in the fluctuation of the output voltage V out However, the air base output V AB Instead of the fluctuation of the air base output V AB The degree of decrease in the fluctuation range, which is the difference between the maximum and minimum values ​​of the air base output V AB Depending on the degree of narrowing of the fluctuation range of the output voltage V out It is also possible to correct the threshold value for determining whether the target gas is present or not. AB When calculating the fluctuation range of the output voltage V, the output voltage V is calculated by removing singular values, etc.out and the accuracy of threshold correction can be improved.

[0029] In the above embodiment, the catalytic combustion type (or adsorption combustion type) gas sensor 1 is taken as an example, but the present invention can also be applied to other types of gas sensors such as semiconductor type and hot wire semiconductor type. Furthermore, the gas sensor of the present invention can be applied not only to gas alarms but also to various gas detectors such as portable checkers and fixed devices. [Explanation of symbols]

[0030] 1 Gas sensor 50 MCU (correction unit, computer) V AB Air Base Output V out Output voltage (sensor output)

Claims

1. A gas sensor including a correction unit that corrects a sensor output or a threshold value for determining detection of a test gas, The correction unit is An air base output, which is a sensor output in an environment in which the test gas is not present, is obtained, and a degree of reduction in the fluctuation or fluctuation range of the air base output is obtained; The gas sensor corrects a threshold value for determining whether the sensor output or the detection of the test gas is detected, depending on the degree of the fluctuation or the decrease in the fluctuation range of the air base output.

2. 2. The gas sensor according to claim 1, wherein the correction section stores an initial value of the fluctuation or fluctuation range of the air base output, and determines a degree of decrease in the fluctuation or fluctuation range of the air base output from the initial value.

3. A gas sensor calibration method for calibrating a sensor output or a threshold value for determining detection of a test gas using a computer, comprising the steps of: An air base output, which is a sensor output in an environment in which the test gas is not present, is obtained, and a degree of reduction in the fluctuation or fluctuation range of the air base output is obtained; A gas sensor correction method for correcting a sensor output or a threshold value for determining detection of a test gas in accordance with the degree of fluctuation or decrease in the fluctuation range of the air base output.

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