gas detector

Abstract

To provide a gas detector that can easily detect mixed gases with high accuracy, and that can calibrate the gas sensor without using actual gas. [Solution] The system is configured to include a sensitivity setting unit 121 that sets the sensor sensitivity of the gas sensor 110 for a gas to be measured, selected from among multiple types of mixed gases in which the first to nth gas components (where n is an integer of 2 or more) are mixed in different proportions, based on composition data relating to the gas to be measured and sensitivity data relating to the sensor sensitivity of the gas sensor 110 for each of the first to nth gas components, and a calibration curve data acquisition unit 122 that acquires calibration curve data for the gas to be measured based on composition data relating to the gas to be measured and reference calibration curve data for each of the first to nth gas components.

Description

[Technical Field]

[0001] The present invention relates to a gas detector that is configured to allow selection of a target gas from among several types of mixed gases, and that can perform gas detection according to the gas composition of the target gas. [Background technology]

[0002] Currently, for detecting city gas, gas detectors are used that are calibrated to indicate a concentration of 100 vol% when, for example, methane gas is introduced. These are so-called methane-specific gas detectors. However, city gas is a mixed gas mainly composed of methane, but also containing ethane, propane, and butane. Because the gas composition varies depending on the provider (gas company), it is difficult to use methane-specific gas detectors to handle it. When high measurement accuracy is required for city gas detection, it is necessary to calibrate the gas sensor with the target gas, which is city gas (actual gas). This calibration work requires cooperation from customers and others, which places a heavy burden on on-site personnel.

[0003] To address such problems, a method is known in which, for sample gases that may contain city gas, LPG, and naturally occurring methane, the concentration of methane gas z1 and the concentration of ethane gas x1 in the sample gas are measured, and the concentration of city gas Ct in the sample gas is determined by the ratio c of the ethane concentration x1 to the methane concentration z1 of the city gas that may be present in the sample gas, and the proportion α of miscellaneous gases that may be present in the city gas, using the formula Ct = x1(1 + 1 / a + 1 / c) / (1 - α) (see Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-169263 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, in the method described in Patent Document 1, gas components other than the three gas components of methane, ethane, and propane are treated as "miscellaneous gases (other gases)" and the concentration of city gas is determined. However, it has become clear that if other paraffinic hydrocarbon gases such as butane and pentane are included in city gas, even if the composition ratio of these paraffinic hydrocarbon gases is only a few percent, it will affect the concentration indication value. Furthermore, city gas often contains butane and pentane gases, and the city gas detection method described in Patent Document 1 has the problem that it is difficult to detect the concentration with high accuracy depending on the type of city gas.

[0006] This invention was completed in view of these circumstances, and aims to provide a gas detector that can easily detect mixed gases with high accuracy, and that can perform calibration of the gas sensor without using actual gas. [Means for solving the problem]

[0007] The present invention provides a gas detector that can select a target gas from among multiple types of mixed gases in which a first gas component to the nth gas component (where n is an integer of 2 or more) is mixed in different proportions, and is equipped with a gas sensor having sensor sensitivity for each of the first to the nth gas components. The gas detector is configured to solve the above problems by providing a sensitivity setting unit that sets the sensor sensitivity of the gas sensor for the target gas based on composition data relating to the gas composition of the target gas and sensitivity data relating to the sensor sensitivity of the gas sensor for each of the first to the nth gas components, and a calibration curve data acquisition unit that acquires calibration curve data for the target gas based on the composition data and reference calibration curve data for each of the first to the nth gas components. [Effects of the Invention]

[0008] According to the invention of claim 1, it is no longer necessary to obtain calibration curve data in advance using actual gas according to the composition of the gas to be measured, and it is also unnecessary to adjust the sensitivity of the gas sensor according to the actual gas, making it possible to detect the gas to be measured accurately and easily. In particular, according to the invention of claim 2, it becomes possible to accurately detect the concentration of approximately 70 types of city gases with a simple operation of selecting the city gas to be measured, making it possible to configure it as an extremely useful device for city gas detection.

[0009] According to the invention of claim 3 or claim 4, it is possible to acquire calibration curve data corresponding to the gas to be measured or to adjust the sensitivity of the gas sensor to the gas to be measured, thereby enabling accurate detection of the gas to be measured. According to the invention of claim 5, since it is not necessary to use actual gas for calibrating the gas sensor, the calibration of the gas sensor can be easily performed, and a high level of convenience can be obtained. [Brief explanation of the drawing]

[0010] [Figure 1] This is a block diagram schematically showing the configuration of a gas detector according to one embodiment of the present invention. [Figure 2] This figure shows the sensor sensitivity ratio for each paraffinic hydrocarbon gas with 1 to 4 carbon atoms relative to methane gas. [Figure 3] This figure shows the reference calibration curve data for each paraffinic hydrocarbon gas with 1 to 4 carbon atoms. [Modes for carrying out the invention]

[0011] The following description of the gas detector according to the present invention will be based on the example of a gas being measured as city gas. City gas typically consists mainly of methane (CH4), ethane (C2H6), propane (C3H8), and n-butane (n-C4H6). 10 ), isobutane (i-C4H 10), isopentane (i-C5H 12 ), normal pentane (n-C5H 12 It contains at least one gas component selected from paraffinic hydrocarbon gases such as ) and other gas components other than paraffinic hydrocarbon gases, and the gas composition differs for each city gas provider.

[0012] As shown in Figure 1, the gas detector 100 according to this embodiment includes a gas sensor 110, a control unit 120 that controls the operation of the gas detector 100, a storage unit 130 that stores various data, an operation unit 140 configured to allow selection of a target gas from among multiple types of city gases with different gas compositions, and a display unit 150.

[0013] The gas sensor 110 is a flammable gas sensor that has sensor sensitivity for each of the paraffinic hydrocarbon gases, which are the first to nth gas components (where n is an integer of 2 or more) contained in city gas. In this embodiment, the gas sensor 110 is configured as a thermal conduction type gas sensor, but it may also be configured as a semiconductor type sensor or a catalytic combustion type gas sensor.

[0014] The control unit 120 is composed of a CPU, which is a central processing unit, and includes a sensitivity setting unit 121 for setting the sensor sensitivity of the gas sensor 110 to the gas to be measured, a calibration curve data acquisition unit 122 for acquiring calibration curve data of the gas to be measured, a gas concentration calculation unit 123 for calculating the concentration of the gas to be measured based on the sensor output of the gas sensor 110, and a gas sensor calibration unit 124 for calibrating the gas sensor 110.

[0015] The sensitivity setting unit 121 sets the sensor sensitivity of the gas sensor 110 to the gas to be measured based on the composition data related to the gas composition of the gas to be measured and the sensitivity data related to the sensor sensitivity of each of the first to nth gas components of the gas sensor 110. Here, the sensor sensitivity is indicated by the span output obtained by subtracting the zero output from the sensor output obtained when a gas with a concentration of 100 vol% is introduced. The zero output is the sensor output obtained when a zero gas in which the gas sensor 110 has no sensor sensitivity is introduced. The setting of the sensor sensitivity of the gas sensor 110 to the gas to be measured is performed as follows.

[0016] FIG. 2 shows the ratio of the span output when each paraffinic hydrocarbon gas with a concentration of 100 vol% is introduced to the span output when methane gas with a concentration of 100 vol% is introduced as the sensor sensitivity ratio. However, the sensor sensitivity of the gas sensor 110 to paraffinic hydrocarbon gases tends to decrease as the number of carbon atoms increases. Therefore, it is possible to set the sensor sensitivity to the gas to be measured by evaluating the weight of the sensor sensitivity to each gas component contained in the gas to be measured by the gas sensor 110 based on the composition ratio.

[0017] Specifically, the sensor sensitivity ratio S of the sensor sensitivity of the gas sensor 110 to the gas to be measured to the sensor sensitivity to methane gas is calculated by the following formula (1). In the following, the "sensor sensitivity ratio" is based on the sensor sensitivity to methane gas. Formula (1) S = Σ(x m ×y m ), In the above formula (1), x is the composition ratio (%) of each paraffinic hydrocarbon gas component contained in the gas to be measured, y is the sensor sensitivity ratio related to each paraffinic hydrocarbon gas component contained in the gas to be measured, and m is the ordinal number of the n paraffinic hydrocarbon gas components contained in the gas to be measured, which is an integer from 1 to n. Taking an example, for example, the gas composition is CH4 (first gas component): C2H6 (second gas component): C3H8 (third gas component): C4H10 Assuming that the target gas for measurement is city gas with (fourth gas component) = x1:x2:x3:x4 (x1+x2+x3+x4=100%), and the sensor sensitivity ratios for each of the first to fourth gas components are y1 (=1), y2, y3, and y4 respectively, The sensor sensitivity ratio S for the gas being measured is: S=(x1×y1)+(x2×y2)+(x3×y3)+(x4×y4) This is the result.

[0018] The sensitivity setting unit 121 obtains the sensor sensitivity indicated by the span output for the target gas at a concentration of 100 vol%, from the sensor sensitivity ratio S for the target gas calculated as described above and the sensor sensitivity for methane gas obtained in advance, i.e., the span output for methane gas at a concentration of 100 vol%, and stores it in the storage unit 130 in a rewritable format.

[0019] <Calibration curve data acquisition unit> The calibration curve data acquisition unit 122 acquires calibration curve data for the target gas based on the composition data and reference calibration curve data for each of the first to nth gas components. The acquisition of calibration curve data for the target gas is performed as follows.

[0020] Figure 3 shows the reference calibration curve data (for convenience, the approximation curve is omitted) illustrating the relationship between gas concentration and power ratio for paraffinic hydrocarbon gases. As shown in Figure 3, the calibration curve data for each paraffinic hydrocarbon gas is represented by a curve that is convex towards the lower concentration side relative to the straight line (shown as a dashed line in Figure 3) connecting the gas concentration value at a power ratio of 0% and the gas concentration value at a power ratio of 100%, and the degree of convexity tends to increase with increasing carbon number. That is, for example, if we focus on the concentration indication value of each paraffinic hydrocarbon gas at a power ratio of 50%, the concentration indication value decreases with increasing carbon number. Therefore, by evaluating the weight of the calibration curve index indicated by the concentration of each gas component at a specific output ratio based on the composition ratio, it becomes possible to obtain the calibration curve index for the gas to be measured. Here, the output ratio is a value indicated by the ratio of the span output obtained for a specific gas at an arbitrary concentration vol% to the span output obtained for a specific gas at a concentration of 100 vol%.

[0021] Specifically, the calibration curve index for the gas to be measured is calculated by the following formula (2). Formula (2) C = Σ(x m × z m ) In the above formula (2), x is the composition ratio (percentage) of each paraffinic hydrocarbon gas component contained in the gas to be measured, z is the calibration curve index related to each paraffinic hydrocarbon gas component contained in the gas to be measured, and m is the ordinal number of n paraffinic hydrocarbon gas components contained in the gas to be measured, which is an integer from 1 to n. Taking an example, for instance, when the gas composition is CH4 (the first gas component): C2H6 (the second gas component): C3H8 (the third gas component): C4H 10 (the fourth gas component) = x1: x2: x3: x4 (x1 + x2 + x3 + x4 = 100%) and the city gas is used as the gas to be measured, and the calibration curve indices related to each gas component from the first gas component to the fourth gas component are z1, z2, z3, and z4 respectively, the calibration curve index C related to the gas to be measured is C = (x1 × z1) + (x2 × z2) + (x3 × z3) + (x4 × z4) and it becomes like this.

[0022] The calibration curve data acquisition unit 122 uses the calibration curve index C obtained as described above, and obtains the calibration curve data for the gas to be measured by the same curve approximation method as when obtaining the calibration curve data for each gas component. In addition, in the reference calibration curve data related to each paraffinic hydrocarbon gas shown in FIG. 3, the concentration indication values of each paraffinic hydrocarbon gas at the reference output ratios set every 10% within the range of 0 to 100% are shown, but the reference output ratio can be set as appropriate.

[0023] The gas concentration calculation unit 123 calculates the span output by subtracting the zero output from the sensor output acquired for the target gas, and then determines the output ratio of the obtained span output to the span output for the target gas at a concentration of 100 vol%. The span output for the target gas at a concentration of 100 vol% is the sensor sensitivity for the target gas, which is acquired by the sensitivity setting unit 121 and stored as sensitivity data related to the target gas. The concentration of the target gas is calculated by comparing the obtained output ratio with the calibration curve data for the target gas obtained as described above.

[0024] The gas sensor calibration unit 124 calibrates the gas sensor 110 so that the span output of the sensor output when 100 vol% methane gas is introduced to the gas sensor 110 as a calibration gas matches the sensitivity data for 100 vol% methane gas that has been stored in advance, i.e., the span output for 100 vol% methane gas.

[0025] The memory unit 130 pre-stores composition data (gas components and composition ratios) for each of the selectable city gases, sensitivity data for the sensor sensitivity of the gas sensor 110 for each of the multiple paraffinic hydrocarbon gas components contained in the city gas, reference calibration curve data for each of the paraffinic hydrocarbon gases, and zero output (zero point) acquired during gas sensor calibration. The span output (sensor sensitivity), sensor sensitivity ratio, and calibration curve data of the target gas acquired by the sensitivity setting unit 121 and the calibration curve data acquisition unit 122 are stored in a rewritable format as the target gas is selected.

[0026] The control unit 140 is configured to allow selection of the gas to be measured based, for example, on the region where the measurement environment is located, the name of the city gas provider (gas company name), etc. Furthermore, the storage unit 130 may store several representative gas compositions as composition data related to the gas composition, and the system may be configured to allow selection of the gas to be measured from among these gas compositions.

[0027] In the gas detector 100 described above, when the user operates the operation unit 140 to select a target gas from the city gases stored in the memory unit 130, the sensitivity setting unit 121 first performs a sensitivity setting process for the gas sensor 110 with respect to the target gas. The sensitivity setting unit 121 calculates the sensor sensitivity ratio for the target gas based on the composition data related to the target gas and the sensitivity data related to each paraffinic hydrocarbon gas component contained in the target gas. Based on the sensor sensitivity ratio S obtained and the sensor sensitivity for methane gas, the sensor sensitivity for the target gas is set. Next, the calibration curve data acquisition unit 122 performs a calibration curve data acquisition process for the target gas. The calibration curve data acquisition unit 122 calculates the calibration curve index at a specific output ratio for the target gas based on the composition data related to the target gas and the reference calibration curve data for each paraffinic hydrocarbon gas that is a gas component contained in the target gas. Based on the calibration curve index obtained, calibration curve data for the target gas is acquired. Then, the gas concentration calculation unit 123 obtains the span output of the sensor output acquired by the gas sensor 110, and calculates the output ratio to the span output for the target gas at a concentration of 100 vol%, which is the sensor sensitivity for the target gas set in the sensitivity setting unit 121. The output ratio obtained in this way is compared with the calibration curve data to calculate the concentration of the target gas. The control unit 120 outputs the concentration indication value to the display unit 150 to display the gas detection result.

[0028] Furthermore, in the gas detector 100 described above, the gas sensor 110 is calibrated using methane gas with a concentration of 100 vol% as the calibration gas. When a calibration gas is introduced, the gas sensor calibration unit 124 calibrates the gas sensor 110 so that the span output for the calibration gas acquired by the gas sensor 110 matches the span output for 100 vol% methane gas stored in the memory unit beforehand. In actual gas detection, the sensor sensitivity of the gas sensor 110 for the target gas is set by selecting the target gas. There is a certain regularity between the sensor sensitivity for each paraffinic hydrocarbon gas and the sensor sensitivity for methane gas. Furthermore, since the sensor sensitivity for the target gas is determined by the sensor sensitivity ratio for each paraffinic hydrocarbon gas and the sensor sensitivity for methane gas, it is possible to set the sensor sensitivity for the target gas appropriately by properly correcting the sensor sensitivity for methane gas through calibration.

[0029] <Effects and Effects> According to the gas detector 100 described above, detecting the concentration of approximately 70 types of city gases is possible with just a simple operation of selecting the city gas to be measured. This eliminates the need to obtain calibration curve data in advance using actual gas according to the composition of the target gas, and also eliminates the need to adjust the sensitivity of the gas sensor 110 according to the actual gas, making it possible to detect the target gas accurately and easily. Furthermore, since it is not necessary to use actual gas to calibrate the gas sensor 110, the calibration of the gas sensor 110 can be easily performed, providing high convenience.

[0030] The following describes experimental examples conducted to confirm the effects of the present invention. Four gas detectors (No. 1 to No. 4) equipped with thermal conduction gas sensors, each with the same configuration, were used to measure the concentration of test gases A and B, which had been adjusted in concentration by dilution with N2 gas. Test gases A and B are mixed gases mainly composed of methane, with ethane, propane, butane, and pentane mixed in different proportions. For concentration measurement, the sensitivity settings of the gas sensors for the test gases and calibration curve data acquisition for the target gases were performed. The measurement results are shown in Table 1 below. Furthermore, each of the above gas detectors (No. 1 to No. 4) was set to methane specifications (the gas sensor was calibrated so that the concentration reading would be 100 vol% when 100 vol% methane gas was introduced), and the measurement results when the concentration was measured while the detectors were still set to methane specifications are shown in Table 2 below as a reference experimental example.

[0031] [Table 1]

[0032] [Table 2]

[0033] As is clear from the results above, it has been confirmed that the gas detector according to the present invention can detect the concentration of the test gas (equivalent to city gas) with high accuracy, regardless of individual differences in the gas sensor.

[0034] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications can be made. For example, the gas to be measured is not limited to city gas; the present invention can also be applied to mixed gases in which the first to nth gas components (where n is 2 or more) are mixed in different proportions. Alternatively, temperature correction indices for each gas component contained in the gas to be measured may be obtained in advance, and the temperature correction index for the gas to be measured may be obtained based on the temperature correction index for each gas component and composition data, similar to the method for determining the sensor sensitivity ratio and calibration curve index described above, and temperature correction may be performed when measuring the concentration of city gas. Furthermore, if the actual sensitivity ratio differs from the theoretical value shown in this invention, it may be approximately corrected based on the distribution of the actual sensitivity ratio and the theoretical value. In addition, the shape of the calibration curve may be finely adjusted according to the magnitude of the sensitivity ratio value. [Explanation of Symbols]

[0035] 100... Gas detector 110... Gas sensor 120 ··· Control Unit 121... Sensitivity setting section 122 ··· Calibration curve data acquisition unit 123... Gas concentration calculation unit 124... Gas Sensor Calibration Department 130... Storage section 140...Operation unit 150... Display section

Claims

1. A gas detector configured to select a target gas from among multiple types of mixed gases in which a first gas component to the nth gas component (where n is an integer of 2 or more) is mixed in different proportions, and equipped with a gas sensor having sensor sensitivity for each of the first gas component to the nth gas component, A sensitivity setting unit sets the sensor sensitivity of the gas sensor to the gas to be measured based on composition data relating to the gas composition of the gas to be measured and sensitivity data relating to the sensor sensitivity of the gas sensor to each of the first to n gas components, A calibration curve data acquisition unit acquires calibration curve data for the gas to be measured based on the composition data and reference calibration curve data for each of the first to n gas components. A gas detector characterized by having the following features.

2. The aforementioned gas sensor is a flammable gas sensor, The gas detector according to claim 1, characterized in that the mixed gas is city gas in which the first to nth gas components are each a paraffinic hydrocarbon gas.

3. The gas detector according to claim 2, characterized in that the sensitivity setting unit sets the sensor sensitivity of the gas sensor for the target gas to be measured as the sum of the product (Sm × Rm) of the sensitivity ratio Sm (where m is an integer from 1 to n) of the sensor sensitivity of the gas sensor for each of the first to n gas components with respect to the sensor sensitivity of the gas sensor for methane gas and the composition ratio Rm of each of the first to n gas components.

4. The calibration curve data acquisition unit sets the sum of the product (Cm × Rm) of the calibration curve index Cm (where m is an integer from 1 to n) which is represented by the gas concentration of each of the first gas component to the n gas component at a specific output ratio [%] and the composition ratio Rm of each of the first gas component to the n gas component, as the calibration curve index for the gas to be measured at the specific output ratio, and acquires calibration curve data for the gas to be measured based on the calibration curve index, as described in claim 2.

5. The gas detector according to claim 3, further comprising a gas sensor calibration unit that calibrates the gas sensor so that the sensor output obtained by introducing 100 vol% methane gas as a calibration gas into the gas sensor becomes a value corresponding to the sensor sensitivity to 100 vol% methane gas that has been previously obtained.

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