JP5844556B2 - Method for correcting output of heat conduction type gas sensor and gas detector - Google Patents

Description

  The present invention relates to an output correction method for a heat conduction gas sensor and a gas detector including the heat conduction gas sensor.

  The detection of combustible gas is required to be performed in a wide concentration range from low concentration to high concentration, for example, a contact combustion type gas sensor for detecting a low concentration combustible gas below the lower explosion limit concentration. For example, a gas detector having a configuration in which a high-concentration combustible gas exceeding 100% LEL or a heat-conducting gas sensor for detecting a combustible gas having an oxygen concentration of 10% or less is switched is proposed. (See Patent Document 1).

  Since the contact combustion type gas sensor detects the amount of heat generated by the combustion of oxygen and combustible gas in the atmosphere as, for example, the amount of change in the resistance value of the heater coil, the combustible gas in the tank of the crude oil tanker is detected. In the case of detection, when a non-combustible gas is present at a high concentration by purging an inert gas such as nitrogen in the tank, the temperature increase of the catalytic combustion type gas sensor due to the oxidation reaction is combustible. There is a problem that an error occurs without corresponding to the gas concentration.

On the other hand, in the heat conduction type gas sensor, the zero point output changes depending on the base gas type in the test gas. Therefore, more specifically, the calibration gas corresponding to the type of the balance gas constituting the base gas is used than the base gas type. Calibration work such as zero point output correction and sensitivity correction is required.
However, for example, when detecting flammable gas in a tank of a crude oil tanker, the base gas type may change even in the same tank. The problem is that it is difficult to measure the concentration of flammable gas with high accuracy because it takes a lot of time and it is practically difficult to always prepare a calibration gas according to the base gas type. was there.

Japanese Patent Laid-Open No. 2005-207879

  The present inventors have found that the sensor output of the heat-conducting gas sensor changes in proportion to the oxygen concentration, and corrects the zero point output of the heat-conducting gas sensor based on the oxygen concentration in the test gas. Therefore, it was considered that the gas concentration measurement of the combustible gas could be performed with high accuracy, and the present invention was completed.

An object of the present invention is to provide an output correction method for a heat conduction type gas sensor that can improve the detection accuracy of the gas concentration of a combustible gas in a wide concentration range from a low concentration to a high concentration.
Another object of the present invention is to provide a gas detector that includes a heat conduction type gas sensor and can accurately and reliably measure the gas concentration of a combustible gas. .

The output correction method of the heat conduction type gas sensor of the present invention is the method of correcting the sensor output obtained from the heat conduction type gas sensor for detecting combustible gas with respect to the gas in the tank of the tanker which is the test gas, the oxygen concentration in the test gas. An output correction method for a heat conduction gas sensor that corrects based on
By performing zero point output calibration of the heat conduction type gas sensor using two types of zero point output calibration gases having different balance gas types , including zero point output calibration gas using exhaust gas inert as balance gas In addition, two zero point outputs for the heat conduction type gas sensor are acquired in advance,
The oxygen concentration contained in the zero point output calibration gas related to _one zero point output (X ₁ ) is Y ₁ , and the oxygen concentration contained in the zero point output calibration gas related to the other zero point output (X ₂ ) is Y _{2. When} the oxygen concentration in the test gas is Y ₀ ,
An output correction amount ΔX for correcting the sensor output of the acquired heat conduction type gas sensor that is the test gas is calculated based on the following formula 1.

The gas detector of the present invention includes a heat conduction gas sensor for detecting a combustible gas, an oxygen sensor for detecting oxygen, and a gas in a tank in a tanker as a test gas based on a sensor output obtained from the oxygen sensor. The oxygen concentration in the test gas is calculated and the sensor output from the heat conduction gas sensor obtained for the test gas is corrected based on the oxygen concentration in the test gas, and the combustible gas in the test gas is corrected. a density calculating mechanism having a function of calculating the gas concentration of the oxygen zero point output X ₁ of the heat-conducting gas sensor during the zero point output calibration of the sensor, the at zero point output calibration of the thermal conductive gas sensor Comprising a memory in which the zero point output X ₂ of the heat conduction gas sensor is recorded,
The concentration calculation mechanism calculates the output correction amount ΔX to be corrected for the sensor output obtained from the heat conduction type gas sensor, and the oxygen concentration contained in the oxygen sensor zero point output calibration gas used for the zero point output calibration of the oxygen sensor. Y _{1 represents} the oxygen concentration contained in the heat conduction gas sensor zero point output calibration gas using the exhaust gas inert as a balance gas, used for calibration of the zero point output of the heat conduction gas sensor, and Y _{2 represents} the detected gas to be detected. When the oxygen concentration of Y is Y ₀ , the calculation is based on Equation 1 above.

According to the output correction method of the heat conduction type gas sensor of the present invention, the output correction of the sensor output obtained by the heat conduction type gas sensor is performed based on the oxygen concentration in the test gas, whereby the base gas type in the test gas is obtained. Because the sensor output fluctuation due to the difference is compensated, the detection accuracy of the combustible gas concentration can be improved in a wide concentration range from a low concentration to a high concentration.
Therefore, according to the gas detector of the present invention in which the concentration measurement of the combustible gas is performed by performing the output correction on the sensor output of the heat conduction type gas sensor, the concentration measurement of the combustible gas over a wide concentration range is performed. Can be performed accurately and with high reliability only by the heat conduction type gas sensor. In addition, since it is not necessary to always prepare a calibration gas corresponding to the base gas type in the test gas, the intended gas concentration measurement can be easily performed.

It is a block diagram which shows the outline of a structure in an example of the gas detector of this invention. It is a graph which shows an example of the output characteristic data which show the relationship between the sensor output and the gas concentration of combustible gas for demonstrating the correction method of the sensor output of the heat conduction type gas sensor in the gas detector of this invention. It is a graph which shows the time-dependent change of the combustible gas density | concentration in the density | concentration measurement of the combustible gas in the tank of a crude oil tanker.

Hereinafter, embodiments of the present invention will be described in detail.
FIG. 1 is a block diagram showing an outline of a configuration in an example of a gas detector of the present invention.
The gas detector according to this embodiment includes a heat conduction gas sensor 10 for detecting a combustible gas, an oxygen sensor 20 for detecting oxygen, and a control for issuing an appropriate operation command signal to each component including these gas sensors. Means 30 and display means 45 for displaying the measurement results are provided. As the oxygen sensor 20, for example, a galvanic cell type oxygen sensor can be used.

The control means 30 includes a concentration calculation mechanism 35 having a function of calculating the gas concentration and the oxygen concentration of the combustible gas based on the sensor outputs obtained from the heat conduction type gas sensor 10 and the oxygen sensor 20, and the calculation of the combustible gas concentration. And a memory 31 in which such data is recorded.
Here, as data recorded in the memory 31, as will be described later, data relating to sensor output (reference sensor output data) acquired by performing calibration work on each of the heat conduction type gas sensor 10 and the oxygen sensor 20. And output characteristic data (calibration curve data) indicating the relationship between the sensor output of the heat conduction type gas sensor 10 and the gas concentration of the combustible gas.

The concentration calculation mechanism 35 is obtained from an oxygen concentration calculation unit 36 that calculates the oxygen concentration Y ₀ in the test gas based on the sensor output of the test gas obtained from the oxygen sensor 20, and the heat conduction gas sensor 10. The output correction amount ΔX for correcting the sensor output (hereinafter referred to as “detection sensor output”) X for the test gas is calculated by the oxygen concentration Y _{0 of the} test gas calculated by the oxygen concentration calculation unit 36 and the memory 31. Based on the reference sensor output data D1 recorded in the output sensor, the output correction amount calculation unit 37 to be calculated and the detection sensor output X of the heat conduction type gas sensor 10 by the output correction amount ΔX calculated by the output correction amount calculation unit 37 are calculated. A corrected output calculation unit 38 for calculating the corrected correction output X ′, and the gas concentration of the combustible gas corresponding to the correction output X ′ calculated by the correction output calculation unit 38 Is calculated based on the output characteristic data D2 recorded in the memory 31, and an output unit 40 that outputs the gas concentration S of the combustible gas calculated by the gas concentration calculation unit 39 to the display means 45. And has.

Hereinafter, a method for calculating the concentration of the combustible gas in the gas detector will be described with reference to FIG.
First, a zero point output calibration of the oxygen sensor 20 is performed with an oxygen sensor zero point output calibration gas using oxygen of a specified concentration (Y ₁ %) as a balance gas, and a heat conduction type gas sensor for this oxygen sensor zero point output calibration gas. Ten sensor outputs are acquired as the first reference zero point output X ₁ and recorded in the memory 31.
Further, the zero point output calibration of the heat conduction type gas sensor 10 is performed with the heat conduction type gas sensor zero point output calibration gas whose balance gas oxygen concentration is Y ₂ [%], and the sensor output of the heat conduction type gas sensor 10 is obtained. Obtained as the second reference zero point output X ₂ and recorded in the memory 31. Furthermore, the heat conduction type gas sensor 10 obtained by performing the span calibration of the heat conduction type gas sensor 10 with the heat conduction type gas sensor span calibration gas containing a flammable gas (detection target gas) having a specified concentration (for example, 100 vol%). The sensor output is acquired as the reference span output X ₃ and recorded in the memory 31.
Then, the output characteristic data (the straight line (A) in FIG. 2) of the balance gas of the heat conduction type gas sensor zero point output calibration gas is based on the second reference zero point output X ₂ and the reference span output X _3. At the same time, output characteristic data (straight line (b)) for the balance gas of the oxygen sensor zero point output calibration gas is acquired based on the first reference zero point output X ₁ and the reference span output X ₃ .

In the detection of the combustible gas, the sensor output obtained from the oxygen sensor 20 is input to the oxygen concentration calculation unit 36 in the concentration calculation mechanism 35, and the oxygen concentration calculation unit 36 calculates the oxygen concentration Y ₀ in the test gas. Is done.

Next, the output correction amount calculation unit 37 calculates an output correction amount ΔX for correcting the detection sensor output X obtained from the heat conduction type gas sensor 10. The output correction amount ΔX is calculated using the proportional relationship between the output characteristic data (A) and the output characteristic data (B), and specifically, the oxygen concentration Y _{0 of the} test gas detected by the oxygen sensor 20. , And the first reference zero point output X ₁ acquired in advance and recorded in the memory 31, the oxygen concentration Y ₁ of the balance gas in the oxygen sensor zero point output calibration gas, and the second reference reference zero point output X ₂ Based on the oxygen concentration Y ₂ of the balance gas in the heat conduction type gas sensor zero point output calibration gas, the following equation 1 is used.

Then, the correction output calculation unit 38 calculates a correction sensor output obtained by correcting the detection sensor output X obtained from the heat conduction gas sensor 10 with the output correction amount ΔX calculated as described above. Here, the correction sensor output is obtained by subtracting the output correction amount ΔX from the detection sensor output X.
The correction sensor output (X−ΔX) acquired in this way is compared with the output characteristic data (b) for the balance gas in the heat conduction type gas sensor zero point output calibration gas acquired in advance and recorded in the memory 31. Thus, a process for calculating the gas concentration S of the combustible gas in the test gas is performed by the gas concentration calculation unit 39, and an operation command signal corresponding to the gas concentration S of the combustible gas obtained thereby is output. 40 is outputted to the display means 45 to display the concentration measurement result.

A specific example of the output correction method of the heat conduction type gas sensor 10 will be described. For example, the oxygen concentration Y ₁ of the balance gas in the oxygen sensor zero point output calibration gas is 20.9%, and the heat conduction type gas sensor zero point output calibration gas. The balance gas is nitrogen, that is, the oxygen concentration Y ₂ at the time of calibration of the zero point output of the heat conduction type gas sensor 10 is 0%, and the output of the first reference zero point output X ₁ and the second reference zero point output X ₂ If the difference (X ₁ −X ₂ ) is a value equivalent to +8 vol% and the oxygen concentration Y _{0 of the} test gas detected by the oxygen sensor 20 is 10.45%, the output correction amount ΔX is expressed by the above equation. 1 is calculated to be a size equivalent to +4 vol%.

Thus, according to the output correction method of the heat conduction type gas sensor 10 as described above, the output correction of the detection sensor output X obtained from the heat conduction type gas sensor 10 is performed based on the oxygen concentration Y ₀ in the test gas. This compensates for variations in sensor output due to the difference in the type of balance gas that constitutes the base gas in the test gas, so that a low concentration to a high concentration can be achieved regardless of the type of balance gas related to the test gas. In a wide concentration range, the gas concentration detection accuracy of the combustible gas can be improved.
Therefore, according to the gas detector having the above-described configuration in which the concentration measurement of the combustible gas is performed by performing the output correction on the sensor output of the heat conduction type gas sensor 10, the concentration of the combustible gas over a wide concentration range. The measurement is accurate and high only by the heat conduction type gas sensor 10 without using the contact combustion type gas sensor for detecting the low concentration combustible gas which is preferably used in the conventional combustible gas detector, for example. Can be done with reliability.

  According to the above gas detector, as described above, fluctuations in the sensor output of the heat conduction type gas sensor 10 due to the difference in the type of balance gas related to the test gas are compensated for, for example, combustible in the tank of a crude oil tanker. It will be extremely useful for measuring the concentration of sex gases.

That is, in measuring the concentration of the combustible gas in the tank of the crude oil tanker, as shown in FIG. 3, measurement is performed on the air in the ambient atmosphere (field) outside the tank filled with the crude oil (concentration measurement). Region A). At this time, the balance gas in the test gas is air (oxygen concentration is, for example, 20.9%), and the concentration of combustible gas, for example, HC in the tank is, for example, 0 vol%.
When the concentration measurement of the combustible gas in the tank is started, the concentration of HC changes with time until it reaches 100 vol%, for example (concentration measurement region B). At this time, the balance gas in the test gas is an exhaust gas inert. Here, the exhaust gas inert has, for example, a humidity of about 80% RH and an oxygen concentration of 8% or less, and includes, for example, carbon dioxide. Crude oil in the tank is pulled out while filling the exhaust gas inert into the tank. At this time, the balance gas related to the atmosphere in the tank is exhaust gas inert, and the concentration of HC changes with time from 100 vol% to, for example, about 1 vol% (concentration measurement region C). Then, after the crude oil is extracted from the tank, air is introduced into the tank by confirming that the HC concentration is 1 vol% or less. At this time, the balance gas in the atmosphere in the tank is air (oxygen concentration is 20.9%, for example).

  As described above, the base gas species changes even in the same tank of the crude oil tanker, and as shown in FIG. 3, a heat conduction gas sensor zero point output calibration gas using a specified concentration of oxygen as a balance gas. If the HC concentration is calculated based on the output characteristic data for the gas, the gas concentration value becomes 0 or less in the concentration measurement region C of the test gas including the base gas using the exhaust gas inert as the balance gas. Will occur.

Therefore, the zero point output calibration by the calibration gas corresponding to the base gas type of the zero point output in the heat conduction type gas sensor 10 is required. According to the above gas detector, the standard gas is used as the calibration gas. The calibration work used is unnecessary, and it is not necessary to always prepare a calibration gas corresponding to the base gas type in the test gas, so that the intended gas concentration measurement can be easily performed. Further, the zero point output calibration of the heat conduction type gas sensor 10 is performed with the heat conduction gas sensor zero point output calibration gas using the exhaust gas inert as the balance gas, whereby the reference zero point output X of the heat conduction type gas sensor 10 for the balance gas is obtained. _{Since 2} can be obtained and the output correction amount ΔX can be calculated using the reference zero point output X ₂ , high convenience in use can be obtained.

Heat conduction gas sensor 10 when the zero point output calibration of the heat conduction gas sensor 10 is performed using the gas for calibration of the zero point output of the heat conduction gas sensor using the exhaust gas inert having an oxygen concentration Y ₂ of 6% as a balance gas. When showing a specific example of the output correction method, the oxygen sensor zero point output oxygen concentration Y ₁ is 20.9 percent of the balance gas in calibration gas, balance gas of the heat conduction gas sensor zero point output calibration gas discharge Gasuinato, That is, the oxygen concentration Y ₂ at the time of calibration of the zero point output of the heat conduction type gas sensor 10 is 6%, for example, and the output difference (X ₁ − between the first reference zero point output X ₁ and the second reference zero point output X _2). X ₂₎ is the + 5 vol% equivalent value, the oxygen concentration Y ₀ of the test gas detected by the oxygen sensor 20 is assumed to be 16.45%, the output correction amount ΔX, from the formula 1 + Is calculated to be 2.5 vol% equivalent value.

As mentioned above, although embodiment of this invention was described, this invention is not limited to said embodiment, A various change can be added.
For example, even if the oxygen concentration Y ₀ of the test gas used when correcting the output of the heat conduction type gas sensor is a value detected by the oxygen sensor included in the gas detector itself, the oxygen concentration detection means uses a separate oxygen concentration detection means. The detected value may be input, and therefore the gas detector itself does not need to be configured to include an oxygen sensor. For example, when measuring the concentration in a tank in a tanker, etc. Thus, when the base gas species changes with time, the gas detector is preferably configured to include an oxygen sensor.
When the gas detector is configured not to have an oxygen sensor, the zero point output of the heat conduction type gas sensor is acquired in advance for two types of zero point output calibration gases having different base gas types. Record it in memory.

DESCRIPTION OF SYMBOLS 10 Thermal conductivity type gas sensor 20 Oxygen sensor 30 Control means 31 Memory 35 Concentration calculation mechanism 36 Oxygen concentration calculation part 37 Output correction amount calculation part 38 Correction output calculation part 39 Gas concentration calculation part 40 Output part 45 Display means

Claims (2)

An output correction method for a heat conduction type gas sensor for correcting the sensor output obtained from a heat conduction type gas sensor for detecting a flammable gas based on the oxygen concentration in the test gas for a gas in a tank in a tanker as a test gas Because
By performing zero point output calibration of the heat conduction type gas sensor using two types of zero point output calibration gases having different balance gas types , including zero point output calibration gas using exhaust gas inert as balance gas In addition, two zero point outputs for the heat conduction type gas sensor are acquired in advance,
The oxygen concentration contained in the zero point output calibration gas related to _one zero point output (X ₁ ) is Y ₁ , and the oxygen concentration contained in the zero point output calibration gas related to the other zero point output (X ₂ ) is Y _{2. When} the oxygen concentration in the test gas is Y ₀ ,
An output correction method for a heat-conducting gas sensor, wherein an output correction amount ΔX for correcting the sensor output of the acquired heat-conducting gas sensor, which is a test gas, is calculated based on the following equation 1.

While calculating the oxygen concentration in the gas in the tank in the tanker that is the test gas based on the heat conduction type gas sensor for detecting the combustible gas, the oxygen sensor for detecting oxygen, and the sensor output obtained from the oxygen sensor A function for correcting the sensor output by the heat conduction gas sensor obtained for the test gas based on the oxygen concentration in the test gas and calculating the gas concentration of the combustible gas in the test gas. a density calculating mechanism having the zero point output X ₁ of the heat-conducting gas sensor of the oxygen sensor at the time of the zero point output calibration, zero point output of the heat conduction gas sensor during the zero point output calibration of the thermal conductive gas sensor X ₂ and recorded memory ,
The concentration calculation mechanism calculates the output correction amount ΔX to be corrected for the sensor output obtained from the heat conduction type gas sensor, and the oxygen concentration contained in the oxygen sensor zero point output calibration gas used for the zero point output calibration of the oxygen sensor. Y _{1 represents} the oxygen concentration contained in the heat conduction gas sensor zero point output calibration gas using the exhaust gas inert as a balance gas, used for calibration of the zero point output of the heat conduction gas sensor, and Y _{2 represents} the detected gas to be detected. When the oxygen concentration of Y is Y ₀ , the gas detector is calculated based on the following formula 1.

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