JP6912348B2 - Gas detector - Google Patents

Description

The present invention relates to a gas detector provided with gas detecting means such as a contact combustion type gas sensor and a heat ray type semiconductor type gas sensor.

For example, in a gas detection means such as a contact combustion type gas sensor or a heat ray type semiconductor type gas sensor, the electric resistance value changes when the test gas comes into contact with the surface of the gas sensitive portion, and is based on the amount of change in the electric resistance value. The concentration of the test gas is detected. Conventionally, in this gas detecting means, a compensating element that is insensitive to the test gas is provided together with a gas detecting element having a gas sensitive portion.
In a gas detector provided with such a gas detecting means, it is necessary to supply electric power to the compensating element in the same manner as the gas detecting element, and therefore, the power saving of the gas detector is aimed at. Is difficult.
Recently, in order to save power of the gas detector, a gas detector provided with a contact combustion type gas sensor having no compensating element has been proposed as a gas detecting means (see, for example, Patent Document 1). .).

In general, the zero output value (zero point) of the contact combustion type gas sensor changes depending on, for example, environmental conditions. Therefore, the zero output value of the contact combustion type sensor stored in the gas detector, for example, the zero output value set at the time of the previous measurement. There are often errors in the level of. Therefore, when using the gas detector, it is necessary to adjust the contact combustion type sensor to a zero output value according to the usage environment by performing a calibration process using zero gas, for example, an Air calibration process.
In the zero point adjustment by the Air calibration process, the output value in a stable state (for example, the instantaneous output current value) is usually set as the zero output value, but the output value of the contact combustion type gas sensor is energized. Since it stabilizes after a predetermined warm-up period has elapsed from the start, it takes a long time until the zero point adjustment is performed and a state in which the test gas concentration can be measured is obtained. In particular, a contact combustion type gas sensor having no compensating element requires a long warm-up time.

Therefore, according to the gas detector described in Patent Document 1, the output value satisfying a specific condition is imitated as a zero output value by the zero output correction process executed by the control means during the warm-up period of the gas sensor. Therefore, even if the configuration does not have a compensating element, it is possible to measure the concentration of the test gas with tentative reliability.

Japanese Unexamined Patent Publication No. 2015-224892

However, the above gas detector has the following problems.
Generally, in a gas detector equipped with a contact combustion type gas sensor or a heat ray type semiconductor type gas sensor as a gas detection means, even after the warm-up treatment period has elapsed, the gas detection means may be affected by fluctuations in the temperature and humidity of the usage environment. The output value changes. Further, when the gas detector is used for a long period of time, the gas sensitive portion and the resistance heating element 13 in the gas detection element change in quality with time, so that the output value of the gas detection means changes. Therefore, the above-mentioned gas detector has a problem that the reliability of the concentration measurement of the test gas is lowered when it is used in an environment where the temperature and humidity fluctuate or when it is used for a long period of time.

Therefore, an object of the present invention is to measure the concentration of the test gas even if the output value from the gas detecting means changes due to warm-up treatment, fluctuation of temperature and humidity in the usage environment, or long-term use. The purpose is to provide a gas detector that can be executed reliably.

The gas detector of the present invention includes a gas detecting means for detecting the concentration of the test gas and a control means having a function of calculating the concentration of the test gas based on the output value from the gas detecting means. It ’s a detector,
The control means
The output value from the gas detecting means is intermittently acquired at specific time intervals, and the output value is obtained intermittently.
Acquired output values P ₁ and the difference value between the output value last output value P ₀ one acquired during the previous 5 to 40 seconds at acquisition of P ₁ (P ₀ -P ₁₎ is a specific A function that performs zero output correction processing that repeatedly executes the zero output value setting process that sets the _{latest output value P 0 as a new zero output value every time the output value P 1} is acquired when it is within the permissible range. It is characterized by having.

In the gas detector of the present invention, it is preferable that the control means has a function of maintaining the zero output value when the _{difference value (P 0} −P _{1) exceeds the specific allowable range.} Further, it is preferable that the gas detecting means has a contact combustion type gas sensor or a heat ray type semiconductor gas sensor as a gas detecting element, and does not have a compensating element that is insensitive to the test gas.

According to the gas detector of the present invention, the concentration of the test gas can be measured even if the output value from the gas detection means changes due to warm-up treatment, fluctuation of temperature and humidity in the usage environment, or long-term use. It can be executed with tentative reliability, and after the power is turned on, a state in which the gas concentration can be measured can be obtained at an early stage.
Further, since it is not necessary to provide a compensating element, the power saving of the gas detector can be achieved. Therefore, when configured as a portable gas detector, the life of the battery, which is the driving power source, can be extended.

It is a block diagram which shows the outline of the structure in the example of the gas detector of this invention. It is a circuit block diagram in an example of the gas detection means used in the gas detector of this invention. When the gas detector of the present invention is used in an environment where the temperature fluctuates, when the test gas is introduced at regular time intervals, the sensor output P ₁ of the gas detecting means and the difference value (P _{0 −} P ₁₎ ) And the graph which schematically shows the change with time of each of the displayed values. FIG. 5 is a graph showing a temperature-humidity program set in a high-temperature and high-humidity tank in Example 1. The gas detector according to Example 1, is a graph showing the change over time of the sensor output value P _1. It is a graph which shows the time-dependent change _{of the difference value (P 0 −} P ₁ ) in the gas detector which concerns on Example 1. FIG. It is a graph which shows the time-dependent change of the display value in the gas detector which concerns on Example 1. FIG. FIG. 5 is a graph showing a temperature-humidity program set in a high-temperature and high-humidity tank in Example 2. The gas detector according to Embodiment 2 is a graph showing the change over time of the sensor output value P _1. It is a graph which shows the time-dependent change _{of the difference value (P 0 −} P ₁ ) in the gas detector which concerns on Example 2. FIG. It is a graph which shows the time-dependent change of the display value in the gas detector which concerns on Example 2. FIG.

Hereinafter, embodiments of the gas detector of the present invention will be described.
FIG. 1 is a block diagram showing an outline of a configuration in an example of the gas detector of the present invention.
This gas detector includes a gas detecting means 10, a controlling means 20, a storage means 30, a timing means 40, a display means 50, and an alarm means 60.

Examples of the gas detecting means 10 include optics such as a contact combustion type gas sensor, a heat ray type semiconductor type gas sensor, a semiconductor type gas sensor, a new ceramic type gas sensor, a solid state sensor such as a heat conduction type gas sensor, an infrared type sensor, and a near infrared type sensor. A type sensor can be used. Among these, a contact combustion type gas sensor or a hot wire type semiconductor type gas sensor is preferable.

FIG. 2 is an explanatory diagram showing a circuit configuration in an example of the gas detecting means 10. The gas detecting means 10 of this example comprises a contact combustion type gas sensor or a heat ray type semiconductor type gas sensor, and has a configuration in which power saving is achieved by not having a compensating element that is insensitive to the test gas. be. Specifically, the gas detecting means 10 includes a gas detecting element 11 and a measuring circuit 15 including a current detecting resistor 14. In the measurement circuit 15, the current detection resistor 14 is connected in series with the gas detection element 11. Further, in the measuring circuit 15, the voltage detecting means 16 is connected in parallel to the gas detecting element 11, and the current detecting means 17 is connected in parallel to the current detecting resistor 14.

The gas detection element 11 is configured such that a gas sensitive portion 12 is formed around a resistance heating element 13 that generates heat when energized.
When the gas detecting means 10 is composed of a contact combustion type gas sensor, as the gas sensitive portion 12 in the gas detecting element 11, one in which an oxidation catalyst is sintered together with, for example, an alumina carrier is used.
When the gas detecting means 10 is composed of a heat ray type semiconductor type gas sensor, the gas sensitive portion 12 in the gas detecting element 11 is a sintered metal oxide semiconductor.
The resistance heating element 13 in the gas detection element 11 is composed of a heater having a coil portion in which a metal wire made of, for example, platinum or an alloy thereof is wound in a coil shape.

When the gas detecting means 10 is composed of a contact combustion type gas sensor, the gas sensitive portion 12 is heated by applying a voltage controlled to a constant magnitude from the power source 18 to the resistance heating element 13. It is considered to be in a state. At this time, the gas detection element 11 maintains a constant resistance value. Then, when the test gas comes into contact with the surface of the gas-sensitive portion 12, the temperature of the surface of the gas-sensitive portion 12 rises, and the resistance value of the resistance heating element 13 changes accordingly. The amount of change in the resistance value is detected by measuring the current value flowing through the current detection resistor 14 with the current detecting means 17.

Further, when the gas detecting means 10 is composed of a heat ray type semiconductor gas sensor, a voltage controlled to a constant magnitude from the power supply 18 is applied to the resistance heating element 13, so that the gas sensitive unit 12 is subjected to. It is said to be in a heated state. At this time, the gas detection element 11 maintains a constant resistance value. Then, when the test gas comes into contact with the surface of the gas-sensitive portion 12, oxygen adsorbed on the surface of the metal oxide semiconductor constituting the gas-sensitive portion 12 is released, and accordingly, the metal oxide semiconductor of the metal oxide semiconductor is released. As a result of the change in the resistance value, the resistance value of the entire gas detection element 11 changes. The amount of change in the resistance value is detected by measuring the current value flowing through the current detection resistor 14 with the current detecting means 17.

The control means 20 has a function of performing a zero output correction process for correcting a zero output value with respect to an output value from the gas detecting means 10 (hereinafter, also referred to as a “sensor output value”) (hereinafter, referred to as a “zero output correction mode”. ) And a function to maintain the set zero output value (hereinafter referred to as "zero output maintenance mode"). In the control means 20, an operation control mechanism for controlling the operation of the gas detector and a calculation for calculating a display value indicating the concentration of the test gas and the gas concentration based on the sensor output value and the set zero output value. A mechanism and a zero output correction mechanism for correcting the zero output value set for the gas detecting means 10 are provided.

The storage means 30 records information related to the gas concentration calculation process by the calculation mechanism in the control means 20 and the zero output correction process by the zero output correction mechanism, information related to the alarm operation by the alarm means 60, and the like.

Information related to the gas concentration calculation process includes, for example, an individual calibration curve (sensitivity curve) peculiar to the gas detection element 11 showing the relationship between the display value indicating the gas concentration and the gas concentration value, and a zero calibration value for the gas detection element 11. Calibration data such as (zero output value) and span calibration value can be mentioned. Here, as the individual calibration curve, a plurality of individual calibration curves set for each of the plurality of types of test gases may be recorded.
Further, in this gas detector, for example, a measurement range for a high concentration range for detecting a test gas in a concentration range of 0 to 100% LEL and a test gas in a concentration range of 0 to 10% LEL are used. Two measurement ranges are set, one for the low concentration range for detection.

The information related to the zero output correction process includes, for example, a set value related to a unit time, which is a time interval in which the zero output value setting process is performed, that is, a specific time interval for acquiring the sensor output value from the gas detecting means 10, and a sensor output. Examples include a set value related to the allowable range for the difference between the value and the latest output value, or a set value related to the total output adjustment amount.
As the information related to the alarm operation, for example, an alarm point of an instantaneous value regarding the gas concentration can be mentioned. In this gas detector, for example, the first alarm point is set to 10% LEL.

The display means 50 displays a display value or a gas concentration calculated by the control means 20 based on the sensor output value and the zero output value of the gas detection means 10, and the gas concentration is, for example, contact combustion. CH ₄ 0.2% LEL units in formula sensor (resolution), the hot wire type semiconductor sensor is a detection-viewable CH ₄ 5 ppm units (resolution).

The operation of the above gas detector will be described below.
In this gas detector, when the power is turned on, energization of the gas detection element 11 is started and the warm-up process is executed. During this warm-up process, the sensor output value of the gas detecting means 10 usually rises once, then gradually decreases with time, and stabilizes at a predetermined value after a predetermined time elapses. It tends to reach a state.
Further, even after the warm-up treatment period has elapsed, the sensor output value of the gas detecting means 10 changes due to fluctuations in the temperature and humidity of the usage environment.
Further, when the gas detector is used for a long period of time, the gas sensitive portion 12 and the resistance heating element 13 in the gas detection element 11 deteriorate with time, so that the sensor output value of the gas detection means 10 changes.
As described above, the sensor output value of the gas detecting means 10 is covered by the warm-up process, the fluctuation of the temperature and humidity of the usage environment, or the deterioration of the gas sensitive portion 12 and the resistance heating element 13 over time due to long-term use. It changes even though there is no gas inspection.
Therefore, in the above gas detector, the zero output correction process for correcting the zero output value of the gas detecting means 10 is performed by the zero output correction mode of the control means 20.

Specifically, first, the sensor output value from the gas detecting means 10 is intermittently acquired at a specific time interval (hereinafter, referred to as “logging interval”). Then, when the sensor output value P ₁ is acquired, one of the sensor output values acquired 5 to 40 seconds before, preferably 5 to 20 seconds before, is selected and acquired as the _{latest output value P 0.} When the difference value (P _{0 −} P ₁ ) between the sensor output value P ₁ and the latest output value P ₀ is within a specific allowable range, the zero output correction mode for performing the zero output correction process is executed. In this zero output correction process, the zero output value setting process for setting the _{latest output value P 0} as a new zero output value is repeatedly executed every time the _{sensor output value P 1 is acquired.}
Then, based on the newly set zero output value and the sensor output value from the gas detecting means 10, the display value indicating the gas concentration and the gas concentration are calculated and displayed on the display means 50.

On the other hand, when the difference value (P ₀ −P ₁ ) exceeds a specific allowable range, the zero output correction mode is switched to the zero output maintenance mode, and the zero output value is maintained as it is.
Further, when the concentration of the test gas becomes sufficiently low after the difference value (P ₀ −P ₁ ) exceeds a specific allowable range, for example, the displayed value corresponds to the concentration of the test gas of 10 ppm or less. When the value is indicated, the zero output maintenance mode is switched to the zero output correction mode, and the zero output correction process is restarted.

_{FIG. 3 shows the sensor output P 1} of the gas detecting means 10 and the difference value (when the gas to be tested is introduced at regular time intervals when the gas detector of the present invention is used in an environment where the temperature fluctuates. It is a graph which shows typically the time-dependent change of each of P _0- P _{1) and the displayed value.} In FIG. 3, (a) is a graph showing the relationship between the ambient temperature of the gas detection element 11 and the elapsed time, and (b) is the sensor output value (current value in this example) P of the gas detection means 10. _{It is a graph showing the relationship between 1} and the elapsed time, (c) is a graph showing the relationship between the difference value (P ₀ −P ₁ ) and the elapsed time, and (d) is the displayed value and the elapsed time. It is a graph which shows the relationship of.

As shown in FIG. 3B _{, the current value, which is the sensor output value P 1} , decreases according to the concentration of the test gas introduced around the gas detection element 11. Further, the current value, which is the sensor output value P ₁ , changes according to the temperature change even if the temperature around the gas detection element 11 fluctuates. Specifically, when the temperature around the gas detection element 11 rises _{, the current value which is the sensor output value P 1} decreases, and when the temperature around the gas detection element 11 decreases, the current value which is the sensor output value P _{1 decreases.} The value goes up.
On the other hand, as shown in FIG. 3C, the difference value (P ₀ −P ₁ ) temporarily increases according to the concentration of the test gas introduced around the gas detection element 11. After that, when the test gas disappears around the gas detection element 11, the concentration temporarily decreases. However, the difference value (P ₀ −P ₁ ) hardly changes when the temperature around the gas detection element 11 fluctuates.
Then, as shown in FIG. 3D, the displayed value increases according to the concentration of the test gas introduced around the gas detection element 11, and then is covered around the gas detection element 11. It decreases when the gas inspection is exhausted. However, the displayed value hardly changes when the temperature around the gas detection element 11 fluctuates.

In the above, the logging interval is preferably selected in the range of 0.3 to 20 seconds. If the logging interval is less than 0.3 seconds, the difference value may become small even when the test gas is detected. On the other hand, when the logging interval exceeds 20 seconds, the difference value may change significantly even due to a sudden change due to temperature and humidity.

If the latest output value P ₀ is acquired after 5 seconds before the sensor output value P ₁ is acquired (for example, 2 seconds before, 3 seconds before, or 4 seconds before), it is new. The zero output value set to may shift slightly from the true zero output value to the gas output side. On the other hand, when the latest output value P ₀ is acquired before 20 seconds before the acquisition of the sensor output value P ₁ (for example, 50 seconds before), in an environment where the temperature and humidity change drastically, The newly set zero output value may be slightly drifted from the true zero output value.

Further, the permissible range of the difference value (P _{0 −} P ₁ ) is appropriately set according to the type and sensitivity of the gas detection element 11. If this permissible range is too small, not only will the gas to be detected be detected even if the concentration is below the minimum concentration, but also due to slight fluctuations in temperature and humidity, even though the test gas does not exist, it will be detected. It may be detected. On the other hand, if this permissible range is excessive, it may not be detected even if the concentration of the gas to be detected reaches the minimum concentration or more.
To show a specific example of the allowable range of the difference value (P ₀ −P ₁ ), the gas detecting means 10 is a contact combustion type methane gas sensor, and the span value of 100% LEL full scale is 5 mA (the sensor output value is the current value). ), The permissible range of the difference value (P ₀ −P ₁ ) can be set to ± 0.01 mA (equivalent to 100 ppm). Further, when the gas detecting means 10 is a hot wire type semiconductor methane sensor and the span value of 5000 ppm full scale is 500 mV (the sensor output value is a voltage value), the allowable range of the _{difference value (P 0} −P _{1) is} It can be set to ± 5 mV (equivalent to 5 ppm).

Even if the above zero output correction process is performed on the sensor output value acquired by introducing zero gas (for example, Air) during the warm-up period of the gas detection element 11, the atmospheric gas in the measurement target space is introduced. Although it may be performed on the sensor output value acquired by Is preferably performed.

Then, when the displayed value calculated by the control means 20 exceeds a predetermined value, it is determined that the gas to be measured contains the test gas, and the alarm means 60 is activated.

According to the above gas detector, the sensor output value from the gas detecting means 10 changes due to warm-up treatment, fluctuation of temperature or humidity, or deterioration of the gas sensitive unit 12 and the resistance heating element 13 over time. However, the concentration of the test gas can be measured with a certain degree of reliability, and a state in which the gas concentration can be measured can be obtained at an early stage after the power is turned on.
Further, since it is not necessary to provide a compensating element, the power saving of the gas detector can be achieved. Therefore, when configured as a portable gas detector, the life of the battery, which is the driving power source, can be extended.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made.
For example, the above embodiment is an example in which the sensor output value is a current value, but the sensor output value may be a voltage value.

Hereinafter, specific examples of the gas detector of the present invention will be described.
<Example 1>
A gas detector having the following specifications was produced according to the configurations shown in FIGS. 1 and 2.
[Gas detection means]
Hot wire type semiconductor gas sensor: A sensor output value (110 mA constant current drive) whose sensitivity has been adjusted so that the sensor output value for a test gas with a concentration of 10 ppm is 10 mV [Control means]
Logging interval: 1 second Most recent output value: Acquired 5 seconds before acquisition Difference value tolerance: ± 2 mV
Switching from zero output maintenance mode to zero output correction mode: When the display value is 10 mV or less

The above gas detector was placed in a high temperature and high humidity tank. While the air was circulated in the high temperature and high humidity tank at a flow velocity of 0.5 L / min, the high temperature and high humidity tank was operated by the temperature-humidity program shown in FIG. 4, and the gas detector was operated. Then, every hour after the start of operation of the high-temperature and high-humidity tank and the gas detector, air containing hydrogen gas having a concentration of 200 ppm was introduced into the high-temperature and high-humidity tank for 1 minute.
In the above gas detector, _{the time-dependent change of the sensor output value P 1} is shown in FIG. 5, the time-dependent change of the difference value (P ₀ −P ₁ ) is shown in FIG. 6, and the time-dependent change of the displayed value is shown in FIG. Shown in.

As can be understood from FIGS. 4 to 7, according to the gas detector according to the first embodiment, even if the sensor output value changes due to fluctuations in temperature and humidity, a difference value (P _{0 −} P ₁ ) is allowed. It was confirmed that the displayed value changes substantially only when the test gas is detected by performing the zero output correction process while it is within the range.

<Example 2>
A gas detector having the following specifications was produced according to the configurations shown in FIGS. 1 and 2.
[Gas detection means]
Contact combustion type gas sensor: The sensor output value is a current value (1.0 V constant voltage drive), and the sensitivity is adjusted so that the sensor output value for the test gas with a concentration of 5% LEL of methane gas is 0.2 mA. [Control means]
Logging interval: 5 seconds Most recent output value: Acquired 5 seconds before acquisition Difference value tolerance: ± 0.02 mA
Switching from zero output maintenance mode to zero output correction mode: When the displayed value is 0.02 mA or less

The above gas detector was placed in a high temperature and high humidity tank. The high-temperature and high-humidity tank was operated by the temperature-humidity program shown in FIG. 8 and the gas detector was operated while the air was circulated in the high-temperature and high-humidity tank at a flow velocity of 0.5 L / min. Then, every 30 minutes after the start of operation of the high-temperature and high-humidity tank and the gas detector, air containing hydrogen gas having a concentration of 5% LEL was introduced into the high-temperature and high-humidity tank for 1 minute.
In the above gas detector, _{the time-dependent change of the sensor output value P 1} is shown in FIG. 9, the time-dependent change of the difference value (P ₀ −P ₁ ) is shown in FIG. 10, and the time-dependent change of the displayed value is shown in FIG. Shown in.

As can be understood from FIGS. 8 to 11, according to the gas detector according to the second embodiment, even if the sensor output value changes due to fluctuations in temperature and humidity, a difference value (P _{0 −} P ₁ ) is allowed. It was confirmed that the displayed value changes substantially only when the test gas is detected by performing the zero output correction process while it is within the range.

10 Gas detection means 11 Gas detection element 12 Gas sensitive part 13 Resistance heating element 14 Current detection resistor 15 Measuring circuit 16 Voltage detection means 17 Current detection means 18 Power supply 20 Control means 30 Storage means 40 Timekeeping means 50 Display means 60 Alarm means

Claims (3)

A gas detector including a gas detecting means for detecting the concentration of the test gas and a control means having a function of calculating the concentration of the test gas based on an output value from the gas detecting means.
The control means
The output value from the gas detecting means is intermittently acquired at specific time intervals, and the output value is obtained intermittently.
Acquired output values P ₁ and the difference value between the output value last output value P ₀ one acquired during the previous 5 to 40 seconds at acquisition of P ₁ (P ₀ -P ₁₎ is a specific A function that performs zero output correction processing that repeatedly executes the zero output value setting process that sets the _{latest output value P 0 as a new zero output value every time the output value P 1} is acquired when it is within the permissible range. A gas detector characterized by having. The gas detection according to claim 1, wherein the control means has a function of maintaining the zero output value when the _{difference value (P 0} −P _{1) exceeds the specific allowable range.} vessel. The gas detecting means is characterized in that it has a contact combustion type gas sensor or a heat ray type semiconductor gas sensor as a gas detecting element, and does not have a compensating element that is insensitive to the test gas. 1 or the gas detector according to claim 2.

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