Gas Detectors

Abstract

To provide a gas detector that can accurately detect detection object gas even in a state that an output value of gas detecting means is unstable, and can be brought into a state capable of detecting the detection object gas early after drive starting.SOLUTION: A gas detector comprises gas detecting means, and controlling means that calculates an instruction value indicating gas concentration of detection object gas on the basis of an output value obtained by the gas detecting means. The controlling means is configured to correct the calculated instruction value to a zero instruction value, in a first predetermined period T from a time point when detecting operation of the detection object gas is started by the gas detector, when the instruction value calculated on the basis of the output value obtained by the gas detecting mean is within a predetermined range R, for each first predetermined time T1.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a gas detector. [Background technology]

[0002] Conventionally, gas detectors such as those disclosed in Patent Document 1 have been used to detect target gases contained in an environmental atmosphere. In such gas detectors, there is generally a problem that the output value of the gas detection means included in the gas detector is not stable for a while after the power is turned on and operation is started. Therefore, in such gas detectors, as disclosed in Patent Document 1, a period (so-called warm-up period) is provided after the operation of the gas detector is started during which the detection operation of the target gas is not performed until the output value of the gas detection means becomes stable. Then, when the output value of the gas detection means becomes stable, the output value of the gas detection means is adjusted to zero, and then the detection operation of the target gas is performed in an environmental atmosphere that may contain the target gas. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 60-109044 Summary of the Invention [Problem to be solved by the invention]

[0004] In a gas detector, it takes a long time for the output value of the gas detection means to stabilize, and therefore it takes a long time for the detector to become capable of detecting the target gas. Therefore, the user of the gas detector must wait for that long time after starting the operation of the gas detector in order to detect the target gas. However, for example, in cases where it is expected that the target gas is highly likely to be contained in the ambient atmosphere, it is desirable to shorten the warm-up period after starting the operation of the gas detector and perform the detection operation of the target gas as soon as possible.

[0005] However, in a gas detector, if the warm-up period after the start of operation is shortened and the detection operation of the target gas is started early, the output value of the gas detection means may not be in a completely stable state, and the target gas may not be detected accurately. Therefore, in order to shorten the warm-up period after the start of operation and to achieve a state in which the target gas can be detected as early as possible, it is necessary to be able to detect the target gas with high accuracy even when the output value of the gas detection means is not stable.

[0006] The present invention has been made in consideration of the above problems, and has an object to provide a gas detector that can accurately detect a target gas even when the output value of the gas detection means is not stable, and can achieve a state in which the target gas can be detected quickly after operation begins. [Means for solving the problem]

[0007] The gas detector of the present invention is a gas detector for detecting a target gas contained in an environmental atmosphere, comprising: a gas detection means; and a control means for calculating an indication value indicating the gas concentration of the target gas based on an output value obtained by the gas detection means, and the control means is configured to correct the calculated indication value to a zero indication value at every first predetermined time during a first predetermined period from the time when the gas detector starts detecting the target gas, if the indication value calculated based on the output value obtained by the gas detection means is within a predetermined range.

[0008] Moreover, it is preferable that the predetermined range is set so as to become smaller with the passage of time during the first predetermined period.

[0009] It is also preferable that the gas detector is configured to maintain operation of the gas detection means for a second predetermined time period after the gas detector is stopped, and the control means is configured not to perform the correction if the gas detector is restarted within the second predetermined time period after the gas detector is stopped.

[0010] Furthermore, it is preferable that the control means is configured to perform the correction when the gas detector is stopped within a third predetermined time from the start of operation of the gas detection means, even if the gas detector is restarted within the second predetermined time from the stop of operation of the gas detector.

[0011] Furthermore, it is preferable that the control means is configured to correct the calculated indication value to a zero indication value during a second predetermined period longer than the first predetermined period from the time when the gas detector starts the detection operation of the target gas, when the indication value calculated based on the output value obtained by the gas detection means is smaller than a zero indication value.

[0012] The gas detection means is preferably a catalytic combustion type gas sensor. Effect of the Invention

[0013] According to the present invention, it is possible to provide a gas detector that can accurately detect a target gas even when the output value of the gas detection means is unstable, and can achieve a state in which the target gas can be detected quickly after operation begins. [Brief description of the drawings]

[0014] [Figure 1] 1 is a block diagram of a gas detector according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a circuit diagram showing the gas detection means of FIG. [Diagram 3] FIG. 1(a) is a schematic diagram showing the operating status of the gas detection means (time change in the voltage applied to the gas detection element) from when the gas detector starts operating until when it stops operating, and FIG. 1(b) is an enlarged view of the vicinity of the start of operation of the gas detector in FIG. 1(a). [Figure 4] FIG. 10 is a diagram showing a schematic diagram of a change in an indication value before and after correction by a control means after the gas detector starts an operation of detecting a target gas. [Diagram 5]FIG. 10 is a diagram showing a schematic diagram of a change in an indication value before and after correction by a control means after the gas detector starts an operation of detecting a target gas. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] A gas detector according to an embodiment of the present invention will be described below with reference to the accompanying drawings. However, the embodiment described below is merely an example, and the gas detector of the present invention is not limited to the following example.

[0016] The gas detector 1 of this embodiment is used to detect a target gas contained in an environmental atmosphere such as the air. The target gas detected by the gas detector 1 is not particularly limited, and examples thereof include flammable gases such as hydrogen, methane, propane, isobutane, and ethylene. As shown in FIG. 1, the gas detector 1 includes a gas detection means 2 for detecting the target gas and a control means 3 for performing arithmetic processing. Furthermore, the gas detector 1 includes a clock means 4 for measuring an elapsed time, a storage means 5 for storing information on the target gas, a notification means 6 for notifying a user of the information on the target gas, and a power source 7 for supplying power to each component. Note that the gas detector 1 is only required to include at least the gas detection means 2 and the control means 3, and the other components may be provided separately from the gas detector 1.

[0017] The gas detection means 2 detects a target gas contained in the environmental atmosphere and outputs an output value corresponding to the concentration of the target gas in the environmental atmosphere. As shown in Fig. 1, the gas detection means 2 is communicatively connected to the control means 3, and is operationally controlled by the control means 3, while transmitting the output value to the control means 3. In this embodiment, the gas detection means 2 is a catalytic combustion type gas sensor.

[0018] 2, the gas detection means 2 in this embodiment includes a catalytic combustion type gas detection element 21 (hereinafter simply referred to as gas detection element 21), a compensation element 22, two resistance elements 23 and 24, a circuit power supply 25, and a potentiometer 26, forming a Wheatstone bridge circuit. Note that, in this embodiment, the circuit power supply 25 is provided separately from the power supply 7 of the gas detector 1, but is not limited to this and may also be used as the power supply 7 of the gas detector 1.

[0019] The gas detection element 21 is configured such that its resistance value changes when it comes into contact with the target gas. As shown in FIG. 2, the gas detection element 21 includes a resistance heating element 21a that is heated by current flow and a sensor 21b that changes in temperature when the target gas comes into contact with it and burns. The resistance heating element 21a is formed by winding a wire of a precious metal such as platinum into a coil shape. The sensor 21b is formed by sintering a precious metal catalyst such as platinum together with an oxide carrier such as alumina so as to cover the resistance heating element 21a so that the target gas can be easily burned. When the gas detection means 2 is driven, the resistance heating element 21a is energized by the circuit power source 25 via the Wheatstone bridge circuit, and the gas detection element 21 is heated. When the target gas comes into contact with the sensor 21b in the heated state, the temperature of the sensor 21b increases as the target gas burns, and the resistance value changes.

[0020] The compensating element 22 is configured so that its resistance value does not change or hardly changes when it comes into contact with the gas to be detected. The compensating element 22 is formed by sintering an oxide such as alumina so as to cover a resistance heater formed by winding a wire of a precious metal such as platinum into a coil shape. When the gas detection means 2 is driven, the compensating element 22 is heated by the resistance heater being energized by the circuit power supply 25 via a Wheatstone bridge circuit. Unlike the gas detection element 21, the compensating element 22 does not contain a precious metal catalyst, so that the compensating element 22 does not burn the gas to be detected or hardly burns the gas to be detected even when it comes into contact with the gas to be detected. Therefore, even when the sintered oxide of the compensating element 22 comes into contact with the gas to be detected, there is no or almost no change in the temperature of the oxide, and therefore the resistance value does not change or hardly changes.

[0021] As described above, in the gas detection means 2, when the gas detection element 21 and the compensation element 22 come into contact with the target gas, a difference occurs in the change in resistance value between the gas detection element 21 and the compensation element 22. The gas detection means 2 detects a potential difference occurring in the Wheatstone bridge circuit due to the difference in the change in resistance value between the gas detection element 21 and the compensation element 22 with the potentiometer 26, and outputs the potential difference as an output value corresponding to the concentration of the target gas. However, the gas detection means is not limited to the illustrated example as long as it can at least output the change in resistance value of the gas detection element 21 occurring when the target gas comes into contact with the gas detection element 21 as an output value, and for example, a resistive element may be used instead of the compensation element 22, or a detection circuit different from the Wheatstone bridge circuit may be configured.

[0022] The control means 3 calculates an indication value indicating the gas concentration of the target gas based on the output value obtained by the gas detection means 2. The indication value calculated by the control means 3 indicates the concentration of the target gas expressed in units such as ppm, vol%, %LEL, etc. The control means 3 calculates an indication value indicating the gas concentration of the target gas from the output value obtained by the gas detection means 2, for example, by using a relational equation (calibration curve) between the output value of the gas detection means 2 and the indication value indicating the concentration of the target gas, which has been obtained in advance. In addition to calculating the indication value, the control means 3 has a calculation processing function for performing the processing described in this specification. The processing by the control means 3 will be described in detail later.

[0023] 1, the control means 3 is communicatively connected to the gas detection means 2, controls the operation of the gas detection means 2, and receives output values ​​obtained by the gas detection means 2. In this embodiment, the control means 3 is communicatively connected to the timing means 4, storage means 5, and notification means 6, and is configured to control the operation of each component and to transmit and receive information. The control means 3 can be configured using, for example, a known central processing unit (CPU).

[0024] The storage means 5 stores information about the target gas. As shown in FIG. 1, the storage means 5 is communicably connected to the control means 3 and configured to communicate information about the target gas with the control means 3. The information about the target gas includes, for example, a relational expression (calibration curve) between the output value of the gas detection means 2 and an indication value indicating the concentration of the target gas, an output value obtained by the gas detection means 2, an indication value calculated by the control means 3, a threshold value for the output value or the indication value, and an elapsed time measured by the timer means 4. The storage means 5 may be configured to store a program capable of executing the functions of the control means 3 described in this specification. The storage means 5 is not particularly limited and can be configured by a known volatile memory such as a RAM, or a known non-volatile memory such as a hard disk or a flash memory.

[0025] The notification means 6 notifies the user of the gas detector 1 of information related to the target gas. As shown in FIG. 1, the notification means 6 is communicably connected to the control means 3, receives information related to the target gas from the control means 3, and notifies the user of the information related to the target gas. The information related to the target gas here includes, for example, an indication value indicating the concentration of the target gas and information indicating that the indication value exceeds a predetermined threshold. The notification means 6 is embodied by, for example, a display means such as a display or an alarm means such as a speaker. For example, the display means displays an indication value indicating the concentration of the target gas, and the alarm means lights up an LED or emits an alarm sound indicating that the indication value exceeds a predetermined threshold.

[0026] Next, the operation of the gas detector 1 of this embodiment will be described in detail with reference to Fig. 3 to Fig. 5. Fig. 3(a) is a diagram showing a schematic diagram of the driving state of the gas detection means 2 (changes over time in the voltage applied to the gas detection element 21) from when the gas detector 1 starts to drive until it stops driving, and Fig. 3(b) is an enlarged diagram of Fig. 3(a) around the time when the gas detector 1 starts to drive. Figs. 4 and 5 are diagrams showing a schematic diagram of the change in the indicated value before and after correction by the control means 3 after the gas detector 1 starts to detect the target gas.

[0027] At the elapsed time t0 shown in Fig. 3(a) and Fig. 3(b), the power supply 7 is turned on and the gas detector 1 is started to operate. At this time, in order to stably start the operation of the gas detection means 2 of the gas detector 1, the voltage applied to the gas detection element 21 and the compensation element 22 of the gas detection means 2 is gradually increased immediately after the operation of the gas detector 1 is started. Then, at the elapsed time t1 after the operation of the gas detector 1 is started, the voltage applied to the gas detection element 21 and the compensation element 22 reaches a predetermined applied voltage V0 required to raise the temperature of the gas detection element 21 and the compensation element 22 to a temperature suitable for detecting the target gas. In this way, a preparatory period Tp is provided from the start of operation of the gas detector 1 until the predetermined applied voltage V0 is applied to the gas detection element 21 and the compensation element 22 of the gas detection means 2 and the operation of the gas detection means 2 is started. The preparatory period Tp can be set appropriately within a range in which the operation of the gas detection means 2 can be stably started, and is set within a range of, for example, 1 to 7 seconds.

[0028] In the gas detector 1, as shown in FIG. 3(b), after the gas detection means 2 starts to be driven at elapsed time t1, a warm-up period Tw is provided for a predetermined period. The warm-up period Tw is a period during which the gas detection means 2 is driven, i.e., a predetermined applied voltage V0 is applied to the gas detection element 21 and the compensation element 22 of the gas detection means 2, but the gas detection means 2 does not perform a detection operation for the target gas. Not performing a detection operation for the target gas means that the indication value calculated by the control means 3 from the output value obtained by the gas detection means 2 is not notified to the user of the gas detector 1 by the notification means 6 (for example, is not displayed by the display means) as at least an indication of the concentration of the target gas contained in the environmental atmosphere. Such a warm-up period Tw is provided in response to the phenomenon that the output value of the gas detection means 2, and therefore the indication value, is not stable at the beginning of the operation of the gas detection means 2. In the gas detector 1, the indication value calculated from the output value obtained by the gas detection means 2 is adjusted to a zero indication value at the elapsed time t2 when the warm-up period Tw ends (zero adjustment of the indication value). The warm-up period is generally set appropriately as a period from the start of driving the gas detection means 2 until the output value of the gas detection means 2 and thus the indication value become stable, and is set to several minutes, for example. In contrast, in the present embodiment, as described in detail below, this warm-up period can be shortened to make it possible to detect the detection target gas soon after the start of driving. Note that if the indication value does not vary significantly from the beginning of driving the gas detection means 2, the warm-up period Tw does not need to be provided. The warm-up period Tw is not particularly limited as long as it is shorter than a warm-up period that is generally set, and is set within a range of 0 to 150 seconds, for example.

[0029] As shown in FIG. 3(a) and FIG. 3(b), the gas detector 1 starts the detection operation of the target gas at the elapsed time t2 when the warm-up period Tw ends and the zero adjustment of the indication value is performed. When the gas detector 1 starts the detection operation of the target gas, it starts notifying the user of the indication value calculated by the control means 3 from the output value of the gas detection means 2. The notification of the indication value to the user generally includes notifying information about the target gas by the notification means 6, and specifically includes, for example, displaying the indication value by the display means, lighting an LED or emitting an alarm sound by the alarm means indicating that the indication value exceeds a predetermined threshold value. In the gas detector 1, a predetermined applied voltage V0 is applied to the gas detection element 21 and the compensation element 22 of the gas detection means 2 from the start to the stop of the operation of the gas detection means 2, and the driving state of the gas detection means 2 is kept constant.

[0030] Here, as described above, the warm-up period is generally set to several minutes. However, for example, when it is expected that the target gas is likely to be contained in the ambient atmosphere, it is desirable to shorten the warm-up period after the start of operation of the gas detector and perform the detection operation of the target gas as soon as possible. However, in a gas detector, if the warm-up period after the start of operation is shortened and the detection operation of the target gas is started early, the output value of the gas detection means may not be completely stable, and the target gas may not be detected accurately. Therefore, in order to shorten the warm-up period after the start of operation and to make the target gas detectable as soon as possible, it is necessary to be able to detect the target gas accurately even when the output value of the gas detection means is not stable.

[0031] In this embodiment, for the above purpose, as shown in FIG. 4, the control means 3 is configured to correct the calculated indication value to a zero indication value for each first predetermined time ta during a first predetermined period T1 from the time (elapsed time t2) when the gas detector 1 starts detecting the target gas, if the indication value calculated based on the output value obtained by the gas detection means 2 is within a predetermined range R (the correction performed here is also referred to as the "first correction" below). The reason why the range of the indication value for which the first correction is performed is limited to the predetermined range R is to suppress the indication value that is increasing due to the detection of the target gas being corrected to a zero indication value erroneously when the target gas is contained in the environmental atmosphere. In the gas detector 1, by shortening the warm-up period, even when the output value of the gas detection means 2, and therefore the indication value, is not stable, the indication value within the predetermined range R is corrected to a zero indication value, so that the target gas can be detected with high accuracy. Therefore, in the gas detector 1, the warm-up period after the start of operation can be shortened to bring the target gas into a state where it can be detected early. Note that correcting the indication value to a zero indication value means that the indication value at the time of correction is set to the zero indication value, and the indication value obtained after the correction is set to the amount of change from the zero indication value.

[0032] Next, the first correction process by the control means 3 will be described in detail with reference to FIG. 4. FIG. 4 shows an example of the change in the indication value with respect to the elapsed time in the first predetermined period T1 from the elapsed time t2 to the elapsed time t3. The thin solid line in FIG. 4 shows the change in the indication value IV0 without correction, the thick solid line in FIG. 4 shows the change in the indication value IV1 after correction at every first predetermined time ta, and the dotted line in FIG. 4 shows a predetermined threshold value (predetermined range R) that is the reference when correcting the indication value. The upper arrow in FIG. 4 shows the timing when the correction process by the control means 3 is performed. At the elapsed time t2 when the detection operation of the detection target gas starts, the uncorrected indication value IV0 shows a zero indication value due to the zero adjustment of the indication value performed at the end of the warm-up period Tw. In the illustrated example, the uncorrected indication value IV0 first drops slightly from the elapsed time t2, then continues to rise relatively significantly from the elapsed time t2 until the elapsed time when four first predetermined times ta have passed, then continues to rise gently from the elapsed time t2 until the elapsed time when seven first predetermined times ta have passed, and then remains almost constant until the elapsed time t3 until the elapsed time when nine first predetermined times ta have passed from the elapsed time t2. By the processing of the control means 3, the indication value IV0 rises from the zero indication value at the point after the elapsed time t2 and the first predetermined time ta, but is within the predetermined range R below the predetermined threshold, so it is corrected to the zero indication value. Next, the indication value IV1 corrected to the zero indication value at the elapsed time when two first predetermined times ta have passed from the elapsed time t2, rises from the zero indication value at the elapsed time when two first predetermined times ta have passed from the elapsed time t2, but is within the predetermined range R below the predetermined threshold, so it is corrected to the zero indication value. In this way, at each first predetermined time ta within the first predetermined period T1, it is determined whether the indication value is within the predetermined range R, and when the indication value is within the predetermined range R, the indication value is corrected to a zero indication value.When the indication value is within the predetermined range R, the indication value IV1 corrected as described above is notified to the user by the notification means 6 (for example, displayed by the display means) as indicating the concentration of the gas to be detected, and when the indication value is outside the predetermined range R and exceeds the predetermined threshold, the indication value calculated from the value previously corrected to zero is notified to the user by the notification means 6 (for example, displayed by the display means) as indicating the concentration of the gas to be detected.

[0033] The above-mentioned first predetermined period T1 is a predetermined time period starting from the elapsed time t2 when the warm-up period Tw ends. The first predetermined period T1 is not particularly limited, and can be appropriately set according to the period during which the indication value is expected to be unstable after the warm-up period Tw has elapsed when the gas detection means 2 is driven in an environmental atmosphere that does not contain the gas to be detected. For example, the first predetermined period T1 can be a period obtained by subtracting a warm-up period Tw that is set shorter than the generally set warm-up period from the generally set warm-up period. In this case, the generally set warm-up period can be shortened by the first predetermined period T1. The first predetermined period T1 is not particularly limited, and can be set within a range of, for example, 30 to 180 seconds.

[0034] The above-mentioned first predetermined time ta is a predetermined time interval during which the indication value is corrected within the first predetermined period T1. The first predetermined time ta is not particularly limited, and can be appropriately set according to the degree of change in the indication value expected within the first predetermined period T1 in an environmental atmosphere not containing the detection target gas and the predetermined range R that is set. For example, the first predetermined time ta can be set so that the increase in the indication value expected within the first predetermined time ta in an environmental atmosphere not containing the detection target gas is within the predetermined range R that is equal to or less than a predetermined threshold value. The first predetermined time ta is not particularly limited, but is set within a range of, for example, 1 to 40 seconds. Note that the first predetermined time ta is a constant time interval regardless of the passage of time in this embodiment, but may be changed over time according to the set predetermined range R. For example, the first predetermined time ta may be set to be longer with the passage of time in the first predetermined period T1, with the predetermined range R being constant regardless of the passage of time.

[0035] The predetermined range R, which is the basis for the correction of the indicated value, is a predetermined range of indicated values ​​within which the indicated value included in the range is corrected to a zero indicated value. The predetermined range R is not particularly limited, and can be appropriately set according to the first predetermined time ta, which is set as the degree of change in the indicated value expected within the first predetermined period T1 in an environmental atmosphere not containing the target gas. For example, the predetermined range R can be set so that the increase in the indicated value expected within the first predetermined time ta in an environmental atmosphere not containing the target gas falls within the predetermined range R below a predetermined threshold value. The predetermined range R is not particularly limited, but is set within the range of 10 to 100 ppm, for example.

[0036] As shown in FIG. 4, the predetermined range R is preferably set to decrease with time in the first predetermined period T1. As can be clearly seen in FIG. 4, the indicated value tends to have a decreasing rate of change (amount of change per unit time) with time in the first predetermined period T1 if it is not corrected. That is, in the illustrated example, the indicated value has a large rate of change in the early period of the elapsed time in the first predetermined period T1 and increases significantly with time, but the rate of change is small in the later period of the elapsed time in the first predetermined period T1 and increases gradually or becomes almost constant with time. By increasing the predetermined range R in the period in the first predetermined period T1 in which the rate of change of the indicated value is large, the indicated value that has changed significantly can be corrected to a zero indicated value more reliably. In addition, by decreasing the predetermined range R in the period in the first predetermined period T1 in which the rate of change is small, the indicated value is prevented from being erroneously corrected to a zero indicated value even when a small amount of the target gas is present. This allows the gas detector 1 to detect the target gas with higher accuracy. From the same viewpoint, it is preferable that the rate of decrease (amount of decrease per unit time) of the predetermined range R decreases with the passage of time within the first predetermined period T1, and more preferably, the rate of decrease is a first rate of decrease in the early period of the elapsed time within the first predetermined period T1, and the rate of decrease is a second rate of decrease smaller than the first rate of decrease in the later period of the elapsed time within the first predetermined period T1. In this embodiment, the predetermined range R is set so as to decrease for each first predetermined time ta in the early period of the first predetermined period T1, and to be constant in the later period of the first predetermined period T1.

[0037] Next, referring to FIG. 3(a) and FIG. 5, the details of the process of the control means 3 performed when the indication value calculated based on the output value obtained by the gas detection means 2 is smaller than the zero indication value will be described. As shown in FIG. 5, the control means 3 is preferably configured to correct the calculated indication value to the zero indication value when the indication value is smaller than the zero indication value during the second predetermined period T2 from the time (elapsed time t2) when the gas detector 1 starts detecting the target gas (the correction performed here is also referred to as the "second correction" below). The indication value will not be smaller than the zero indication value basically unless there is a fluctuation in the gas detector 1, particularly the gas detection means 2 itself. Therefore, in the gas detector 1 of this embodiment, when the indication value is smaller than the zero indication value, it is determined that a fluctuation has occurred in the gas detector 1, particularly the gas detection means 2, and the calculated indication value is corrected to the zero indication value. As a result, in gas detector 1, even if the output value of gas detection means 2, and therefore the indicated value, is not stable and becomes smaller than the zero indicated value, the indicated value is corrected to the zero indicated value by shortening the warm-up period, thereby enabling the gas detector 1 to detect the target gas with greater accuracy. Therefore, in gas detector 1, the warm-up period after the start of operation can be shortened to quickly bring the gas detector 1 into a state where it can detect the target gas.

[0038] The second predetermined period T2 is a predetermined time period starting from the elapsed time t2 at which the warm-up period Tw ends. In this embodiment, the second predetermined period T2 is set to be longer than the first predetermined period T1, as shown in FIG. 3(a). In the gas detector 1, when the target gas is contained in the environmental atmosphere, the indication value is almost never smaller than the zero indication value, and even if the target gas is contained in the environmental atmosphere, the indication value is almost never erroneously corrected to the zero indication value. For this reason, by setting the second predetermined period T2 longer, it is possible to correct the indication value that decreases over a long period of time to the zero indication value while avoiding the indication value from being erroneously corrected to the zero indication value as much as possible. The second predetermined period T2 is not particularly limited as long as it is longer than the first predetermined period T1, and can be appropriately set according to the period during which the indication value is expected to be smaller than the zero indication value in an environmental atmosphere that does not contain the target gas. The second predetermined period T2 is set within a range of, for example, 3 minutes to the time (t5) at which the gas detector 1 stops driving.

[0039] The control means 3 is not particularly limited as long as it is configured to correct the indicated value to the zero indicated value when the indicated value is smaller than the zero indicated value, but is preferably configured to correct the average indicated value over a predetermined number of measurements (for example, 50 measurements at 0.1 second intervals) to the zero indicated value when the indicated value is smaller than the zero indicated value consecutively as shown in FIG. 5. In the example shown in FIG. 5, this correction is performed at the timing indicated by the up arrow. By correcting the average indicated value to the zero indicated value when the indicated value is smaller than the zero indicated value consecutively in this way, the fluctuation in the indicated value due to the fluctuation of the gas detection means 2 can be distinguished from mere noise and corrected more accurately. This allows the gas detector 1 to detect the target gas with higher accuracy.

[0040] The control means 3 may be configured to regard an indicated value as noise when the indicated value is smaller than the zero indicated value and smaller than a predetermined threshold value, and not to correct the indicated value to the zero indicated value. This enables the gas detector 1 to avoid correction of the indicated value that may be erroneous, and to correct the indicated value more accurately.

[0041] The control means 3 may be configured to determine whether or not to perform the above-mentioned second correction and, optionally, the first correction, depending on the concentration of another gas (e.g., oxygen) that is always present in the environmental atmosphere. For that purpose, the gas detector 1 may further include another gas detection means for detecting the other gas. For example, the control means 3 is configured to perform the above-mentioned second correction and, optionally, the first correction, when the other indication value calculated based on the other output value obtained by the other gas detection means is within a predetermined range around the normal concentration of the other gas (e.g., 20.9±1.0 vol% for oxygen). In this case, the gas detector 1 notifies the user of the corrected indication value as indicating the concentration of the target gas. Also, the control means 3 is configured not to perform the above-mentioned second correction and, optionally, the first correction, when the other indication value is outside the predetermined range around the normal concentration of the other gas. In this case, the gas detector 1 notifies the user of the uncorrected indication value as indicating the concentration of the target gas. This makes it possible to avoid correction of the indicated value, which may be erroneous, even if the indicated value calculated based on the output value obtained by the gas detection means 2 is affected by changes in the concentration of the other gas, and to indicate the indicated value more accurately. The concentration of the other gas may be measured by a device other than the gas detector 1.

[0042] As shown in FIG. 3(a), the gas detector 1 is stopped at, for example, elapsed time t5 when the detection operation of the target gas is completed. The gas detector 1 may be configured to maintain the operation of the gas detection means 2 for a second predetermined time tb from the stop of the operation of the gas detector 1. In this case, the control means 3 is configured not to perform the above-mentioned first correction and, optionally, the second correction when the gas detector 1 is restarted within the second predetermined time tb from the stop of the operation of the gas detector 1. The gas detector 1 may require restart due to, for example, a malfunction. Even in such a case, by maintaining the operation of the gas detection means 2 even after the stop of the operation of the gas detector 1, the output value of the gas detection means 2 is maintained in a stable state, and when the gas detector 1 is restarted during the operation time of the gas detection means 2, the above-mentioned first correction and, optionally, the second correction can be omitted. Thereby, by omitting the first correction and, optionally, the second correction, it is possible to improve the detection accuracy of the target gas by stabilizing the output value of the gas detection means 2 soon after the start of operation of the gas detector 1. Furthermore, the gas detector 1 may omit the preparation period Tp and the warm-up period Tw and start the detection operation of the target gas when the gas detector 1 starts to operate.

[0043] The above-mentioned second predetermined time tb is a time interval during which the operation of the gas detection means 2 is maintained after the operation of the gas detector 1 is stopped. The second predetermined time tb is not particularly limited, and can be set appropriately depending on the time required to restart the gas detector 1 after it has been stopped. The second predetermined time tb is set, for example, within the range of 10 to 60 seconds.

[0044] The control means 3 is configured not to maintain the operation of the gas detection means 2 after the gas detector 1 is stopped within a third predetermined time tc from the start of the operation of the gas detection means 2, and is configured to perform the first correction and, optionally, the second correction even if the gas detector 1 is restarted within a second predetermined time tb from the stop of the operation of the gas detector 1. If the gas detection means 2 is stopped before a certain time has elapsed from the start of its operation, there is a possibility that the output value has not yet reached a stable state. In such a case, by performing the first correction and, optionally, the second correction, regardless of the time from the stop of the operation of the gas detector 1 to the restart, the gas to be detected can be detected more accurately.

[0045] The above-mentioned third predetermined time tc is a predetermined time interval from when a predetermined applied voltage V0 is applied to the gas detection element 21 and the compensation element 22 of the gas detection means 2 and the gas detection means 2 starts to operate. The third predetermined time tc is not particularly limited, and can be set appropriately depending on the time from when the gas detection means 2 starts to operate until the output value of the gas detection means 2 becomes stable. The third predetermined time tc can be set from the elapsed time t1 after the gas detection means 2 starts to operate to, for example, a time that is approximately the same as the elapsed time t3 after the end of the first predetermined period T1. More specifically, the third predetermined time tc is set within a range of, for example, 60 to 180 seconds. [Explanation of symbols]

[0046] 1 Gas detector 2 Gas detection means 21 Catalytic combustion type gas detector 21a Resistance heating element 21b Sensor 22 Compensation element 23, 24 Resistance element 25 Circuit power supply 26 Potentiometer 3. Control Measures 4 Timekeeping means 5 Memory means 6 Means of notification 7 Power supply

Claims

1. A gas detector for detecting a detection target gas contained in an environmental atmosphere, The gas detector comprises: A gas detection means; A control means for calculating an indication value indicating a gas concentration of the detection target gas based on an output value obtained by the gas detection means; Equipped with the control means is configured to, during a first predetermined period from the time when the gas detector starts an operation of detecting the target gas, correct the calculated indication value to a zero indication value when the indication value calculated based on the output value obtained by the gas detection means is within a predetermined range, The predetermined range is set to become smaller with the passage of time during the first predetermined period. Gas detector.

2. the control means is configured to correct the calculated indication value to a zero indication value when the indication value calculated based on the output value obtained by the gas detection means is smaller than a zero indication value during a second predetermined period longer than the first predetermined period from the time when the gas detector starts an operation of detecting the target gas.

2. The gas detector of claim 1.

3. The gas detection means is a catalytic combustion type gas sensor.

3. A gas detector according to claim 1 or 2.

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