JP7619852B2 - Gas Detectors - Google Patents

Description

The present invention relates to a gas detector.

Conventionally, gas detectors such as those disclosed in Patent Document 1 have been used to detect target gases contained in the ambient atmosphere. Such gas detectors generally have a problem in that the output value of the gas detection means contained in the gas detector is not stable for a while after the power is turned on and operation starts. Therefore, as disclosed in Patent Document 1, such gas detectors are provided with a period (a so-called warm-up period) during which the detection operation of the target gas is not performed after the operation of the gas detector starts until the output value of the gas detection means stabilizes. Then, when the output value of the gas detection means stabilizes, the output value of the gas detection means is adjusted to zero, and then the detection operation of the target gas is performed in the ambient atmosphere which may contain the target gas.

Japanese Utility Model Application Publication No. 60-109044

In a gas detector, it takes a long time for the output value of the gas detection means to stabilize, and therefore a long time for it to become capable of detecting the target gas. Therefore, the user of the gas detector must wait for that long of a 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 there is a high possibility that the target gas is contained in the ambient atmosphere, it is desirable to shorten the warm-up period after starting 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 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 make the target gas detectable as early as possible, it is necessary to make it possible to detect the target gas accurately even when the output value of the gas detection means is not stable.

The present invention has been made in consideration of the above problems, and aims to provide a gas detector that can accurately detect the 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 the start of operation.

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

It is also preferable that the predetermined range is set to become smaller with the passage of time during the first predetermined period.

Furthermore, it is preferable that the gas detector is configured to maintain operation of the gas detection means for a second predetermined time from when 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 from when the gas detector is stopped.

The control means is preferably 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.

The control means is preferably 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 the detection operation of the target gas.

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

The present invention provides a gas detector that can accurately detect the target gas even when the output value of the gas detection means is unstable, and can quickly become capable of detecting the target gas after starting operation.

1 is a block diagram of a gas detector according to an embodiment of the present invention; FIG. 2 is a circuit diagram showing the gas detection means of FIG. 1. FIG. 1A 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. 1B is an enlarged view of the area around the time when the gas detector starts operating in FIG. 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. 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.

The following describes a gas detector according to one embodiment of the present invention with reference to the attached drawings. However, the embodiment shown below is merely an example, and the gas detector of the present invention is not limited to the following example.

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 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 timer means 4 for measuring elapsed time, a storage means 5 for storing information about the target gas, a notification means 6 for notifying a user of information about the target gas, and a power source 7 for supplying power to each component. Note that the gas detector 1 is 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.

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, is operationally controlled by the control means 3, and transmits the output value to the control means 3. In this embodiment, the gas detection means 2 is a catalytic combustion type gas sensor.

In this embodiment, as shown in FIG. 2, the gas detection means 2 includes a catalytic combustion gas detection element 21 (hereinafter simply referred to as the 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 and independently 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.

The gas detection element 21 is configured so that its resistance value changes when it comes into contact with the gas to be detected. 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 element 21b that changes in temperature when the gas to be detected 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 element 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 gas to be detected can be easily burned. When the gas detection means 2 is driven, the resistance heating element 21a is energized by the circuit power supply 25 via the Wheatstone bridge circuit, and the gas detection element 21 is heated. When the gas detection element 21 comes into contact with the sensor element 21b in the heated state, the temperature of the sensor element 21b increases as the gas to be detected burns, and the resistance value changes.

The compensation 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 compensation element 22 is formed by sintering an oxide such as alumina 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 compensation element 22 is heated by the circuit power supply 25 passing electricity through the resistance heater via the Wheatstone bridge circuit. Unlike the gas detection element 21, the compensation element 22 does not contain a precious metal catalyst, so that it 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 compensation 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 as a result, the resistance value does not change or hardly changes.

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 the resistance value of the gas detection element 21 and the compensation element 22. The gas detection means 2 detects the potential difference generated in the Wheatstone bridge circuit due to the difference in the change in the resistance value of 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 only required to be able to output as an output value the change in the resistance value of the gas detection element 21 generated when the target gas comes into contact with the gas detection element 21, 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, and is not limited to the example shown in the figure.

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, 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 of the control means 3 will be described in detail later.

As shown in FIG. 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 clock means 4, the storage means 5, and the notification means 6, and is configured to control the operation of each component and to be able to send and receive information. The control means 3 can be configured, for example, using a known central processing unit (CPU).

The storage means 5 stores information about the gas to be detected. As shown in FIG. 1, the storage means 5 is communicably connected to the control means 3 and is configured to communicate information about the gas to be detected with the control means 3. The information about the gas to be detected here includes, for example, a relational equation (calibration curve) between the output value of the gas detection means 2 and the indication value indicating the concentration of the gas to be detected, the output value obtained by the gas detection means 2, the indication value calculated by the control means 3, a threshold value for the output value or the indication value, and the elapsed time measured by the timer means 4. The storage means 5 may also 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 with a known volatile memory such as a RAM, or a known non-volatile memory such as a hard disk or a flash memory.

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 communicatively 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 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, for example, by 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.

Next, the operation of the gas detector 1 of this embodiment will be described in detail with reference to Figures 3 to 5. Figure 3(a) is a diagram that shows a schematic diagram of the operation status 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 operate until it stops operating, and Figure 3(b) is an enlarged diagram of Figure 3(a) near the start of operation of the gas detector 1. Figures 4 and 5 are diagrams that show a schematic diagram of the change in the indication value before and after correction by the control means 3 after the gas detector 1 starts to detect the target gas.

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 starts 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 starts. Then, at the elapsed time t1 after the operation of the gas detector 1 starts, 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 detection target gas. In this way, a preparation 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 starts. The preparation 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.

3(b), in the gas detector 1, after the gas detection means 2 starts to operate at the 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 operated, 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 detection operation of the target gas is not performed. Not performing the detection operation of 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, not displayed by the display means) as indicating at least 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 the period from the start of operation of 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, for example, several minutes. In contrast, in this 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 operation. Note that if the indication value does not fluctuate significantly from the beginning of operation of 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 the warm-up period that is generally set, and is set, for example, within the range of 0 to 150 seconds.

As shown in FIG. 3(a) and FIG. 3(b), the gas detector 1 starts detecting the target gas at elapsed time t2 when the warm-up period Tw ends and the indication value is zero-adjusted. When the gas detector 1 starts detecting 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 indication value notifying the user includes notifying information about the target gas by the notification means 6 in general, 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 to indicate 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 compensation element 22 of the gas detection means 2 from when the operation of the gas detection means 2 starts until it is stopped, and the operating state of the gas detection means 2 is kept constant.

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 gas detector starts operating and perform the target gas detection operation as soon as possible. However, if the warm-up period after the gas detector starts operating is shortened and the target gas detection operation 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 gas detector starts operating and to make the target gas detectable as soon as possible, it is necessary to make it possible to detect the target gas accurately even when the output value of the gas detection means is not stable.

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 the 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 in the case where the target gas is contained in the environmental atmosphere. In the gas detector 1, by shortening the warm-up period, even if the output value of the gas detection means 2 and therefore the indication value are 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 make the target gas detectable 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 a zero indication value, and the indication value obtained after the correction is set to the amount of change from the zero indication value.

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 each 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 indicates 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 slightly drops 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 from the elapsed time t2 until the elapsed time t3 until the elapsed time when nine first predetermined times ta have passed. By the processing of the control means 3, the indication value IV0 rises from the zero indication value at the point in time after the elapsed time t2 until the first predetermined time ta, but is corrected to the zero indication value because it is within the predetermined range R below the predetermined threshold value. Next, the indication value IV1 corrected to the zero indication value at the elapsed time when the first predetermined time ta has 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 corrected to the zero indication value because it is within the predetermined range R below the predetermined threshold value. In this way, for 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 zero. If 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 if 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.

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 set appropriately 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, but is set within a range of 30 to 180 seconds, for example.

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 set appropriately according to the degree of change in the indication value expected within the first predetermined period T1 in an environmental atmosphere that does not contain 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 that does not contain the detection target gas is within the predetermined range R that is equal to or less than a predetermined threshold. 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 as time passes in the first predetermined period T1, with the predetermined range R being constant regardless of the passage of time.

The predetermined range R, which is the basis for the correction of the indicated value described above, 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 set appropriately 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 that does not contain 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 that does not contain the target gas is within the predetermined range R below a predetermined threshold value. The predetermined range R is not particularly limited, but is set, for example, within the range of 10 to 100 ppm.

As shown in FIG. 4, the predetermined range R is preferably set to become smaller as time passes in the first predetermined period T1. As can be clearly seen in FIG. 4, if the indicated value is not corrected, the rate of change (amount of change per unit time) tends to decrease as time passes in the first predetermined period T1. 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 as time passes, 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 as time passes. By increasing the predetermined range R in the period in which the rate of change of the indicated value is large in the first predetermined period T1, 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 which the rate of change is small in the first predetermined period T1, the indicated value is prevented from being erroneously corrected to a zero indicated value even if a small amount of the target gas is present. This allows the gas detector 1 to detect the target gas more accurately. From a similar 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 decreases at a first rate of decrease in the early period of the elapsed time within the first predetermined period T1 and decreases at 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 to decrease every 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.

Next, referring to FIG. 3(a) and FIG. 5, the details of the processing 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 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 the gas detector 1, by shortening the warm-up period, even if the output value of the gas detection means 2, and therefore the indicated value, is unstable and becomes smaller than the zero indicated value, the indicated value is corrected to the zero indicated value, so that the gas to be detected can be detected more accurately. Therefore, in the gas detector 1, the warm-up period after the start of operation can be shortened to quickly bring the gas to be detected into a state where it can be detected.

The second predetermined period T2 described above 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 erroneous correction of the indication value 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, for example, within a range from 3 minutes to the time (t5) at which the gas detector 1 stops operating.

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 to the zero indicated value when the indicated value is smaller than the zero indicated value consecutively over a predetermined number of measurements (for example, 50 measurements at 0.1 second intervals) 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 greater accuracy.

The control means 3 may be configured to treat 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 correct the indicated value to the zero indicated value. This allows the gas detector 1 to avoid correction of the indicated value that may be erroneous, and to correct the indicated value more accurately.

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 detection target gas. In addition, 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 detection target gas. This makes it possible to avoid potentially erroneous corrections to the indicated value 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 another 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.

As shown in FIG. 3(a), when the detection operation of the gas to be detected is completed, the gas detector 1 is stopped, for example, at elapsed time t5. The gas detector 1 may be configured to maintain the operation of the gas detection means 2 within a second predetermined time tb from the stop of the operation of the gas detector 1. In that 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 operation of the gas detector 1 is stopped, 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. As a result, by omitting the first correction and, optionally, the second correction, the output value of the gas detection means 2 stabilizes soon after the gas detector 1 starts to operate, improving the detection accuracy of the target gas. 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.

The above-mentioned second predetermined time tb is the 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 stopping its operation. The second predetermined time tb is set, for example, within the range of 10 to 60 seconds.

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 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 operation of the gas detector 1. If the gas detection means 2 is stopped before a certain time has elapsed from the start of operation, there is a possibility that the output value has not yet reached a stable state. In such a case, the detection target gas can be detected more accurately by performing the first correction and, optionally, the second correction, regardless of the time from the stop of operation of the gas detector 1 to the restart.

The third predetermined time tc described above is a predetermined time interval from when a predetermined applied voltage V0 is applied to the gas detection element 21 and 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 when the gas detection means 2 starts to operate to, for example, a time approximately equal to the elapsed time t3 when the first predetermined period T1 ends. More specifically, the third predetermined time tc is set within the range of, for example, 60 to 180 seconds.

REFERENCE SIGNS LIST 1 Gas detector 2 Gas detection means 21 Catalytic combustion type gas detection element 21a Resistive heating element 21b Sensitive element 22 Compensating element 23, 24 Resistive element 25 Circuit power supply 26 Potentiometer 3 Control means 4 Timer means 5 Storage means 6 Notification means 7 Power supply

Claims (3)

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,
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. 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 . The gas detection means is a catalytic combustion type gas sensor.
3. A gas detector according to claim 1 or 2 .

Images