JP4046403B2 - Gas detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas detection device capable of compensating for a change in detection sensitivity of a gas sensor due to a change in environmental conditions, and more particularly to a gas detection device capable of correcting absolute humidity when the detection sensitivity changes depending on absolute humidity. .
[0002]
[Prior art]
As this type of gas detection device, there is one using a semiconductor gas sensor. Since the characteristics of this semiconductor gas sensor change depending on the absolute humidity, in a home gas alarm device, for example, an inexpensive temperature sensor such as a thermistor is used, and the correlation between the sensor output and the absolute humidity is Humidity compensation was simply performed using the correlation with the approximate temperature.
[0003]
For example, in the case of a hot-wire semiconductor sensor, the humidity characteristic as shown in FIG. 7 is shown, and as the absolute humidity increases, the resistance value of the sensor changes and the sensor output increases. As shown in FIG. 8, the correction amount of the sensor output by the thermistor is set such that three or more temperature / humidity conditions are set and the sensor output becomes constant.
However, when the relative humidity is uniquely determined from the relationship between the absolute humidity and the temperature corresponding to the appropriate correction amount (for example, when the absolute humidity is 33 g / m ³ and the temperature is 40 ° C., the relative humidity is 65%), the appropriate correction amount is Although the sensor output is lower than the constant output in the low humidity state even at the same temperature, and conversely the sensor output exceeds the constant output in the high humidity state, an appropriate correction amount cannot be obtained, resulting in high accuracy and Highly sensitive gas detection was difficult.
[0004]
Therefore, if the absolute humidity correction of the sensor output is to be performed with high accuracy, correction using a temperature sensor and a relative humidity sensor and correction using an absolute humidity sensor can be considered as shown in FIGS. In both cases, the humidity sensor is expensive, which causes a rise in the manufacturing cost of the gas detection device, making it difficult to employ it in a home gas alarm device.
[0005]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described problems, and an object of the present invention is to eliminate the above-described problems, and to accurately and easily detect fluctuations in environmental conditions, in particular, fluctuations in sensor output due to fluctuations in absolute humidity. Therefore, it is possible to provide a gas detection device capable of detecting low concentration gas with high accuracy.
[0006]
[Means for Solving the Problems]
In order to achieve this object, the first characteristic configuration of the gas detection device according to the present invention samples and holds the output signal of the gas sensor at a predetermined sampling period as described in claim 1 of the claims. A sampling unit, an average value calculating unit for calculating an average value of predetermined sampling values in a past predetermined period, a latest sampling value, and a sampling value at a sampling timing immediately before the sampling timing at which the latest sampling value is obtained average value and the first difference value is a difference between the old sampling value is is calculated by the first determination unit determines whether greater than a predetermined first threshold value, the latest sampled value and said average value calculation unit A second determination unit that determines whether a second difference value that is a difference between the second difference value is larger than a predetermined second threshold value, the first determination unit, and the second determination unit A notification processing unit configured to perform a predetermined notification process when the first difference value is greater than the first threshold value and the second difference value is greater than the second threshold value based on the determination result; In the point.
[0007]
The second feature structure, as set forth in claim 2 column claims, in addition to the first characterizing feature, if the notification processing unit performs notification processing, the old sampling value The point is that the latest sampling value is maintained without being updated.
[0008]
In the third feature configuration, in addition to the first or second feature configuration, whether the second difference value is greater than a predetermined third threshold value, as described in claim 3 of the claims. A third determination unit that determines whether or not the notification processing unit performs the notification processing when the second difference value is greater than the third threshold value based on a determination result of the third determination unit. is there.
[0009]
In the fourth feature configuration, as described in claim 4 in the column of the claims, in addition to the first, second, or third feature configuration, the minimum value of the sampling values within the past predetermined period. a minimum value storing unit for storing, the fourth determination determines the third differential value is the difference between the most recent minimum value stored in the minimum value storage section and the sampled value is greater than a predetermined fourth threshold value And the notification processing unit is configured such that, based on the determination results of the second determination unit and the fourth determination unit, the second difference value is greater than the second threshold value, and the third difference value is In the case where it is larger than the fourth threshold, the notification process is performed.
[0010]
The operation and effect will be described below.
The first characteristic configuration of the present invention is made paying attention to the difference between the case where the transient characteristic of the sensor output of the gas sensor is due to a change in gas concentration and the case where it is due to a change in environmental conditions such as absolute humidity. For example, when the gas sensor is a hot-wire semiconductor sensor, the response characteristics of the sensor output when the gas concentration is changed and when the absolute humidity is changed are steeper when the gas concentration is changed.
[0011]
Therefore, according to this characteristic configuration, the first determination unit first determines the amount of change in the sensor output over time for each predetermined sampling period based on the difference in the transient characteristics, that is, the first difference value. Detect certain gas concentration changes reliably. However, since the first determination unit cannot determine whether or not the absolute value of the gas concentration is at the detection level, the second determination unit makes this determination. Here, the second determination unit uses the average value of the sensor output in the past predetermined period without using the detection level based on the fixed threshold value, so that the absolute humidity or the like can be obtained when the gas concentration changes or before and after the change. Even if the environmental conditions change and the sensor output fluctuates, the fluctuation of the sensor sensitivity can be suppressed within a certain range by absorbing the fluctuation by the average value. In other words, the second difference value changes mainly following only the change in gas concentration, regardless of changes in environmental conditions, and the second determination unit can detect the absolute value of the gas concentration. It should be noted that an extremely low concentration gas can be detected by setting the second threshold value to 0 while securing a constant value as the first threshold value. A predetermined notification process such as issuing an alarm when the first determination unit determines that the first difference value is greater than the first threshold value and the second determination unit determines that the second difference value is greater than the second threshold value. To notify the detection result.
[0012]
As a result of the above, according to this feature configuration, the gas detection capable of accurately detecting a low-concentration gas with high accuracy and simple compensation for fluctuations in environmental conditions, in particular, fluctuations in sensor output due to fluctuations in absolute humidity. Providing equipment.
[0013]
According to the second characteristic configuration, since the old sampling value is not updated at the time of gas detection, the value in the clean atmosphere when the gas concentration is at a low level is used as the reference value for generating the first difference value. The gas detection state can be maintained continuously after gas detection. That is, once the gas is detected, even if the gas concentration does not change or changes slowly, it can be detected reliably.
[0014]
According to the third characteristic configuration, even when the gas concentration in the normal state before the gas detection is gradually increasing at a rate of change below the level that can be determined by the first determination unit, the absolute gas concentration The third determination unit can determine and detect that the value has reached a predetermined level or more. That is, in the first feature configuration, when the first threshold value is set low in order to cope with a gradual change in gas concentration, this feature configuration has the adverse effect of easily reacting to a change in environmental conditions and causing a malfunction. It can be avoided.
Here, when the feature configuration is independent from the first feature configuration, that is, when the first determination unit and the second determination unit are not used, for example, the absolute humidity is changed due to a change in environmental conditions. When the sensor output is gradually decreasing due to a gradual decrease in the gas value, the second difference value becomes a negative value. At that time, even if the gas concentration increases, if the third threshold value is high, the gas concentration is surely increased. On the other hand, if the third threshold value is set too small, there is a possibility that a malfunction may occur due to a steeper fluctuation of environmental conditions than usual. In particular, in the calculation of the average value of the average value calculation unit, in order to save the storage capacity for storing a large amount of sampling values while ensuring the length of the predetermined period for obtaining the average value, the update period of the average value is set. When it is made longer than the sampling period, the possibility of the malfunction occurring within the update period is increased. Therefore, by using this feature configuration and the first feature configuration together, this problem can be avoided and highly accurate gas detection can be performed.
[0015]
According to the fourth characteristic configuration, when a very small amount of gas is gradually accumulated in the room, the sensor output is at a moderate change rate that the first determination unit or the third determination unit cannot determine. Even when it rises, it is possible to reliably detect a change in gas concentration. It should be noted that by setting the fourth threshold value to be high to some extent, it is possible to avoid malfunction due to fluctuations in environmental conditions.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of a gas detection device according to the present invention (hereinafter referred to as the present invention device) will be described with reference to the drawings.
[0017]
As shown in FIG. 1, the apparatus of the present invention samples and holds the gas sensor 1 and the sensor output signal S of the gas sensor 1 at a predetermined sampling period T ₁ , performs A / D conversion, and stores it as the latest sampling value S _NEW. The sampling unit 2 that stores the latest N points for every _second sampling cycle T _{2 that} is an integral multiple of the sampling cycle T ₁ among the sampling values that have been A / D converted by the sampling unit 2. An average value calculation unit 3 that calculates an average value S _AVE of sampling values for N points for each sampling period T ₂ , and a first difference that is a difference between the old sampling value S _OLD and the sampling value S _NEW A first determination unit 4 that calculates a value Δ ₁ (= S _NEW −S _OLD ) and determines whether the first difference value Δ ₁ is greater than a predetermined first threshold value V _1, and the sampling value S _NEW. And a second difference value Δ ₂ (= S _NEW −S _AVE ), which is a difference between the average value S _AVE and the average value S _AVE , to determine whether the second difference value Δ ₂ is greater than a predetermined second threshold value V _2. The second determination unit 5, the third determination unit 6 that determines whether the second difference value Δ ₂ calculated by the second determination unit 5 is greater than a predetermined third threshold value V _3, and the sampling unit 2 The minimum value S _MIN for 24 hours of the sampled sampling values is obtained, and the minimum value S _MIN for updating the minimum value S _MIN every 24 hours, and the sampling value S _NEW and the minimum value storage 7 A third difference value Δ ₃ (= S _NEW −S _MIN ) that is a difference from the updated minimum value S _MIN is calculated, and it is determined whether the third difference value Δ ₃ is greater than a predetermined fourth threshold value V _4. Any one of the determination results of the fourth determination unit 8, the first determination unit 4, the third determination unit 6, and the fourth determination unit 8 is true. I, and, if the determination result of the second judging unit 5 is true, and a notification processing unit 9 for performing a predetermined notification processing of alarm occurrence.
[0018]
The gas sensor 1 is composed of a hot-wire semiconductor sensor 1a formed by coating and firing a metal oxide semiconductor on a noble metal wire such as a platinum wire coil, and detects gas by a change in electric resistance due to adsorption of a gas component. In general, the bridge circuit shown in FIG. 2 is configured to read the sensor output signal S as a voltage value.
[0019]
The sampling unit 2, the average value calculation unit 3, the first determination unit 4, the second determination unit 5, the third determination unit 6, the minimum value storage unit 7, and the first Specifically, the sensor output determination unit 10 including the 4 determination unit 8 includes a microcomputer having an analog input terminal, a built-in A / D converter, and the like. The sampling unit 2, the average value calculation unit 3, the first determination unit 4, the second determination unit 5, the third determination unit 6, the minimum value storage unit 7, and the fourth determination unit 8 Are realized by software processing by allocating a predetermined storage area such as a built-in memory or a register and executing an execution program built in the microcomputer.
Therefore, the connection of each functional block shown in FIG. 1 indicates the flow of calculation results or determination results in each block, and does not indicate the actual flow of electrical signals or wiring. Further, when using a microcomputer or dedicated hardware capable of parallel processing, the execution of each functional block may be partially processed in parallel.
[0020]
Hereinafter, the operation of the apparatus of the present invention will be described based on the flowchart shown in FIG.
[0021]
The process starts when the power is turned on. First, in step # 1, initial values of the old sampling value S _OLD , the average value S _AVE , and the minimum value S _MIN are set.
Thereafter, the following processing is performed every sampling period T ₁ . In the present embodiment, the sampling period T ₁ is set to 10 seconds.
[0022]
In step # 2, the sampling unit 2 samples and holds the sensor output signal S and performs A / D conversion, and stores it as the latest sampling value _SNEW .
Next, in step # 3, the first determination unit 4 sets the first difference value Δ ₁ (= S _NEW −S _OLD ), and the second determination unit 5 sets the second difference value Δ ₂ (= S _{NEW). -SAVE} ) is calculated.
[0023]
In step # 4, the first determination unit 4 determines whether the first difference value Δ ₁ is greater than the first threshold value V ₁ . If this determination is true (Δ ₁ > V ₁ ), step # 8 is executed without executing steps # 5 to # 7. If this determination is false (Δ ₁ ≦ V ₁ ), step # 5 is executed.
[0024]
In step # 5, the third determination unit 6 determines whether the second difference value Δ ₂ is greater than a predetermined third threshold value V ₃ . If this determination is true (Δ ₂ > V ₃ ), step # 8 is executed without executing steps # 6 to # 7. If this determination is false (Δ ₂ ≦ V ₃ ), step # 6 is executed.
[0025]
In step # 6, the fourth determination unit 8 calculates the third difference value Δ ₃ (= S _NEW −S _MIN ), and determines whether the third difference value Δ ₃ is greater than the fourth threshold value V _4. To do. If this determination is true (Δ ₃ > V ₄ ), step # 8 is executed without executing step # 7. If this determination is false (Δ ₃ ≦ V ₄ ), step # 7 is executed.
[0026]
In step # 7, the second difference value Δ ₂ is reset to 0, and the old sampling value S _NEW is substituted into the old sampling value S _OLD stored in the first determination unit 4 to substitute the old sampling value S _NEW. Update _OLD . Next, step # 8 is executed.
[0027]
In step # 8, the second determination unit 5, the second difference value delta ₂ computed in step # 3, or Step # 7 the second difference value if it is reset by the delta ₂ is the second determines whether or not greater than the threshold value V _2. If this determination is true (Δ ₂ > V ₂ ), in step # 9, the notification processing unit 9 executes predetermined notification processing such as generation of an alarm. If this determination is false (Δ ₂ ≦ V ₂ ), step # 9 is not executed.
The second threshold value V ₂ is set to a value smaller than the third threshold value V ₃ , for example, 0. Therefore, if the determination at step # 5 (Δ ₂ > V ₃ ) is true, the determination at step # 8 (Δ ₂ > V ₂ ) is always true, so step # 9 may be executed directly. Absent.
[0028]
In step # 10, the average value S _AVE and the minimum value S _MIN are calculated and updated. However, without executing the each of the sampling period T _1, carried out in the manner described below.
[0029]
A series of processes in steps # 10 from step # 2 above is performed by the sampling period T ₁ interval.
[0030]
In the present embodiment, the sampling period T ₁ is set to 10 seconds. This sampling period T ₁ differs depending on whether the transient characteristic of the sensor output value of the gas sensor 1 is accompanied by a change in absolute humidity or a change in the gas concentration of the gas to be detected, and the response of the sensor output value is in the former case. The optimum value is set corresponding to the fact that the value is moderate.
FIG. 4 shows a unit of the sampling period T ₁ of three seconds of 1 second, 5 seconds, and 10 seconds when smoking is started halfway while gradually increasing the absolute humidity at a substantially constant rate of time change. It shows the change of the first difference value Δ ₁ (= S _NEW −S _OLD ) per time. Accordingly, when the sampling period T ₁ is 5 seconds or less, the first difference value Δ ₁ cannot sufficiently cope with the change in gas concentration due to smoking, and the first threshold value V ₁ needs to be set low. The value when the sampling period T ₁ is 10 seconds is more than twice that of 5 seconds or less, which suggests that the first determination unit 4 can sufficiently detect the change in gas concentration. If the sampling period T ₁ is longer than 10 seconds, the gas concentration cannot be sufficiently changed.
[0031]
Further, the sampling period T ₂ is set to 10 minutes, that is, 60 periods of the sampling period T ₁ . The number N of points for calculating the average value S _AVE is set to 7. Therefore, the average value S _AVE approximately represents the average value of the sensor output for the past one hour. Therefore, in step # 10, the average value calculation unit 3 samples the sampling value for 7 points at the rate of once every 60 times of the series of processing from step # 2 to step # 10. The value is updated to a new average value S _AVE .
[0032]
In step # 10, the calculation of the minimum value S _MIN and the update process are different in the first 24 hours from power-on and thereafter.
In the first 24 hours after turning on the power, the minimum value S _MIN and the old sampling value S _OLD at that time are compared in magnitude at the sampling period T _2, that is, at an interval of 10 minutes, as in the calculation of the average value S _AVE. The smaller one is newly updated as the minimum value S _MIN . Accordingly, the calculation and the update are performed simultaneously, and the updated minimum value S _MIN is used in the processing after the next step # 2.
When the first 24 hours have passed since the power was turned on, the calculation is similarly performed at intervals of 10 minutes, but the update is performed at intervals of 24 hours from the time when the first 24 hours are exceeded. Here, the minimum value S _MIN is appropriate for the determination of the fourth determination unit 8 following the tendency of gradual fluctuation (up and down) of environmental conditions such as gas concentration and absolute humidity over a long period of time. since the correction in which the applying, the minimum value S _MIN update before 24 hours on the calculated computed minimum value S _MINC forcibly substitutes and updates the minimum value S _MIN, immediately after this update, The operation minimum value S _MINC is initialized with the old sampling value S _OLD at that time.
[0033]
Next, the humidity compensation performance of the device of the present invention will be described.
FIG. 5 shows the static characteristics of the sensor output of the gas sensor 1, and it can be seen that the sensitivity to the gas concentration varies with the absolute humidity.
FIG. 6 is a plot of the second difference value Δ ₂ (= S _NEW −S _AVE ) calculated in step # 3 for each gas concentration and absolute humidity. The second difference value Δ ₂ is a change in absolute humidity. It is shown that the absolute humidity compensation is properly performed because it changes only following the gas concentration. Also, this is, because the gas concentration is conspicuous low concentrations, at step # 8, the second threshold value V ₂ a very small value, for example, is set to 0, which can detect a low concentration gas I understand that.
[0034]
[Another embodiment]
Another embodiment will be described below.
<1> The sensor output determination unit 10 may not necessarily be configured by a microcomputer. For example, the function of each unit may be configured by hardware only by combining an A / D converter, a random logic circuit, and a semiconductor memory, or a gate array incorporating them.
[0035]
<2> The gas sensor 1 is not necessarily limited to the above-described embodiment. Another type of gas sensor in which the sensor output varies due to the variation in absolute humidity may be used. Further, the device of the present invention can perform the same sensor output correction even when the sensor output fluctuates due to fluctuations in environmental conditions other than absolute humidity.
[0036]
<3> The flowchart illustrated in FIG. 3 shows an example of an operation procedure for realizing the device of the present invention, in particular, the sensor output determination unit 10 by software. Each step is executed by another procedure. You may make it acquire the same effect.
For example, the following changes are possible.
Similar results can be obtained even if the execution order of steps # 4, # 5, and # 6 is changed as appropriate. Steps # 5 and # 6 are not necessarily executed.
Further, without calculating the second difference value delta ₂ in Step # 3, before that determination process when executing step # 5, and the second in the course proceeds from Step # 4 and 6 to step # 8 Two difference values Δ ₂ may be calculated.
Furthermore, step # 10 may be before each step # 3, # 4 or # 8. Whereas the updating of the average value S _AVE and the minimum value S _MIN is respectively 10 min and 24 hour intervals, for the operation of the sensor output determination unit 10 is a 10 second interval, the average value S _AVE and What is used for the calculation of the minimum value S _MIN and the execution of the sensor output determination unit 10 is only shifted by 10 seconds every 10 minutes or 24 hours, and the same effect is obtained as a whole.
[0037]
<4> The update cycle of the sampling cycle T ₁ , the sampling cycle T ₂ , the number of points N, or the minimum value S _MIN is not necessarily limited to that of the above-described embodiment, and depends on use conditions. Can be changed or adjusted as appropriate.
[Brief description of the drawings]
FIG. 1 is a functional block configuration diagram showing an embodiment of a gas detection device according to the present invention. FIG. 2 is a circuit configuration diagram showing an embodiment of a gas sensor. FIG. 3 is an operation of the gas detection device according to the invention. flow [4] first difference value delta ₁ of the time rate of change showing the procedure (V / sec) transient characteristic diagram showing separately the sampling period T ₁ to FIG. 5 characteristic diagram showing the static characteristics of the sensor output of the gas sensor Figure 6 shows a prior art example using the temperature correction characteristic diagram [9] the relative humidity sensor of the sensor output at humidity characteristic diagram [8] prior art second difference value delta ₂ of the humidity characteristic diagram [7] the gas sensor Circuit block diagram [Fig. 10] Circuit block diagram showing a prior art example using an absolute humidity sensor [Explanation of symbols]
1 gas sensor 2 sampling unit 3 average calculator 4 first determination unit 5 fourth determination unit 9 notification processing unit 10 sensor output determination unit second determination unit 6 a third determination unit 7 minimum value storage portion 8 T ₁ sampling period S _NEW Latest sampling value S _OLD Old sampling value S _AVE average value Δ ₁ first difference value Δ ₂ second difference value V ₁ first threshold value V ₂ second threshold value

Claims (4)

A sampling unit that samples and holds the output signal of the gas sensor at a predetermined sampling period, an average value calculation unit that calculates an average value of predetermined sampling values in the past predetermined period, the latest sampling value, and the latest sampling value a first determination unit determines whether the first difference value is greater than a predetermined first threshold value which is the difference between the old sampling value is the sampling value at the sampling time immediately before sampling timing is obtained, the latest sampled value And a second determination unit that determines whether a second difference value that is a difference between the average value calculated by the average value calculation unit is greater than a predetermined second threshold, the first determination unit, and the second determination unit And when the first difference value is larger than the first threshold value and the second difference value is larger than the second threshold value. Gas detection device comprising a notification processing unit that performs a predetermined notification processing. The notification when the processing unit performs the notification process, the gas detection apparatus according to claim 1, wherein the former sampling values, characterized in that it held without updating by the latest sampling values.   A third determination unit configured to determine whether the second difference value is greater than a predetermined third threshold; The gas detection device according to claim 1 or 2, wherein the notification process is performed when the threshold value is larger than three threshold values. A minimum value storing unit for storing the minimum value of the sampling values of the past within a predetermined period, the third difference value is a difference between the latest minimum value stored in the minimum value storage section and the sampling value is given 4 A fourth determination unit that determines whether the second difference value is greater than the threshold value, and the notification processing unit determines that the second difference value is greater than the second threshold value based on determination results of the second determination unit and the fourth determination unit. 4. The gas detection device according to claim 1, wherein the notification process is performed when the third difference value is greater than the fourth threshold value.

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