JPH01199147A - Apparatus of detecting gas - Google Patents

Abstract

PURPOSE:To make it possible to process a temporary peak of a sensor output as noise, by determining an amount corresponding to a noise level of a gas sensor and by setting said amount as a lower limit value of a significant signal in detection of gas. CONSTITUTION:A detecting apparatus is constituted by a power source 2, a gas sensor 4 using a change of a resistance value of a metal oxide semiconductor 6, a load resistance 10 of the sensor 4, a heater 8, etc. An output signal of the sensor 4 is sent to a microcomputer 12 for signal processing. In the microcomputer 12, an amount corresponding to a noise level of the output signal of the gas sensor 4 is determined, and the determined amount corresponding to the noise level is set as a lower limit value of a significant signal of the output of the gas sensor 4. A gas detector is so designed as to obtain a detection signal of gas through comparison of the output of the sensor 4 with a reference value, and the reference value is modified in accordance with the determined amount corresponding to the noise level. It is judged from the duration of the sensor output being shorter than a prescribed time that the sensor output is caused by noise.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] This invention relates to gas detection, and more particularly to noise removal for detection.

[Prior Art] The inventors have studied the detection of low concentration gases. In this case, the reliability of the sensor output is low, and false detections occur due to temporary fluctuations in the sensor output. For example, assume that a 5nOt gas sensor is installed in a living room and detects air pollution. In this case, peaks in the sensor output for unknown reasons occur intermittently and last for several seconds. This peak is thought to be caused by the local distribution of gas concentration, the influence of airflow, temporary fluctuations in sensor temperature, or instability of the detection circuit. According to the inventors' observations, this peak has nothing to do with contamination in a more or less large space, which hinders the detection of air contamination. However, when it is necessary to detect extremely low concentration gases such as air pollution, such peaks also interfere with detection. That is, if the detection reference value is brought close to the sensor output in the air, it becomes impossible to distinguish between air pollution and noise peaks.

Of course, there is also the possibility that this peak is caused by air pollution such as a local increase in gas concentration. However, from the standpoint of gas detection, a signal that occurs only temporarily and is unrelated to the overall contamination of the atmosphere must be treated as noise. Furthermore, the size of the peak depends on the usage environment, etc.
It was difficult to take measures against the law. To solve these problems, it is necessary to directly or indirectly detect the magnitude of the noise level and modify the reference value according to the noise level.

Incidentally, related known techniques will be shown here. Special Public Service 1984-1984
, No. 327, samples the minimum value of the sensor output (the sensor output for the cleanest atmosphere when the sensor output increases with the gas concentration) as a reference value,
It is proposed to detect gas based on future changes. Furthermore, Japanese Patent Application Laid-Open No. 60-27,849 proposes to use the minimum value of the sensor output within a six-hour period as the reference value. These techniques are effective in detecting low-concentration gases because they eliminate error factors such as changes in the sensor over time and ambient temperature and humidity. These technologies sample a reference value from past sensor outputs and detect gas based on this reference value.

[Problem of the Invention] An object of the present invention is to obtain a noise level correspondence amount of a sensor and to be able to process a temporary peak of the sensor output as noise.

[Structure of the Invention] In the present invention, an amount corresponding to the noise level of the gas sensor is determined, and this amount is used as the lower limit value of a significant signal in gas detection. In this way, gas detection accuracy can be improved and noise can be removed.

FIG. 1 and FIG. 2 illustrate an example of a device that detects the presence or absence of gas exceeding a detection threshold by comparing the output of a gas sensor with a reference value. Taking this as an example, the inventor's basic points of interest will be illustrated. Find the amount corresponding to the noise level from the sensor output. Noise can be removed by feeding back this amount to the reference value and modifying the reference value. The operating waveform here is
As shown in the figure. Assume that the output Vout of the sensor changes as shown in the figure. A signal that lasts only a short time can be judged as noise. That is, it is possible to determine whether the signal is noise or not based on the duration of the signal. If it can be determined that a certain signal is noise, the magnitude of the noise (noise level) can be determined. For example, the noise level is the maximum slope of the output when the noise peak -1 or the time differential value of the sensor output is used, or the integrated value of the noise output when the sensor output is integrated. The noise level correspondence amount obtained there may be used as the lower limit of detection. Here, an example in which a detection threshold is provided is illustrated, but any method may be used as long as the obtained noise level correspondence amount is set as the lower limit value of the significant signal. Third
The figure below uses air conditioning control (especially air purifier control) as an example.
An example is shown.

[Nomenclature] In this specification, the gas sensor output is indicated as increasing with the generation of the gas to be detected. However, this is for convenience of explanation, and the actual sensor output may exhibit the opposite characteristics. In that case, the magnitude of the sensor output, increase and decrease, can be interpreted in reverse □.

[Example 1] An example aimed at controlling the air cleaner 30 is shown in FIGS. 3 to 5. The basic points of interest in this example are shown. Let M be the noise level corresponding amount. In a certain section (in the example, the section from time 0 to T3), the number of noises having a size of M or more is determined. If this number is too small, it means that M is too large. Conversely, if this number is too large, it means that M is too small. Then, M is corrected according to the measured number. In this way, a value M that approximately corresponds to the actual noise level is obtained.

In the figure, 2 is an appropriate power supply, 4 is a metal oxide semiconductor 6
8 is a heater thereof. Here, the sensor 4 used was one that utilized changes in the resistance value of Snow.

The sensor 4 is a catalytic combustion gas sensor that detects combustible gas from the heat of combustion in the catalytic oxidation catalyst.
Any gas sensor can be used, such as a solid electrolyte gas sensor that detects gas from an ionically conductive solid electrolyte such as O, antimonic acid, or the like. IO is the load resistance of the sensor 4. The voltage V out etc. to the load resistor 10 is detected by the sensor 4.
Let the output be

As the sensor output, any output such as a differential value or an integrated value of Vout, a voltage obtained by dividing Vout, or even a voltage applied to the sensor 4 can be used.

Reference numeral 12 denotes a microcomputer for signal processing, which may be replaced with an individual logic circuit using LSI or the like.

14 is an A/D converter for A/D converting the sensor output Vout.
D converter, 16 is arithmetic logic unit, 18.2
0 is a RAM for storing data related to detection, which is shown divided into two parts for convenience of illustration.

In the example, the reference value is based on the average value A of the sensor output in the air. Here, the average value A is the average value of sensor outputs over a 10-minute period sampled at 1-minute intervals.

Instead of the average value over 10 minutes, the average value over an unlimited period may be used. Also, unlimited sections or 5 minutes to 20 minutes
The minimum value of the sensor output in an interval of about minutes may be used.

The reason why the reference value is set based on the past sensor output in this way is to learn the sensor output in the air and set the reference value near it. Of course, the reference value may be started based on a fixed value input from the outside.

The following three standard values were used for detection.

(1) Operating strength of air purifier 30 Strong: J-K
l-A (2) Operating strength of air purifier 30 Medium: J-,
・A(3) Operating strength of air purifier 30 Weak: A+J
"Ks・M Here, J is a constant input from the outside. For example, it may be two types, one on the low sensitivity side and one on the high sensitivity side. Also, KI>
Kt, and the upper limit of the weak detection standard value was set to be less than the medium detection standard value. When the operating strength was medium or strong, malfunctions due to noise were rare, so the reference value was made independent of M. K3 is a constant corresponding to the tolerance rate from the noise level M, and a value of about 1.5 to 2 is used, for example. In addition, the noise level M and the average value A were separated into variables so as to be able to cope with changes in the average value A, and the lower limit of the reference value was set by multiplying M by 5. Of course, a value obtained by adding the allowable width to M may also be used. In addition to this, control outputs to the air cleaner 30 were stored in the RAM 1B. Numerical examples used in Examples are shown below. The value of J was 1.2 on the high sensitivity side and 1.2 on the low sensitivity side. K, is 1
．． 3. To! is 1.2) K is set to 1.6.

The RAM 20 stores a noise level corresponding amount M1, the number of noises having a size greater than or equal to M during time T, and a change L indicating whether sampling of C1 noise is possible (sampling is possible when L=0).
to remember.

2'2. is a timer, from which T3, T*, T
Take out the three signals of s. T1 is a signal for sampling the average value A, and here it is assumed to be at 1 minute intervals.

T is a signal for determining whether the fluctuation in the sensor output is due to noise or not. When the sensor output increases to more than A+M and then decreases to less than A+0.5M during time T, it is considered noise. . In the case of controlling the air cleaner 30, T is, for example, approximately 10 seconds to 2 minutes. In detecting gas leaks, when distinguishing between gas leaks and temporary increases in gas concentration due to the use of organic solvents, etc., gas leaks are a slow phenomenon compared to air purifier control, and the time T is longer. The time, for example, is about 5 minutes to 2 hours. T is the time required to count the number of noises at a level below M, for example lO
It will take about 30 minutes. T3 is T.

, for example, 10 times or more.

24 is a switch for inputting the constant J, and 30 is an air cleaner as a load.

The operation of the device will be explained with reference to FIG. After turning on the power, wait for example 2 minutes until the output of sensor 4 becomes stable, and then
8. Perform initialization of 20. First, the sensor output Vout at that point in time is sampled, and this is set as the initial value of the average value A. Further, for example, 0.05A is used as the initial value of the noise level correspondence amount M (step 100). From now on V ou
It is assumed that t is read at intervals of 2 seconds, for example.

Air contamination is detected when the sensor output Vout reaches the lowest reference value A+J- and exceeds M (step 1).
02) When contamination is detected, the process moves from connector S to a contamination detection subroutine. In this subroutine, Vout
is compared with three reference values, and the operating conditions of the air cleaner 30 are determined depending on the degree of contamination (step 104). When Vout falls below the lowest reference value A+J-Ks·M, the connector Y returns to the main loop. This time is set to 1, and noise sampling is prohibited until L is reset to 0 (step 107).

A is changed every time the time TI (for example, 1 minute) elapses (step 11B), and A=0.9A+0. Change A according to IVout (step 120). Next, return to connector Y and continue monitoring Vout again.

Noise sampling is performed as follows.

In step 108, it is detected that the sensor output has decreased below A+0.5M, and the variable is reset to 0 (
Step 110). In this embodiment, since the number of noises exceeding the noise level correspondence amount M is important, counting is started when Vout exceeds A+M (step 112).
). Here, confirm that L is O. Step 114
), if 0, the noise sampling subroutine T
to move to.

If Lh<1, noise sampling is not performed. When L is 1, after vout exceeds A+M, -degrees have not fallen below A+0.5M, and it can be determined that the increase in Vout is continuous. Such signals are continuous and do not have the characteristics of isolated noise. Therefore, noise sampling is performed only when L is 0.

This subroutine starts counting the time T, step 122), and by the time T has elapsed, V out has reached A+.
A case where the value decreases to 0.5M or less is considered to be noise. On the contrary, Vo
When ut exceeds the contamination detection reference value, the process moves to subroutine S (step 124).

If Vout does not fall below A+0.5M even after T has elapsed (steps 126 and 128), the duration of the peak of Vout is long and it is not determined to be noise.

In this case, L is set to 1 and the process returns to the main loop (step 132). Separately from these cases, if Vout falls below A+0.5M before time T has elapsed (step 128), the value of C is added, assuming that noise at a level below M exists (step 128). 130).

The number of noises having a size less than or equal to M is determined every time T elapses. When time T3 has elapsed (step 116), M
The process moves to the change subroutine U.

Here, M is changed depending on the value of C, and in the case of C=1, M
(step 132), and decrease M as it is considered too high at C=0 (step 134).
. Furthermore, if C≧2, M is considered too low and M is increased (steps 136 and 138). In addition, set an upper limit for the value of M so that it does not exceed 0.12A (Step 1
40). After these processes, the connector X returns to the main loop. Note that the relationship between the correction conditions for C and M shown here is only one example, and may be changed as appropriate.

FIG. 5 shows the meaning of M. Among the noises generated during time T3, M is determined so as to take a value intermediate between the maximum value and the second value. Then, a standard value is established by adding 3 to this value as a tolerance level.

Here, M and A are treated as separate variables, so that even if A is changed, M can be used.

[Example 2] Another example is shown in FIGS. 6 to 8. In this embodiment, the maximum value l of the noise level during time T is measured, and this is set as the next noise level correspondence amount M. Further, as an intermediate quantity for measuring I, the maximum value S of Vout during noise is used. The changes in the device are that the data RAM 20 is replaced with a data RAM 21, and the microcomputer 12
is replaced with a microcomputer 13.

FIG. 7 shows an operation flowchart. Note that the same steps as in FIG. 4 represent the same processing, and the same symbols represent the same contents. In this embodiment, the initialization conditions of the data RAMs 1B and 21 are changed, and a process is added to initialize the initial value of m to an appropriate value such as O (step 101).Similar to FIG. If A+J- exceeds 3.M, it is determined that there is contamination, and the process proceeds to the same subroutine S shown in FIG. 4. Next, a sufficiently small constant Δ (preferable value is 0.01 to 0
．． 02A) is prepared, and when Vout exceeds A+Δ, the noise level is sampled. Further, when Vout falls below A+Δ, L is reset to 0 (step 150.110). When Vout exceeds A+Δ(
step 150), if L is 0 (step 114)
, the process moves to a noise level sampling subroutine T°.

When this subroutine is entered, counting of time T is started (step 122), and the noise level is measured from Vout during this time. To measure the noise level, the maximum value of Vout during this period is taken out as 8 (step 15).
4,156,158). Further, when Vout exceeds the contamination detection reference value (step 124), the process moves to subroutine S and the noise level is not measured. During time T, Vo
Even if ut does not fall below A+Δ (step 12
6,160), do not measure noise level. In this case, L is set to 1 (step 132). If Vout falls below A+Δ before time T has elapsed (step 160), it is determined that the peak of Vout is due to noise, and the maximum value S of Vout is extracted. Then, s-A is set as a noise level and compared with the previously stored noise level m (step 162).

If s-A is greater than or equal to U, this value is assigned to m. In this way, the maximum value of the noise level m is extracted (step 164).

When the time Ts has elapsed (step! 16), - is substituted into the next M, and for example l/2 ts is used as the initial value of the turtle for the new section (step 152).

The meaning of sampling M in the embodiments shown in FIGS. 6 and 7 is not shown in FIG. M is the maximum value of the noise level during time T, and there is a tolerance K to this.

The reference value is the value that takes into account the above.

[Third example] A simple embodiment is shown in FIG. 9 and FIG. 1θ.

The changes on the device are that the data RAM 21 in FIG. 6 is changed to variable 8, data of X l-X n, and X.

- the maximum value y of Xn-+ is stored. Also, the timer 22 is modified so that a signal obtained by dividing time T into N equal parts is taken out.

Turning to FIG. 9, the operation of the device will be explained. Note that the meaning of each symbol is the same as in the embodiments shown in FIGS. 1 to 8, and the parts whose details are not shown in the flowchart are the same as in the flowchart of FIG. In this flowchart, data is initialized after waiting for two minutes after the start of operation. then 2
The sensor output V out is read at second intervals, and the average value A of the sensor output V out for 10 minutes is calculated. The average value A is calculated by correcting A every time T (1 minute). Modified formula % formula %. Next, contamination of the atmosphere is detected by comparison with each reference value, and when contamination is detected, the air cleaner 30 is operated according to the degree of contamination.

Vout is sampled every period of about T, /N, and the noise level is measured. The operation of this part is shown in FIG. 1O. The time T, which is approximately 2 minutes, is divided into N equal parts, and X,=Xn (X, to x, in the figure) are sampled.

If the difference between X and Xn is as small as Δ or less, it means that there is no signal of essential significance between them.

Sample the maximum value of,X,~Xn,and,X,.

Alternatively, let the difference from Xn be y. y corresponds to the noise level.

Returning to FIG. 9, an interrupt is performed every time Tt/N elapses. First, the already measured X n=
and discard Xl. Another newly sampled V
Let out be Xn. Assuming that there is no significant signal when 1Xn-X+l≦Δ, the difference between the maximum value of Xn-t to Xt and xl is extracted as y, and this is taken as the noise level. Next, y and m are compared in size, and the larger one is set as the new m.

When the time T has elapsed, m is substituted into M, and is used as the noise level corresponding amount in the next section.

In the embodiment, control of the air cleaner 30 has been described as an example, but the detection may be used for any purpose.

[Effects of the Invention] In the present invention, an amount corresponding to the noise level of the gas sensor is determined, and the detection signal and the noise are separated according to this amount.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a basic embodiment, and FIG. 2 is a characteristic diagram thereof. FIG. 3 is a circuit diagram of another embodiment, FIG. 4 is an operation flowchart thereof, and FIG. 5 is a characteristic diagram thereof. FIG. 6 is a circuit diagram of a main part of still another embodiment, FIG. 7 is an operation flowchart thereof, and FIG. 8 is a characteristic diagram thereof. FIG. 9 is an operation flowchart of a modified example, and FIG. 10 is a characteristic diagram thereof. In the figure, 4 gas sensor, 12.13 microcomputer.

Claims (8)

[Claims] (1) In a device configured to detect gas based on the gas sensor output, a means is provided to determine an amount corresponding to the noise level of the gas sensor output, and the determined amount corresponding to the noise level is set as the lower limit value of the significant signal of the gas sensor output. A gas detection device characterized by: (2) In the device according to claim 1, the gas detection device compares the sensor output with a reference value to obtain a gas detection signal, and the gas detection device corresponds to the determined noise level. A gas detection device, characterized in that it is provided with means for correcting a reference value according to the amount. (3) In the device according to claim 1 or 2, a means is provided for determining that the sensor output is due to noise since the duration of the sensor output is less than or equal to a predetermined time. A gas detection device characterized by: (4) In the device according to claim 3, means for storing a noise level corresponding amount of the gas sensor output, means for determining the frequency at which noise of a magnitude greater than the noise level corresponding amount occurs, and this frequency is 1. A gas detection device comprising: means for correcting a noise level correspondence amount so that it becomes approximately constant. (5) A gas detection device according to claim 3, further comprising noise level detection means. (6) In the apparatus according to claim 4 or 5, means is provided for setting the obtained noise level corrected by a predetermined tolerance as a reference value for gas detection. Features: Gas detection device. (7) The gas detection device according to claim 2, wherein the reference value is determined based on past gas sensor outputs. (8) A gas detection device according to claim 7, characterized in that the noise level corresponding amount is separated from the reference value as a variable.