JPH0785066B2 - Gas detector - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a gas detection device using a metal oxide semiconductor gas sensor.

[0002]

2. Description of the Related Art A gas sensor is heated alternately in a high temperature region and a low temperature region periodically, and C is detected from the output of the gas sensor in the low temperature region.
An apparatus for detecting O gas is known (Japanese Patent Publication No. 53-43320). By the way, the danger of CO is determined by the concentration and time. Nevertheless, there is no known circuit for converting the detection signal of the gas sensor into a signal corresponding to the danger of CO. A technique for averaging the output of the humidity sensor and processing it is known (Japanese Patent Laid-Open No. 58-135445).
However, simply using the average requires a large memory, and processing to the memory is complicated. For example, the past 20
In order to obtain the average value for the points, 20 memories are required, and when 20 points or more have passed, the memories must be sequentially updated. Furthermore, it is necessary to determine in advance how much time the average should be calculated with a simple average. For example, if 20 points of data are read every 1 minute and averaged,
Data older than 20 minutes do not contribute to the average value. To compensate for this, for example, data for the past 40 minutes is averaged. Then, on the contrary, the following problem occurs. For example, it is assumed that the gas concentration is low for the first 20 minutes and the gas concentration is high for the next 20 minutes. In the case of the average of 40 minutes, the average gas concentration appears lower than in the case of the average of 20 minutes.

[0003]

The present invention is (1) a simple circuit, (2) it is not necessary to consider the width of the time taken in the average value, and (3) the gas concentration increases even if the integrated value of the gas sensor output is the same value. (4) It is an object to provide a new kind of average value of the gas sensor output so that a larger value can be obtained when the gas concentration is decreasing than when the gas concentration is decreasing.

[0004]

The present invention relates to a gas detection device provided with a metal oxide semiconductor gas sensor and an AD converter for converting the output of the gas sensor into a digital quantity, which includes an AD
An arithmetic circuit for processing the output of the converter is provided, and this arithmetic circuit adds a value obtained by multiplying the output of the arithmetic circuit by a number between 0 and 1 and the output of the AD converter to a new arithmetic circuit. The gas detection device is characterized in that the loop stored as the output of is repeated in a predetermined cycle.

In the embodiment, the detection of CO is shown as an example.
It can also be used to detect other gases. In the embodiment, the output of the gas sensor is AD-converted as it is, and the AD is converted by the arithmetic circuit.
I tried to add the output of the converter as it is.
Processing such as exponentiation may be performed before D conversion or between AD conversion and calculation. To add the output of the AD converter in the present invention means to add the values using the increasing function of the gas sensor output. Further, the value by which the output of the arithmetic circuit is multiplied can be arbitrarily set between 0 and 1, and in principle, a constant may be used, and a plurality of constants may be selectively used for convenience of calculation. The output of the AD converter is sampled and calculated at a predetermined interval, and the sampling interval is basically constant, but may be variable or may be changed depending on the case. This arithmetic circuit may be a part of a microcomputer or may be realized by software.

[0006]

An example of the present invention is shown in FIG. When the AD converter output is P, the number r between 0 and 1 is added to the data stored in the arithmetic circuit every time P is sampled once.
To reduce the weight. The converter output P is added to this value and stored as new data in the arithmetic circuit. Here, n = 0 represents the present, n represents the process n times before, and n repeats the process loop from 0 to infinity. By updating the stored value of the output of the arithmetic circuit in this manner, a new type of average value (convolution) of the gas sensor output can be obtained.
At this time, the already stored data is repeatedly processed by multiplying the number r between 0 and 1, so in the previous process,
Since the data has a weight of r ¹ and the data n times before is multiplied by r ⁿ , the weight naturally becomes smaller for older data. As described above, since the weight of the past data contributes to the average value while the weight thereof is gradually reduced, it is not necessary to consider the time width when obtaining the average output of the gas sensor. Here, from n = 0 to infinity, for example, but the convolution may be reset once when the gas sensor output continuously shows a small value. The value of r can be set arbitrarily, and the value may be different depending on n.

FIG. 2 shows an example of the sensor output and the convolution output when gas is temporarily generated. Since the sensor output is sampled at a predetermined interval, the stored past data is multiplied by r, and new data is added,
Even when the sensor output sharply increases as shown in the figure, the compensation output gradually increases. Next, when the sensor output sharply decreases, the past data gradually decreases due to the weighting factor of r, and the convolution output gradually decreases. By convolution, the noise of the gas sensor output can be removed.

FIG. 3 shows an example of a waveform diagram when the sensor output gradually decreases and when it gradually increases. These convolution outputs are shown in FIG. The dotted line waveform in FIG. 3 also corresponds to the dotted line waveform in FIG. 4, and the solid line in FIG. 3 also corresponds to the solid line in FIG. When the sensor output of FIG. 3 is integrated, both integrated values become equal, but in convolution, a larger output is obtained when the sensor output increases, that is, when the gas concentration increases than when it decreases. This is because the stored past data is multiplied by r and the newly obtained data is added to this, so that the convolution output increases as the latest data value increases. Also, this convolution does not diverge unlike mere integration.

When the arithmetic circuit of the present invention is implemented as a microcomputer, only one memory needs to be allocated to calculate the convolution output. Simply averaging the data of the past n points requires n memories,
It is necessary to rewrite the memory each time data is taken in. However, according to the present invention, since the contents of the memory are multiplied, the data obtained each time is added, and the result is stored again in the memory, there is no process corresponding to the rewriting or rearranging of the memory. The present invention has a simple processing algorithm, and can therefore be implemented by a simple arithmetic circuit.

[0010]

EXAMPLES Examples of the CO gas detector will be described below with reference to numerical examples, but the present invention is not limited thereto. Although only a circuit block diagram is shown in FIG. 5, a specific circuit can be easily designed from the following description.

In FIG. 5, 2 is a timer, 4 is a heater control power source consisting of an output variable stabilizing power source with two-stage output, G
S is a sensor circuit, which is a gas sensor 10 including a heater 6 and a metal oxide semiconductor 8 in which a small amount of Pd catalyst is added to SnO2, a protective resistor R1 and an operational amplifier 12, and an inverter 14 for inverting the polarity of a detection signal. Consists of.

AD is an AD converter and comprises a comparison circuit 16, an AND circuit 18, a counter 20, and a DA converter 22. The AD converter AD uses at least 2 bits, here 7 bits. Also counter 2
The strobe input En of 0 resets the counter 20 when the signal T1 changes from off to on, continues counting while it is on, and holds the output while it is off.

An arithmetic circuit 24 stores the output of the adder circuit 26 in the shift register 28, feeds it back to the augend input A of the adder circuit 26 via the multiplier circuit 30 which operates by the signal T2, and outputs it by the signal T3. The outputs of the AD converter AD are added.

Next, a decoder 32 is operable by the signal of the OR circuit 34, and is an output of the arithmetic circuit 24. The ventilation fan 36 as a detection load, the LED 38, the buzzer 40,
The solenoid valve 42 for shutting off the fuel is operated. A display circuit (not shown) is provided on the output side of the arithmetic circuit 24 to reduce CO
The integrated value of the concentration may be directly displayed. The operation of this device will be described below with reference to FIG.

As shown in FIG. 6, the timer 2 has, for example, 15 timers.
It operates in a cycle of 0 seconds and emits a heat cleaning signal TH for the first 60 seconds to heat the sensor 10 to, for example, 300 ° C. The sensor 10 is kept at, for example, 80 ° C. for the next 90 seconds, and at this temperature, the electrical conductivity δs of the sensor 10 is proportional to the CO concentration (Pco). The electric conductivity δs is converted into an electric signal by the operational amplifier 12, and after having the polarity by the inverter 14, it becomes an output proportional to the CO concentration.

The AD converter AD converts the output of the inverter 14 into a digital value by the signal T1 of the timer 2 immediately before the end of one cycle, for example. The conversion standard is, for example, C
O20ppm as threshold level, CO0
Output is 0 at ~ 20ppm, output 1 at 20 ~ 40ppm, and 1 digit is added every 20ppm. Next, the multiplication rate r of the multiplication circuit 30 is set to 7/8. In addition, the sampling number n is indicated as 0 at present, 1 as before, and n as n before. Then, the output L of the arithmetic circuit 24
Is given by n = ∞ L = ΣPco · r ^{+ n} n = 0. Then, by the digital output corresponding to the output L, as an example here, the ventilation fan 36 and the light emitting diode 38 at 10, the buzzer 40 at 25, and the solenoid valve 4 at 35.
2 works.

Next, the conditions for determining various parameters will be described. Here, assuming that the buzzer 40 is the center of detection, the operating condition of the buzzer 40 means the allowable upper limit level of the instantaneous value of the CO concentration during the duration of the CO concentration of about the sampling interval. Then, this density is calculated by the 1-digit weight of the output of the AD converter AD and the arithmetic circuit 24.
It is determined by the product of the number of digits of the output of
Each digit is 1 digit and the buzzer 40 sounds at 25 digits, which corresponds to 500 ppm. The preferred range of variation of this concentration is 300 to 1000 ppm, more preferably 400 to 700 ppm.

Allowable level N for long-term average CO concentration
Is the permissible level M of the instantaneous CO concentration and the multiplication rate r
And the threshold level Q for the AD converter AD to generate the addition signal.

First, when M (1-r) is larger than Q, N
Is approximately equal to M (1-r), and conversely, when M (1-r) is smaller than Q, N is approximately equal to Q. This is because when the CO concentration (Pco) is constant, the up / down counter 22
This is because the output L of 6 becomes almost equal to Pco / (1-r). This is because the first term is Pco and the infinite geometric series with the common ratio r converges to Pco / (1-r). In this example, M is 500ppm, r is 7/8, and Q is 20pp.
Since m is set, N becomes about 60 ppm. The preferable range of deformation to N is 20 to 120 ppm, more preferably 30 to 100 ppm. The size of Q and M (1-r) may be either.

In the embodiment shown in FIG. 5, the output L of the arithmetic circuit 24 is obtained by using the CO concentration Pco. However, an increasing function f (Pco) of Pco such as a power or other Pco minus a predetermined value. Etc. may be used. The output of the arithmetic circuit 24 is not a simple time integration of the CO concentration, but if the time integration is constant as shown in FIG. 3, the output is increased if the CO concentration is increased (FIG. 4). Thus, the second function of the multiplication circuit 30 is to correct the output of the arithmetic circuit 24 according to the risk of CO.

The multiplication circuit 30 can be replaced by a simple shift register (not shown). In this case, for example, the output of the adder circuit 26 is divided into a number of 8 or more and a number of less than 8, the addend of 8 or more is transformed into a number obtained by subtracting 1/8, and the number of less than 8 is left unchanged. It suffices to provide feedback to the adder circuit 26. For example, in binary notation,
(0.1.1.1) remains as it is, (1.0.0.0) becomes (0.1.1.1), and (1.0.0.0.0) becomes (0.1. (1.1.0) is fed back to the adder circuit 26. By doing so, it is possible to perform the approximate multiplication so that the multiplication rate r becomes an intermediate value between 7/8 and 15/16.

[0022]

According to the present invention, the average value of the gas sensor output can be obtained by a simple arithmetic circuit having a multiplication function and an addition function. Also, a small memory is required, and the data processing procedure is simple by repeating a loop of multiplication of stored values of the arithmetic circuit and addition of new data. In the present invention, the weight of old data is gradually reduced, and it is not necessary to consider the average of a specific time range, that is, the time width of averaging. In addition, the present invention provides a weighted average of the current data,
Even if the integrated value of the gas sensor output is the same, a larger output can be obtained when the sensor output is increasing.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of the present invention.

FIG. 2 is a characteristic diagram of the present invention with respect to noise output.

FIG. 3 is a characteristic diagram showing an example of an output waveform of a gas sensor.

FIG. 4 is a characteristic diagram showing convolution output for the waveform of FIG.

FIG. 5 is a block diagram of a CO gas detection device according to an embodiment.

FIG. 6 is an operation waveform diagram of the CO gas detection device according to the embodiment.

[Explanation of symbols]

 2 timer 10 gas sensor AD AD converter 24 arithmetic circuit 26 addition circuit 28 shift register 30 multiplication circuit

Claims (1)

[Claims] 1. A gas detection device provided with a metal oxide semiconductor gas sensor and an AD converter for converting the output of the gas sensor into a digital quantity, wherein an arithmetic circuit for processing the output of the AD converter is provided. The circuit repeats a loop for storing a value obtained by adding the output of the AD converter to the value obtained by multiplying the output of the arithmetic circuit by a number between 0 and 1 as the output of the new arithmetic circuit at a predetermined cycle. A gas detector characterized by being configured.