JP3085449B2 - 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 a gas detector, and more particularly to a gas detector in which the temperature dependency of a gas sensor is corrected.

[0002]

2. Description of the Related Art Conventionally, in a gas detection device using a semiconductor gas sensor, for example, a device shown in FIG. 5 is known which corrects the temperature dependency of the semiconductor gas sensor. In the figure, 1 is an outlet connected to a commercial power supply, 2 is a transformer for transforming the commercial power supply, and 3 is a semiconductor sensor having a semiconductor 3a made of, for example, a metal oxide, a heater 3b, and a detection electrode 3c.
The heater 3b of the semiconductor sensor 3 is connected between one end of the primary winding 2a of the transformer 2 and an intermediate tap thereof, and the detection electrode 3b is connected to the other end of the primary winding via a current-voltage conversion resistor 4a. ing.

In the semiconductor sensor 3, a semiconductor 3a is heated to a predetermined temperature by passing an alternating current through a heater 3b, and a resistance value between the heater 3b and the detection electrode 3c in a reducing gas atmosphere according to the concentration. Changes and a current corresponding to it changes. An alternating current according to the resistance value flows through the semiconductor sensor 3, and the alternating current is converted into an alternating voltage by a current-voltage conversion resistor 4a.

The current-voltage conversion resistor 4a includes a resistor 4
A temperature compensating circuit composed of a series circuit composed of a resistor b and a thermistor 4c and a voltage dividing circuit composed of a series circuit composed of resistors 4d and 4e are connected in parallel to form a detection circuit. An AC voltage appearing at a connection point between the resistors 4d and 4e of the voltage dividing circuit is rectified by a rectifier diode 5 connected to the connection point and smoothed by a smoothing capacitor 6 to form an operational amplifier of a comparator 7. Applied to inverting input.

The AC voltage appearing on the secondary winding 2b of the transformer 2 is rectified by the rectifier diode 8 and smoothed by the smoothing capacitor 9. This DC voltage is divided by a voltage dividing circuit including a resistor 4f, a variable resistor 4g, and a resistor 4h connected between the cathode of the rectifier diode 8 and the other end of the secondary winding 2b. A voltage is taken out from the movable contact of the variable resistor 4g and applied as a reference voltage to a non-inverting input of an operational amplifier constituting the comparator 7. A buzzer B is connected between the cathode of the rectifier diode 8 and the output of the comparator 7, so that the voltage applied to the inverting input of the comparator 7 becomes larger than the voltage applied to the non-inverting input, and the comparison is performed. When the output level of the device 7 becomes L level, it sounds and emits an alarm sound. 10a is a fuse, 10b is a varistor, and 10c is a discharge gap.

In the above-described configuration, when the gas concentration increases, the resistance value of the semiconductor gas sensor 3 decreases and the current flowing through the sensor 3 increases, so that the connection between the sensor 3 and the current-voltage conversion resistor 4a is increased. The voltage at the point increases. And when the gas concentration increases beyond the alarm point,
The voltage applied to the inverting input of the comparator 7 becomes higher than the reference voltage applied to the non-inverting input, and the output of the comparator 7 is inverted to the L level. As a result, the buzzer B starts sounding to warn of a gas leak or the like.

As shown in FIG. 6, the semiconductor gas sensor 3 generally has a temperature dependence in which the resistance value of the sensor changes logarithmically with respect to the temperature. The temperature coefficient of the detection circuit composed of the resistors 4a, 4b, thermistor 4c, and the resistors 4d and 4e is given by
The temperature is corrected in accordance with the temperature coefficient (β constant) of the resistance value of the sensor. Incidentally, the β constant in the case of FIG.
Since it is 0K, in the apparatus of FIG. 5 using a thermistor having a β constant of 3000K, the resistances 4b, 4d and 4e are adjusted to be 860K by adjusting the constants.

[0008]

The temperature dependency of the resistance value of the sensor as shown in FIG. 6 is shown for a menthan gas which has a relatively high heating temperature of a semiconductor type sensor. And the temperature coefficient in the gas are substantially the same, so that it is possible to cope with this by using a detection circuit having a single temperature coefficient.

However, in the case of the temperature dependency of the resistance value of the sensor with respect to carbon monoxide (CO) gas, as shown in FIG. Even at one gas concentration, the temperature dependence of the resistance value of the sensor is not linear, and exhibits a non-linear characteristic. Therefore, if a conventional detection circuit having only a single temperature coefficient is used, there is a problem that correction cannot be performed with high accuracy.

Accordingly, the present invention has been made in consideration of the above-described conventional problems, and has been developed to reduce the temperature dependence of the resistance value of a gas sensor that detects a gas such as CO gas whose temperature coefficient varies greatly depending on the gas concentration between air and gas. It is a main object of the present invention to provide a gas detection device that can perform good correction.

In view of the above-mentioned conventional problems, the present invention also relates to a gas sensor for detecting a gas such as a CO gas having a temperature coefficient that greatly differs depending on not only the gas concentration but also the temperature in air and gas. Another object of the present invention is to provide a gas detection device capable of correcting the dependency with higher accuracy.

[0012]

In order to achieve the above-mentioned main object, a gas detecting apparatus according to the present invention is provided with a gas sensor 3 which has a function of detecting the ambient temperature dependency of a gas sensor 3 as shown in FIG. In the gas detection device corrected in step 12, a gas detection means 10a-1 for A / D converting and inputting a gas detection voltage of a magnitude corresponding to the gas concentration detected by the gas sensor, and the temperature sensing element A temperature detecting means 10a-2 for A / D converting and inputting a temperature-sensitive voltage of a magnitude corresponding to the detected ambient temperature, and a plurality of gas concentrations corresponding to the magnitude of the gas detection voltage inputted by the gas detecting means. Correction data storage means 1 for storing correction data including a predetermined correction formula and correction coefficient for each of the ranges
0b-1 and correction data reading means 10a-3 for detecting the gas concentration range based on the gas detection voltage and reading predetermined correction data for the detected gas concentration range from the correction data storage means. And a correction calculating means for calculating a corrected gas detection voltage based on the gas detection voltage, the temperature-sensitive voltage, and the correction data read by the correction data reading means.

According to another aspect of the present invention, there is provided a gas detecting apparatus comprising:
A plurality of gas concentration ranges corresponding to the magnitude of the gas detection voltage input by the gas detection means and a plurality of temperature ranges corresponding to the magnitude of the temperature sensing voltage input by the temperature detection means correspond to a range in which the ranges overlap each other. Correction data including a predetermined correction formula and a correction coefficient, and the correction data reading means detects the overlapping range based on the gas detection voltage and the temperature-sensitive voltage. The correction data is read from the correction data storage means, and the correction calculation means determines the gas detection voltage, the temperature-sensitive voltage, and the overlapping range read by the correction data read means. It is characterized by calculating the corrected gas detection voltage by using the corrected data.

[0014]

In the configuration for achieving the above-mentioned main object, the gas detection means 10a-1 outputs a gas detection voltage having a magnitude corresponding to the gas concentration detected by the gas sensor 3 to an A / D converter.
After conversion and input, the temperature detecting means 10a-2
A / D-converts and inputs a temperature-sensitive voltage having a magnitude corresponding to the ambient temperature detected in step 2. Correction data storage means 10b-
Numeral 1 stores correction data including a predetermined correction formula and a correction coefficient for each of a plurality of gas concentration ranges corresponding to the magnitude of the gas detection voltage input by the gas detection means. The reading means 10a-3 detects a gas concentration range based on the gas detection voltage, and reads predetermined correction data for the detected gas concentration range from the correction data storage means. The correction calculation means 10a-4 calculates the gas detection voltage after correction by calculating based on the gas detection voltage, the temperature-sensitive voltage, and the correction data read by the correction data reading means.

Therefore, the corrected gas detection voltage obtained by the correction calculation means 10a-4 is predetermined for each of a plurality of gas concentration ranges corresponding to the magnitude of the gas detection voltage inputted by the gas detection means. Since it is based on the correction data including the correction equation and the correction coefficient obtained, the temperature dependency of the resistance value of the gas sensor for detecting the gas can be accurately corrected even in the case of a gas whose temperature coefficient varies greatly depending on the gas concentration. be able to.

In a configuration for achieving the other object, the correction data storage means 10b-1 is provided with the gas detection means 1b.
A plurality of gas concentration ranges corresponding to the magnitude of the gas detection voltage inputted by Oa-1 and a plurality of temperature ranges corresponding to the magnitude of the temperature sensing voltage inputted by the temperature detecting means 10a-2 are set to overlap each other. On the other hand, correction data including a predetermined correction formula, a correction coefficient, and the like are stored, and the correction data reading means 10a-3 detects the overlapping range based on the gas detection voltage and the temperature-sensitive voltage. Is read from the correction data storage means 10b-1, and the correction calculation means 10a-4 reads the gas detection voltage, the temperature-sensitive voltage, and the correction data read out by the correction data reading means 10a-3. On the other hand, calculation is performed using predetermined correction data to obtain a corrected gas detection voltage.

Therefore, the corrected gas detection voltage obtained by the correction calculation means 10a-4 is predetermined with respect to the gas detection voltage, the temperature-sensitive voltage, and the overlapping range read by the correction data reading means 10a-3. Therefore, even in the case of a gas whose temperature coefficient varies greatly depending not only on the gas concentration but also on the temperature, the temperature dependence of the resistance value of the gas sensor for detecting the gas can be corrected more accurately. .

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a circuit diagram showing an embodiment of the gas detection device according to the present invention. In FIG. 2, an outlet 1, a transformer 2, a semiconductor sensor 3, and a current source connected to a commercial power supply are shown.
The voltage conversion resistor 4a and the connection between them are the same as the conventional one described above with reference to FIG. 5, but in this embodiment,
The heating temperature of the semiconductor gas sensor 3 is set low so that the CO gas can be effectively detected.

The current - voltage obtained by voltage conversion resistor 4a, on which is smoothed by the smoothing capacitor 6 while being rectified by the rectifier diode 5, the input port I ₁ of the controller 10 comprising a microcomputer as a gas detection voltage Applied.

The AC voltage appearing in the secondary winding 2b of the transformer 2 is rectified by the rectifying diode 8 and smoothed by the smoothing capacitor 9, and then stabilized by the constant voltage circuit 11 formed as an IC. . Between the constant voltage circuit 11 and the reference potential point, a series circuit of a temperature sensing element 12 such as a thermistor and a fixed resistor 13 and a variable resistor 1
4 and a series circuit of the fixed resistor 15 are connected. C is a noise removing capacitor.

The voltage at the connection point between the temperature-sensitive element 12 and the fixed resistor 13 changes in accordance with the resistance value of the temperature-sensitive element 12 that changes with the ambient temperature, and is applied to the input port I ₂ of the control unit 10 as a temperature-sensitive voltage. is applied, the voltage is taken out from the movable contact of the variable resistor 14 is applied to the input port I ₃ as an alarm point voltage. Between the output of the constant voltage circuit 11 and the reference potential point, a series circuit of a buzzer B and a switching transistor 16 as a switch is connected. The switching transistor 16 is connected to the output port O of the control unit 10.
ON / OFF control by a signal from

The control unit 10 is a central processing unit (CPU) 1 that performs processing according to a predetermined control program.
0a, a ROM 10b storing various fixed data in addition to the control program, and an RA storing various work areas in addition to an area storing various rewritable data.
M10c. The fixed data stored in the ROM 10b is the data in the air and the gas concentration 300 described above with reference to FIG.
This is correction coefficient data for correcting a sensor resistance value at an arbitrary temperature in ppm to a resistance value at a temperature of 20 ° C. during circuit adjustment.

When the semiconductor gas sensor having the temperature dependency shown in FIG. 7 is applied to the circuit shown in FIG. 2, the gas detection voltage v ₁ applied to the input port I ₁ , which is the output of the rectifier diode 5, becomes A temperature-sensitive voltage v ₂ applied to an input port I ₂ which is a voltage at a connection point between the temperature-sensitive element 12 and the resistor 13.
Changes as shown in FIG.

In the curve in the air in FIG.
The values of the gas detection voltage and the temperature-sensitive voltage at₁₂₀as well as
v₂₂₀Of gas detection voltage and temperature sensing voltage at a temperature of 36 ° C
V₁₃₆And v₂₃₆20 ° C or less, 20 ° C to 36 ° C
And gas detection voltage v above 36 ° C ₁Is the temperature change rate of
₁, A_TwoAnd A_ThreeAnd Due to the above,
The temperature-sensitive voltage v corresponding to the desired temperature (_TwoGas detection power
Pressure v₁Is v₁= V₁₂₀-A ₁(V₂₂₀-V_Two)
It is. Therefore, the temperature-sensitive voltage v corresponding to the arbitrary temperature (_Two)
Gas detection voltage v₁Detection voltage v after correcting
₁′ Is v₁'= V₁+ A₁(V₂₂₀-V_Two).
Where v₁And v_TwoIs the input port I₁And I _TwoKaraso
The voltage value read, v₂₂₀And A₁Is ROM10
Fixed data stored in advance as correction coefficient data in b
It is.

Next, an arbitrary temperature between 20 ° C. and 36 ° C.
Corresponding temperature-sensitive voltage v_TwoGas detection voltage v)₁Is
v₁= V₁₂₀+ A_Twov_TwoIt is represented by Therefore, any temperature
(The temperature-sensitive voltage v corresponding to_TwoGas detection voltage v)₁
Detection voltage v after correcting₁′ Is v₁'= V₁−
A_Twov_TwoBecomes Where v₁And v_TwoIs the input port I
₁And I_TwoVoltage values read from_TwoIs RO
Fixed stored in advance as correction coefficient data in M10b
Data. In addition, it corresponds to an arbitrary temperature of 36 ° C or more.
Temperature voltage v_TwoGas detection voltage v)₁Is v₁=
v₁₃₆+ V₂₃₆+ A_Threev_TwoIt is represented by Therefore, any temperature
Temperature (the temperature-sensitive voltage v corresponding to_TwoGas detection voltage v)
₁Detection voltage v after correcting₁′ Is v₁₃₆-V
₁₂₀= Δv ₁Then v₁'= V₁− (Δv₁+ A_Three
v_Two). Where v₁And v _TwoIs the input port I₁
And I_TwoVoltage value, Δv₁And A
₁Is previously stored as correction coefficient data in the ROM 10b.
Fixed data.

Therefore, the correction equation v ₁ ′ for 20 ° C. or less.
= V ₁ + A ₁ (v ₂₂₀ −v ₂ ) and the correction coefficients v ₂₂₀ and A
₁ is the correction equation v ₁ ′ = v ₁ − for 20 ° C. to 36 ° C.
A ₂ v ₂ and the correction factor A ₂ is and the correction expression for 36 ° C. or higher _{v 1 '= v 1 - (} Δv 1 + A 3 v 2) and the correction coefficient Delta] v ₁ and A ₁ are, in ROM10b It is stored in advance.

A similar correction equation and correction coefficient are given by a gas concentration of 3
Correction for curves in 00 ppm for temperatures below 20 ° C
Equation v₁'= V₁+ A_Four(V₂₂₀-V_Two) And correction factor v
₂₂₀And A_FourAnd correction formula for 20 ° C to 36 ° C
v₁'= V₁-A_Fivev_TwoAnd correction coefficient A_FiveAnd 3
Correction formula v for 6 ° C or higher₁'= V₁− (Δv₁'+ A
₆v _Two) And correction coefficient Δv₁'And A₆And ROM 10b
Is stored in advance. Note that Δv₁'Is a gas concentration of 300
ppm Gas detection voltage v at medium temperature 20 ℃ and 36 ℃₁₂₀′
And v₁₃₆′ (= V₁₃₆'-V₁₂₀')
available.

[0028] In FIG. 3, the temperature sensitive voltage v ₂ and the gas detection voltage v ₁ as shown by black dots are to have been detected, the operation according to the formula v ₁ '= v ₁ -A ₂ v ₂ in the figure The obtained corrected gas detection voltage v ₁ ′ is corrected to a point indicated by an x mark, and it is determined whether or not the gas concentration has reached the alarm level based on the corrected gas detection voltage.

Therefore, the predetermined area (not shown) in the ROM 10b is set to a range where a plurality of gas concentration ranges corresponding to the magnitude of the gas detection voltage and a plurality of temperature ranges corresponding to the magnitude of the temperature-sensitive voltage overlap each other. And serves as correction data storage means 10b-1 for storing correction data including a predetermined correction formula and correction coefficient.

In the above configuration, the CP of the control unit 10
U10a is the input port I ₁ ~I ₃ Gas detection voltage v ₁ which is applied to read by converting the temperature-sensitive voltage v ₂ and alarm point voltage v ₃ into a digital signal at a predetermined timing, the read voltage value Is stored in a predetermined area of the RAM 10c. Thereafter, the following determination processing is performed for each voltage value.

First, the gas detection voltage v₁And predetermined R
The predetermined voltage value v stored in the OM 10b₀Compare with
However, the resistance value of the semiconductor gas sensor 3 is large and v₁<V₀
When the semiconductor gas sensor 3 is air or concentrated,
Judgment that low-level gas is detected, and
The resistance value of the sensor 3 is small and v₁≧ v₀When
Indicates that the semiconductor gas sensor 3 detects a gas having a relatively high concentration.
Judge that it is out. Next, the temperature-sensitive voltage v_TwoBut the temperature is 20
Voltage value v corresponding to ℃ and 36 ℃₂₂₀And v₂₃₆Against
V_Two<V₂₂₀, V₂₂₀≤
v_Two≤v₂₃₆And v ₂₃₆<V_TwoCheck and judge by
I do.

And v₁<V₀And v_Two<V₂₂₀
, The correction equation v₁'= V ₁+ A₁(V₂₂₀−
v_Two) And correction factor v₂₂₀And A₁And the gas after correction by
Detection voltage v₁'. Also, v₂₂₀≤v_Two≤v₂₃₆
, The correction equation v₁'= V₁-A_Twov_TwoAnd correction clerk
Number A_TwoAnd v₂₃₆<V_Two, The correction equation v
₁'= V₁− (Δv₁+ A_Threev_Two) And correction coefficient Δv₁Passing
And A₁And the gas detection voltage v after correction₁′
Ask.

On the other hand, when v ₁ ≧ v ₀ and v ₂ <v ₂₂₀ , the correction equation v ₁ ′ = v ₁ + A ₄ (v ₂₂₀ −
v ₂ ) and the correction coefficients v ₂₂₀ and A ₄ , v ₂₂₀ ≦ v
₂ ≦ v _{23 6} correction equation v ₁ when a '= v ₁ -A ₅ v
The ₂ and the correction coefficients A _5, and v ₂₃₆ <v correction equation when a _{2 v 1 '= v 1 -} (Δv 1' + A 6 v 2)
And the correction coefficient Δv ₁ ′ and A ₆ to obtain the corrected gas detection voltage v ₁ ′.

Gas detection after correction obtained as described above
Voltage v₁'Is the alarm point voltage v in the CPU 10a._ThreeWhen
Be compared. v₁'≧ v_Three, The CPU 10
a indicates that the concentration of the gas detected by the semiconductor gas sensor 3 is
Judging that the level is more than dangerous level, output port O
From the L level to the H level, and the switching transistor
Turn on the heater 16 and supply current to the buzzer B to make it sound and alarm
Generate a beep. v ₁'<V_Three, The CP
U10a is the gas detected by the semiconductor gas sensor 3.
Determines that the concentration has not reached a dangerous level and sounds an alarm.
Elapsed time set in advance without generating
And the above operation is repeated.

The details of the operation outlined above are described in the CPU 1
This will be described below with reference to the flowchart of FIG. CP
U10a starts operation when the power is turned on, and performs initialization in the first step S0. Subsequent step S
1, the gas detection voltage v ₁ applied to the input port I ₁ is A / D converted and read, and the subsequent step S
2 the temperature-sensitive voltage v input to the input port I _2
2 is A / D converted and read, and further subsequent step S
In 3 the alarm point voltage v ₃ which is input to the input port I ₃ read converted A / D, respectively store the voltage value data read at each step in a predetermined area predetermined in RAM 10 c.

[0036] then proceeds to step S4, where the voltage value of the gas detection voltage v ₁ stored in a predetermined area of RAM10c in step S1, compared with the voltage value v ₀ which defines stored in advance ROM 10b, v ₁ determines whether v ₀ is less than or not. Proceed to step S5 when the determination in step S4 is YES, the voltage value v ₂₂₀ which here determined and stored in advance in ROM10b voltage value of the temperature sensitive voltage v ₂ stored in a predetermined area of RAM10b in step S2 To determine whether v ₂ is smaller than v ₂₂₀ . When the determination in step S5 is YES,
That is, when v ₂ <v ₂₂₀ , the process proceeds to step S6, and the corrected gas detection voltage is calculated as v ₁ ′ = v ₁ + A ₁ (v
_After calculating ₂₂₀₋ v ₂ ), the process proceeds to step S7.

When the determination in step S5 is $ O,
That is, v_Two<V₂₂₀If not, proceed to step S8.
Then v_TwoIs v₂₂₀And v₂₃₆Judge whether it is between
Set. If the determination in step S8 is YES,
That, v₂₂₀≤v_Two≤v₂₃₆If step S
Proceed to 9 to set the corrected gas detection voltage to v₁'= V₁-A _Two
v_TwoAnd then proceed to step S7.
No. Also, if the determination in step S8 is ΝO and v₂₂₀≤v_Two≤
v₂₃₆But v₂₃₆<V_TwoWhen step S10
To the corrected gas detection voltage v₁'= V₁− (Δv
₁+ A_Threev_Two) To calculate
Proceed to step S7.

In step S7, the corrected gas detection voltage v ₁ ′ calculated and calculated in steps S6, S9 and S10 is stored in the RAM in step S3.
It determines smaller or not than the voltage value of the alarm point voltage v ₃ which is stored in a predetermined area of 10b. When the determination in step S7 is YES, that is, when v ₁ ′ <v ₃ , the process proceeds to step S11 to switch the output port O from the L level to the H level, and then proceeds to step S12 to perform the predetermined fixed time t. Is determined, and after elapse of a predetermined time, the process returns to step S1 to repeat the above-described operation. When the determination in step S7 is ΝO, that is, when v ₁ ′ <v ₃ is not satisfied, step S11 is skipped and the process proceeds to step S12. After waiting for a predetermined time t, the process returns to step S1 and returns to step S1. Repeat the operation.

If the determination in step S4 is $ O,
That is, in the above-mentioned step S1, the predetermined
Gas detection voltage v stored in area₁The voltage value of RO
Voltage value v stored and determined in M10b₀When greater
Next proceeds to step S13, where the temperature-sensitive voltage v_TwoNo electricity
Pressure value to voltage value v₂₂₀And v_TwoIs v₂₂₀Less than
It is determined whether or not. YES in step S13
, Ie, v _Two<V₂₂₀If it is
Proceeding to step S14, the corrected gas detection voltage is set to v₁'= V₁
+ A_Four(V₂₂₀-V_Two) By calculating
Then, the process proceeds to step S7.

When the determination in step S13 is ΝO,
That is, when v ₂ <v ₂₂₀ is not satisfied, step S16
It determines whether there between then v ₂ is v ₂₂₀ and v ₂₃₆ proceeds to. If the determination in step S16 is YES, that is, if v ₂₂₀ ≦ v ₂ ≦ v ₂₃₆ , the process proceeds to step S17, where the corrected gas detection voltage is set to v ₁ ′ =
v proceeds from seeking by calculating ₁ -A ₅ v ₂ in step S7. Also, if the determination in step S16 is ΝO and v
_{If not 220} ≦ v ₂ ≦ v ₂₃₆ and v ₂₃₆ <v ₂ , the routine proceeds to step S18, where the corrected gas detection voltage is set to v ₁ ′ =
After calculating v ₁ − (Δv ₁ + A ₆ v ₂ ), the process proceeds to step S 7.

As described above with reference to the flowchart of FIG. 4, the CPU 10a operating according to the predetermined program generates the gas detection voltage having the magnitude corresponding to the gas concentration detected by the gas sensor by the process of step S1. It functions as gas detection means 10a-1 for A / D conversion and input. In addition, the processing in step S2 serves as a temperature detection unit 10a-2 for A / D converting and inputting a temperature-sensitive voltage having a magnitude corresponding to the ambient temperature detected by the thermistor 12, which is a temperature-sensitive element.

Further, steps S4, S5, S8, S1
3, the gas concentration range is detected by the gas detection voltage by the processing of S16, and correction data predetermined for the detected gas concentration range is read out from a predetermined area of the ROM 10b, or It functions as a correction data reading means 10a-3 for detecting an overlapping range based on the temperature-sensitive voltage and reading predetermined correction data for the detected overlapping range from a predetermined area of the ROM 10b.

In addition, the CPU 10a determines in step S6
By the processing of S9, S10, S14, S17 and S18, the gas detection voltage, the temperature-sensitive voltage and the read correction data are used to calculate the corrected gas detection voltage, or
It functions as a correction calculation unit 10a-4 that calculates the gas detection voltage, the temperature-sensitive voltage, and the read-out overlapping range by using predetermined correction data to obtain a corrected gas detection voltage. The CPU 10a also compares the corrected gas detection voltage with a predetermined alarm point voltage by the process of step S7, and outputs an alarm signal when the corrected gas detection voltage corresponds to a gas concentration exceeding the gas alarm level. It works as a means of comparison.

The comparing means compares the corrected gas detection voltage with a predetermined alarm point voltage, and detects that the corrected gas detection voltage exceeds the gas alarm level. It can be performed with high accuracy even in the case of a gas whose temperature coefficient varies greatly depending on the temperature. In addition, the buzzer B as an alarm unit can issue an alarm in response to the alarm signal output from the comparison unit with high accuracy. Therefore, not only is it possible to detect that the corrected gas detection voltage has exceeded the gas alarm level, but also to issue an alarm in response to the alarm signal output by this detection, and not only based on the gas concentration but also on the temperature. Even in the case of a gas whose temperature coefficient differs greatly, it can be performed with high accuracy.

In the embodiment described above, the CPU 10a
Detects the overlapping range based on the gas detection voltage and the temperature sensing voltage in the processing of steps S4, S5, S8, S13, and S16, and stores predetermined correction data for the detected overlapping range in the ROM 10b in a predetermined manner. Although reading is performed from the area, the present invention calculates the gas detection voltage after correction by calculating based on the gas detection voltage, the temperature-sensitive voltage, and the read correction data, so that the gas sensor can be used in the air and the CO gas. In addition, the temperature dependency of the resistance value of a gas sensor for detecting a gas whose temperature coefficient varies greatly depending on the gas concentration can be accurately corrected.

However, as in the embodiment, the overlapping range is detected based on the gas detection voltage and the temperature sensing voltage, and predetermined correction data for the detected overlapping range is stored in the ROM 10b.
By reading from a predetermined area of the gas sensor, the temperature of the resistance value of the gas sensor that detects a gas such as in air and CO gas that has a temperature coefficient greatly different not only by gas concentration but also by temperature is used. The dependency can be corrected with higher accuracy.

In the above-described embodiment, an example of a semiconductor gas sensor is shown as a gas sensor having an ambient temperature dependency, and the ambient temperature dependency is corrected by a temperature-sensitive element. As a gas sensor having the same ambient temperature dependency as a gas sensor, there is a gas sensor such as a solid electrolytic gas sensor.

In the embodiment, the correction data storage means includes a plurality of gas concentration ranges directly corresponding to the magnitude of the gas detection voltage and a plurality of temperature ranges directly corresponding to the magnitude of the temperature-sensitive voltage. Correction data including a predetermined correction formula and a correction coefficient for each of the predetermined ranges is stored. However, it does not directly correspond to the magnitude of the gas detection voltage and the temperature-sensitive voltage, but converts the gas detection voltage and the temperature-sensitive voltage once to the resistance values of the semiconductor gas sensor and the thermistor, and directly corresponds to the magnitudes of these resistance values. In addition, correction data including a predetermined correction formula and a correction coefficient for each of a plurality of gas concentration ranges and a plurality of temperature ranges indirectly corresponding to the magnitude of the gas detection voltage and the temperature sensing voltage is stored. You may do so.

[0049] Further, in the above-described embodiment, for determining the gas concentration by the gas detection voltage, one predetermined voltage value v ₀
However, by providing three or more of them, more accurate correction becomes possible. In the three cases, for example, between air and 100 ppm, between 100 ppm and 20 ppm
It is preferable to provide between 0 ppm and between 200 ppm and 400 ppm, respectively.

[0050]

As described above, according to the present invention, a gas detection voltage having a magnitude corresponding to a gas concentration detected by a gas sensor is inputted, and a plurality of gas concentration ranges corresponding to the magnitude of the gas detection voltage are input. From the correction data including a predetermined correction formula and a correction coefficient stored for each, a predetermined value is read out for a gas concentration range detected by a gas detection voltage, and a gas detection voltage, a temperature-sensitive voltage, and Since the corrected gas detection voltage is calculated based on the read correction data, the corrected gas detection voltage is a semiconductor type that detects this even if the gas has a temperature coefficient that greatly differs depending on the gas concentration. The temperature dependency of the resistance value of the gas sensor is accurately corrected.

In particular, the corrected gas detection voltage includes a gas detection voltage, a temperature sensing voltage, a plurality of gas concentration ranges corresponding to the magnitude of the gas detection voltage, and a plurality of temperature ranges corresponding to the magnitude of the temperature sensing voltage. Is based on correction data determined in advance for an overlapping range, which is a range overlapping with each other, so that even in the case of a gas whose temperature coefficient varies greatly depending not only on the gas concentration but also on the temperature, a gas sensor for detecting this is used. The temperature dependency of the resistance value is corrected more accurately.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of a gas detection device according to the present invention.

FIG. 2 is a circuit diagram showing one embodiment of a gas detection device according to the present invention.

FIG. 3 is a graph for explaining a method of correcting a gas detection voltage in a gas detection device according to the present invention.

FIG. 4 is a flowchart illustrating a process performed by a CPU in FIG. 2;

FIG. 5 is a circuit diagram showing an example of a conventional gas detection device.

FIG. 6 is a graph showing the temperature dependence of the sensor resistance of the semiconductor gas sensor with respect to air and methane gas.

FIG. 7 is a graph showing the temperature dependence of the sensor resistance of the semiconductor gas sensor with respect to air and CO gas.

[Explanation of symbols]

 Reference Signs List 3 gas sensor (semiconductor gas sensor) 12 temperature sensing element 10a-1 gas detecting means (CPU) 10a-2 temperature detecting means (CPU) 10a-3 correction data reading means (CPU) 10a-4 correction calculating means (CPU) 10b- 1 Correction data storage means (ROM)

Continuation of the front page (56) References JP-A-4-328459 (JP, A) JP-A-2-232798 (JP, A) JP-A-58-63560 (JP, A) JP-A-2-114164 (JP) JP-A-3-72252 (JP, A) JP-A-63-210652 (JP, A) JP-A-7-260730 (JP, A) JP-A-7-311178 (JP, A) JP-A-4-307295 (JP, A) JP-A-61-181616 (JP, A) JP-A-60-146143 (JP, A) JP-A-5-64762 (JP, A) U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/12 G01N 27/04 G01N 5/00 G01N 27/26 G01N 27/58

Claims (2)

(57) [Claims] 1. A gas detection device in which the ambient temperature dependency of a gas sensor is corrected by a temperature sensing element, wherein a gas detection voltage having a magnitude corresponding to a gas concentration detected by the gas sensor is A / D converted. Gas detecting means for inputting, temperature detecting means for A / D converting and inputting a temperature-sensitive voltage having a magnitude corresponding to the ambient temperature detected by the temperature-sensitive element, and a gas detecting voltage input by the gas detecting means. Correction data storage means for storing correction data including a predetermined correction formula and a correction coefficient for each of a plurality of gas concentration ranges corresponding to the size, and detecting the gas concentration range by the gas detection voltage. ,
Correction data reading means for reading predetermined correction data for the detected gas concentration range from the correction data storage means, and the gas detection voltage, the temperature-sensitive voltage, and the correction data read by the correction data reading means. And a correction calculating means for calculating a corrected gas detection voltage. 2. The apparatus according to claim 1, wherein the correction data storage means is adapted to correspond to a plurality of gas concentration ranges corresponding to the magnitude of the gas detection voltage inputted by the gas detection means and to the magnitude of the temperature sensing voltage inputted to the temperature detection means. A plurality of temperature ranges store correction data including a predetermined correction formula and a correction coefficient for a range where the temperature ranges overlap with each other, and the correction data reading means stores the correction data based on the gas detection voltage and the temperature-sensitive voltage. Detecting an overlapping range, and reading predetermined correction data for the detected overlapping range from the correction data storage means, wherein the correction calculating means includes the gas detection voltage, the temperature-sensitive voltage, and the correction data reading means. And calculating a corrected gas detection voltage by calculating predetermined correction data with respect to the overlapping range read by the method.
The gas detection device according to any one of the preceding claims.