JPH09178687A - Gas detection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an apparatus whose thermal response speed is large and whose gas detection accuracy is high by providing a circuit which obtains a computing output in such a way that an adjusted output voltage and a voltage at a connection point between elements in an element-connected body are added or subtracted. SOLUTION: A gas detection apparatus is provided with a circuit in which a first series- connected body by a gas detection element D, by a compensation element C and by at least one addition resistance 14 and a power supply E are connected in parallel or with a circuit wherein a second series-connected body whose ratio of resistance values is identical to that of the first series-connected body and in which resistances are connected in series and a power supply E are connected in parallel. In the former circuit, a voltage which is generated in the addition resistance 14 is amplified by a differential amplifier 31 or it is divided by a variable resistance 15 so as to be added to, or subtracted from, a voltage at a connection point X between elements by a computing circuit 21. In the latter circuit, the difference between a voltage generated in the addition resistance 14 and a voltage generated in the resistances of the second series-connected body is amplified so as to be added to, or subtracted from, a voltage at a connection point X between elements by a computing circuit 21, and the temperature of the voltage at the connection point X between the elements is corrected.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to city gas, LP
The present invention relates to a gas detection device for incomplete combustion detection provided in a water heater or the like that uses gas or kerosene as fuel.

[0002]

2. Description of the Related Art When a water heater or the like using city gas, LP gas or kerosene as a fuel is incompletely burned, a toxic gas such as carbon monoxide gas is generated, which may cause a gas poisoning accident. In order to prevent such an accident, it is effective to install a carbon monoxide gas sensor in the flue of the water heater to quickly detect carbon monoxide gas.

When carbon monoxide gas is detected in the flue of a water heater, it is sufficient if the gas can be detected for a carbon monoxide gas concentration of about 3000 ppm, and the detection limit concentration is 50 ppm, which is highly sensitive and expensive. A carbon gas sensor may be used,
Since the cost is wasted, a catalytic combustion gas sensor, which is a combustible gas sensor for home use, is often used. The temperature range covered by a catalytic combustion gas sensor for home use is -20.
~ 40 ℃, but the temperature range when applied to the water heater is
It is as high as 70-230 ℃, and it is wide area. This temperature range exceeds the temperature compensation range of the pair of gas detection element and compensation element incorporated in the catalytic combustion gas sensor, and the temperature compensation becomes insufficient. In order to enable gas detection even in this temperature range, a temperature measuring element for detecting gas temperature is additionally provided, and its output and the output of the bridge circuit are calculated to perform temperature correction. When the resistor forming the gas detecting element and the compensating element is platinum, a small platinum thin-film resistor for general temperature measurement is used as a temperature measuring element having the same temperature coefficient as those. The gas detecting element, the compensating element, and the temperature measuring element are installed close to each other in the flue of the water heater so that no temperature difference occurs between the elements.

FIG. 13 is a temperature correction gas detection circuit diagram of a conventional high temperature gas detection device. Gas detection element D and compensation element C
In addition to the normal bridge circuit in which the series connection body of, the series connection body of resistors 11 and 12, and the power supply E are connected in parallel,
A series connection of S and resistor 13 is connected in parallel to form a high temperature bridge circuit. Connection point between gas detection element and compensation element
The voltage at X is Vx, the voltage at the connection point Y of the resistors 11 and 12 is Vy, and Vx-Vy when there is no detection gas is called the zero point output.
Since the temperature coefficients of the resistances of the gas sensing element and the compensating element are not completely the same, the zero point output becomes non-zero when the ambient temperature of the element becomes high, that is, it has a temperature dependence. If the zero-point output is properly amplified by the differential amplifier 32 to V41, V41 is the voltage Vz at the connection point Z between the temperature measuring element S and the resistor 13.
It can be made equal to the temperature dependence of (the temperature signal corresponding to the ambient temperature). If the arithmetic circuit 22 calculates the difference between V41 and Vz (the sum when they have different signs), its output has an offset but has no temperature dependence. Therefore, when the flammable gas comes into contact with the gas detection element, only the gas detection signal is obtained as the variation value.

[0005]

In the above temperature correction method, even if the third element (temperature measuring element) is installed close to the gas sensor, it is difficult to avoid the temperature nonuniformity of the three elements, and the temperature correction is performed. The accuracy of is not high. Further, since the platinum thin film resistor used as the temperature measuring element has a large heat capacity as compared with the gas detecting element, the thermal response speed of the temperature measuring element is small and temperature compensation is sufficiently performed to start the gas detecting operation. There was a problem that it took time to get there. Further, the increase in cost due to the increase in the number of third elements is also a problem.

An object of the present invention is to solve the above-mentioned problems, and to provide a gas detection device having a high thermal response speed and sufficient temperature correction and high gas detection accuracy.

[0007]

To achieve the above object, a series connection body in which one additional resistor is connected to at least one side of an element connection body in which a gas detection element and a compensation element are connected in series, and a power supply. Circuit connected in parallel, a variable resistor for dividing and adjusting output the voltage across the additional resistance or a differential amplifier for amplifying and adjusting output, and the adjusted output voltage and the element connection A gas detection device having a calculation circuit for adding or subtracting a voltage at a connection point between elements to obtain a calculation output, wherein when the detection gas is not in contact with the gas detection element and the compensation element, the calculation output is 2 above
The voltage division ratio of the variable resistor or the amplification factor of the differential amplifier is adjusted so as not to depend on the ambient temperature of the element.

In this case, it is preferable that the series connection body has additional resistances having the same resistance value connected to both sides of the element connection body. Alternatively, a circuit in which a power source is connected in parallel with a series connection body in which an additional resistance having an equal resistance value is connected to both sides of an element connection body in which a gas detection element and a compensation element are connected in series,
A variable resistor for dividing and adjusting and outputting the voltage across the element connection body or a differential amplifier for amplifying and adjusting and outputting, and a voltage at a connection point between the adjustment output voltage and the element of the element connection body. A gas detection device having a calculation circuit that adds or subtracts to obtain a calculation output, wherein the calculation output depends on the ambient temperature of the two elements when the detection gas is not in contact with the gas detection element and the compensating element. In order not to do so, the voltage division ratio of the variable resistor or the amplification factor of the differential amplifier is adjusted.

Alternatively, the first series connection body in which one additional resistor is connected to at least one side of the element connection body in which the gas detection element and the compensating element are connected in series and the element connection body are regarded as one resistance. The same number of resistances as the resistances in the first series connection body are connected, and the ratio of these resistance values is the resistance value of the additional resistance in the first series connection body and the resistance of the gas detection element and the compensation element at the reference temperature. A second series connection body having a ratio equal to the sum of the values, a circuit in which power supplies are connected in parallel, a voltage at a connection point between the additional resistance of the first series connection body and the element connection body,
Variable resistance for amplifying and adjusting output by dividing the difference between the resistance of the ratio corresponding to the resistance of the first series connecting body of and the voltage at the connection point of the other resistance. A differential amplifier and a calculation circuit for adding or subtracting the adjusted output voltage and the voltage at the connection point between the elements of the element connection body to obtain a calculation output. When the element and the compensating element are not in contact,
The voltage division ratio of the variable resistor or the amplification factor of the differential amplifier is adjusted so that the calculation output does not depend on the ambient temperature of the two elements.

In this case, it is preferable that the first series connection body has additional resistances having the same resistance value connected to both sides of the element connection body. Alternatively, a first series connection body in which one additional resistance having the same resistance value is connected to both sides of the series connection of the gas detection element and the compensation element and three resistances are connected in series. A second series having the same ratio to the sum of the resistance value of the resistance in the first series connection body and the resistance value of the gas detection element and the compensation element at the reference temperature, and the resistance value of the other resistance in the same order. A circuit in which a connection body and a power supply are connected in parallel, and a connection between two elements of the second series connection body corresponding to the voltage at each connection point of the element connection body of the first series connection body and the additional resistance. Two arithmetic circuits for subtracting the voltage at the point, a variable resistor for dividing and adjusting and outputting the output difference of the arithmetic circuit, or a differential amplifier for amplifying and outputting for adjustment, and the adjusted output voltage and the element The voltage at the connection point between the elements of the connection body is added to or subtracted from the calculation output A gas detection device having an arithmetic circuit for controlling the variable resistance so that the arithmetic output does not depend on the ambient temperature of the two elements when the detection gas is not in contact with the gas detection element and the compensation element. The pressure ratio or the amplification factor of the differential amplifier is adjusted.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a gas detection circuit diagram of one additional resistor in which the voltage across the additional resistor according to the present invention is used for temperature compensation. (A) shows a case where the voltage is divided, and (b) shows This is the case where the voltage is amplified. FIG. 2 is a gas detection circuit diagram of two additional resistors that use the voltage across the additional resistor according to the present invention for temperature correction. (A) shows a case where the voltage is divided and (b) shows a case where the voltage is amplified. .

In FIG. 1, one additional resistor 14 is connected to one side of a series connection (hereinafter referred to as an element connecting body) of the gas detection element D and the compensating element C, and in FIG. 2, two additional resistors 14 and an element connecting body are connected. The power supply E is connected in parallel to these series connections. Additional resistor 14 and power supply
The voltage at the connection point (earth) of E is set to 0. Let X be the connection point between the two elements and Vx be the voltage at X. Also, additional resistance
The connection point between 14 and the element is Xd, and the voltage of Xd is Vd. A current is flowing in the element, and the element temperature is always higher than the ambient temperature. In FIG. 1 (a), the fixed resistor side of the variable resistor 15 is connected in parallel to the additional resistor 14. The voltage division ratio of the variable resistance terminal of variable resistance 15 is K11. The divided voltage is added or subtracted from Vx by the arithmetic circuit 21, and the output is V11. Figure
In 1 (b), the voltage across the additional resistor 14 is amplified by the differential amplifier 31 with the amplification factor A1 and this output voltage is calculated by the arithmetic circuit 21.
Add or subtract to Vx and set the calculated output as V12. Similarly, in Fig. 2, the voltage division ratio is K21, the output is V21, and the amplification factor is A2.
2 、 Calculation output is V22. In the circuit of Fig. 2, Vx has no offset with respect to 1/2 of the power supply voltage, and in the circuit of Fig. 1, there is an offset due to the additional resistance.

FIG. 3 shows the voltage across the two elements according to the present invention.
FIG. 2 is a gas detection circuit diagram of two additional resistors used for temperature compensation, where (a) is a case where the voltage is divided and (b) is a case where the voltage is amplified. In Fig. 3 (a), the fixed resistor side of the variable resistor 15 is connected in parallel to both ends Xc and Xd of the element connection body, and the voltage division ratio at the variable resistor terminal of the variable resistor 15 is K23,
The divided voltage is added to or subtracted from Vx by the arithmetic circuit 21, and the arithmetic output is V23. In Fig. 3 (b), the voltage at both ends Xc and Xd of the element connection body is set to A2 by the differential amplifier 31.
It is amplified by 4, and this amplified output is added or subtracted from Vx by the arithmetic circuit 21, and the output is set as V24.

Although the six cases have been described above, the methods for temperature correction have almost the same form, so they will be described in unification. Since a voltage is applied to these elements as in a normal bridge circuit and a current is passed through them, the element temperature is higher than the ambient temperature.
When the ambient temperature of the gas sensing element D and the compensating element C is the reference temperature (room temperature or 25 ° C), the resistance values are Do and Co, and their temperature coefficients are d and c, respectively. And the resistance of the element at that time is D, C
And The voltage of the power supply E is set to 1 for the sake of clarity of the formula. Do and Co are around several Ω. The resistance value r of the additional resistance is set so that the additional resistance and variable resistance do not significantly reduce the gas sensitivity.
Is about 1/10 of the resistance value of the element, and the fixed resistance value Rv of the variable resistor 15 is larger than the resistance value of the element by two digits or more. The input resistance of the differential amplifier and the arithmetic circuit is high.

Equation 1 shows the resistance value of the series connection of each element and additional resistance, Equation 2 shows the voltage at each connection point, and Equation 3 shows the voltage after calculation. However, the approximation by Rv >> D and C is performed.

[0016]

[Equation 1] Resistance value of gas detection element D ≡ Do * (1 + d * T) Resistance value of compensation element C ≡ Co * (1 + c * T) 1 resistance and series resistance value of 2 elements Rt1 ≡r + C + D 2 resistance and series resistance value of 2 elements Rt2 ≡2r + (C + D) * Rv / (D + C + Rv) ≒ 2r + C + D

[0017]

[Equation 2] Voltage at connection point Xc Vc = r / Rti Voltage at connection point X Vx = (r + D) ti Voltage at connection point Xd Vd = 1-r / Rt Rti is Rt1 (i = 1 for 1 resistance) ) Or Rt2 (for two resistors i =
2)

[0018]

[Equation 3] 1 resistance V11 = Vx-K11 * Vd = ((1-K11) * r + D) / Rt1 V12 = Vx-A11 * Vd = ((1-A11) * r + D) / Rt1 For 2 resistors V21 = Vx-K21 * Vd = (1-K21) * (r / (1-K21) + D) / Rt2 V22 = Vx-A22 * Vd = (1-A22) * (r / (1 -A22) + D) / Rt2 V23 = Vx- (K23 * (Vc-Vd) + Vd) =-K23 + (2 * K23 * r + D) / Rt2 V24 = Vx-A24 * (Vc-Vd) =- A24 + ((1 + A24) * r + D) / Rt2 All of the above formulas are in the form of constant + (M * r + D) / Rt, and temperature compensation is possible if the temperature dependence of the second term is eliminated. is there. The second term is

[0019]

[Formula 4] (M * r + D) / Rt = (M * r + Do + Do * d * T) / (2r + Do + Co + (Do * d + Co * c) T)
The numerator and denominator should have the same temperature dependence, and the following equation can be obtained as M and the voltage after temperature correction.

[0020]

[Equation 5] 1 resistance M = (r * d + (dc)) * Co) * Do / ((Do * d + Co * c) * r) V11 = V12 = Do * d / (Do * d + Co * c) 2 resistance M = (2r * d + (dc)) * Co) * Do / ((Do * d + Co * c) * r) V21 = V22 = r * d / (2r * d + ( dc) * Co) D V23 = -Do * Co * (dc) / (2r * (Do * d + Co * c)) V24 = V23 + 1/2 No voltage is dependent on temperature T. Therefore, it can be seen that the temperature can be corrected in all 6 cases.

In any case, the temperature-corrected voltage includes resistance values Do and Co at the ambient temperature of the element at room temperature, and their temperature coefficient d. Therefore, these values are measured in advance. Need to ask. If these are known, first, the voltage division or the amplification factor is adjusted while actually measuring the corrected voltage so as to obtain the voltage obtained by substituting into Equation 5, and addition or subtraction is determined. Then, the ambient temperature of the gas sensor is raised to a predetermined temperature and it is confirmed that the corrected voltage does not change. As described above, since the temperature can be corrected with high accuracy, the gas detection output has high accuracy. Further, since the temperature can be corrected without using the temperature measuring element, there is no time delay of the temperature correction due to the heat capacity of the temperature measuring element.

Next, a gas detection circuit capable of temperature correction even if only the resistance values of the elements are known and their temperature coefficients are unknown will be collectively described. FIG. 4 is a gas detection circuit diagram in which the difference between the voltage of the additional resistance and the voltage at the connection point of the resistance of another resistance series body according to the present invention is used for temperature correction.
In the case of additional resistance, (b) is the case of 2 additional resistance.

Regarding FIG. 4, in the case of 2 additional resistors (see FIG.
(a)) is explained, but in the case of 1 additional resistance (Fig. 4 (b)
) Can be considered by adding one additional resistor 14 and one resistor 16 respectively, and the formula has the same form. 1 resistor per element connection
First series connection with 14 added, resistor 16 and variable resistor 17
It is a parallel connection circuit of the second series connection body connected to and the power supply E. By adjusting the variable resistor 17, the ratio of the resistance values of the resistor 16 and the variable resistor 17 can be made equal to the ratio of the resistance value of the resistor 14, the element connection body at the reference temperature (room temperature) and the resistor 14. it can. Voltage at the connection points Xd and Zd between resistors 14 and 16
The difference between Vd and Vdo is amplified by the differential amplifier 31, and this is calculated by the voltage Vx at the connection point X between the elements and the calculation circuit 21 and output. Each connection point X when the gas sensor is at the reference temperature
The voltages Vdo and Vco of d and Xc are equal to the voltage of each connection point Zd of the connection body of the resistor, and when the gas sensor is higher than the reference temperature, the voltage Vd of each connection point Xd is different from Vdo and Vco. Therefore, the subtraction Vd-Vdo of each two voltages is 0 at the reference temperature and has a temperature coefficient. Therefore, these can be used to correct the temperature of the voltage Vx at the connection point X of the two elements. The latter voltage is Vxo.

FIG. 5 is a gas detection circuit diagram in which the difference between the voltage of the two additional resistors according to the present invention and the voltage at the connection point of two resistors of another resistor series is used for temperature correction. As in Figure 4 (b),
Since it is composed of one series-connected body and a second series-connected body, description thereof will be omitted. In this case, the difference (subtraction) between resistors 14 and 16 connected to the same side of the element is set first, the difference between the outputs is amplified, and the voltage Vx at the connection point between the amplified output and the element is increased. And add or subtract.

Equation 6 shows only the calculation results of the temperature correction in the above three cases. Since each amplification factor A3j (j = 1 to 3) includes M in the same format as described above, it is not shown.

[0026]

[Equation 6] V31 = Vx-A31 * (Vd-Vdo) V32 = Vx-A32 * (Vd-Vdo) V33 = Vx-A33 * (Vd-Vc-Vdo-Vco) As can be seen from Equation 6, V3j ( The second term of j = 1 to 3) is equal to Vxo if the ambient temperature of the device is the reference temperature. Since Vxo does not include the temperature coefficient of the resistance of the element, temperature correction can be performed even if the temperature coefficient is unknown.

The circuit is adjusted as follows. First, the ambient temperature of the device is set to the reference temperature (for example, 25 ° C), and the variable resistor 17 is adjusted so that the voltage across it is Vdo and Vc, respectively.
be equal to o. Measure the voltage Vxo between the elements. The element is energized and the temperature of the element is higher than ambient temperature. Next, the ambient temperature of the element is raised to the temperature when the gas sensor is attached to the water heater (for example, 150 ° C), and while measuring Vx, the amplification factor of the differential amplifier is adjusted so that it becomes equal to Vxo. According to the above procedure, the resistance value of the element at the reference temperature may be unknown. As described above, since the temperature can be corrected with high accuracy, the gas detection output has high accuracy. Further, since the temperature can be corrected without using the temperature measuring element, there is no time delay of the temperature correction due to the heat capacity of the temperature measuring element.

The above case is the simplest and basic circuit, and as long as the voltages of Vd and Vc are used for temperature correction, for example,
It is clear that the same principle can be obtained by separately amplifying or dividing the voltages of Vd and Vc and then calculating Vx. It is also clear that the same operation is performed even if the positions of the gas detecting element and the compensating element are exchanged. In addition, a series connection of two resistors is connected in parallel to the power supply of these circuits to make a circuit configuration similar to that of a conventional bridge circuit, and the voltage at the connection point between the resistors is offset canceled by a zero point output or an alarm output is generated. It may be used by applying an offset for the convenience of the user. An embodiment of a gas detection device to which the above basic circuit is applied will be described below. Embodiment 1 FIG. 6 is a gas detection circuit diagram of a gas detection device according to an embodiment of the present invention.

This circuit is a modification of the case where the voltage of one resistance of two additional resistances connected in series with the element (FIG. 2 (b)) is applied to a bridge circuit without a conventional temperature compensation circuit. Since the reference numerals of the connection points including each element have already been described, the description thereof will be omitted. The temperature is corrected as follows. For simplicity of calculation, resistors 11 and 12 are set equal, voltage Vy at Y point is 1/2
It is. First, Vy-Vd is amplified by the differential amplifier 31, and its output and Vx are calculated by the calculation circuit 22 to correct the temperature.
Since Vy is amplified first, the offset voltage Ve1 is
Unlike, it becomes the following equation (see Eq. 6).

[0030]

[Equation 7] Ve1 ≡ Vx-A22 * (Vd-Vy) = V22 + A22 / 2 = V22 + (1-1 / m) / 2 As the gas detection element D, an alumina carrier carrying a palladium catalyst is attached to a platinum coil. The element to which the alumina carrier carrying the copper oxide catalyst was attached as the compensating element C was placed in air at 230 ° C., and the temperature correction ability was examined. The resistance value of the element is about 2 Ω, and the resistance value of the additional resistance is
0.3 Ω, resistance value of balance resistor is 1 kΩ, power supply voltage is 1.
It was set to 1V.

FIG. 7 is a graph of the response of the bridge output of the embodiment of the gas detecting device according to the present invention. The curve a is the temperature-corrected bridge output according to the present invention, and the curve b is the temperature-corrected bridge output using the conventional temperature measuring element measured under the same conditions (the bridge circuit is FIG. 13).
Comparing the 90% response time of the bridge output, the bridge output according to the present invention reached 90% about 6 s after the start of temperature rise, but the conventional bridge output required 5 min. In the case of the present invention, it is only the time until the temperature of the temperature gas detection element having a small heat capacity and the temperature of the compensating element are stabilized, but in the case of the conventional case, it takes time until the temperature of the temperature measuring element having a large heat capacity is stabilized. Because they are doing it.

FIG. 8 is a graph showing the ambient temperature dependence of the difference between the output in the high temperature steady state and the output at 25 ° C. in the example according to the present invention. The curve c is the case where the temperature is corrected according to the present invention, the curve d is the case where the conventional temperature is corrected, and the curve e is the case where the temperature is not corrected. The curve without temperature correction deviates greatly from 0 V as the temperature rises, but the curve without temperature correction shows almost no fluctuation at 0 V. In this way, the same temperature correction can be performed only by adding the resistance without adding the temperature measuring element which is conventionally used. Second Embodiment FIG. 9 is a gas detection circuit diagram of a gas detection device according to another embodiment of the present invention.

This is a modification of the case of the above-mentioned two additional resistors and voltage division across the element (FIG. 3 (a)), and is combined with the conventional bridge circuit. Variable resistor for temperature compensation 15
The voltage of the variable contact P and the voltage Vy of the connection point Y of the resistors 11 and 12 are calculated by the calculation circuit 21, and then this output and the voltage Vx of the connection point X between the elements are calculated in the same manner. Variable contact for temperature compensation
It is determined only by the P position and does not depend on the order of the two operations. The voltage Vy at the connection point Y of the resistors 11 and 12 is only the offset voltage added to the zero point output, and when the circuit configuration is one power supply.
This is to prevent an output with a different sign from that of the power supply (positive in the case of Fig. 9). Since Vy is added to V23, the output voltage Ve2 is given by the following equation.

[0034]

[Equation 8] Ve2 ≡ Vx- (K23 * (Vc-Vd) + Vd-Vy) = V23 + Vy By changing the position of the variable contact P, the sign of the temperature coefficient of the voltage of the variable contact P can be arbitrarily changed. You can Therefore, the arithmetic operation of the arithmetic circuit 21 can be limited to the subtraction circuit which requires only one differential amplifier, regardless of the magnitude of the temperature coefficient of resistance of the gas sensing element and the compensating element to be combined.

The total resistance of the variable resistor 15 was set as high as 10 kΩ so as not to affect the current flowing through the device, and the temperature correction ability of this circuit was examined in the same manner as in Example 1 except for the above. FIG. 10 is a graph of output responsiveness of another embodiment according to the present invention. The curve f is the temperature-corrected output according to the present invention, and the curve b is the conventional temperature-corrected output measured under the same conditions (the bridge circuit is FIG. 14). The bridge output according to the present invention reached 90% in about 6 s after the start of temperature rise, but the conventional temperature-corrected output requires 5 min. In the case of the present invention, it takes a short time until the temperatures of the temperature gas detection element having a small heat capacity and the compensating element become stable, but in the conventional case, it takes time until the temperature of the temperature measuring element having a large heat capacity becomes stable. Because they are doing it.

FIG. 11 is a graph of the ambient temperature dependence of the difference between the output at high temperature steady state and the output at 25 ° C. according to another embodiment of the present invention. The curve g is the case where the temperature is corrected according to the present invention, the curve d is the case where the conventional temperature is corrected, and the curve e is the case where the temperature is not corrected. The curve without temperature correction deviates greatly from 0 V as the temperature rises, but the curve without temperature correction shows almost no fluctuation at 0 V. In this way, it is possible to achieve the same degree of temperature correction only by adding a resistance without loading a temperature measuring element that has been conventionally used. Third Embodiment FIG. 12 is a gas detection circuit diagram of a gas detection device according to another embodiment of the present invention.

In this embodiment, the case where the voltage across the element is divided by the above-mentioned two additional resistors (FIG. 6 (b)) is adapted to the conventional bridge circuit. First, the variable resistor 17 was adjusted to equalize the voltages at the connection point Xc and the connection point Zc. Next, when the amplification factor of the differential amplifier is maximized and the ambient temperature of the two elements is the reference temperature, the ratio of the resistance values of the resistor 11 and the variable resistor 12 is set to the sum of the resistance values of the compensating element and the resistor 14 and the gas detection. The resistance value of the variable resistor 12 was adjusted so that it became equal to the ratio of the sum of the resistance values of the element and the resistor 14, that is, the voltages of the two output terminals O became equal. Then raise the ambient temperature of the element to the same as when it was installed in the actual water heater (for example 150 ° C) and use the two output terminals.
The amplification factor of the differential amplifier 31 was adjusted so that the potential difference between O 2 was 0.

The temperature correction ability of the adjusted gas detection circuit was examined. The temperature correction ability of the adjusted gas detection circuit was examined by changing the ambient temperature of the element from the reference temperature to a temperature higher than the adjustment temperature of the amplification factor. However, as in FIG. 8 of Example 1, the variation was extremely small. As described above, the feature of this circuit is that the temperature correction can be adjusted even if the resistance values of the elements and their temperature coefficients are unknown. Therefore, it is not necessary to measure these with high accuracy in advance, and the manufacturing process of the gas detection device is speeded up.

[0039]

According to the present invention, a circuit in which a power source is connected in parallel with a series connection body of a gas sensing element, a compensating element and at least one resistor, or a gas sensing element, a compensating element and at least one resistor in series. A gas detector having a circuit in which a power supply is connected in parallel with a series connection body of a connection body and a series connection body of two or three resistors having the same resistance value ratio as that of the series connection body. In the former circuit, the resistance connected to the element is used. Amplifies or divides the voltage generated at, and adds or subtracts from the voltage at the connection point of the element, and in the latter circuit, amplifies the difference between the voltage generated at the resistance connected to the element and the voltage generated at the resistance of the series connection of the resistance, Since the temperature of the voltage at the connection point of the element is corrected by adjusting the voltage at the connection point of the element, the temperature correction accuracy is good and the gas detection accuracy is high. Further, since the temperature measuring element is not used, the temperature does not become slower than the temperature response speed of the element itself, the gas can be detected almost at the same time as the start of combustion of the water heater, and the safety regarding incomplete combustion of the water heater is improved. .

Further, since the temperature measuring element is not required, the gas sensor portion may be composed of two elements, a gas detecting element and a compensating element, which is simple and inexpensive.

[Brief description of the drawings]

FIG. 1 is a diagram showing a gas detection circuit of an additional resistance, in which the voltage across the additional resistance according to the present invention is used for temperature correction, (a) When the voltage is divided, (b) When the voltage is amplified.

FIG. 2 is a gas detection circuit diagram of two additional resistors, which uses the voltage across the additional resistor according to the present invention for temperature correction, (a) voltage dividing, (b) voltage amplifying

FIG. 3 is a gas detection circuit diagram of two additional resistors, in which the voltage across the two elements according to the present invention is used for the temperature compensation of the two additional resistors,
(a) When dividing the voltage, (b) When amplifying the voltage

FIG. 4 is a gas detection circuit diagram in which the difference between the voltage of the additional resistance according to the present invention and the voltage at the connection point of the resistance of another resistance series body is used for temperature correction; (a) 1 additional resistance; In case of additional resistance

FIG. 5 is a gas detection circuit diagram in which the difference between the voltage of two additional resistors according to the present invention and the voltage at the connection point of two resistors of another resistor series is used for temperature correction.

FIG. 6 is a gas detection circuit diagram of a gas detection device according to an embodiment of the present invention.

FIG. 7 is a graph of output responsiveness of an example according to the present invention.

FIG. 8 is a graph of the ambient temperature dependence of the difference between the output in the high temperature steady state and the output at 25 ° C. in the example according to the present invention.

FIG. 9 is a gas detection circuit diagram of a gas detection device according to another embodiment of the present invention.

FIG. 10 is a graph of output responsiveness of another embodiment according to the present invention.

FIG. 11 is a graph of the ambient temperature dependence of the difference between the output at high temperature steady state and the output at 25 ° C. in another example according to the present invention.

FIG. 12 is a gas detection circuit diagram of a gas detection device according to another embodiment of the present invention.

FIG. 13 is a temperature correction gas detection circuit diagram of a conventional high temperature gas detection device.

[Explanation of symbols]

 D Gas detection element C Compensation element S Temperature measurement element E Power supply 11 Resistance 12 Resistance 12a Variable resistance 13 Resistance 14 Resistance 15 Resistance 16 Resistance 17 Variable resistance P Variable resistance variable contact X Connection point of two elements Xd Gas detection element and resistance 13 connection point Xc connection point between compensating element and resistor 14 Zd connection point between two resistors 16 and 17 on gas sensing element side Zc connection point between two resistors 16 and 17 on compensating element Zz temperature measuring element and resistor 13 Connection point Y Connection point of two resistors 11 and 12 21 Arithmetic circuit 22 Arithmetic circuit 31 Differential amplifier 32 Differential amplifier

Claims (6)

[Claims] 1. A circuit in which a power source is connected in parallel to a series connection body in which one additional resistance is connected to at least one side of an element connection body in which a gas detection element and a compensation element are connected in series, and a circuit in which the additional resistance is connected. A variable resistor for dividing and adjusting output of the voltage at both ends or a differential amplifier for amplifying and outputting for adjustment and this adjusted output voltage and the voltage at the connection point between the elements of the element connection body are added or subtracted. A gas detection device having a calculation circuit for generating a calculation output, wherein the calculation output does not depend on the ambient temperature of the two elements when the detection gas is not in contact with the gas detection element and the compensation element. A gas detection device characterized by adjusting a voltage division ratio of a variable resistor or an amplification factor of the differential amplifier. 2. The gas detection device according to claim 1, wherein the series connection body is formed by connecting additional resistors having the same resistance value to both sides of the element connection body. 3. A circuit in which a power source is connected in parallel with a series connection body in which an additional resistance having the same resistance value is connected to both sides of an element connection body in which a gas detection element and a compensation element are connected in series, and the element connection body. A variable resistor for dividing the voltage across both ends of the output for adjustment and output or a differential amplifier for amplifying and outputting for adjustment, and the addition or subtraction of this adjustment output voltage and the voltage at the connection point between the elements of the element connection body. A gas detection device having a calculation circuit for calculating a calculation output, wherein the calculation output does not depend on the ambient temperature of the two elements when the detection gas is not in contact with the gas detection element and the compensating element, A gas detection device, wherein a voltage division ratio of the variable resistor or an amplification factor of the differential amplifier is adjusted. 4. A first series connection body in which one additional resistor is connected to at least one side of an element connection body in which a gas detection element and a compensating element are connected in series, and the element connection body is regarded as one resistance. The same number of resistances as the resistances in the first series connection body are connected, and the ratio of these resistance values is the resistance value of the additional resistance in the first series connection body and the resistance of the gas detection element and the compensation element at the reference temperature. A second series connection body having a ratio equal to the sum of the values, a circuit in which power supplies are connected in parallel, a voltage at a connection point between the additional resistance of the first series connection body and the element connection body, and a second series connection Variable resistor for dividing and adjusting and outputting the difference between the resistance of the ratio corresponding to the resistance of the first series-connected body of the connecting body and the voltage of the connection point of the other resistance or the difference for amplifying and outputting for adjustment. The dynamic amplifier and this adjusted output voltage are added to the voltage at the connection point between the elements of the element connection body. Is a gas detection device having a calculation circuit that subtracts and outputs a calculation output. When the detection gas is not in contact with the gas detection element and the compensation element, the calculation output does not depend on the ambient temperature of the two elements. In addition, the gas detection device is characterized in that the voltage division ratio of the variable resistor or the amplification factor of the differential amplifier is adjusted. 5. The gas detection device according to claim 4, wherein the first series connection body is formed by connecting additional resistors having the same resistance value to both sides of the element connection body. 6. A first series connection body in which one additional resistance having the same resistance value is connected to each side of the series connection of the gas detection element and the compensation element, and three resistances are connected in series. The ratio of one resistance value is equal to the ratio of the resistance value of the resistance in the first series connection member and the resistance value of the gas detection element and the compensating element at the reference temperature, and the ratio of the resistance values of the other resistances. Two
, A circuit in which power supplies are connected in parallel, two resistors of the second series connection body corresponding to the voltage at each connection point of the element connection body of the first series connection body and the additional resistance. And two differential circuits for subtracting the voltage at the connection point, a variable resistor for dividing and adjusting and outputting the output difference of the arithmetic circuit, or a differential amplifier for amplifying and outputting for adjustment, and the adjusted output voltage. And a voltage at a connection point between the elements of the element connection body are added to or subtracted from each other to obtain a calculation output, which is a gas detection device, wherein the detection gas is not in contact with the gas detection element and the compensation element. The gas detection device is characterized in that the voltage division ratio of the variable resistor or the amplification factor of the differential amplifier is adjusted so that the operation output does not depend on the ambient temperature of the two elements.