JP3371675B2 - Combustible 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 combustible gas detection device, and more particularly to a combustible gas detection device for detecting a CO (carbon monoxide) concentration in exhaust gas to detect an abnormal condition and operating a predetermined safety device. Regarding the device.

[0002]

[Prior art]

(General Combustible Gas Detection Device) Conventionally, a gas combustion device such as an indoor water heater (FE type) is known, and in such a gas combustion device, a so-called CO sensor is used to measure the CO concentration in the exhaust gas. Is provided and a combustible gas detection device for activating a predetermined safety device is provided.

For example, in the FE type water heater using an AC100V power source, a CO sensor is provided in the exhaust passage of the main body, and the CO sensor measures the CO concentration contained in the exhaust gas to detect an abnormal state. Therefore, the gas supply pipe leading to the gas burner is shut off by the original solenoid valve.

The CO sensor has a so-called catalytic combustion type combustible gas detection element. When the combustible gas detection element touches the exhaust gas of the gas combustion apparatus, heat is generated according to the CO concentration in the exhaust gas, and The CO sensor output (voltage output) Vs corresponding to the change in resistance value is output. When the CO sensor output Vs exceeds a predetermined alarm level Vr, it is determined that the CO concentration in the exhaust gas is in a dangerous state, an alarm signal is output to shut off the gas supply source, and It prevents the poisoning accident from occurring due to carbon monoxide filling.

By the way, since the combustible gas detection device compares a predetermined fixed alarm level Vr with the CO sensor output Vs, it is premised whether the CO sensor output Vs exceeds the alarm level Vr. The 0-point reference value V ₀ , which is the determination reference, that is, CO is not detected (C
It is necessary to accurately set the CO sensor output when the O concentration is 0%), and conventionally, the CO sensor zero point adjustment was performed at the factory shipment stage.

However, even if the CO sensor is adjusted to the zero point at the factory shipment stage, the CO sensor may be adjusted to zero due to vibration, shock, etc. during combustion of the water heater, or due to secular change.
The point reference value V ₀ may deviate from the correct value. In that case, the criterion for determining whether or not the CO sensor output Vs exceeds the alarm level Vr is incorrect, so the actual CO concentration is equal to or higher than the alarm level Vr, but the flammable gas detection device does not reach the alarm level Vr. There is a risk that the safety device will not operate at all.

(Combustible gas detection device having a calibration function for 0-point reference value) Therefore, in the combustible gas detection device disclosed in Japanese Utility Model Laid-Open No. 5-90148, the CO sensor output Vs when the gas burner is not in the combustion state. the stored read as 0 point reference value V _0, 0 point in the CO sensor reference value V ₀
Is calibrated for drift. That is, the CO sensor output Vs is read after a lapse of a predetermined time after the power source is turned on by inserting the power outlet of the gas combustion device, or the CO sensor output Vs is read at every predetermined time while combustion is stopped, or after the gas burner extinguishes a fire. 0 after reading CO sensor output Vs after a lapse of a predetermined time
Set point reference value V _0, and detects an abnormality in the CO sensor by comparing the difference Vs-V ₀ of the sensor output Vs referenced to this value V ₀ and warning level Vr.

[0008]

According to the combustible gas detection device of the 0-point correction method described above, it is possible to periodically correct the drift of the 0-point reference value V ₀ caused by vibration during combustion, aging, or the like. it can. However, if the CO sensor fails, or if water or dust adheres to the CO sensor,
The CO sensor output Vs largely drifts. For this reason,
As described above, when the CO sensor output Vs is read at every predetermined time while the combustion is stopped and the 0-point reference value V ₀ is corrected, an abnormal 0-point reference value V ₀ is set and the gas combustion device There was a risk of poor combustion. On the contrary, even if the gas combustion device is normal, the 0-point reference value V ₀ is abnormal, and therefore the gas combustion device may operate safely and become unusable.

The present invention has been made in view of the drawbacks of the above conventional examples, and its object is to perform a calibration process of a zero point reference value which is a reference of a sensor output from a combustible gas detection element. An object of the present invention is to provide a combustible gas detection device that can be accurately executed.

[0010]

According to a first aspect of the present invention, there is provided a combustible gas detection device for detecting a combustible gas contained in exhaust gas discharged from a gas combustion device having a burner, which is a catalytic combustion type combustible gas. A detection element, a means for storing the 0-point reference value of the output of the combustible gas detection element, and an output of the combustible gas detection element and the storage means when a calibration request for the 0-point reference value is made. When the difference from the existing zero point reference value is abnormally large, the zero point reference value is not calibrated, and the gas combustion apparatus is provided with a drift calibrating means for performing a safe operation.

Whether or not the difference between the output of the combustible gas detection element and the zero-point reference value is abnormally large may be judged by whether or not the difference is a certain value or more, and the fuzzy control is performed. It may depend on whether or not it is judged to be abnormally large in the method.

According to the present invention, the output of the combustible gas detection element is compared with the zero point reference value stored in the storage means, and if the difference is abnormally large, the gas combustion device is abnormal. Judge that the gas combustion device operates safely. Further, it is determined that the output of the combustible gas detection element is not a normal value, and the rewriting of the 0-point reference value is prevented.

Therefore, according to the present invention, it is possible to prevent the gas combustion apparatus from malfunctioning by storing the abnormal value as the 0-point reference value in the storage means.
It is also possible to make a CO sensor abnormality determination.

According to a second aspect of the present invention, in the combustible gas detection device according to the first aspect, a switch for forcibly operating the drift calibration means in the safe operation state is provided. .

When the 0-point reference value is corrected to an erroneous 0-point reference value, the gas combustor operates safely even though the output of the combustible gas detection element is within the normal range. There is a risk that the gas combustion device cannot be used.
In such a case, according to this embodiment, the zero point reference value can be set again by turning on the switch for operating the drift forming means, and the gas combustion apparatus can be returned to the usable state. .

According to a third aspect of the present invention, in the combustible gas detection device according to the first aspect, the drift calibration means is an output of the combustible gas detection element and a zero point reference stored in the storage means. When the difference from the value exceeds a predetermined value within the normal range, the combustible gas detection element is heat-cleaned.

According to this embodiment, when the deviation of the zero-point reference value tends to deviate beyond a certain value, the combustible gas detection element is heat-cleaned, so that the characteristics of the combustible gas detection element can be stabilized. .

According to a fourth aspect of the present invention, in the combustible gas detection device according to the first aspect, the drift calibration means is an output of the combustible gas detection element and a zero point reference stored in the storage means. If the difference from the value exceeds the first predetermined value within the normal range, calibrate the 0-point reference value,
If the difference between the output of the combustible gas detection element and the 0-point reference value stored in the storage means is equal to or less than the first predetermined value within the normal range, the 0-point reference value is not calibrated, Further, when the second predetermined value smaller than the first predetermined value is exceeded, the combustible gas detection element is heat-cleaned.

In this embodiment, the zero point is not corrected for a minute drift of the zero point reference value, and the same zero point reference value as before is used. Therefore, by accumulating the minute drifts, the zero point reference value is obtained. The drift of the value is eventually detected as a certain value or more and is detected and heat-cleaned. Therefore, according to this embodiment, the heat cleaning can be performed in good timing.

[0020]

DETAILED DESCRIPTION OF THE INVENTION

(First Embodiment) FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention. This is an application of the combustible gas detection device of the present invention to a gas water heater. A gas burner 4 is disposed below the can body 3 that forms the combustion chamber 2 of the gas water heater 1. Combustion gas is supplied to the gas burner 4 from a fuel source through a gas supply path 7 provided with an original solenoid valve 5 and a proportional control valve 6. The original solenoid valve 5 is a valve that only opens and closes the gas supply passage 7, and the proportional control valve 6 is a solenoid valve that is set to an opening degree according to a control signal and adjusts the gas flow rate to a desired value.
A frame rod 8 for detecting whether or not the gas burner 4 is burning is provided near the gas burner 4. A fan 10 driven by a fan motor 9 is arranged at the bottom of the can body 3 and supplies combustion air into the can body 3 in an amount corresponding to the gas supply amount.

A heat exchanger 11 is arranged above the gas burner 4, heats the water passed through the water supply pipe 12 by the combustion heat of the gas burner 4, and sends the heated hot water to the hot water supply pipe 13. A hood (collecting cylinder) 17 is provided above the can body 3 located above the heat exchanger 11.
An exhaust stack 23 is connected to 7. In this hood 17,
A CO sensor 15 for detecting the CO concentration and a temperature sensor 16 for detecting the ambient temperature of the CO sensor 15 are provided.

(Structure of the hood part) FIGS. 2 and 3 show CO
FIG. 3 is a partially cutaway perspective view and a sectional view showing the structure of a hood 17 to which the sensor 15 is attached. The hood 17 is composed of a collecting cylinder base portion 18 and a collecting cylinder body 19 installed thereon.

The collecting cylinder base 18 has a hollow structure,
It is placed on the top of the can body 3. A mixing chamber 20 is provided in the center of the collecting cylinder base 18, a discharge port 21 is opened on the upper surface of the mixing chamber 20, and an exhaust introduction port 22 is opened on the outer peripheral surface and the lower surface of the mixing chamber 20. A wind direction rectifying plate (not shown) is provided in the mixing chamber 20.

When the exhaust gas after passing through the heat exchanger 11 enters the mixing chamber 20 through the exhaust introduction port 22, the exhaust gas is converted into a vortex by the wind direction rectifying plate in the mixing chamber 20 and becomes uniform. After stirring and mixing so that the CO concentration is high, the gas is discharged upward from the discharge port 21 on the upper surface.

A connecting cylinder portion 2 for connecting an exhaust cylinder 23 to the collecting cylinder body 19 placed on the collecting cylinder base 18.
An exhaust passage 25 and a sensor chamber 26 formed inside the exhaust passage 4 are provided, and the lower surface of the exhaust passage 25 communicates with the outlet 21 of the collecting cylinder base portion 18. The sensor chamber 26 includes the partition plate 2
It is partitioned from the exhaust passage 25 by 7 and has a substantially sealed structure. A CO sensor 15 and a temperature sensor 16 are provided in the sensor chamber 26. The CO sensor 15 used here is, for example, a platinum coil wrapped with a mixed catalyst containing alumina beads.
When O gas comes in contact with it, an oxidation reaction occurs and the temperature rises,
Since the sensor resistance increases as the temperature rises, the CO concentration is detected by electrically detecting the change in the sensor resistance. A heater 28 for heat cleaning the CO sensor 15 is wound around the CO sensor 15. Alternatively, the heater 28 may be installed near the CO sensor 15. What is heat cleaning?
That is, the CO sensor 15 is cleaned by incinerating dust and the like adhering to the sensor 15 by heating.

As shown in FIGS. 2 and 3, an intake pipe 29 and an exhaust pipe 30 are arranged between the central portion of the exhaust passage 25 and the sensor chamber 26. here,
The upper end opening of the suction pipe 29 is opened horizontally, and the upper end opening of the discharge pipe 30 is opened upward. Further, as shown in FIG. 4, the lower end openings of the intake pipe 29 and the exhaust pipe 30 are open inside the sensor chamber 26, and the space between the intake pipe 29 and the CO sensor 15 is L.
A shaped exhaust baffle 31 is provided, and a portion of the exhaust baffle 31 is in thermal contact with the sensing portion of the CO sensor 15.

Since the exhaust gas discharged from the discharge port 21 of the collecting cylinder base 18 rises in the exhaust passage 25 in the connecting cylinder portion 24, the upper end portion of the discharge pipe 30 is caused by the rising flow of the exhaust gas. Becomes a negative pressure, and the exhaust gas in the sensor chamber 26 is sucked through the exhaust pipe 30. Therefore, the exhaust gas in the exhaust passage 25 is sucked into the sensor chamber 26 from the upper end of the suction pipe 29. The exhaust gas sucked into the sensor chamber 26 from the suction pipe 29 is directly fed to the CO sensor 15
After hitting the exhaust baffle plate 31 without hitting the
It flows to the sensor 15 side, and the CO concentration is measured by the CO sensor 15.

According to the hood 17 having such a structure, the CO concentration can be detected after the exhaust gas is uniformly mixed in the mixing chamber 20, so that the unevenness of the CO concentration can be reduced and the sensor chamber 2
It is possible to reduce the amount of exhaust gas sampled in No. 6 and to reduce the temperature of the exhaust gas sampled in the sensor chamber 26. Therefore, it is possible to make the contact of the exhaust gas with the CO sensor 15 gentle.
The effect of exhaust gas on the engine can be reduced.

Further, the exhaust gas generated by burning the gas contains a large amount of moisture, and the CO sensor 15 has a problem in water resistance when moisture adheres thereto. Especially, in the early stage of ignition of the gas burner, the exhaust gas temperature does not rise above the dew point, so when the exhaust gas comes into contact with the CO sensor 15, condensed water condenses on the surface of the CO sensor 15 and accelerates the deterioration of the CO sensor 15. . Therefore, in this embodiment, the exhaust baffle plate 31 is provided between the intake pipe 29 and the CO sensor 15, so that the water in the exhaust gas sucked through the intake pipe 29 is exhausted while the exhaust gas temperature is low. By colliding with 31, the dew is condensed on the surface of the exhaust baffle plate 31, and the exhaust gas after the water is removed by the exhaust baffle plate 31 contacts the CO sensor 15 to measure the CO concentration. Moreover, since a part of the exhaust baffle plate 31 is in contact with the CO sensor 15, when the exhaust gas temperature rises and the temperature of the exhaust baffle plate 31 rises, the temperature is transmitted to the CO sensor 15. The temperature of the CO sensor 15 also rises promptly, further enhancing the dew condensation prevention effect of the CO sensor 15. Therefore,
Since it is not necessary to use a waterproof CO sensor as the CO sensor 15, the cost of the CO sensor 15 can be reduced. Further, the life of the CO sensor 15 can be extended.

The structure of the exhaust baffle plate 31 may be a structure that does not contact the CO sensor 15, as shown in FIG.

FIG. 6 is a block diagram showing a configuration of a portion of the function of the controller 14 of the gas water heater 1 which is associated with the combustible gas detection device 32. The water heater control circuit 33 is composed of a microcomputer (CPU) and mainly controls the proportional current of the proportional control valve 6 through the burner control circuit 34 so as to discharge hot water having a set temperature set by a remote controller (not shown). , Adjust the heating power of the gas burner 4.

Further, the water heater control circuit 33 corresponds to the CO concentration detected by the combustible gas detection device 32,
Burner control circuit 3 so that the gas burns at an appropriate air-fuel ratio
4, the proportional control valve 6 controls the gas supply amount, and the fan drive circuit 35 controls the fan rotation speed. Further, when the combustible gas detection device 32 detects an abnormality in the CO concentration, the water heater control circuit 33
Performs safe operation according to the degree. That is, a warning is displayed on the display panel 36 provided in the remote controller or the like, or the original solenoid valve 5 is closed to forcibly stop the combustion and the combustion stopped state is maintained. When the reset switch 37 is pressed to release the safety operation after repairing the abnormal portion of the gas water heater 1, the gas water heater 1 can burn the gas burner 4 again to supply hot water.

The combustible gas detection device 32 is a contact combustion type C
O sensor 15 and CO sensor drive circuit (bridge circuit)
38, a CO concentration determination unit 39, and a memory (E ² PROM) 40 that holds the 0-point reference value V _{0 of} the CO sensor output and the like. When the power of the gas water heater 1 is turned on by inserting the outlet 41 into the AC 100V power source, the CPU of the water heater control circuit 33 is activated and the CO sensor drive circuit 38 is supplied with power. The CO sensor drive circuit 38 outputs the CO concentration detected by the CO sensor 15 to the CO concentration determination unit 39 as a voltage value (CO sensor output) Vs.
The memory 40 holds a zero point reference value V ₀ for calibrating the CO sensor output Vs from the CO sensor 15 and two alarm levels Vr1 and Vr2.

Therefore, the CO concentration determination unit 39 calculates the deviation Vs-V ₀ between the 0-point reference value V 0 held in the memory 40 and the CO sensor output Vs, and this is calculated as the warning level V
It is compared with r1 and Vr2 (Vr1 <Vr2), and the result is output to the water heater control circuit 33. When the deviation Vs-V ₀ is equal to or higher than the alarm level Vr1, the water heater control circuit 33
Displays a warning on the display panel 36 as described above. When the deviation Vs-V ₀ is equal to or higher than the warning level Vr2, the water heater control circuit 33 forcibly closes the original solenoid valve 5 as described above to maintain the combustion stopped state.

0 point reference value V stored in the memory 40
The calibration unit 42 for calibrating ₀ monitors through the frame rod 8 whether the gas burner 4 is burning. Further, information indicating the ambient temperature Ts of the CO sensor 15 is transmitted from the temperature sensor 16 to the calibration unit 42, and at the same time, the rate of change (time) of the CO sensor output Vs from the CO sensor driving circuit 38 via the differentiating circuit 44. The absolute value of the differential) | dVs / dt | is input, and if these input information satisfy 25 ° C. ≦ Ts ≦ 50 ° C .... And | dVs / dt | <0.04V / 5 sec. The calibration request is accepted, and the 0-point reference value V ₀ stored in the memory 40 is immediately rewritten with the value of the CO sensor output Vs to update (correct) the 0-point reference value V ₀ .

In the combustible gas detection device 32, the 0-point reference value V ₀ is not corrected immediately even if there is a reference value calibration request. _{Since 0} is updated, it is possible to gain time until the zero point adjustment of the CO sensor 15 is executed after combustion is stopped. Therefore, the CO component in the exhaust gas left in the vicinity of the CO sensor 15 immediately after the combustion is stopped is discharged to the outside of the gas water heater 1 and waits until no CO gas remains in the ambient atmosphere, and the CO in a stable state is maintained. The zero point reference value V ₀ can be updated using the sensor output Vs. Therefore, it is possible to prevent the calibration work for the 0-point reference value V _{0 from} being performed incompletely. The formulas and the numerical values used in the formulas are examples.

Before calibrating the zero point reference value V ₀ , the calibration section 42 compares the CO sensor output Vs with the zero point reference value (that is, the previously calibrated value) V ₀ in the memory 40. ,
The change of 0-point reference value | Vs−V ₀ | is set to three predetermined values α,
Compared with β and γ (α>β> γ), processing corresponding to the magnitude is executed. That is, a) When | Vs−V ₀ |> α and the change in the 0-point reference value is abnormally large, it is determined that an abnormality has occurred, the water heater control circuit 33 is operated safely, and the gas burner 4 is turned on. Combustion is forcibly stopped to maintain the combustion stopped state. B) When α ≧ | Vs−V ₀ |> β, and the change in the 0-point reference value is within the normal range and correction is necessary, the CO sensor output Vs is used as usual to store the memory 40. 0 point reference value of is updated. C) If β ≧ | Vs−V ₀ |> γ and the change in the 0-point reference value is such that correction is unnecessary but a minute change occurs, the processing is performed by omitting the calibration of the 0-point reference value. And heat cleaning. D) When γ ≧ | Vs−V ₀ | and there is almost no change in the 0-point reference value, the calibration of the 0-point reference value is omitted to simplify the process. The predetermined value α is set to serve as a reference for determining whether the gas water heater 1 is burning within a normal range or is abnormal. Further, β can be determined so as to serve as a reference as to whether correction of the 0-point reference value is unnecessary, for example.

Reference numeral 43 is a 0-point adjusting switch, and when the user turns on the 0-point adjusting switch 43 after the gas water heater 1 operates safely, the calibrating section 42 forces the 0-point reference value V _0. Calibrate and release safe operation. That is, the 0-point reference value V ₀ of the memory 40 is calibrated with the CO sensor output Vs regardless of the conditions of the above equations to equations. The zero-point adjustment switch 43 may be activated even when it is not operating safely.

For the reference value calibration request, the outlet 41 is AC
When the gas water heater 1 is turned on by being turned on by the 100V power source, the water heater control circuit 33 transmits the data to the calibration unit 42. Alternatively, it is transmitted from the water heater control circuit 33 to the calibration unit 42 after the first combustion is stopped after the power is turned on. further,
When the calibration unit 42 rewrites and updates the 0-point reference value V ₀ of the memory 40, at the same time, the calibration timer 30 is reset and then started, and the calibration timer 30 starts a predetermined time T1 (for example, 24).
After a lapse of time, a reference value calibration request is issued to the calibration unit 42.

FIG. 7 is a flow chart for explaining the calibration operation of the zero point reference value V ₀ of the CO sensor output by the controller 14. FIG. 8 is a partial flow chart showing the processing of the reference value calibration request in FIG. Hereinafter, the calibration operation of the 0-point reference value V ₀ by the combustible gas detection device 32 will be described with reference to FIGS. 7 and 8. First, the timing at which the reference value calibration request is output will be described with reference to FIG. The reference value calibration request is first output when the power is turned on and the outlet 41
Plug in the AC100V power supply and turn on the power (S8
1), power is supplied to the CO sensor drive circuit 38, and CO
The sensor 15 (CO sensor drive circuit 38) is turned on (S82), and the water heater control circuit 33 outputs a reference value calibration request (S83). Further, normally, when the gas water heater 1 performs the first combustion and is stopped (S84), the second
A reference value calibration request for the second time is output (S83). Therefore, the low-precision zero-point reference value V ₀ set at power-on
Is updated to a more accurate 0-point reference value V ₀ within a short time. When the 0-point reference value V ₀ in the memory 40 is rewritten and updated, the calibration timer 30 is reset and counting is started (S68). When the elapsed time reaches a predetermined time T1 (for example, 24 hours) monitored by the timer 30 (S85), the calibration unit 42 issues a reference value calibration request (S83).

When the reference value calibration request is generated in this way (S61, S83), the processes of step S62 and thereafter in FIG. 7 are executed. That is, the calibration unit 42 determines from the output of the frame rod 8 whether the gas burner 4 is in combustion or combustion stop (S62). If combustion is stopped, the output of the temperature sensor 16 is read and the ambient temperature T of the CO sensor 15 is read.
It is checked whether s is in a predetermined range, that is, in the range of 25 ° C to 50 ° C (S63). If the temperature detected by the temperature sensor 16 is within this range, then the rate of change | dVs / dt | of the CO sensor output output from the differentiating circuit 44 is continuously less than 0.008 V / sec for 5 seconds. Check (S64).

The ambient temperature Ts of the CO sensor 15 is 25 ° C.
If ≦ Ts ≦ 50 ° C., and the rate of change of the CO sensor output is | dVs / dt | <0.008V / sec, the gas water heater 1 will stop combustion for a sufficient time after the combustion has stopped. Since it is considered that the state has been reached, the calibration unit 42 next checks the drift of the 0-point reference value V ₀ .

That is, the CO sensor output Vs immediately before the 0-point reference value V ₀ is updated and the 0-point reference value V ₀ (previously calibrated value) are compared, and the change of the 0-point reference value | Vs-V ₀
If | is equal to or smaller than the reference value α indicating an abnormality and is larger than the reference value β indicating the necessity of correction (S65, S66), CO
The CO sensor output Vs of the sensor drive circuit 38 is read,
The 0-point reference value in the memory 40 is updated (S67).

After updating the zero point reference value V ₀ in the memory 40, the calibration section 42 resets the calibration timer 30 to start counting (S68), and monitors the time until the next reference value calibration request. (S85). Then, the calibration timer 3
When 0 reaches the predetermined time T1, the standard value calibration request is generated again (S83).

On the other hand, even if a reference value calibration request is generated (S6
1, S83), among the conditions of steps S62 to S64,
If any one of the conditions is not satisfied, the 0-point reference value V ₀ is not updated until those conditions are met.

In step S65, if the change in the 0-point reference value | Vs-V ₀ |> α, it is judged that an abnormality has occurred, and the water heater control circuit 33 is caused to operate safely. Combustion of the gas burner 4 is forcibly stopped to maintain the combustion stopped state (S69).

However, the gas water heater 1 and the CO sensor 15 are not faulty but may operate safely because the zero point reference value V ₀ is updated with an abnormal value. In that case,
When the 0-point adjustment switch 43 is pressed (S70), C at that time
The 0-point reference value V _{0 of the} memory 40 depends on the O sensor output Vs
Is updated and the safe operation is also canceled.

In step S65, the change of the 0-point reference value | Vs-V ₀ | ≦ α, and in step S66 | V
If s−V ₀ | ≦ β and the change in the 0-point reference value is very small, step S67 of the 0-point reference value calibration is skipped (S71, S72). However, when | Vs−V ₀ | is compared with a small predetermined value γ, and if there is a slight change in the 0-point reference value and | Vs−V ₀ |> γ, the CO sensor 15 is heat cleaned. Execute (S72). That is, the 0 point reference value is used as it is without correcting the 0 point with a minute change of the 0 point reference value V _0. However, due to the accumulation of the minute changes, the change of the 0 point reference value will eventually become a constant value. When it is γ or more, heat cleaning is performed so that heat cleaning can be performed in a timely manner.

(Issuing another reference value calibration request) It is also possible to generate the reference value calibration request under a condition different from that shown in FIG. For example, when the CO sensor is installed in the exhaust passage, if it burns satisfactorily, the CO sensor is less damaged, but if the combustion becomes worse, dew condensation or soot may occur in the exhaust passage. do it,
The CO sensor is likely to be damaged. Therefore, the controller counts or integrates the time or number of times when the CO concentration detected by the CO sensor exceeds a certain value, and when the number of times or the number of times of integration exceeds a certain value, a reference value calibration request is generated. May be.

(Others) Since the characteristics of the CO sensor are different from each other, the 0-point reference value V ₀ is set when the power is turned on as described above, and the 0-point reference value V ₀ is corrected thereafter, and the correction value and the like are obtained. It is stored in the memory (E ² PROM). Therefore, when the CO sensor fails, it is necessary to replace it with a new CO sensor and also replace the memory. For example, unless the memory is also replaced at the same time, the data of the previous CO sensor is held in the existing memory, so the sensor output value of the new CO sensor and the 0-point reference value V ₀ in the memory.
And the gas combustion device operates safely (Fig. 7
(See step S69), the 0-point reference value V ₀ cannot be rewritten.

In order to solve this, it is sufficient to provide a means capable of clearing only the data concerning the CO sensor in the stored contents of the memory. For example, a memory data clear button for clearing CO data is provided,
When the user keeps pressing the clear button for a certain time while the gas water heater is powered on, the data regarding the CO sensor in the memory is cleared. After that, disconnect the outlet, turn off the power of the gas water heater, replace the CO sensor, plug the outlet back into the AC100V power supply, and turn on the power of the gas water heater, the standard value calibration request is output when the power is turned on. 0 point reference value of CO sensor V
₀ is set in the memory (the zero-point reference value V ₀ does not exist in the memory, so the gas combustion apparatus does not operate safely in step S69 in FIG. 7). Therefore, only the CO sensor needs to be replaced, and there is no need to replace the memory.

[0052]

According to the present invention, the output of the combustible gas detection element is compared with the zero point reference value stored in the storage means, and if the difference is extremely large, the gas combustion device is abnormal. Judge that there is and operate the gas combustion device safely. Further, it is determined that the output of the combustible gas detection element is not a normal value, and the rewriting of the 0-point reference value is prevented. Therefore, according to the present invention, it is possible to prevent an abnormal value from being erroneously operated by storing an abnormal value in the storage means as a zero point reference value.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a gas water heater to which a combustible gas detection device according to an embodiment of the present invention is applied.

FIG. 2 is a partially cutaway perspective view showing a hood of the above gas water heater.

FIG. 3 is a cross-sectional view showing the hood of the above.

FIG. 4 is a partially cutaway perspective view showing the structure of the inside of the sensor chamber of the hood.

FIG. 5 is a partially cutaway perspective view showing another structure of the exhaust baffle in the sensor chamber.

FIG. 6 is a block diagram showing the function of the above-described combustible gas detection device and a part of the function of the gas water heater.

FIG. 7 is a flowchart illustrating the operation of the above-described combustible gas detection device.

FIG. 8 is a partial flowchart illustrating in detail the processing of the reference value calibration request in the above flowchart.

[Explanation of symbols]

1 Gas Water Heater 4 Gas Burner 15 CO Sensor 16 Temperature Sensor 28 Heater 32 Combustible Gas Detection Device 40 Memory 42 Calibration Unit 43 0 Point Adjustment Switch 44 Differential Circuit Vs CO Sensor Output V ₀ 0 Point Reference Value

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiko Obayashi 93, Edo-cho, Chuo-ku, Kobe-shi, Hyogo In stock company Noritsu (72) Inventor Yashiro Sugawara 93-edo, Chuo-ku, Kobe-shi, Hyogo In stock company Noritsu (72) Inventor Takuji Saeki 93, Edo-machi, Chuo-ku, Kobe, Hyogo Prefecture Noritsu (72) Inventor Atsushiya Yamamoto 93, Edo-cho, Chuo-ku, Kobe, Hyogo (72) Inventor Nobuhiro Takeda Hyogo No. 93, Edo-machi, Chuo-ku, Kobe, Japan (72) Inventor, Shunichi Miki, No. 93, Edo-machi, Chuo-ku, Kobe-shi, Hyogo, In-house (72), Noritsu, Ltd. Hideyuki Okada, 93, Edo-machi, Chuo-ku, Kobe, Hyogo Address No. of stock company Noritsu (72) Inventor Keiichi Miura 93, Edo-machi, Chuo-ku, Kobe-shi, Hyogo No. Stock company In Tsu (56) Reference Patent flat 8-101155 (JP, A) (58 ) investigated the field (Int.Cl. ^7, DB name) F23N 5/24 107

Claims (4)

(57) [Claims] 1. A combustible gas detection device for detecting a combustible gas contained in exhaust gas discharged from a gas combustion device having a burner, wherein a contact combustion type combustible gas detection element and an output of the combustible gas detection element are 0. A means for storing a point reference value, and when there is a calibration request for the 0 point reference value, when the difference between the output of the combustible gas detection element and the 0 point reference value stored in the storage means is abnormally large. Is provided with a drift calibration means for safely operating the gas combustion device without calibrating the zero point reference value. 2. The combustible gas detection device according to claim 1, further comprising a switch for forcibly operating the drift calibration means in the safe operation state. 3. If the difference between the output of the combustible gas detection element and the 0-point reference value stored in the storage means exceeds a predetermined value within a normal range, the drift calibration means sets the flammable gas The combustible gas detection device according to claim 1, wherein the gas detection element is heat-cleaned. 4. If the difference between the output of the combustible gas detection element and the 0-point reference value stored in the storage means exceeds a first predetermined value within a normal range, the drift calibration means If the difference between the output of the combustible gas detection element and the 0-point reference value stored in the storage means is less than or equal to a first predetermined value within a normal range, the zero point reference value uncorrected, further, if it exceeds the smaller second predetermined value than the first predetermined value, characterized by heat cleaning said combustible gas detecting element according to claim 1 The combustible gas detection device described in .