JP3691647B2 - Combustible gas detection device and zero point correction method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a combustible gas detection device that detects the concentration of a combustible gas contained in an atmosphere using a contact combustion type detection element, and a zero point correction method thereof.
[0002]
[Prior art]
The catalytic combustion detector used in the combustible gas detector has a structure in which the surface of the resistor is covered with a catalyst that generates heat in response to a combustible gas such as carbon monoxide. The internal resistance value is changed by heat generated by reaction with the combustible gas therein.
[0003]
The flammable gas detection device detects the concentration of flammable gas from the voltage at both ends of the sensing element whose resistance changes due to heat generated by the reaction of the catalyst on the surface with the flammable gas in the atmosphere. It is like that. The current value is set to a value that allows the resistor in the sensing element to generate heat and heats the catalyst on the surface to a temperature range sufficiently reacting with the combustible gas.
[0004]
In order to convert the voltage appearing at both ends of the sensing element into the concentration of the combustible gas, the value of the voltage in the absence of the combustible gas (0 reference voltage) is necessary, and in order to ensure the detection accuracy, The zero point correction is performed in an atmosphere where there is almost no combustible gas.
[0005]
For example, in a flammable gas detection device arranged in the exhaust path of a water heater, after the burner is extinguished, the air supply / exhaust fan is operated to exhaust the exhaust gas containing flammable gas such as carbon monoxide almost completely. Under the condition, zero point correction is performed.
[0006]
[Problems to be solved by the invention]
However, in such a conventional technique, the zero point correction is performed under the situation where there is no flammable gas in the atmosphere, so when the situation where no flammable gas exists in the atmosphere is formed. When it cannot be grasped, there is a problem that zero point correction cannot be performed.
[0007]
For example, when supplying and exhausting air to an FF-type water heater or stove through a collective duct installed in a multi-storey apartment such as an apartment, the exhaust discharged from the hot water heater installed downstairs to the collective duct It will be mixed in the intake air taken in by a water heater installed on the upper floor. Therefore, even after the burner is extinguished and the exhaust in the appliance is exhausted, combustible gas exhausted from downstairs appliances may be mixed in the supply air. The zero point correction could not be performed.
[0008]
In addition, in an FE type water heater that takes in indoor air and exhausts the exhaust through the duct, the stove is still indoors even after the burner is extinguished and the exhaust is exhausted outdoors. In that case, the exhaust gas is taken into the water heater. For this reason, it was not possible to grasp the timing at which a state in which no flammable gas exists in the atmosphere was formed, and the zero point correction could not be performed appropriately.
[0009]
The present invention has been made paying attention to such problems of the conventional technology, and a combustible gas detection device capable of accurately performing zero-point correction even when a combustible gas is present in the atmosphere, and The object is to provide a zero-point correction method.
[0010]
[Means for Solving the Problems]
The gist of the present invention for achieving the object lies in the inventions of the following items.
[1] In the combustible gas detection device that detects the concentration of the combustible gas contained in the atmosphere using the contact combustion type detection element (41),
The combustible gas detection device includes correlation information storage means (53), calibration drive means (52), and zero point correction means (54).
The correlation information storage means (53) outputs an output value of the detection element (41) and flammability when the detection element (41) is driven at the first operating point (72) having no sensitivity to the flammable gas. Storing in advance a correlation with the output value of the detection element (41) when the detection element (41) is driven at a second operating point (71) having sensitivity to combustible gas in an atmosphere without gas;
The calibration driving means (52) drives the sensing element (41) at the first operating point (72) when correcting the output value of the sensing element (41) by 0 points.
The zero-point correcting means (54) is an output value of the sensing element (41) when the calibration driving means (52) drives the sensing element (41) at the first operating point (72). Based on the correlation stored in the correlation information storage means, the detection element (41) when the detection element (41) is driven at the second operating point (71) in an atmosphere without flammable gas. A predicted output value is obtained, and the output value of the detection element (41) when the detection element (41) is driven at the second operating point (71) is corrected by zero based on the predicted value. A combustible gas detector.
[0011]
[2] The first operating point (72) is set in the vicinity of a boundary with an operating region in which the sensing element (41) does not have sensitivity to the combustible gas and has sensitivity to the combustible gas. The combustible gas detection device according to [1], wherein
[0012]
[3] In the zero point correction method of the combustible gas detection device that detects the concentration of the combustible gas contained in the atmosphere using the contact combustion type detection element (41),
When the detection element (41) is driven at the first operating point (72) having no sensitivity to the combustible gas, the output value of the detection element (41) and the detection element in the atmosphere without the combustible gas ( 41) is previously obtained and stored in correlation with the output value of the sensing element (41) when driven at the second operating point (71) having sensitivity to combustible gas,
In an atmosphere free of flammable gas from the output value of the detection element (41) when the detection element (41) is driven at the first operating point (72) and the correlation obtained and stored in advance. When the sensing element (41) is driven at the second operating point (71), a predicted output value of the sensing element (41) is obtained, and the sensing element (41) is moved to the second operating point (71). The zero-point correction method of the combustible gas detection device, wherein the output value of the detection element (41) at the time of driving is corrected by zero based on the predicted value.
[0013]
The present invention operates as follows.
The correlation information storage means (53) outputs the output value of the detection element (41) and the combustible gas when the detection element (41) is driven at the first operating point (72) having no sensitivity to the flammable gas. The correlation with the output value of the detection element (41) when the detection element (41) is driven at the second operating point (71) having sensitivity to the flammable gas in a non-existing atmosphere is stored in advance.
[0014]
The calibration drive means (52) drives the detection element (41) at the first operating point (72) when the output value of the detection element (41) is corrected to 0 point, and the 0 point correction means (54) When the calibration drive means (52) drives the detection element (41) at the first operating point (72), the output value of the detection element (41) and the correlation information storage means (53) are stored. Based on the correlation, a predicted value of the output of the sensing element (41) when the sensing element (41) is driven at the second operating point (71) in an atmosphere without flammable gas is obtained. Then, using the predicted value, the output value of the detection element (41) when the detection element (41) is driven at the second operating point (71) is corrected by zero.
[0015]
At the first operating point (72), the sensing element (41) does not have sensitivity to combustible gas, so the output value of the sensing element (41) when driven at the operating point is the concentration of combustible gas. It does not depend, but depends only on factors other than the concentration of the combustible gas, such as the secular change of the sensing element (41). Further, the output value at the first operating point (72) indicates that the sensing element (41) operates in the atmosphere without flammable gas at the second operating point (71) (operation having sufficient sensitivity to the flammable gas). It has a sufficient correlation with the output value when driven at point).
[0016]
Therefore, this correlation is stored in advance, and detected in an atmosphere free of flammable gas from the output value when driven at the first operating point (72) having no sensitivity to the flammable gas and the correlation. The predicted value of the output when the element (41) is driven at the second operating point (71) is obtained, and thereby the zero point correction is performed.
[0017]
As described above, the zero point correction is performed based on the output value when driven at the first operating point (72) having no sensitivity to the flammable gas and the correlation obtained and stored in advance. Regardless of the combustible gas concentration in the medium, the zero point correction can be accurately performed at any time.
[0018]
In addition, the first operating point (72) is set in the vicinity of the boundary with the operating region in which the sensing element (41) does not have sensitivity to the combustible gas and has sensitivity to the combustible gas. Thereby, since the change of the resistance value of the sensing element (41) due to secular change or the like appears relatively significantly in the output value when the sensing element (41) is driven at the first operating point (72), Based on the output value and the correlation, the predicted value can be obtained with high accuracy.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
Each figure shows an embodiment of the present invention.
As shown in FIG. 2, the combustible gas detection device according to the present invention is applied to the water heater 10 here. The water heater 10 is installed in a room, adopts a forced exhaust type in which air in the room is supplied for combustion and exhaust is discharged to the outside through an exhaust pipe.
[0020]
A housing 11 which is a main body of the water heater 10 has a box shape, and an air supply port 12 for taking indoor air into the appliance is opened on the right side surface thereof.
[0021]
A combustion chamber 21 is provided at a substantially central portion in the housing 11, a burner 22 is disposed at the lower portion thereof, and a heat exchanger 23 for heating the feed water by heat from the air supply port 12 is disposed at the upper portion thereof. ing.
[0022]
At the lower left end of the combustion chamber 21, a combustion fan 24 for sending air taken from the air supply port 12 to the burner 22 is provided, and an exhaust port 25 is provided at the center of the upper surface of the combustion chamber 21. A CO sensor unit 40 for detecting a carbon monoxide (CO) concentration or the like is attached to the upper right end of the combustion chamber 21. The location where the CO sensor unit 40 is disposed is a place where the wind from the combustion fan 24 is not directly applied and the exhaust does not stop.
[0023]
Various valves such as an original gas solenoid 27, a gas solenoid valve 28, a gas proportional valve 29, and a gas capacity switching valve 30 are attached to the gas supply path 26 leading to the burner 22. An igniter electrode 31 and a frame rod electrode 32 are disposed adjacent to the burner 22.
[0024]
In the middle of the water supply pipe 33 leading to the inlet side of the heat exchanger 23, a water inlet thermistor 34 that detects the water temperature, a water amount sensor 35 that detects the flow rate at the time of hot water, and the like are provided. The hot water supply pipe 36 extending from the outlet side of the heat exchanger 23 is provided with a flow rate control valve 37 for controlling the total flow rate of the hot water to be discharged, and the water supply pipe 33 and the hot water supply pipe 36 are bypassed by the heat exchanger 23. A flow rate control valve 39 for controlling the bypass ratio is provided in the middle of the connecting bypass passage 38.
[0025]
An operation unit 13 including an operation switch that accepts various operations such as temperature setting of hot water to be discharged, a small liquid crystal display, and the like is provided at the lower front portion of the housing 11. A control base 14 that controls various controls in the water heater 10 is disposed at the upper right end in the housing 11. A combustible gas concentration detection circuit 50, which will be described later, is mounted in the control board 14.
[0026]
The control board 14 includes a CPU (central processing unit) (not shown), a ROM for storing programs and various fixed data, a RAM for storing data temporarily necessary for executing the programs, and the like. It is comprised by the circuit which makes main part.
[0027]
FIG. 3 shows the configuration of the CO sensor unit 40. The CO sensor unit 40 includes a contact combustion type detection element 41 and a temperature compensation comparison element 42 connected in series. The detection element 41 and the comparison element are provided at a location where the contact can be made with the atmosphere in the combustion chamber 21. 42 are arranged close to each other.
[0028]
The contact combustion type detection element 41 has a structure in which a resistor 43 is wrapped with a ceramic 44 and the surface thereof is covered with a catalyst 45 that generates heat in response to a combustible gas such as carbon monoxide. The resistance value of the internal resistor 43 is changed by heat generated by the reaction of the catalyst 45 on the surface with the combustible gas in the atmosphere. The comparison element 42 has a structure in which a resistor 46 is covered with a ceramic 47.
[0029]
The combustible gas concentration detection circuit 50 allows a predetermined current to flow through the detection element 41 and the comparison element 42, and is based on the voltage across the detection element 41 (Vsns) and the voltage across the comparison element 42 (Vref). It detects the concentration of flammable gases such as carbon oxide.
[0030]
FIG. 1 shows a configuration of a combustible gas concentration detection circuit 50 that drives the CO sensor unit 40. The combustible gas concentration detection circuit 50 includes a detection drive unit 51, a calibration drive unit 52, a correlation information storage unit 53, and a zero point correction unit 54. The detection drive unit 51 is a circuit portion that drives the CO sensor unit 40 at a constant current when detecting the concentration of a combustible gas such as carbon monoxide, and in this case, a current of 170 milliamperes flows.
[0031]
The calibration drive unit 52 is a circuit part that drives the CO sensor unit 40 at a constant current when correcting the zero point. The correlation information storage unit 53 drives the CO sensor unit 40 by the detection drive unit 51 in a state where there is no flammable gas in the atmosphere, based on the output voltage of the detection element 41 when driven by the calibration drive unit 52. It is a circuit part which memorize | stores the correlation information used in order to obtain | require the predicted value of the output voltage of the said detection element 41 in the case of having performed.
[0032]
The zero point correction unit 54 is arranged in the atmosphere based on the output voltage of the detection element 41 when the CO sensor unit 40 is driven by the calibration driving unit 52 and the correlation information stored in the correlation information storage unit 53. This is a circuit portion that obtains a predicted value of the output voltage of the detection element 41 when the CO sensor unit 40 is driven by the detection drive unit 51 in the absence of flammable gas and performs zero point correction. Note that the value of Vsns 61 that is the voltage across the detection element 41 is temperature-compensated using Vref 62 that is the voltage across the comparison element 42, and in practice, zero-point correction is performed based on the value after temperature compensation and the correlation information. It is supposed to be. In the following description, it is assumed that Vsns 61 is temperature compensated by Vref 62 using a bridge circuit or the like.
[0033]
FIG. 4 shows the relationship between the drive current flowing through the CO sensor unit 40 and the sensitivity of the detection element 41 to combustible gas. When driven by the detection drive unit 51 and a normal current (second operating point) 71 is passed through the detection element 41, the detection element 41 exhibits a considerably high sensitivity to combustible gas. On the other hand, when driven by the calibration drive unit 52 and the current flowing through the sensing element 41 is lowered to the dead current (first operating point) 72, the sensing element 41 has no sensitivity to the flammable gas. Not.
[0034]
The catalyst 45 covering the surface of the detection element 41 does not appear to generate heat in response to a combustible gas such as carbon monoxide unless it is at a certain temperature or higher. At the second operating point 71, since the drive current is large, the resistor 43 included in the sensing element 41 generates heat, and the surface catalyst 45 is heated to a temperature at which it sufficiently reacts with the combustible gas. For this reason, when driven at the second operating point 71, the sensing element 41 has high sensitivity to combustible gas.
[0035]
On the other hand, when driven at the first operating point 72, since the amount of heat generated by the resistor 43 is small, the surface catalyst 45 is not heated to a temperature at which it reacts with the combustible gas. For this reason, when driven at the first operating point 72, the sensing element 41 does not show any sensitivity to the combustible gas.
[0036]
FIG. 5 shows the relationship between the drive current supplied to the sensing element 41 and the output voltage of the sensing element 41 in a state where there is no flammable gas in the atmosphere. As shown, there is a strong correlation between the output voltage of the sensing element 41 at the first operating point 72 and the output voltage of the sensing element 41 at the second operating point 71.
[0037]
For example, when the output value of the sensing element 41 when driven at the first operating point 72 is the voltage 81a, the output value when driven at the second operating point 71 is uniquely the voltage 81b. Similarly, when the output value when driven at the first operating point 72 is the voltage 82a, the output value when driven at the second operating point 71 is the voltage 82b.
[0038]
The correlation information storage unit 53 stores such a correlation in advance. Specifically, the output voltage when the sensing element 41 is driven at the first operating point 72, and the output voltage when the sensing element 41 is driven at the second operating point 71 in an atmosphere without flammable gas. Are stored in correspondence with each other in accordance with the correlation shown in FIG. The reference table is such that when the temperature of the detection element 41 is low, the output voltage change follows Ohm's law, but as the temperature of the detection element 41 increases, the output voltage change rate increases and the temperature characteristic becomes linear. This is because it must not.
[0039]
Next, the operation will be described.
When performing the zero point correction, the combustible gas concentration detection circuit 50 drives the CO sensor unit 40 at a first operating point 72 by the calibration driving unit 52 at a constant current. In this state, the zero point correction unit 54 reads Vsns 61 (actually, the value after temperature compensation by the Vref 62) that is the voltage across the detection element 41, and the predicted value corresponding to this value is read from the correlation information storage unit 53. get. The value acquired from the correlation information storage unit 53 is a predicted value of the voltage across the detection element 41 when the CO sensor unit 40 is driven at a constant current at the second operating point 71 in a state where there is no flammable gas in the atmosphere. .
[0040]
Therefore, the zero value can be corrected by treating the value as a zero reference voltage (output value when there is no flammable gas in the atmosphere) when the CO sensor unit 40 is driven at the second operating point 71. it can.
[0041]
When driven at the first operating point 72, the sensing element 41 does not have sensitivity to combustible gas as shown in FIG. Therefore, by obtaining the predicted value based on the output value of the sensing element 41 when driven at the first operating point 72 and the correlation stored in the correlation information storage unit 53, the combustible gas concentration in the atmosphere Regardless of this, zero point correction can be performed.
[0042]
In addition, since the first operating point 72 is set in the vicinity of the boundary with the operating region in which the sensing element 41 does not have sensitivity to the combustible gas and has sensitivity to the combustible gas, the first operating point 72 is When driven, a change in the resistance value of the detection element 41 due to a secular change or the like appears significantly in the output value, and the predicted value can be obtained with high accuracy based on the output value and the correlation.
[0043]
FIG. 6 shows the output voltage characteristics of the sensing element 41 with respect to the combustible gas concentration when driven at the second operating point 71. As shown in the figure, the output voltage characteristics of the sensing element 41 have the same slope regardless of the difference between the zero reference voltages 91a to 91c. Therefore, if the 0 reference voltage is known, the concentration of the combustible gas can be accurately obtained from the output voltage of the sensing element 41.
[0044]
Thus, based on the output value of the sensing element 41 when driven at the first operating point 72 having no sensitivity to the flammable gas and the correlation stored in the correlation information storage unit 53 in advance, the flammable gas. Since the output value of the sensing element 41 is estimated and determined when the CO sensor unit 40 is driven at the second operating point 71 exhibiting sufficient sensitivity to combustible gas in an atmosphere having no flammability, the flammability in the atmosphere The zero point correction of the detection element 41 can be performed regardless of the gas concentration.
[0045]
Thereby, even if it is a hot water heater of the system which takes in indoor air, zero point correction | amendment can be performed exactly. For example, even when the C0 sensor provided in the water heater is also used as a C0 concentration detector for indoor air, such as when the timing at which no flammable gas is formed in the atmosphere cannot be grasped, it is precisely 0. Point correction can be performed.
[0046]
Further, as shown in FIG. 7, when supplying and exhausting air to and from the FF type water heaters and stoves 93a and 93b through the collective duct 92 provided in a multi-storey apartment house such as an apartment, it is installed on the lower floor. The exhaust gas from the hot water heater 93a is mixed with the intake air taken in by the hot water heater 93b installed on the upper floor. Therefore, even after the burner is extinguished and the exhaust in the appliance is exhausted, combustible gas exhausted from the appliance below the floor may be mixed in the supply air. 0 point correction can be performed.
[0047]
In the embodiment described above, when the detection element is driven at the first operating point that does not have sensitivity to the flammable gas, the detection element is set in the atmosphere without the flammable gas and the output value of the detection element. The correlation with the output value of the detection element when driven at the second operating point having sensitivity to is stored in the correlation information storage unit 53 in the form of a reference table. A predicted value may be obtained. Note that the first operating point 72 shown in FIG. 4 may be somewhat sensitive to flammable gas within a range where there is no problem in performance, for example, a location shown by a dotted line 73 in FIG. .
[0048]
【The invention's effect】
According to the combustible gas detection device and the zero point correction method according to the present invention, the output value of the detection element and the combustible gas when the detection element is driven at the first operating point having no sensitivity to the combustible gas. When the sensing element is driven at the second operating point having sensitivity to the flammable gas in an atmosphere free from the correlation with the output value of the sensing element in advance, and driven at the first operating point Since the zero point correction is performed based on the output value and the correlation stored in advance, the zero point correction can be performed accurately at any time regardless of the combustible gas concentration in the atmosphere.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an outline of a circuit configuration of a combustible gas detection device according to an embodiment of the present invention.
FIG. 2 is an explanatory view showing a water heater to which a combustible gas detection device according to an embodiment of the present invention is applied.
FIG. 3 is an explanatory diagram showing a sensor unit of the combustible gas detection device according to one embodiment of the present invention.
FIG. 4 is an explanatory diagram showing a relationship between a drive current flowing through a contact combustion type detection element and sensitivity to combustible gas.
FIG. 5 is an explanatory diagram showing the relationship between the current supplied to the sensing element and the output voltage of the sensing element when there is no flammable gas in the atmosphere.
FIG. 6 is an explanatory diagram showing an output voltage characteristic of a sensing element with respect to a combustible gas concentration when driven at a second operating point.
FIG. 7 is an explanatory diagram showing a state where air is supplied to and exhausted from an FF type water heater, a stove, and the like through a collective duct provided in a multi-storey apartment house.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Water heater 40 ... CO sensor part 41 ... Detection element 42 ... Comparison element 43 ... Resistor 45 ... Catalyst 50 ... Combustible gas concentration detection circuit 51 ... Detection drive part 52 ... Calibration drive part 53 ... Correlation information storage part 54 ... 0 point correction unit 71 ... second operating point 72 ... first operating point

Claims (3)

In the combustible gas detection device that detects the concentration of the combustible gas contained in the atmosphere using a contact combustion type detection element,
The combustible gas detection device includes correlation information storage means, calibration drive means, and zero point correction means,
The correlation information storage means combusts the sensing element in an atmosphere free from flammable gas and an output value of the sensing element when the sensing element is driven at a first operating point having no sensitivity to the combustible gas. Storing in advance a correlation with the output value of the sensing element when driven at a second operating point having sensitivity to gas;
The calibration driving means drives the sensing element at the first operating point when correcting the output value of the sensing element by 0 point,
The zero point correction means is based on the output value of the detection element when the calibration driving means drives the detection element at the first operating point and the correlation stored in the correlation information storage means. When the sensing element is driven at the second operating point in an atmosphere free of flammable gas, a predicted value of the output of the sensing element is obtained, and the sensing element is driven at the second operating point. A combustible gas detection device, wherein the output value of the detection element is corrected by 0 based on the predicted value. The first operating point is set in the vicinity of a boundary with an operating region in which the sensing element has sensitivity to the combustible gas among operating regions in which the sensing element does not have sensitivity to the combustible gas. The combustible gas detector described. In the 0 point correction method of the flammable gas detection device that detects the concentration of the flammable gas contained in the atmosphere using a contact combustion type detection element,
When the sensing element is driven at a first operating point that does not have sensitivity to flammable gas, the output value of the sensing element and a second sensitivity of the sensing element to flammable gas in an atmosphere without flammable gas. Previously obtained and stored a correlation with the output value of the sensing element when driven at the operating point,
From the output value of the sensing element when the sensing element is driven at the first operating point and the correlation obtained and stored in advance, the sensing element is moved in the atmosphere free from combustible gas. A predicted value of the output of the detection element when driven at the operating point is obtained, and the output value of the detection element when the detection element is driven at the second operating point is corrected by zero based on the predicted value. A zero-point correction method for a combustible gas detector.

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