JP2002357588A - Combustible gas sensor, and method of measuring concentration of combustible gas using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously reduce the cost of a combustible gas sensor and improve the reliability of the sensor by improving the sensor in hydrogen selectivity and enabling the sensor to selectively measure the concentration of a hydrogen gas, and at the same time, the concentrations of combustible gases other than the hydrogen gas. SOLUTION: The combustible gas sensor is provided with a gas diffusion rate determining section 10a which limits the diffusing amount of a gas to be measured, a gas diffusing chamber 12 in which the gas passed through the section 10a is diffused, and a sensor control circuit 20 provided in the chamber 12. The sensor is also provided with another sensor control circuit 120, which can oxidize a combustible gas in the chamber 12, a gas composition conversion intermittent driving means 130 which intermittently drives the control circuit 120, and an operating and outputting means 30, which finds the concentration of the combustible gas by separating the concentration to a desired combustible gas concentration, based on the output of the sensor control circuit 120, obtained when the circuit 120 is intermittently driven by means of the driving means 130.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustible gas sensor excellent in combustible gas selectivity and a method for measuring a combustible gas concentration using the sensor.

[0002] As sensors using an oxygen ion conductive solid electrolyte, there are an oxygen sensor for detecting the oxygen concentration in the exhaust gas of an automobile and an air-fuel ratio sensor for obtaining an air-fuel ratio from the oxygen concentration. It is known that such a conventional sensor also reacts to a combustible gas such as hydrogen or carbon monoxide.

[0003] The sensor element of the sensor is configured so that the gas to be measured can pass through the diffusion rate controlling section and reach the gas diffusion chamber. Further, the oxygen pump cell is formed by an oxygen ion conductive solid electrolyte, and outer and inner electrodes disposed on both surfaces thereof. Further, the oxygen sensing cell is formed by an oxygen ion conductive solid electrolyte and oxygen reference electrodes and oxygen measuring electrodes provided on both surfaces thereof, and the oxygen pump cell and the oxygen sensing cell are a sensor control circuit having an operational amplifier. Connected to each other. Furthermore, a heater unit for controlling the sensor element to the activation temperature is provided.

[0004] Sensor elements having such a configuration are described, for example, in SAE paper (No. 850378), automobile technology (Vol. 41, No. 12, 1987), and Japanese Patent Laid-Open No.
No. 00-9686.

[0005]

The sensor element of such a sensor shown in the prior art has a gas diffusion rate-limiting portion for limiting the amount of diffusion of the gas to be measured, and a gas diffusion portion for diffusing the gas passing through the gas diffusion rate-limiting portion. Chamber, an oxygen detection cell that measures the oxygen partial pressure of the gas diffusion chamber, and an oxygen pump cell that has an action of pumping oxygen into the gas diffusion chamber and an action of pumping oxygen from the gas diffusion chamber based on the output of the oxygen detection cell. Since the configuration is such that the pump current Ip flowing through the oxygen pump cell is measured to obtain the oxygen concentration and the hydrogen concentration, the reaction component gases in the gas to be measured are continuously supplied to the gas diffusion chamber based on the respective diffusion coefficients. It will spread.

That is, the pump current Ip to be measured is the total value of all the reaction components, and the pump current Ip for each reaction component cannot be obtained. That is,
When a plurality of combustible gas properties coexist,
Although there are combustible gases such as various hydrocarbons such as oxygen, carbon monoxide, hydrogen, and methane, and various alcohols, conventional sensors have poor gas selectivity, and it has been difficult to detect a specific gas.

For example, in the case of combustion in a gasoline engine, when the amount of fuel is larger than the stoichiometric air-fuel ratio, that is, in the case of so-called rich combustion, carbon monoxide exists about three times as much as several percent of hydrogen. In a fuel cell system that extracts hydrogen from various fuels and generates electric power from the hydrogen and oxygen (air), combustible gases other than hydrogen, such as carbon monoxide, may be present in the fuel reforming process. is there.

In this fuel cell system, from the viewpoint of improving the efficiency of power generation and the reliability of the fuel cell system, the appearance of a sensor capable of selectively detecting hydrogen and carbon monoxide is strongly desired. Therefore, solving this has been a conventional problem.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and is excellent in hydrogen selectivity and capable of selectively measuring hydrogen gas concentration.
Combustible gas concentrations other than hydrogen gas can also be measured simultaneously.For example, in a fuel cell system, when the high-concentration reactive component is only carbon monoxide other than hydrogen, the hydrogen concentration and the carbon monoxide concentration are simultaneously measured. Measurement is possible, and low cost and high reliability can be realized at the same time by using an oxygen ion conductive solid electrolyte that has a long track record in durability and reliability widely used as an engine control sensor. An object of the present invention is to provide a combustible gas sensor and a combustible gas concentration measuring method using the same.

[0010]

According to a first aspect of the present invention, there is provided a combustible gas sensor which passes through a gas diffusion rate controlling section for limiting a diffusion amount of a gas to be measured and a gas diffusion rate controlling section. A gas diffusion chamber in which gas diffuses, a gas concentration measuring means provided in the gas diffusion chamber, a gas composition conversion means having an ability to oxidize combustible gas in the gas diffusion chamber, and a gas composition for intermittently driving the gas composition conversion means It is configured to include a conversion intermittent drive unit and a combustible gas concentration measurement unit that separates and obtains a desired combustible gas concentration based on an output result of the gas concentration measurement unit obtained by the intermittent drive by the gas composition conversion intermittent drive unit. It is characterized by:

In the flammable gas sensor according to the present invention, as described in claim 2, the flammable gas concentration measuring means, after a predetermined time has elapsed since the gas composition converting means stopped the composition conversion, It is possible to calculate the hydrogen concentration and / or the concentration of combustible gas other than hydrogen from the measurement result obtained after the hydrogen is saturated in the gas diffusion chamber obtained by the gas concentration measuring means.

Similarly, in the flammable gas sensor according to the present invention, the flammable gas concentration measuring means may be configured to perform a predetermined time after the gas composition converting means stops the composition conversion. Calculating the hydrogen concentration and / or the concentration of combustible gas other than hydrogen from the measurement result obtained by the gas concentration measuring means until the hydrogen is saturated in the gas diffusion chamber and the measurement result after the hydrogen is saturated in the gas diffusion chamber. It can be.

Similarly, in the combustible gas sensor according to the present invention, as described in claim 4, the gas composition conversion intermittent driving means includes a hydrogen dependent setting mode in which the measured value of the gas concentration measuring means strongly depends on hydrogen. In addition, a configuration may be provided having a function of switching at a predetermined cycle between a combustible gas dependent setting mode in which the measured value of the gas concentration measuring means depends on the combustible gas containing hydrogen.

[0014] Similarly, in the combustible gas sensor according to the present invention, as described in claim 5, a second gas diffusion controlling portion is provided between the gas concentration measuring means and the gas composition converting means. be able to.

Similarly, in the flammable gas sensor according to the present invention, the second gas diffusion-controlling portion may be a hydrogen separator that selectively permeates hydrogen.

Similarly, in the flammable gas sensor according to the present invention, the second gas diffusion-controlling part is a carbon monoxide adsorbent for selectively adsorbing carbon monoxide. be able to.

On the other hand, in the method for measuring the concentration of combustible gas using the combustible gas sensor according to the present invention, as described in claim 8, a gas diffusion rate-limiting unit for limiting the amount of diffusion of the gas to be measured, A gas diffusion chamber in which the gas passing through the gas diffusion part diffuses, a gas concentration measuring means provided in the gas diffusion chamber, a gas composition conversion means capable of oxidizing combustible gas in the gas diffusion chamber, and a gas composition conversion means intermittently A gas composition conversion intermittent driving means to be driven; and a combustible gas concentration measuring means for separating and obtaining a desired combustible gas concentration based on an output result of the gas concentration measuring means obtained by the intermittent driving by the gas composition conversion intermittent driving means. And a configuration using a combustible gas sensor.

In the flammable gas concentration measuring method using a flammable gas sensor according to the present invention, the flammable gas concentration measuring means of the flammable gas sensor comprises a gas composition converting means for performing the composition conversion. After a lapse of a predetermined time from the stop, the hydrogen concentration and / or the concentration of combustible gas other than hydrogen may be calculated from the measurement result after saturation of hydrogen in the gas diffusion chamber obtained by the gas concentration measurement means. it can.

Similarly, in the flammable gas concentration measuring method using a flammable gas sensor according to the present invention, the flammable gas concentration measuring means of the flammable gas sensor is characterized in that the gas composition converting means performs the composition conversion. After a lapse of a predetermined time from the stop, the measurement result until the hydrogen is saturated in the gas diffusion chamber obtained by the gas concentration measurement means and the measurement result after the hydrogen is saturated in the gas diffusion chamber are used to determine the hydrogen concentration and / or Alternatively, the concentration of a combustible gas other than hydrogen can be calculated.

Similarly, in the flammable gas concentration measuring method using the flammable gas sensor according to the present invention, as described in claim 11, the gas composition conversion intermittent driving means of the flammable gas sensor uses the measured value by the gas concentration measuring means. Has a function of switching at a predetermined cycle between a hydrogen-dependent setting mode in which the gas strongly depends on hydrogen and a combustible gas-dependent setting mode in which the measured value of the gas concentration measuring means depends on the combustible gas containing hydrogen. Can be.

Similarly, in the flammable gas concentration measuring method using the flammable gas sensor according to the present invention, as described in claim 12, the measured value by the gas concentration measuring means in the hydrogen dependent setting mode and the flammable gas The hydrogen concentration and / or the concentration of combustible gas other than hydrogen can be calculated from the value measured by the gas concentration measuring means in the dependent setting mode.

Similarly, in the flammable gas concentration measuring method using the flammable gas sensor according to the present invention, the measured value by the gas concentration measuring means in the hydrogen dependent setting mode and the flammable gas It is possible to adopt a configuration in which the values measured by the gas concentration measuring means in the dependent setting mode are all maximum values.

Similarly, in the flammable gas concentration measuring method using the flammable gas sensor according to the present invention, as described in claim 14, the flammable gas sensor is provided between the gas concentration measuring means and the gas composition converting means. A two-gas diffusion-controlling part may be provided.

Similarly, in the flammable gas concentration measuring method using the flammable gas sensor according to the present invention, the second gas diffusion-controlling portion of the flammable gas sensor may be configured to selectively transmit hydrogen. It can be as a separator.

Similarly, in the flammable gas concentration measuring method using the flammable gas sensor according to the present invention, the second gas diffusion-controlling portion of the flammable gas sensor selectively adsorbs carbon monoxide. The carbon monoxide adsorbent to be used can be a carbon monoxide adsorbent.

[0026]

According to the first and eighth aspects of the present invention, there is provided a gas diffusion control section for limiting the diffusion amount of the gas to be measured;
A gas diffusion chamber in which the gas that has passed through the gas diffusion control section is diffused,
Gas concentration measuring means provided in the gas diffusion chamber, gas composition conversion means capable of oxidizing combustible gas in the gas diffusion chamber, gas composition conversion intermittent driving means for intermittently driving the gas composition conversion means, and gas composition conversion Since the combustible gas sensor is provided with a combustible gas concentration measuring unit that separates and obtains a desired combustible gas concentration based on the output result of the gas concentration measuring unit obtained by the intermittent driving by the intermittent driving unit, the diffusion speed of the hydrogen gas is reduced. By utilizing the characteristic that it is much faster than other components, hydrogen can be measured selectively.

That is, the gas composition conversion means switches between a state in which the gas has the composition of the gas to be measured as it is and a state in which the combustible gas (component gas to which the sensor reacts) is substantially zero, and gas diffusion when the two states are switched. If the measurement timing is adjusted according to the speed, the concentration of hydrogen gas can be selectively measured, and at this time, the concentration of combustible gas other than hydrogen can be measured at the same time.

In the second and ninth aspects of the present invention,
Hydrogen saturates earliest among the reaction components of the gas to be measured, and the change in the measured value after hydrogen saturation is a reaction component other than hydrogen.Therefore, the saturation timing of this hydrogen is determined in advance. If so, the concentration of the combustible gas other than hydrogen can be calculated from the change amount or the change rate after hydrogen saturation.

In the third and tenth aspects of the present invention, the hydrogen component that saturates most quickly among the reaction components of the gas to be measured is hydrogen, and before the change to the measured value due to another combustible gas appears, only hydrogen is used. The hydrogen concentration is determined from the measured value during this period, and the concentration of combustible gas other than hydrogen is determined by removing the hydrogen concentration from the measured value to which changes due to components other than hydrogen have been added. It will be.

Here, the measurement timing depending only on hydrogen and the measurement timing of the total value including other flammable gas components may be obtained in advance, and the respective timings are determined after saturation of hydrogen and flammable gas. Desirably after gas saturation, the effect will be produced even during saturation.

According to the fourth and eleventh aspects of the present invention, since the above-described configuration is adopted, the separability between hydrogen and a combustible gas containing hydrogen can be enhanced by making the transient state of the gas variable. .

According to the fifth and fourteenth aspects of the present invention, the difference between the saturation time of hydrogen and the saturation time of other flammable gas can be enlarged, and the hydrogen concentration and flammability other than hydrogen can be increased. The measurement accuracy of the gas concentration is improved.

According to the sixth and fifteenth aspects of the present invention, since the above-described configuration is employed, the measurement accuracy of the hydrogen concentration and the concentration of combustible gas other than hydrogen is further improved.

According to the seventh and sixteenth aspects of the present invention, since the above-described configuration is employed, for example, in a fuel cell system in which hydrogen and carbon monoxide coexist, the measurement accuracy of carbon monoxide is significantly improved. Becomes

According to the twelfth aspect of the present invention, by using the flammable gas sensor according to the fourth aspect, a measured value strongly dependent on the hydrogen concentration and a measured value dependent on the flammable gas concentration containing hydrogen can be easily taken out. As a result, the calculation error of each concentration is reduced, and the measurement accuracy is improved.

According to the thirteenth aspect of the present invention, since the above-described configuration is employed, the calculation resolution can be maximized, so that the measurement accuracy is improved and the pointing stability is good.

[0037]

According to the first and eighth aspects of the present invention, since the above-mentioned structure is employed, the concentration of hydrogen gas can be selectively measured, and the concentration of combustible gas other than hydrogen can be simultaneously measured. For example, in a fuel cell system, when the high-concentration reaction component is only carbon monoxide other than hydrogen, it is possible to simultaneously measure the hydrogen concentration and the carbon monoxide concentration, and furthermore, the engine By using an oxygen ion conductive solid electrolyte that is widely used as a control sensor, it is possible to obtain a configuration that has a proven record in durability and reliability, and at the same time reduce costs and improve reliability. A remarkably excellent effect that it can be realized is brought about.

According to the second and ninth aspects of the present invention, by obtaining the saturation timing of hydrogen in advance, an extremely excellent effect that the concentration of combustible gas other than hydrogen can be calculated is obtained. According to the third and tenth aspects of the present invention, the concentration of combustible gas other than hydrogen is calculated by removing the hydrogen concentration from the measured value to which a change due to components other than hydrogen has been added after saturation of hydrogen. Significantly improved effect.

Further, according to the fourth and eleventh aspects of the present invention, since the above-mentioned structure is provided, hydrogen and
A remarkably excellent effect of being able to enhance the separability from the combustible gas containing hydrogen is provided.

According to the fifth and fourteenth aspects of the present invention, the difference between the saturation time of hydrogen and the saturation time of other flammable gas can be enlarged, and the hydrogen concentration and the hydrogen concentration other than hydrogen can be increased. A remarkably excellent effect that the measurement accuracy of the flammable gas concentration can be improved.

Further, in the inventions according to the sixth and fifteenth aspects, the configuration described above has an extremely excellent effect that the measurement accuracy of the hydrogen concentration and the concentration of combustible gas other than hydrogen can be further improved. Brought.

Further, in the invention according to claims 7 and 16, since the above-mentioned configuration is adopted, for example,
In a fuel cell system in which hydrogen and carbon monoxide coexist, an extremely excellent effect is obtained in that the measurement accuracy of carbon monoxide in particular can be greatly improved.

According to the twelfth aspect of the present invention, by using the flammable gas sensor according to the fourth aspect, a measured value strongly dependent on the concentration of hydrogen and a measured value dependent on the concentration of the flammable gas containing hydrogen can be obtained. It can be easily taken out, and as a result, an extremely excellent effect that it is possible to reduce the calculation error of each concentration and improve the measurement accuracy can be achieved.

According to the thirteenth aspect of the present invention, since the above-described configuration is adopted, the calculation resolution can be maximized, and therefore, the measurement accuracy can be improved. A remarkably excellent effect that the pointing stability can be improved is provided.

[0045]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments, but it goes without saying that the present invention is not limited to only such embodiments. Also, what is shown in the drawings of this embodiment is the size and aspect ratio of the actual sensor element.
It is needless to say that this is not a shape but an explanation for easy understanding of the configuration and operation.

(Embodiment 1) First, a first embodiment is shown in FIG. The sensor element 110 of the hydrogen sensor (combustible gas sensor) shown in FIG.
The sensor element 110 measures the oxygen concentration in the gas diffusion chamber 12 based on the oxygen concentration in the atmosphere (approximately 20.9%). A first oxygen detection cell 13 and a first oxygen pump cell 11 driven based on the measurement result of the first oxygen detection cell 13 are formed so as to sandwich the gas diffusion chamber 12, and the first oxygen pump cell 11 and the first oxygen Oxygen detection cell 1
Reference numerals 3 are connected to a sensor control circuit (gas concentration measuring means) 20, respectively.

Here, the first oxygen sensing cell 13 is composed of a pair of electrodes (platinum) 13b, 13c having a catalytic action on both surfaces of an oxygen ion conductive solid electrolyte 13a (zirconia having a property of selectively transmitting oxygen). Are arranged. One of the pair of electrodes 13b and 13c is an oxygen reference electrode 1 facing an oxygen reference chamber 14 communicating with the atmosphere.
3b, and the other is constituted by an oxygen measurement electrode 13c facing the gas diffusion chamber 12.

Similarly, the first oxygen pump cell 11 has a structure in which a pair of electrodes (platinum) 11b and 11c having a catalytic action are arranged on both surfaces of an oxygen ion conductive solid electrolyte body 11a. One of the pair of electrodes 11b and 11c is constituted by an oxygen pump outer electrode 11b facing the outside of the gas diffusion chamber 12, and the other is constituted by an oxygen pump inner electrode 11c facing the gas diffusion chamber 12. I have.

Further, as the gas composition conversion means, the second oxygen detection cell 13 and the second oxygen pump cell 11 are respectively provided at a diffusion upstream position separated by a predetermined diffusion distance.
An oxygen detection cell 113 and a second oxygen pump cell 111 are provided, and are configured to be driven by the sensor control circuit 120.

Here, the second oxygen sensing cell 113 is composed of a pair of electrodes (platinum) 113b, 113c having a catalytic action on both surfaces of the oxygen ion conductive solid electrolyte 13a (zirconia having a property of selectively transmitting oxygen). And one of the pair of electrodes 113b and 113c is constituted by an oxygen reference electrode 113b facing the oxygen reference chamber 14 which communicates with the atmosphere, and the other is formed of an oxygen reference electrode 113b facing the gas diffusion chamber 12. It is composed of a measurement electrode 113c.

Similarly, the second oxygen pump cell 111 has a configuration in which a pair of electrodes (platinum) 111b and 111c having a catalytic action are disposed on both surfaces of the oxygen ion conductive solid electrolyte body 11a. , 111c is constituted by an oxygen pump outer electrode 111c facing the outside of the gas diffusion chamber 12, and the other is constituted by an oxygen pump inner electrode 111b facing the gas diffusion chamber 12.

In this case, the sensor control circuit 1 for driving the second oxygen pump cell 111 and the second oxygen detection cell 113
20 is connected to a gas composition conversion intermittent driving means 130 for intermittently driving the same, and a sensor control circuit 2 for driving the first oxygen pump cell 11 and the first oxygen detection cell 13.
0 is connected to the arithmetic output means 30 as a combustible gas concentration measuring means for separating and obtaining a desired combustible gas concentration based on the output result of the sensor control circuit 20 obtained by the intermittent driving by the gas composition conversion intermittent driving means 130. I have.

Reference numeral 15 denotes a heater section 15 for controlling the sensor element 110 to an active temperature. The heater section 15 is provided with a heater 15b in a ceramic substrate 15a and connected to a heater control circuit 15c. It is constituted by.

Reference numerals 12a and 14a are both spacers.

Next, the operation of the hydrogen sensor having such a configuration will be described with reference to FIG. The first oxygen detection cell 13 and the first oxygen pump cell 11 are always in a measurement state (always ON). On the other hand, the second oxygen detection cell 113 and the second oxygen pump cell 111, which form the basic configuration of the present invention.
Is a periodic drive control (ON) as shown in [B] of FIG.
/ OFF chopping drive). This state is shown by enlarging part A in FIG. 1 to schematically show a gas reaction state [C].
Explaining with (image diagram), (a) of [C] in FIG. 2 shows that the second oxygen pump cell 111 supplies oxygen into the gas diffusion chamber 12 based on the detection result of the first oxygen detection cell 13 (the pumping current Ip ( 2), and the atmosphere from the second oxygen detection cell 113 to the first oxygen detection cell 13 is not the state of the gas to be measured.
It will be converted to an atmosphere with almost no flammable gas.

At this time, the pumping current Ip (2) is large (thick arrow) as shown by the arrow in FIG.
p (1) is almost zero (thin arrow). this is,
The set oxygen partial pressure of the second oxygen detection cell 113 is set to, for example, 10
^It may be adjusted to about ^-6 to ^10-9 .

Next, (c) of [C] in FIG. 2 shows a state in which the second oxygen pump cell 111 is stopped (OFF state).
The gas to be measured reaches the first oxygen detection cell 13, and the first oxygen pump cell 11 is connected to the gas diffusion chamber 1 according to the detection result.
Supply oxygen in 2 (supply with pumping current Ip (1))
Will do. The stop control of the second oxygen pump cell 111 can be relatively easily performed by the drive signal processing means in the sensor control circuit 120 for driving the second oxygen pump cell 111. At this time, the pumping current Ip (2) instantaneously becomes zero (thin arrow) as indicated by the arrow [C] in FIG.
p (1) becomes large (thick arrow).

Further, the state during this period (after switching from ON to OFF) is represented by (b) in [C] of FIG. That is, the state in which the atmosphere from the second oxygen detection cell 113 to the first oxygen detection cell 13 is changing in accordance with the diffusion speed of each component gas in the gas to be measured is shown.

FIG. 3 shows the diffusion coefficients of the main components of the combustible gas. [A] in FIG. 3 shows the self-diffusion coefficient D11 and the mutual diffusion coefficient D12 of two components using air as the medium gas, and is disclosed in a specialized book (Physical Property Constants 8; edited by The Chemical Industry Association). . Further, the mutual diffusion coefficient D12
Is shown by a bar graph in [B] of FIG.

Thus, it can be seen that the diffusion rate of hydrogen gas is much higher than that of other gases. From this characteristic, as shown in (b) of [C] of FIG.
After reaching the oxygen sensing cell 13, other components sequentially arrive after a predetermined time has elapsed. FIG. 2 shows the behavior of the pumping current Ip (1) of the first oxygen pump cell 13 that is driven and controlled according to the detection result of the first oxygen detection cell 13 at this time.
[A], the pumping current Ip (1) remains almost zero output for the time Td0 from the start of the stop of the second oxygen pump cell 111 (Ip (2) is turned off), and the leading hydrogen gas is 1 After reaching the oxygen measurement electrode 13c of the oxygen detection cell 13, the pumping current Ip (1) increases in accordance with the amount of diffusion of hydrogen that diffuses with almost a first-order delay, and the arrival of combustible gas other than hydrogen (Td1) After (time), a pumping current Ip (X) corresponding to another gas component is applied. Here, hydrogen is the fastest pumping current Ip (h ₂ )
Saturates. The pumping current Ip (1) after the hydrogen content is saturated is relatively short (several milliseconds to several tens of milliseconds).
Since the measurement is performed in c), the hydrogen content can be regarded as a substantially constant value. Therefore, the change in the pumping current Ip (1) after the hydrogen content is saturated depends on the combustible gas other than hydrogen.

The above calculation flow will be further described with reference to FIG. 4. In the initial setting in step S1, the time Ton (set) for turning on the second oxygen pump cell 111 and the time Toff (se) for turning off the second oxygen pump cell 111 are set.
t), measurement timings Td2 (set), Td3 (se
t) is set in storage means (not shown). FIG.
Are associated using the same reference numerals as in FIG. Also, the initial setting (step S1), the previously set in a storage means (not shown) of combustible gas sensitivity coefficient K _X and the hydrogen gas sensitivity coefficient Kh _2.

Therefore, in step S2, after the heater control is started by the heater control circuit 15c so that the sensor element 110 becomes the active temperature (about 600 ° C. to 800 ° C.), in step S3, the sensor element 110 is set to the active temperature. If it is determined that the control has been completed, the control of the first oxygen pump cell 11 and the second oxygen pump cell 111 by the sensor control circuits 20 and 120 is started in steps S4 and S5, and at the same time, in step S6, the timer T
Clear on and start counting up.

Here, in managing the activation state of the sensor element 110, instead of the sensor element temperature, the sensor element resistance value or the time (for example, 30 seconds) from when the heater is turned on may be managed.

Next, when the Ton determination is Yes in step S7, that is, when the timer Ton is set to To
When n (set) is reached, the timer Td2, Td3 and timer Toff are cleared and count-up is started in steps S9 and S10 at the same time as the second oxygen pump cell 111 is stopped in step S8.

Subsequently, when the Td2 determination is Yes in step S11, that is, when the timer Td2 reaches Td2 (set), in step S12, the current pumping current Ip (1) is read.
Write to Ip (1) a.

Next, when the Td3 determination is Yes in step S13, that is, when the timer Td3 is set to T
When d3 (set) is reached, in step S14, the current pumping current Ip (1) is read,
Write to Ip (1) b.

Here, in step S15, Ip
(1) Calculate ΔIp changed from a to Ip (1) b,
In step S16, ΔIp−
When the _CX table (Table 1) is used, the combustible gas concentration _CX other than hydrogen is determined.

Next, in step S17, the combustible gas concentration C _X and the combustible gas sensitivity coefficient K determined in advance.
By multiplying by _X , the pumping current Ip (X) corresponding to the combustible gas concentration in Ip (1) b is obtained. In step S18, the pumping current Ip (X) corresponding to the combustible gas concentration is calculated from Ip (1) b. After removal, the pumping current Ip (h ₂ ) for the hydrogen concentration is calculated, and in step S19,
Using the Ip (h ₂ ) -Ch ₂ table (Table 2) prepared in advance, the hydrogen concentration Ch ₂ is obtained.

In step S20, the calculation result is output as a digital signal or an analog signal to a display (not shown) or an external device. Next, when the Toff determination is Yes in step S21, When Toff reaches Toff (set), the process returns to step S5 and repeats steps S5 to S21.

In this embodiment, the concentration is determined from the measured values at two points after the saturation of hydrogen.
The number of points is not limited to two,
Also, the second measurement timing here is desirably at the time when the combustible gas is saturated. Furthermore, the same effect as that of the present embodiment can be obtained by adopting a method of obtaining not only the change amount of the pumping current Ip (1) within a predetermined time but also the change rate of a plurality of pumping currents Ip (1). it can. Furthermore, the hydrogen concentration Ch ₂ may be determined from the hydrogen gas sensitivity coefficient Kh ₂ obtained beforehand pumping current Ip _{(h 2).}

As described above, it is possible to provide a low-cost and highly reliable combustible gas sensor and a method for measuring a combustible gas concentration using the same without requiring a complicated and large-scale device.

(Embodiment 2) Next, a second embodiment will be described with reference to FIG.

First, the behavior of the pumping current Ip (1) will be described with reference to FIG.
Current (pumping current Ip (2) is OFF), the pumping current Ip (1) remains substantially zero output for the time Td0, and then the first hydrogen gas is supplied to the first oxygen detection cell 1
After reaching the oxygen measurement electrode 13c of No. 3, the pumping current I
p (1) increases and the arrival of combustible gas other than hydrogen (Td1
After time), the pumping current Ip according to the other gas components
(X) is added. That is, since the pumping current Ip (1) within the time Td1 is the hydrogen gas component Ip (h ₂ ), the hydrogen concentration can be obtained from the pumping current Ip (1) within the time Td1.

The measurement timing at this time may be set to a constant value without depending on the gas concentration, and may be an arbitrary time as long as it is before reaching a combustible gas other than hydrogen. For example, the pumping current Ip (h ₂ ) after hydrogen saturation can be estimated from the amount of change (or the rate of change) of at least two points of the pumping current Ip (1) before reaching the combustible gas other than hydrogen.

In the above-described first embodiment, the case where the concentration of the combustible gas other than hydrogen and the concentration of hydrogen are obtained after estimating and calculating the pumping current Ip (X) of the combustible gas component other than hydrogen has been described. In the second embodiment, the hydrogen concentration pumping current Ip (h ₂ ) is estimated and calculated, and then the hydrogen concentration and the concentration of combustible gas other than hydrogen are obtained. 4 can be constructed with a relatively simple algorithm.

(Embodiment 3) Next, a third embodiment will be described with reference to FIG.

In FIG. 6B, Tc1 is the stop setting time of the second oxygen pump cell 111 set so that the pumping current Ip (h ₂ ) for only hydrogen can be measured. Tc2 is a control time of the second oxygen pump cell 111 for oxidizing the combustible gas after Tc1, and is a set time at which the pumping current Ip (h ₂ ) becomes zero or almost zero. Further, Tc3 is a stop setting time of the second oxygen pump cell 111 set so that the pumping current Ip (h ₂ + _X ) of the combustible gas including hydrogen can be measured. Further, Tc4 is a control time of the second oxygen pump cell 111 for oxidizing the combustible gas after Tc3, and similarly to Tc2, the pumping current Ip
(H ₂ ) is a set time at which it becomes zero or almost zero.

Here, Tc1, Tc2, Tc3, Tc4
And Td1 may be set in advance, whereby
The pumping current Ip (h ₂ ) for the hydrogen and the pumping current Ip (h ₂ + _X ) for the combustible gas including the hydrogen can be separated by the chopping action of the gas. As in the second embodiment, the hydrogen concentration and the concentration of combustible gas other than hydrogen can be obtained.

In the above-described first, second and third embodiments, the method of converting the pumping current value into each gas concentration will be further described. The relationship between the gas concentration and the pumping current Ip (h ₂ ) of hydrogen may be determined in advance using hydrogen gas, and when the concentration of combustible gas is determined, the measurement target gas may be hydrogen and carbon monoxide. For example, the relationship between the gas concentration and the pumping current Ip (X) may be obtained in advance using a predetermined concentration of carbon monoxide gas. In this case, the sensor is a hydrogen sensor and can be a carbon monoxide sensor. It is.

(Embodiment 4) Next, a fourth embodiment will be described with reference to FIG.

As shown in FIG. 7, the sensor element 210 in this embodiment is different from the sensor element 110 in the first embodiment.
The difference is that the sensor control circuit 12 that drives the second oxygen pump cell 111 and the second oxygen detection cell 113
0, and a second gas diffusion rate controlling section 212 having a larger diffusion resistance than the gas diffusion rate controlling section 10a is provided between the sensor control circuit 20 for driving the first oxygen pump cell 11 and the first oxygen detection cell 13, This second gas diffusion control section 212
The combustible gas conversion unit 212b and the combustible gas measurement unit 212 are provided on the sensor control circuit 120 side and the sensor control circuit 20 side.
The other configuration is the same as the sensor element 110 in the first embodiment in that a is formed.

In this embodiment, the second gas diffusion controlling section 2
With the provision of 12, the difference between the diffusion speed of hydrogen (diffusion amount per unit time) to the combustible gas measuring unit 212a and the diffusion speed of combustible gas other than hydrogen (diffusion amount per unit time) is enlarged. Therefore, the separability between hydrogen and combustible gas other than hydrogen is enhanced, and the measurement accuracy of the hydrogen concentration and the concentration of combustible gas other than hydrogen is further improved.

Here, a porous ceramic body can be used for the second gas diffusion controlling section 212, and the diffusion resistance when the porous ceramic body is used can be adjusted by the average pore diameter. is there.

If the second gas diffusion rate-controlling portion 212 is formed of a known hydrogen separator (not shown), the measurement accuracy of the hydrogen concentration and the concentration of combustible gas other than hydrogen is further improved. As the body, palladium having hydrogen separation ability or a ceramic porous body formed with a palladium alloy film can be used.

Further, when the second gas diffusion controlling portion 212 is formed of a known carbon monoxide adsorbent (not shown), particularly when the main components of the combustible gas are hydrogen and carbon monoxide as in a fuel cell system. In this method, the measurement accuracy of the hydrogen concentration and the carbon monoxide concentration is further improved. At this time, ZnO or SnO ₂ porous material can be used as the carbon monoxide adsorbent.

As described above, it is possible to provide a compact and inexpensive combustible gas sensor (concentration sensor other than hydrogen and hydrogen) having high reliability and high hydrogen selectivity, and a method for measuring a combustible gas concentration using the same. it can.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view showing a configuration of a combustible gas sensor according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the operation of the invention according to the first embodiment of the present invention divided into [A], [B], and [C].

FIG. 3 is a table showing a diffusion coefficient of a combustible gas in a table and a bar graph.

FIG. 4 is an explanatory diagram showing a control and calculation flow according to the first embodiment of the present invention.

FIG. 5 is an explanatory diagram showing the operation of the invention according to the second embodiment of the present invention divided into [A] and [B].

FIG. 6 is an explanatory diagram showing the operation of the invention according to the third embodiment of the present invention divided into [A] and [B].

FIG. 7 is an explanatory sectional view showing a configuration of a combustible gas sensor according to a fourth embodiment of the present invention.

[Explanation of symbols]

10a Gas diffusion control section 12 Gas diffusion chamber 20 Sensor control circuit (gas concentration measuring means) 30 Calculation output means (flammable gas concentration measuring means) 110, 210 Sensor element of hydrogen sensor (flammable gas sensor) 120 Sensor control circuit (gas composition conversion) Means) 130 Gas composition conversion intermittent driving means 212 Second gas diffusion rate controlling part

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G01N 27/46 327N 327R

Claims (16)

[Claims] A gas diffusion control section for restricting a diffusion amount of a gas to be measured; a gas diffusion chamber in which gas passing through the gas diffusion control section is diffused; and a gas concentration measuring means provided in the gas diffusion chamber;
Gas composition conversion means capable of oxidizing combustible gas in the gas diffusion chamber, gas composition conversion intermittent driving means for intermittently driving the gas composition conversion means, and gas concentration measurement obtained by intermittent driving by the gas composition conversion intermittent driving means A combustible gas sensor characterized by comprising a combustible gas concentration measuring means for separating and obtaining a desired combustible gas concentration based on an output result of the means. 2. The combustible gas concentration measuring means, after a predetermined time has elapsed since the gas composition conversion means stopped the composition conversion,
The combustible gas sensor according to claim 1, wherein a hydrogen concentration and / or a combustible gas concentration other than hydrogen is calculated from a measurement result obtained after hydrogen saturation in the gas diffusion chamber obtained by the gas concentration measurement unit. 3. The combustible gas concentration measuring means, after a predetermined time has elapsed since the gas composition conversion means stopped the composition conversion,
Calculating a hydrogen concentration and / or a combustible gas concentration other than hydrogen from a measurement result obtained by the gas concentration measuring means until hydrogen is saturated in the gas diffusion chamber and a measurement result after hydrogen is saturated in the gas diffusion chamber. Item 3. The combustible gas sensor according to Item 1. 4. The gas composition conversion intermittent driving means includes a hydrogen-dependent setting mode in which a measured value of the gas concentration measuring means strongly depends on hydrogen, and a combustible gas in which the measured value of the gas concentration measuring means depends on a combustible gas containing hydrogen. 4. A function for switching between a dependent setting mode and a dependent setting mode at a predetermined cycle.
The combustible gas sensor according to any one of the above. 5. A gas diffusion rate controlling part is provided between a gas concentration measuring means and a gas composition converting means.
The combustible gas sensor according to any one of the above. 6. The combustible gas sensor according to claim 5, wherein the second gas diffusion-controlling part is a hydrogen separator that selectively permeates hydrogen. 7. The combustible gas sensor according to claim 5, wherein the second gas diffusion-controlling part is a carbon monoxide adsorbent for selectively adsorbing carbon monoxide. 8. A gas diffusion control part for limiting the diffusion amount of the gas to be measured, a gas diffusion chamber in which gas passing through the gas diffusion control part is diffused, and a gas concentration measuring means provided in the gas diffusion chamber;
Gas composition conversion means capable of oxidizing combustible gas in the gas diffusion chamber, gas composition conversion intermittent driving means for intermittently driving the gas composition conversion means, and gas concentration measurement obtained by intermittent driving by the gas composition conversion intermittent driving means A combustible gas concentration measuring method using a combustible gas sensor, comprising a combustible gas concentration measuring means for separating and obtaining a desired combustible gas concentration based on an output result of the means. 9. The flammable gas concentration measuring means of the flammable gas sensor comprises: after a predetermined time has elapsed since the gas composition converting means stopped the composition conversion, after the hydrogen was saturated in the gas diffusion chamber obtained by the gas concentration measuring means. 9. The method for measuring a combustible gas concentration using a combustible gas sensor according to claim 8, wherein a hydrogen concentration and / or a combustible gas concentration other than hydrogen is calculated from the measurement result. 10. A combustible gas concentration measuring means of a combustible gas sensor, wherein after a predetermined time has elapsed since the gas composition converting means stopped the composition conversion, hydrogen is saturated in the gas diffusion chamber obtained by the gas concentration measuring means. 9. The flammable gas sensor according to claim 8, wherein the hydrogen concentration and / or the flammable gas concentration other than hydrogen are calculated from the measurement result of the hydrogen gas and the measurement result after the hydrogen is saturated in the gas diffusion chamber. Gas concentration measurement method. 11. The gas composition conversion intermittent driving means of the combustible gas sensor includes a hydrogen-dependent setting mode in which the measured value of the gas concentration measuring means strongly depends on hydrogen, and a gas-dependent setting mode in which the measured value of the gas concentration measuring means depends on combustible gas containing hydrogen. The method for measuring the concentration of a combustible gas using a combustible gas sensor according to any one of claims 8 to 10, further comprising a function of switching between a settable mode and a combustible gas dependent setting mode at a predetermined cycle. 12. A hydrogen concentration and / or a non-hydrogen combustible gas concentration based on a value measured by the gas concentration measuring means in the hydrogen dependent setting mode and a value measured by the gas concentration measuring means in the combustible gas dependent setting mode. A combustible gas concentration measuring method using the combustible gas sensor according to claim 11. 13. The flammable fuel according to claim 12, wherein a value measured by the gas concentration measuring means in the hydrogen-dependent setting mode and a value measured by the gas concentration measuring means in the flammable gas-dependent setting mode are both maximum values. Combustible gas concentration measurement method using a gas sensor. 14. The combustible gas sensor according to claim 8, wherein the combustible gas sensor is provided with a second gas diffusion rate controlling part between the gas concentration measuring means and the gas composition converting means. Combustible gas concentration measurement method used. 15. The method for measuring the concentration of a combustible gas using a combustible gas sensor according to claim 14, wherein the second gas diffusion-controlling portion of the combustible gas sensor is a hydrogen separator that selectively permeates hydrogen. 16. The method for measuring a concentration of a combustible gas using a combustible gas sensor according to claim 14, wherein the second gas diffusion-controlling portion of the combustible gas sensor is a carbon monoxide adsorbent for selectively adsorbing carbon monoxide.