JP2002250714A - Carbon monoxide sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon monoxide sensor which can be refreshed even for high concentration carbon monoxide gas. SOLUTION: The carbon monoxide sensor comprises a proton conductive electrolyte film 1, electrodes 2 arranged on the opposite sides of the electrolyte film 1 while having a catalyst, a first current collecting plate 8 provided with a gas channel 7 having gas inlet and outlet and arranged such that the gas channel 7 touches the surface of one electrode 2, a second current collecting plate 10 having a hole 9 arranged to touch the surface of the other electrode 2, a DC power supply 17 connected such that the first current collecting plate 8 serves as the positive pole and the second current collecting plate 10 serves as a negative pole and having a measuring voltage not lower than the decomposition potential of water, and means (ammeter 18) for detecting a current variable depending on the concentration of carbon monoxide gas in a gas to be detected flowing through the gas channel 7 while containing hydrogen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon monoxide sensor for detecting the concentration of carbon monoxide gas contained in a fuel gas used for a fuel cell, for example.

[0002]

2. Description of the Related Art In recent years, fuel cells using solid polymer proton conductive membranes for home use and automobile use have been actively developed. Since this fuel cell uses hydrogen gas when operating, a reformer for extracting hydrogen gas by reforming liquid fuel such as methanol or city gas is required. However, the fuel gas coming out of the reformer contains a very small amount of carbon monoxide gas at a level of tens of ppm in addition to hydrogen gas, water (generated as steam), carbon dioxide gas, and the like. If this is adsorbed on the platinum catalyst constituting the electrode of the fuel cell (this phenomenon is called poisoning), the electromotive force will decrease. Therefore, it is necessary to monitor the concentration of carbon monoxide gas in the fuel gas and control the fuel cell system.

[0003] As described above, a fuel gas (contains a large amount of hydrogen gas) supplied to function as a fuel cell
As a carbon monoxide sensor for detecting carbon monoxide gas therein, a sensor described in JP-A-11-219716 is known.

FIG. 12 is an exploded perspective view of a schematic structure of the carbon monoxide sensor. Reference numeral 150 denotes an electrolyte membrane made of a polymer having proton conductivity as a proton exchange membrane {for example, NA
FION (trademark of DuPont), having an anode 142 and a cathode 144 containing catalyst particles on both surfaces.
Reference numerals 143 and 145 denote conductive diffusion portions made of carbon paper, which contact the anode 142 and the cathode 144, respectively.
The diffusion conduction part 143 contacts a housing 154 having a gas to be detected inlet 159, an anode flow channel 146 through which the gas to be detected flows, and an outlet 151 of the gas to be detected. Cathode 1
44 is exposed to the surrounding air through the opening 152 of the housing 154. Perforated metal current collector 14
9 is in contact with the diffusion conduction part 145 and its terminal 147
Current is transmitted to Terminal 147 is slot 155
Exits the housing 154 through the housing.

Next, the operation of the carbon monoxide sensor will be described. The gas to be detected containing a large amount of hydrogen gas (same as the fuel gas) reaches the channel 146 through the gas to be detected inlet 159. From here, it passes through the diffusion conduction part 143 and is discharged from the outlet 151. On the other hand, the cathode 144 is always in contact with oxygen gas in the atmosphere. Therefore, the anode 142
And the surface of the electrolyte membrane 150 in contact with the cathode 144,
A cell reaction similar to that of a fuel cell that generates power using hydrogen gas and oxygen gas as fuel occurs, and an electromotive force is generated between the anode 142 and the cathode 144. The current and voltage at this time are detected by a current detection device and a voltage detection device (not shown) connected to the terminal 147 and the housing 154.

In this state, if carbon monoxide gas is mixed in the gas to be detected, the carbon monoxide gas is adsorbed on the catalyst particles in the anode 142 and the anode 142 is poisoned. As a result, the battery reaction caused by the hydrogen gas and the oxygen gas is inhibited, and the electromotive force between the anode 142 and the cathode 144 decreases. Since the concentration of carbon monoxide gas is reflected in the degree of poisoning, the concentration of carbon monoxide gas in the gas to be detected can be known by measuring the current fluctuation and voltage fluctuation accompanying the decrease in electromotive force. .

In such a carbon monoxide sensor, if the catalyst particles are continuously exposed to the carbon monoxide gas, the catalyst particles continue to be poisoned, and the sensitivity gradually decreases. As a countermeasure, refresh is periodically performed to remove carbon monoxide gas from poisoned catalyst particles. To this end, the anode potential is raised to a level (at least 0.8 V) sufficient to electrochemically oxidize carbon monoxide gas to carbon dioxide gas in the presence of water. Thus, the concentration of carbon monoxide gas is repeatedly obtained.

[0008]

The above-described reformer has a carbon monoxide gas concentration of several tens ppm in the fuel gas immediately after starting.
It does not mean that it is at the level, and initially produces a% level of carbon monoxide gas. Therefore, to such a carbon monoxide sensor, a high-concentration (1%) hydrogen gas containing a carbon monoxide gas was humidified and assumed immediately after the reformer was started, and the output behavior was measured. . As a result, the anode potential becomes 0.8
It was found that the output of the carbon monoxide sensor hardly returned with time even if the refresh operation for increasing the voltage to V was performed. This is because high-concentration carbon monoxide is completely adsorbed on the adsorption sites on the catalyst particles in a short time, and there is no site where water contained in the fuel gas can be decomposed on the catalyst no matter how much refreshing is performed. I think it's done.

The present invention solves this problem,
An object of the present invention is to provide a carbon monoxide sensor that can be refreshed even with a high concentration of carbon monoxide gas.

[0010]

Means for Solving the Problems To solve this problem, the invention according to claim 1 of the present invention provides a proton conductive electrolyte membrane and an electrode having a catalyst disposed on both sides of the electrolyte membrane. A first current collector plate having a gas flow path having a gas inlet and an outlet and disposed so that the gas flow path is in contact with one surface of the electrode, and the other surface of the electrode A second current collector having a hole disposed so as to be in contact with the first current collector, a first current collector being connected to a positive electrode, and a second current collector being connected so as to be a negative electrode. A direct current power supply having a voltage, and a current detecting means for detecting a current that changes in accordance with the concentration of carbon monoxide gas in the gas to be detected including hydrogen flowing in the gas flow path, so that the current is always measured even during measurement. Water vapor is electrolyzed on the catalyst and oxygen is generated, resulting in high concentration of monoxide. Adsorption sites on the catalyst even-containing gas is introduced has an effect such complete Fusagarezu allows refresh.

According to a second aspect of the present invention, in the first aspect, detection of a current change at a measured voltage higher than the decomposition potential of water and catalyst refresh at a refresh voltage higher than the measured voltage are performed in one cycle. Since the concentration of the carbon monoxide gas is obtained by changing the voltage of the DC power supply and repeating the above-described cycle, the output current returns to the original level, and the output has good reproducibility.

According to a third aspect of the present invention, in the second aspect of the present invention, since the measurement voltage and the refresh voltage are continuously changed, the output fluctuation at the time of voltage switching is smaller than that of intermittent voltage switching. It has the effect of being reduced.

According to a fourth aspect of the present invention, in the second aspect of the invention, the time for applying the refresh voltage is:
Since the time is shorter than the time for applying the measurement voltage, it has the effect of speeding up the response.

According to a fifth aspect of the present invention, in the invention of the second aspect, at the time of startup, first, a refresh voltage is applied for a predetermined time, and then measurement is started. Since the control is performed such that a large amount of water can be taken into the proton-conductive electrolyte membrane in a short time at the time of startup, stability after startup is improved. In addition, since the carbon monoxide gas adsorbed on the catalyst at the time of shutdown is removed, a large amount of water can be taken into the proton conductive electrolyte membrane in a short time without interference of the carbon monoxide gas adsorbed at the next startup. Have.

According to a sixth aspect of the present invention, in the second aspect of the present invention, the variation of the current change acceleration when the measured voltage is applied, and the variation value of the variation are compared with respective predetermined values. Since the concentration of the carbon monoxide gas is obtained by the above, the carbon monoxide gas has an effect of being able to detect the carbon monoxide concentration with high accuracy by separating from the output of the high concentration (on the order of several hundred ppm).

According to a seventh aspect of the present invention, in the second aspect of the present invention, the variation of the current change speed and the current change acceleration when the measurement voltage is applied, the variation value of the variation, and a predetermined value of each of the variations are provided. Are compared with each other to determine the concentration of carbon monoxide gas, so that it has an effect that the concentration of carbon monoxide can be detected with high accuracy by separating it from the output of low concentration (several ppm order).

According to an eighth aspect of the present invention, in the invention of the sixth or seventh aspect, since the variation is a difference between the maximum value and the minimum value of the current change acceleration within a predetermined time, the calculation is easy, and This has the effect that the variation can be reliably obtained.

According to a ninth aspect of the present invention, in the invention of the sixth or seventh aspect, the variation value is an absolute value of a difference between the variation one cycle before and the current variation.
This has the effect that the calculation is easy and the fluctuation value can be obtained reliably.

According to a tenth aspect of the present invention, in accordance with the sixth aspect of the present invention, an on signal or an off signal is output depending on whether the variation and the variation value are equal to or greater than respective predetermined values. It has the effect that the concentration switch can easily and accurately detect whether it is on the order of several hundred ppm.

[0020] According to an eleventh aspect of the present invention, in accordance with the seventh aspect of the present invention, the current changing speed, the variation, and
Since the ON signal or the OFF signal is output depending on whether or not the fluctuation value is equal to or more than the respective predetermined value, it is possible to easily and highly accurately detect whether or not the order is several ppm as a carbon monoxide concentration switch.

According to a twelfth aspect of the present invention, in accordance with the tenth or eleventh aspect of the present invention, a current ON signal or OFF signal and an even number of ON signals or OFF signals for a predetermined even cycle before the current ON signal or OFF signal. , The ON signal, and the total number of OFF signals were obtained, and the larger signal was output, so that the output chattering of the ON signal and the OFF signal in the transition period of the carbon monoxide concentration change can be reduced,
This has the effect of stably detecting the concentration of carbon monoxide.

According to a thirteenth aspect of the present invention, there is provided an electrode comprising a proton conductive electrolyte membrane, electrodes having catalysts disposed on both sides of the electrolyte membrane, and a gas flow path having a gas inlet and an outlet. A first current collector provided so that the gas flow path is in contact with one surface of the electrodes; and a second current collector having holes provided so as to be in contact with the other surface of the electrodes. When,
A DC power supply for applying a measurement voltage and a refresh voltage connected so that the first current collector plate is connected to the positive electrode and the second current collector plate is connected to the negative electrode, and a detection target gas containing hydrogen flowing in the gas flow path. Current detecting means for detecting a current that changes in accordance with the concentration of the carbon monoxide gas, the current change rate when the measurement voltage is applied is equal to or higher than a predetermined value, and the current change acceleration varies, and When the fluctuation value is equal to or less than each predetermined value, the measurement voltage is reduced to the decomposition potential of water or less, and the concentration of carbon monoxide gas is output from the current change rate at that time, and the measurement is performed when the current is equal to or less than the predetermined value. Since the voltage is returned to a predetermined value equal to or higher than the decomposition potential of water and the control for performing the refresh operation is performed, refresh can be surely performed when a high concentration of carbon monoxide gas is introduced, and at the time of low concentration. You can increase the force sensitivity, an effect that can be obtained an output of the multi-point density.

According to a fourteenth aspect of the present invention, in the invention according to the thirteenth aspect, since the measured voltage at the time of the decrease is 0.1 V or more and 0.4 V or less, high accuracy and high sensitivity even at a low concentration are provided. This has the effect that a simple carbon monoxide sensor can be constructed.

According to a fifteenth aspect of the present invention, since the measured voltage is continuously reduced and restored in the thirteenth aspect of the present invention, compared with intermittent voltage switching,
This has the effect that output fluctuations at the time of voltage switching are reduced.

According to a sixteenth aspect of the present invention, in the invention according to the thirteenth aspect, since the control for invalidating the output of the cycle when the measured voltage is restored is performed, the unstable behavior at the time of the voltage restoration is reduced. There is no output, and the carbon monoxide concentration can be detected with high accuracy.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS.

(Embodiment 1) FIG. 1 is an explanatory view for explaining a schematic structure of a carbon monoxide sensor according to Embodiment 1 of the present invention. FIG. 2 is an output current characteristic diagram at the time of one cycle measurement according to the carbon monoxide concentration of the sensor, wherein a) is an output current characteristic at a carbon monoxide concentration of 1%, and b) is a carbon monoxide concentration of 100 ppm. And c) show the output current characteristics when the carbon monoxide concentration is 5 ppm. FIG. 3 is a characteristic diagram showing the carbon monoxide concentration dependency of the current change rate of the sensor. FIG. 4 is a characteristic diagram showing the carbon monoxide concentration dependency of the current change acceleration variation of the sensor. FIG. 5 is a characteristic diagram showing the carbon monoxide concentration dependency of the variation value of the variation of the sensor. FIG. 6 is a characteristic diagram showing the carbon monoxide concentration dependency of the sensor output before and after the correction of the ON signal and the OFF signal obtained from the output calculation result. FIG. 7 is an output calculation and control flowchart of the sensor.

In FIG. 1, reference numeral 1 denotes a proton conductive electrolyte membrane made of a fluorine-based polymer material having a diameter of 1.4 cm, and a catalyst alloyed on both surfaces thereof so that the ratio of platinum to gold is 3: 1. Is loaded with carbon powder having a diameter of 1c.
Two electrodes 2 fixed on a carbon cloth of m with a fluorine-based polymer material are provided. A thickness of 0.25 mm on each of the outer circumferences of the two electrodes 2 for preventing gas leakage.
The sealing material 3 made of a silicon-based polymer is disposed. The electrolyte membrane 1 sandwiched between the two electrodes 2 and the sealing material 3 is fixed by a hot press at a temperature of 130 ° C.

Thus, the electrolyte membrane 1 and the two electrodes 2
A first current collecting plate 8 is arranged on one surface of a detection element 4 composed of the first sealing plate 3 and the two sealing materials 3 so that a gas flow path 7 having a gas inlet 5 and a gas outlet 6 is in contact with the detection element 4. ing. The gas flow path 7 has a width and a pitch of 0.5 mm and a depth of 0.3 mm so as to fit within the area of the electrode 2.
It is formed by cutting the surface of the first current collector 8 made of stainless steel (for example, JIS SUS304). The dimensions of the gas flow path 7 are not limited to the above-described dimensions, as long as a predetermined gas flow rate (100 cc / min in the present embodiment) can be secured. First current collector 8
After a cutting process, a gold plated layer having a thickness of 1 μm is formed on the surface.

The other surface of the detecting element 4 has a diameter of 1.5
A second current collector plate 10 made of stainless steel (for example, SUS304 of JIS standard) provided with a large number of holes 9 of mm is provided. A gold plating layer having a thickness of 1 μm is also formed on the surface of the second current collector plate 10.

A gas outlet 11 is provided on the surface of the second current collector plate 10 where the electrode 2 is not in contact, and a stainless steel (for example, JI
A gas chamber 12 formed by cutting S standard SUS 304) is provided. An orifice 13 having a diameter of 0.8 mm is connected to the outlet 11 as a flow control means.

First current collector 8, detecting element 4, second current collector 1
0 and the gas chamber 12 are fixed by four screws 14 in this order.

A gas inlet 15 and a gas outlet 16 are connected to the gas inlet 5 and outlet 6, respectively, each of which is formed of a pipe member having a tapered thread. The gas discharge part 16 and the outlet side of the orifice 13 are connected so as to merge.

A DC power source 17 is connected to the first current collector 8 and the second current collector 10 such that the former is a positive electrode and the latter is a negative electrode. In order to detect a current flowing between the first current collecting plate 8 and the second current collecting plate 10, an ammeter 18 as current detecting means is connected in series with the DC power supply 17. Ammeter 1
The output of 8 is connected to a microcomputer 19. The microcomputer 19 performs a predetermined calculation based on the current detected by the ammeter 20, outputs the carbon monoxide concentration, and refreshes the catalyst.
7 is continuously controlled.

Next, the operation of the carbon monoxide sensor according to this embodiment will be described.

The gas to be detected passes through the gas inlet 15 and the inlet 5 and is led to the gas channel 7. Since the gas flow path 7 is in contact with the electrode 2, the gas to be detected flows through the gas flow path 7 and diffuses evenly into the carbon paper constituting the electrode 2 to reach the catalyst. Thereafter, the detected gas is supplied to the outlet 6,
The gas is exhausted through the gas exhaust unit 16. Between the first current collector 8 and the second current collector 10, the microcomputer 19 continuously applies the measurement voltage and the refresh voltage without interruption. In this embodiment, the measured voltage is 1.3 or more, which is higher than the decomposition potential of water (theoretical value: 1.23 V).
V and the refresh voltage were set to 4 V which is higher than the measured voltage. The measurement and the refresh were performed in one cycle of 8 seconds for the former and 2 seconds for the latter, for a total of 10 seconds. By this operation, the reaction of the hydrogen gas in the detected gas on the catalyst of the electrode 2 occurs as shown in the equations (1) and (2) for the positive electrode and the negative electrode.

[0037]

Embedded image

As shown in equation (1), a dissociation reaction of hydrogen gas occurs at the electrode 2 on the positive electrode side, and the proton (H
⁺ ) Reaches the electrode 2 on the negative electrode side through the electrolyte membrane 1 and receives the electrons (e ⁻ ) again as shown in the equation (2) to generate hydrogen gas. Therefore, in the presence of hydrogen gas, an electric closed circuit is formed between the detection element 4 and the DC power supply 17, and a current flows according to the proton conductivity. The hydrogen gas generated at the electrode 2 on the negative electrode side has holes 9, a gas chamber 12, and an outlet 1.
1. Exhausted through the orifice 13.

The current value is detected by the above operation, and the microcomputer 19 outputs a signal corresponding to the concentration of carbon monoxide gas.

Next, the signal processing calculated in the microcomputer 19 will be described in detail below.

The gas inlet 15 of the carbon monoxide sensor
Assuming the gas state of the reformer immediately after the start, the concentration of the carbon monoxide gas was set to 1% for 30 minutes, 0.2% for 10 minutes, and 100 p.
The humid simulated gas to be detected was introduced by gradually decreasing the pm for 10 minutes, 20 ppm for 10 minutes, and 5 ppm for 60 minutes. The gas flow rate at the time of measurement was 100 cc / min.

FIG. 2 shows the output current characteristics detected by the ammeter 18 in the above measurement. a) when the concentration of carbon monoxide gas is 1%, b) when the concentration is 100 ppm, and c) when the concentration is 5%.
ppm, for one cycle of measurement (8 seconds)
The transition of is shown. As shown in FIG. 2A), when the concentration of carbon monoxide gas is high, the output current fluctuates, and the second half of the cycle (3 seconds)
To 8 seconds). This is because the output current decreases due to the adsorption of the carbon monoxide gas to the catalyst contained in the electrode, and the adsorbed carbon monoxide gas reacts with oxygen generated by the decomposition of water in the gas to be detected to obtain the equation (3). ,
This is because the recovery (refresh) of the output current due to the generation of carbon dioxide gas occurs alternately as shown in equation (4).

[0043]

Embedded image

Incidentally, in the equations (3) and (4),
(G) shows gas, and (a) shows adsorption to the catalyst.

Therefore, according to this configuration, the site on the catalyst for decomposing water to generate oxygen is not completely covered with carbon monoxide gas, and even if 1% of carbon monoxide gas continues to flow, The output of the carbon monoxide sensor hardly returns with time as in the conventional example. In the conventional example, since the change in electromotive force due to poisoning is observed, measurement cannot be performed while water is always decomposed on the catalyst as described above. Since the change is observed, the measurement voltage can be freely changed, and therefore, the measurement can always be performed while water is decomposed on the catalyst.

When the carbon monoxide gas concentration is reduced to about 100 ppm, as shown in FIG. 2B), the output current gradually decreases in the last 5 seconds of the cycle. This is because the concentration of carbon monoxide is low, and the adsorption site on the catalyst is in a sufficiently empty state, and the oxygen generated from water and the adsorbed carbon monoxide are present at adjacent sites, and the equation (4) is used. It is considered that the probability that the reaction as shown in FIG. Therefore, the output current gradually decreases due to the poisoning of the catalyst.

Further, when the concentration of the carbon monoxide gas is extremely reduced to about 5 ppm, as shown in FIG. 2C), the output current hardly changes in the latter 5 seconds of the cycle. It is considered that the output current does not change because the carbon monoxide gas hardly adsorbs to the site on the catalyst.

From the above, it has become clear that there is a difference in the behavior of the change of the output current in the latter 5 seconds of the cycle depending on the concentration. Therefore, as a parameter for knowing the change in the output current, the average current change rate MV in the latter 5 seconds of the cycle is used.
(Corresponding to the slope) was determined. MV was calculated from equation (5). In the equation (5), I (3) represents 3 of the measurement cycle.
I (8) indicates the output current after 8 seconds, and I (8) indicates the output current after 8 seconds.

[0049]

(Equation 1)

FIG. 3 shows changes in the MV with respect to the concentration of carbon monoxide gas thus obtained. It was found that the MV was unstable at high concentrations, but tended to stabilize at a constant value below 100 ppm. However, at a high concentration, the output was too unstable.
At 0 ppm, the B portion overlaps at 5 ppm, and at 5 ppm, the C portion overlaps, so that it is impossible to judge from the MV alone whether the portion is a high concentration unstable portion or really low concentration.

Therefore, by focusing on the output instability when the concentration of carbon monoxide gas is high, and judging that the concentration is high if the output is unstable, the overlap portion can be separated. As a method for determining the instability, FIG.
The fact that the output fluctuates every second as shown in Fig. 4 means that the rate of change and the rate of change of the output current every second fluctuate in the positive and negative directions and fluctuate greatly. It is thought that it is possible to distinguish between high and low concentrations in large and small.

Variations of these parameters were actually calculated and obtained. Here, the variation is defined as the difference between the maximum value and the minimum value of the current change speed or the current change acceleration in the latter 5 seconds of the measurement cycle as the method most easily obtained.
The calculation formulas are shown in formulas (6) to (9). In addition, (6)-
In equation (9), V (i) is the current change rate between i seconds and i + 1 seconds, that is, the slope of the output current, I (i) is the output current in i seconds, and i is the output current from 3 seconds to 7 seconds. The number of seconds, VW represents the variation in current change speed, and MAX (V (3 to 7)) represents V
The maximum value of the current change rate from (3) to V (7) is represented by M
IN (V (3 to 7)) is the minimum value, G (i) is the current change acceleration of i seconds and i + 1 seconds, that is, the gradient of the current change speed, GW is the current change acceleration variation, MAX (G
(3-6)) indicates the maximum value of the current change acceleration from G (3) to G (6), and MIN (G (3-6)) indicates the same minimum value.

[0053]

(Equation 2)

As a result of the calculation, the current change speed variation VW partially overlaps the value at the time of high-concentration carbon monoxide and the value at the time of low-concentration carbon monoxide. I understood. On the other hand, FIG. 4 shows the result of obtaining the current change acceleration variation GW. As shown by the dotted line D in the figure, although there is a point where the density slightly overlaps with the high density and the low density, it is considered that the two can be generally distinguished. That is, whether or not the carbon monoxide gas is at or above a certain concentration can be determined based on whether or not the GW is at or above a predetermined value. Therefore, it was found that the GW tends to be more easily distinguished from the VW and the GW.

However, if there is a point where the high density and the low density cannot be distinguished even if they are slight, the output accuracy as a sensor is impaired. This point occurs instantaneously as is apparent from the portion D in FIG. 4, and is a region where the GW is extremely unstable. Therefore, a variation value DGW of variation was obtained as a parameter for checking the stability of the GW. here,
DGW was calculated from the difference between the current GW and the GW (GWO) of the previous cycle as shown in equation (10). According to this method, if the GW is stable, the value of the DGW becomes small, so that the stability of the GW can be determined.

[0056]

(Equation 3)

FIG. 5 shows the result of actually obtaining the DGW.
It can be seen that the value of DGW is clearly different between high density and low density. However, with DGW alone, even at high concentrations, DGW ≒
Since there is a region of 0, the concentration of carbon monoxide cannot be known accurately. This is because the GW happens to be 2 at high concentration.
This is because the values may be almost the same over the cycle.

From the above, by determining whether or not the values of both GW and DGW are equal to or higher than the predetermined values set respectively, it is determined whether or not the concentration of carbon monoxide gas is equal to or higher than a certain concentration. A sensor output is obtained.

Next, it was examined whether a sensor output can be specifically obtained by the above method. In this embodiment, an example of an output as a switch for determining whether the carbon monoxide concentration is 100 ppm or more will be described. In addition, carbon monoxide concentration is 1
An off signal is output when the level is 00 ppm or more, and an on signal is output when the level is less than 100 ppm.

As a result of examining FIGS. 4 and 5 in detail, in order to construct a switch having a carbon monoxide concentration of 100 ppm, the default value of GW is set to 0.9 mA / s ² , and the default value of DGW is set to 0.4 mA / it was found that may be set to s ^2. That, GW is 0.9 mA / s ² or less, and the carbon monoxide concentration when the absolute value of 0.4 mA / s ² or less DGW 1
It was determined that it was less than 00 ppm, and an ON signal was output.

The sensor output obtained in this way is shown in FIG.
(Before correction). It has been found that, although the off signal changes to the on signal in the vicinity where the carbon monoxide concentration switches from 100 ppm to 20 ppm as a whole, chattering occurs in the sensor output, and the output accuracy during that period deteriorates.

Therefore, as chattering correction means,
We focused on the continuity of the sensor output (ON signal, OFF signal). That is, since chattering occurs suddenly, an ON signal or an OFF signal obtained from the current measurement cycle and an even number of ON signals or OFF signals for a predetermined even cycle before the ON signal, , And the total number of off signals was obtained, and correction was performed to output the signal with the larger number. In this embodiment, an ON signal or an OFF signal for four cycles is used as a predetermined even-numbered cycle. As a result, an ON signal or an OFF signal for five cycles can be obtained in addition to the current ON signal or the OFF signal, so that the number of times of either signal is always increased. For example,
If the current signal is on and all of the previous four cycles of signals are off, then on is once and off is four, so the current on signal is considered chattering and the sensor output is off.

The result of such a correction is shown in the lower part of FIG. 6 (after the correction is noted). Carbon monoxide concentration of 10
From 0 ppm to 20 ppm, the sensor output was turned on, and chattering at other concentrations did not occur at all.

From the above, it is clear that a highly accurate carbon monoxide sensor can be obtained.

FIG. 7 is a flowchart summarizing the control and calculation method of the carbon monoxide sensor for determining whether or not the concentration is 100 ppm or more.

When the power of the carbon monoxide sensor is turned on,
A refresh voltage of 4 V is applied to the electrode 2 (S
1). After that, it waits for 2 seconds as a predetermined time (S2), and checks whether a signal for stopping the fuel cell is transmitted from a fuel cell control circuit (not shown) (S3). If there is a signal to stop the fuel cell (Yes in S3), the voltage applied to the electrode 2 is turned off (S4), and the operation of the carbon monoxide sensor is ended.

If there is no signal to stop the fuel cell (S3
No), a voltage of 1.3 V is applied to the electrode 2 as a measurement voltage (S5). Thereafter, the current value is taken into the memory of the microcomputer 19 at predetermined time intervals (1 second in the present embodiment) (S6).

If the current value data for the predetermined time of 8 seconds is taken in (Yes in S7), the current change speed V (i) is calculated according to the equation (6) (S8). Next, the current change acceleration G (i) is calculated based on the value of V (i) according to the equation (8) (S9). Then, based on the value of G (i), the variation GW of the current change acceleration is calculated according to the equation (9) (S1).
0), a variation value DGW of variation is calculated from the GW and the GW value (GWO) one cycle before according to the equation (10) (S11).

The GW and DGW thus obtained are respectively set to predetermined values (in this embodiment, GW is 0.9 mA / s).
^{2. It} is compared whether DGW is 0.4 mA / s ² ) or less (S12). If both values are equal to or smaller than the predetermined values (Yes in S12), information for turning on the output determination in the current cycle is stored in the memory of the microcomputer 19 (S13). Next, since the output determination is ON in the current cycle, the number obtained by adding 1 to the number of the ON signal of the even number before (four in the present embodiment) stored in advance, and the number of the ON signal of the even number before Is compared with the number of off signals (S1).
4). If the number of ON signals is large (yes in S14)
s), output an ON signal (S15), and jump to A (return to S1). On the other hand, if the number of off signals is large (S1
No. 4), an off signal is output (S16), and the process jumps to A (return to S1).

If the GW and DGW are equal to or smaller than the predetermined values (No in S12), information for turning off the output determination in the current cycle is stored in the memory of the microcomputer 19 (S17). Next, since the output determination is off in the current cycle, the number obtained by adding 1 to the number of the off-signals beforehand stored in memory (four in this embodiment), (S18). If the number of off signals is large (y in S18)
es), and outputs an off signal (S16), and jumps to A (return to S1). On the other hand, if the number of ON signals is large (S
18; no), jump to B and output an ON signal (S
15) Jump to A (return to S1).

By repeating such an operation, it is possible to output whether or not the concentration of carbon monoxide is 100 ppm or more.

With the above configuration and operation, a high-precision carbon monoxide sensor which can be refreshed even with a high concentration of carbon monoxide gas was obtained.

(Embodiment 2) FIG. 8 is a flow chart of output and calculation of a carbon monoxide sensor according to Embodiment 2 of the present invention. FIG. 9 is a characteristic diagram showing the carbon monoxide concentration dependency of the sensor output.

Since the structure of this embodiment is exactly the same as that of the carbon monoxide sensor described in the first embodiment, a detailed description of the structure will be omitted. The output calculation and control flowcharts are almost the same as those in the first embodiment. Therefore, the same portions are denoted by the same reference numerals and detailed description thereof will be omitted.

That is, the feature of this embodiment is that the current value is measured for a predetermined time as shown in FIG. 8 (yes in S7).
s), the average current change rate MV is calculated according to the formula (7) (S19), and the MV is used to determine whether not only the GW or DGW but also the MV is an on signal or an off signal (S20). . In the measurement method of the first embodiment, as shown in FIGS. 4 and 5, it is possible to distinguish whether or not the concentration of carbon monoxide is 100 ppm or more using the values of GW and DGW. It is not possible to distinguish whether the concentration is low, for example, the concentration of carbon monoxide is 20 ppm or more. Therefore, attention was paid to the average current change rate MV as a parameter that can be distinguished between 20 ppm and 5 ppm. As is clear from FIG. 3, the MV is larger at 5 ppm than at 20 ppm, so if this is applied to the concentration determination, it is possible to detect a low concentration of 20 ppm carbon monoxide. However, as described in Embodiment 1, at 20 ppm, the dotted line B in FIG.
At 5 ppm, the C portion overlaps with the MV value at the time of high concentration, so that not only MV but also GW and DGW need to be applied to the concentration judgment.

A carbon monoxide sensor having such an output calculation and control flowchart was operated. Here, the default values of GW and DGW were the same as in Embodiment 1, and the default value of MV was -0.2 mA / s. That is, MV is -0.2 mA / s or more, and GW is 0.9
mA / s ² or less, and the absolute value of DGW is 0.4 mA /
When s ² or less, it was determined that the carbon monoxide concentration was less than 20 ppm, and an ON signal was output. FIG. 9 shows the results.
Shown in When the carbon monoxide concentration was changed from 20 ppm to 5 ppm, the sensor output was turned on, and it was found that chattering did not occur.

With the above configuration and operation, a carbon monoxide sensor which can be refreshed even with a high concentration of carbon monoxide gas and can be measured with high accuracy even at a low concentration is obtained.

(Embodiment 3) FIG. 10 is a flowchart for calculating and controlling the output of a carbon monoxide sensor according to Embodiment 3 of the present invention. FIG. 11 is a characteristic diagram showing the carbon monoxide concentration dependency of the current change rate of the sensor.

Since the structure of this embodiment is exactly the same as that of the carbon monoxide sensor described in the first embodiment, a detailed description of the structure will be omitted.

Next, the operation of the carbon monoxide sensor according to the present embodiment will be described.

The gas to be detected passes through the gas inlet 15 and the inlet 5 and is led to the gas channel 7. Since the gas flow path 7 is in contact with the electrode 2, the gas to be detected flows through the gas flow path 7 and diffuses evenly into the carbon paper constituting the electrode 2 to reach the catalyst. Thereafter, the detected gas is supplied to the outlet 6,
The gas is exhausted through the gas exhaust unit 16. Between the first current collector 8 and the second current collector 10, the microcomputer 19 continuously applies the measurement voltage and the refresh voltage without interruption. As for the measurement voltage, the average current change rate MV described in the second embodiment is equal to or more than a predetermined value (-4 mA / s in the present embodiment), and the current change acceleration variation GW is a predetermined value (0 in the present embodiment). 9 mA / s ² ) or less and when the absolute value of the variation value DGW of the GW variation is equal to or less than a predetermined value (0.4 mA / s ² in the present embodiment), the decomposition potential of water (theoretical value 1.23 V) 0)
3V, when the above condition is not satisfied, or when the ammeter 1
When the output of No. 8 was equal to or lower than a predetermined value (50 mA in the present embodiment), the voltage was set to 1.3 V which is higher than the decomposition potential of water. Note that 0.
The measurement voltage of 3 V may be basically equal to or lower than the decomposition potential of water, but is preferably 0.1 V or higher and 0.4 V or lower.
If the voltage is 0.1 V or less, the value of the current flowing through the sensor becomes too small, so that it is difficult to accurately measure the current with the ammeter 18. Since the carbon oxide gas slightly starts to dissociate, the sensitivity is reduced in the case of detecting the low concentration of carbon monoxide. From these facts, in order to obtain a carbon monoxide sensor with high accuracy and high sensitivity even at a low concentration, the voltage is preferably 0.1 V or more and 0.4 V or less.

The refresh voltage was set to 4 V which is higher than the measured voltage. The measurement and the refresh were performed in one cycle of 8 seconds for the former and 2 seconds for the latter, for a total of 10 seconds.

By the above operation, the reaction of the hydrogen gas in the gas to be detected on the catalyst of the electrode 2 as shown in the positive electrode and the negative electrode, respectively, occurs.

As shown in equation (1), a dissociation reaction of hydrogen gas occurs at the electrode 2 on the positive electrode side, and the proton (H
⁺ ) Reaches the electrode 2 on the negative electrode side through the electrolyte membrane 1 and receives the electrons (e ⁻ ) again as shown in the equation (2) to generate hydrogen gas. Therefore, in the presence of hydrogen gas, an electric closed circuit is formed between the detection element 4 and the DC power supply 17, and a current flows according to the proton conductivity. The hydrogen gas generated at the electrode 2 on the negative electrode side has holes 9, a gas chamber 12, and an outlet 1.
1. Exhausted through the orifice 13.

The current value is detected by the above operation, and the microcomputer 19 outputs a signal corresponding to the concentration of carbon monoxide gas.

Next, the signal processing calculated in the microcomputer 19 will be described in detail with reference to FIG.

When the power of the carbon monoxide sensor is turned on,
A refresh voltage of 4 V is applied to the electrode 2 (S2
1). Then, wait for 2 seconds as a predetermined time (S22),
It is checked whether a signal to stop the fuel cell is transmitted from a fuel cell control circuit (not shown) (S23). If there is a signal to stop the fuel cell, (yes in S23)
s), the voltage applied to the electrode 2 is turned off (S2
4) End the operation of the carbon monoxide sensor.

If there is no signal to stop the fuel cell (S2
No. 3), a voltage of 0.3 V or 1.3 V is applied to the electrode 2 as a measurement voltage according to the above conditions (S)
25). Thereafter, the current value is taken into the memory of the microcomputer 19 at a predetermined time interval (1 second in the present embodiment) (S26).

Next, if the current value is equal to or less than the predetermined value (50 mA) (yes in S27), it is considered that a rich carbon monoxide gas has been introduced into the sensor. Can not be done. Therefore, the measured voltage is restored (set to 1.3 V) and (S2
8) Jump to A to refresh the element (S
21). With such an operation, the element was protected from excessive poisoning, and at the same time, control was provided to invalidate the output of the cycle when the measured voltage was restored.
No longer output unstable behavior at voltage recovery,
Carbon monoxide concentration can be detected with high accuracy. When the measurement voltage is set to 1.3 V, water is decomposed and oxygen is constantly generated on the catalyst, so that carbon monoxide can be oxidized. Does not deteriorate.

If the current value is equal to or more than the predetermined value (n in S27)
o), current value data for a predetermined time of 8 seconds is fetched (yes in S29). Next, the average current change rate MV is calculated according to the equation (5) (S30).

If the current measured voltage is in a lowered state (0.3 V in the present embodiment) (yes in S31), the value of MV is compared with a predetermined value (S32), and the monoxide according to the MV value is compared. The carbon concentration is output (S33). Details of this part will be described later.

If the current measured voltage has not decreased, that is, if it is 1.3 V in this embodiment (n in S31)
o), the current change acceleration G (i) is calculated according to the equation (8) (S34). Thereafter, the variation GW of the current change acceleration is calculated based on the value of G (i) according to the equation (9) (S3).
5) The variation value DGW of the variation is calculated from the GW and the GW value (GWO) one cycle before according to the equation (10) (S36).

MV, GW and DGW thus obtained
Is compared with the respective default values (S37). In the present embodiment, MV is -4 mA / s or more, and GW is 0.9
mA / s ² or less, and the absolute value of DGW is 0.4 mA /
If it is equal to or less than s ² (yes in S37), it can be determined that the carbon monoxide concentration is 100 ppm or less, so that even if the measurement voltage is lowered, the element will not be excessively poisoned. Therefore, by lowering the measurement voltage (S38), the output sensitivity can be increased at the time of low density, and multipoint density output can be obtained. Thereafter, the process jumps to A (return to S21).

If the determination in S37 is no, the concentration of carbon monoxide is 100 ppm or more, so that the measured voltage is kept at 1.3 V which does not cause excessive poisoning, and jumps to A (S21).
Return to ).

By repeating such an operation, refresh can be surely performed when the high concentration carbon monoxide gas is introduced, and when the carbon monoxide concentration is 100 ppm or less, the current concentration can be output. .

FIG. 11 shows the result of operating the above carbon monoxide sensor. It can be seen that when the carbon monoxide concentration is 100 ppm or less, the average current change rate MV changes according to the concentration. As shown by the dotted line in FIG.
The default value of 00 ppm is -0.5 mA / s, the default value of 20 ppm is 0 mA / s, and the default value of 5 ppm is 0.4 mA / s.
By setting s, by comparing the current MV value with these predetermined values (S32), the concentration of carbon monoxide can be obtained, and only the switch-like output described in the first and second embodiments can be used. And the absolute value of the concentration can be known. In addition,
The reason why the default value of the MV value described in the first and second embodiments is different from the above value is that the measured voltage is different.

By the above configuration and operation, a carbon monoxide sensor is obtained which can surely be refreshed when a high concentration carbon monoxide gas is introduced and which can obtain a multipoint concentration output at a low concentration.

The specific material names described in Embodiments 1, 2 and 3 are all examples for constituting the carbon monoxide sensor of the present invention, and are not limited to these materials. Not something. Also, specific numerical values are not limited to the numerical values described in the first, second, and third embodiments except for those limited by the claims.

[0099]

As described above, the present invention provides a proton conductive electrolyte membrane, an electrode having a catalyst disposed on both sides of the electrolyte membrane, and a gas flow path having a gas inlet and an outlet. A first current collector provided so that the gas flow path is in contact with one surface of the electrodes; and a second current collector having holes provided so as to be in contact with the other surface of the electrodes. A DC power supply having a measurement voltage equal to or higher than the decomposition potential of water and connected to the first current collector plate as a positive electrode and the second current collector plate as a negative electrode, and hydrogen flowing through the gas flow path. A carbon monoxide sensor capable of refreshing even a high-concentration carbon monoxide gas by including current detection means for detecting a current that changes in accordance with the concentration of the carbon monoxide gas in the gas to be detected Is obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram for explaining a schematic structure of a carbon monoxide sensor according to a first embodiment of the present invention;

FIG. 2 is an output current characteristic diagram at the time of one cycle measurement according to the carbon monoxide concentration of the sensor.

FIG. 3 is a characteristic diagram showing a carbon monoxide concentration dependency of a current change rate of the sensor.

FIG. 4 is a characteristic diagram showing a carbon monoxide concentration dependency of variation in current change acceleration of the sensor.

FIG. 5 is a characteristic diagram showing a carbon monoxide concentration dependency of a variation value of variation of the sensor.

FIG. 6 is a characteristic diagram showing a carbon monoxide concentration dependency of a sensor output before and after correction of an ON signal and an OFF signal obtained from an output calculation result.

FIG. 7 is an output calculation and control flowchart of the sensor.

FIG. 8 is a flowchart of output calculation and control according to a second embodiment of the carbon monoxide sensor of the present invention.

FIG. 9 is a characteristic diagram showing the carbon monoxide concentration dependency of the sensor output.

FIG. 10 is a flowchart of output calculation and control of a carbon monoxide sensor according to a third embodiment of the present invention.

FIG. 11 is a characteristic diagram showing a carbon monoxide concentration dependency of a current change rate of the sensor.

FIG. 12 is an exploded perspective view of a schematic structure of a conventional carbon monoxide sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Proton conductive electrolyte membrane 2 Electrode 3 Sealing material 4 Detecting element 5 Inlet 6 Outlet 7 Gas flow path 8 First current collector 9 Hole 10 Second current collector 11 Outlet 12 Gas chamber 13 Orifice 14 Screw 15 Gas inlet 16 Gas discharge unit 17 DC power supply 18 Ammeter 19 Microcomputer

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takashi Ida 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F-term (reference) 5H026 AA06 5H027 AA06 KK31 KK54 KK56

Claims (16)

[Claims] The present invention has a proton conductive electrolyte membrane, electrodes having catalysts disposed on both sides of the electrolyte membrane, and a gas flow path having a gas inlet and an outlet, and has one surface of the electrodes. A first current collector disposed so as to be in contact with the gas flow path, a second current collector having a hole disposed to be in contact with the other surface of the electrode, and the first current collector. The plate becomes the positive electrode,
A DC power supply having a measurement voltage equal to or higher than the decomposition potential of water connected so that the second current collector plate becomes a negative electrode, and a concentration of carbon monoxide gas in the gas to be detected including hydrogen flowing through the gas flow path. And a current detecting means for detecting a current that changes in response to the current. 2. A method of detecting a current change at a measured voltage higher than the decomposition potential of water and a catalyst refresh at a refresh voltage higher than the measured voltage as one cycle to change the voltage of a DC power supply. The carbon monoxide sensor according to claim 1, wherein the concentration of the carbon gas is determined. 3. The carbon monoxide sensor according to claim 2, wherein the measurement voltage and the refresh voltage are continuously changed. 4. The carbon monoxide sensor according to claim 2, wherein the time for applying the refresh voltage is shorter than the time for applying the measurement voltage. 5. The carbon monoxide sensor according to claim 2, further comprising control means for starting a measurement after applying a refresh voltage for a predetermined time at start-up, and stopping the measurement after applying a refresh voltage for a predetermined time at stop. 6. The method according to claim 2, wherein the concentration of the carbon monoxide gas is obtained by comparing the variation of the current change acceleration when the measured voltage is applied, and comparing the variation value of the variation with each predetermined value. Carbon oxide sensor. 7. A method for obtaining a concentration of carbon monoxide gas by comparing a variation of a current change speed and a current change acceleration when a measurement voltage is applied and a variation value of the variation with a predetermined value. Item 3. A carbon monoxide sensor according to item 2. 8. The carbon monoxide sensor according to claim 6, wherein the variation is a difference between a maximum value and a minimum value of a current change acceleration within a predetermined time. 9. The method according to claim 1, wherein the variation value is a variation one cycle before, and
8. An absolute value of a difference from a current variation.
2. The carbon monoxide sensor according to item 1. 10. The carbon monoxide sensor according to claim 6, wherein an on signal or an off signal is output depending on whether the variation and the variation value are equal to or greater than respective predetermined values. 11. The carbon monoxide sensor according to claim 7, wherein an on signal or an off signal is output depending on whether the current change rate, the variation, and the variation value are each equal to or greater than a predetermined value. 12. A total number of ON signals and OFF signals is obtained from a current ON signal or OFF signal and an even number of ON signals or OFF signals of a predetermined even cycle before the current ON signal or OFF signal. The carbon monoxide sensor according to claim 10, which outputs a signal. 13. A proton conductive electrolyte membrane, electrodes having catalysts disposed on both sides of the electrolyte membrane, and a gas flow path having a gas inlet and an outlet, and one of the electrodes has a gas flow path. A first current collector disposed so as to be in contact with the gas flow path, a second current collector having a hole disposed to be in contact with the other surface of the electrode, and the first current collector. A DC power supply for applying a measurement voltage and a refresh voltage connected so that the plate is a positive electrode and the second current collector is a negative electrode, and a carbon monoxide gas in a gas to be detected containing hydrogen flowing in the gas flow path. Current detection means for detecting a current that changes in accordance with the concentration of the current, the current change speed at the time of application of the measurement voltage is a predetermined value or more, and the variation of the current change acceleration, and the variation value of the variation, respectively, When the measured voltage is below the predetermined value of The concentration of carbon monoxide gas is output from the current change rate at that time, and when the current falls below a predetermined value, the measured voltage is returned to a predetermined value higher than the decomposition potential of water and a refresh operation is performed. Controlling the carbon monoxide sensor. 14. The measured voltage at the time of drop is 0.1 V or more and 0.1 V or more.
14. The carbon monoxide sensor according to claim 13, wherein the voltage is 4 V or less. 15. The carbon monoxide sensor according to claim 13, wherein the measurement voltage is continuously reduced and returned. 16. The carbon monoxide sensor according to claim 13, wherein control is performed so that the output of the cycle when the measurement voltage is restored is invalidated.