JP2004239611A - Co sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a CO sensor for enabling high precision measurement of CO of low concentration in gas. <P>SOLUTION: A light source 5 for generating light in an infrared region, a detector 6 for detecting the light of the infrared region from the light source 5, a filter 7, provided in the middle of a light passage L between the light source 5 and the detector 6 are provided for a wave guide tube 2 to which the gas to be measured is supplied. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a CO sensor used for, for example, a fuel cell.
[0002]
[Prior art]
In a polymer electrolyte fuel cell, which is expected to be a new energy source for electric vehicles and the like, when power is generated using a reformed gas of methanol, propane, etc. instead of pure hydrogen (hereinafter referred to as reformed gas) The problem is that the concentration of carbon monoxide (CO) contained in the reformed gas is problematic.
[0003]
Since CO has a poisoning effect on the catalyst of the electrode part and lowers the battery performance, it is usually 100 ppm or less by selective oxidation (CO → CO ₂ ) or reduction (CO + 3H ₂ → CH ₄ + H ₂ O). It is necessary to introduce at a concentration.
[0004]
The composition of the reformed gas, for example, _{H 2:} about 75% CO _2: 24%, other (CO, etc. _{H 2} 0): about 1%.
[0005]
The measurement of the CO concentration in the prior art is often performed by a metal oxide semiconductor type sensor typically represented by tin oxide.
[0006]
In this metal oxide semiconductor type sensor, a gas to be detected is adsorbed to a detection region of the element while the element itself is heated (for example, at about 200 to 600 ° C.), and the resulting change in the electric resistance of the element is used. It is.
[0007]
Further, the measurement of the CO concentration in the fuel cell system is described in, for example, JP-A-8-138710 and JP-A-8-329969. A method for measuring is described.
[0008]
This electrochemical method for measuring the CO concentration is based on a method in which an electrolyte membrane is sandwiched between electrodes and a voltage difference between the electrodes generated when the electrolyte membrane comes into contact with gas is measured.
[0009]
[Problems to be solved by the invention]
However, when measuring the CO concentration with a metal oxide semiconductor type sensor, when the organic gas contains CO as in the above-mentioned reformed gas, it is difficult to measure because CO is not contained in the reformed gas. It becomes.
[0010]
This is because the sensor uses the oxygen adsorption amount (constant value) in the state of the oxygen partial pressure which is almost constant, such as in the atmosphere, so that the gas concentration (in this case, the CO concentration ) Can be measured.
[0011]
Since the polymer electrolyte fuel cell is a low-temperature operation type in which the temperature of the reformed gas used is lower than the heating temperature of the element itself of the metal oxide semiconductor type sensor, the reformed gas is used. Although it is a small area, it is exposed to high temperature, and there is a concern about power generation efficiency and the like due to temperature rise.
[0012]
In addition, when the selectivity to various gases is relatively low, and CO is contained in an organic gas like a reformed gas (particularly, when the CO concentration is as low as about 0 to 100 ppm), the former stage of the sensor is used. A filter (carbon filter) is placed in the filter, and after absorbing most of the organic gas with the filter to relatively increase the CO concentration, a method of sending the gas to be measured to the sensor may be necessary. Has a complicated configuration.
[0013]
On the other hand, in the electrochemical CO concentration measurement method, an electrolyte membrane is disposed in a stagnation section provided in the middle of a gas supply path used as fuel, and the gas introduced into the stagnation section is measured. There is a high possibility that a difference (including a time difference) will occur in the gas concentration state between the gas flow path and the stagnation area, and it is also possible to measure the concentration of the entire gas flow rate (entire area) passing through the supply path. Problems such as difficulty may occur.
[0014]
The present invention solves the above-mentioned problems of the prior art, and aims to enable high-precision measurement of low-concentration CO present in a gas to be measured, and to reduce the amount of the gas to be measured. It is an object of the present invention to provide a CO sensor with improved measurement performance that enables the increase and the like.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, in the CO sensor of the present invention,
A light source that emits light in the infrared region;
Detection means for detecting light in the infrared region from the light source,
Filter means disposed in the optical path between the light source and the detection means, and having a transmission window in a wavelength band where infrared absorption by CO is performed in light in the infrared region,
Is provided in the waveguide to which the gas to be measured is supplied.
[0016]
Further, the wavelength band in which infrared absorption by CO is performed in light in the infrared region is preferably from 4.4 μm to 5.0 μm.
[0017]
It is also preferable that the inner surface of the waveguide is subjected to a process of reflecting light in the infrared region.
[0018]
A second filter unit disposed in the optical path between the light source and the detection unit, and having a transmission window in a wavelength band excluding a wavelength band in which infrared absorption by CO is performed in light in an infrared region;
Second detection means for detecting light in the infrared region that has passed through the second filter means,
Detection value processing means for generating an output related to the concentration of CO from a differential output of two detection means, the detection means and the second detection means;
It is also preferable to provide
[0019]
Gas compression means for compressing the gas to be measured in the waveguide,
Pressure detection means for detecting the pressure of the gas to be measured in the waveguide,
When the gas to be measured is compressed by the gas compression means, a concentration correction means for calculating the CO concentration in the gas to be measured at normal pressure from the CO concentration output of the detection means and the detection pressure of the pressure detection means,
It is also preferable to provide
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
(Embodiment 1)
Hereinafter, the configuration of the CO sensor will be described with reference to the drawings.
[0021]
FIG. 1 shows a configuration in which a light source and detection means are arranged opposite to both ends of a waveguide, and FIG. 2 shows a configuration in which a light source and detection means are arranged on the same side of a waveguide.
[0022]
In the CO sensor 1 shown in FIG. 1, reference numeral 2 denotes a waveguide used in a polymer electrolyte fuel cell and supplied with a reformed gas (measurement target gas) obtained by reforming methanol, propane, or the like. The waveguide 2 of this embodiment has a cylindrical shape, and is provided with a supply port 3 and a discharge port 4 for reformed gas at both ends.
[0023]
Note that the supply side port 3 and the discharge side port 4 may be arranged in reverse. Further, in the case of a configuration in which the reformed gas once supplied into the waveguide 2 can be exchanged, a configuration having only one port can be adopted.
[0024]
The shape of the waveguide is arbitrary, and the installation state may be all or a part of the passage of the reformed gas, or may be provided at a branch from the passage.
[0025]
Reference numeral 5 denotes a light source for generating light in the infrared region, and reference numeral 6 denotes a detector as detection means for detecting light in the infrared region from the light source 5.
[0026]
Reference numeral 7 denotes a filter as filter means having a transmission window in a wavelength band where infrared absorption by CO is performed in light in an infrared region. The filter 7 is arranged in the optical path L between the light source 5 and the detector 6.
[0027]
The wavelength band in which infrared absorption by CO is performed is a wavelength band of 4.4 μm to 5.0 μm, preferably 4.5 μm to 4.8 μm, and more preferably 4.55 μm to 4.75 μm. Reason, the CO ₂ is detected If it is below 4.4 [mu] m, due to the fact that would detect the NO is above the 5.2 .mu.m.
[0028]
As processing of the inner surface of the waveguide 2 (and, in some cases, including a mirror), it is necessary to efficiently reflect infrared light, and thus a glossy metal surface is desirable. The inner wall of the waveguide 2 may be subjected to surface treatment (by plating, vapor deposition, sputtering, or the like) with gold, aluminum, nickel, or the like.
[0029]
As the light source 5, since infrared absorption of CO appears in a wavelength band of about 4.6 μm, any light source that emits infrared light (infrared light) of at least up to 5 μm may be used. For example, tungsten or the like is used for the filament. Lamps are small and easy to use.
[0030]
As the detector 6, there are a quantum type photoconductive sensor and a photovoltaic type sensor, a thermal type thermopile bolometer, a pyroelectric sensor, and the like, all of which are applicable. Among them, the thermal type is more suitable.
[0031]
Only infrared light that has passed through a filter 7 having a transmission window in a wavelength band of about 4.6 μm, which is an absorption band of CO, is incident on the detector 6.
[0032]
In the CO sensor 11 of FIG. 2, the light source 5, the detector 6 and the filter 7 are arranged on the same side of the waveguide 2, and the optical path L is folded by a mirror 8. Other configurations are the same as those in FIG. 1 and are denoted by the same reference numerals.
[0033]
The CO sensors 1 and 11 having the above-described configuration are arranged so that the CO sensors 1 and 11 pass through the filter 7 and pass through the filter 7 in accordance with the amount of absorption of infrared light in the wavelength band of about 4.6 μm depending on the concentration of CO in the reformed gas. The amount of infrared light changes, and the CO output can be measured by changing the detection output of the detector 6.
[0034]
Therefore, it is possible to accurately measure the CO gas concentration in an environment with less oxygen without being affected by other gases (for example, CO ₂ ).
[0035]
Since the infrared light is used, the temperature rise of the reformed gas is suppressed, the power generation efficiency is maintained, and the gas passage in the waveguide 2 has an explosion-proof structure. is not used), it is safe to measurable, even if containing H ₂ gas, such as reformed gas.
[0036]
In addition, since the entire gas passage in the waveguide 2 is a CO concentration measurement target region, the measurement target gas amount can be increased, or the gas is flowing (used for power generation of the fuel cell). By using the gas itself as a measurement target, it is possible to perform more accurate measurement.
[0037]
(Embodiment 2)
FIG. 3 is a diagram schematically illustrating a configuration of a CO sensor 21 according to the second embodiment. The same components as those in the first embodiment are denoted by the same reference numerals.
[0038]
In this embodiment, a set of a second filter 7b and a detector 6b are further provided as a reference to the filter 7 and the detector 6 in response to a case where higher accuracy is required or a case where the sensor is used in a wide range of temperatures. It is provided adjacent.
[0039]
The transmission window of the second filter 7b needs to be set to a wavelength other than the absorption wavelength band of CO and the infrared absorption wavelength band included in the target environment. If the infrared light of the light source 5 has wavelength dependency, When the wavelength band is closer to the wavelength band of about 4.6 μm, which is the absorption wavelength band of CO, the difference in the intensity of infrared light is smaller and the same level of output can be easily obtained. Furthermore, in a region where there is no absorption of CO ₂ , H ₂ O, CH ₃ OH, etc., (1) a wavelength band of 4.0 μm, (2) a wavelength band of 5.0 μm, and (3) a wavelength band of 2.5 μm are desirable.
[0040]
Then, using the outputs of the two detectors, the detector 7 and the second detector 7b, as differential outputs, an output related to the CO concentration is obtained by the detection value processing means.
[0041]
FIG. 4 is a block diagram showing a circuit configuration of the detection value processing means.
[0042]
By taking the difference signal between the CO output signal S1 (output value related to the CO concentration) and the reference output signal S2 by the operation circuit K1, a subtle signal change of the CO output signal S1 is detected.
[0043]
This utilizes the fact that the reference output signal S2 does not depend on the CO concentration, and amplifies this operation output to obtain a sensor output signal S4 indicating a change in the CO concentration.
[0044]
As for the temperature correction, since the CO output signal S1 and the reference output signal S2 change relatively, it is possible to detect a more accurate change in density by taking the difference. The correction only needs to take into account the variation due to a slight difference in the temperature dependency of each output signal. The difference signal between the output signal S1 (output value related to the CO concentration) and the reference output signal S2 is added to the temperature difference. The correction by the output signal S3 is added.
[0045]
By providing the reference output in this way, in addition to the effects of the first embodiment, it is possible to measure the CO concentration with higher accuracy over a wide range of temperatures.
[0046]
Specific examples of the CO sensor 21 include a tungsten lamp that emits infrared light as the light source 5 and a thermopile with a filter as the detectors 6 and 6b (the CO filter 7 has a transmission window of 4.6 μm +/− 0.1 μm, Filter 7b is a dual type having a transmission window of 4.0 μm +/− 0.1 μm), and the waveguide 2 is a copper pipe obtained by polishing the inner surface of a copper pipe and subjecting it to nickel plating and further gold plating (glossy plating). The light source 5 and the detectors 6 and 6b were arranged to face each other.
[0047]
Since the thermopile has a filter 7 having a transmission window in a 4.6 μm wavelength band for CO and a filter 7b having a transmission window in a 4 μm wavelength band for reference, the output voltages of the two thermopiles were adjusted. By taking the differential output later, the low-concentration CO concentration of 0 to several hundred ppm can be accurately measured.
[0048]
(Embodiment 3)
When the CO concentration in the waveguide is as low as 100 ppm or less, the output value output to the detector is small and weak, so that it is difficult to detect. Also, small and weak output values output to the detector are easily affected by noise components.For example, a high-performance amplifier is required on the circuit that detects the output value, the shield is strengthened, By limiting the specifications of the CO sensor peripheral device, such as minimizing the distance between the terminal of the device and the first-stage input amplifier on the board, it was necessary to prevent the CO sensor from being affected by noise components.
[0049]
Therefore, in the third embodiment, a large output value can be obtained even when the CO concentration of the reformed gas is low by compressing the reformed gas itself and outputting a rich CO concentration to the detector. Thus, highly accurate measurement can be performed.
[0050]
FIG. 5 is a diagram schematically illustrating a configuration of a CO sensor 31 according to the third embodiment. The same components as those in the first embodiment are denoted by the same reference numerals.
[0051]
The CO sensor 31 has a configuration in which a light source 5 and a detector 6 are arranged opposite to both ends of the waveguide 2, as in FIG. 1 of the first embodiment. The filter 7 is arranged adjacent to the detector 6.
[0052]
The waveguide 2 is provided with a supply port 3 and a discharge port 4, and valves 12 and 13 are provided respectively. By closing these valves 12 and 13, the inside of the waveguide 2 can be sealed.
[0053]
The supply-side port 3 has, on the side sealed by the valves 12 and 13, a reformed gas compression device 14 as gas compression means for compressing reformed gas in the waveguide 2, and a pressure in the waveguide. And a pressure sensor 15 as pressure detecting means for detecting the pressure.
[0054]
As the reformed gas compression device 14, any device that can compress the reformed gas in the waveguide 2 may be used. For example, an accumulator, an air cylinder, an air compressor, or the like may be used.
[0055]
The pressure sensor 15 monitors the pressure fluctuation of the reformed gas compressed by the reformed gas compression device 14 to control the inside of the waveguide 2 to a predetermined measurement set pressure, and to control the actual pressure at the time of gas concentration measurement. It is used to monitor the pressure in the waveguide 2 and perform concentration correction.
[0056]
The control for detecting the CO concentration by the CO sensor 31 having the above configuration will be described below with reference to FIG. FIG. 6 is a flowchart showing the gas concentration measurement.
[0057]
First, the valves 12 and 13 are closed to seal the inside of the waveguide 2 (S601).
[0058]
Next, the reformed gas compression device 14 is turned on to compress the reformed gas in the waveguide 2 (S602). The compression of the reformed gas is performed until the inside of the waveguide 2 reaches a predetermined set pressure while monitoring the pressure value of the pressure sensor 15 (S603, S604).
[0059]
When the pressure inside the waveguide 2 reaches the set pressure, the reformed gas compression device 14 is turned off to stop the compression of the reformed gas (S605).
[0060]
Next, in this state, the light source 5 is turned on to emit infrared light (S606), and the infrared light that has passed through the filter 7 is detected by the detector 6 (S607). At this time, the actual pressure in the waveguide 2 is monitored by the pressure sensor 15 (S608).
[0061]
Then, the concentration is corrected by the concentration correcting means using the output value of the detector 6 detected in S607 and the pressure value of the pressure sensor 15 monitored in S608, and the value of the CO concentration at the normal pressure is calculated (S609). .
[0062]
The value of the CO concentration at the normal pressure by the concentration correction is calculated by calculating the ratio (A / B) between the pressure value (A) of the pressure sensor 15 and the normal pressure (B) when the pressure is not compressed. By dividing the detected output value (C) by this ratio, the value of the CO concentration at normal pressure (BC / A) is calculated.
[0063]
The sampling of the CO concentration calculated from S607 to S609 is repeated n times in advance (S610).
[0064]
Thereby, the density is output (S611). The output of the concentration is obtained by, for example, averaging the CO concentration calculated by sampling.
[0065]
Thereafter, the light source 5 is turned off to turn off the infrared light (S612), the valves 12 and 13 are opened (S613), and the compressed reformed gas is exhausted from the inside of the waveguide 2 (S614). finish.
[0066]
As described above, in the present embodiment, the CO concentration is detected by the detector 6 in a state where the reformed gas in the waveguide 2 is compressed, so that the detector 6 has a lower CO concentration than at the normal pressure. It can be detected with a large value, and can be accurately detected even when it is difficult to detect at normal pressure due to low concentration. In addition, at a normal pressure, a minute difference in density, which has no difference in output value, can also be distinguished and detected, and the resolution is improved.
[0067]
Further, since the detector 6 detects the CO concentration at a value larger than that at the time of the normal pressure, the output value of the detector 6 is not affected by the noise component, and the specification of the CO sensor peripheral device is not required. This eliminates the need to use a high-performance amplifier or a strengthened shield, thereby reducing costs. In addition, it is not necessary to minimize the distance between the terminal of the detector 6 and the first-stage input amplifier on the board. It is possible to perform a simple design.
[0068]
Specific examples of the CO sensor 31 include a tungsten lamp that emits infrared light as the light source 5, and a thermopile with a filter as the detector 6 (the filter 7 for CO is a dual type having a transmission window of 4.6 μm +/− 0.1 μm). The waveguide 2 is made of a copper pipe having an inner surface polished and plated with nickel and further with gold (glossy plating), and the light source 5 and the detector 6 are arranged to face each other.
[0069]
The result of the CO concentration measurement by the CO sensor 31 is, for example, when the reformed gas having the CO concentration of 100 ppm at normal time is compressed to twice the normal pressure and compressed, the CO concentration at normal time is 200 ppm. 6, the output value of the detector 6 is large, and the low-concentration CO concentration of 0 to 100 ppm can be measured with high accuracy, and the resolution is about twice as high as the measurement without compression. Having. Further, the output value of the detector 6 is not significantly affected by the noise component.
[0070]
【The invention's effect】
According to the present invention described above, it is possible to accurately measure the CO concentration in an environment with little oxygen without being affected by other gases.
[0071]
Since infrared light is used, a decrease in power generation efficiency is suppressed, and the CO concentration can be measured more safely.
[0072]
Further, when the second filter means serving as a reference and the detection means are used together, the CO concentration can be measured with higher accuracy over a wide range of temperatures.
[0073]
In addition, since the entire region of the gas passage in the waveguide is the region to be measured for the CO concentration, the amount of gas to be measured can be increased, and highly accurate measurement can be performed.
[0074]
Further, when the gas in the waveguide is compressed and measured, the output value of the detecting means increases, so that the low-concentration CO concentration can be measured with high accuracy and the resolution is improved. Further, the output value of the detecting means is not affected by the noise component.
[Brief description of the drawings]
FIG. 1 is a diagram schematically illustrating a configuration of a CO sensor according to a first embodiment.
FIG. 2 is a diagram schematically illustrating a configuration of a CO sensor according to the first embodiment.
FIG. 3 is a diagram schematically illustrating a configuration of a CO sensor according to a second embodiment.
FIG. 4 is a block diagram showing a circuit configuration of a detection value processing unit.
FIG. 5 is a diagram schematically illustrating a configuration of a CO sensor according to a third embodiment.
FIG. 6 is a flowchart illustrating gas concentration measurement according to a third embodiment.
[Explanation of symbols]
1, 11, 21, 31 CO sensor 2 Waveguide 3 Supply side port 4 Discharge side port 5 Light source 6 Detector 7 Filter 8 Mirror 12, 13 Valve 14 Reformed gas compressor 15 Pressure sensor L Optical path S1 CO output signal S2 Reference output signal S3 Temperature output signal S4 Sensor output signal K1 Operation circuit

Claims (5)

A light source that emits light in the infrared region;
Detection means for detecting light in the infrared region from the light source,
Filter means disposed in the optical path between the light source and the detection means, and having a transmission window in a wavelength band where infrared absorption by CO is performed in light in the infrared region,
A CO2 sensor provided in the waveguide to which the gas to be measured is supplied. The CO sensor according to claim 1, wherein the wavelength band in which infrared absorption by CO is performed in light in an infrared region is from 4.4 μm to 5.0 μm. The CO sensor according to claim 1, wherein the waveguide has an inner surface subjected to a process of reflecting light in an infrared region. A second filter unit disposed in the optical path between the light source and the detection unit, and having a transmission window in a wavelength band excluding a wavelength band in which infrared absorption by CO is performed in light in an infrared region;
Second detection means for detecting light in the infrared region that has passed through the second filter means,
Detection value processing means for generating an output related to the concentration of CO from a differential output of two detection means, the detection means and the second detection means;
The CO sensor according to claim 1, 2, or 3, further comprising: Gas compression means for compressing the gas to be measured in the waveguide,
Pressure detection means for detecting the pressure of the gas to be measured in the waveguide,
When the gas to be measured is compressed by the gas compression means, a concentration correction means for calculating the CO concentration in the gas to be measured at normal pressure from the CO concentration output of the detection means and the detection pressure of the pressure detection means,
The CO sensor according to claim 1, 2, 3, or 4, further comprising:

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