JPH06160347A - Co2 sensor - Google Patents

Abstract

PURPOSE:To suppress the temperature change in a sensor element section and increase the fitting strength therein by forming a solid electrolyte thin film on a heater. CONSTITUTION:A reference electrode 3, solid electrolyte thin film 2, and detecting electrode 1 are successively piled up on a heater 4 to form a sensor element section 7 in a manner that the film 3 will be engaged with the electrodes 1 and 3 like a comb. Or, the electrodes 1 and 3 are formed as being engaged with each other like a comb on the heater 4, and the film 2 is formed between the electrodes 1 and 3. Thus, since the section 7 becomes thin in thickness and is brought into contact with the heater 4 overally, the heater 4 and section 7 will show the same temperature. Therefore the temperature in the section 7 can be always kept to be constant by controlling the temperature in the heater 4 accurately. Further, the vibration resistance and impact resistance can be improved because the section 7 and heater 4 are formed as one body.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a CO ₂ sensor for measuring CO ₂ concentration in a gas phase using a solid electrolyte. CO ₂ sensor of the present invention, environmental control, medical, agricultural, the number of fields including the Fermentation Process CO ₂
It can be used for concentration measurement and concentration control.

[0002]

_2. Description of the Related Art As a means for measuring CO ₂ concentration in a gas phase, various types of CO ₂ sensors such as a diaphragm glass electrode method and a non-dispersive infrared absorption method (NDIR) have been developed and used. . However, most of them have various problems such as response speed and reliability. In order to solve these problems, C using a solid electrolyte as shown in FIGS. 4 and 5 is used.
Various O ₂ sensors have been proposed. In the case of FIG. 4, for example, NASICON, β-alumina, other solid electrolyte 2 having Na ion conductivity, detection electrode 1 containing Na ₂ CO ₃ in dissociation equilibrium with CO _{2 in} the gas phase, and reference electrode 3. The sensor element portion 7 composed of the above is fixed on the planar heater 21 by the adhesive layer 20 and kept at 200 ° C. to 800 ° C.

In the case of FIG. 5, the sensor element portion 7 is fixed inside the coil heater 22 by a signal lead-out wire 5, a lead wire for fixing the sensor element portion or a ceramic insulating material, or together with a ceramic insulating material in the coil heater. It has a structure to be embedded. The electromotive force of this sensor is
It is represented by.

As shown in Equation 1, the sensor electromotive force is proportional to the logarithm of the CO ₂ partial pressure PCO _{2 in} the gas phase and the sensor temperature T. Specifically, when the sensor temperature is kept constant at 500 ° C., the CO ₂ concentration in the gas phase is 350 ppm to 360 p
By changing to pm, the sensor electromotive force changes by about 1 mV. On the other hand, by changing the sensor temperature from 500 ° C. to 501 ° C. while keeping the CO ₂ concentration in the gas phase constant, the sensor electromotive force changes by about 1 mV.

[0004]

Although the sensor is sensitive to the change in temperature as described above, the sensor element portion 7 is currently projected and adhered onto the planar heater 21 as shown in FIG. For this reason, the heater temperature and the sensor element portion temperature are not always the same, the temperature of the sensor element portion 7 is likely to change due to wind, temperature fluctuations, and the like, and the temperature difference between the reference electrode 3 and the detection electrode 1 is further increased. There was a drawback that it would occur. When the sensor element portion is housed in the coil heater 22 as shown in FIG. 5, if the sensor element portion is not fixed sufficiently, the sensor element portion approaches the heater wall surface due to vibration or the like, and There were cases where the temperature changed and the sensor output fluctuated. Furthermore, when the sensor element part 7 contacts the coil heater wall surface, the sensor element part 7
Since the temperature of 1 changes greatly, the sensor output also fluctuates greatly, and in some cases it becomes unusable. Further, both the sensors shown in FIGS. 4 and 5 have a drawback that the mounting strength of the sensor element portion is not sufficient.

The present invention has been made to solve these problems. That is, the first purpose is to eliminate the temperature change of the sensor element portion, and the second purpose is to increase the mounting strength of the sensor element portion.

[0006]

The first means for solving these problems is to form a sensor element portion composed of a reference electrode, a detection electrode, a solid electrolyte thin film or a thick film on a heater. The second means is a reference electrode film on the heater,
It is formed by stacking a solid electrolyte thin film or thick film and a detection electrode film. In the third means, the reference electrode and the detection electrode are formed on the solid electrolyte thin film or thick film formed on the heater so as to be engaged with each other in a comb shape. In the fourth means, a reference electrode and a detection electrode are formed on a heater so as to be engaged with each other in a comb shape, and a solid electrolyte thin film or a thick film is formed between the electrodes.

[0007]

With the above structure, the sensor element portion including the reference electrode, the solid electrolyte thin film, and the detection electrode on the heater has a small thickness and is in close contact with the heater over the entire surface. Therefore, since the heater temperature and the sensor element temperature are the same,
By controlling the heater temperature with high accuracy, it is possible to keep the temperature of the sensor element part constant. further,
Since the sensor element portion and the heater are integrated, vibration resistance and impact resistance are improved.

[0008]

FIG. 1 shows an embodiment of the present invention. FIG. 1 is a sectional view of a CO ₂ sensor of the present invention. It has a structure in which a reference electrode, a solid electrolyte thin film, and a detection electrode are sequentially formed on a flat heater. In this embodiment, the heater is formed on the alumina plate by sputtering Pt. The heater may be formed of a material such as Pt, Pt-rhodium alloy or nickel-chromium alloy on one surface of a ceramic plate such as alumina, forsterite or mullite by a vapor deposition method, a sputtering method, a plating method, a coating baking method or the like. . The reference electrode is Pt formed by a sputtering method. The electrode material may be Au,
The forming method may be a vapor deposition method. Further, it may be formed as a thick film by a coating and baking method. If, for example, a Na ion conductive solid electrolyte is used as the material of the solid electrolyte, NAS
ICON and β-alumina are common, but NaAl
_{Si 4 O 10, NaAl 2 Si} 3 O 10 also Na ion conductivity such as very high although not be used. In the case of Li ion conductive solid electrolyte, LISICON, Li _3.6
Although Si _0.6 P _0.4 O ₄ or the like is generally used, a solid electrolyte having a low Li ion conductivity can also be used. In this example, Li _3.6 Si which is a Li ion conductive solid electrolyte.
_0.6 P _0.4 O ₄ is formed by the sputtering method. A vapor deposition method may be used as another forming method. The sensing electrode is P
t is formed in a lattice shape by the sputtering method, and L is further formed on it.
Although the i ₂ CO ₃ film is formed by sputtering, a vapor deposition method or a coating / baking method may be used, and Au may be used as the detection electrode material in addition to Pt. Further, the detection electrode may be formed as a thick film in which the electrode material and Li ₂ CO ₃ are integrated by a coating and baking method using a paste in which the electrode material and a metal carbonate are mixed. Finally, the signal lead-out wire and the heater lead wire are attached, and are attached as shown in FIG.

The CO ₂ sensor manufactured as described above is
For example, it is used by using the circuit shown in FIG. That is, when the sensor temperature decreases due to wind or temperature fluctuations, the heater resistance value also decreases, so the voltage applied to the heater increases by the change in the resistance value, and the sensor temperature is kept constant.

On the other hand, since the temperature of the sensor element portion 7 is the same as the heater temperature, the sensor element portion always has a constant temperature. Also, since it is not necessary to bond the element part and the heater,
It is possible to prevent falling due to poor adhesion, damage due to vibration, and shock.

[0011]

As described above, since the extremely thin sensor element portion including the reference electrode, the solid electrolyte thin film and the detection electrode is formed on the heater plate, there is no difference between the heater plate temperature and the sensor element portion temperature, and the heater A stable output can always be obtained by controlling the temperature. In addition, since the sensor element and the heater are made integrally, the vibration resistance and shock resistance are greatly improved compared to the conventional sensor of the type in which the sensor element and the heater are bonded, and in a more severe environment It can also be used.

[0012]

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is a CO ₂ sensor mounting view of the present invention.

FIG. 3 is a diagram showing an example of a measurement circuit.

FIG. 4 is a sectional view of a conventional CO ₂ sensor.

FIG. 5 is a sectional view of a conventional CO ₂ sensor. Sensor element (detection electrode 1 + solid electrolyte 2 + in the coil heater)
A reference electrode 3) is installed.

[Explanation of sign]

1 Detection Electrode 2 Solid Electrolyte Thin Film 3 Reference Electrode 4 Heater 5 Signal Extraction Line 6 Heater Lead Wire 7 Sensor Element Section 8 Heater Plate 9 Stainless Steel Mesh Cap 10 Stem 11 Ni Pin 12 Transistor 13 Amplifier 14 Resistor 15 Resistor 16 Resistor 17 CO ₂ Sensor 18 Output 19 Heater 20 Adhesive Layer 21 Planar Heater 22 Coil Heater

Claims (4)

[Claims] 1. An alkali metal ion or alkaline earth metal ion conductive solid electrolyte (hereinafter referred to as a solid electrolyte).
When a detection electrode holding the metal carbonate that forms the CO ₂ dissociation equilibrium in CO ₂ sensor composed of a heater for heating the reference electrode and these pairs, a solid electrolyte thin film or thick film on a heater formed C characterized by
O ₂ sensor. _2. A CO ₂ sensor according to claim 1, wherein a reference electrode film, a solid electrolyte thin film or a thick film, and a detection electrode film are laminated on the heater. 3. The CO according to claim 1, wherein the reference electrode and the detection electrode are formed on the solid electrolyte thin film or thick film formed on the heater so as to be engaged with each other in a comb shape.
₂ sensors. 4. The CO ₂ sensor according to claim 1, wherein the reference electrode and the detection electrode are formed so as to be engaged with each other in a comb shape, and a solid electrolyte charge membrane or a thick membrane is formed between the electrodes.