JPH0810213B2 - Carbon dioxide sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a solid structure having an ionic conductor used in a place where carbon dioxide concentration is measured or controlled for facility horticulture, environmental hygiene, disaster prevention, industrial use and the like. The present invention relates to an electrolyte type carbon dioxide gas sensor.

2. Description of the Related Art In recent years, there has been an increasing need for carbon dioxide sensors mainly in the fields of air conditioning and agriculture and livestock, and various gas sensors have been developed and put into practical use, but many problems remain in their reliability. Especially, water vapor, salt particles, cigarette smoke, oil smoke, etc.
Durability to the polluted environment where is present is a concern.

Hereinafter, an example of the conventional carbon dioxide gas sensor described above will be described with reference to FIGS. 4 and 5.

In the figure, thin plate NASICON as an ion conductor
The plate (sodium ion conductor ceramics) 11 is provided with a pair of electrodes 12a, 12b for extracting a voltage signal at both ends thereof, and further, a part of one of the electrodes 12a, 12b,
Alternatively, sodium carbonate 13 is attached to all of them to form the gas sensing unit 1. The composition of NASICON is Na _{1 + X} Zr ₂ Si _X P
_3-X O ₁₂ , (0 ≦ X ≦ 3).

The gas sensing unit 1 includes a heater 2 for heating at the lower part of one side,
It is fixed to the lower pedestal 6 via lead wires 3a and 3b drawn from a pair of electrodes and two lead wires 5a and 5b drawn from a heater for heating. The lead wires 3a and 3b and the lead wires 5a and 5b are for signal output and voltage application, respectively, and penetrate the pedestal 6.

The protector 4b includes a gas detector 1, a heater 2,
In order to protect the lead wires 3a, 3b, 5a, 5b from mechanical damage and to improve the contact with the measurement atmosphere, they are made of stainless wire mesh and are fixed to the base 6.

In the above configuration, first, the gas sensing unit 1 is heated to the measurement temperature by the heater 2 and brought into contact with the outside atmosphere. The carbon dioxide gas in the atmosphere reaches the gas sensing portion 1 by diffusion or convection through the through hole of the protector 4b, and causes electromotive force to be generated in the electrodes 12a, 12b according to the carbon dioxide concentration at that time. This electromotive force was taken out from the electrodes 12a and 12b through the lead wire 3 to electrically detect the carbon dioxide concentration in the atmosphere.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, the above configuration has the following problems. That is, when the measurement atmosphere is in a high humidity environment or in a state where dew condensation is likely to occur, and when the carbon dioxide sensor is in an unheated state, the metal carbonate of the gas sensing portion is hydrated by its own hygroscopic action and water solubility. In some cases, elements or hydrides are formed, or the elements are dissolved in dew condensation water to be eluted and detached from the electrodes, which deteriorates the element and makes regeneration impossible.

The present invention solves the above problems, and a first object is to
It is intended to provide a carbon dioxide sensor having high reliability even when exposed to a high humidity environment when the gas sensing unit is not heated.

A second object is to provide a carbon dioxide sensor having high reliability even when exposed to a dew condensation environment when the gas sensing part is not heated.

Means for Solving the Problems In order to achieve this object, a carbon dioxide gas sensor according to the first means of the present invention is an ion having a pair of electrode layers and having conductivity with respect to a metal ion capable of forming a metal carbonate. A gas sensing unit composed of a conductor and a metal carbonate capable of forming dissociation equilibrium with carbon dioxide in a shape that covers a part or all of one of the electrode layers of the ionic conductor; and the gas sensing unit. A heating unit provided for heating to a measurement temperature; and a casing unit including the gas sensing unit and the heating unit and having an opening / closing port formed to open when the gas sensing unit is heated and to close when the gas sensing unit is not heated. It is provided and configured.

In order to achieve this object, in addition to the above-mentioned means, the second means has a structure in which a moisture absorption part for removing the water adsorbed by the metal carbonate of the gas sensing part is built in the housing part.

Action With this configuration, the first action is that when the gas sensing unit is in an unheated state, the moisture in the atmosphere is shut off by closing the opening / closing port of the housing, and the metal carbonate of the gas sensing unit is prevented from absorbing moisture. it can. On the other hand, in the heated state, the element deterioration due to moisture absorption and dew condensation can be avoided by keeping the gas sensing part at a temperature at which the metal carbonate hydrate and hydride are completely thermally decomposed.

The second effect of this configuration is that when the sensor changes from a heated state to a non-heated state in a high-humidity atmosphere, when the opening / closing port of the casing changes from the “open” state to the “closed” state, Since the moisture trapped in the body is adsorbed by the hygroscopic agent, even if the temperature of the atmosphere is lowered thereafter, the inside of the housing is unlikely to be in a dew condensation state.

Example 1 Hereinafter, a first example of the present invention will be described with reference to the drawings of FIGS. 1 and 2.

FIG. 1 shows the configuration of a carbon dioxide gas sensor according to an embodiment of the present invention 1. In FIG. 1, the gas sensing unit 1, the heater 2, the lead wires 3a, 3b, 5a, 5b, and the pedestal 6 have the same configurations as those shown in FIGS. Attach it and omit the details.

The protector 4a is a bottomed cylindrical housing that contains the gas sensing unit 1 and the heater 2, and has an opening / closing port 7 formed in the cylindrical portion to directly contact the gas sensing unit 1 with the external atmosphere. The drive part of the door that closes the opening / closing port 7 is formed of a shape memory alloy of a material that changes its shape thermally (not shown), and the spring contracts and opens when the temperature rises. Therefore, the opening / closing port 7 has its opening area changed by heating and cooling, and as shown in FIG. 2 (a), when the gas sensing part is heated to the measurement temperature, it is fully opened, and the heating of the heater 2 is stopped and cooled. When the measured ambient temperature is reached, it is fully closed as shown in FIG.

The operation of the carbon dioxide sensor configured as described above will be described below.

In the above structure, a predetermined voltage is applied to the heater via the lead wires 3a and 3b to heat the gas sensing unit 1 to the measurement temperature. Then, the opening / closing port 7 is fully opened, and the gas sensing unit 1 comes into contact with the external atmosphere through the opening / closing port 7 to detect carbon dioxide gas. In this case, even if the measurement atmosphere is a high humidity environment, if the measurement temperature is set to 450 ° C. or higher at which the hydrate or hydride of sodium carbonate 13 shown in FIG. 4 is completely pyrolyzed. , Element deterioration is prevented.

On the other hand, when the gas sensing unit is in the non-heated state, the opening / closing port 7 is fully closed, completely shut off from the atmosphere, and the moisture absorption of the sodium carbonate 13 is suppressed. Therefore, the formation of the hydrate or hydride is reduced, and deterioration of the device is avoided. In this way, in any state, sodium carbonate 13 can reduce the conversion into hydrates and hydrides due to moisture in the atmosphere.

As described above, the opening / closing port 7 provided in the protector 4a
However, since it opens when heated and closes when not heated, the gas sensing portion is always cut off from the outside atmosphere when not heated. Therefore, it is possible to prevent deterioration of the gas sensing unit due to moisture absorption of sodium carbonate 13 in the gas sensing unit.

Second Embodiment A second embodiment of the present invention will be described below with reference to FIG.

In the figure, the gas sensing unit 1, the heater 2, the lead wires 3a, 3
Since b, 5a, 5b, protector 4a, opening / closing port 7, and pedestal 6 are the same as those in FIG. 1, the same reference numerals are given and their details are omitted. The silica gel 8 formed in a plate shape and arranged and fixed on the upper portion of the pedestal 6 adsorbs the moisture remaining in the protector 4a when the gas sensing portion is changed from the heated state to the non-heated state, and the inside of the protector 4a has low humidity. It is for keeping the state, and many through holes are provided to improve hygroscopicity.

The operation of the carbon dioxide sensor configured as described above will be described.

In the above configuration, the carbon dioxide gas detecting operation during heating of the carbon dioxide gas sensor is the same as that in the first embodiment, and therefore its details are omitted here.

On the other hand, the power source of the heater 2 is turned off, the gas sensing portion is moved from the heating state to the non-heating state, the opening / closing port 7 is closed accordingly, and the moisture in the atmosphere is partially trapped in the protector 4. In such a state, the ambient temperature may drop and the protector 4a may be dewed. Even in such a case, the silica gel 8 in the protector 4a absorbs the residual moisture, so that the gas sensing unit 1 can avoid dew condensation.

As described above, since the silica gel 8 is provided in the protector 4a, it absorbs residual moisture when the gas sensing unit is in the non-heated state, which lowers the dew point temperature in the protector and the ambient temperature It is possible to make it difficult for the dew condensation state to occur even when it is lowered, and to prevent deterioration of the element due to dew condensation.

EFFECTS OF THE INVENTION As is clear from the above description of the embodiments, according to the present invention, the opening / closing port provided in the housing opens when the gas sensing unit is heated during measurement, and closes when not heated. The gas sensing unit is always shut off from the outside atmosphere when it is not heated. Therefore, it is possible to prevent the metal carbonate of the gas sensing portion from being deteriorated due to moisture absorption.

Further, since the moisture absorption section is provided in the housing, when the gas sensing section is in the non-heated state, it absorbs residual moisture, which lowers the dew point temperature in the housing, and even if the ambient temperature drops, Therefore, it is possible to prevent the element from deteriorating without causing dew condensation, and to produce a great effect in practical use.

[Brief description of drawings]

FIG. 1 is a partially cutaway side view showing the configuration of a carbon dioxide sensor according to an embodiment of the present invention, and FIGS. 2a and 2b are opening / closing operation diagrams of the opening / closing port when the carbon dioxide is heated or not heated, and FIG. FIG. 4 is a partially cutaway side view showing the configuration of a carbon dioxide sensor of another embodiment of the present invention, FIG. 4 is a vertical sectional view of a gas sensing portion of the carbon dioxide gas sensor, and FIG. 5 is a partially cutaway side view of a conventional carbon dioxide sensor. Is. 1 ... Gas sensing part, 2 ... Heater, 3a, 3b ... Lead wire, 4a ... Protector, 5a, 5b ... Lead wire, 6 ... Pedestal, 7 ... Open / close port, 8 ... Silica gel, 11 ...... NASICON
Plates, 12a, 12b ... Electrodes, 13 ... Sodium carbonate.

Claims (2)

[Claims] 1. An ion conductor having a pair of electrode layers at both ends and having conductivity with respect to metal ions capable of forming a metal carbonate, and a part of one of the electrode layers of the ion conductor or A gas sensing part composed of a metal carbonate capable of forming a dissociation equilibrium with carbon dioxide in a shape covering the whole, a heating part heating the gas sensing part to a measurement temperature, and including the gas sensing part and the heating part. And a case part having an opening / closing opening formed so as to close when the gas sensing part is opened and not heated. 2. The carbon dioxide gas sensor according to claim 1, further comprising a moisture absorption unit for removing moisture adsorbed on the metal carbonate of the gas detection unit, in the housing unit.