JPH04324352A - Humidity sensor - Google Patents

Abstract

PURPOSE:To achieve higher accuracy, a smaller size and an inexpensive production as well as high stability of outputs. CONSTITUTION:A hunmidity sensor contains an alkali metal ion transmitting solid electrolyte 1, a detection electrode 2 formed in contact with one 1a of the alkali metal ion transmitting solid electrolyte 1, an oxygen ion transmitting solid electrolyte 3 arranged by joining one end 3a of the alkali metal ion transmitting solid electrolyte 1 to the other end 1b thereof and a reference electrode 4 formed in contact with the other end 3b of the oxygen ion transmitting solid electrolyte 3. The alkali metal ion transmitting solid electrolyte 1 detects a change in moisture and the oxygen ion transmitting solid electrolyte 3 does not detect the change in the moisure and hence, the combination of the both enables measurement of the moisture. This achieves high stability of outputs from a sensor and also does a higher accuracy, a smaller size and inexpensive production.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a humidity sensor that can accurately measure humidity in a gas to be detected.

0002

[Prior Art] Hygrometers for measuring the humidity in a sample gas have conventionally been used, such as a psychrometer that converts humidity from the relationship between the temperature difference between a dry bulb and a wet bulb and the air temperature; A dew point meter that uses dew condensation phenomenon, a hair hygrometer that uses the expansion and contraction of hair due to humidity, an absorption hygrometer that uses the weight increase due to the absorption of phosphorus pentoxide, and a hygrometer that uses the moisture absorption of lithium chloride and the absorption of moisture into semiconductor or ceramic powders. Electric hygrometers that utilize changes in electrical conductivity that occur with chemisorption, and infrared absorption hygrometers that utilize absorption at specific wavelengths, are known.

However, each of the hygrometers listed above,
None of them meet all of the performance requirements for a general-purpose humidity sensor, such as being small in size, being able to obtain highly accurate and stable measurement values, and being able to be manufactured at low cost. The present invention is a novel humidity sensor that satisfies all of the requirements for a general-purpose humidity sensor as described above, has a stable and highly accurate sensor output, is small in size, and can be manufactured at low cost. For the purpose of providing.

0004

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an alkali metal ion conductive solid electrolyte and an alkali metal ion conductive solid electrolyte formed in contact with one end of the alkali metal ion conductive solid electrolyte. an oxygen ion (O2-) conductive solid electrolyte disposed with one end joined to the other end of the alkali metal ion conductive solid electrolyte, and the O2- conductive solid electrolyte. a reference electrode formed in contact with the other end of the electrolyte; and an electrically insulating support substrate; and a humidity sensor disposed on the support substrate. , an alkali metal ion conductive solid electrolyte, a sensing electrode formed in contact with one end of the alkali metal ion conductive solid electrolyte, and one end of the alkali metal ion conductive solid electrolyte. O placed by joining the ends
2-A humidity sensor comprising a conductive solid electrolyte and a reference electrode formed in contact with the other end of the O2-conductive solid electrolyte; Ru.

[0005]

[Operation] This humidity sensor is used in a heated state at a temperature of 300 to 650°C. When this humidity sensor is placed in a test gas at the above temperature, an electromotive force proportional to the humidity in the test gas is generated between the detection electrode and the reference electrode. In this case, although the reason is not clear, the sensing electrode formed on the alkali metal ion-conducting solid electrolyte detects humidity changes, and the reference electrode formed on the oxygen ion-conducting solid electrolyte detects the influence of humidity changes. I don't accept it.

[0006] When the operating temperature of this humidity sensor is lower than 300°C, if the thickness of the above-mentioned alkali metal ion conductive solid electrolyte or O2- conductive solid electrolyte is about 1 mm, the impedance of these solid electrolytes is large. , measurement accuracy deteriorates. However, if these solid electrolytes are made thinner and thinner, the measurement temperature can be further increased by 100%.
The temperature can also be lowered to ℃ or higher.

[0007] When the operating temperature of the humidity sensor is higher than 650°C, not only does it lead to an increase in cost, but also the potential change at the sensing electrode becomes small in response to a change in humidity in the gas being tested, which also reduces measurement accuracy. Resulting in.

[0008]

[Embodiments] Each embodiment of the present invention will be explained in detail below based on the drawings. FIG. 1 is a side view showing the humidity sensor of the first embodiment. For this humidity sensor,
Cylindrical alkali metal ion conductive solid electrolyte 1
A sensing electrode 2 is formed in contact with one end 1a of the alkali metal ion conductive solid electrolyte 1, and one end of an O2-conductive solid electrolyte 3, which also has a cylindrical shape, is formed on the other end 1b of the alkali metal ion conductive solid electrolyte 1. The reference electrode 4 is formed in contact with the other end 3b of the O2-conductive solid electrolyte 3, with the ends 3a being joined together. Then, the sensing electrode 2 and the reference electrode 4
Lead wires 5a and 5b are attached to the respective leads.

In this case, the shape of the alkali metal ion conductive solid electrolyte 1 may be a prism with a polygonal cross section, or may be a disk or a square plate. The alkali metal ion conductive solid electrolyte 1 having such a shape is produced by molding a predetermined raw material powder, sintering the obtained molded body, and then processing the sintered body as described above using a processing machine such as a diamond cutter or a lathe. It can be manufactured by cutting into a shape.

Examples of the alkali metal ion conductive solid electrolytes include sodium ion (Na+) conductive solid electrolytes, lithium ion (Li+) conductive solid electrolytes, potassium ion (K+) conductive solid electrolytes, and cesium ion (Cs+) conductive solid electrolytes. A conductive solid electrolyte or the like can be used. Among these, as the Na+ conductive solid electrolyte, for example, the following formula: Na1+x Zr2 Si
NASICON represented by P3-x O12 (0≦x≦3); following formula: Na2 O x Al2 O3
(In the formula, 5≦x≦11) β-alumina; Following formula: Na1+x MxAl11-XO17 (In the formula, M is
Mg2+, Ca2+, Sr2+, Ba2+, Co2+,
Represents divalent cations of Ni2+ and Cu2+, 0≦x≦2
) β”-alumina; Na1+x Zr2-
X MxP3 O12 (wherein, M is Fe3+, In3
+, Sc3+, Y3+, Sm3+, Eu3+, Gd3+
, Tb3+, Dy3+, Ho3+, Er3+, Tm3+
, represents trivalent cations of Yb3+ and Lu3+, and 0≦x≦
2) Compound represented by the following formula: Na1+2xZr2-x
MxP3 O12 (wherein M is Mg2+, Ca2+
, Sr2+, Ba2+, Co2+, Ni2+, Cu2+
A compound representing a divalent cation of 0≦x≦2; the following formula: NaMSi4 O12 (wherein, M is Fe3+
, In3+, Sc3+, Y3+, Sm3+, Eu3+,
Gd3+, Tb3+, Dy3+, Ho3+, Er3+,
represents trivalent cations of Tm3+, Yb3+, Lu3+)
A compound represented by and called NMS-NASICON;
The following formula: Na3 MSi4 O12 (wherein M is Fe3
+, In3+, Sc3+, Y3+, Sm3+, Eu3+
, Gd3+, Tb3+, Dy3+, Ho3+, Er3+
, representing trivalent cations of Tm3+, Yb3+, Lu3+); Na1.7 Al1.7 Si0
．． 3 O4 ; Na3 ScP3 O12 can be used.

[0011] Also, Japanese Patent Application Laid-Open No. 57-135714,
Japanese Patent Application Publication No. 59-213609, European Patent Publication No. 0
Na+ proposed in Publication No. 067 274 etc.
Conductive solid electrolyte or the following formula: Na2 O・Al2 O3
・Compounds represented by xSiO2 (in the formula, x is 2, 4, 6, 8) also have high Na+ conductivity, that is, low internal impedance, even at relatively low temperatures of 300 to 700°C. Also Na+ according to the present invention
It can be used as a conductive solid electrolyte.

[0012] Furthermore, the following formula: (PEO)xNaSCN, (
PPO)xNaSCN, (PEO)xNaI, (PPO
)xNaI, (PEO)xNaCF3SO3, (P
PO)xNaCF3 SO3 etc. (where PEO is (
CH2 CH2 O)n, PPO is (CH2 CH(C
The polymer complex represented by H3)O)n, where x represents the number of oxygen atoms per cation, also has N
Since the conductivity of a+ is high, it can be used as the Na+ conductive solid electrolyte according to the present invention.

Examples of the Li+ conductive solid electrolyte include LiI, LiI-CaI2, LiI-CaO, L
iAlCl4, LiAlF4, LiI-Al2O
3, LiF・(H2O)-Al2O3, 2Li
Br・(H2O)-Al2O3, Li3N, L
i3 NI2, Li3 N-LiI-LiOH, Li
3N-LiCl, Li6NBr3, Li2Si
O4, following formula: xLi3 PO4 -(1-x)Li4
A solid solution represented by SiO4 (wherein 0≦x≦1),
The following formula: xLi4GeO4-(1-x)Zn2Ge
O4 (wherein, 0≦x≦1) is a solid solution (x is 3
/4 compound: Li14Zn(GeO4)4
is called LISICON), the following formula: xLi4Si
O4 −(1-x)Li4 ZrO4 (wherein, 0≦x
Solid solution shown in 1), LiAlSiO4, Li5
B7 O12.5Cl, Li2 TiO7, Li2
Ti2O5, 0.8(LiTi2(PO4)3
)-0.2Li3PO4, Li4SiO4-
Li3 BO3, Li2 O-Na2 O-B2 O3
, the following formula: Li4-2XMgxSiO4 (where 0<
A compound represented by x<2) can be used.

[0014] In addition, K+ conductive solid electrolytes and Cs+
As a conductive solid electrolyte, β-alumina or β”-alumina in which Na+ is replaced with K+, the following formula: KxMgX/
2 Ti8-X/2 O16 (in the formula, 1.6<x<2)
A compound represented by the following formula: K2 O-Fe2 O3 -
Compounds represented by ZnO, (PEO)xKSCN, (P
EO)xCsSCN, (PPO)xKSCN, (PPO
)xCsSCN (PEO, PPO, x all have the same meanings as above), etc. can be used.

[0015] Since the alkali metal ion conductive solid electrolytes described above have slightly different alkali metal ion concentrations and internal impedances, the electromotive force and response speed of each sensor obtained also differ. . However, in this regard, for example, with regard to electromotive force, by creating a unique calibration curve for each sensor in advance, differences in sensor performance can be eliminated, and with regard to response speed, Since all of the compounds exhibit high alkali metal ion conductivity, there is no problem in practical performance as a sensor.

[0016] The O2-conductive solid electrolyte 3 is produced by molding a predetermined raw material powder and then sintering the resulting molded body.
Then, the sintered body can be manufactured by cutting the sintered body into the above shape using a processing machine such as a diamond cutter or a lathe. Here, as the O2-conductive solid electrolyte, the following formula: (MO2)1-x (RyOz)
x (where M is Zr4+, Th4+, Hf4+, Ce4
+ represents a tetravalent cation, R is Mg2+, Ca2+,
Divalent cations of Sr2+, Ba2+, Co2+, Ni2+, Cu2+ or Fe3+, In3+, Sc3+, Y
3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy
3+, Ho3+, Er3+, Tm3+, Yb3+, Lu
Represents a 3+ trivalent cation, 0.05≦x≦0.3, y and z are numbers that make (RyOz) electrically neutral)
Compound represented by; following formula: (Bi2O3)1-x
(RyOz)x (wherein R is Mg2+, Ca2+, Sr
2+, Ba2+, Co2+, Ni2+, Cu2+, Pb
2+ divalent cation, Fe3+, In3+, Sc3+,
Y3+, Sm3+, Eu3+, Gd3+, Tb3+, D
y3+, Ho3+, Er3+, Tm3+, Yb3+, L
Represents the trivalent cation of u3+, or W6+, 0.0
A compound represented by 5≦x≦0.3, where y and z are numbers that make (RyOz) electrically neutral can be used.

A sensing electrode 2 formed at one end 1a of such alkali metal ion conductive solid electrolyte 1,
2-The reference electrode 4 formed at the other end 3b of the conductive solid electrolyte 3 is a porous gas diffusion electrode. These electrodes can also be formed by sputtering or vapor deposition, but the space containing the fine powder of each electrode material is formed between one end 1a of the alkali metal ion conductive solid electrolyte 1 and the O2-conductive solid electrolyte. It is believed that forming the electrode by a paste coating pyrolysis method, in which the paste is applied to the other end 3b of the electrode 3 and then baked at a predetermined temperature, is easy to operate and can reliably form the electrode. suitable.

The materials used for forming the sensing electrode 2 are as follows:
Although platinum (Pt) may be used, gold (Au) is preferable because alkali metals and oxygen do not form a solid solution even at high temperatures and change over time is less likely to occur. The material used to form the reference electrode 4 may be gold as in the case of the detection electrode, but it must be a material that does not dissolve the constituent elements of the O2-conductive solid electrolyte or oxygen even at high temperatures. Moreover, platinum (Pt) is a material that exhibits a catalytic effect on the dissociation reaction of oxygen.
is a suitable material.

Further, the material of the reference electrode 4 is known as an oxide electrode material, for example, the material of the following formula: La1-X
SrX MO3 (where M is Co2+, Mn2+,
A compound representing a divalent cation of Fe2+ and represented by 0≦x<1), the following formula: La1-XSrX M11-yM2
yO3 (where M1 is Mn2+, Fe3+, Ca2
+, represents a cation such as Mg2+, M2 is Co2+
, Cr3+, Al3+, etc., and x and y may be compounds represented by 0≦x<1 and 0≦y<1, respectively.

Lead wires 5a and 5b are attached to the sensing electrode 2 and the reference electrode 4, respectively, from which an electromotive force signal during humidity measurement is extracted. These lead wires 5a and 5b are preferably made of the same material as the detection electrode 2 and the reference electrode 4, and for example, these electrodes are coated with gold paste, platinum paste, etc. before or at the same time as the formation of both electrodes. Preferably, it is fixedly attached.

FIG. 2 is a plan view showing another embodiment. The humidity sensor of this embodiment has an electrically insulating support substrate 6
On top of the alkali metal ion conductive solid electrolyte 1 having a thin plate shape, a sensing electrode 2 formed in contact with one end 1a of this alkali metal ion conductive solid electrolyte 1, and this alkali metal ion conductive solid electrolyte 1. An O2-conductive solid electrolyte 3 in the form of a thin plate, with one end 3a joined to the other end 1b of the O2-conductive solid electrolyte 1, and the other end of the O2-conductive solid electrolyte 3. A humidity detection section A is formed including a reference electrode 4 formed in contact with the section 3b.

In order to form the thin plate-shaped alkali metal ion conductive solid electrolyte 1 and O2-conductive solid electrolyte 3 on the support substrate 6, for example, a powder mixing method, a coprecipitation method,
A raw material powder of a predetermined composition synthesized by a wet synthesis method using a hydrolysis method, an alkoxide method, etc. is thoroughly pulverized using a pulverizer such as a ball mill, and the resulting fine powder is made into a heat-resistant electric material by a screen printing method or the like. After patterning on the insulating support substrate 6, apply a coating-baking method in which the whole is heated to the sintering temperature of each fine powder to burn the printed pattern of the fine powder onto the support substrate. is preferred. At this time, by changing the coating amount during patterning, each solid electrolyte can be applied to the support substrate 6 in the form of a thick film or thin film, a cylinder or a prismatic column or a semi-column, or even a plate. can be formed on top. In addition, sintered blocks of each solid electrolyte are manufactured in advance, and columnar bodies and plate-shaped bodies are cut from these blocks.
Each of them can also be bonded onto the support substrate 6 using an inorganic adhesive containing alumina as a main component.

For this reason, it is necessary that the support substrate 6 has sufficient heat resistance to withstand the sintering temperature of each of the fine powders mentioned above. In order to prevent a short circuit between the electrode 2 and the reference electrode 4, it is necessary to have electrical insulation properties. Examples of materials that satisfy these characteristics include alumina, zirconia, silicon nitride, and aluminum nitride. Further, the support substrate may be a substrate obtained by coating the surface of another substrate with the above-mentioned material by the above-described coating and baking method, vapor deposition method, CVD method, sputtering method, plasma spraying method, or the like.

In addition to the above-mentioned coating and baking method, after applying a predetermined masking to the supporting substrate 6, alkali metal ion conductivity of a predetermined composition can be applied thereto by vapor deposition, CVD, sputtering, plasma spraying, etc. A solid electrolyte 1 or an O2-conductive solid electrolyte 3 can also be formed. The detection electrode 2, the reference electrode 4, the lead wire 5a, and the lead wire 5b are all made in the same manner as in the first embodiment.
formed in each location.

FIGS. 3 and 4 are a plan view and a side view, respectively, showing still another embodiment. The humidity sensor of this embodiment is of a type in which a heating element is mounted on the sensor itself. As mentioned above, the sensor of the present invention has 30
It exhibits its sensor function in the temperature range of 0 to 750 degrees Celsius, but
A device equipped with a heating element like this type can improve the accuracy of temperature control.

In FIG. 3, a heating element 7 is formed in a zigzag pattern on the back surface of the electrically insulating support substrate 6 in the sensor shown in FIG. ing. The heating element 7 can be formed by, for example, patterning a paste prepared by dispersing fine platinum powder in turpentine oil or the like on the back surface of the support substrate 6 by a method such as screen printing, and then baking the paste. In addition to platinum, rhodium, platinum-rhodium alloy, tungsten, and nickel-chromium alloy can also be used as the material at that time. In addition to the above-described baking method, the heating element 7 can also be formed by masking the back surface of the substrate 6 and applying a vapor deposition method, a CVD method, a sputtering method, a plasma spraying method, or the like.

[0027]

【Example】

Example 1 The humidity sensor shown in FIG. 1 was manufactured as follows. That is, first, a Na3PO4 reagent (anhydrous) with a purity of 99.9% and a ZrSiO4 reagent were weighed so that the molar ratio was 1:2, and then the two were mixed. The obtained mixed powder was heat treated at 1147° C. for 48 hours to cause a solid phase reaction and homogenized, and then pulverized in a ball mill for 24 hours. The obtained powder was press-molded into a cylindrical shape with a pressure of 1 ton/cm2, and then the molded body was
Heat treatment was performed at 247°C for 12 hours. A cylindrical NASICON sintered body 1 having a diameter of about 2 mm and a length of about 4 mm was obtained.

Next, the special grade reagent yttrium oxide (Y
2O3) powder and special grade reagent zirconium oxide (ZrO2
) powder were weighed so that the molar ratio was 8:92, and then the two were mixed. The obtained mixed powder was heat-treated in the atmosphere at 1000° C. for 2 hours to cause a solid phase reaction and homogenized, and then pulverized in a ball mill for 24 hours. The obtained powder was rubber press molded at a pressure of 1 ton/cm 2 , and then the molded product was heat treated at 1750° C. for 2 hours. A sintered block of yttria stabilized zirconia (hereinafter referred to as YSZ) was obtained. This YSZ block was processed using a diamond cutter and a lathe to form a disk 3 having a diameter of 4 mm and a thickness of 0.5 mm.

[0029] N on one end surface of the NASICON sintered body 1
ASICON powder is attached, YSZ disk 3 is placed on it, and the whole is heated to 1350℃ on a ceramic heater.
by heating one end 3a of the YSZ disk 3 to N.
It was fused to one end surface 1b of the ASICON sintered body 1 to integrate the two. Another end 1a of the NASICON sintered body 1
A gold wire 5a with a diameter of 0.2 mm is wound around the outer circumference of the YS, and gold paste is applied to the part where the gold wire is wound.
A diameter of 0.2 m is attached to the end surface of the other end 3b of the disk 3 of Z.
A gold wire of m was attached, and gold paste was applied thereon. Then, the whole was fired at 700° C. for 1 hour to form the sensing electrode 2 and the reference electrode 4.

The obtained sensor was set in the electromotive force measurement system shown in FIG. That is, a sensor 10 was set in a quartz tube 9 placed in an electric furnace 8, and lead wires 10a and 10b of this sensor were connected to a signal processing circuit 11, respectively. The electromotive force signal is displayed on a display circuit 12 connected to a signal processing circuit 11. The quartz tube 9 contains water 1
3 is connected via a flow meter 15 to a flask 14 containing the liquid. A hygrometer 16 is inserted into the flask 14, and a standard carbon dioxide gas cylinder 17 is connected thereto.

In this measurement system, the operating temperature of the sensor 10 is maintained at 525°C, and the relative humidity is 0 from the cylinder 17.
%, a standard gas having a carbon dioxide concentration of 400 ppm was continued to flow at a gas flow rate of 150 ml/min. Then, the temperature of the water 13 in the flask 14 was adjusted by operating the heater 18, and the relative humidity in the standard gas was measured with the hygrometer 16. The sensor electromotive force was measured when the relative humidity in the standard gas was changed from 0% to 100%. The results are shown in Table 1. Furthermore, once the electromotive force measurement is stopped,
After a month, the electromotive force was measured in the same manner. The results are shown in Table 1.

[0032]

[Table 1] Example 2 The alkali metal ion solid electrolyte was
Instead of ASICON, Li+ manufactured by the following method
A sensor was manufactured in the same manner as in Example 1, except that the conductive solid electrolyte was used.

[0033] Reagent grade lithium carbonate, silicon dioxide, and vanadium pentoxide in a solid solution composition (mole ratio) of 0.4L.
i4 SiO4 -0.6Li3 VO4, mixed and dispersed in n-hexane, dried, heat treated at 600°C for 5 hours to drive out carbon dioxide gas, and further heated at 700°C for 4 hours. After heat treatment for 1 hour to cause a solid phase reaction and homogenization, pulverization treatment was performed in a ball mill for 24 hours. The obtained powder was rubber press molded at a pressure of 1 ton/cm2,
The molded body was heat treated at 1000° C. for 1 hour to produce a sintered body block.

The electromotive force of this sensor was also measured in the same manner as in Example 1. The results are shown in Table 2.

[0035]

[Table 2] Example 3 The humidity sensor shown in FIGS. 3 and 4 was manufactured as follows. That is, first, an alumina substrate 6 with a purity of 99.9% is prepared.
On top of this, the fine YSZ powder produced by the method of Example 1 was patterned by screen printing, and then the whole was
Baked at a temperature of 0℃ for 2 hours, length 4mm, width 2mm,
A YSZ film with a thickness of 0.5 mm was formed.

Next, NAS manufactured by the method of Example 1
After patterning the fine powder of ICON on the alumina substrate 6 by a screen printing method so that it is in contact with the YSZ film, the whole is baked at a temperature of 1247° C. for 12 hours, and on the alumina substrate 6, A NASICON film having a length of 4 mm, a width of 2 mm, and a thickness of 0.5 mm was formed. Also,
A platinum paste was patterned on the back surface of the alumina substrate 6 by a screen printing method, and then the whole was subjected to heat treatment at 1000° C. for 1 hour to form a heating element 7. At this time, the platinum wires 7a and 7b, which are the lead wires of the heating element 7, were also baked together with the platinum paste. Then, on one end of the NASICON membrane and on the other end of the YSZ membrane, a diameter of 0.2
A gold wire of mm thick was attached, and gold paste was further applied thereon. After drying, the whole was fired at 700° C. for 1 hour to form a sensing electrode and a reference electrode, respectively.

This sensor was set in the electromotive force measurement system shown in FIG. 5, the electric furnace 10 was not operated, and the temperature was controlled by operating the heating element mounted on the sensor to measure the electromotive force. The results are shown in Table 3.

[0038]

[Table 3]

[0039]

As is clear from the above description, the sensor of the present invention can measure the humidity in the sample gas. The measured values obtained are highly accurate and stable. In addition, it has a small size and is easy to manufacture, so it has high value as a general-purpose humidity sensor.

[Brief explanation of the drawing]

FIG. 1 is a side view showing a first embodiment of the present invention.

FIG. 2 is a plan view showing a second embodiment of the invention.

FIG. 3 is a plan view showing a third embodiment of the invention.

FIG. 4 is a side view showing a third embodiment of the invention.

FIG. 5 is a schematic configuration diagram showing an electromotive force measurement system of a humidity sensor.

[Explanation of symbols] 1 Alkali metal ion conductive solid electrolyte 1a One end portion 1b of alkali metal ion conductive solid electrolyte 1 Other end portion 2 of alkali metal ion conductive solid electrolyte 1 Sensing electrode 3 Oxygen ion conductive solid Electrolyte 3a One end 3 of oxygen ion conductive solid electrolyte 3
b The other end 4 of the oxygen ion conductive solid electrolyte 3
Reference electrodes 5a, 5b Lead wires 6 Support substrate 7 Heating elements 7a, 7b Lead wires of heating element 7 8 Electric furnace 9 Quartz tube 10 Humidity sensors 10a, 10b Lead wires 11 Signal processing circuit 12 Display circuit 13 Water 14 Flask 15 Flowmeter 16 Hygrometer 17 Standard gas cylinder 18 Heater

Claims (2)

[Claims] 1. An alkali metal ion conductive solid electrolyte, a sensing electrode formed in contact with one end of the alkali metal ion conductive solid electrolyte, and the other end of the alkali metal ion conductive solid electrolyte. and a reference electrode formed in contact with the other end of the oxygen ion conductive solid electrolyte. humidity sensor. 2. An electrically insulating support substrate; and an alkali metal ion conductive solid electrolyte disposed on the support substrate and in contact with one end of the alkali metal ion conductive solid electrolyte. an oxygen ion conductive solid electrolyte whose one end is joined to the other end of the alkali metal ion conductive solid electrolyte; A humidity sensor comprising: a humidity detection section including a reference electrode formed in contact with the other end.