JPH039257A - Humidity sensor - Google Patents

Abstract

PURPOSE:To allow cleaning at a specified heating temp. by providing a planar constant temp. heating element via an insulating layer on one surface of a planar moisture sensitive element and constituting the two elements by providing electrodes on both surfaces of planar sintered bodies of oxides. CONSTITUTION:The humidity sensor is formed by joining the planar moisture sensitive element 2 and the planar constant temp. heating element 4 via the insulating layer 3. The element 2 is formed by providing the planar electrodes 22, 23 on both surfaces of the planar sintered body 31 of the oxide and the element 4 is formed by providing the planar electrodes 43, 43 on both surfaces of the planar sintered body 41 of the oxide. The measurement with the humidity measuring element 2 is executed by measur ing the change in the electric resistance of the sintered body 21 by the two electrodes 21, 22. The cleaning of the surface of the element 2 is executed while the element 4 is kept energized. The current corresponding to the initial resistance flows in the sintered body 41 of the element 4 and the heat thereof is raised by the self-heat genera tion when a specified voltage is impressed to this element. However, the resistance increases sharply and the current decreases when the Curie temp, is attained. The electric power for the heat generation and the surface temp. are then made constant.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a humidity sensor formed of an oxide sintered body.

(Prior Art and Problems to be Solved) A moisture sensing element formed of an oxide sintered body is used to detect the amount of water vapor, that is, humidity, in the atmosphere or gas.

This utilizes the property that when an oxide sintered body adsorbs water vapor, its electrical resistance changes depending on the amount of water vapor adsorbed.

When impurities such as dust and oil adhere to the surface of this moisture-sensitive element, the moisture-sensing characteristics deteriorate and accurate detection cannot be performed.

Therefore, as shown in Fig. 3, a plate-shaped oxide sintered body (21)
is sandwiched between a pair of plate-shaped electrodes (22) (23), and a moisture sensing element (
2), and the moisture sensing element (2) is heated with a nichrome wire heater (
5), an enclosed humidity sensor has been proposed.

When cleaning the surface of the humidity sensing element (2), the heater (5) is energized to heat the surface of the temperature sensing element (2) to about 400°C for a short time to incinerate impurities attached to the surface. Alternatively, it is removed by volatilization to clean the surface of the moisture sensitive element (2).

Further, as shown in FIG. 4, the moisture sensing element (2) is sandwiched between the plate-shaped oxide sintered body (21) and a pair of plate-shaped electrodes (22) (23).
), and one electrode (22) is provided with two terminals (21a) and (21b) at both ends.

When measuring humidity, the change in electrical resistance of the oxide sintered body (21) is measured between the terminal (21a) or (21b) of one electrode (22) and the terminal (23a) of the other electrode (22).

During cleaning, both terminals of one electrode (22) (
21a) (21b) to generate resistance heat in the electrode (22) to heat the oxide sintered body (21).

In both of the above two examples, a temperature control device must be connected to the heater or the electrodes (22), (23), (42) and (43) that also serve as heaters, making the device large-scale.

The present invention focuses on the fact that oxide sintered bodies self-heat and maintain a constant temperature when a constant voltage is applied, and by combining two oxide sintered bodies, there is no need for a temperature control device. This paper also reveals a humidity sensor equipped with a cleaning function that can maintain a constant heating temperature.

(Means for Solving the Problems) The humidity sensor of the present invention includes a plate-shaped constant temperature heating element (4) provided on one surface of a plate-shaped humidity sensing element (2) with an insulating layer (3) interposed therebetween. (2) and the constant temperature heating element (4) have electrodes (
22)(23), (42)(43).

(Operation and Effect) Humidity measurement is performed using two electrodes (22) (2) of the humidity sensing element (2).
3), the change in electrical resistance of the oxide sintered body (21) between the electrodes (22) and (23) is measured.

When cleaning the surface of the temperature sensing element, clean the constant temperature heating element (
4) The picture electrodes (42) and (43) are energized.

When a constant voltage is applied to the oxide sintered body (41) of the constant temperature heating element (4), a current according to the initial resistance flows and the temperature rises due to self-heating. When the Curie temperature is reached, the resistance increases rapidly, the current decreases, and the generated power and surface temperature become constant.

Therefore, by selecting the Curie point of the oxide sintered body (41) of the constant temperature heating element (4), during cleaning,
Dust and oil on the surface of the moisture sensing element (2) can be removed by incineration or volatilization by maintaining a constant temperature.

(Example) FIG. 1 is a humidity sensor of the present invention, and FIG. 2 is an exploded perspective view thereof.

The humidity sensor is constructed by joining a plate-shaped humidity sensing element (2) and a plate-shaped constant temperature heating element (4) with an insulating layer (3) interposed therebetween.

The humidity sensing element (2) is formed by providing plate-shaped electrodes (22) and (23) on both sides of a plate-shaped oxide sintered body (21).

In the example, the oxide sintered body (21) is formed of barium titanate (BaTiOs), but the present invention is not limited to this, and other oxide sintered bodies that have a moisture-sensitive effect can also be used. .

The electrodes (22) (23) are formed by applying a highly conductive metal paste onto the plate-shaped oxide sintered body (21) in the desired shape and then baking it, or by applying gold, platinum, etc. to the plate. Formed by vapor deposition on oxides.

The constant temperature heating element (4) has plate electrodes (42) on both sides of a plate-shaped oxide sintered body (41) in the same manner as the moisture-sensitive element (2).
(43).

In the embodiment, the plate-shaped oxidized story body (41) is made of barium titanate.

As is known, the Curie point of barium titanate is raised by replacing barium with lead, that is, a constant temperature is maintained at a high temperature.

In the example, the barium of barium titanate is 60% lead.
By making the above substitutions, the Curie point is raised to about 400°C.

However, humidity measurement is performed using two electrodes (2) of the humidity sensing element (2).
1) (22), the change in electrical resistance of the oxide sintered body (21) sandwiched between the electrodes is measured.

When cleaning the surface of the temperature sensing element, use the constant temperature heating element (4)
energize.

When a constant voltage is applied to the oxide sintered body (41) of the constant temperature heating element (4), a current according to the initial resistance flows and the temperature rises due to self-heating, but when the Curie temperature is reached, the resistance increases rapidly. However, the current decreases, and the generated power and surface temperature become constant.

Therefore, by selecting the Curie point of the oxide sintered body (41) of the constant temperature heating element (4), during cleaning,
Dust and oil on the surface of the moisture sensing element (2) can be removed by incineration or volatilization by maintaining a constant temperature.

4 The present invention is not limited to the configuration of the above embodiment,
Various changes are possible within the scope of the claims.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a humidity sensor, FIG. 2 is an exploded perspective view of the same, and FIGS. 3 and 4 are front views of a conventional humidity sensor. (2)...Moisture sensing element (21)...Plate-shaped oxide sintered body (22) (23)...Electrode (3)...Insulating layer (4)...Constant temperature heating element (41)... Plate-shaped oxide sintered body (42) (43)... Electrode 419-

Claims (1)

[Claims] [1] A plate-shaped constant temperature heating element (4) is provided on one surface of the plate-shaped humidity sensing element (2) with an insulating layer (3) interposed therebetween.
2) and the constant temperature heating element (4) have electrodes (22), (23), (
42) A humidity sensor configured by providing (43).