JPH0640083B2 - Humidity sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a humidity sensor using a lanthanum fluoride sintered body.

(Prior Art) Conventionally, among sensors using ceramics, a sensor using lanthanum fluoride (LaF3) is generally used for detecting oxygen concentration or fluorine ion concentration. When lanthanum fluoride is used as a humidity sensor, a thin film of lanthanum fluoride and a single crystal slice are used as disclosed in JP-A-64-500222.

(Problems to be Solved by the Invention) A humidity sensor using the above-mentioned conventional lanthanum fluoride (LaF3) requires a high-precision processing technique when forming a thin film of lanthanum fluoride and a single crystal slice. There is a problem that the manufacturing cost is high because the manufacturing apparatus is expensive and there are many processes. Further, there is a problem that an additive such as a catalyst must be used in order to increase the humidity detection ability, that is, the so-called humidity detection sensitivity.

Therefore, in the present invention, it is a technical problem to be solved that the humidity sensor using lanthanum fluoride is made inexpensive and highly sensitive by forming the sensor main body with a porous lanthanum fluoride sintered body. Is.

(Means for Solving the Problem) The technical means for solving the above problem is that a humidity sensor is obtained by crushing particles of lanthanum fluoride (LaF3) and molding the mixture under a required pressure, and then at a required temperature. A sensor body formed by shaping a porous sintered body obtained by sintering into a flat plate shape, planar electrodes deposited on both sides of the sensor body, and leads connected to the respective planar electrodes. And a member.

(Operation) According to the humidity sensor having the above configuration, lanthanum fluoride (La
F3) particles are crushed, shaped by applying the required pressure, and then sintered at the required temperature. The porous sintered body obtained is shaped into a flat plate, and the sensor body has a simple manufacturing process. In addition, since the surface area is large due to the porosity, the water molecule adsorption capacity is high, and if humidity is mainly detected based on the capacitance change due to the use of the space charge layer, the humidity detection sensitivity can be improved. Can be higher.

(Example) Next, the Example of this invention is described, referring drawings.

FIG. 1 is a side view of the humidity sensor 1 according to the present invention.
As described in the manufacturing process diagram of FIG. 3, the sensor body 2 of the humidity sensor 1 crushes particles of lanthanum fluoride (LaF3), molds them by applying a required pressure, and then sinters them at a required temperature. The porous sintered body thus obtained is polished and shaped into, for example, a disc having a thickness of 1 mm and a diameter of 15 mm. Gold electrodes 3 and 4 are formed by depositing gold in a thickness of angstrom order on both surfaces of the sensor body 2 respectively. The gold electrodes 3 and 4 serve as lead wires at the central portions of the gold electrodes 3 and 4, respectively. Platinum wire 5,
6 are electrically connected by silver pastes 7 and 8, and the respective connection portions are fixed by resin adhesives 9 and 10.

FIG. 2 is an enlarged view of part A of FIG. As shown in this figure, the sensor main body 2 has a large number of porous pores 2A of submicron to 5 microns, and the porosity is formed to about 20% to 50%.

Since the sensor body 2 has a large surface area due to its porosity, it has a high water molecule adsorption capacity, and as described later, it mainly detects humidity based on a change in capacitance due to the use of a space charge layer, and therefore has a humidity detection sensitivity. It has the characteristic of being high.

FIG. 3 shows a manufacturing process of the center main body 2.

As shown in FIG. 3, the sensor main body 2 is formed by crushing particles of lanthanum fluoride (LaF3) into particles of 60 microns or less in the first step, and then molding it at a pressure of 7 t / cm ² in the second step. After being sintered in an air atmosphere at 800 ° C. in the step, it is polished and shaped in the fourth step so as to have a disk shape having a diameter of 15 mm and a thickness of 1 mm.

FIG. 4 is an experimental circuit for measuring the current flowing through the humidity sensor 1 when the humidity sensor 1 is arranged at the humidity measuring position and the relative humidity at the humidity measuring position is changed. As shown in FIG. 4, in this experimental circuit, for the humidity sensor 1, an effective value of 30 V output from the function generator 12 via the resistor 11 of 100Ω,
An AC voltage of 10 Hz is applied, and the value of the current flowing through the humidity sensor 1 when the relative humidity at the humidity measurement position is changed is measured by the digital multimeter 13 in the order of microamperes. This experiment was conducted at 20 ° C,
The experimental results are shown in FIG.

Since the humidity detection characteristic of the humidity sensor 1 is established as described above, the AC voltage applied to the humidity sensor 1 is kept constant and the current flowing through the humidity sensor 1 or the voltage corresponding to the current is detected. This makes it possible to detect the relative humidity of the measurement location.

FIG. 6 shows an experimental circuit different from that of FIG.

In FIG. 6, the timer 21 has a normally open switch A and a normally closed switch B. When the normally open switch A is closed, the normally closed switch B is opened, and conversely the normally open switch A is closed. The normally-closed switch B is closed when is opened. In this experimental circuit, the timer 21 controls the normally-opened switch A to be closed for 0.05 seconds and then opened for 4.95 seconds. Has become. Therefore, when a pulse voltage is applied for 0.05 seconds to the humidity sensor 1 arranged at the humidity measurement position from the power supply PS that outputs a voltage of DC 5 V through the resistor 22 of 100Ω, the current flows to the humidity sensor 1. The current is measured by the digital multimeter 23. Then, after the pulse voltage is applied, the normally open switch A is opened to close the normally closed switch B for 4.95 seconds to discharge the electric charge charged in the humidity sensor 1 through the resistor 24 of 100Ω. Is.

In the above experimental circuit, the result of measuring the value of the current flowing through the humidity sensor 1 by the digital multimeter 23 in the order of microamperes when the relative humidity at the humidity measuring position was changed at 25 ° C. Is shown in FIG.

The relative humidity at the measurement location can be detected by detecting the current flowing through the humidity sensor 1 or the voltage corresponding to the current on the basis of the result of the measurement as described above.

The humidity sensor 1 having the humidity detection characteristics as described above has the characteristics of a dielectric, and in an atmosphere without water vapor, the current value flowing through the humidity sensor 1 is changed by the impedance of the humidity sensor 1 itself and the impedance of the resistance. Decided. On the other hand, as the amount of water vapor in the atmosphere increases, water molecules are adsorbed inside the sensor body 2 through the surfaces of the gold electrodes 3 and 4, the sensor body 2 or the pores 2A, forming a water molecule layer. Become. The water molecule layer on the surface of the gold electrodes 3 and 4 forms a space charge layer, and the water molecule layer on the surface and inside of the sensor body 2 reduces the internal resistance of the sensor body 2, thus reducing the impedance of the humidity sensor 1 as a whole. Therefore, the humidity can be detected by utilizing this impedance change.

(Effects of the Invention) As described above, according to the present invention, a sensor body is obtained by crushing particles of lanthanum fluoride (LaF3), applying a required pressure to the particles, and then sintering the particles at a required temperature. Since a porous sintered body was used, compared to the conventional process for producing a thin film and a single crystal slice of lanthanum fluoride, the steps are simple, and a high-precision production apparatus is not required, so that the humidity is low. There is an effect that the manufacturing cost of the sensor can be reduced.

In addition, since the sensor body and the planar electrode portion have a large surface area due to their porous nature, the water molecule adsorption capacity is high,
Since the humidity is detected based on the change in the electrostatic capacity of the space charge layer corresponding to the amount of adsorbed water molecules, there is an effect that the humidity detection sensitivity can be increased.

[Brief description of drawings]

1 is a side view of a humidity sensor 1, FIG.
FIG. 2 is a partial detailed view of FIG. 1, FIG. 3 is a manufacturing process diagram of the sensor body, FIG. 4 is a first experimental circuit diagram, and FIG. 5 is a data diagram showing the first experimental result. FIG. 6 is a second experimental circuit diagram, and FIG. 7 is a data diagram showing the second experimental result. 1: Humidity sensor 2: Sensor body 2A: Pore 3,4: Gold electrode 5,6: Platinum wire 7,8: Silver paste

Claims (1)

[Claims] 1. A porous sintered body obtained by crushing particles of lanthanum fluoride (LaF3), applying a required pressure to the particles, and then sintering the particles at a required temperature to form a flat plate. A humidity sensor, comprising: the sensor main body; planar electrodes deposited on both surfaces of the sensor main body; and lead members connected to the respective planar electrodes.