JPS6262285B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a relative humidity sensor, and more particularly to a relative humidity sensor for detecting high relative humidity or condensation conditions.

Conventionally, various sensors for detecting high relative humidity or dew condensation conditions have been proposed and realized for various uses. In some conventional devices, a moisture-sensitive substance is interposed between a pair of electrodes, and the state of dew condensation is detected by a sudden decrease in resistance value when condensation occurs. In addition, in other methods, conductive particles such as carbon powder are mixed with organic polymers such as epoxy, and the contact between the conductive particles is weakened due to swelling of the organic polymer during condensation, resulting in resistance. A condensation condition is detected by a sudden increase in value. All of these conventional devices detect a high relative humidity state or a dew condensation state based on a change in the resistance value of a humidity sensing element unit. Therefore, it is necessary to keep a certain amount of current flowing through the humidity sensing element unit.
Therefore, if dust or the like adheres to the moisture sensing element unit, there is a problem that the dust may cause false detection due to its influence.

Therefore, the main object of the present invention is to provide a relative humidity sensor that can stably detect high relative humidity conditions or dew condensation conditions based on a completely new principle.

In summary, this invention provides a semiconductor unit having a thermoelectromotive force effect, such as a barium titanate-based semiconductor, with a pair of electrodes for extracting the thermoelectromotive force, and one of the pair of electrodes. The vicinity of the side is heated, and a state of high relative humidity or a state of dew condensation is detected based on a change in thermoelectromotive force generated between the electrodes.

The above objects and other objects and features of the invention will become more apparent from the following detailed description with reference to the drawings.

FIG. 1 is an illustrative view showing an embodiment of the present invention. In the structure, a pair of electrodes 2 and 3 are formed at both ends of a semiconductor unit 1 made of a semiconductor material such as ferrite, barium titanate, or strontium titanate. Then, a heater 5 is integrally attached to the electrode 2 side of the semiconductor unit 1 via an insulator 4. This heater 5 is, for example, a tungsten heater, and is configured as a solid heater made by applying and baking tungsten paste. This heater 5 is supplied with relatively small power from a heater power source 6.
Further, leads 21 and 31 are connected to each of the pair of electrodes 2 and 3, and these leads 21 and 31 are connected to each other.
and 31 are connected to a detector 7, for example a voltmeter.

Note that in place of the heater 5, a lamp 8 may be used as a heating means.

Embodiment The semiconductor unit 1 was made of barium titanate ceramic, and its dimensions were 20 mm long x 10 mm wide x 0.2 mm thick. Further, the heating power by the heater 5 or the lamp 8 was 300 mW. Then, the relative humidity was varied from zero to 100%, and the voltage (thermoelectromotive force) from the leads 21 and 31 at that time was measured. The results are shown in FIG. As can be seen from Figure 2, there is no significant change in the generated electromotive force when the relative humidity ranges from zero to 90%. However, when it exceeds 90%, the generated electromotive force decreases rapidly, and at 100% it becomes about 1/10 of that at 0%. Furthermore, in the dew condensation state, the thermoelectromotive force was almost zero.

Thereafter, the relative humidity was lowered again by, for example, being left in the natural environment, and the relative humidity was changed again in the direction of increasing it. At that time, the characteristics shown in FIG. 2 were detected with good reproducibility.

This rapid change in thermoelectromotive force is due to
This is thought to be due to the fact that the heat distribution in the semiconductor unit 1 is made uniform due to moisture as the relative humidity changes, and also due to current leakage.

Such relative humidity sensors can be used for various purposes. For example, it can be used as a dew condensation sensor for the rear window of a passenger car, or as a humidity sensor for the magnetic head of a video tape recorder. Even when used in such applications, the thermoelectromotive force generated is relatively large, so stable detection operations can be performed.

As described above, according to the present invention, since humidity changes are not detected based on resistance changes as in the prior art, it is not necessary to supply current to the humidity sensing element unit. Furthermore, since the current flowing through the unit is extremely small, there is almost no change in characteristics due to it. Furthermore, the power consumed by the heating means may be very small, thus making it possible to reduce power consumption. In addition, since the moisture-sensitive element unit is made of a semiconductor material, it is extremely stable compared to conventional ones using organic polymer resin or the like. Furthermore, unlike the conventional method based on resistance change, the detection is based on the generated thermoelectromotive force, so the detection is reliable and has good reproducibility.
Since its structure is relatively simple, it is suitable for mass production.

If a ceramic semiconductor is used as the semiconductor unit, a sensor having stable detection characteristics can be obtained at a very low cost.

[Brief explanation of the drawing]

FIG. 1 is an illustrative view showing an embodiment of the present invention. FIG. 2 is a graph showing an example of detection characteristics achieved by a preferred embodiment of the present invention;
Relative humidity is plotted on the horizontal axis, and generated electromotive force is plotted on the vertical axis. In the figure, 1 is a semiconductor unit, 2 and 3 are electrodes, 21 and 31 are leads, 4 is an insulator, 5 is a heater, 6 is a heater power source, 7 is a detector, and 8 is a lamp.

Claims (1)

[Scope of Claims] 1. A semiconductor unit that generates a thermoelectromotive force, a pair of electrodes formed on the semiconductor unit and for extracting the thermoelectromotive force, and heating one side of the pair of electrodes of the semiconductor unit. and a means for extracting the thermoelectromotive force from the pair of electrodes. 2. The relative humidity sensor according to claim 1, wherein the heating means is a solid-state heater integrally attached to a predetermined position of the semiconductor unit. 3. The relative humidity sensor according to claim 1, wherein the heating means is a lamp.