JPH05215702A - Water content detector - Google Patents

Abstract

PURPOSE:To obtain a compact water content detector in a simple configuration which can detect water content constantly with nearly a fixed sensitivity regardless of the fluctuation of the temperature of external air. CONSTITUTION:A PTC thermistor 5 is mounted to the rear surface of an insulation substrate which is provided on the surface of a pair of electrodes 4a and 4b and a power-supply part 20 for applying a constant voltage is provided at the PTC thermistor. Since the PTC thermistor operates as a constant- temperature heating element, the temperature of a water content detection part is nearly maintained to be constant, thus eliminating change in water conductivity due to change in the temperature of an external air and detecting the water content constantly with a certain sensitivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moisture detecting device for detecting moisture on the basis of an electric quantity between a pair of electrodes provided in a moisture detecting portion, the amount of electricity varying according to moisture.

[0002]

2. Description of the Related Art The above-described moisture detecting device is particularly suitable for use as a moisture sensor for detecting rainfall, snowfall, etc. on a house, a road surface or the like. The basic structure of such a moisture detecting device is described in, for example, Japanese Patent Application Laid-Open No. 57-182620. That is, a pair of electrodes are arranged with a certain distance between them, a voltage is applied between these electrodes, and when no water exists between the electrodes, no current flows between the electrodes, but When water is present, the presence or absence of water is detected by detecting the flow of an electric current between the electrodes. The device described in this publication is for detecting the presence or absence of water, and the electrode is immersed in water. The basic structure of this device is to detect moisture used as a rainfall sensor or a snowfall sensor. The configuration is the same as that of the device.

[0003]

In the conventional moisture detecting device, the temperature of the moisture detecting portion provided with the electrodes is not kept constant, and the temperature of the water between the electrodes is equal to the outside air temperature. However, when moisture is detected based on changes in the electrical resistance between the electrodes, the conductivity of water changes significantly with changes in temperature, so the temperature of water changes with changes in outside air temperature. If it changes, there is a drawback that the detection sensitivity of water changes and the detection accuracy decreases. Such a temperature change of water due to the outside air temperature is not limited to the difference in temperature depending on the season, and the temperature difference between daytime and nighttime is also a problem.

On the other hand, Japanese Utility Model Publication No. 63-86105, Japanese Utility Model Publication No. 2-11
JP-A-8885 and JP-A-3-25185 disclose that a resistance heater such as a nichrome wire is placed near a pair of electrodes in order to detect snowfall or freezing in a road heating system in cold regions. Has been done. However, this resistance heater is provided to heat and melt the snow or ice between the electrodes, and does not maintain the temperature of the moisture detector constant. Therefore, the temperature of water existing between the electrodes is not constant only by providing such a resistance heater, and the moisture detection sensitivity fluctuates due to the influence of the outside air temperature, resulting in erroneous detection. There are drawbacks. Since the permittivity of water also changes depending on temperature, the above-mentioned problem is not limited to the case of detecting moisture by utilizing the change in electrical resistance between electrodes, but the detection of moisture by utilizing the change in electrostatic capacitance. It also happens in some cases.

In order to eliminate such drawbacks and keep the temperature of water existing between the electrodes constant, a temperature sensor for detecting the temperature of the moisture detecting section and an output of this temperature sensor are preset. A power supply that can control the electric power applied to the resistance heater so that it becomes a constant value is required,
It has a drawback that the structure is complicated, the size is large, and the cost is high.

The object of the present invention is to eliminate the above-mentioned drawbacks and to always detect moisture with a constant sensitivity without being affected by changes in the outside air temperature. An object of the present invention is to provide a moisture detection device that can be implemented easily and inexpensively without using a power supply that can control the power to be applied.

[0007]

SUMMARY OF THE INVENTION The present invention is an apparatus for detecting moisture based on an amount of electricity that changes according to moisture between a pair of electrodes provided in the moisture detecting unit, which is close to the moisture detecting unit. The PTC thermistor provided as above and a power supply circuit for applying a predetermined voltage to the PTC thermistor are provided.

[0008]

In such a moisture detecting device according to the present invention, a PTC thermistor is provided and a predetermined voltage is applied to the PTC thermistor. However, the resistance of the PTC thermistor changes in proportion to temperature. Therefore, when the temperature rises, the resistance value increases and the current flowing through it decreases, so the amount of heat generation decreases.On the other hand, when the temperature decreases, the resistance value decreases, so the current flowing through it increases and heat is generated. The amount will increase. Therefore, it is possible to keep the temperature of the moisture detecting portion substantially constant without providing any other temperature control circuit, and as a result, the moisture detecting sensitivity can be kept almost constant regardless of the change of the outside air temperature. The detection accuracy can be improved and erroneous detection can be eliminated.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1A and 1B are a plan view and a partially cutaway front view showing the construction of a moisture detecting portion of an embodiment of a moisture detecting apparatus according to the present invention configured as a rainfall sensor,
FIG. 2 is a block diagram showing the configuration of the entire apparatus. The moisture detector 1 has an insulating substrate 3 arranged so as to cover the upper opening of the case 2, and a pair of comb-shaped electrodes 4a and 4b are arranged on the surface of the insulating substrate at regular intervals to the other electrode. Place it so that it goes in. In addition, a PTC thermistor (positive temperature coeff
icient) 5 is placed. Lead wires 6 and 7 are connected to the electrodes 4a, 4b and the PTC thermistor 5, respectively,
These lead wires are grouped together to form a conductive wire 8 which is drawn out from the bottom surface of the case 2. It is preferable that the insulating substrate 3 has good electrical insulation properties and high thermal conductivity. For example, alumina, which is widely used in hybrid ICs and the like, satisfies the above-mentioned conditions and has excellent durability, and can be advantageously used as the insulating substrate 3 according to the present invention. Further, as the insulating substrate 3, other materials such as glass epoxy may be used. Also, a metal composite substrate or the like can be used.
Also, it is preferable that the thickness is as thin as possible.
It is possible to use one with a size of 5 to 1.6 mm.

As shown in FIG. 2, a DC power supply unit 20 is provided, and this DC power supply unit is connected to an oscillating unit 21 to generate an AC voltage having a predetermined amplitude and frequency. The oscillating unit 21 is connected to a pair of electrodes 4a and 4b provided in the moisture detecting unit 1 via a lead wire 6 so that an AC voltage having a constant amplitude is applied between the electrodes. One electrode 4
The current detector 22 is connected to the lead wire connected to a,
It is configured so that the current flowing between the electrodes can be detected. The current detection unit 22 is connected to the comparison unit 23, compares the detected current with a predetermined reference value, and when it exceeds the reference value, determines that there is rainfall and outputs a rainfall signal. That is, if there is rainfall above a certain level, the resistance value between the electrodes 4a and 4b will be below a certain value, and therefore the current flowing between the electrodes will exceed the reference value. Therefore, in that case, a rain signal should be output. To configure.

In the present invention, the DC power supply unit 20 for generating a constant DC voltage is further connected to the PTC via the lead wire 7.
It is connected to the thermistor 5 so that a constant voltage is applied to the PTC thermistor. In this way, a substantially constant voltage is applied to the PTC thermistor 5, but since the PTC thermistor has a positive temperature coefficient, the resistance value increases and the current decreases as the temperature increases, When the calorific value decreases and the temperature decreases, the resistance value also decreases, and the current increases, so that the calorific value increases. Therefore, if the PTC thermistor 5 is configured to apply a constant voltage, the temperature of the water content detection unit 1 is maintained substantially constant without being affected by the outside air temperature. That is, since the PTC thermistor 5 has a function as a constant temperature heating element, it is not necessary to provide a temperature sensor or control the energization of the heater based on the detected temperature, but simply insulate the PTC thermistor. Since it suffices to attach it to the back surface of the substrate and apply a constant voltage thereto, the structure is simple and compact, and the cost is low.

FIG. 3 shows the temperature characteristics of one embodiment of the above-described moisture detector according to the present invention, in which the horizontal axis represents the outside air temperature and the vertical axis represents the rate of change in moisture detection sensitivity. .. This moisture detection sensitivity change rate shows the change with the detection sensitivity at 25 ° C being 100%. Figure 3
Curve A shows the temperature characteristics of the embodiment according to the present invention, and is close to the ideal curve B, and the rate of change in moisture detection sensitivity when the outside air temperature changes from 0 to 50 ° C is ± 20% or less. , I found that there is no problem in practice. The curve C shows the temperature characteristics of the comparative example in which the PTC thermistor is removed from the above-described embodiment of the present invention, and the rate of change in moisture detection sensitivity changes significantly with changes in the outside air temperature, which may lead to erroneous detection. is there. As described above, according to the present invention, it was confirmed that the water content can be accurately detected with almost no influence of the temperature difference due to the season, the temperature difference due to the night and the like, and the like.

According to the present invention, the PTC thermistor is used to maintain the temperature of the moisture detecting portion substantially constant, but the set temperature is at least higher than the outside air temperature.
It is desirable to set the temperature higher than 10 ° C. However, if the set temperature is set too high, water may evaporate too quickly and moisture detection may not be performed well.
A temperature of 60 ° C is preferred. By setting such a temperature, snow or ice can be melted, and therefore it also has a function as a resistance heater for the above-mentioned conventional snow melting or ice melting, and such a resistance heater is separately provided. The configuration can be simplified as compared with the case where it is provided.

The present invention is not limited to the above-described embodiments, but many modifications and variations are possible. For example, although an AC voltage is applied between the electrodes in the above-mentioned embodiment, a DC voltage can be applied. Further, in order to detect the change in the resistance value between the electrodes, it is possible to provide a constant current source and detect the change in the voltage generated between the electrodes. Further, the voltage applied to the PTC thermistor does not have to be a DC voltage, but can be an AC voltage having a constant peak-peak value. Further, instead of detecting the resistance change between the electrodes, it is possible to detect the change in capacitance.
Also in this case, by keeping the temperature of the moisture detector substantially constant, it is possible to eliminate the change in the detection sensitivity due to the temperature dependence of the dielectric constant of water, and it is possible to perform accurate moisture detection. Further, in the above-described embodiment, the sensor is configured as a rainfall sensor, but it may be configured as a snowfall sensor or a freeze sensor.

[0015]

According to the moisture detector of the present invention, the PTC thermistor is arranged in the vicinity of the pair of electrodes.
Since it is configured to apply a predetermined voltage to the C thermistor, the temperature of the moisture detector is kept almost constant, the influence of the change in the conductivity or permittivity of water due to the temperature disappears, and it depends on the outside air temperature. Therefore, it is possible to always detect moisture with a substantially constant sensitivity, and it is possible to eliminate erroneous detection. Further, since it is not necessary to control the temperature sensor for detecting the temperature of the water content detecting portion and the energization of the heater based on the detected temperature, the structure is simple and small, and the cost is low.

[Brief description of drawings]

1A and 1B are a plan view and a front view showing a configuration of an embodiment of a moisture detector according to the present invention.

FIG. 2 is a block diagram showing an overall configuration of the embodiment.

FIG. 3 is a graph showing the temperature characteristics of the detection sensitivity change rate of the moisture detector according to the present invention and the comparative example.

[Explanation of Codes] 1 moisture detector 2 case 3 insulating substrate 4a, 4b electrode 5 PTC thermistor 6, 7 lead wire 8 conductor 20 DC power supply unit 21 oscillator unit 22 current detector unit 23 comparison unit

Claims (2)

[Claims] 1. A device for detecting moisture based on an electric quantity that changes according to moisture between a pair of electrodes provided in the moisture detector, and a PTC thermistor provided close to the moisture detector, A water content detection device comprising a PTC thermistor and a power supply circuit for applying a predetermined voltage. 2. The pair of electrodes are formed in a comb shape on the surface of an insulating substrate having a high thermal conductivity, and the P on the back surface of the insulating substrate.
2. A TC thermistor is attached.
The moisture detection device described.