JPS6212469B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frost/dew condensation sensor that includes both a moisture-sensitive film and a thermistor and detects each state of frost/dew condensation based on a change in electrical resistance.

BACKGROUND ART A dew condensation sensor using a moisture-sensitive film whose electrical resistance changes in accordance with changes in humidity is known. However, a moisture-sensitive membrane that can accurately detect frost conditions has not yet been known. Therefore, a frost/dew condensation sensor has been proposed that incorporates a thermistor for detecting frost formation in addition to a moisture-sensitive film. However, in conventional frost/dew condensation sensors of this kind, a circuit for detecting changes in the electrical resistance of the moisture-sensitive membrane and a circuit for detecting changes in the electrical resistance of the thermistor must be installed independently, and the device The disadvantage was that it became complicated.

Furthermore, in order to achieve miniaturization, there is a demand for the use of chip-type thermistors. However, since the chip-type thermistor has a small heat capacity and a small surface area, the chip-type thermistor exhibits an electrical resistance that corresponds to the temperature of the air in the portion that is in direct contact with the thermistor. Therefore, if there is a difference between the temperature of the object to be measured and the temperature of the air in contact with the thermistor, that is, if the temperature distribution of the air around the thermistor is not uniform, it may malfunction and indicate an incorrect temperature. It was hot.

Therefore, it is an object of the present invention to eliminate the above-mentioned drawbacks, provide a small-sized frost/dew condensation sensor with excellent detection accuracy.

In summary, this invention comprises a moisture-sensitive film whose electrical resistance suddenly changes in the state of dew condensation and a thermistor whose electrical resistance suddenly changes near 0°C on the same substrate, and which is thermally coupled to the thermistor on this substrate. This is a frost/dew condensation sensor that features a metal cover with excellent conductivity.

Other objects and features of the invention will become apparent from the following detailed description with reference to the drawings.

FIG. 1 is a schematic plan view of an embodiment of the present invention, and FIG. 2 is a sectional view taken along the line -- in FIG.

With reference to FIGS. 1 and 2, an insulating substrate 1
Interdigital electrodes 2 and 3 facing each other are formed on the top. A moisture-sensitive film 4 is placed so as to cover the electrodes 2 and 3.
is formed. The moisture sensitive film 4 is made of a material whose electrical resistance suddenly changes in a dew-condensed state, and the electrical resistance is extracted by the electrodes 2 and 3.

On the other hand, as is clear from FIG. 2, a chip thermistor 5 is also bonded onto the insulating substrate 1. The chip thermistor 5 has a characteristic that its electrical resistance changes suddenly near 0°C. A metal cover 6 is attached to the insulating substrate 1 with screws 7 so as to cover the thermistor 5. The metal cover 6 is
Constructed of a metal material with excellent thermal conductivity. A resin mold layer 8 made of a material having excellent thermal conductivity is also filled between the metal cover 6 and the chip thermistor 5. The screw 7 is inserted through a screw hole 1a provided in the insulating substrate 1, and further extends below the insulating substrate 1. This is because the frost/dew condensation detection sensor of this embodiment is screwed directly to the object to be measured. In other words, the chip thermistor 5 is
It is thermally coupled to the object to be measured via a metal cover 6 and screws 7. Therefore, the temperature of the object to be measured is accurately conducted to the chip thermistor 5 via the screw 7 and the metal cover 6.

Returning to FIG. 1, three terminals 11, 12, and 13 are formed on the insulating substrate 1. terminal 11,
12 are connected to electrodes 2 and 3 that are in contact with the humidity sensitive membrane 4, respectively, and are provided to measure the electrical resistance of the humidity sensitive membrane 4. On the other hand, the terminal 13 is connected to the chip thermistor 5. Further, the lead-out electrode portion 13a of the chip thermistor 5 and one of the comb-shaped electrodes 3 are connected.

In the embodiment shown in FIGS. 1 and 2, since each terminal 11, 12, 13 is configured as described above, the moisture sensitive membrane 4 and the chip thermistor 5 are connected in series to obtain their combined resistance. It is also possible to take out the combined resistance by connecting them in parallel. Furthermore, by sharing the terminal 12,
The electrical resistance of the humidity sensitive film 4 and the chip thermistor 5 can be taken out individually, and therefore it is also possible to detect the dew condensation state by the humidity sensitive film 4 and the frost state by the chip thermistor 5, respectively. .

Now, a description will be given of the detection operation in the case where the electrical resistance, that is, the moisture sensitive membrane 4 and the chip thermistor 5 are connected in series through the terminals 11 and 13, and the combined resistance is taken out and used. If a moisture-sensitive membrane 4 having a structure in which conductive particles are dispersed in a resin is used, such a known moisture-sensitive membrane 4 may be used.
In this case, the resin swells in a dew-condensed state, and therefore the electrical resistance increases rapidly in a dew-condensed state. When such a moisture-sensitive film 4 has a resistance-temperature characteristic shown by a dashed line A in FIG. 3, a negative characteristic thermistor (NTC) having a resistance-temperature characteristic shown by a broken line B in FIG. If used as
It will be understood that the combined resistance value has the temperature characteristic shown by the solid line C in FIG. That is, by appropriately selecting the resistance-temperature characteristics of the moisture-sensitive film 2 and the chip thermistor 5, it is possible to make the combined resistance value increase rapidly at 0° C. and remain constant at other temperatures.

By preparing the moisture-sensitive film 4 and the chip thermistor 5 having the above-mentioned characteristics, the resistance value of the moisture-sensitive film 2 rapidly increases under dew condensation. The combined resistance value between the two increases rapidly compared to that in a dry state, and it can be detected that the surface of the object to be measured is in a dew condensation state. Next, when dew condensation occurs, the surface temperature of the object to be measured becomes 0°C.
The combined resistance value between 13 and 13 increases rapidly. Therefore, the terminal 11,
It can be accurately determined by the resistance change between 13 and 13. In the end, the combined resistance values in the dry state, dew condensation state, and frost condensation state are as shown in the graph shown in FIG. 4, and each state can be detected accurately with a single circuit.

Note that the resistance value during dew condensation and frost formation is determined by the characteristics of the moisture sensitive film and chip thermistor. Therefore, in the graph shown in FIG. 4, the levels of the combined resistance values in the dew condensation state and the frost condensation state may be reversed.

In the above-described embodiment, the case where the moisture sensitive membrane 4 and the chip thermistor 5 are connected in series has been described, but as described above, the present invention is not limited to such a connection. That is, by sharing the terminals 11 and 13, the moisture-sensitive membrane 4 and the chip thermistor 5 can be connected in parallel, and by sharing the terminal 12, the moisture-sensitive membrane 4 and the chip thermistor can be connected. It is also possible to detect the resistance changes of 5 independently. Further, in the above embodiment, since the moisture sensitive membrane 4 and the chip thermistor 5 are used in series connection, it is necessary to select the resistance temperature characteristics of each so that the combined resistance value thereof is constant at room temperature. However, when the moisture sensitive film 4 and the chip thermistor 5 are used independently, it is not necessary to select the resistance temperature characteristics of each element in this manner. However, if the resistance of the moisture sensitive film 4 and the resistance of the chip thermistor 5 are to be extracted and detected separately, two detection circuits are required, so this is not advantageous for downsizing the frost/dew condensation detection sensor. I can not say.

In the above-mentioned embodiment, a film whose resistance value rapidly increases in a dew-condensing state is used as the moisture-sensitive film 4, but on the other hand, a film that utilizes ionic conduction and whose resistance value rapidly decreases in a dew-condensing state is used. may also be used. Furthermore, the chip thermistor 5 is not limited to a so-called negative characteristic thermistor (NIC), but may also be a positive characteristic thermistor (PTC) whose resistance value rapidly decreases as the temperature decreases. That is, in the frost/dew condensation sensor of the present invention, sensors with various characteristics can be used by appropriately combining the resistance change characteristics of the moisture sensitive film and thermistor.

FIG. 5 is a cross-sectional view of a main part showing a modification of the metal cover used in the frost/dew condensation sensor of the present invention.
As shown in FIG. 5, a case-like metal cover 16 covering the chip thermistor 15 may be used. The metal cover 16 is fixed to metal parts 17a and 17b formed on the insulating substrate 1 by soldering. A resin mold layer 18 is filled between the metal cover 16 and the chip thermistor 15.

As described above, according to the present invention, since the metal cover that is thermally coupled to the thermistor and has excellent thermal conductivity is provided on the substrate, it can accurately follow the temperature and humidity changes of the object to be measured. can,
It becomes possible to obtain a frost/dew condensation sensor that achieves excellent detection accuracy. In addition, since a chip thermistor can be used, and by appropriately selecting the characteristics and mutual connections of the moisture-sensitive film and thermistor, it is possible to detect the three states of dryness, dew condensation, and frost with a single circuit. - The dew condensation sensor can be made smaller.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view of an embodiment of the present invention. FIG. 2 is a sectional view taken along the line -- in FIG. 1. FIG. 3 is a diagram showing a temperature change in the combined resistance value when a moisture sensitive film and a thermistor are connected in series.
FIG. 4 is a diagram showing changes in the combined resistance value in a dry state, a dew condensation state, and a frost condensation state in one embodiment of the present invention. FIG. 5 is a sectional view of a main part showing a modification of the metal cover. 1...Substrate, 4...Moisture sensitive film, 5, 15...Thermistor, 6, 16...Metal cover.

Claims (1)

[Claims] 1. A moisture-sensitive film whose electrical resistance suddenly changes under dew condensation;
A thermistor whose electrical resistance changes suddenly around ℃ is provided on the same substrate, and a metal cover which is thermally coupled to the thermistor and has excellent thermal conductivity is provided on the substrate.・Condensation sensor.