JPH0310070B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a dryness/condensation/frost identification sensor that detects the three states of dryness, dew condensation, and frost formation as changes in impedance. Humidity control is an important issue in various electrical devices, and there is a demand for the development of excellent humidity sensors. Further, in certain devices, in addition to deterioration of characteristics due to dew condensation, deterioration of characteristics due to frost formation becomes a problem. For example, in refrigerators, frost formation reduces efficiency, so it is necessary to remove the frost. Therefore, it is desired to develop a sensor that can detect frost formation. Conventionally, various types of dew condensation sensors have been developed, such as those that utilize changes in resistance due to dew condensation. On the other hand, as a frost sensor,
Some have been developed that take advantage of the fact that the resonant frequency of a resonator changes due to the adhesion of frost. However, there has not yet been a single device capable of detecting both dew condensation and frost formation, that is, the three states of dryness, dew condensation, and frost formation. Therefore, in order to detect whether the device is in one of the three states of dryness, dew condensation, and frost formation, at least two independent detection elements are required, which complicates the device. Therefore, the main purpose of this invention is to
It is an object of the present invention to provide a dryness, dew condensation, and frost formation identification sensor that can accurately detect which of the three states of dew condensation and frost formation it is in. In summary, the present invention includes a sensor unit in which an electrode is formed on one side of a sensing element made of dielectric ceramics, a plurality of sensing elements are separated by a predetermined interval by an insulating spacer, and the sensing element is separated by a predetermined interval. By facing each other so that the surfaces on which the electrodes are formed face outward, a space is formed between the sensor units to form the sensor body, and drying, dew condensation, and frost formation in the space are prevented. This is a dry/condensation/frost discrimination sensor that detects changes in each impedance between opposing electrodes and identifies three states: dry, dew condensation, and frost. Other objects and features of the present invention will become more apparent from the following detailed description with reference to the drawings. FIG. 1 is a perspective view for explaining a specific example of the dryness, dew condensation, and frost formation identification sensor of the present invention.
Referring to FIG. 1, disk-shaped sensing elements 1 and 2 made of dielectric ceramics are prepared. Detection element 1, 2
On one side, electrodes 3 and 4 (electrode 4 is the sensing element body 2
It is not shown in FIG. 1 because it is formed on the lower surface of the . ) is formed. Lead wires 5 and 6 are connected to each electrode 3 and 4. In this way, two sensor units 7 and 8 are prepared. Next, the sensor units 7 and 8 are arranged facing each other at a predetermined distance so that the electrodes 3 and 4 are on the outside. The distance between sensor unit 7 and sensor unit 8 is ensured by using insulating spacers 9a, 9b, as shown in longitudinal section in FIG. Next, as is clear from FIG. 2, the electrodes 3, 4 and the connections between the electrodes 3, 4 and the lead wires 5, 6 (the lead wires 5, 6 are not shown in FIG. 2).
By coating with epoxy resins 3a, 4a, etc., a drying/condensation/frosting identification sensor as a specific example of the present invention is obtained. In this invention, the sensor units 7 and 8 are arranged facing each other with the surfaces on which the electrodes 3 and 4 are formed on the outside. This is because I tried not to let it happen. Therefore, according to this configuration, even if water or ice exists in the air, corrosion of the electrodes does not occur, and the drying, dew condensation, and
A frost identification sensor can be obtained. It should be noted that the dryness, dew condensation, and frost formation identification sensor of the present invention is not limited to that described with reference to FIGS. 1 and 2, and may be modified in various ways. For example, the sensing elements 1 and 2 are not limited to disk shapes, but may be formed into square plates. electrode 3,
The same applies to 4. The dielectric ceramics constituting the sensing elements 1 and 2 are not limited to disk-shaped electrodes, and may be electrodes of various planar shapes. Further, the shapes of the ceramic plates 1 and 2 can also be changed as appropriate. Moreover, even if the sizes of the electrodes 3 and 4 are the same,
Either one may be larger. By increasing the size of one electrode, positioning when arranging the electrodes facing each other becomes easier, and variations in impedance caused by assembly work can be reduced. This is because the tolerance range for alignment of one electrode with respect to the other electrode becomes larger. Next, the detection principle of the dryness/condensation/frosting discrimination sensor of the present invention will be explained. The three states of dryness, dew condensation, and frost formation can be detected as changes in impedance between the electrodes 3 and 4. First, in a dry state, the impedance between the electrodes 3 and 4 is determined by the dielectric constant of the ceramic plates 1 and 2 and the air gap A formed between the ceramic plates 1 and 2 (see FIG. 2). ) is determined by the air layer present in the area. Next, in a dew condensation state, dew condensation occurs between the ceramic plates 1 and 2, and the impedance between the electrodes 3 and 4 becomes extremely small due to the condensation, that is, the electrical conduction of water. Further, in the frosted state, the dew condensation adhering between the ceramic plates 1 and 2 freezes, and ice crystals adhere between the ceramic plates 1 and 2. Therefore, the impedance between the electrodes 3 and 4 is determined by the dielectric constant of the ceramic plates 1 and 2 and the dielectric constant of the ice attached to the air A. The impedance between the electrodes 3 and 4 in the frosted state is determined by the change in dielectric constant caused by the temperature drop of the sensing elements 1 and 2, the amount of ice crystals generated in the air A, and the dielectric constant thereof. be done. Furthermore, the impedance value between the electrodes 3 and 4 is determined by the lead wires 5 and 6.
It also depends on the frequency of the measurement current passed through. According to experiments, by increasing the measurement frequency,
It has been confirmed that impedance values can be reduced. Therefore, by constructing the sensing elements 1 and 2 from dielectric ceramics having arbitrary dielectric constant temperature characteristics, and setting the measurement frequency appropriately,
The impedance values of the three states of dryness, dew condensation and frost formation can be clearly distinguished. Various ceramics can be used as the dielectric ceramics constituting the sensing element of the present invention, but such dielectric ceramics include:
Either one that can extract ions in a dew-condensed state or one that does not extract ions may be used. Even if ceramics that do not derive ions are used, the configuration of this sensor shows that in a dry state, the impedance is determined by the dielectric constants of the dielectric ceramic and the air in the sky, and this value changes depending on the state of dew condensation and adhesion. It is larger than each impedance of frost state, and it is possible to distinguish between dry state and dew condensation or frost state. Furthermore, naturally, the dew condensation state and the frost formation state are respectively
Since the impedance of water and ice differs based on the difference in dielectric constant, it is possible to distinguish these states, and as a result, it is possible to detect each state of dryness, dew condensation, and frost formation. On the other hand, by configuring the sensing elements 1 and 2 with a ceramic material that can lead out ions into water droplets adhering to the air A (see Fig. 2) in a dew condensation state, the impedance in a dew condensation state can be reduced. The value can be made smaller and therefore easier to distinguish from the other two states. Specifically, materials that can lead out ions into water droplets include, for example,
Titanium composite oxide ceramics with ilmenite crystal structure such as MgTiO ₃ , ZnTiO ₃ , FeTiO ₃ , BaO−TiO ₂ −NdO ^3/2 ceramics, sulfate and phosphate ceramics, steatite, forsterite, etc. Many ceramics can be used, such as ceramics mainly containing MgO.SiO ₂ , spinel type, virochlore type, tungsten bronze type, rutile type, and fluorite type. In the case of ceramics mainly composed of titanium composite oxide with an ilmenite crystal structure, ceramics with other crystal structures such as perovskite, spinel, pyrochlore, tungsten bronze, etc. may be used as long as they do not adversely affect the properties. One type or a mixture of multiple types may be used. Furthermore, for example clay, rare earth, TiO ₂ , SiO ₂ , BiO ₂ O ₃ , ZnO,
Additives consisting of inorganic compounds such as Fe ₂ O ₃ , Sb ₂ O ₃ , MnCO ₃ , WO ₃ etc. may also be added. Further, for other crystalline ceramics, the coexistence of various additives for forming ceramics is permitted in the same manner as described for the titanium composite oxide having an ilmenite crystal structure. During dew condensation, a small amount of ions are eluted from the ceramics, so that the inter-electrode impedance decreases significantly during dew condensation. For this purpose, ceramics containing cations such as alkali metal ions and alkaline earth metal ions, and anions such as phosphate ions and sulfate ions are effective. As described above, according to the present invention, the sensor unit includes a sensor unit in which an electrode is formed on one side of a sensing element made of dielectric ceramic, and a plurality of sensing elements are separated by a predetermined interval by an insulating spacer, and By arranging the sensing elements facing each other so that the electrode-formed surfaces face outward, a space is formed between the sensor units to form the sensor body, and drying and condensation in the space are prevented. By measuring the change in each impedance in the frosted state between opposing electrodes, it becomes possible to clearly distinguish between the three states: dry state, dew condensation state, and frosted state. In addition, since the structure is relatively simple, a sensor for identifying dryness, dew condensation, and frost formation with excellent reliability and excellent reproducibility can be obtained. Furthermore, the dryness, dew condensation, and frost formation identification sensor of the present invention is configured such that the surface on which the electrodes are formed is on the outside. Since no electrodes are formed, there is no deterioration of characteristics due to corrosion of the electrodes, and therefore it can withstand long-term use. Example 1 Two pieces of BaTiO ₃ −Bi ₂ O ₃ − with a diameter of 14 mm
A SnO ₂ -based dielectric ceramic plate (ε = 2700) was prepared. This ceramic was obtained by firing using a known method. On one side of each ceramic plate,
A silver electrode with a diameter of 10 mm was formed. After connecting a lead wire to this silver electrode by soldering, the electrode and the lead wire near the portion connected to the electrode were coated with epoxy resin. Next, turn the surface of each ceramic plate with no electrodes on the inside,
They were placed facing each other with an interval of 0.5 mm between them. Regarding the dryness, dew condensation, and frost formation identification sensor configured in this way, the impedance in the dry, dew condensation, and frost conditions is 1V (50Hz) and
It was measured by applying a voltage of 1V (100kHz). The results are shown in Table 1.

[Table] As is clear from Table 1, it is understood that the three states of dryness, dew condensation and frost formation can be distinguished very accurately. Example 2 Two pieces of BaTiO ₃ −CaSnO ₃ with a diameter of 14 mm
A dielectric ceramic board (ε=20000) was prepared.
A silver electrode with a diameter of 10 mm was formed on one side of each ceramic plate. After the lead wires were connected to each silver electrode by soldering, the electrodes and the lead wires near the portions connected to the electrodes were coated with epoxy resin. Next, the ceramic plates were placed facing each other at an interval of 0.5 mm, with the surfaces on which no electrodes were formed facing inside. Regarding the dryness, dew condensation, and frost formation identification sensor configured in this way, the dryness, dew condensation, and frost formation conditions were measured in the same manner as in Example 1. The results are shown in Table 2.

[Table] It is understood that in Example 2 as well, the three states of dryness, dew condensation, and frost formation can be distinguished very accurately. In addition, as is clear from Tables 1 and 2 showing the results of Example 1 and Example 2, under two conditions where the frequency of the measured current was 50 Hz and 100 KHz,
The result is that the impedance value in the dry state and the impedance value in the frosted state are reversed. This is considered to be because, as described above, the impedance during frosting depends on the change in dielectric constant of the dielectric ceramic due to a decrease in temperature, and the impedance value changes depending on the measurement frequency. Next, a description will be given of a dew condensation/frost formation detection device using the dryness/dew condensation/frost formation identification sensor of the present invention. In order to facilitate understanding, a description will be given of a dew condensation/frost detection device using a dryness/dew condensation/frost detection sensor having impedance characteristics as shown in FIG. FIG. 4 is a block diagram for explaining an example of a dew condensation/frost formation detection device using the dryness/dew condensation/frost formation discrimination sensor of the present invention. Referring to Figure 4,
This device includes a detection section 10 including a dryness/condensation/frosting identification sensor of the present invention, two comparison circuits 11 and 12 to which the output of the detection section 10 is given, and a comparison circuit 11.
a first reference level setting means 13 that inputs a first reference level signal as a comparison signal to the comparison circuit 12, a second reference level setting means 14 that inputs a second reference level signal as a comparison signal of the comparison circuit 12, and a comparison circuit 1.
It is comprised of a discrimination circuit 15 (the part surrounded by a dashed line in FIG. 4) which discriminates between three states of dryness, dew condensation, and frost formation based on the outputs of signals 1 and 12. The detection unit 10 includes the dryness, dew condensation, and frost formation discrimination sensor of the present invention, and outputs a signal corresponding to the impedance that changes as shown in FIG. 3 in the three states of dryness, dew condensation, and frost formation. The output of the detection section 10 is given to a comparison circuit 11 as a first comparison means and a second comparison circuit 12 as a second comparison means. A first reference level signal is input to the first comparison circuit 11 by the first reference level setting means. As is clear from FIG. 3, the first reference level of this signal is set between the impedance of the detection section 10 in the dew condensation state and the impedance of the detection section 10 in the frost formation state. First comparison circuit 11
compares the impedance of the detection unit 10 and the first reference level, and outputs a high level signal when the impedance of the detection unit 10 is larger, and outputs a low level signal when the impedance of the detection unit 10 is smaller. Outputs the output signal. On the other hand, the second comparison circuit 12 receives a second reference level signal from the second reference level setting means. As is clear from Figure 3, the second reference level of this signal is
It is set to a value between the impedance of the detection unit 10 in a dry state and the impedance of the detection unit 10 in a frosted state. Therefore, the second comparison circuit 12 compares the impedance of the detection section 10 with the second comparison circuit 12.
When the impedance of the detection unit 10 is larger than the reference level, a high level signal is output, and in the opposite case, a low level signal is output. In this way, the first and second comparison circuits 11,
12 outputs a high-level or low-level signal according to a change in the impedance of the detection unit 10. The output of each of the comparison circuits 11 and 12 is
As is clear from the relationships shown in the figure, they are shown in Table 3 below. In Table 3, H indicates a high level signal, and L indicates a low level signal.

[Table] The outputs of the comparison circuits 11 and 12 are given to the discrimination circuit 15. The discrimination circuit 15 includes two inverters.
It is composed of I ₁ , I ₂ and three Noah gates G ₁ , G ₂ , and G ₃ . The output of the first comparator circuit 11 is applied to an input terminal of an inverter _I1 and one input terminal of a NOR gate _G3 . The output of inverter I ₁ is given to one input terminal of each of NOR gates G ₁ and G ₂ .
On the other hand, the output of the second comparison circuit 12 is
It is applied to the input terminal of _I2 , the other terminal of NOR gate _G2 , and the other input terminal of NOR gate _G3 . The output of inverter _I2 is given to the other input terminal of NOR gate _G1 . Note that this discrimination circuit 15 employs positive logic. The determination circuit 15 configured as described above determines the three states of dryness, dew condensation, and frost formation as follows. Now, in a dry state, as is clear from Table 3, both comparison circuits 11 and 12 output high level signals. A high level signal from the first comparator circuit 11 is applied to an inverter _I1 and a NOR gate _G3 . The high level signal input to the inverter _I1 is inverted to a low level signal and is applied to the NOR gates _G1 and _G2 . On the other hand, the second
The high level signal from the comparison circuit 12 is applied to the inverter I ₂ , the NOR gate G ₂ and the NOR gate G ₃ . The high level signal input to the inverter _I2 is inverted to a low level signal and is applied to the NOR gate _G1 . As described above, in a dry state, only the NOR gate _G1 receives a low level signal to both of its input terminals. Therefore, only NOR gate _G1 outputs a high level signal. Similarly, when the detection unit 10 is in a frosted state, as is clear from Table 3, the first comparison circuit 11 outputs a high level signal, and the second comparison circuit 12 outputs a low level signal. In order to output , only NOR gate G ₂ receives a low level signal to both of its input terminals. Therefore, only NOR gate _G2 outputs a high level signal. Furthermore, when the detection unit 10 is in a dew condensation state, both the first and second comparison circuits 11 and 12 output low-level signals, so only the NOR gate G ₃ has both input terminals at a low level. Since the signal is input, only NOR gate _G3 outputs a high level signal. As is clear from the above description, the NOR gate G ₁ outputs a signal in a dry state, the NOR gate G ₂ outputs a signal in a frosted state, and the NOR gate G ₃ outputs a signal in a dewy state. Therefore, drying
It becomes possible to distinguish between three states: dew condensation and frost formation. FIG. 5 is a circuit diagram for more specifically explaining the dew condensation and frost formation detection device shown in FIG.
FIGS. 6 and 7 are diagrams for explaining the operation of the circuit shown in FIG. 5. The circuit shown in FIG. 5 includes a drying/condensation/frosting identification sensor 20 of the present invention, a MOS-FET 26, comparators 21, 22, and a discrimination circuit 25 similar to that shown in FIG. The part indicated by the dashed line) is the basic component. As shown in FIG. 3, the impedance of the dryness, dew condensation, and frost formation identification sensor 20 changes in three states: dryness, dew condensation, and frost formation. Dry/condensation/frost identification sensor 20
The change in impedance of is expressed as the change in voltage,
It is input to the gate terminal of MOS-FET26. This input is amplified and inverted by the MOS-FET 26 and input to operational amplifiers 21 and 22 as comparators. Each operation amplifier 21, 22 has a first
and a second reference level voltage are respectively input. The outputs of the operational amplifiers 21 and 22 are
The signal is applied to the discrimination circuit 25. The configuration of the discrimination circuit 25 is the same as that of the discrimination circuit 15 shown in FIG. 4, so the explanation thereof will be omitted by assigning corresponding reference numerals. In the circuit shown in FIG. 5 configured in this way, the impedance of the dryness/condensation/frost identification sensor 20 changes in the three states of dryness, dew condensation, and frost formation. Outputs voltage changes corresponding to changes in impedance. The change in voltage at node X of the circuit of FIG. 5 is shown in FIG. Dry/condensation/frost identification sensor 2
The output voltage from 0 is amplified by MOS-FET26.
It is inverted and output. This output voltage, ie, the voltage at node Y in FIG. 5, is shown in FIG. As is clear from FIG. 7, the output voltage at the connection point Y has a maximum value in a dry state, a minimum value in a dew condensation state, and an intermediate value in a frosted state.
The output voltage of the MOS-FET 26 is input to the operational amplifiers 21 and 22. On the other hand, each operational amplifier 21, 22 has variable resistors 23, 2.
The first and second reference level voltages whose levels are set by 4 are input. The first and second reference level voltages are chosen to have values as shown in FIG. That is, the first reference level voltage is selected to be between the output voltage in the frosted state and the output voltage in the dew state, and the second reference level voltage is selected to be between the output voltage in the dry state and the output voltage in the frosted state. A value between . Each of the operational amplifiers 21 and 22 compares the output voltage of the MOS-FET 26 with a first reference level voltage or a second reference level voltage. Therefore, the change in impedance of the dryness/condensation/frost identification sensor 20 is compared as a change in voltage. Each of the operational amplifiers 21 and 22 outputs a high level signal when the output voltage of the MOS-FET 26 is higher, and outputs a low level signal in the opposite case. The output signals of the operational amplifiers 21 and 22 are similar to the output truth values shown in Table 3 for the comparison circuits 11 and 12 of FIG. 4. The output signals of each operational amplifier 21 and 22 are output to the discrimination circuit 2.
The operation of the discriminating circuit 25 is the same as that of the discriminating circuit 15 in FIG. 4, so a description thereof will be omitted. The circuits shown in FIGS. 4 and 5 are merely examples of a dew condensation/frost detection device using the dryness/condensation/frost detection sensor of the present invention.
Therefore, it should be pointed out that the first and second comparison circuits and discrimination circuit can be modified in various ways within the range that can be easily conceived by those skilled in the art.

[Brief explanation of the drawing]

FIG. 1 is a perspective view for explaining a specific example of the dryness, dew condensation, and frost formation identification sensor of the present invention.
FIG. 2 is a longitudinal cross-sectional view of a specific example of the dryness/condensation/frost identification sensor of the present invention. FIG. 3 is a diagram showing an example of the impedance characteristics of the dryness, dew condensation, and frost formation identification sensor of the present invention. FIG. 4 is a block diagram of an example of a dew/frost detection device using the dryness/condensation/frost identification sensor of the present invention, and FIG. It is a specific circuit diagram of a frost detection device. FIG. 6 is a diagram showing the output voltage at the connection point X of the circuit of FIG. FIG. 7 is a diagram showing the output voltage at connection point Y of the circuit of FIG. In the figure, 1 and 2 are dielectric ceramic plates as sensing elements, 3 and 4 are electrodes, and 7 and 8 are sensor units.

Claims (1)

[Claims] 1. A sensor unit comprising a sensing element made of dielectric ceramic and an electrode formed on one side, a plurality of sensing elements separated by a predetermined interval by an insulating spacer, By facing each other so that the surfaces on which the electrodes are formed face outward, a space is formed between the sensor units to form the sensor body, and drying, dew condensation, and frost formation in the space are prevented. A dry/condensation/frost identification sensor that detects changes in each impedance between opposing electrodes and distinguishes between dryness, dew condensation, and frost formation. 2. The drying/condensation/frosting discrimination sensor according to claim 1, wherein the sensing element is made of a material that can extract ions into water droplets in a dew condensation state.