WO2008018425A1

WO2008018425A1 - Liquid surface sensor

Info

Publication number: WO2008018425A1
Application number: PCT/JP2007/065394
Authority: WO
Inventors: Yoshinori Takashima; Mikihiro Ohshima; Motoki Ogata
Original assignee: Panasonic Corporation
Priority date: 2006-08-10
Filing date: 2007-08-07
Publication date: 2008-02-14

Abstract

A liquid surface sensor in which a heater layer (32) for supplying heat to a liquid level detection resistance layer (24), a gas temperature detection resistance layer (26), and a liquid temperature detection resistance layer (28) are placed between a protective layer (35), the liquid level detection resistance layer (24), the liquid temperature detection resistance layer (28), and the gas temperature detection resistance layer (26). Even if the level of the liquid surface of a solution to be measured varies rapidly, the liquid surface sensor can measure the liquid surface instantly and has excellent temporal response.

Description

Specification

Liquid level detection sensor

Technical field

The present invention particularly relates to a liquid level detection sensor that detects the liquid level of a water tank.

Background art

[0002] This type of conventional liquid level detection sensor has a configuration as shown in FIGS.

FIG. 12 is a front view of a conventional liquid level detection sensor. FIG. 13 is a side sectional view of a conventional liquid level detection sensor. In FIGS. 12 and 13, the insulating substrate 1 is a rectangular parallelepiped substrate made of polyethylene terephthalate configured in a film shape. The insulating substrate 1 is erected almost vertically in the longitudinal direction, and an insulating layer 2 made of an epoxy resin is provided on one side surface. Further, a heater layer 3 made of a mixture of silver (Ag) resin and epoxy resin is provided between the insulating substrate 1 and the insulating layer 2.

[0004] On the side surface of the insulating layer 2 in the insulating substrate 1, a liquid level detecting resistance layer 4 composed of a thermistor having a resin material made of a mixture of Ag-based resin and epoxy-based resin as a binder from above to below in the longitudinal direction. Is provided. A pair of liquid level detection electrodes 5 are provided on both ends of the liquid level detection resistance layer 4 in the direction perpendicular to the longitudinal direction. The liquid level detection electrodes 5 are connected to the external electrodes 7 via the wiring pattern 6. Electrically connected. Further, on the side surface of the insulating layer 2 in the insulating substrate 1, there is provided a gas temperature detecting resistance layer 8 which is located above and is composed of a thermistor having a resin material made of a mixture of Ag-based resin and epoxy-based resin as a binder. ing. A gas temperature detection electrode 9 made of a pair of Ag is provided at both ends of the gas temperature detection resistance layer 8, and the gas temperature detection electrode 9 is electrically connected to the external electrode 7 through the wiring pattern 6. is doing. Furthermore, on the side surface of the insulating layer 2 in the insulating substrate 1, a liquid temperature detecting resistance layer 10 is formed which is located below and is composed of a thermistor using a mixture of Ag-based resin and epoxy-based resin as a binder. Is provided. A liquid temperature detection electrode 11 made of a pair of Ag is provided at both ends of the liquid temperature detection resistance layer 10, and the liquid temperature detection electrode 11 is electrically connected to the external electrode 7 through the wiring pattern 6. Connected to. Here, a pair of gas temperature detectors The length between the poles 9 and the length between the pair of liquid temperature detection electrodes 11 are substantially the same, and this length is defined as a unit length.

[0005] The adhesive layer 12 is made of Si or acrylic. This adhesive layer 12 is a side surface of the insulating substrate 1, the liquid level detection resistance layer 4, the liquid level detection electrode 5, the gas temperature detection resistance layer 8, the gas temperature detection electrode 9, the liquid temperature detection resistance layer 10, and the liquid temperature detection electrode 11. Is provided.

[0006] The operation of the conventional liquid level detection sensor configured as described above will now be described with reference to the drawings.

FIG. 14 is a side sectional view showing a state in which a conventional liquid level detection sensor operates. As shown in FIG. 14, the liquid level detection sensor is first attached to the outer surface of the drip container 13 filled with the drip solution 14. In this case, the gas temperature detection resistance layer 8 (not shown) faces the gas in the drip container 13. Further, the liquid temperature detection resistance layer 10 faces the liquid in the drip container 13. Further, the liquid level detection resistance layer 4 is attached to the outer surface of the drip container 13.

In this state, when a voltage is applied to the heater layer 3 embedded in the insulating substrate 1, Joule heat is generated from the heater layer 3 by the current flowing through the heater layer 3. This Joule heat reaches the liquid level detection resistance layer 4, the gas temperature detection resistance layer 8, and the liquid temperature detection resistance layer 10 through the insulating layer 2. At this time, there is a difference in self-heating value per unit length due to the difference in heat dissipation constant between the portion of the liquid level detection resistance layer 4 facing the liquid and the portion facing the gas. As a result, there is a temperature difference between the portion of the liquid level detection resistance layer 4 facing the gas and the portion facing the liquid, which causes a difference in resistance value per unit length due to the resistance-temperature characteristics of the thermistor. . The difference between the resistance values is the resistance value of the gas temperature detection resistance layer 8 positioned between the pair of gas temperature detection electrodes 9 and the resistance value of the liquid temperature detection resistance layer 10 positioned between the pair of liquid temperature detection electrodes 11. The liquid level of the drip solution 14 in the drip container 13 is detected by calculating in comparison with. For example, Patent Document 1 is known as prior art document information relating to the invention of this application.

However, in the conventional configuration described above, the insulating layer 2, the liquid level detection resistance layer 4, the liquid level detection electrode 5, and the liquid temperature detection are provided between the drip container 13 for detecting the liquid level and the heater layer 3. Since the resistance layer 10, the liquid temperature detection electrode 11, the gas temperature detection resistance layer 8, the gas temperature detection electrode 9 and the adhesive layer 12 are provided, the distance between the drip container 13 and the heater layer 3 is increased. this Therefore, it takes time until Joule heat generated from the heater layer 3 is cooled by the drip liquid 14 filled in the drip container 13. Therefore, if the liquid level of the drip solution 14 in the drip container 13 changes suddenly, measurement of the liquid level cannot be performed instantaneously, and the time response of the liquid level detection sensor is good.

[0010] Further, since the liquid level detection resistance layer 4 is provided from the upper side to the lower side of the insulating substrate 1, the cross-sectional area thereof is provided only above or below the insulating substrate 1. Larger than the cross-sectional area of the resistance layer 8 and the liquid temperature detection resistance layer 10. In this case, when the resistance value of the liquid level detection resistance layer 4 is compared with the resistance values of the gas temperature detection resistance layer 8 and the liquid temperature detection resistance layer 10, the resistance of the liquid level detection resistance layer 4 is calculated. The output signal due to the resistance value must be amplified more than the output signal due to the resistance value of the gas temperature detection resistance layer 8 and the liquid temperature detection resistance layer 10. Therefore, the output signal generated in the liquid level detection resistance layer 4 becomes unstable.

Patent Document 1: Japanese Unexamined Patent Application Publication No. 2006-90714

Disclosure of the invention

[0011] The present invention provides a liquid level detection sensor that can measure the liquid level instantaneously and has good temporal response even when the liquid level of the solution to be measured changes abruptly. In addition, the output signal generated in the liquid level detection resistance layer is not amplified more greatly than the output signal due to the resistance value of the gas temperature detection resistance layer and the liquid temperature detection resistance layer. Provided is a liquid level detection sensor that is detected in a stable state.

The liquid level detection sensor according to the present invention includes an insulating substrate standing in the longitudinal direction, a liquid level detection resistance layer provided on one side in the longitudinal direction of the insulating substrate from above to below. A pair of liquid level detection electrodes provided at both ends of the liquid level detection resistance layer, a gas temperature detection resistance layer provided above one side surface of the insulating substrate, and both ends of the gas temperature detection resistance layer A pair of gas temperature detection electrodes provided, a liquid temperature detection resistance layer provided below one side of the insulating substrate, and a pair of liquid temperature detection electrodes provided at both ends of the liquid temperature detection resistance layer And a heater layer for supplying heat to the liquid level detection resistance layer, the gas temperature detection resistance layer, and the liquid temperature detection resistance layer, the liquid level detection resistance layer, the liquid level detection electrode, the gas temperature detection resistance layer, and the gas temperature detection electrode. , Liquid temperature detection resistance layer, Liquid temperature detection current And a protective layer provided to cover the electrode and the heater layer. A heater layer is provided between the liquid level detection resistance layer, the liquid temperature detection resistance layer, the gas temperature detection resistance layer, and the protective layer.

[0013] According to this configuration, the heater layer is provided between the liquid level detection resistance layer, the liquid temperature detection resistance layer, the base temperature detection resistance layer, and the protective layer. The distance is reduced, so that the Joule heat generated from the heater layer is immediately cooled by the solution to be measured. Therefore, even when the liquid level of the solution to be measured changes suddenly, the liquid level detection can be performed instantaneously, and it is possible to provide a liquid level detection sensor with good temporal response.

[0014] In addition, the liquid level detection sensor according to the present invention includes a liquid level detection resistance layer including a plurality of parallel resistance layers electrically connected in parallel to a pair of liquid level detection electrodes. The parallel resistance layer is installed at the same angle with respect to the vertical.

[0015] According to such a configuration, even if the liquid level detection resistance layer is provided from the upper side to the lower side of the insulating substrate, the cross-sectional area of the entire liquid level detection resistance layer is reduced, and the resistance of the liquid level detection resistance layer is reduced. The value is almost the same as the resistance value of the gas temperature detection resistance layer and the liquid temperature detection resistance layer. Therefore, the output signal generated in the liquid level detection resistance layer is detected in a stable state. Brief Description of Drawings

FIG. 1 is a side sectional view of a liquid level detection sensor according to Embodiment 1 of the present invention.

FIG. 2 is a front view showing a state before the insulating substrate is bent in the liquid level detection sensor according to Embodiment 1 of the present invention.

FIG. 3 is a side sectional view showing a state before the insulating substrate is bent in the liquid level detection sensor according to Embodiment 1 of the present invention.

FIG. 4 is a front view showing a state in which an insulating substrate force protection layer and a heater layer are removed from the liquid level detection sensor according to Embodiment 1 of the present invention.

FIG. 5 is a side sectional view showing a state in which the liquid level detection sensor according to Embodiment 1 of the present invention operates.

FIG. 6 is a side sectional view of a liquid level detection sensor according to Embodiment 2 of the present invention.

FIG. 7 is a front view of an insulating substrate in the liquid level detection sensor according to Embodiment 2 of the present invention. FIG.

FIG. 8 is a side cross-sectional view of the insulating substrate in the liquid level detection sensor according to Embodiment 2 of the present invention.

9] FIG. 9 is a front view showing a state in which the protective layer and the heater layer made of the insulating substrate of the liquid level detection sensor according to Embodiment 2 of the present invention are removed.

FIG. 10 is a side sectional view showing a state in which the liquid level detection sensor according to Embodiment 2 of the present invention operates.

FIG. 11 is a circuit diagram of a liquid level detection sensor according to Embodiment 2 of the present invention.

FIG. 12 is a front view of a conventional liquid level detection sensor.

13] FIG. 13 is a side sectional view of a conventional liquid level detection sensor.

14] FIG. 14 is a side sectional view showing a state in which a conventional liquid level detection sensor operates. Explanation of symbols

21 Insulating substrate

22 Bend

23 Liquid level detection electrode

24 Liquid level detection resistor layer

24a Parallel resistance layer

24b Edge of parallel resistance layer

25 Gas temperature detection electrode

26 Gas temperature detection resistor layer

27 Liquid temperature detection electrode

28 Liquid temperature sensing resistor layer

32 Heater layer

36 cases

37 Contact member

40 Constant current source

41 Amplifier

42 AD converter 43 Microcomputer

BEST MODE FOR CARRYING OUT THE INVENTION

[0018] (Embodiment 1)

Embodiment 1 of the present invention will be described below with reference to the drawings. FIG. 1 is a side sectional view of a liquid level detection sensor according to Embodiment 1 of the present invention. FIG. 2 is a front view of the liquid level detection sensor according to Embodiment 1 of the present invention before the insulating substrate is bent. FIG. 3 is a side sectional view of the liquid level detection sensor according to Embodiment 1 of the present invention in a state before the insulating substrate is bent. FIG. 4 is a front view showing a state in which the protective layer and the heater layer are removed from the insulating substrate of the liquid level detection sensor according to Embodiment 1 of the present invention.

In FIGS. 1 to 4, an insulating substrate 21 is a rectangular parallelepiped substrate made of polyethylene terephthalate configured in a film shape. The insulating substrate 21 is erected substantially perpendicularly to the longitudinal direction, and as shown in FIG. 1, a bent portion 22 bent at a substantially right angle is provided at the lower end. Further, the insulating substrate 21 is provided with a liquid level detection electrode 23 made of a pair of Ag from the upper part to the lower part of one side surface in the longitudinal direction. Further, the liquid level detection electrode 23 is provided with a liquid level detection resistance layer 24 so that both ends thereof are electrically connected to the liquid level detection electrode 23. The liquid level detection resistance layer 24 is composed of a thermistor having a resin material made of a mixture of an Ag-based resin and an epoxy-based resin as a binder.

[0020] On one side surface of the insulating substrate 21, a gas temperature detection electrode 25 comprising a pair of Ag forces is provided above the pair of liquid level detection electrodes 23. A gas temperature detection resistance layer 26 is provided so that both ends of the gas temperature detection electrode 25 are electrically connected. This gas temperature detection resistance layer 26 is composed of a thermistor using a resin material made of a mixture of an Ag-based resin and an epoxy-based resin as a binder.

[0021] The bent portion 22 of the insulating substrate 21 is provided with a liquid temperature detection electrode 27 made of a pair of Ag. A liquid temperature detection resistance layer 28 having a thermistor force using a resin material made of a mixture of an Ag-based resin and an epoxy-based resin as a binder is provided so that both ends of the liquid temperature detection electrode 27 are electrically connected. . Here, the length between the pair of gas temperature detection electrodes 25 and the length between the pair of liquid temperature detection electrodes 27 are substantially the same. Is defined as a unit length. The liquid temperature detection electrode 27 and the liquid temperature detection resistance layer 28 on the insulating substrate 21 are configured to have substantially the same height by being provided at the bent portion 22 provided at the lower end of the insulating substrate 21. The liquid level detection electrode 23, the gas temperature detection electrode 25, and the liquid temperature detection electrode 27 are electrically connected to the external electrode 30 through a wiring pattern 29 provided on one side surface of the insulating substrate 21.

[0022] The insulating layer 31 includes a liquid level detection electrode 23, a liquid level detection resistance layer 24, a gas temperature detection electrode 25, a gas temperature detection resistance layer 26, a liquid temperature detection electrode 27, and a liquid temperature detection electrode 27 provided on the upper surface of the insulating substrate 21. And the liquid temperature detection resistance layer 28 is provided. The heater layer 32 is provided so as to meander the upper surface of the insulating layer 31 and is electrically connected to the heater electrode 34 via the circuit pattern 33. The protective layer 35 is provided so as to cover the upper surface of the heater layer 32. The case 36 is made of metal and accommodates the insulating substrate 21 inside. A contact member 37 is attached to the bottom surface of the case 36 and holds a bent portion 22 provided at the lower end of the insulating substrate 21.

As described above, in the first embodiment of the present invention, the bent portion that is bent substantially at right angles to the portion provided with the liquid temperature detecting resistor layer 28 and the liquid temperature detecting electrode 27 in the insulating substrate 21. By providing 22, the liquid temperature detection resistance layer 28 and the liquid temperature detection electrode 27 are configured to have substantially the same height. Therefore, the liquid temperature detection resistance layer 28 and the liquid temperature detection electrode 27 can be provided on the inner bottom surface of the case 36. As a result, if the solution to be measured (not shown) fills the case 36 even a little, the liquid temperature detection resistance layer 28 and the liquid temperature detection electrode 27 are always in contact with the solution to be measured (not shown). The liquid level can be detected from the inner bottom surface to the top of 36, and the measurement range of the liquid level detection sensor is expanded.

Next, a manufacturing method of the liquid level detection sensor according to the first embodiment of the present invention configured as described above will be described.

[0025] First, on one side of an insulating substrate 21 made of polyimide, at a position where the liquid level detection electrode 23, the gas temperature detection electrode 25, the liquid temperature detection electrode 27, the wiring pattern 29, the external electrode 30 and the heater electrode 34 are provided. Ag paste is printed by thick film printing method. After that, the liquid level detection electrode 23, the gas temperature detection electrode 25, and the liquid are baked at about 250 ° C for about 30 minutes. Form temperature detection electrode 27, wiring pattern 29, external electrode 30 and heater electrode 34

Yes

Next, the thermistor paste is printed on the upper surface of the insulating substrate 21 at a position where the liquid level detection resistance layer 24, the gas temperature detection resistance layer 26, and the liquid temperature detection resistance layer 28 are provided. Thereafter, the liquid level detection resistance layer 24, the gas temperature detection resistance layer 26, and the liquid temperature detection resistance layer 28 are formed on the upper surface of the insulating substrate 21 by baking at about 270 ° C. for about 2 hours.

[0027] Further, the wiring pattern 29 on one side of the insulating substrate 21, the liquid level detection resistance layer 24, the gas temperature detection resistance layer 26, the liquid temperature detection resistance layer 28, the gas temperature detection electrode 25, the liquid temperature detection electrode 27, and An insulating layer paste is printed on the upper surface of the liquid level detection electrode 23. Then, the insulating layer 31 is formed by curing by irradiating with ultraviolet rays.

Next, a heater paste is printed at a position where the heater layer 32 is provided on the upper surface of the insulating layer 31. Thereafter, the heater layer 32 is formed on the upper surface of the insulating layer 31 by baking at about 150 ° C. for about 30 minutes.

Furthermore, a protective layer paste is printed on the upper surfaces of the insulating substrate 21 and the heater layer 32. Then, the protective layer 35 is formed on the upper surfaces of the insulating substrate 21 and the heater layer 32 by curing by irradiating ultraviolet rays.

Finally, the insulating substrate 21 is stored inside the case 36. Thereafter, the contact member 37 is attached to the bottom surface of the case 36.

The operation of the liquid level detection sensor according to the first embodiment of the present invention configured and manufactured as described above will be described with reference to the drawings.

FIG. 5 is a side sectional view showing a state in which the liquid level detection sensor according to Embodiment 1 of the present invention operates. As shown in FIG. 5, after a water conductive plastic container 38 used in a steam type microwave oven (not shown) or the like is filled with water 39 in advance, the liquid level detection sensor housed in the case 36 is used as the plastic container. Attach to 38.

In this state, when a voltage is applied to the heater layer 32 in the insulating substrate 21, Joule heat is generated from the heater layer 32 due to the current flowing through the heater layer 32. This Julian heat reaches the liquid level detection resistance layer 24, the gas temperature detection resistance layer 26, and the liquid temperature detection resistance layer 28 through the insulating layer 31. At this time, the liquid level detection resistance layer 24 is opposed to the liquid. The self-heating value per unit length is different due to the difference in the heat dissipation constant between the part that faces the gas and the part that faces the gas. Therefore, there is a temperature difference between the portion of the liquid level detection resistance layer 24 facing the gas and the portion facing the liquid, and this causes a difference in resistance value per unit length due to the resistance temperature characteristics of the thermistor. . This difference in resistance value is compared with the resistance value of the gas temperature detection resistor layer 26 located between the pair of gas temperature detection electrodes 25 and the resistance value of the liquid temperature detection resistor layer 28 located between the pair of liquid temperature detection electrodes 27. The liquid level of the water 39 in the plastic container 38 is detected by calculating the above.

Here, consider a case where the liquid level of the water 39 in the plastic container 38 changes abruptly. In the liquid level detection sensor according to Embodiment 1 of the present invention, the heater layer 32 is provided between the liquid level detection resistance layer 24, the liquid temperature detection resistance layer 28, and the gas temperature detection resistance layer 26 and the protective layer 35. Therefore, the distance between the water 39 to be measured and the heater layer 32 is small. Therefore, the Joule heat generated from the heater layer 32 is immediately cooled by the water 39 filled in the plastic container 38. Therefore, even when the liquid level of the water 39 in the plastic container 38 changes abruptly, the liquid level detection can be performed instantaneously, and a liquid level detection sensor with good temporal response can be realized.

[Embodiment 2]

Hereinafter, Embodiment 2 of the present invention will be described with reference to the drawings. FIG. 6 is a side sectional view of a liquid level detection sensor according to Embodiment 2 of the present invention. FIG. 7 is a front view of the insulating substrate in the liquid level detection sensor according to Embodiment 2 of the present invention. FIG. 8 is a side sectional view of the insulating substrate in the liquid level detection sensor according to Embodiment 2 of the present invention. FIG. 9 is a front view showing a state in which the protective layer and the heater layer are removed from the insulating substrate of the liquid level detection sensor according to the second embodiment of the present invention. 6 to 9, the insulating substrate 21 is a rectangular parallelepiped substrate made of polyethylene terephthalate formed in a film shape. The insulating substrate 21 is erected substantially perpendicularly to the longitudinal direction, and a bent portion 22 bent at a substantially right angle is provided at the lower end. Further, the insulating substrate 21 is provided with a pair of liquid level detection electrodes 23 made of Ag from the upper part to the lower part of one side, and both ends of the liquid level detection electrode 23 are liquid level detection electrodes. A liquid level detection resistance layer 24 is provided so as to be electrically connected to the power supply 23. This liquid level detection resistance layer 24 is made of Ag resin and epoxy resin. It consists of a thermistor with a resin material made of a mixture with resin as a binder. The liquid level detection resistance layer 24 includes a plurality of parallel resistance layers 24 a and is electrically connected in parallel to the pair of liquid level detection electrodes 23.

[0036] The resistance value of the liquid level detection resistor layer 24 at room temperature is about 40 kΩ. The plurality of parallel resistance layers 24a in the liquid level detection resistance layer 24 are inclined at an angle of about 45 degrees, which is the same angle with respect to the vertical. Then, by making the end portions 24b of the adjacent parallel resistance layers 24a overlap each other in the horizontal direction, the cross-sectional area force when the liquid level detection resistance layer 24 is cut in the horizontal direction is almost the same from above to below. It is comprised so that. On one side of the insulating substrate 21, a gas temperature detection electrode 25 made of a pair of Ag is provided above the pair of liquid level detection electrodes 23, and both ends are electrically connected to the gas temperature detection electrode 25. A gas temperature detection resistor layer 26 is provided so as to be connected. This gas temperature detection resistance layer 26 is composed of a thermistor having a resin material made of a mixture of an Ag-based resin and an epoxy-based resin as a binder, and its resistance value is about 40 kΩ.

[0037] The bent portion 22 of the insulating substrate 21 is provided with a pair of Ag liquid temperature detection electrodes 27, and an Ag-based resin and an epoxy are connected so that both ends are electrically connected to the liquid temperature detection electrodes 27. There is provided a liquid temperature detecting resistance layer 28 which also has a thermistor force using a resin material made of a mixture with a resin as a binder. The resistance value of the liquid temperature detecting resistor layer 28 is about 40 kΩ. Here, the length between the pair of gas temperature detection electrodes 25 and the length between the pair of liquid temperature detection electrodes 27 are substantially the same, and this length is defined as a unit length. The liquid temperature detection electrode 27 and the liquid temperature detection resistance layer 28 on the insulating substrate 21 are configured to have substantially the same height by providing the bent portion 22 provided at the lower end of the insulating substrate 21. Furthermore, the liquid level detection electrode 23, the gas temperature detection electrode 25, and the liquid temperature detection electrode 27 are electrically connected to the external electrode 30 via a wiring pattern 29 provided on one side surface of the insulating substrate 21.

[0038] The insulating layer 31 includes a liquid level detection electrode 23, a liquid level detection resistance layer 24, a gas temperature detection electrode 25, a gas temperature detection resistance layer 26, a liquid temperature detection electrode 27, and a liquid provided on the upper surface of the insulating substrate 21. It is provided so as to cover the temperature detection resistance layer 28. The heater layer 32 is provided so as to meander the upper surface of the insulating layer 31, and is electrically connected to the heater electrode 34 via the circuit pattern 33. Connected with care. The protective layer 35 is provided so as to cover the upper surface of the heater layer 32. 36 is a metal case, and this case 36 is made of metal and accommodates the insulating substrate 21 inside. A contact member 37 is attached to the bottom surface of the case 36 and holds the bent portion 22 provided on the insulating substrate 21.

Next, a manufacturing method of the liquid level detection sensor according to the second embodiment of the present invention configured as described above will be described.

[0040] First, on one side of the insulating substrate 21 made of polyimide, at a position where the liquid level detection electrode 23, the gas temperature detection electrode 25, the liquid temperature detection electrode 27, the wiring pattern 29, the external electrode 30 and the heater electrode 34 are provided. Ag paste is printed by thick film printing method. Thereafter, the liquid level detection electrode 23, the gas temperature detection electrode 25, the liquid temperature detection electrode 27, the wiring pattern 29, the external electrode 30 and the heater electrode 34 are formed by baking at about 250 ° C. for about 30 minutes.

Yes

[0042] Further, the wiring pattern 29 on one side of the insulating substrate 21, the liquid level detection resistance layer 24, the gas temperature detection resistance layer 26, the liquid temperature detection resistance layer 28, the gas temperature detection electrode 25, the liquid temperature detection electrode 27, and An insulating layer paste is printed on the upper surface of the liquid level detection electrode 23. Then, the insulating layer 31 is formed by curing by irradiating with ultraviolet rays.

Next, a heater paste is printed on the upper surface of the insulating layer 31 at a position where the heater layer 32 is provided. Thereafter, the heater layer 32 is formed on the upper surface of the insulating layer 31 by baking at about 150 ° C. for about 30 minutes.

Finally, after the insulating substrate 21 is stored inside the case 36, the contact member 37 is attached to the lower end portion of the case 36. By attaching this contact member 37, it is stored inside the case 36. The bent portion 22 provided at the lower end of the insulating substrate 21 is held by the contact member 37. Therefore, the liquid temperature detection resistance layer 28 and the liquid temperature detection electrode 27 are easily formed so as to have substantially the same height.

The operation of the liquid level detection sensor according to the second embodiment of the present invention configured and manufactured as described above will be described with reference to the drawings.

FIG. 10 is a side sectional view showing a state in which the liquid level detection sensor according to Embodiment 2 of the present invention operates. As shown in FIG. 10, after filling a water conductive plastic container 38 used in a steam type microwave oven (not shown) in advance with water 39, the liquid level detection sensor housed in the case 36 is replaced with a plastic container. Attach to 38.

In this state, when a voltage is applied to the heater layer 32 in the insulating substrate 21, Joule heat is generated from the heater layer 32 due to the current flowing through the heater layer 32. This Julian heat reaches the liquid level detection resistance layer 24, the gas temperature detection resistance layer 26, and the liquid temperature detection resistance layer 28 through the insulating layer 31. At this time, there is a difference in the amount of self-heat generation per unit length due to the difference in heat dissipation constant between the portion of the liquid level detection resistance layer 24 facing the liquid and the portion facing the gas. As a result, a temperature difference occurs between the portion of the liquid level detection resistance layer 24 facing the gas and the portion facing the liquid, and the resistance value per unit length varies depending on the resistance temperature characteristics of the thermistor.

FIG. 11 is a circuit diagram of a liquid level detection sensor according to Embodiment 2 of the present invention. As shown in FIG. 11, a constant current is supplied from the three constant current sources 40 to the liquid level detection resistance layer 24, the gas temperature detection resistance layer 26, and the liquid temperature detection resistance layer 28. In this state, output signals generated in the liquid level detection resistance layer 24, the gas temperature detection resistance layer 26, and the liquid temperature detection resistance layer 28 are amplified by the amplifier 41, and then output from the digital converter signal by the AD converter 42. Converted to a signal. Thereafter, the microcomputer 43 compares the digital signals from the liquid level detection resistance layer 24, the gas temperature detection resistance layer 26, and the liquid temperature detection resistance layer 28 to calculate the water 39 in the plastic container 38. Detect the liquid level.

[0050] As described above, in the liquid level detection sensor according to Embodiment 2 of the present invention, a plurality of liquid level detection resistance layers 24 are electrically connected to the pair of liquid level detection electrodes 23 in parallel. The parallel resistance layer 24a. Therefore, the liquid level detection resistance layer 24 is located above the insulating substrate 21. Even if the force is provided downward, the cross-sectional area of the entire liquid level detection resistance layer 24 is small. Therefore, the resistance value of the liquid level detection resistance layer 24 is almost the same as the resistance value of the gas temperature detection resistance layer 26 and the liquid temperature detection resistance layer 28. Therefore, the amplification factor of the output signal due to the resistance value of the liquid level detection resistance layer 24 need not be larger than the amplification factor of the output signal due to the resistance values of the gas temperature detection resistance layer 26 and the liquid temperature detection resistance layer 28. . That is, the amplification factors of the amplifier 41 of the liquid level detection resistance layer 24, the gas temperature detection resistance layer 26, and the liquid temperature detection resistance layer 28 can be made substantially the same. As a result, an output signal generated in the liquid level detection resistance layer 24 is obtained in a stable state. In addition, the plurality of parallel resistance layers 24a are installed at the same angle with respect to the vertical. Therefore, the output signal generated in the liquid level detection resistance layer 24 can be continuously output as an analog signal with respect to the change in the liquid level of the water 39 as the solution to be measured.

[0051] In the liquid level detection sensor according to Embodiment 2 of the present invention, the end portions 24b of the adjacent parallel resistance layers in the liquid level detection resistance layer 24 overlap each other in the horizontal direction. Therefore, the cross-sectional area force when the liquid level detection resistance layer 24 is cut in the horizontal direction is substantially the same from above to below. Therefore, the resistance value of the liquid level detection resistance layer 24 changes in proportion to the amount of change in the liquid level of the water 39 that is the solution to be measured, and the linearity of the output signal generated in the liquid level detection resistance layer 24 is also improved.

Industrial applicability

[0052] The liquid level detection sensor according to the present invention is a liquid level detection sensor that can perform liquid level detection instantaneously and has good temporal response even when the liquid level of the solution to be measured changes suddenly. The ability to provide S. In addition, the liquid level detection sensor according to the present invention has an amplification factor of the output signal based on the resistance value of the liquid level detection resistance layer, which is greater than the amplification factor of the output signal based on the resistance values of the gas temperature detection resistance layer and the liquid temperature detection resistance layer. Since the output signal generated in the liquid level detection resistance layer that needs to be increased can be obtained in a stable state, it is particularly useful in a liquid level detection sensor for detecting the liquid level of a water tank used in a steam type microwave oven.

Claims

The scope of the claims

[1] an insulating substrate erected in the longitudinal direction;

A liquid level detection resistance layer provided on one side surface in the longitudinal direction of the insulating substrate;

A pair of liquid level detection electrodes provided at both ends of the liquid level detection resistance layer;

A gas temperature detecting resistor layer provided above one side surface of the insulating substrate; a pair of gas temperature detecting electrodes provided at both ends of the gas temperature detecting resistor layer; and below one side surface of the insulating substrate. A liquid temperature detection resistance layer provided at a position of the liquid temperature detection resistance layer, a pair of liquid temperature detection electrodes provided at both ends of the liquid temperature detection resistance layer, the liquid level detection resistance layer, the gas temperature detection resistance layer, and the liquid A heater layer for supplying heat to the temperature detection resistance layer;

A protection provided to cover the liquid level detection resistance layer, the liquid level detection electrode, the gas temperature detection resistance layer, the gas temperature detection electrode, the liquid temperature detection resistance layer, the liquid temperature detection electrode, and the heater layer. Layers,

With

The heater layer is provided between the liquid level detection resistance layer, the liquid temperature detection resistance layer, and the gas temperature detection resistance layer and the protective layer.

Liquid level detection sensor.

[2] It further includes a bent portion bent at a right angle to a portion where the liquid temperature detection resistance layer and the liquid temperature detection electrode are provided on the insulating substrate,

The liquid temperature detection resistance layer and the liquid temperature detection electrode are configured to have the same height.

The liquid level detection sensor according to claim 1.

[3] It further comprises a case for storing the insulating substrate,

The contact member holds the bent portion by attaching a contact member that contacts the insulating substrate to a bottom surface of the case.

The liquid level detection sensor according to claim 2.

[4] The liquid level detection resistance layer includes a plurality of parallel resistance layers electrically connected in parallel to the pair of liquid level detection electrodes, and the parallel resistance layer is the same with respect to the vertical. It is characterized by being installed at an angle

The liquid level detection sensor according to claim 1.

The ends of the parallel resistance layers adjacent to each other in the liquid level detection resistance layer are configured to overlap each other in the horizontal direction,

The liquid level detection resistance layer has the same cross-sectional area when cut in the horizontal direction.

The liquid level detection sensor according to claim 4.