JPH09250943A - Water level sensor - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a water level sensor having excellent environment resistance and improved measurement accuracy. SOLUTION: In a water level sensor 1 having a surface opposite to a strain gauge mounting surface of a semiconductor pressure sensor as a surface for receiving pressure of a pressure transmission chamber 10, a pressure transmission chamber 10 is filled with a very soft insulating material 7, The wire substrate including the mounting surface of the strain gauge and the bonding wire was covered with the extremely soft insulating material 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water level sensor, and more particularly to a water level sensor used in a washing machine, a bath water heater or the like.

[0002]

2. Description of the Related Art Conventionally, a water level sensor has been used to detect the water level of a bathtub of a fully automatic bath water heater, and as an example of this water level sensor, a sensor disclosed in Japanese Patent Laid-Open No. 4-42580. Is shown in FIG.

This sensor is an absolute pressure type water level sensor, and is a positive pressure oil-filled type sensor. This sensor includes a sensor element 101 and a diaphragm 10.
3, housing 105, intermediate wall 107, and working fluid 1
09 and.

The sensor element 101 comprises a sensor chip 111 and a pedestal 113, and is attached to the inner bottom surface of the housing 105 with an adhesive 115. The sensor chip 111 has a diaphragm structure, and strain resistances are formed at four locations. The four corners of the sensor chip 111 are
By a bonding wire 121, it is connected to a lead 123 for taking out a signal, and this lead 123 is connected to the housing 10.
5 is penetrated and guided to the outside. The outer periphery of the diaphragm 103 is seam-welded to the housing 105, and the housing 1
The inside of 05 is kept airtight.

The intermediate wall 107 is formed by the sensor element 10.
A plurality of communication holes 125 are formed in the side wall of the intermediate wall 107 so as to cover 1 and the chamber A in which the sensor element 101 is located and the chamber B in which the diaphragm 103 is present communicate with each other. The working fluid is filled in these two chambers.

A conventional water level sensor 10 having the above structure
In No. 1, the working fluid 109 moves between the chamber A and the chamber B through the communication hole 125 of the intermediate wall 107 according to the magnitude of the external force that pushes the diaphragm 103. The sensor chip 111 is deformed by a force according to the force. Then, due to the deformation of the sensor chip 111, the resistance value of the strain resistance increases or decreases, and a voltage signal corresponding to the external pressure is detected from the lead 123.

Next, another conventional example of the water level sensor will be shown.
FIG. 5 shows a water level sensor disclosed in Japanese Utility Model Publication No. 60-11479, which is a so-called reverse pressure type water level sensor in which pressure is sensed on the surface of the pressure sensitive element 213 opposite to the surface on which the strain gauge is attached. is there. In this sensor, a pressure-sensitive element 213 is installed via a pedestal 212 on a base 210 made of synthetic resin or the like except for the metal flange 232 on the outer peripheral portion, and the pressure of the fluid to be detected in the passage 214 rises. The pressure-sensitive element 213 is deformed by this, and an electric signal corresponding to the pressure is led out below the base 210 to the lead piece 21.
6 and 217.

The lead pieces 216 and 217 are the wires 2
The pressure-sensitive element 213 and the wires 218 and 219 are connected to the pressure-sensitive element 213 by 18, 219.
It is protected by the soft insulating material 220. A metal cap 221 is attached to the outer periphery of the base 210.

[0009]

However, in the above-mentioned first conventional example, since the pressure is applied from the positive pressure direction of the sensor chip, that is, from the mounting side of the strain resistor, the sensor chip is protected from the fluid. As the gel, an extremely soft gel should be used in order to prevent stress inside the gel. However, the vibration due to the pulsation of the fluid may cause the diaphragm and the gel to slightly move, which may break the bonding wire.

Further, in the second conventional example, the surface of the pressure-sensitive element that is not subjected to the pressure of the fluid to be detected, that is, the positive pressure side is protected by the soft insulating material, but the pressure is applied to the reverse pressure side. There is no soft insulating material on the surface. Therefore, due to the intrusion of water or the like, the pressure sensitive element 213 and the pedestal 212 or the bonding portion of the base 210 and the pedestal 212 are directly affected by the pressure detection medium.

Therefore, the present invention has been made in view of the problems of the conventional water level sensor described above, and an object of the present invention is to provide a water level sensor having excellent environmental resistance and improved measurement accuracy. Another object of the present invention is to provide a water level sensor capable of coping with a sudden change in pressure of the pressure detection medium and having excellent environmental resistance.

[0012]

According to the first aspect of the present invention,
A water level sensor that detects pressure with a semiconductor pressure sensor, wherein the surface opposite to the strain gauge mounting surface is the surface that receives the pressure in the pressure transfer chamber, and the pressure transfer chamber is filled with a very soft insulating material. The strain gauge mounting surface and the wire substrate including the bonding wire are covered with an extremely soft insulating material.

According to a second aspect of the present invention, the extremely soft insulating material is silicon gel.

According to a third aspect of the present invention, there is provided a water level sensor for detecting pressure with a semiconductor pressure sensor, wherein the surface opposite to the mounting surface of the strain gauge is a surface for receiving the pressure of the pressure transmission chamber. The pressure transmission chamber is filled with silicon oil or fluorine oil, a baffle plate is attached to the inner wall of the pressure introducing pipe leading to the pressure transmission chamber, and the baffle plate attachment portion is filled with silicon oil or fluorine oil to form a damper chamber. And the wire substrate including the mounting surface of the strain gauge and the bonding wire is covered with an extremely soft insulating material.

According to the present invention, since the surface opposite to the mounting surface of the semiconductor pressure sensor is the surface for receiving the pressure of the pressure transmission chamber, it is not necessary to consider the influence of the fine movement of the gel on the bonding wire connection. Extremely soft gels can be used. In addition, since water stains and the like do not accumulate in the pressure transmission chamber, clogging of the pressure transmission chamber does not occur.

Further, according to the present invention, since the damper chamber is provided in the pressure introducing pipe leading to the pressure transmitting chamber, a sudden pressure change is not transmitted to the sensor chip.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a specific example of an embodiment of a water level sensor according to the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing a first embodiment of the water level sensor according to the present invention. The water level sensor 1 is a so-called reverse pressure type water level sensor, and includes a main body 2, a sensor chip 3, a wire substrate 5, a circuit substrate 6, a silicon gel 7, a cover 8 and the like.

The main body 2 is made of resin or the like, and an upper portion 2a thereof is formed in a dish shape with an open upper side, and a sensor chip 3 and the like, which will be described later, are arranged in the central portion. A cover 8 is attached to the upper portion 2a to form a space between the inner wall of the cover 8 and the inner wall of the upper portion 2a. In addition, a vent hole 8a communicating with the atmosphere is formed in the center of the cover 8.

The lower part 2b of the main body 2 is attached to the pressure measurement site. FIG. 2 shows a state in which the water level sensor 1 in this embodiment is attached to the pressure measuring pipe 14. The lower portion 2b is fixed to the flange portion 14a of the pressure measuring pipe 14, the pressure introducing port 2c of the main body 2 communicates with the inside of the pressure measuring pipe 14, and water or the like in the bathroom to be measured is introduced. An O-ring 15 is attached to seal between the pressure measuring pipe 14 and the lower portion 2b of the main body 2.

A sensor chip 3 joined to a pedestal 11 is fixed to the center of the main body 2 with an adhesive or the like. The sensor chip 3 is made of silicon and is formed in a square shape. The sensor chip 3 has a diaphragm structure in which a central portion thereof is thinner than a peripheral portion as a pressure receiving portion, and a strain gauge formed by diffusion resistance is provided on the diaphragm.

By using a die-bonding material having an extremely small volume collection rate upon curing as an adhesive, an effective adhesive area can be secured and the stress of the adhesive at the time of adhesion can be suppressed to a small level. The strength of the tip 3 is increased. Further, by making the area of the pressure receiving portion of the silicon gel 7 as small as possible, it is possible to suppress the load generated at the time of pressurization and to suppress the amount of expensive gel used as much as possible.

A pressure transmission chamber 10 is formed in a pedestal 11 made of Pyrex glass which is anodically bonded to the sensor chip 3. The sensor chip is deformed by the pressure increase of the pressure detection medium in the pressure transmission chamber 10, and an electric signal corresponding to the pressure is output. The strain gauge is the upper surface 3 of the sensor chip 3.
The sensor chip 3 is connected to the signal extraction bonding wire 12 at the end of the sensor chip 3 and the surface thereof is covered with a silicon gel 17 for protection.

The upper part of the pressure introducing port 2c of the main body 2 has a smaller inner diameter than the lower part, and this small diameter portion communicates with the pressure transmission chamber 10. Then, the pressure transmission chamber 10 and the upper space 2d of the pressure introduction port 2c of the main body 2 are filled with the silicon gel 7 to protect the sensor chip 3.

The silicon gel 7 with which the pressure transmission chamber 10 and the like are filled has a very low viscosity in the state before the silicone gel 7 is hardened, and by adopting a vacuum sealing method, the inside of the thin tube hole is closed. It becomes possible to fill the silicon gel 7 into the. Further, after curing, by using a gel that maintains extremely softness, the influence of the gel in measuring the water level can be suppressed.

In the case of the conventional positive pressure gel type water level sensor, the gel for protecting the sensor chip should be an extremely soft gel so as not to generate stress inside the gel. However, the gel is slightly moved by the vibration due to the pulsation of the fluid, which has a bad influence on the connection of the bonding wire, so that there is a limit to the extreme softening. Therefore, it was easily affected by the temperature characteristics associated with hardening of the gel. However, in the present embodiment, since the back pressure gel type is used, it is not necessary to consider the influence of the fine movement of the gel on the connection of the bonding wire, and an extremely soft gel can be used as the silicon gel 7.

The chip 3 is connected to the wire substrate 5 via the bonding wire 12, is connected to the circuit substrate 6 by the lead wire 13, is supplied with power via the connector 9, and is electrically connected to the external circuit according to the measured pressure. The signal is transmitted.

In the water level sensor 1 having the above structure, the pressure of the silicon gel 7 rises according to the pressure in the X direction of the pressure detecting medium introduced into the pressure introducing port 2c, and this pressure is transmitted to the pressure transmitting chamber 10. Then, the sensor chip 3 is deformed. As a result, the resistance value of the strain gauge increases and decreases, and a voltage signal corresponding to the pressure of the pressure detection medium is detected from the bonding wire 12.

In the present invention, since the strain gauge mounting surface on the sensor chip 3 is the surface opposite to the detection pressure surface and the soft insulating material is filled, it is directly affected by the pressure detection medium. In addition, the soft insulating material can be relatively softened.

Next, a second embodiment of the water level sensor according to the present invention will be described with reference to FIG. This water level sensor 2
Since the main part of No. 1 is the same as that of the first embodiment, the same components as those of the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted. Also in this embodiment, the water level sensor according to the present invention is composed of a main body 22, a sensor chip 3, a wire substrate 5, a circuit board 6, a cover 8 and the like as a back pressure type water level sensor 21.

The main body 22 is made of resin or the like, and its upper portion 22
a has the same shape as in the first embodiment. Also, the main body 22
The lower part 22b of is attached to the pressure measurement site. The mounting procedure is the same as in the case of the first embodiment shown in FIG. A through hole 22d is formed in the center of the main body 22, and the sensor chip 3 is fixed to the pedestal 11 with an adhesive or the like.

The characteristic part of this embodiment is that the lower part 2 of the main body 22 is
It is located in the damper chamber 25 formed on the inner wall of the pressure introduction port 22c formed inside 2b. This damper chamber 25
It has a labyrinth structure formed by the baffle plate 24 and the like provided upright on the inner wall of the pressure introducing port 22c. The space formed between the baffles 24 is filled with a liquid 23 such as silicone oil or fluorine oil. Further, in this embodiment, instead of the silicon gel 7, the pressure transmission chamber 1
Zero is also filled with a liquid such as silicone oil or fluorine oil. In this embodiment also, the pressure of the pressure detection medium is applied from the Y direction in FIG.

In the water level sensor 21 having the above structure, the pressure of the liquid 23 rises according to the pressure in the Y direction of the pressure detecting medium introduced into the pressure introducing port 22c, and this pressure is transmitted to the pressure transmitting chamber 10. , Deform the sensor chip 3. As a result, the resistance value of the strain gauge increases and decreases, and a voltage signal corresponding to the pressure of the pressure detection medium is detected from the bonding wire 12. At this time, even if the pressure of the pressure detection medium changes rapidly by a water hammer or the like, the damper chamber 25
Since the sensor chip 3 is installed
Therefore, the sensor chip 3 can be protected from sudden pressure changes. 1 and 3, the wire substrate 5 and the circuit substrate 6 are separated and connected by lead wires, but the circuit substrate 6 may be integrated with the wire substrate 5 and connected to the connector 9.

[0033]

EFFECTS OF THE INVENTION According to the present invention, scales and the like can be accumulated in the pressure transmission chamber without being directly affected by the pressure detection medium such as the breakage of the bonding wire and the deterioration of the strain gauge due to the entry of water. Since the hole clogging does not occur, it is possible to provide a water level sensor having excellent environment resistance. Moreover, since the influence of the temperature characteristics of the soft insulating material can be reduced, it is possible to provide a water level sensor with improved measurement accuracy.

Further, according to the present invention, since it is possible to cope with a sudden change in pressure of the pressure detection medium, it is possible to provide a water level sensor having further excellent environmental resistance.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of a water level sensor according to the present invention.

FIG. 2 is a partial cross-sectional view showing a state in which the water level sensor of FIG. 1 is attached to a pressure measuring pipe.

FIG. 3 is a sectional view showing a second embodiment of the water level sensor according to the present invention.

FIG. 4 is a sectional view showing a conventional water level sensor.

FIG. 5 is a sectional view showing another conventional water level sensor.

[Explanation of symbols]

 1, 21 Water level sensor 2, 22 Main body 3 Sensor chip 5 Wire substrate 6 Circuit board 7, 17 Silicon gel 8 Cover 9 Connector 10 Pressure transmission chamber 11 Pedestal 12 Bonding wire 23 Liquid 24 Baffle plate 25 Damper chamber

Front page continued (72) Inventor Masaya Kitou 1311 Aobadai, Tokorozawa, Saitama Prefecture Sagimiya Seisakusho Co., Ltd.

Claims (3)

[Claims] 1. A water level sensor for detecting pressure with a semiconductor pressure sensor, wherein the surface opposite to the mounting surface of the strain gauge is the surface for receiving the pressure in the pressure transfer chamber, and a pole is provided in the pressure transfer chamber. A water level sensor characterized by being filled with a soft insulating material, and a wire substrate including the mounting surface of the strain gauge and a bonding wire being covered with an extremely soft insulating material. 2. The water level sensor according to claim 1, wherein the extremely soft insulating material is silicon gel. 3. A water level sensor for detecting pressure with a semiconductor pressure sensor, wherein the surface opposite to the mounting surface of the strain gauge is the surface for receiving the pressure in the pressure transfer chamber. Oil or fluorine oil is filled, a baffle plate is attached to the inner wall of the pressure introducing pipe leading to the pressure transmission chamber, and the baffle plate attachment portion is filled with silicon oil or fluorine oil to form a damper chamber, A water level sensor characterized in that a gauge mounting surface and a wire substrate including a bonding wire are covered with an extremely soft insulating material.