JP2001041805A - Liquid-level sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise a detection precision even when a liquid level is low. SOLUTION: A water-level sensor 1 incorporates a sensor chip 5 on which a magneto-resistance element 7 is mounted. The sensor chip 5 is enclosed with a bias magnet 6, and the magneto-resistance element 7 is so arranged as to follow magnetic field from the bias magnet 6. A magnetic material 13 comprising a float 12 is housed in a space part 11 formed at the tip of the water-level sensor 1, with the magnetic material 13 moving vertically according to a water level. When the magnetic material 13 rises, the magnetic-field direction from the bias magnet 6 changes for interlinkage with magnet-resistance element 7, changing the resistance value of the magneto-resistance element 7. A detection signal is outputted according to the water level based on the resistance value, for detecting the water level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid level sensor for detecting a liquid level based on an output from a magnetoresistive element.

[0002]

2. Description of the Related Art Conventionally, as a water level sensor, a sensor using a mechanical float type has been used. However, since the float type has low detection accuracy, a semiconductor pressure sensor is used. That is, the water pressure in water is measured by a semiconductor pressure sensor, and the water level is detected by converting the water pressure into a water head pressure.

[0003]

However, when the water level is low (for example, 10 cm or less), there is a problem that the detection accuracy is limited because the water pressure applied to the semiconductor pressure sensor is low.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a liquid level sensor having high detection accuracy even when the liquid level is low.

[0005]

According to the first aspect of the present invention, when the magnetic body moves up and down according to the liquid level, the direction of the magnetic field from the bias magnet changes accordingly. This allows
Since a detection signal is output from the magnetoresistive element in accordance with the direction of linkage of the magnetic field, the liquid level can be determined based on the detection signal from the magnetoresistive element. In this case, since the resistance value of the magnetoresistive element largely changes in accordance with the change in the direction of interlinkage of the magnetic field, it is possible to accurately detect even when the liquid level is low.

According to the second aspect of the present invention, as shown in FIG. 4, the interlinkage angle of the magnetic field is 0 °, that is, when the magnetic field is along the magnetoresistive element, the resistance change rate ΔR /
R becomes the maximum and the magnetic field linkage angle is 90 °, that is, the resistance change rate ΔR / R becomes the minimum when the magnetic field is orthogonal to the magnetoresistive element. By setting the angle to be approximately 0 ° to approximately 45 °, sufficient sensitivity can be ensured and the liquid level can be reliably detected.

According to the third aspect of the present invention, the magnetic body is movably disposed in a state where the magnetic body is prevented from being pulled out.
The liquid level can be detected only by installing the liquid level sensor.

According to the fourth aspect of the present invention, the magnetic material or the wall surface of the space portion comes into point contact with each other while the magnetic material is in contact with the space portion, so that the magnetic material comes into surface contact with the wall surface of the space portion. Compared with the configuration, it is possible to prevent a problem that the magnetic substance is adsorbed on the wall surface of the space and the liquid level cannot be detected.

According to the fifth aspect of the present invention, when the liquid level rises, the magnetic body moves up and down with the liquid level reduced by the displacement reducing means. Thereby, the detectable liquid level range can be expanded.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment A first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a front view of the water level sensor, and FIG. 2 shows a side view of the main part of the water level sensor. 1 and 2, a water level sensor (corresponding to a liquid level sensor) 1 includes a sensor main body 2 and a sensor fixing section 3.

The sensor main body 2 is formed of a resin mold, and is integrally formed in such a manner that a rear end 2b is inclined by 45 ° with respect to a front end 2a. A recess 4 is formed on the front surface of the front end 2a of the sensor main body 2. A sensor chip 5 is built in the rear end 2b, and a bias magnet 6 surrounds the outer periphery of the sensor chip 5.

In the sensor chip 5, a magnetoresistive element 7 is provided on a substrate (not shown) in the direction of the center axis of the bias magnet 6,
That is, they are arranged in the same plane as the magnetic field direction of the bias magnet 6 so as to be along the magnetic field direction. This magnetoresistive element 7 has a characteristic that the resistance value changes according to the direction of the intersecting magnetic field. If the direction of the magnetic field intersecting with the magnetoresistive element 7 is θ as shown in FIG. As described above, when a magnetic field acts on the magnetoresistive element 7 in a parallel direction (θ = 0
°), the rate of change of resistance becomes maximum, and when a magnetic field acts on the magnetoresistive element 7 in a direction perpendicular to the direction (θ = 90 °), the rate of change of resistance becomes minimum. That is, since the resistance of the magnetoresistive element 7 has a characteristic that the resistance value changes according to the angle of the interlinking magnetic field, the direction of the magnetic field can be determined by detecting the resistance value.

In FIG. 1, an output circuit 8 is mounted on a substrate (not shown), and a lead 9 is connected to a terminal of the output circuit 8 so as to protrude from the sensor chip 5. Terminal 10 is connected. In this case, the output circuit 8 outputs a detection signal at a level proportional to the water level based on the resistance value of the magnetoresistive element 7 as shown in FIG.

On the other hand, the bias magnet 6 made of a ferrite-based plastic magnet has a rectangular tube shape, and the sensor chip 5 is inserted and fixed in the bias magnet 6.

The sensor chip 5 in which the bias magnet 6 is integrated as described above is built in the sensor main body 2 by resin molding, and the terminal 10 protruding from the sensor main body 2 is connected to an external device. It has become.

In the sensor main body 2 having the above-described structure, a space 11 having an open lower end is formed by fixing the sensor fixing portion 3 to the distal end portion 2a.
By storing the float 12 in a state where it is prevented from being pulled out, the inside of the space 11 can be moved up and down. A magnetic body 13 is attached to the upper surface of the float 12 in the drawing (hereinafter, the magnetic body is referred to as a magnetic float). In this case, an inclined surface portion 14 is formed in a portion of the sensor fixing portion 3 which comes into contact with the sensor fixing portion 3 in a state where the magnetic float 13 is located at the lowest position. It is in contact with the inclined surface portion 14 in this state.

The water level sensor 1 having the above structure is mounted on an upper part of a water pipe or the like, so that tap water enters the space 11 and the magnetic float 13 moves up and down.

Here, a method of manufacturing the water level sensor 1 having the above configuration will be described. The sensor chip 5 is inserted into the bias magnet 6. The terminal 10 is caulked (or welded) to the lead 9 of the sensor chip 5. The sensor main body 2 is formed by insert molding. The magnetic float 13 is inserted into the recess 4 at the tip of the sensor body 2. The sensor main body 2 and the sensor fixing part 3 are fixed by bonding or the like.

Next, the operation of the above configuration will be described. When the water pressure in the water pipe is low, the magnetic float 13 is lowered to the lowest position, and the magnetic float 13 is
Far away from In this state, the direction of the magnetic field from the bias magnet 6 is changed to the magnetic float 1 as shown in FIG.
3, the direction of the magnetic field is parallel to the magnetoresistive element 7.

When the tap water pressure rises and tap water enters the space 11, the magnetic float 13 rises, so that the direction of the magnetic field from the bias magnet 6 changes as shown in FIG. The magnetic resistance element 7 is linked. Accordingly, the resistance value of the magnetoresistive element 7 changes, and the output circuit 8 outputs a detection signal corresponding to the resistance value of the magnetoresistive element 7. In this case, since the signal level from the water level sensor 1 corresponds to the water level as shown in FIG. 5, the water level can be determined based on the signal level output from the water level sensor 1.

Although the output from the sensor chip 5 (or the magnetoresistive element 7) constantly fluctuates following a slight vertical movement of the magnetic float 13, the output is binarized, for example, by a comparator with hysteresis. This can prevent chattering from occurring in the output. Alternatively, a signal output from the sensor chip 5 may be sampled at a predetermined time interval and averaged at a predetermined timing to obtain a sensor output. Further, an output from the sensor chip 5 may be connected to an integrating circuit composed of a resistor and a capacitor to average the output.

According to such an embodiment, the position of the magnetic float 13 which moves up and down according to the water level is detected by the magnetoresistive element 7 whose resistance value largely changes according to the direction of the interlinking magnetic field. Therefore, even if the water level is lower than that of the semiconductor pressure sensor, it can be detected with high accuracy.

Further, since the direction of the magnetic field interlinking with the magnetoresistive element 7 is set to be about 0 ° to about 45 ° according to the vertical movement position of the magnetic float 13, the magnetoresistive element 7 can be detected with high sensitivity. Magnetic float 1 can be used under the conditions
3 can be accurately detected.

Since the magnetic float 13 is housed in the space 11 formed in the water level sensor 1 so as to be vertically movable, the magnetic float 13 can be integrated with the water level sensor 1 and the water level sensor 1 can be detected. The water level can be detected immediately by simply installing it on the target.

Further, when the magnetic float 13 is located at the lowest position of the space 11, the magnetic float 13 is
As a result, the magnetic float 13 does not stick to the wall surface of the space 11, as compared with the configuration in which the magnetic float 13 makes surface contact with the wall surface of the space 11. The problem that the water level cannot be detected can be prevented.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. 8, and the same parts as those in the first embodiment are designated by the same reference numerals. The description will be omitted, and only different portions will be described. The second embodiment is characterized in that the sensor main body 1 is formed in a linear shape.

That is, the sensor main body 1 is formed in a linear shape, and the magnetic float 13 moves on the center axis of the magnetoresistive element 7. In this case, the surface of the magnetic float 13 is inclined at a predetermined angle, preferably 45 °, with respect to the movement locus of the magnetic float 13.

Now, according to the fluctuation of the water level, the magnetic float 1
As the magnetic field 3 rises, the magnetic field from the bias magnet 6 becomes inclined and interlinks with the magnetic float 13, so that the water level is determined based on the output from the water level sensor 1 in the same manner as in the first embodiment. Can be detected.

According to the second embodiment, since the magnetoresistive element 7 of the sensor chip 5 is provided along the moving direction of the magnetic float 13, the water level sensor 1 can be formed in a linear shape. Compared to the first embodiment, the size can be reduced and the design can be improved.

(Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIG. 9. The same parts as those in the first embodiment are designated by the same reference numerals. Description is omitted.
The third embodiment is characterized in that the magnetic substance to be detected is displaced while the displacement of the water level is reduced.

That is, in FIG. 9 showing the entire water level sensor 1, a swing member (corresponding to a displacement reducing means) 21 is swingably supported by the sensor fixing portion 3. This swing member 2
1 includes a first arm 21a and a second arm 21b having a predetermined angle, and the magnetic body 13 is fixed to a tip of the first arm 21a. Further, a float 22 is supported at the tip of the second arm 21b, and the float 22 is designed to float on the water surface to be detected.

When the water level rises, the float 22 rises, so that the second arm 21b of the swing member 21 rotates. Thereby, the first arm 21 of the swing member 21
a rotates by the same angle.
3 rises. In this case, since the first arm 21a is set shorter than the second arm 21b, the moving distance of the tip of the first arm 21a is smaller than the second arm 21b.
Is a value reduced substantially in proportion to the ratio of the lengths of the arms 21a and 21b as compared with the moving distance of the tip of.

Accordingly, the magnetic body 13 provided at the tip of the first arm 21a is displaced in a state where the displacement of the water level is reduced, and the water level sensor 1 detects the reduced displacement of the water level. Will be.

According to the third embodiment, since the displacement of the water level is detected in a reduced state by using the swinging member 21, the range of the detectable water level is widened, and the large liquid level is obtained. Displacement can also be measured.

The present invention is not limited to the above embodiments, but can be modified or expanded as follows. By arranging a plurality of magnetoresistance elements 7 in parallel, the resistance change rate of the magnetoresistance element 7 may be increased. By forming the lower surface of the magnetic float 13 in an uneven shape, the magnetic float 13 may be prevented from adsorbing to the space 11. The present invention is not limited to the detection of the water level, and can be applied to the detection of various liquid levels.

[Brief description of the drawings]

FIG. 1 is an overall longitudinal sectional front view according to a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional side view showing the sensor body in a cutaway manner.

FIG. 3 is a plan view of the magnetoresistive element shown in a state where a magnetic field is interlinked.

FIG. 4 is a diagram showing a relationship between a direction of interlinkage of a magnetic field to a magnetoresistive element and a resistance change rate

FIG. 5 is a diagram showing a relationship between a water level and a sensor output.

FIG. 6 is a diagram illustrating a magnetic field direction when the float is lowered.

FIG. 7 is a diagram showing a magnetic field direction in a state where the float is raised.

FIG. 8 is an overall longitudinal sectional side view showing a second embodiment of the present invention.

FIG. 9 is a view corresponding to FIG. 1, showing a third embodiment of the present invention.

[Explanation of symbols]

1 is a water level sensor (liquid level sensor), 6 is a bias magnet, 7
Is a magnetic resistance element, 11 is a space, 13 is a magnetic material, 14 is an inclined surface, and 21 is a swing member (displacement reducing means).

Claims (5)

[Claims] 1. A magnetic body that moves up and down according to a liquid level, a bias magnet whose magnetic field direction changes according to the vertical movement of the magnetic body, and a magnetic field from the bias magnet is provided so as to be able to interlink, And a magnetoresistive element that outputs a detection signal in accordance with the direction of linkage. 2. The magneto-resistive element is arranged such that a direction of interlinkage of a magnetic field from the bias magnet changes in a range of approximately 0 ° to approximately 45 ° as the magnetic body moves in a movable range. The liquid level sensor according to claim 1, wherein: 3. The liquid level sensor according to claim 1, wherein the magnetic body is vertically movably housed in a space into which a liquid can enter. 4. The magnetic body or the wall of the space is formed in a shape such that the magnetic body comes into point contact with each other when the magnetic body is in contact with the space. A liquid level sensor as described. 5. The liquid level sensor according to claim 1, further comprising a displacement reducing unit that moves the magnetic body up and down while reducing the liquid level displacement.