WO2017209170A1

WO2017209170A1 - Liquid level detecting device

Info

Publication number: WO2017209170A1
Application number: PCT/JP2017/020203
Authority: WO
Inventors: 英楠張
Original assignee: 株式会社村田製作所
Priority date: 2016-06-03
Filing date: 2017-05-31
Publication date: 2017-12-07
Also published as: CN107462304A; CN107462304B

Abstract

This liquid surface detecting device is provided with: a float which rises and falls, following a liquid level; two ore more magnets which are attached to the float and are disposed with identical poles facing one another; a guiding member which guides the rising and falling of the float; a plurality of magnetic sensors which are attached to the guiding member, detect a magnetic flux density that varies in accordance with the rising and falling position of the magnets, and output an electrical signal corresponding to the magnetic flux density; and a detecting circuit which detects the position of the float on the basis of the electrical signals output by the plurality of magnetic sensors. The distance between adjacent magnetic sensors in the rising and falling direction is set to a first length. The distance between the magnets and the magnetic sensors in a horizontal direction that is perpendicular to the rising and falling direction is set to a second length. The first length is greater than the second length. The detecting circuit detects the position of the float on the basis of the electrical signals output by two adjacent magnetic sensors from among the plurality of magnetic sensors.

Description

Liquid level detector

The present invention relates to a liquid level detection device, and more specifically, a liquid level that is mounted on a tank that stores a liquid such as gasoline, engine oil, or urea water in an automobile and that detects the position of the liquid level using a magnet. The present invention relates to a detection device.

Conventionally, a liquid level detection device including a magnet and a magnetic sensor is known. For example, liquid level detection that includes a float having a magnet that moves up and down in response to a change in the position of the liquid level and a magnetic sensor that detects the magnetic flux density of the magnet, and detects the position of the liquid level from the output signal of the magnetic sensor The device is known.

In this regard, Patent Document 1 discloses a float 1, a cylindrical pipe 2 in which the float 1 is disposed, a magnetized body 3 fixed to one end of the float 1, and a magnetized body. 3 is disclosed, which includes a magnetoresistive element 4 arranged in the vicinity of 3 and detects the position of the liquid level based on the position of the magnetized body 3 corresponding to the float 1 (see Patent Document 1). FIG. 1 and FIG. 2).

Further, the magnetized body 3 is magnetized along the moving direction of the float 1 in accordance with a predetermined magnetization pattern (SN, NS, SN,...). . Further, the magnetized body 3 protrudes outside the cylindrical pipe 2 from a through hole provided on the top surface of the cylindrical pipe 2. The magnetoresistive element 4 is disposed outside the cylindrical pipe 2 and in the vicinity of the magnetized body 3. The magnetoresistive element 4 includes eight resistance elements that constitute two bridge circuits.

In Patent Document 2, a liquid level sensor 21, a liquid tank 18 in which the liquid level sensor 21 is disposed, a displacement magnet 24 provided at the upper end of a detection rod 23, and a double detection unit housing 20 are provided. A liquid level detection device is disclosed that includes a detector main body 25 that is attached and includes a plurality of Hall elements 5 and 5 (see FIGS. 1 to 4 and 12 to 13 of Patent Document 2).

The detector main body 25 has a structure in which a plurality of Hall elements 5 are provided on the printed circuit board 6 on the same straight line at a required arrangement interval so as to be parallel to the moving direction of the displacement magnet 24. Each Hall element is provided such that the magnetosensitive surface 5 a is parallel to the magnetization direction of the displacement magnet 24. The liquid level sensor 21 is suspended in the tank via a detection rod 23 by a tension spring 22 having an upper end attached to the lower surface of the detection unit housing 20, and the upper end of the detection rod 23 faces the detection unit housing 20. It is out. The liquid level detection device detects the displacement of the upper end portion of the detection rod 23 in the detection unit housing 20 by the detector main body 25 as the displacement of the displacement magnet 24 and measures the liquid level. The detector main body 25 calculates the position of the magnet from the output voltage of each Hall element via the control circuit 7 and further converts it into a liquid level value, and the liquid level value from the calculation circuit is displayed on the screen or the like. It is connected to an output device 9 for outputting.

In the liquid level detection apparatus described in Patent Document 1, the magnetized body 3 protrudes outside the cylindrical pipe 2 from a through hole provided in the top surface of the cylindrical pipe 2. For this reason, it is difficult to reduce the size, and depending on the device, it may be difficult to mount.

In the liquid level detection device described in Patent Document 2, the detection rod 23 and the displacement magnet 24 protrude from the through hole provided on the top surface of the liquid tank 18 to the outside of the liquid tank 18. For this reason, similarly to the liquid level detection device described in Patent Document 1, it is difficult to reduce the size, and it may be difficult to mount depending on the device.

On the other hand, a liquid level detection device in which a magnet is arranged in a tank has been devised.
In Patent Document 3, a float 23, a glass tube 21 in which the float 23 is disposed, magnets 22A and 22B fixed to two opposite ends of the float 23, and the glass tube 21 are adjacent to each other. There is disclosed a liquid level detection device that includes sensor units 31A to 31E mounted on a sensor case 32 that is arranged in the manner described above and detects the position of the liquid level based on the positions of magnets 22A and 22B corresponding to the float 23. (See FIGS. 2 to 4 of Patent Document 3).

Magnets 22 </ b> A and 22 </ b> B are arranged at both ends in the movement direction of the float 23 so as to be NS and SN along the movement direction of the float 23. The sensor units 31A to 31E are arranged along the moving direction of the float 23. The sensor units 31A to 31E detect angle sensors 34A to 34E that detect magnetism by the first magnet 22A and the second magnet 22B according to the displacement of the float 23, and that the float 23 has reached the vicinity by magnetism. Magnetic intensity sensors 35A to 35E.

Patent Document 4 includes a magnet 3, a tank 2 in which the magnet 3 is disposed, a rod 4, a plurality of magnetic intensity sensors S [1] to S [4], and a control unit 10. A liquid level detection device that detects the position of the liquid level based on the position of the magnet 3 is disclosed (see FIGS. 1, 4, and 5 of Patent Document 4).

The rod 4 has a long cylindrical shape and is disposed in the tank 2 so that the axial direction is parallel to the vertical direction (vertical direction). The magnet 3 has an annular shape and is configured to float on the liquid level of the liquid stored in the tank 2. The rod 4 is inserted through the magnet 3, and the magnet 3 is guided by the rod 4 in the state where it floats on the liquid surface of the liquid stored in the tank 2 and moves in the vertical direction. The plurality of magnetic intensity sensors S [1] to S [4] are each embedded in the rod 4, and are arranged so as to be sequentially arranged at intervals from above to below.

The control unit 10 includes a difference value calculation unit 11 having a changeover switch 12 and a subtractor 13, and a microcomputer 20. The changeover switch 12 has input terminals I11, I12, I13, I21, I22, I23, and output terminals O1, O2. Any one of the input terminals I11, I12, and I13 is connected to the output terminal O1 by switching the switch according to a control signal from the microcomputer 20. Any one of the input terminals I21, I22, and I23 is connected to the output terminal O2 by switch switching. The input terminal I11 is connected to the magnetic intensity sensor S [1]. The input terminal I12 is connected to the magnetic intensity sensor S [2]. The input terminal I13 is connected to the magnetic intensity sensor S [3]. The input terminal I21 is connected to the magnetic intensity sensor S [2]. The input terminal I22 is connected to the magnetic intensity sensor S [3]. The input terminal I23 is connected to the magnetic intensity sensor S [4]. Thereby, the changeover switch 12 (1) when the voltage signal of the magnetic intensity sensor S [1] is output from the output terminal O1, the voltage signal of the magnetic intensity sensor S [2] is output from the output terminal O2. (2) When the voltage signal of the magnetic intensity sensor S [2] is output from the output terminal O1, the voltage signal of the magnetic intensity sensor S [3] is output from the output terminal O2, and (3) the magnetism is output from the output terminal O1. When the voltage signal of the intensity sensor S [3] is output, the voltage signal of the magnetic intensity sensor S [4] is output from the output terminal O2. The subtractor 13 includes one input terminal to which the output terminal O1 is connected, the other input terminal to which the output terminal O2 is connected, and an output terminal that outputs a differential voltage signal.

The microcomputer 20 is connected to the changeover switch 12 and the subtractor 13. The microcomputer 20 is a high level indicating the relationship between the difference value of the voltage signal (output value) of the magnetic strength sensor arranged adjacent to the position of the magnet 3 (that is, the liquid level of the liquid stored in the tank 2). Precision liquid level detection reference information G [1] to G [3], standard precision liquid level detection reference information H [1] to H [3], high precision liquid level detection reference information for detecting the liquid level A ROM in which high-precision detection conditions for determining which of G [1] to G [3] and standard precision liquid level detection reference information H [1] to H [3] is used is stored in advance. ing.

The microcomputer 20 further includes a CPU. The CPU includes a differential voltage signal from the subtractor 13, high-precision liquid level detection reference information G [1] to G [3], and standard precision liquid level detection reference information H [ 1] to H [3] and signal processing using high-precision detection conditions are performed to detect the position of the magnet 3, that is, the liquid level of the liquid stored in the tank 2.

In Patent Document 5, a float 3, a tank in which the float 3 is arranged, a substantially ring-shaped permanent magnet 5 fixed in a concave groove 3 h of the float 3, and a hole in the float 3 are loosely inserted. The guide member 11 has a substantially cylindrical stem portion 13 and guides the lifting and lowering of the float 3, and two Hall elements (first Hall element 21 and the first Hall element 21) that are magnetic sensors arranged in the stem portion 13. 2 level element 23) and a drive control circuit 31 for guiding the detection output of the liquid level to the outside, and detects the position of the liquid level from the position of the float 3 (= permanent magnet 5) Is disclosed (see FIGS. 1 and 2 of Patent Document 5).

The permanent magnet 5 is uniformly magnetized with an N pole on the inner peripheral surface 5n side and an S pole on the outer peripheral surface 5g side. The first hall element 21 and the second hall element 23 are fixedly spaced apart from each other in the vertical direction. When a driving voltage is applied to the first and second Hall elements 21 and 23, the magnetic flux density that changes in accordance with the ascending / descending position of the permanent magnet 5 disposed on the float 3 following the liquid surface is detected, and the magnetic flux density A corresponding electric signal, more specifically, a voltage corresponding to the magnetic flux density almost linearly is output. The drive control circuit 31 includes a first amplifier circuit 33 that amplifies the output voltage from the first Hall element 21 and a second amplifier circuit 35 that amplifies the output voltage from the second Hall element 23. The first amplifier circuit 33 and the second amplifier circuit 35 exhibit similar amplification factors.

The output voltage of the first hall element 21 is amplified by the first amplifier circuit 33 at a predetermined rate. The amplified output voltage is input to the output adjustment circuit 37 and the inverting amplification circuit 41, and a voltage corresponding to the liquid level is output from the output adjustment circuit 37 to the outside. The output voltage of the second hall element 23 is amplified at a predetermined rate by the second amplifier circuit 35. The amplified output voltage is input to the inverting amplifier circuit 41. The inverting amplifier circuit 41 receives an output voltage obtained by combining the output voltage obtained by amplifying the output of the first Hall element 21 and the output voltage obtained by amplifying the output of the second Hall element 23. This is used for feedback control of driving of the elements 21 and 23. Thereby, the magnetic flux density, that is, the liquid level can be accurately measured regardless of the influence of the fluctuation of the liquid temperature and the variation of the characteristics of the permanent magnet 5.

Japanese Patent Laid-Open No. 1-222120 Japanese Patent Laid-Open No. 2002-22403 JP 2009-236615 A JP 2014-145714 A JP 2002-277308 A

However, in the liquid level detection device described in Patent Document 3, the sensor units 31A to 31E include angle sensors 34A to 34E and magnetic intensity sensors 35A to 35E, respectively, and an output monitor circuit to which the angle sensors 34A to 34E are connected. Since it further includes the switching circuit 12 to which the magnetic intensity sensors 35A to 35E are connected, it is difficult to reduce the circuit configuration. Further, when the angle sensors 34A to 34E and the magnetic intensity sensors 35A to 35E are GMR elements, they can cope with a magnetic field intensity of 30 to 200G, but when a magnetic field larger than 200G is applied, the magnetic saturation occurs. It cannot be detected. For this reason, the freedom degree with respect to the kind and position of magnet 22A, 22B is low. In particular, the distance between the angle sensors 34A to 34E and the magnetic intensity sensors 35A to 35E and the magnets 22A and 22B cannot be shortened depending on the magnets 22A and 22B, and it is difficult to reduce the circuit configuration.

The liquid level detection device described in Patent Document 4 requires the selector switch 12, the subtractor 13, and the ROM of the microcomputer 20, which complicates the circuit configuration and is difficult to reduce in size.

In the liquid level detection device described in Patent Document 5, the liquid level is detected only by the first hall element 21, and the second hole is used to correct the influence of fluctuations in liquid temperature and variations in the characteristics of the permanent magnet 5. Since a feedback control circuit including the element 23 and the inverting amplifier circuit 41 is required, the circuit configuration is complicated and downsizing is difficult.

Therefore, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a liquid level detection device capable of simplifying and downsizing the circuit configuration.

A liquid level detection device according to an aspect of the present invention includes a float that moves up and down following the liquid level, at least two magnets that are attached to the float and are disposed so that the same poles face each other, and guides the lift of the float A plurality of magnetic sensors that are attached to the guide member, detect a magnetic flux density that changes according to the raising and lowering position of the magnet, and output an electrical signal corresponding to the magnetic flux density, and a plurality of magnetic sensors And a detection circuit for detecting the position of the float based on each output electric signal. A first length is set between adjacent magnetic sensors in the ascending / descending direction. The length of the magnet and the magnetic sensor in the horizontal direction perpendicular to the ascending / descending direction is set to a second length. The first length is longer than the second length. The detection circuit detects the position of the float based on electrical signals output from two adjacent magnetic sensors among the plurality of magnetic sensors.

Preferably, each magnetic sensor has a bias magnet that applies a bias magnetic field in the horizontal direction.

Preferably, each magnetic sensor outputs an electrical signal based on a magnetic vector of magnetic lines of force generated by the magnet.

Preferably, the detection circuit extracts an electric signal output from two adjacent magnetic sensors based on a comparison with an intermediate voltage among the electric signals output from the plurality of magnetic sensors.

Preferably, the detection circuit calculates angle information when one of the two extracted electric signals is a sine wave and the other is a cosine wave, and detects the position of the float based on the calculated angle information.

Preferably, each magnetic sensor includes first to fourth magnetoresistive elements to which a bias magnetic field vector generated by a bias magnet is applied, and resistance values of the first to fourth magnetoresistive elements based on a change in the bias magnetic field vector. And an output circuit that outputs an electrical signal corresponding to the change in the output.

Preferably, a correction circuit for correcting the electrical signal output from the output circuit is further provided.
Preferably, the correction circuit raises or raises the power of the output electric signal by a predetermined coefficient.

Preferably, each magnetic sensor outputs linearly with respect to the magnetic field intensity, and is provided so that the polarity can be discriminated.

The liquid level detection device of the present invention can be simply and miniaturized in circuit configuration.

It is a figure explaining the external appearance structure of the liquid level detection apparatus based on Embodiment 1. FIG. It is a figure explaining the some magnetic sensor 5 attached to the guide 10 based on Embodiment 1. FIG. 1 is a circuit configuration diagram of a liquid level detection device 1 based on Embodiment 1. FIG. It is a figure explaining the pattern of the magnetoresistive element of the magnetic sensor 5 based on Embodiment 1. FIG. It is a figure explaining the detection principle of the magnetic sensor 5 based on Embodiment 1. FIG. It is a figure explaining arrangement | positioning of the magnet 2 attached to the float 20 based on Embodiment 1. FIG. It is a figure explaining the layout of

magnet

2A, 2B attached to the float 20 based on Embodiment 1, and the several magnetic sensor 5. FIG. It is a figure explaining the relationship with the magnetic sensor when the float 20 based on Embodiment 1 changes the position by raising / lowering operation | movement. It is a figure explaining the output signal waveform of the some magnetic sensor according to the raising / lowering operation | movement of the float 20 based on Embodiment 1. FIG. FIG. 10 is an enlarged image view of a predetermined area in FIG. 9. It is a figure which illustrates typically the relationship between the magnetic sensor 5 and magnetic vector P based on Embodiment 1. FIG. It is a figure explaining the precision of angle information theta based on Embodiment 1. FIG. It is a flowchart explaining the detection system of the liquid level detection apparatus 1 based on Embodiment 1. FIG. FIG. 6 is a circuit configuration diagram of a liquid level detection device 1 based on Embodiment 2. It is a figure explaining the signal before correction of magnetic sensors 5PA and 5PB, and after correction. It is a figure explaining the precision of angle information theta based on Embodiment 2. FIG. It is a figure explaining the layout of the magnet attached to the float 20 and magnetic sensor 5PA, 5PB, 5PC based on another embodiment.

This embodiment will be described in detail with reference to the drawings. Note that the same or corresponding parts in the drawings are denoted by the same reference numerals and description thereof will not be repeated.

(Embodiment 1)
FIG. 1 is a diagram illustrating an external configuration of a liquid level detection device based on the first embodiment.

As shown in FIG. 1, the liquid level detection device 1 includes a float 20 that moves up and down following the liquid level, a guide (guide member) 10, and a detection circuit 50.

The detection circuit 50 detects the position of the float 20 based on output signals detected from a plurality of magnetic sensors attached to the guide member 10.

FIG. 2 is a diagram illustrating a plurality of magnetic sensors 5 attached to the guide 10 based on the first embodiment.

As shown in FIG. 2, the plurality of magnetic sensors 5 are arranged at predetermined intervals along the ascending / descending direction.

The magnet 20 is provided in the float 20. Specifically,

magnets

2A and 2B are attached as magnet units. A magnet unit is composed of the

magnets

2A and 2B.

The plurality of magnetic sensors 5 detect the magnetic flux density according to the lifting / lowering operation of the magnet 2 attached to the float 20 and output an electric signal corresponding to the magnetic flux density. In this example, the configuration of the 4-pin magnetic sensor 5 will be described as an example. However, the number of pins is not particularly limited to this, and those skilled in the art can appropriately change the design.

FIG. 3 is a circuit configuration diagram of the liquid level detection device 1 based on the first embodiment.
As shown in FIG. 3, the liquid level detection device 1 based on the first embodiment includes a plurality of magnetic sensors 5 and a detection circuit 50. In this example, a case where n magnetic sensors are provided is shown.

The detection circuit 50 includes an A / D circuit 60 that is an analog / digital conversion circuit, a P / S conversion circuit 30 that is a parallel / serial conversion circuit, and an MPU (Micro-processing unit) 40 that executes arithmetic processing. .

The A / D circuit 60 is connected to a plurality (n) of magnetic sensors 5 and converts an input analog signal into a digital signal.

The P / S conversion circuit 30 converts the digital signal input from the A / D circuit 60 input in parallel in synchronization with the clock CLK input from the MPU 40 in series and outputs it to the MPU 40.

The MPU 40 detects the position of the float 20 by performing arithmetic processing on signals from a plurality (n) of magnetic sensors 5 input from the P / S conversion circuit 30.

Note that the MPU 40 in this example will be described with respect to the signal from the A / D circuit 60 that receives the output of the P / S conversion circuit 30 synchronized with the clock CLK. It is also possible to change to a configuration that receives a digital signal input from the / D circuit 60.

FIG. 4 is a diagram for explaining the pattern of the magnetoresistive element of the magnetic sensor 5 based on the first embodiment.

As shown in FIG. 4, here, the magnetic sensor 5 includes four magnetoresistive elements MR1 to MR4 (also collectively referred to as magnetoresistive elements MR).

These magnetoresistive elements MR are anisotropic magnetoresistive elements (AMR (Anisotropic Magneto Resistance) elements) and have a folded pattern structure.

The resistance value when the magnetic field of the magnetoresistive element MR is applied is minimized when a saturation magnetic field perpendicular (90 °) to the longitudinal direction of the folded pattern is applied, and a parallel (0 °) saturation magnetic field is applied. Sometimes it has the greatest characteristics.

As shown in FIG. 4, in these magnetoresistive elements MR, MR1 and MR4 have the same longitudinal direction of the folded pattern. MR2 and MR3 have the same longitudinal direction of the folded pattern. The longitudinal directions of the folded pattern of MR1 (MR4) and MR2 (MR3) are different by 90 °.

Then, as shown in FIG. 4, these magnetoresistive elements MR constitute a bridge circuit between the power supply voltage Vcc and the ground GND.

When a magnetic field is applied, the magnetic sensor 5 outputs signals V + and V− according to the resistance value change to the midpoint output portion of the bridge circuit due to the resistance value change of the magnetoresistive elements MR1 to MR4. The magnetic sensor 5 outputs a difference ΔV between the signals V + and V−.

The magnetic sensor 5 is provided with

bias magnets

3A and 3B. The

bias magnets

3A and 3B are arranged so that a bias magnetic field is applied to the magnetoresistive elements MR1 to MR4 from the upper left to the lower right in FIG.

The magnetoresistive element MR of the magnetic sensor 5 of this example will be described as a folded pattern structure as an example. However, the pattern structure is not limited to a folded shape, and those skilled in the art can improve the detection characteristics of the magnetic sensor 5. If so, the design can be changed as appropriate. In addition, regarding the arrangement (orientation) of the

bias magnets

3A and 3B as an example in this example, a bias magnetic field vector having an angle of 45 ° from the upper left to the lower right in FIG. 4 with respect to the longitudinal direction of the magnetoresistive element MR1. However, the arrangement or angle of the magnetic sensor 5 can be changed as appropriate by those skilled in the art so as to enhance the detection characteristics of the magnetic sensor 5.

In this example, a configuration in which the bias magnetic field vector is applied based on the two

bias magnets

3A and 3B will be described, but it is also possible to apply the bias magnetic field vector using one bias magnet instead of the two bias magnets. is there. For example, a bias magnet may be disposed on the substrate on which the magnetoresistive elements MR1 to MR4 are provided, or a bias magnet may be disposed on the back surface of the base.

FIG. 5 is a diagram for explaining the detection principle of the magnetic sensor 5 based on the first embodiment.
FIG. 5A is a diagram for explaining a bias magnetic field vector that changes in accordance with an external magnetic field.

As shown in FIG. 5 (A), the bias magnetic field vector of the magnetic sensor 5 changes its vector direction according to the external magnetic field with respect to the ascending / descending direction. In this example, the bias magnetic field vector V0 in the absence of an external magnetic field is indicated by a solid line. The bias magnet is set so that the magnetic sensor 5 has a magnetic field intensity that reaches the saturation sensitivity region.

The bias magnetic field vector V0 changes to the bias magnetic field vector V1 according to the external magnetic field from right to left in FIG.

On the other hand, the bias magnetic field vector V0 changes to the bias magnetic field vector V2 according to the external magnetic field from the left to the right in FIG.

The bias magnetic field vector changes according to the change in magnetic flux density of the external magnetic field. The magnetic sensor 5 detects a change in the bias magnetic field vector and outputs an output signal (potential difference ΔV) corresponding to the detection result.

FIG. 5B shows the change characteristic of the output signal of the magnetic sensor 5 according to the change of the magnetic flux density of the external magnetic field.

As shown in FIG. 5B, a predetermined magnetic flux density ST is applied based on the bias magnetic field according to the

bias magnets

3A and 3B. The output in this case is set to an intermediate value, and the potential difference ΔV changes according to the change in the direction of the magnetic field applied to the magnetic sensor 5.

As the external magnetic field, the potential difference ΔV shifts to the ΔV1 side in accordance with the change in the magnetic flux density of the external magnetic field from right to left.

On the other hand, as the external magnetic field, the potential difference ΔV shifts to the ΔV2 side in accordance with the change in the magnetic flux density of the external magnetic field from the left to the right.

It is possible to detect the polarity (from which direction) of the magnetic field applied to the magnetic sensor 5 according to the increase / decrease of the potential difference ΔV from the intermediate value. Also, the saturation magnetic field strength can be increased by changing the magnetic strength of the

bias magnets

3A and 3B.

As will be described later, it is possible to detect the position of the float 20 based on a signal waveform (potential difference ΔV) corresponding to a change in the magnetic flux density of the external magnetic field.

FIG. 6 is a view for explaining the arrangement of the magnets 2 attached to the float 20 based on the first embodiment.

As shown in FIG. 6, here, a diagram when the float 20 is viewed from above is shown. Moreover, the magnet unit formed by the

magnets

2A and 2B is provided so as to face each other through the guide member. In this example, the N poles of the

magnets

2A and 2B are provided so as to face each other. It is also possible to arrange the south poles of the

magnets

2A and 2B so as to face each other. A magnetic sensor 5 is disposed between the opposing

magnets

2A and 2B.

With this arrangement, the direction of magnetic force is in the direction along the guide member (the up-and-down direction of the float 20), and the magnetic component in the direction perpendicular to the direction along the guide member is canceled. Preferably, the magnetic sensor 5 is arranged so that the center of the magnetic sensor 5, in other words, the center of the region where the magnetoresistive element MR is formed is located between the opposing magnets 2 </ b> A and 2 </ b> B. In this case, even if the float 20 rotates, there is almost no change in the direction of magnetic force and magnetic flux density, and the magnetic sensor 5 can accurately measure the amount of displacement of the magnetic flux density.

In addition, as long as a parallel magnetic field can be applied to the line on which the magnetic sensors 5 are arranged, the

magnets

2A and 2B may not be disposed so that the same poles face each other.

FIG. 7 is a view for explaining the layout of the

magnets

2A and 2B attached to the float 20 and the plurality of magnetic sensors 5 according to the first embodiment.

As shown in FIG. 7,

magnets

2A and 2B form a set of magnet units.
The magnet units formed by the

magnets

2A and 2B are arranged so that the N poles face each other.

In this example, a case where three magnetic sensors 5PA to 5PC (collectively referred to as magnetic sensors 5) are provided as the plurality of magnetic sensors 5 is shown.

Here, the distance between the centers of the magnetic sensors 5 in the up and down direction is the first length. Further, the distance in the horizontal direction between the facing surface of the magnet 2A or the magnet 2B and the center of the magnetic sensor 5, in other words, half of the distance between the facing surfaces of the magnet 2A and the magnet 2B is set to the second length. To do. In this example, the first length is set longer than the second length.

Specifically, when the distance in the horizontal direction is the distance a, the distance between the adjacent magnetic sensors 5 in the ascending / descending direction is set to an interval twice the distance a.

Also, when one of the two adjacent magnetic sensors 5 is positioned at the end of the magnet 2A in the up-and-down direction, the other of the adjacent magnetic sensors 5 is set to be positioned at the center in the up-and-down direction of the magnet 2A. That is, the length of the magnet 2A and the magnet 2B in the ascending / descending direction is set to twice the distance between the centers of the adjacent magnetic sensors 5 in the ascending / descending direction, that is, four times the distance a.

The magnetic sensor 5 is attached to the guide member along the raising / lowering direction.
In this example, the case where the three magnetic sensors 5PA to 5PC are arranged to detect the position of the float 20 will be described, but the same applies to the case where a plurality of magnetic sensors are arranged.

In this example, for example, as the position of the float 20, the center in the ascending / descending direction of the magnet 2A and the magnet 2B is set as a reference position (center point). In this case, the case where the magnetic sensor 5PB is located at the reference position (center point) is shown.

The three magnetic sensors 5PA to 5PC are arranged so that the bias magnetic field vectors of the magnetic sensors are parallel to the horizontal direction. In this example, the case where the direction of the bias magnetic field vector is the same as the horizontal direction from the magnet 2B to the magnet 2A will be described. However, the present invention is not limited to this and is the same as the horizontal direction from the magnet 2A to the magnet 2B. You may make it become a direction.

The white arrows in the horizontal direction of the paper shown in each of the magnetic sensors 5PA to 5PC indicate the maximum magnetic sensing direction of the magnetic sensor. In addition, a horizontal arrow pointing downward in each of the magnetic sensors 5PA to 5PC indicates a magnetic field generated by a bias magnet. However, description up to rotation of the bias magnetic field by the magnetic field of the float magnet is omitted.

FIG. 8 is a diagram for explaining the relationship with the magnetic sensor when the position of the float 20 based on the first embodiment is changed by the lifting / lowering operation.

In this example, a case where the float 20 changes from the right to the left in FIG. 8 (ascending direction as an example) will be described. In FIG. 8, the illustration of the change of the bias magnetic field vector V0 to the V1 side or the V2 side is omitted.

FIG. 8A shows a case where the float 20 moves up and approaches the magnetic sensor 5PA (state S0).

The magnetic sensor 5PA is affected by the magnetic field (lines of magnetic force) generated by the

magnets

2A and 2B of the float 20. Specifically, the magnetic sensor 5PA is affected by a magnetic field from right to left as the magnetic lines of force of the

magnets

2A and 2B. Therefore, the bias magnetic field vector V0 of the magnetic sensor 5PA changes to the bias magnetic field vector V1 side. The potential difference ΔV decreases as the bias magnetic field vector changes. The other magnetic sensors 5PB and 5PC are also affected by the magnetic field from right to left as the magnetic lines of force of the

magnets

2A and 2B. The potential difference ΔV decreases as the bias magnetic field vector V1 changes.

FIG. 8 (B) shows the case where the float 20 has further increased by the distance 2a (state S1) from FIG. 8 (A).

The magnetic sensor 5PA is in a state of being positioned on the center line between the float 20 and the

magnets

2A and 2B. In this example, this state is the initial state.

The magnetic sensor 5PB is affected by the magnetic field from right to left as the magnetic lines of force of the

magnets

2A and 2B. Therefore, the bias magnetic field vector V0 of the magnetic sensor 5PB changes to the bias magnetic field vector V1 side. The potential difference ΔV decreases as the bias magnetic field vector changes. The other magnetic sensor 5PC is also affected by the magnetic field from right to left as the magnetic lines of force of the

magnets

FIG. 8 (C) shows the case where the float 20 has further increased by the distance 2a (state S2) from FIG. 8 (B).

magnets

2A and 2B. Specifically, the magnetic sensor 5PA is affected by a magnetic field from left to right as the magnetic lines of force of the

magnets

2A and 2B. Therefore, the bias magnetic field vector V0 of the magnetic sensor 5PA changes toward the bias magnetic field vector V2. The potential difference V increases as the bias magnetic field vector V2 changes.

The magnetic sensor 5PB is in a state of being located on the center line between the

magnets

2A and 2B. Therefore, it is an initial state.

The magnetic sensor 5PC is affected by the magnetic field generated by the

magnets

2A and 2B. Specifically, the magnetic sensor 5PC is affected by a magnetic field from right to left as the magnetic lines of force of the

magnets

FIG. 8D shows the case where the float 20 has further increased the distance 2a from FIG. 8C (state S3).

The magnetic sensor 5PB is affected by the magnetic field (lines of magnetic force) generated by the

magnets

2A and 2B. Specifically, the magnetic sensor 5PB is affected by a magnetic field from left to right as the magnetic lines of force of the

magnets

2A and 2B. Therefore, the bias magnetic field vector V0 of the magnetic sensor 5PB changes to the bias magnetic field vector V2. The potential difference ΔV increases as the bias magnetic field vector V2 changes.

The magnetic sensor 5PA is affected by the magnetic field from left to right as the magnetic lines of force of the

magnets

2A and 2B. Since the influence of the magnetic field is small, the change toward the bias magnetic field vector V2 is small.

The magnetic sensor 5PC is in a state located on the center line between the

magnets

2A and 2B. Therefore, it is an initial state.

FIG. 8 (E) shows the case where the float 20 has further increased by the distance 2a (state S4) from FIG. 8 (D).

The magnetic sensor 5PC is affected by the magnetic field (lines of magnetic force) generated by the

magnets

2A and 2B. Specifically, the magnetic sensor 5PC is affected by a magnetic field from left to right as the magnetic lines of force of the

magnets

2A and 2B.

Therefore, the bias magnetic field vector V0 of the magnetic sensor 5PC changes to the bias magnetic field vector V2. The potential difference ΔV increases as the bias magnetic field vector V2 changes.

In the magnetic sensors 5PA and 5PB, a case where a magnetic field is applied in the up-and-down direction by the magnetic field generated by the

magnets

2A and 2B is shown. Specifically, the magnetic sensors 5PA and 5PB are affected by a magnetic field from left to right as a magnetic field (lines of magnetic force) generated by the

magnets

2A and 2B. Since the influence of the magnetic field is reduced according to the distance, the change to the bias magnetic field vector V2 side is reduced.

FIG. 8 (F) shows a case where the float 20 further increases the distance 2a from FIG. 8 (E) (state S5).

In the magnetic sensors 5PA, 5PB, and 5PC, a magnetic field is applied in the up and down direction by the magnetic field generated by the

magnets

2A and 2B. Specifically, the magnetic sensors 5PA, 5PB, and 5PC are affected by a magnetic field from left to right as a magnetic field (lines of magnetic force) generated by the

magnets

2A and 2B. Since the influence of the magnetic field is reduced according to the distance, the change to the bias magnetic field vector V2 side is reduced. The same applies thereafter.

FIG. 9 is a diagram for explaining output signal waveforms of a plurality of magnetic sensors following the lifting / lowering operation of the float 20 based on the first embodiment.

As shown in FIG. 9, the positional relationship between the states S0 to S5 and the output signal relationship are shown.
For example, focusing on the magnetic sensor 5PA, a signal corresponding to the magnetic flux density of the external magnetic field received by the magnetic sensor 5PA is output.

As the float 20 approaches the magnetic sensor 5PA, the magnetic sensor 5PA is affected by the magnetic field from right to left as the magnetic lines of force of the

magnets

2A and 2B. Therefore, the bias magnetic field vector V0 of the magnetic sensor 5PA changes to the bias magnetic field vector V1 side. The potential difference ΔV decreases as the bias magnetic field vector V1 changes. The other magnetic sensors 5PB and 5PC are also affected by the magnetic field from the right to the left as the magnetic lines of force of the

magnets

2A and 2B, so that the potential difference ΔV decreases as the bias magnetic field vector V1 changes.

In the state S0, the case where the bias magnetic field vector changes according to the external magnetic field received by the magnetic sensor 5PA and becomes the minimum as an output signal (potential difference ΔV) is shown.

In the state S1, the magnetic sensor 5PA is in an initial state located on the center line between the

magnets

2A and 2B. In this example, the voltage of the output signal (potential difference ΔV) in the initial state is an intermediate value. (Intermediate voltage).

In the state S2, the case where the output signal becomes maximum when the bias magnetic field vector of the magnetic sensor 5PA changes to the bias magnetic field vector V2 side is shown.

In the state S3, the magnetic sensor 5PA shows a case where the output signal (potential difference ΔV) decreases.

After the state S4, the case where the output signal of the magnetic sensor 5PA changes based on the external magnetic field that changes according to the distance is shown.

Further, focusing on the magnetic sensor 5PB, a waveform obtained by shifting the output signal of the magnetic sensor 5PA by a distance 2a is shown. Focusing on the magnetic sensor 5PC, a waveform obtained by shifting the output signal of the magnetic sensor 5PB by a distance 2a is shown.

FIG. 10 is an image view in which the predetermined area of FIG. 9 is enlarged.
As shown in FIG. 10, here, output signal waveforms of a plurality of magnetic sensors 5PA and 5PB in the hatching area of FIG. 9 are shown as the predetermined area.

The output signal waveforms of the magnetic sensors 5PA and 5PB can be modeled (approximated) in the horizontal component (in the up-and-down direction) of the magnetic vector P of the external magnetic field that changes along a circle, which will be described later, when the intermediate voltage is used as a reference. Is possible.

Specifically, it is possible to detect a signal waveform whose phase is shifted by 90 ° as an electrical signal output from two adjacent magnetic sensors.

In this example, since the phase is shifted by 90 °, one output signal (electric signal) can be represented by a sine wave (sin θ) and the other output signal (electric signal) can be represented by a cosine wave (cos θ). Then, the angle θ of the magnetic vector P of the external magnetic field is calculated based on the two output signals (electric signals).

In the present embodiment, an electrical signal output from two adjacent magnetic sensors among the output signals of a plurality of magnetic sensors is detected to calculate the angle of the magnetic vector of the external magnetic field, and the calculated angle of the magnetic vector The position of the float is detected based on the above.

FIG. 11 is a diagram schematically illustrating the relationship between the magnetic sensor 5 and the magnetic vector P based on the first embodiment.

FIG. 11 shows magnetic vectors with respect to the lifting / lowering direction of the float 20 with respect to the magnetic sensors 5PA and 5PB when the state S1 is shifted to the state S2. Here, the raising / lowering direction is a direction along the X-axis. As an example, the magnetic vector P indicates the direction of the magnetic field lines of the magnetic field generated by the N pole of the magnet 2A.

In order to simplify the explanation, the magnetic field lines of the magnetic field generated by the N pole of the magnet 2B are omitted, but the component perpendicular to the ascending / descending direction of the magnetic vector P is the magnetic field generated by the N pole of the magnet 2B. It is canceled out by the magnetic vector of the magnetic field lines. Therefore, the external magnetic field for the magnetic sensors 5PA and 5PB has only the up-down direction component. As described above, the bias magnetic field vector in each magnetic sensor 5 changes according to the external magnetic field.

As an example, since the magnitude of the magnetic vector that is an external magnetic field and the magnetic flux density (potential difference ΔV) are correlated, the output signal detected by the magnetic sensor 5PA in the up-and-down direction is Psinθ, and the output signal detected by the magnetic sensor 5PB Can be represented by -Pcosθ. And it calculates as angle (theta) of the magnetic vector P based on two output signals (electrical signal).

Specifically, tan θ (Psin θ / | −P cos θ |) is calculated based on two output signals (electrical signals), and angle information θ is calculated by calculating arctan θ.

Note that the amplitude value P of the sine wave Psinθ and the cosine wave Pcosθ is canceled by calculating tanθ.

The above process is a process executed by the detection circuit 50. Specifically, the calculation process is executed in the MPU 40.

The position of the float 20 changes by a distance 2a corresponding to a change of 0 ° to 90 ° as the angle information θ of the magnetic vector.

For example, as a position of the float 20, the center in the ascending / descending direction of the

magnets

2A and 2B is set as a reference position (center point) as an example. In this case, the reference position (center point) of the float 20 shown in the state S1 in FIG. 8B is the same position as the position of the magnetic sensor 5PA.

In this example, the angle information θ of the magnetic vector is calculated using the electrical signals of the magnetic sensor 5PA and the magnetic sensor 5PB, and the positional relationship is determined. For example, when the angle information θ is calculated as 45 °, it is detected that the reference position (center point) of the float is at a position moved a distance a from the position of the magnetic sensor 5PA to the magnetic sensor 5PB side. Is possible.

In the present example, the case where the positional information from the magnetic sensor 5PA is determined by calculating the angle information θ of the magnetic vector using the electrical signals of the magnetic sensors 5PA and 5PB has been described. It is also possible to determine the positional relationship from Of course, it is possible to determine the positional relationship from the magnetic sensor 5PB by calculating the angle information θ of the magnetic vector using the electrical signals of the magnetic sensors 5PB and 5PC according to the same method. The same applies to other systems.

FIG. 12 is a diagram illustrating the accuracy of the angle information θ based on the first embodiment.
FIG. 12A shows arctan θ when one output signal (electrical signal) is set to Pcosθ and the other output signal (electrical signal) is set to Psinθ when the angle θ is changed from 0 ° to 90 °. And a comparison with the reference value is shown.

As a result of simulation, there is almost no difference from the reference value.
Also, as the accuracy of the angle obtained as the difference between the simulation results from the reference value, there is shown a case where there is only a deviation of ± 10 ° with respect to the reference value as shown in FIG. The position of the high float 20 can be detected.

FIG. 13 is a flowchart for explaining the detection method of the liquid level detection apparatus 1 based on the first embodiment.
As shown in FIG. 13, two signals based on a predetermined combination of signal relationships are extracted (step SP2). In this example, a signal (first signal) of a magnetic sensor that exceeds the intermediate voltage from the intermediate voltage or less and a signal of the adjacent magnetic sensor (second signal) that outputs a signal of the intermediate voltage or less at that time. ) Are extracted. In this example, the intermediate voltage is set to the voltage of the output signal in the initial state as an example. Specifically, as described with reference to FIG. 8, for example, the magnetic sensor 5PA is intermediately measured by measuring the voltage in advance in the state where the magnetic sensor 5PA is positioned at the center of the

magnet

2A or 2B (FIG. 8B). It is possible to set the voltage. There are various methods for setting the intermediate voltage, and the method is not limited to the method. For example, the intermediate voltage may be set to an intermediate value between the maximum value and the minimum value of the peak value.

Then, two electrical signals in the hatched area described with reference to FIG. 9 are extracted.
Next, the angle θ of the magnetic vector is calculated based on the two extracted signals (step SP4). Specifically, one output signal (electric signal) of the two electric signals is set to Pcosθ, and the other output signal (electric signal) is set to Psinθ, and magnetism is performed based on the two output signals (electric signals). The angle θ of the vector is calculated. Then, tan θ is calculated based on the two output signals (electrical signals), and the angle information θ is calculated by calculating arctan θ.

Next, the position of the float 20 is calculated based on the angle θ of the magnetic vector (step SP6). Based on the calculated angle information θ, the reference position (center point) of the float 20 is calculated from the position of the magnetic sensor. For example, when the angle information θ is calculated as 45 ° as described above, the reference position (center point) of the float has moved to the magnetic sensor 5PB side by a distance a from the position of the magnetic sensor 5PA. It is possible to detect that it is in position.

Then, the process ends (END).
The liquid level detection device 1 according to the first embodiment can detect the position of the float 20 with high accuracy based on two electrical signals. With this method, there is no need to provide a switching circuit for switching signals, the circuit configuration can be simplified, and the size can be reduced.

In addition, the output signal may change due to changes in the characteristics of the magnet or the magnetic sensor following the change in the environmental temperature. In the angle calculation, tanθ (Psinθ / Pcosθ) of the two output signals is calculated. Therefore, the fluctuation amount according to the environmental temperature is canceled out, so that the error due to the influence of the environmental temperature is reduced, and the position detection with high accuracy is possible.

In this example, the distance in the horizontal direction (second length) between the magnet 2A and the magnetic sensor 5 is set to the distance a, and the distance in the ascending / descending direction of the adjacent magnetic sensor 5 (first A case has been described in which the length) is set to be twice the distance a. However, the magnetic sensor 5 can be detected by changing the magnetic force of the external magnetic field by adjusting the dimensions of the

magnets

2A, 2B, etc. (the lengths of the

magnets

2A, 2B in FIG. 7 in the horizontal direction and the depth direction). It is possible to appropriately change the design of the distance in the ascending / descending direction between the magnetic sensors 5 while improving the characteristics. Similarly, the lengths of the magnet 2A and the magnet 2B in the ascending / descending direction can be appropriately changed in design.

It is possible to reduce the number of magnetic sensors 5 attached to the guide member by extending the distance in the up-and-down direction of the magnetic sensor 5 (however, the minimum number of magnetic sensors is two), and the circuit configuration can be simplified and miniaturized. Is possible. In addition, the cost of the liquid level detection device can be reduced.

(Embodiment 2)
In the second embodiment, the configuration of the liquid level detection device 1 that detects the position of the float 20 with high accuracy will be described.

FIG. 14 is a circuit configuration diagram of the liquid level detection device 1 based on the second embodiment.
As shown in FIG. 14, liquid level detection device 1 based on Embodiment 2 includes a plurality of magnetic sensors 5 and detection circuit 50 #. In this example, a case where n magnetic sensors are provided is shown.

The detection circuit 50 # includes an A / D circuit 60 that is an analog / digital conversion circuit, a P / S conversion circuit 30 that is a parallel / serial conversion circuit, and an MPU (Micro-processing unit) 40 # that executes arithmetic processing. including.

The MPU 40 # detects the position of the float 20 by performing arithmetic processing on signals from a plurality (n) of magnetic sensors 5 input from the P / S conversion circuit 30. Specifically, MPU 40 # further includes a correction unit 45.

The correction unit 45 corrects the signal from the magnetic sensor 5.
In this example, an electric signal output from two adjacent magnetic sensors among the corrected output signals of the plurality of magnetic sensors is detected to calculate the angle of the magnetic vector of the external magnetic field, and the calculated magnetic vector The position of the float is detected based on the angle.

FIG. 15 is a diagram illustrating signals before and after correction of the magnetic sensors 5PA and 5PB.

FIG. 15 (A) shows output signals detected by the magnetic sensors 5PA and 5PB before correction. As described above, the output signal of the magnetic sensor 5PA is represented by Psinθ, and the output signal of the magnetic sensor 5PB is represented by -Pcosθ. Here, a signal obtained by inverting the output signal of the magnetic sensor 5PB is shown.

If the ratio of the signal waveform of the output signal is the same as the ideal ratio of sin wave and cos wave, it is possible to detect the position without error, but the ratio of the signal waveform of the actual output signal and the ideal ratio Since there is a deviation between the ratio of the sine wave and the cos wave, the angular accuracy varies.

In this example, it is possible to suppress the deviation and improve the angle accuracy by executing a correction process that powers the output signal with a predetermined coefficient.

In this example, the distance in the up-and-down direction (first length) between the magnetic sensors 5 is set to be longer than the horizontal distance (second length) between the magnet 2A and the magnetic sensor 5. . Therefore, since the change in the magnetic vector P of the external magnetic field with respect to the moving distance becomes smaller as the distance in the vertical direction between the magnetic sensors 5 becomes longer than the horizontal distance between the magnet 2A and the magnetic sensor 5, an ideal sin wave is obtained. A concave signal waveform is detected below the ideal line of the cos wave.

Therefore, in order to correct the signal waveform that is concave downward, a correction process that performs a power root with a predetermined coefficient is executed.

FIG. 15B shows the output signals of the corrected magnetic sensors 5PA and 5PB.
The angle of the magnetic vector of the external magnetic field is calculated based on the corrected signal, and the position of the float is detected based on the calculated angle of the magnetic vector.

FIG. 16 is a diagram for explaining the accuracy of the angle information θ based on the second embodiment.
FIG. 16A shows arctanθ when one output signal (electrical signal) is set to Pcosθ and the other output signal (electrical signal) is set to Psinθ when the angle θ is changed from 0 ° to 90 °. And a comparison with the reference value is shown.

As a result of the simulation, there is almost no difference from the reference value.
Further, as shown in FIG. 16B, the accuracy of the angle shows a case where there is only a deviation of ± 2 ° from the reference value, and the position of the float 20 can be detected with higher accuracy.

By correcting the output signal output from the magnetic sensor 5 by the liquid level detection device 1 according to the second embodiment, the position of the float 20 can be detected with high accuracy, and the circuit configuration can be simplified. In addition, it is possible to reduce the size.

That is, the angle accuracy can be improved by changing the

magnets

2A and 2B and the magnetic sensor 5 from the positional relationship shown in FIG. Specifically, for example, the length of the magnet 2A and the magnet 2B in FIG. 7 is changed to a length that is smaller than twice the distance between the centers of adjacent magnetic sensors 5 in the lift direction. In addition, it is possible to improve the angle accuracy by executing the correction process.

In the above correction processing, correction processing has been described in which the root of the power is increased by a predetermined coefficient to correct the signal waveform. However, the length of the magnet 2A and the magnet 2B in the vertical direction and the horizontal direction of the magnet 2A and the magnet 2B are described. Depending on the relationship between the lengths, a correction process in which power is raised by a predetermined coefficient may be effective. In that case, it is also possible to improve the angular accuracy by suppressing the deviation by executing a correction process of raising the output signals of the magnetic sensors (AMR) 5PA and 5PB by a predetermined coefficient. That is, by raising the value of the AMR output by a predetermined coefficient, the signal waveform ratio can be made close to the ideal ratio of the sin waveform and the cos waveform. Then, by using the above-described equation for the angle θ, it is possible to derive an angle with improved accuracy.

FIG. 17 is a diagram illustrating a layout of magnets and magnetic sensors 5PA, 5PB, and 5PC attached to the float 20 according to another embodiment.

As shown in FIG. 17, a magnet unit different from the

magnets

2A and 2B is provided. In this example,

magnets

2E and 2F are provided as separate magnet units.

Magnets

2E and 2F are arranged so that the south poles face each other. With this configuration, the position of the float 20 can be detected based on the same method as described above.

Magnets

2A and 2E and

magnets

2B and 2F may be formed separately or integrally.

In this embodiment, the AMR element is disclosed, but the present invention is not limited thereto. Any magnetic sensor that outputs linearly with respect to the magnetic field intensity and can determine the polarity is applicable.

The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present disclosure is shown not by the above description but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 liquid level detection device, 2 magnets, 5, 5 PA to 5 PC magnetic sensor, 10 guide, 20 float, 30 P / S conversion circuit, 40, 40 # MPU, 45 correction unit, 50, 50 # detection circuit, 60 A / D circuit.

Claims

A float that moves up and down following the liquid level;
At least two magnets attached to the float and having the same poles disposed opposite to each other;
A guide member that guides the raising and lowering of the float;
A plurality of magnetic sensors that are attached to the guide member, detect a magnetic flux density that changes in accordance with an elevation position of the magnet, and output an electrical signal corresponding to the magnetic flux density;
A detection circuit that detects the position of the float based on electrical signals output from the plurality of magnetic sensors,
A distance between adjacent magnetic sensors in the ascending / descending direction is set to a first length,
The length of the magnet and the magnetic sensor in the horizontal direction perpendicular to the elevation direction is set to a second length,
The first length is longer than the second length,
The said detection circuit is a liquid level detection apparatus which detects the position of the said float based on the electrical signal output from two adjacent magnetic sensors among these magnetic sensors.
2. The liquid level detection device according to claim 1, wherein each magnetic sensor includes a bias magnet that applies a bias magnetic field in the horizontal direction.
The liquid level detection device according to claim 1, wherein each of the magnetic sensors outputs an electric signal based on a magnetic vector of a magnetic force line generated by the magnet.
2. The liquid surface according to claim 1, wherein the detection circuit extracts an electrical signal output from two adjacent magnetic sensors based on a comparison with an intermediate voltage among electrical signals output from the plurality of magnetic sensors. Detection device.
The detection circuit includes:
Calculate angle information when one of the two extracted electrical signals is a sine wave and the other is a cosine wave,
The liquid level detection apparatus according to claim 4, wherein the position of the float is detected based on the calculated angle information.
Each magnetic sensor
First to fourth magnetoresistive elements to which a bias magnetic field vector generated by the bias magnet is applied;
3. The liquid level detection apparatus according to claim 2, further comprising: an output circuit that outputs an electrical signal corresponding to a change in resistance value of the first to fourth magnetoresistive elements based on a change in the bias magnetic field vector.
The liquid level detection device according to claim 6, further comprising a correction circuit for correcting an electric signal output from the output circuit.
The liquid level detection device according to claim 7, wherein the correction circuit raises the electric signal output from the output circuit to a power root or a power with a predetermined coefficient.
The liquid level detection device according to any one of claims 1 to 8, wherein each of the magnetic sensors is provided so as to output linearly with respect to a magnetic field intensity so that the polarity can be discriminated.