JPH08285511A - Shaft displacement sensor and sensor of amount of opening and closing of valve element of valve device - Google Patents

Abstract

PURPOSE: To detect displacement of a shaft magnetically and thereby to attain improvement in working properties and in environmental resistance and measuring accuracy by disposing a magnetoresistance element so that the maximum sensitivity is set in the direction intersecting the direction of magnetic poles of a magnet body at a right angle practically. CONSTITUTION: A magnetoresistance element 18 is provided at a position where it intersects the direction of magnetic poles of a magnet body 15 at a right angle practically and is apart from the magnet body 15 by a prescribed distance. When a shaft 3 is rotated by a rotating operation of a handle 6, a valve element is displaced vertically. The amount of opening and closing of the valve element corresponds to the amount of displacement of the magnet body 15. Since a magnetic field in the direction intersecting the direction of the magnetic poles of the magnet body 15 perpendicularly becomes zero, in the element 18, at a position located at 1/2 practically between the magnetic poles of the magnet body 15, an output voltage due to the magnetic field is not generated at this time. By setting this point at 1/2 of the whole stroke of the magnet body 15, accordingly, the output voltage of the element 18 corresponding to the amount of opening and closing of the valve element is obtained. By processing signals in a circuit board 20 and by transferring them to a concentrated control chamber, the amount of opening and closing of the valve element can always be known at a remote place.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shaft displacement sensor for detecting shaft displacement, and for example, for detecting displacement of a shaft for opening and closing a valve body of a flow control valve device for controlling a flow rate of liquid or gas, The present invention relates to a valve body opening / closing amount sensor of a valve device that detects the opening / closing amount of the valve body.

[0002]

2. Description of the Related Art Conventionally, as a structure for detecting the opening / closing amount (opening / closing state) of a valve body of a flow control valve device for controlling the flow rate of liquid or gas, there are three structures, mechanical, mechanical-electrical and electrical. Has been taken.

In a configuration in which the opening / closing amount is mechanically detected, for example, "open" and "closed" are displayed on a handle portion for opening / closing the valve body, and an intermediate display between "open" and "closed" is displayed. The approximate opening / closing amount is displayed so that the opening / closing amount of the valve body can be confirmed by the position of the handle.

Further, in the construction in which the opening / closing amount is detected mechanically and electrically, for example, an arm that moves in accordance with the opening / closing operation of the valve body is provided, and a position to be detected (for example, a fully opened or fully closed state of the valve body). A microswitch is attached to the arm, and the opening / closing amount of the valve body is detected by the operation of the microswitch by the arm.

Further, in the configuration for electrically detecting the opening / closing amount, a proximity sensor such as a high-frequency oscillation type is used instead of the microswitch to detect the opening / closing amount of the valve element.

[0006]

However, each of the conventional configurations for detecting the opening / closing amount of the valve body has the following problems.

That is, in the structure for mechanically detecting the opening / closing amount of the valve element, since the opening / closing amount of the valve is confirmed by the position of the handle, the opening / closing amount can be confirmed only at the installation site of the valve device. It is very inconvenient and inferior in usability.

Further, since the structure for detecting the opening / closing amount of the valve element mechanically and electrically has a contact structure, considering that most of the valve devices are used outdoors, there is concern about the environment resistance.

Further, in the structure that mechanically and electrically detects the opening / closing amount of the valve element, only the points can be detected by the microswitch and the proximity sensor, respectively.
For example, two switches and sensors are required to detect the "fully open" and "fully closed" states, and to detect the intermediate state between "fully open" and "fully closed". ,
As many switches and sensors are required as the number of detection points, which is disadvantageous in terms of equipment and cost.

In view of the above conventional problems, the present invention is directed to, for example, a shaft displacement sensor for detecting a shaft displacement and a shaft for opening and closing a valve body of a flow control valve device for controlling a flow rate of liquid or gas. To provide a valve body opening / closing amount sensor of a valve device for detecting the displacement of the valve body to detect the opening / closing amount of the valve body,
Improved usability due to the configuration that magnetically detects axial displacement,
The object of the present invention is to improve the environment resistance, improve the facility and cost, and improve the detection accuracy.

[0011]

Therefore, an axial displacement sensor according to a first aspect of the present invention has a displacement member that is displaced in the axial direction of the shaft by the rotational movement of the shaft, and a magnetic pole in the axial direction. ,
A magnet body that is displaced according to the displacement of the displacement member; a magnetoresistive element that is formed of a ferromagnetic thin film with a built-in bias magnet and that is provided at a position substantially orthogonal to the direction of the magnetic poles of the magnet body and is separated from the magnet body by a predetermined distance; A detection circuit that processes a signal output from the magnetoresistive element to detect a displacement of the shaft, and the magnetoresistive element is arranged such that its maximum sensitivity direction is orthogonal to the magnetic pole direction of the magnet body. Further, the magnetic field is arranged so that the direction of the bias magnetic field of the magnetoresistive element is substantially coincident with the direction of the magnetic pole of the magnet body.

According to a second aspect of the present invention, there is provided a valve element opening / closing amount sensor for a valve device, wherein a shaft for rotating and opening and closing the valve body of the valve device and a valve device main body in which the valve body is housed are connected to each other. , A shaft support portion that rotatably supports the shaft in a state where the end portion opposite to the valve body is protruded, and a protruding end portion of the shaft from the shaft support portion, and the valve is rotated by rotating the shaft. A handle for opening and closing a body, the handle being displaced in the axial direction of the shaft by a rotating operation, and being fitted and inserted between the handle and the shaft support portion at the end protruding from the shaft support portion of the shaft. , Axially slidably fitted in the housing fixedly attached to the shaft support portion and the handle at the protruding end portion of the shaft from the shaft support portion and the housing, and displacing the handle. The pressing member that is displaced by being pressed by the shaft and the shaft in the housing portion provided in the housing. A magnet body that is slidable in the direction and has a magnetic pole in the axial direction and that is slid by being pressed in the axial direction by the pressing member, and the magnet body is always elastic in a direction opposite to the pressing slide direction. A bias magnet built-in type strong member which is arranged at a position substantially perpendicular to the direction of the magnetic poles of the magnet body and is separated from the magnet body by a predetermined distance, and is attached to an attachment portion provided in the housing. A magnetoresistive element composed of a magnetic thin film;
A detection circuit for processing a signal output from the magnetoresistive element to detect the opening / closing amount of the valve element from the displacement of the shaft, and the magnetoresistive element having the maximum sensitivity direction of the magnet body. It was arranged so as to be orthogonal to the magnetic pole direction and the direction of the bias magnetic field of the magnetoresistive element substantially coincided with the direction of the magnetic pole of the magnet body.

[0013]

According to the first aspect of the invention, when the shaft is rotated, the displacement member is displaced in the axial direction of the shaft, and the magnet body is displaced according to the displacement of the displacement member.

Here, the change in magnetic flux density in the vicinity of the magnet body is
The direction that is different from the direction from the magnet body and is inversely proportional to the square of the general distance is the direction orthogonal to the magnetic pole surface. In the direction orthogonal to the magnetic pole direction, the magnetic field becomes zero at a position of approximately 1/2 between the magnetic poles, but before and after that, although the magnetic field is weak, a change in magnetic flux density approximately proportional to the moving distance can be obtained.

The magnetoresistive element arranged with the maximum sensitivity direction oriented in a direction substantially orthogonal to the magnetic pole direction of the magnet body has a position of approximately ½ between the magnetic poles of the magnet body and is in a direction orthogonal to the magnetic pole direction of the magnet body. Since the magnetic field is zero, no output voltage due to the magnetic field is generated at this time.

Therefore, if this point is set to 1/2 of the total stroke of the magnet body, the output voltage of the magnet body corresponding to the displacement amount of the shaft can be obtained, and the displacement amount of the shaft can be always grasped.

According to the second aspect of the invention, when the valve body is opened and closed, the handle is rotated to adjust the opening and closing amount of the valve body according to the rotation amount. In this case, when the shaft is rotated by rotating the handle, the valve body is displaced.

Therefore, when the handle is rotated, the handle is displaced along with the displacement of the valve body, and the pressing member is displaced in the same direction. Due to the displacement of the pressing member, the magnet body is displaced in the same direction by the elastic biasing force of the elastic member or against the elastic biasing force.

In this case, the opening / closing amount of the valve body and the displacement amount of the magnet body correspond to each other, and by detecting the displacement amount of the magnet body, the opening / closing amount of the valve body can be determined in the same manner as the invention of claim 1. Can be detected.

In particular, according to the first and second aspects of the invention, among the magnetoresistive elements, the one having a built-in bias magnet has a small hysteresis, and a linear output voltage with respect to the applied magnetic field is obtained in the weak magnetic field region. It is known that Therefore, by using the MR element with the built-in bias magnet, a linear output voltage corresponding to the displacement of the magnet body can be obtained.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings. 1 and 2 show the configuration of an opening / closing amount sensor for a flow control valve, which is a common embodiment of the inventions described in claims 1 and 2. In these figures, the flow control valve device 2 interposed in the pipe 1 is provided with a valve body (not shown) that can be opened and closed in the main body of the valve device 2.

A shaft 3 is connected to the valve body to open and close the valve body by rotating the valve body. This valve body has a mechanism that when the shaft 3 is rotated about 1.5 times, it is displaced by about 2 mm in the vertical direction.
The vertical displacement amount of is 2 mm.

The main body of the valve device 2 to which the valve body is attached is
A shaft support portion is provided so as to rotatably support the shaft 3 in a state where the opposite end of the shaft 3 is projected. This shaft support portion is provided with a pipe portion 4 and a nut 5 screwed onto the outer peripheral surface of the pipe portion 4.
Consists of

At the protruding end of the shaft 3 from the nut 5,
A handle 6 for rotating the shaft 3 to open and close the valve body is connected. In this case, the handle 6 is formed in a cylindrical shape with an open bottom surface, and the boss portion 6 protruding inward is formed at the center of the end wall.
A is integrally formed.

The central hole 6a of the boss portion 6A is formed in a square shape, and the central hole 6a is formed in the square portion 3 provided at the end of the shaft 3.
It is fitted to a. Further, a nut 7 is screwed onto the outer peripheral surface of the end of the shaft 3 protruding from the handle 6, whereby the handle 6 is fixedly attached to the end of the shaft 3.

Here, a housing 8 is fitted and inserted in a portion between the handle 6 and the nut 5 at the end portion of the shaft 3 protruding from the nut 5. The housing 8 has an inner cylindrical portion 8A.
And an outer cylinder portion 8B located apart from the outer peripheral surface of the inner cylinder portion 8A by a predetermined annular space. The inner cylinder portion 8A and the outer cylinder portion 8B.
Are connected by the end wall portion 8C.

The inner cylindrical portion 8A of the housing 8 is annularly stretched in the direction perpendicular to the axis from the inner surface of the lower small diameter portion 8a, the upper large diameter portion 8b, and the boundary between the small diameter portion 8a and the large diameter portion 8b. It is composed of a projecting flange portion 8c.

The inner peripheral surface of the small diameter portion 8a of the inner cylindrical portion 8A of the housing 8 is fitted and fixed to the outer peripheral surface of the nut 5, and the flange portion 8c is locked to the upper surface of the nut 5 via the wave washer 9. The wave washer 9 is provided to prevent the housing 8 and the nut 5 from rattling. In this case, between the inner periphery of the flange portion 8c of the inner cylindrical portion 8A and the outer periphery of the shaft 3 and between the inner periphery of the large diameter portion 8b and the outer periphery of the boss portion 6A of the handle 6, there are annular space portions A and B, respectively. Is formed. Further, the outer peripheral surface of the outer cylindrical portion 8B is superposed on the inner peripheral surface of the handle 6 through a gap.

Between the handle 6 at the end projecting from the nut 5 of the shaft 3 and the large diameter portion 8b of the inner cylindrical portion 8A of the housing 8, a pressing member that is axially pressed by the displacement of the handle 6 is displaced. The member 10 is slidably inserted in the axial direction. In this case, the pressing member 10 is composed of a bottomed tubular portion 10A in which a center hole 10a is formed, and a flange portion 10B extending from the outer periphery of the upper end of the tubular portion 10A in a direction perpendicular to the axis. Is on the outer periphery of the shaft 3, the outer peripheral portion of the tubular portion 10A is on the boss portion 6A of the handle 6, and the flange portion 10B.
Are slidably inserted into the large diameter portion 8b of the housing 8, respectively.

It should be noted that recessed grooves 11 are formed at a plurality of locations on the outer peripheral surface of the flange portion 10B of the pressing member 10.
The rotation preventing projections 12 formed on the inner peripheral surface of the inner cylindrical portion 8A of the housing 8 at a plurality of positions are engaged to prevent the pressing member 10 from rotating. Further, in the space portion B, a compression spring 13 which is locked to the bottom surface of the tubular portion 10A of the pressing member 10 and the upper end surface of the nut 5 is interposed, and the pressing member 10 is normally raised via the washer 14. Direction is elastically biased.

The washer 14 is for preventing wear when transmitting the vertical movement due to the rotation of the handle 6 to the pressing member 10.

A housing portion 17 provided in the housing 8
A magnet body 15 is provided which is housed so as to be slidable in the axial direction and has magnetic poles in the axial direction and which is slid by being pressed in the axial direction by the pressing member 10.

That is, the accommodating portion 17 is formed in a cylindrical shape having an open upper end at a portion of the inner cylindrical portion 8A of the housing 8 on the inner peripheral surface side, and the magnet body 15 is provided at the inner bottom portion of the accommodating portion 17. A compression spring 16 is interposed as an elastic member that normally elastically biases in a direction opposite to the pressing slide direction.

Therefore, the magnet body 15 includes the compression spring 16
The pressing member 10 facing the open upper surface of the storage portion 17 by the
When the pressing member 10 is moved downward, the pressing member 10 slides downward against the elastic biasing force of the compression spring 16.

On the other hand, at a position substantially perpendicular to the direction of the magnetic pole of the magnet body 15, the magnet body 15 is separated from the magnet body 15 by a predetermined distance (for example, 0.5).
mm to 10 mm) away from each other, and is attached to an attachment portion provided in the housing 8 and is a magnetoresistive element (hereinafter, referred to as MR) made of a ferromagnetic thin film with a built-in bias magnet.
18 is provided.

Here, the mounting portion extends from the outer peripheral surface of the inner cylindrical portion 8A of the housing 8 on both sides of the magnet housing 17 and is connected to the corresponding inner peripheral surface portion of the outer cylindrical portion 8B. The MR element 18 is electrically connected to both of the plate portions 19, and a circuit board 20 for processing a signal from the MR element 18 is attached to each of the plate portions 19.

A cord 21 for electrically supplying power to the circuit board 20 and transmitting a processing signal to a detection circuit provided in a centralized control room at a remote place is electrically connected to the circuit board 20. The MR element 18 has a maximum sensitivity direction orthogonal to the magnetic pole direction of the magnet body 15,
In addition, the bias magnetic field is arranged so that the direction thereof substantially coincides with the direction of the magnetic pole of the magnet body 15.

Next, the operation of the opening / closing amount sensor of the flow control valve having the above construction will be described. When the flow rate control is performed by the flow rate control valve, the handle 6 is rotated to adjust the opening / closing amount of the valve body according to the rotation amount. In this case, handle 6
When the shaft 3 is rotated by the rotating operation, the valve element is displaced in the vertical direction as described above.

Therefore, when the handle 6 is rotated, the handle 6 is displaced in the vertical direction as the valve body is displaced in the vertical direction, and the pressing member 10 is elastically biased by the compression spring 13 by its boss 6A, or It is displaced in the same direction against the elastic biasing force. Due to the displacement of the pressing member 10, the magnet body 15 is displaced in the same direction by the elastic biasing force of the compression spring 16 or against the elastic biasing force.

In this case, the opening / closing amount of the valve body and the displacement amount of the magnet body 15 correspond to each other, and by detecting the displacement amount of the magnet body 15, the opening / closing amount of the valve body can be detected.

The function of detecting the opening / closing amount of the valve body will be described in detail. The change in the magnetic flux density in the vicinity of the magnet body 15 differs depending on the direction from the magnet body 15, and the direction inversely proportional to the square of the general distance is the direction orthogonal to the magnetic pole surface. In the direction orthogonal to the magnetic pole direction, the magnetic field becomes zero at a position of approximately 1/2 between the magnetic poles, but before and after that, although the magnetic field is weak, a change in magnetic flux density approximately proportional to the moving distance can be obtained.

In the sensor for detecting the opening / closing amount of the valve element,
The MR element 18 arranged with the maximum sensitivity direction oriented in a direction substantially orthogonal to the magnetic pole direction of the magnet body 15 has a position of approximately ½ between the magnetic poles of the magnet body 15 in a direction orthogonal to the magnetic pole direction of the magnet body 15. Since the magnetic field is zero, no output voltage due to the magnetic field is generated at this time.

Therefore, if this point is set to 1/2 of the total stroke of the magnet body 15, the MR corresponding to the opening / closing amount of the valve body is set.
The output voltage of the element 18 is obtained, signal processing is performed by the circuit board 20, and the signal is transmitted to the central control room, so that the opening / closing amount of the valve body can be always grasped at a remote place.

According to the valve opening / closing amount sensor having such a configuration, the opening / closing amount can be confirmed even at the installation site of the valve device, which is very convenient and excellent in usability. In addition, since it does not have a contact structure, even if it is a valve device used outdoors, there is no environmental concern, and a single sensor detects the state of the intermediate point between "fully open" and "fully closed". Therefore, it is advantageous in terms of equipment and cost.

Further, according to the valve opening / closing amount sensor having such a configuration, as a result of using the MR element 18 having the built-in bias magnet, there are the following advantages. That is, as shown in FIG.
When the magnet body a is made to face a probe b of a Gauss meter and the magnet body a is displaced with respect to the probe b, the magnetic flux density is measured by a Gauss meter. When the magnet body a is displaced, the magnetic pole direction of the magnet body a is Magnet body a in a direction substantially orthogonal to
The magnetic flux density B at a point between both magnetic pole surfaces with respect to the displacement of 1 changes according to the distance d from the magnet a to the probe b and the displacement 1 of the magnet as shown in FIG.

On the other hand, among the MR elements used for the valve opening / closing amount sensor, which have a built-in bias magnet, the hysteresis is small, and a linear output voltage with respect to the applied magnetic field is obtained in the weak magnetic field region. Is known.
Therefore, if a bias magnet built-in type MR element is used instead of the probe b of the Gauss meter used for measuring the magnetic flux density in FIG. 3, a linear output voltage corresponding to the displacement of the magnet body can be obtained.

That is, as shown in FIG.
When the output voltage when the R element 18 is opposed to each other and the magnet body 15 is displaced with respect to the MR element 18 is measured, the output voltage (center voltage) is the distance d from the magnet body 15 to the MR element 18 and the magnet voltage. It changes as shown in FIG. 6 according to the displacement l of the body 15.

Therefore, in the valve opening / closing amount sensor shown in FIGS. 1 and 2, if the magnet body 15 and the MR element 18 are arranged in the same positional relationship as in the experimental apparatus shown in FIG. A linear output voltage corresponding to the displacement of the magnet body 15 associated with the displacement of the shaft 3 corresponding to the amount is obtained, and the displacement of the shaft 3 and thus the opening / closing amount of the valve body can be accurately detected from this output voltage.
The valve opening / closing amount sensor is an absolute detection sensor that always detects the rotation angle information of the shaft operating handle as a voltage signal corresponding to the angle information at that time, not by the addition method (incremental) from the reference point. Therefore, it is resistant to external noise, and a voltage signal corresponding to the angle information can be obtained immediately after restoration even in the case of a power failure.

In the above-mentioned valve body opening / closing amount sensor, the magnet body 15 is preferably a rare earth magnet having a small temperature coefficient.

[0050]

As described above, according to the first aspect of the invention, the direction of the magnetic pole of the magnet body which is displaced in accordance with the displacement of the displacement member which is displaced in the axial direction of the shaft by the rotational movement of the shaft is approximately the same. A structure in which a magnetic resistance element made of a ferromagnetic thin film with a built-in bias magnet and provided at a predetermined distance from the magnet body is provided at an orthogonal position, and a signal output from the magnetic resistance element is processed to detect a displacement of the shaft. And the magnetoresistive element with its maximum sensitivity direction orthogonal to the magnetic pole direction of the magnet body,
Moreover, since the bias magnetic field direction of the magnetoresistive element is arranged so as to substantially coincide with the direction of the magnetic poles of the magnet body, it is possible to improve usability and environmental resistance, and at the same time, in terms of equipment,
The cost can be improved. Especially, as a result of using the magnetoresistive element consisting of a ferromagnetic thin film with a built-in bias magnet, a linear output voltage corresponding to the displacement of the magnet body can be obtained, and the displacement of the axis is accurate from this output voltage. Can be detected.

According to the second aspect of the present invention, according to the displacement of the shaft operating handle and the pressing member, which is displaced in the axial direction of the shaft by the rotational motion of the shaft for rotating and opening and closing the valve body of the valve device. A magnetic resistance element made of a ferromagnetic thin film with a built-in bias magnet is provided at a position substantially orthogonal to the direction of the magnetic pole of the displacing magnet body, and the signal output from this magnetic resistance element is provided. The magnetic resistance element has a structure in which the axial displacement is processed to detect the opening / closing amount of the valve body, and the maximum sensitivity direction is perpendicular to the magnetic pole direction of the magnet body and the bias magnetic field of the magnetic resistance element is detected. Since it is arranged so that the direction of is almost the same as the direction of the magnetic pole of the magnet body, it is possible to always know the opening and closing amount of the valve body in a remote place, improving usability and environmental resistance. It is possible to achieve In particular, as a result of using a magnetoresistive element consisting of a ferromagnetic thin film with a built-in bias magnet, a linear output voltage corresponding to the displacement of the magnet body was obtained. The opening / closing amount of the valve body can be accurately detected.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a valve body opening / closing amount sensor of a flow control valve device according to a common embodiment of the invention described in claims 1 and 2.

FIG. 2 is a plan view of the above embodiment.

FIG. 3 is a schematic diagram of a magnetic flux density measuring device using a Gauss meter probe.

FIG. 4 is a characteristic diagram showing a change in magnetic flux density by the above measuring device.

FIG. 5 is a schematic diagram of a magnetic flux density measuring device using an MR element.

FIG. 6 is a characteristic diagram showing a change in output voltage by the measuring device of the above.

[Explanation of Codes] 2 Flow Control Valve Device 3 Shaft 4 Pipe Section 5 Nut 6 Handle 8 Housing 10 Holding Member 15 Magnet Body 17 Storage Section 18 MR Element

Claims (2)

[Claims] 1. A displacement member that is displaced in the axial direction of the shaft by a rotational movement of the shaft, a magnet body that has a magnetic pole in the axial direction, and is displaced according to the displacement of the displacement member, and a direction of the magnetic pole of the magnet body. A magnetoresistive element made of a ferromagnetic thin film with a built-in bias magnet provided at a position substantially orthogonal to the magnet body and a predetermined distance, and a signal output from the magnetoresistive element is processed to detect displacement of the shaft. A detection circuit, wherein the maximum sensitivity direction of the magnetic resistance element is orthogonal to the magnetic pole direction of the magnet body, and the bias magnetic field direction of the magnetic resistance element is the magnetic pole direction of the magnet body. An axial displacement sensor characterized in that they are arranged so as to substantially coincide with each other. 2. A state in which a shaft for rotating and opening and closing a valve body of a valve device is connected to a valve device body in which the valve body is housed, and the shaft has an end portion opposite to the valve body protruding. A handle for connecting a shaft support portion that is freely rotatably supported by a shaft and a protruding end portion of the shaft from the shaft support portion, and rotating the shaft to open and close the valve element. A handle that is displaced in the axial direction of the shaft, a housing that is inserted between the handle and the shaft support part at a protruding end of the shaft from the shaft support part, and is fixedly attached to the shaft support part; A pressing member that is slidably inserted in the axial direction between the handle and the housing at the end protruding from the shaft support portion, and is pressed and displaced in the axial direction by the displacement of the handle, and is provided in the housing. Has a magnetic pole in the axial direction so that it can slide freely in the axial direction A magnet body that is housed as described above and slides by being pressed in the axial direction by the pressing member; an elastic member that normally elastically biases the magnet body in a direction opposite to the pressing slide direction; and a magnetic pole direction of the magnet body. A magnetoresistive element comprising a ferromagnetic thin film with a built-in bias magnet, the magnetoresistive element being disposed at a position that is substantially orthogonal to the magnet body and separated from the magnet body by a predetermined distance, and attached to an attachment portion provided in the housing. And a detection circuit for detecting the opening / closing amount of the valve body from the displacement of the shaft by processing the signal output from the magnetic resistance element, the maximum sensitivity direction of which is perpendicular to the magnetic pole direction of the magnet body. A valve body opening / closing amount sensor for a valve device, wherein the bias magnetic field of the magnetoresistive element is arranged so as to substantially coincide with the direction of the magnetic pole of the magnet body.