JPH10170377A - Pressure detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure detecting device which utilizes magnetism and has a stable temperature characteristic. SOLUTION: A pressure detecting device is provided with a magnetism sensitive body which outputs the signal corresponding to magnetism, a housing 1 on which the magnetism sensitive body is placed, a diaphragm 2 which is attached to the housing 1 so as to shield the magnetism sensitive body from the outside, and a permanent magnet 5 which is confronted with the magnetism sensitive body on the inside of the diaphragm 2 and the materials constituting the diaphragm 2 and housing 1 contain ferromagnetic materials. Therefore, the pressure detecting device is constituted so that the magnetism sensitive body and magnet 5 can be surrounded roughly by the ferromagnetic materials.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure detecting device for detecting a pressure and outputting an electric signal corresponding to the pressure, and in particular, to a signal corresponding to magnetism such as a Hall element or a magnetoresistive element. The present invention relates to a pressure detecting device using a magnetic responsive body for outputting.

[0002]

2. Description of the Related Art As a pressure detecting device of this type, there is, for example, a "pressure sensor" disclosed in Japanese Patent Application Laid-Open No. 62-46222. This conventional technology has a structure in which a permanent magnet is mounted on a magnetic sensor via an elastic elastomer.When an external force acts on the permanent magnet, an elastic deformation occurs in the elastic elastomer in proportion to the external force, and the permanent magnet The distance between the magnetic sensor and the magnetic sensor changes, and the strength of the magnetic field exerted by the permanent magnet on the magnetic sensor changes. This change is detected by the magnetic sensor. The size of is calculated.

[0003]

However, according to this conventional pressure-sensitive sensor, the external pressure applied to the permanent magnet is applied to the magnetic sensor via the elastic elastomer. The stress applied to the magnetic sensor may directly destroy the magnetic sensor, and may have a large effect on the output fluctuation of the magnetic sensor. In addition, since the elastic elastomer (resin) generally has a large coefficient of thermal expansion, the heat changes the distance between the permanent magnet and the magnetic sensor, and the output becomes unstable. Further, since the elastic elastomer has high thermal conductivity, the heat of the pressing portion is easily transmitted to the magnetic sensor, and the output is easily changed by the temperature characteristic of the magnetic sensor.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and has a magnetic sensible body for outputting a signal corresponding to magnetism and a magnetic susceptor mounted thereon. The diaphragm includes a housing, a diaphragm attached to the housing so as to shield the magnetic sensor from the outside, and a permanent magnet provided inside the diaphragm at a position facing the magnetic sensor. It is characterized in that a ferromagnetic material is contained in the material, so that the magnetic sensitive body and the permanent magnet are substantially surrounded by the ferromagnetic material.

When pressure is applied to the diaphragm from the outside, the diaphragm is deformed in accordance with the pressure, and the distance between the magnetic sensitive body and the permanent magnet changes, and the strength of the magnetic field applied to the magnetic sensitive body by the permanent magnet changes. I do. In this case, when the distance between the magnet and the magnet is short, the strength of the magnetic field applied to the magnet by the permanent magnet increases, and when the distance increases, the strength decreases. The change in the strength of the magnetic field is detected by the magnetic sensitizer, and the applied pressure can be obtained from the relationship between the pressure applied to the diaphragm measured or calculated in advance and the magnetic field applied to the magnetic sensitizer.

Further, since the magnetic responsive body and the permanent magnet have a structure surrounded by a ferromagnetic material included in the diaphragm and the housing, a magnetic field generated from the permanent magnet toward the diaphragm is confined in the ferromagnetic material of the diaphragm. Then, it reaches the housing, and further passes through the magnetically responsive body from the magnetically responsive body mounting portion via the ferromagnetic body of the housing to reach the surface of the permanent magnet on the housing side. As described above, since the magnetic field lines pass through the closed magnetic path of the ferromagnetic material, the dispersion of the magnetic force is reduced, and the magnetic field lines of high density penetrate the magnetic sensitive body.
Therefore, the linearity of the sensitivity of the magnetic sensitive body to the distance between the permanent magnet and the magnetic sensitive body is high.

[0007]

FIG. 1 is a sectional view showing the structure of a pressure detecting device according to an embodiment of the present invention. The housing 1 is made of a ferromagnetic metal material, and has a substrate 6 on which four magnetoresistive elements are incorporated at the center of the upper surface. The magnetoresistive element is one of the magnetic responsive elements, and is a two-terminal element whose resistivity changes according to the strength of the magnetic field received. The arrangement and connection relationship of this magnetoresistive element on the substrate 6 will be described later.
It is connected to the outside via a plurality of leads.

The lead wires 3 and 4 shown in FIG. 1 are two of the lead wires of the present apparatus, and project downward through a through hole provided in the housing 1. Glasses 7 and 8 are filled between the lead wires 3 and 4 and the housing 1 so that the through holes are sealed and the insulation between the housing 1 and the lead wires 3 and 4 is maintained. . The upper ends of the lead wires 3 and 4 are bonded wires 9 and 1
0 is connected to a terminal provided on the substrate 6.

The housing 1 is provided with a diaphragm (partition) 2 which covers the entire upper portion of the housing 1 with a predetermined clearance (gap). The diaphragm 2 is made of an elastic ferromagnetic metal, and its skirt is fixed to the side surface of the housing 1 by welding 11 without any gap. Accordingly, the substrate 6 is sealed in a space formed by the housing 1 and the diaphragm 2 in combination with a so-called hermetic terminal sealed with glass, and this space is evacuated (depressurized) or inert. It has a gas atmosphere. When the diaphragm 2 receives the pressing force in the direction of the arrow 12, the upper surface is pushed downward according to the pressing force, but returns to the original shape by the restoring force when the pressing force is released.

On the back surface of the center of the diaphragm 2,
A disk-shaped permanent magnet 5 having upper and lower opposite magnetic poles is fixed by its own magnetic force. Thus, the permanent magnet 5 and the substrate 6 face each other with a predetermined clearance.

FIG. 2 shows four magnetoresistive elements 21 on the substrate 6.
3 and 4 show a planar positional relationship between the permanent magnet 5 fixed to the back surface of the diaphragm 2 and FIG. 3 is a circuit diagram showing a connection relationship between the magnetoresistive elements 21 to 24.

In FIG. 2, each of the magnetoresistive elements 21 to 24
Are arranged at substantially equal distances from the center point O inside the permanent magnet 5. Then, the magneto-resistive elements 21 and 24 and the magneto-resistive
2 and 24 are respectively connected in series as shown in FIG. 3, and each series circuit forms one side of the bridge circuit. The other two sides of the bridge circuit are composed of ordinary resistors 31 and 32 mounted on the substrate 6.

The resistance values and the magnetoresistive characteristics of the magnetoresistive elements 21 to 24 are adjusted to be the same.
The resistances of the resistors 31 and 32 are equal to each other, and each is set to be approximately twice the resistance of the magnetoresistive elements 21 to 24. Therefore, when the upper terminal 35 of the bridge circuit shown in FIG. 3 is connected to a positive power supply and the lower terminal 36 is connected to a negative power supply, the potentials of the left and right terminals 33 and 34 are substantially equal to each other.

In this bridge circuit, when the density of lines of magnetic force applied to each of the magnetoresistive elements 21 to 24 increases,
Since the resistance values of the magnetoresistive elements 21 to 24 increase, the balance of the bridge circuit is broken, and the potential of the terminal 33 becomes relatively higher than the potential of the terminal 34. Conversely, if the density of the lines of magnetic force applied to the magnetoresistive elements 21 to 24 decreases, the potential of the terminal 33 becomes relatively lower than the potential of the terminal 34. The terminals 33 to 36 of the bridge circuit are electrically drawn out of the housing 1 via the lead wires 3, 4 and the like.

Next, the operation of the thus configured pressure detecting device of the present embodiment will be described. Since the diaphragm 2 and the housing 1 are made of a ferromagnetic material, the magnetic field generated from the permanent magnet 5 toward the diaphragm 2 is indicated by broken lines A and B.
As shown by, the housing is confined in the diaphragm 2 and reaches the housing 1, and further passes through the housing 1 from the center thereof to the lower surface of the permanent magnet 5 through the substrate 6. Note that this magnetic field is generated when the upper surface of the permanent magnet 5 is N
The case where the pole and the lower surface are S-poles, and when the magnetic poles are upside down, a magnetic field having the opposite direction along the same path. As described above, since the magnetic force lines of the permanent magnet 5 pass through the closed magnetic path made of the ferromagnetic material, the dispersion of the magnetic force is reduced, so that the magnetic lines of high density penetrate the magnetoresistive elements 21 to 24 on the substrate 6.

When no external pressure is applied to the diaphragm 1, the substrate 6 and the permanent magnet 5 are parallel to each other, the distance between them is a predetermined value, and the permanent magnet 5 is connected to each of the magnetoresistive elements 21 to 24. Is also a predetermined value. On the other hand, as described above, the values of the resistors 31 and 32 are
The resistance is adjusted to be twice the resistance value of the magnetoresistive element at this time.
34 have the same potential.

When a pressure from above as shown by an arrow 12 in FIG. 1 is applied to the diaphragm 2 from this state, the diaphragm 2 bends and the permanent magnet 5 approaches the substrate 6. When the permanent magnet 5 approaches the substrate 6, the density of lines of magnetic force passing through each of the magnetoresistive elements 21 to 24 increases, and the resistance value increases. Then, as described above, the potential of the output terminal 33 increases and the potential of the output terminal 34 decreases.
, A potential difference occurs. From this potential difference, the pressing force is calculated based on the relationship between the pressing force and the potential difference obtained experimentally or by calculation in advance.

If the pressing force applied to the diaphragm 1 from above has an inclination or the pressing portion is deviated from the center, the parallelism between the permanent magnet 5 and the substrate 6 is not maintained, and each magnetic resistance Variations appear in the increase in magnetic force in the elements 21 to 24. For example, in FIG. 2, the point of application of the pressing force is the center point O of the permanent magnet 5 as indicated by an arrow 51.
, The distance between the magneto-resistive element 21 and the permanent magnet 5 is smaller than the distance between the magneto-resistive element 24 and the permanent magnet 5, and the magneto-resistive element 2
The distance between 2, 23 and the permanent magnet 5 has an intermediate value.
As a result, the resistance of the magnetoresistive element 21 is relatively large, the resistance of the magnetoresistive element 24 is relatively small, and the resistances of the magnetoresistive elements 22 and 23 are average values of the four elements.

On the other hand, since the four magnetoresistive elements are connected as shown in FIG. 3, the resistance of the series circuit composed of the magnetoresistive elements 22 and 23 having an average resistance and the resistance of a relatively high resistance The resistance value of the series circuit including the magnetoresistive element 21 and the magnetoresistive element 24 having a relatively low resistance value is substantially equal to the resistance value. As a result, the potential difference between the output terminals 33 and 34 is equal to the potential difference when the permanent magnets 5 approach each other while maintaining the state parallel to the substrate 6 and the resistance values of the magnetoresistive elements 21 to 24 increase equally. Is equivalent to

The self-correcting action of the output potential difference with respect to the inclination of the permanent magnet 5 is achieved by connecting the diagonal magneto-resistive elements in series. Also,
This self-correction effect works not only when it is pushed deeply into the magnetoresistive element 21 side as in the example described above, but also when it is pushed deeply in other directions.

As described above, according to the pressure detecting device of this embodiment, when the pressure 12 is applied to the diaphragm 2 from the outside, the diaphragm 2 bends according to the magnitude of the pressure, and the magnetoresistive element and the permanent magnet And the resistance value of the magnetoresistive element changes according to the change, and the potential difference between the output terminals 33 and 34 changes. This potential difference is taken out to the outside via the lead wires 3 and 4, and the pressure 1 applied to the diaphragm 2 measured or calculated in advance is
The applied pressure can be determined from the relationship between 2 and the output potential difference.

Further, according to the pressure detecting device of this embodiment, since the housing 1 and the diaphragm 2 are made of a ferromagnetic material, the dispersion of the magnetic force of the permanent magnet 5 is reduced, and the lines of magnetic force penetrating the magnetoresistive element. And the linearity of sensitivity of the magnetoresistive element increases.

Further, since the housing 1 and the diaphragm 2 are made of a ferromagnetic material, a magnetic shield can be performed. As a result, the magnetoresistive element can sense the magnetic field of the permanent magnet without being affected by the external magnetic field, and the possibility of demagnetization of the permanent magnet due to an external strong magnetic field is reduced. Further, the housing 1 and the diaphragm 2
Since it is a ferromagnetic metal, it has conductivity, so that the penetration of electromagnetic noise can be prevented and the S / N of the magnetoresistive element can be improved.

In general, permanent magnets are fragile,
In order to prevent cracking, it is necessary to have a structure in which stress is not transmitted to the permanent magnet. According to the pressure detecting device of this embodiment, since the permanent magnet 5 is fixed to the diaphragm 2 by its own magnetic force, the permanent magnet 5 receives an external pressure to be detected and receives the external pressure.
When the metal is deformed, a stress that breaks the permanent magnet 5 is not applied. Further, when the permanent magnet 5 is attached with an adhesive or the like when the diaphragm 2 is not a ferromagnetic material, a stress may be repeatedly applied to the bonded portion and the permanent magnet 5 may fall off. There is no such problem.

Further, since the inside of the housing 1 and the diaphragm 2 are sealed by seam welding, a vacuum (reduced pressure) is used.
Alternatively, by using an atmosphere of an inert gas such as nitrogen or argon, it is possible to completely prevent the substrate 6 in which the magnetoresistive element is incorporated from being damaged by water or oxygen. Further, since the space between the magnetoresistive element and the diaphragm 2 is a gas such as a vacuum or an inert gas, stress or heat applied to the diaphragm 2 is not easily transmitted to the magnetoresistive element. Therefore, the characteristics of the magnetoresistive element are stable and do not deteriorate for a long time.

FIG. 4 is a plan layout view showing an example in which a Hall element is used as a magnetic responsive body instead of the above-described magnetoresistive elements 21 to 24. The Hall elements 41 to 44 are respectively arranged at the positions of the magnetoresistive elements 21 to 24 shown in FIG.

The Hall element is a four-terminal element. When a magnetic field is applied in a direction orthogonal to the first direction while a current flows in the first direction, a voltage corresponding to the magnetic field is generated in the direction orthogonal to both directions. This element detects the strength of magnetic force by utilizing the effect.

In FIG. 4, among the terminals of the Hall elements 41 to 44, terminals 411, 421, 431, and 441 are upper power supply terminals for driving current.
432 and 442 are lower power supply terminals for driving current. Terminals 413, 423, 433, and 443 are first output terminals, and terminals 414, 424, 434, and 444 are second output terminals.
Output terminal. In each Hall element, the potential difference between the first output terminal and the second output terminal changes according to the applied magnetic field.

The first of each of the Hall elements 41 to 44
And the second output terminal are connected in series with a cross as shown in the figure, and the potential difference between the respective elements is added so that the potential difference between the first output terminal 413 of the Hall element 41 and the second output terminal 424 of the Hall element 42 is added. Is output as the potential difference of

This potential difference is amplified using a general differential amplifier using an operational amplifier 60 as shown in FIG. This differential amplifier comprises an operational amplifier 60 and resistors 64-67.
And amplifies the potential difference between the voltages input to the input terminals 61 and 62 and outputs the amplified voltage from the output terminal 63. The first output terminal 413 and the second output terminal 424 of FIG.
Are input terminals 61 and 62 of the differential amplifier, respectively.
, A voltage corresponding to the strength of the magnetic field applied to the Hall elements 41 to 44 is obtained from the output terminal 63. Moreover, as in the case where the magnetoresistive elements 21 to 24 are used, by using the four elements, even if the permanent magnet 5 is pressed in a tilted state, the influence of the tilt is averaged, and the output does not vary.

In the above-described embodiment, in both the case where the magnetoresistive element is used as the magnetic sensing element and the case where the Hall element is used, the output variation when the permanent magnet is tilted using four elements. Is adopted, but when high detection accuracy is not required,
A single magnetic sensitive body may be used. Of course, conversely, more than four elements may be arranged.

[0032]

As described above, according to the pressure detecting device of the present invention, the distance between the permanent magnet and the magnetic sensitive body changes according to the pressure applied to the diaphragm. The applied pressure can be determined. Moreover,
Since there is no solid inclusion between the permanent magnet and the magnetic sensible body, external stress and heat are not easily transmitted to the magnetic sensible body, and the sensitivity characteristics are stable for a long time. Further, since the diaphragm and the housing are made of a ferromagnetic material, the leakage of the magnetic flux of the permanent magnet is small, the magnetic flux penetrating the magnetic sensitive body is high, and the linearity of sensitivity is high.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the structure of a pressure detecting device according to an embodiment of the present invention.

FIG. 2 is a plan view showing an arrangement of a magnetoresistive element, which is a magnetic sensor, used in the embodiment shown in FIG. 1;

FIG. 3 is a circuit diagram showing a connection state of the magnetoresistive element shown in FIG. 2;

FIG. 4 is a view showing another embodiment of the present invention in which a Hall element is used as a magnetic sensing element, and shows an arrangement of the Hall element.

5 is a circuit diagram showing a differential amplifier circuit for amplifying an output potential difference of a detection circuit using the Hall element shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Housing, 2 ... Diaphragm, 3 ... 4 Lead terminal, 5 ... Permanent magnet, 6 ... Magnetic resistance element mounting board, 7, 8
... glass, 11 ... welded parts, 21 to 24 ... magnetoresistive elements,
41 to 44: Hall elements.

Claims (3)

[Claims] A magnetic sensor for outputting a signal corresponding to magnetism, a housing for mounting the magnetic sensor, a diaphragm attached to the housing so as to shield the magnetic sensor from the outside; A permanent magnet provided inside the diaphragm at a position facing the magnetically responsive body, wherein a material forming the diaphragm and the housing includes a ferromagnetic material, whereby the magnetically responsive body and the permanent magnet are included. A pressure detecting device, wherein a magnet and a ferromagnetic material are substantially surrounded. 2. The pressure detecting device according to claim 1, wherein the permanent magnet is fixed to the diaphragm by its own magnetic force. 3. The pressure detecting device according to claim 1, wherein a plurality of said magnetic responsive bodies are provided.