JP2008128979A - Differential pressure sensor and flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a differential pressure sensor usable favorably even in combustion gas or the like, and allowing precise measurement by simple constitution. <P>SOLUTION: This differential pressure sensor outputs, as a detection result, an electrification quantity in a balance position between an external force for displacing a movable member 5 to a position detecting part 4 side in response to a differential pressure generated between pressure chambers 1a, 1b, and an electromagnetic force for returning the movable member 5 generated by an electromagnetic coil 8 with the electrification quantity in response to electric resistance of a position detecting part 4 varied by a contact degree with the movable member 5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a differential pressure sensor and a flow meter using the same.

  In combustion equipment such as a water heater and a boiler, proportional control is performed to save energy. Proportional control is to measure the flow rate of gas or air and to control the entire combustion amount to be the required heat amount while keeping the flow rate ratio of air and gas constant using a proportional valve. The flow rates of gas and air can be obtained by measuring the differential pressure of the orifices provided in these flow paths with a differential pressure sensor and converting the differential pressure of the measurement result into a flow rate. Here, since the flow rate is proportional to the square root of the orifice differential pressure, for example, when measuring a flow rate ratio of 1/10, the differential pressure sensor must be able to accurately measure a range width of 1/100.

  As a conventional differential pressure sensor for measuring the orifice differential pressure with high accuracy, for example, there is one disclosed in Patent Document 1. The configuration will be briefly described. As shown in FIG. 12, the measurement diaphragm M is arranged in a chamber formed inside by sealing and fixing the halved main bodies A and B to each other. In the measurement diaphragm M, the chamber is divided into half chambers HA and HB, and a rigid block N made of a material with high magnetic permeability is provided as a center plate.

  A magnetic core 100 provided with an electromagnetic coil 101 is fixed to the halved bodies A and B so as to face the rigid block N of the diaphragm M for measurement. The magnetic flux lines generated by energizing these electromagnetic coils 101 form a loop passing through the magnetic core 100 and the metal rigid block N. Thereby, two magnetic paths having the same magnetic quantity are formed at the position of the measurement diaphragm M in the initial state where there is no differential pressure between the half chambers HA and HB.

  One of the passages 102a and 102b provided in the halved main bodies A and B is open to the half chambers A and B, and the other is a gap defined by the halved main bodies A and B and the sealing diaphragms 103a and 103b. It is open. The filling liquid is introduced into the chamber through these passages 102a and 102b.

  When a differential pressure is generated in the half chambers HA and HB via the sealing diaphragms 103a and 103b and the filling liquid, the measurement diaphragm M is bent, the rigid block N is displaced, and the gaps TA and TB are changed. The difference in inductance thus changed becomes the output of the differential pressure transmitter.

  In addition, as shown in FIG. 12, resistors RA and RB made of paste carbon sensitive to pressure changes are arranged in this differential pressure transmitter, and the resistors RA and RB receive static pressure from the filling liquid and are static. Measure the pressure. By correcting the differential pressure measurement value with the variation of the static pressure, an accurate differential pressure excluding the influence of the static pressure variation can be obtained.

JP 60-38634 A

  Since the conventional differential pressure sensor is generally configured such that an electric circuit such as a strain gauge is disposed in a pressure sensing unit such as a diaphragm, a fluid such as combustion gas that affects the electric circuit is directly introduced into the pressure chamber. I couldn't. In addition, since the characteristics of an electric circuit including electric elements such as transistors and resistors change depending on the temperature, accurate detection may not be possible without temperature compensation even if the diaphragm has the same deflection amount, for example.

  In Patent Document 1, since the amount of change in inductance due to changes in the gaps TA and TB is converted into a differential pressure, measurement accuracy may vary unless the rigid block N and the electromagnetic coil 101 are accurately arranged. .

  The present invention has been made in order to solve the above-described problems. A differential pressure sensor that can be suitably used even with a combustion gas or the like and can perform high-accuracy measurement with a simple configuration, and An object is to obtain a flow meter using this.

  The differential pressure sensor according to the present invention includes a hollow container having an interior partitioned into two pressure chambers, an external force transmission mechanism that transmits a differential pressure generated between the pressure chambers as an external force, and an external force transmitted from the external force transmission mechanism. A moving member that is displaced, a position detection unit whose electrical resistance changes according to the degree of contact with the movable member, and a direction in which an amount of electricity is applied according to the electrical resistance of the position detection unit and the position detection unit is contacted by an external force And an electromagnet that generates an electromagnetic force that pulls back the displaced movable member, and outputs an energization amount at a balance position between the external force and the electromagnetic force applied to the movable member as a detection result.

  In the differential pressure sensor according to the present invention, the position detection unit is formed of a conductive elastic member in which a conductive material is provided on a contact surface with the movable member, and an electrical resistance decreases as the contact area with the movable member increases. It is a feature.

  The differential pressure sensor according to the present invention includes an electrical contact that opens and closes the energization of the electromagnet depending on whether or not the position detection unit is in contact with the movable member, and relaxes the change in the energization amount due to the opening and closing of the electrical contact to a certain time response. It is provided with a relaxation means.

  In the differential pressure sensor according to the present invention, the external force transmission mechanism includes a diaphragm that divides the hollow container into two pressure chambers, and an engagement portion that is provided orthogonal to the diaphragm and engages the movable member at the end. And a shaft member that transmits the differential pressure as an external force to the movable member via the engaging portion by being displaced together with the diaphragm by the differential pressure between the pressure chambers.

  In the differential pressure sensor according to the present invention, the electromagnet and the movable member constitute a magnetic circuit that generates a constant electromagnetic force regardless of the position along the displacement direction of the movable member when the energization amount to the electromagnet is constant. It is characterized by this.

  In the flowmeter according to the present invention, the fluid flow path, the orifice provided in the flow path, the upstream fluid via the orifice is introduced into one of the pressure chambers, and the downstream fluid is introduced into the other A differential pressure sensor is provided, and the flow rate is calculated based on the energization amount corresponding to the differential pressure between the upstream side and the downstream side of the orifice output from the differential pressure sensor.

  According to the differential pressure sensor according to the present invention, the external force that displaces the movable member toward the position detection unit according to the differential pressure generated between the pressure chambers, and the electrical resistance of the position detection unit that changes depending on the degree of contact with the movable member. Because the energization amount at the position balanced with the electromagnetic force that pulls back the movable member generated by the electromagnet with the energization amount according to the output is output as the detection result, an electric circuit is not required in the hollow container, and even if it is combustion gas etc. Can be used. Further, since the energization amount at the balance position of the external force and the electromagnetic force is proportional to the square root of the differential pressure, the output level is high even with a minute differential pressure, and high-precision detection is possible.

  According to the differential pressure sensor according to the present invention, the position detection unit includes the conductive elastic member in which the conductive material is provided on the contact surface with the movable member, and the electrical resistance decreases as the contact area with the movable member increases. Therefore, it is possible to energize the electromagnet in an amount corresponding to the degree of contact with the movable member.

  According to the differential pressure sensor according to the present invention, the position detection unit includes the electrical contact that opens and closes the energization of the electromagnet depending on whether or not the movable member is in contact, and the change in the energization amount due to the opening and closing of the electrical contact is a certain time response. Therefore, the electromagnet can be energized according to the presence or absence of contact between the movable member and the position detector.

  According to the differential pressure sensor of the present invention, the external force transmission mechanism includes a diaphragm that divides the hollow container into two pressure chambers, and an engaging portion that is provided orthogonal to the diaphragm and that engages the movable member at the end. And a shaft member that transmits the differential pressure as an external force to the movable member via the engaging portion by displacing together with the diaphragm due to the differential pressure between the pressure chambers. It can be transmitted to the movable member as an external force.

  According to the differential pressure sensor of the present invention, when the electromagnet and the movable member have a constant energization amount to the electromagnet, the magnetic circuit that generates a constant electromagnetic force regardless of the position along the displacement direction of the movable member. Since the configuration is characterized, the movable member may be arranged slightly deviated, and the magnetic circuit can be easily assembled to the differential pressure sensor.

  According to the flowmeter of the present invention, the flow path for flowing fluid, the orifice provided in the flow path, the upstream fluid via the orifice is introduced into one of the pressure chambers, and the downstream fluid is introduced into the other And the flow rate is calculated based on the energization amount corresponding to the upstream and downstream differential pressures of the orifice output from the differential pressure sensor. Since it is proportional to the square root of the pressure, the current value can be directly set to a value corresponding to the flow rate, and a flow meter with a simple configuration can be obtained.

Embodiment 1 FIG.
FIG. 1 is a principle diagram of a differential pressure sensor according to the present invention, and shows a case where a flow meter for measuring an orifice differential pressure in a flow path is configured using this differential pressure sensor. In FIG. 1, the hollow container 1 is partitioned into pressure chambers 1 a and 1 b by a main diaphragm 2. Further, the fluid flows in the flow path 10 in the direction indicated by the thick arrow in FIG. The pressure chamber 1a communicates with the low pressure side of the flow path 10 through the orifice 11 (indicated by a broken arrow in FIG. 1), and the pressure chamber 1b communicates with the high pressure side (indicated by a solid arrow in FIG. 1). Show)

  The support spring 3 applies a biasing force to the movable member 5 that is displaced in the directions of arrows A and B in FIG. 1 (the direction orthogonal to the main diaphragm 2), and there is a differential pressure between the pressure chambers 1a and 1b. The urging force becomes 0 in the initial state.

  The position detector 4 is configured such that the electrical resistance changes as it is pressed against the movable member 5. For example, conductive silicon rubber or the like in which a conductive material such as carbon is disposed on the contact surface with the movable member 5 is used, and the electric resistance in the initial state in which there is no differential pressure between the pressure chamber 1a and the pressure chamber 1b is infinite. As the contact area increases when pressed against the movable member 5, the electrical resistance is reduced.

  In addition, the infinite electric resistance value of the position detection unit 4 in the present invention means that the resistance value of the electromagnetic coil 8 is sufficiently large in practice, and the electric resistance value of the position detection unit 4 0 means that the resistance value of the electromagnetic coil 8 is sufficiently small in practice.

  The movable member 5 is applied with a force generated in the main diaphragm 2 due to a differential pressure between the pressure chambers 1a and 1b and an attractive force by a magnetic circuit described later, and is blocked from the outside of the hollow container 1 by the seal diaphragm 2a. It is displaced together with the shaft 12 in the directions of arrows A and B. The displacement of the movable member 5 is proportional to the applied force difference and inversely proportional to the spring constant of the support spring 3.

  The movable member 5 functions as a plunger of a magnetic circuit including the yoke 7 and the electromagnetic coil 8 wound around the yoke 7. In such a plunger type magnetic circuit, as shown in FIG. 1, the yoke 7 has a gap along the displacement direction of the movable member 5 surrounding the outer periphery of the movable member 5, and the magnetic flux generated by the electromagnetic coil 8 is the yoke. 7 and the movable member 5 constitute a closed system. For the movable member 5 and the yoke 7 serving as the magnetic path, a material having a high magnetic permeability, for example, a permalloy having a high saturation magnetic flux and a small residual magnetism is used.

  The position detection unit 4 is disposed on a lower plate 6 provided outside the hollow container 1 and connected to a DC power source 9 via the lower plate 6 (indicated by a two-dot broken line in FIG. 1). On the other hand, the movable member 5 is connected to a DC power source 9 via an electromagnetic coil 8. Thereby, when the movable member 5 contacts the position detection unit 4, the position detection unit 4 and the electromagnetic coil 8 are electrically connected in series.

  When the electric resistance of the position detection unit 4 is pressed against the movable member 5 from an infinite initial state, the electric resistance is lowered and a current from the DC power source 9 flows to the electromagnetic coil 8. Thereby, the attractive force of the movable member 5 by the magnetic circuit is generated. Thereafter, when the movable member 5 is further pressed against the position detection unit 4 and the electric resistance thereof decreases, the current flowing from the DC power source 9 to the electromagnetic coil 8 increases and is applied to the movable member 5 by the magnetic circuit. The suction force becomes even stronger.

  For example, when the pressure chamber 1a is higher than the pressure chamber 1b, the main diaphragm 2 is displaced toward the pressure chamber 1b (in the direction of arrow A) due to the differential pressure between the pressure chambers 1a and 1b. The shaft 12 together with the main diaphragm 2 is also displaced in the direction of arrow A, and the differential pressure is transmitted to the movable member 5 as an external force. Due to this external force, the movable member 5 is also displaced in the direction of arrow A and is pressed against the position detection unit 4 and energized to the electromagnetic coil 8 of the magnetic circuit, thereby generating a force for pulling back the movable member 5 in the direction of arrow B.

  The differential pressure sensor of the present invention outputs a current value at a position where the external force due to the differential pressure between the pressure chambers 1a and 1b described above and the electromagnetic force attracting the movable member 5 by the magnetic circuit are balanced. For example, the current value at the balance position is configured to be in a general range of 0 to 20 mA as the sensor output. Note that the differential pressure sensor of the present invention can be easily wired because it can be connected to the DC power source 9 as shown in FIG.

  2A and 2B are diagrams for explaining the characteristics of the magnetic circuit of the differential pressure sensor according to the first embodiment. FIG. 2A is a magnetic circuit that attracts an ordinary flat plate with an electromagnet, and FIG. The plunger type magnetic circuit used with the differential pressure sensor according to the invention is shown, and FIG. 2C shows the relationship between the attractive force and the gap when the current value of the electromagnetic coil is constant.

  As shown in FIG. 2 (a), when the movable member 5 is attracted by the electromagnetic coil 8A wound around the yoke 7A having a U-shaped cross section, a magnetic path as shown by a broken line in FIG. 2 (a) is formed. To do. The attractive force f in this configuration changes in inverse proportion to the square of the gap εa in which a magnetic field is formed between the yoke 7A and the movable member 5.

  The plunger-type magnetic circuit shown in FIG. 2B constitutes a magnetic path as indicated by a broken line in FIG. In this configuration, the amount of movement εb (area defined by the amount of movement εb) of the movable member 5 in which a magnetic field is formed between the yoke 7A and the movable member 5 is proportional to the reciprocal (permeance) of the magnetic resistance. Even if the amount εb changes, there is almost no change in the magnetic resistance. For this reason, the suction force f is not greatly influenced by the movement amount εb as compared with the configuration of FIG.

  Therefore, when the current value flowing through the electromagnetic coil is the same, in the configuration of FIG. 2A, the attractive force f changes significantly with respect to the change of the gap εa as shown by the curve a in FIG. In the configuration of FIG. 2B, the suction force f is substantially constant with respect to the change in the movement amount εb, as indicated by the straight line b in FIG.

  Therefore, when the magnetic circuit shown in FIG. 2A is applied to the differential pressure sensor shown in FIG. 1, the balance position between the attractive force f of the movable member 5 and the force pressed against the position detection unit 4 varies, and high-precision measurement is possible. Can not. On the other hand, in the plunger-type magnetic circuit shown in FIG. 2B, the attractive force f is substantially constant regardless of the position of the movable member 5 in the displacement direction. Even if it is arranged, there is almost no influence on the characteristics, and the magnetic circuit can be easily assembled to the differential pressure sensor.

  Although it is conceivable to use a permanent magnet for attracting the movable member 5, since the permanent magnet has a large characteristic change due to temperature, it is necessary to provide a special configuration such as a temperature compensation circuit when the permanent magnet is used for the differential pressure sensor. There is.

  In the plunger type magnetic circuit, the magnetic resistance of the yoke 7 and the movable member 5 made of a magnetic material having a high magnetic permeability is very small, which is determined by the air resistance in the gap between the yoke 7 and the movable member 5. For this reason, although the magnetic resistance of the movable member 5 and the yoke 7 changes depending on the temperature, the ratio of the change to the magnetic resistance of the entire magnetic circuit is small, and a special configuration such as a temperature compensation circuit is unnecessary. That is, in the differential pressure sensor according to the present invention, the characteristics hardly change depending on the temperature, so that highly reliable measurement is possible in a wide temperature range (for example, −20 to 90 ° C.).

  Further, it is desirable that the position detection unit 4 according to the first embodiment is highly sensitive to contact with the movable member 5. That is, there is no differential pressure between the pressure chambers 1a and 1b, and the position detection unit 4 and the movable member 5 are not in contact (or a position where electrical resistance can be regarded as infinite even if they are in contact). It is important that a differential pressure is generated between 1b and it is possible to accurately detect whether or not a load is applied to the position detector 4 by the movable member 5.

  In this case, it is only necessary that the zero point which is the position in the initial state is stable, and even if the change in the electrical resistance of the position detection unit 4 with respect to the load applied from the movable member 5 is nonlinear or varies. I do not care. In order to improve the sensitivity of the position detection unit 4, for example, it is conceivable to amplify the current value supplied from the DC power supply 9 to the position detection unit 4 with a transistor or the like.

Next, the operating principle of the differential pressure sensor according to the present invention will be described in detail.
FIG. 3 is a block diagram of differential pressure detection by the differential pressure sensor in FIG. In FIG. 3, the diaphragm generating force f _D generated in the main diaphragm 2 due to the differential pressure between the pressure chambers 1a and 1b is expressed as follows, assuming that the area of the main diaphragm 2 is S and the differential pressure P between the pressure chambers 1a and 1b. It can be expressed as equation (1). The diaphragm generating force f _D corresponds to a force (force in the direction of arrow A) that presses the position detector 4 and the movable member 5.
f _D = PS (1)

Further, since the actuator generating force f _A that is the attractive force of the movable member 5 by the magnetic circuit is proportional to the square of the current value i flowing through the electromagnetic coil 8, assuming that the proportionality constant is K ₂ , the following equation (2) It becomes like this.
f _A = K ₂ i ² (2)

In the configuration of FIG. 1, since the high-pressure fluid is introduced into the pressure chamber 1b, the displacement amount x of the movable member 5 is such that the actuator generated force f _A is a negative value with respect to the diaphragm generated force f _{D as} shown in FIG. It is fed back and can be expressed by the relationship of the following formula (3) corresponding to the spring constant k of the support spring 3.
x = (f _D −f _A ) / k (3)

When the voltage applied to the position detection unit 4 is V and the electrical resistance of the position detection unit 4 is R, the current value i flowing through the electromagnetic coil 8 when the movable member 5 contacts the position detection unit 4 is expressed by the following equation (4). There is a relationship.
i = V / R (4)

Further, since the electric resistance R of the position detection unit 4 decreases as the contact area with the movable member 5 displaced by the diaphragm generating force f _D increases, it can be assumed that the electric resistance R is inversely proportional to the displacement amount x of the movable member 5. It can represent with following formula (5). However, K ₁ is a proportionality constant.
R = K ₁ / x (5)

Difference of the above formula (2) to (5) using the diaphragm generated force f _D and the actuator generating force f _A is expressed by the following equation (6).
f _D −f _A = kx
= KK ₁ / x = (k / K ₁ ) (i / V) = (k / K ₁ V√K ₂ ) (√f _A ) (6)

In the differential pressure sensor according to the present invention, the actuator generating force f _A (force in the direction of arrow B) that is the attractive force of the movable member 5 by the magnetic circuit, and the diaphragm generating force f that is the force pressing the position detection unit 4 and the movable member 5 are used. The current value i at a position balanced with _D (force in the direction of arrow A) is output. If (k / K ₁ V√K ₂ ) << ₁ in the above equation (6), f _D ≈f _A, and therefore the relationship of the following equation (7) using the above equation (1): Is obtained.
K ₂ i ² = f _D = PS
i = (√S / √K ₂ ) (√P) (7)

Here, the constant K ₂ in (k / K ₁ V√K ₂ ) corresponds to a parameter that determines the gain of the differential pressure sensor of the present invention, and should be fixed to a predetermined value according to the specification. V is a voltage supplied from the DC power supply 9 and is constant. Therefore, in order to satisfy (k / K ₁ V√K ₂ ) << ₁ , the configuration may be such that (k / K ₁ ) << ₁ .

In order to set (k / K ₁ ) << ₁ , a spring having a sufficiently small spring constant k is used as the support spring 3, and the position detector 4 has a large resistance change with respect to the pressing displacement of the movable member 5, that is, the constant K _{Use one} with a large ₁ In order to output the current value i at a position where f _D ≈f _A as a detection result, if the current value supplied to the electromagnetic coil 8 is constant, the movable member 5 is moved to a position in the displacement direction. Regardless, it is desirable that the actuator generation force f _A is constant. Thereby, in this invention, the plunger type magnetic circuit mentioned above is employ | adopted.

  Further, from the relationship of the above formula (7), the current value i which is the output of the differential pressure sensor according to the present invention is proportional to the square root of the differential pressure P. For this reason, even when the differential pressure P is a minute differential pressure, the output level rises sharply, and even if it is a minute differential pressure, highly accurate detection is possible.

  Furthermore, since the orifice differential pressure is proportional to the square of the flow rate, in the flow meter using the differential pressure sensor according to the present invention, the current value i and the flow rate of the detection result are 1: 1, that is, the flow rate and the current value i are The control system can be configured to have a proportional relationship. Thus, by measuring the orifice differential pressure, the output current value can be directly set to a value corresponding to the flow rate, and a flow meter with a simple configuration can be obtained.

Next, the differential pressure sensor according to Embodiment 1 will be described.
4 is a top view showing the differential pressure sensor according to Embodiment 1 of the present invention, FIG. 5 is a cross-sectional view taken along line AA in FIG. 4, and FIG. 6 is a region C in FIG. FIG. In the differential pressure sensor according to the first embodiment, as shown in FIG. 4, a yoke 7 is provided so as to surround a circular movable member 5, and an electromagnetic coil 8 is wound around the yoke 7. A lever 13 that presses the movable member 5 from above is provided. Note that FIG. 4 omits the description of the cover 17 of FIG. 5 described later in order to make the internal configuration visible.

  The movable member 5 of the differential pressure sensor according to the first embodiment is composed of a thin bowl-shaped member (see FIG. 5) obtained by press-molding a metal plate (for example, permalloy). Stored. As a result, a gap D is formed between the movable member 5 and the yoke 7 as shown in FIG. For example, the gap D is configured to be about 0.2 mm.

  The movable member 5 has a hole at the center, and the shaft 12 is inserted through the hole. The shaft 12 is fixed to the main diaphragm 2 and is displaced in the directions of arrows A and B together with the main diaphragm 2 due to the differential pressure between the pressure chambers 1a and 1b. That is, the shaft 12 is displaced by the diaphragm generating force due to the differential pressure between the pressure chambers 1a and 1b. When the shaft 12 is displaced, the flange portion (engagement portion) 12 a engages with the opening peripheral portion of the hole portion of the movable member 5, and the diaphragm generating force is transmitted to the movable member 5. Thus, the main diaphragm 2 and the shaft 12 constitute an external force transmission mechanism that transmits the differential pressure to the movable member 5 as an external force.

  Furthermore, the movable member 5 is supported by the housing 1A via the leaf spring 3a. The leaf springs 3 a are elastic members that are formed by punching out a thin metal plate and have a shape having a bend at the end portion, and a plurality of leaf springs 3 a are arranged symmetrically with respect to the central portion of the movable member 5. By bending the end portion of the leaf spring 3a, the movable member 5 can be displaced only in the directions of the arrows A and B without shaking along the shaft 12.

  The position detection unit 4 is made of conductive rubber such as conductive silicon in which a conductive material such as carbon is arranged on the contact surface with the movable member 5, and is pressed against the movable member 5 to increase the contact area, for example, from 2 MΩ. The electric resistance changes in the range up to 200Ω. Further, as shown in FIGS. 5 and 6, the lower plate 6 is disposed between the housing 1 </ b> A and the movable member 5 so as to face the movable member 5.

  A hollow container 1 formed inside by sealing and fixing the casings 1A and 1B is partitioned into a pressure chamber 1a and a pressure chamber 1b by a main diaphragm 2. The pressure chamber 1a communicates with the low pressure side piping port 14a, and the pressure chamber 1b communicates with the high pressure side piping port 14b. The cover 17 is formed by press-molding an iron plate, and prevents the magnetism generated in the magnetic circuit from leaking to the outside.

  The main diaphragm 2 is composed of a thin film of an elastic member such as silicon rubber in order to enable displacement with a minute differential pressure. When the main diaphragm 2 is formed of an elastic thin film, for example, the maximum value of the detected differential pressure is set to about 100 Pa. In addition, a center plate 2b having rigidity is disposed on the main diaphragm 2 so as to face from both sides of the pressure chambers 1a and 1b. The center plate 2b is made of, for example, plastic.

  The counter spring 3b supports the main diaphragm 2 from the pressure chamber 1a side. As described above, it is desirable that the spring constant of the counter spring 3b is very small in order to obtain a balanced position by a minute displacement of the movable member 5. Therefore, as the counter spring 3b, a spring designed to have a desired spring constant by increasing the pitch is used.

  A bushing portion 12 a facing the main diaphragm 2 is provided on the shaft 12 orthogonal to the main diaphragm 2. The bushing portion 12a is in close contact with the shaft 12, and is blocked from the outside of the hollow container 1 by a seal diaphragm 2a. The seal diaphragm 2a is made of an elastic material that deforms as the shaft 12 moves.

  The lever 13 functions as a spring that applies a biasing force to the movable member 5 from the opposite direction to the counter spring 3b, and is in an initial state where there is no differential pressure in the pressure chambers 1a and 1b. Become. As described above, since the counter spring 3b is a spring having a small spring constant, it is necessary to make the equivalent spring constant of the lever 13 small in order to apply the same urging force to the movable member 5 as the counter spring 3b.

  Therefore, as shown in FIG. 5, the lever 13 has a part a serving as a base part of the lever 13 as a fulcrum, is inserted into the screw part 16b at a part b away from the fulcrum by a predetermined distance, and is supported by the spring 15. c, a load is applied to the end face of the shaft 12 from the electromagnetic coil 8 side.

FIG. 7 is a view for explaining the principle of the lever 13. If the length from the part a to the part b is 1 and the length from the part b to the tip c is L, the lever 13 can be schematically represented as shown in FIG. Here, assuming that the spring constant of the spring 15 is k ₁ and α = (L / l), the equivalent spring constant k ₂ of the tip end portion a which is a mass portion balanced with the spring 15 with the part c as a fulcrum is expressed by the following formula ( 8).
k ₂ = k ₁ / α ² (8)

Therefore, even if the spring constant k ₁ of the spring 15 is large, the equivalent spring constant k ₂ of the tip a is reduced by appropriately setting α which is the link ratio of the lever 13 from the relationship of the above formula (8). be able to. Further, with this configuration, a support spring having a small spring constant can be obtained even in a narrow space.

Next, the operation will be described.
When a differential pressure is generated between the pressure chambers 1a and 1b by the fluid flowing into the pressure chambers 1a and 1b from the low-pressure side piping port 14a and the high-pressure side piping port 14b, the main diaphragm 2 is displaced according to the differential pressure. For example, when the pressure chamber 1b becomes higher than the pressure chamber 1a, the main diaphragm 2 and the shaft 12 are displaced in the direction of arrow A. When the shaft 12 is displaced in the direction of arrow A, the movable member 5 is moved in the direction of arrow A by the collar portion 12a and is pressed against the position detection unit 4.

  When the position detection unit 4 made of conductive rubber is pressed against the movable member 5, the contact area between the carbon provided on the contact surface and the movable member 5 increases, and the electrical resistance of the position detection unit 4 decreases. As a result, the value of current flowing from the DC power source 5 to the electromagnetic coil 8 via the position detection unit 4 and the movable member 5 increases. Thereby, the magnetic circuit is driven to generate a force in the direction of arrow B that attracts the movable member 5.

In the differential pressure sensor according to the first embodiment, the counter spring 2b and the lever 13 functioning as the support spring 3 in FIG. 1 are configured so that each spring constant becomes small, and the minute pressing displacement of the movable member 5 as described above. In contrast, the electrical resistance of the position detector 4 varies greatly. Thus, while the movable member 5 is small displacement, and the diaphragm generation force f _D and the actuator generating force f _A shown in FIG. 3 becomes balanced position. The current value i at this balance position is the output of the differential pressure sensor according to the first embodiment.

  As described above, according to the first embodiment, the main diaphragm 2 and the shaft 12 that transmit the differential pressure generated between the hollow chamber 1 partitioned into the pressure chambers 1a and 1b and the pressure chambers 1a and 1b as an external force. An external force transmission mechanism comprising: a movable member 5 that is displaced by an external force transmitted from the external force transmission mechanism; a position detection unit 4 that varies in electrical resistance in accordance with the degree of contact with the movable member 5; An electromagnetic coil 8 that is energized in an amount corresponding to the resistance and generates an electromagnetic force that pulls back the movable member 5 that is displaced in a direction in contact with the position detection unit 4 by an external force, and the external force applied to the movable member 5 Since an energization amount at a position balanced with the electromagnetic force is output, an electric circuit having an electric element such as a transistor or a resistor is not required in the hollow container 1, so that even a combustion gas or the like can be suitably used. so That.

  Further, as shown in the above formula (7), since the current value i at the balance position of the diaphragm generating force and the actuator generating force is proportional to the square root of the orifice differential pressure, the output level is high even for a minute differential pressure, High-precision detection is possible. For example, it can be used for differential pressure measurement with a fluid in the vicinity of atmospheric pressure, or for pressure equalization control in consideration of minute differential pressure.

  Further, according to the first embodiment, since the output current value i is proportional to the square root of the orifice differential pressure, similarly to the relationship between the flow rate and the orifice differential pressure, the current value i is directly set to a value corresponding to the flow rate. Therefore, a flow meter having a simple configuration can be obtained.

Embodiment 2. FIG.
In the first embodiment, a conductive rubber or the like is used as the position detection unit 4 so that the electric resistance changes according to the degree of contact with the movable member 5, but in the second embodiment, the movable member 5 The position detection unit is a switch that turns on and off when is pressed.

  FIG. 8 is a diagram showing a schematic configuration of a differential pressure sensor according to Embodiment 2 of the present invention. In FIG. 8, the position detection unit 4 </ b> A is electrically connected to the electromagnetic coil 8 when it is turned on by contacting the movable member 5, and is turned off when the movable member 5 is separated and is disconnected from the electromagnetic coil 8. (Electrical contact). In the switch shown in FIG. 8, one end is connected to the voltage + V of the DC power supply, and the other end is electrically connected to the electromagnetic coil 8 and the diode 18.

  The electromagnetic coil 8 is wound around a yoke 7 provided so as to surround the outer periphery of the movable member 5 as in the first embodiment, and constitutes a magnetic circuit similar to that in the first embodiment. The electromagnetic coil 8 is connected in series with the reference resistor 19 and is connected in parallel with the diode 18. The diode 18 functions as a flywheel diode for reducing the arc of the metal contact, and is connected in parallel with the electromagnetic coil 8 and the reference resistor 19.

  The reference resistor 19 has one end connected to the electromagnetic coil 8 and the other end grounded. The current value obtained from the output voltage Vout applied to the reference resistor 19 becomes the output of the differential pressure sensor according to the second embodiment. Other configurations are the same as those in FIG. 1 in the first embodiment.

Next, the operation will be described.
The fluid pressure applied to the pressure chamber 1b increases and a differential pressure is generated between the pressure chambers 1a and 1b. The main diaphragm 2 is displaced according to this differential pressure, and the movable member 5 is pressed against the position detection unit 4A by the external force transmission mechanism as shown in the first embodiment. As a result, the position detection unit 4A, which is a switch, is turned on.

When the position detection unit 4A is turned on, current flows to the electromagnetic coil 8 and the reference resistor 19 as indicated by an arrow in FIG. 9B, and the current flowing to the reference resistor 19 according to the relationship of the following equation (9) The value i increases gradually.
i = V (1-e- ^{(t / τ)} ) / (R ₁ + R ₂ ) (9)
τ = L / (R ₁ + R ₂ )
Here, R ₁ and L are the resistance value and inductance value of the electromagnetic coil 8, respectively, and R ₂ is the resistance value of the reference resistor 19. V is an applied voltage.

As described above, when the position detector 4A is turned on, the time response determined by the resistance value R ₁ and inductance value L of the electromagnetic coil 8 and the resistance value R ₂ of the reference resistor 19 is as shown in FIG. The current value i of the electromagnetic coil 8 increases.

Thereafter, when the current value i increases to increase the attractive force of the movable member 5 and the movable member 5 is pulled back from the position detection unit 4A, the position detection unit 4A is turned off. At this time, as indicated by an arrow in FIG. 10B, a current flows through a loop including the electromagnetic coil 8, the diode 18, and the reference resistor 19, and is determined by the resistance value R ₁ , the inductance value L, and the resistance value R _2. Current response i decreases as shown in FIG.

  A current value of ripple width F as shown in FIG. 11 flows through the reference resistor 19 by repeating ON / OFF of the position detection unit 4A in the vicinity of a balance position between the diaphragm generation force applied to the movable member 5 and the actuator generation force. In the differential pressure sensor according to the second embodiment, this current value is output as a differential pressure detection result.

  The ripple width F can be reduced by increasing the response speed of the mechanical part. In order to increase the response speed of the mechanical part, it is conceivable to reduce the mass of each part such as the movable member 5 and the shaft 12 and increase the spring constant of the support spring 3.

  As described above, according to the second embodiment, the position detection unit 4A is configured by the switch that turns on and off the electromagnetic coil 8 according to the contact with the movable member 5, and the on / off of this switch is used as a trigger. Since the diode 18 and the reference resistor 19 are provided as a relaxation means for relaxing the change in the current value to a certain time response, an electric circuit is not required in the hollow container 1, and it can be suitably used even if it is a combustion gas or the like. it can. Similarly to the first embodiment, since the current value i at the balance position of the diaphragm generating force and the actuator generating force is proportional to the square root of the orifice differential pressure, the output level is high even at a minute differential pressure. The accuracy can be detected.

  Further, since the output current value i is proportional to the square root of the orifice differential pressure as in the relationship between the flow rate and the orifice differential pressure, the current value i can be set to a value corresponding to the flow rate as it is, and the flow rate with a simple configuration. You can get a total.

It is a principle figure of the differential pressure sensor by this invention. FIG. 6 is a diagram for explaining characteristics of a magnetic circuit of the differential pressure sensor according to the first embodiment. It is a block diagram of the differential pressure detection by the differential pressure sensor in FIG. It is a top view which shows the differential pressure sensor by Embodiment 1 of this invention. It is sectional drawing cut | disconnected by the AA line in FIG. It is an enlarged view of the area | region C in FIG. It is a figure for demonstrating the principle of the lever in FIG. It is a figure which shows schematic structure of the differential pressure sensor by Embodiment 2 of this invention. It is a figure explaining the ON state of a position detection part. It is a figure explaining the OFF state of a position detection part. It is a graph which shows the time-dependent change of the electric current value which flows into a reference resistance in the on-off repetition of a position detection part. It is a longitudinal cross-sectional view which shows the structure of the conventional differential pressure sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hollow container 1a, 1b Pressure chamber 2 Main diaphragm 2a Sealing diaphragm 2b Center plate 3 Support spring 3a Leaf spring 3b Counter spring 4, 4A Position detection part 5 Movable member 6 Lower board 7 Yoke 8 Electromagnetic coil 9 DC power supply 10 Flow path 11 Orifice 12 Shaft 12a Collar portion 12b Bushing portion 13 Lever 14a Low pressure side piping port 14b High pressure side piping port 15 Spring 16a Nut 16b Screw portion 17 Cover 18 Diode 19 Reference resistance

Claims (6)

A hollow container whose interior is divided into two pressure chambers;
An external force transmission mechanism for transmitting a differential pressure generated between the pressure chambers as an external force;
A movable member that is displaced by an external force transmitted from the external force transmission mechanism;
A position detector that changes electrical resistance in accordance with the degree of contact with the movable member;
An electromagnet that is energized in an amount corresponding to the electrical resistance of the position detection unit and generates an electromagnetic force that pulls back a movable member that is displaced in a direction in contact with the position detection unit by the external force;
A differential pressure sensor that outputs an energization amount at a balance position between the external force and the electromagnetic force applied to the movable member as a detection result.   2. The position detection unit is formed of a conductive elastic member in which a conductive material is provided on a contact surface with a movable member, and an electric resistance decreases as a contact area with the movable member increases. Differential pressure sensor. The position detection unit consists of an electrical contact that opens and closes energization to the electromagnet depending on the presence or absence of contact with the movable member,
2. The differential pressure sensor according to claim 1, further comprising a mitigating means for mitigating a change in energization amount due to opening and closing of the electrical contact to a certain time response.   The external force transmission mechanism includes a diaphragm that divides the hollow container into two pressure chambers, and an engagement portion that is provided orthogonal to the diaphragm and that engages with a movable member at an end thereof. And a shaft member that transmits the differential pressure as an external force to the movable member through the engagement portion by being displaced together with the diaphragm. The differential pressure sensor according to 1.   The electromagnet and the movable member constitute a magnetic circuit that generates a constant electromagnetic force regardless of the position along the displacement direction of the movable member when the amount of current supplied to the electromagnet is constant. The differential pressure sensor according to any one of claims 1 to 4. A flow path for fluid flow;
An orifice provided in the flow path;
The differential pressure sensor according to any one of claims 1 to 5, wherein an upstream fluid is introduced into one of the pressure chambers through the orifice, and a downstream fluid is introduced into the other. ,
A flow meter that calculates a flow rate based on an energization amount corresponding to a differential pressure between the upstream side and the downstream side of the orifice output from the differential pressure sensor.

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