JPH0628680U - Differential pressure sensor - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a differential pressure sensor capable of ensuring measurement accuracy even when the free length of the bellows varies. [Structure] A bellows 2 and a displacement sensor 5 are provided in a box 1.
And a stopper 7 capable of coming into contact with and separating from the bellows 2
To provide. The bellows 2 has a tubular shape that opens to one side and is displaced according to the acting pressure. The upper box 1a having the external pressure port 8 and the lower box 1b having the internal pressure port 9 hold the peripheral edge portion of the open end of the bellows 2 to partition the inside of the box 1 into the external pressure chamber 3 and the internal pressure chamber 4. At this time, bellows 2
Is provided in a slightly compressed state by the stopper 7 in the box 1 and is initialized. As a result, even if the free length of the bellows varies, the measurement start point is always set at a fixed position, so that the correction process of the detection signal is reduced and the measurement accuracy is ensured.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a differential pressure sensor that detects a differential pressure, and more particularly to a differential pressure sensor that uses a bellows that is displaced according to an acting pressure to measure a pressure difference between its internal pressure and external pressure.

[0002]

[Prior art and its problems]

 Conventionally, a so-called diaphragm type sensor has been widely used as a differential pressure sensor for measuring the differential pressure, but in this case, the diaphragm has a large spring constant, so a slight differential pressure is applied. The amount of displacement at that time was small and the measurement accuracy was low. In addition, in the case of such a diaphragm type, the spring constant has a characteristic curve between the displacement amount and the load, so that the calculated displacement amount is subjected to complicated arithmetic processing to obtain a spring constant of the spring constant. It was necessary to correct the characteristics linearly.

Therefore, as shown in FIG. 2, a bellows having a low spring constant and a linear characteristic is used instead of the diaphragm to facilitate the correction process for the characteristic between the displacement amount and the load. Recently, the differential pressure sensor has become popular.

That is, the differential pressure sensor shown in FIG. 2 includes an upper box 21 a having an outer pressure port 28 and a lower box 21 b having an inner pressure port 29, which are displaced in accordance with an acting pressure and are opened at one side. The box 21 is divided into two chambers, an outer pressure chamber 23 and an inner pressure chamber 24, by sandwiching the peripheral edge portion of the opening end of the bellows 22 in a shape of a box 21 formed by an upper box 21a and a lower box 21b. The displacement sensor 25 is provided inside.

When a pressure difference occurs between the pressure P1 in the external pressure chamber 23 and the pressure P2 in the internal pressure chamber 24, the bellows 22 is displaced by the pressure difference (P1−P2> 0). The generated differential pressure is detected by the displacement sensor 25, and thereafter, the differential pressure is measured by outputting the detection signal generated in the displacement sensor 25 to the outside.

In FIG. 2, a box 21 forms an internal space that is tightly closed by an upper box 21a and a lower box 21b. An outer pressure port 28 is provided in the upper box 21a and an inner pressure is provided in the lower box 21b. Each of the ports 29 is formed so that the internal space of the box 21 is electrically connected to the outside through the external pressure port 28 and the internal pressure port 29.

A bellows 22 is provided inside the box 21. The bellows 22 is, for example, an electrodeposited bellows or a molded bellows, and has a tubular shape made of metal with one side closed as a whole, and elastically deforms and expands and contracts according to the magnitude of pressure applied from the outside. However, this enables displacement in the axial direction.

The bellows 22 is provided so that the inner space of the box 21 is divided into two chambers by sandwiching the peripheral portion of the open end between the upper box 21a and the lower box 21b. Thus, in the box 21, the void outside the bellows 22 is formed as the external pressure chamber 23, and the void including the inside portion of the bellows 22 is formed as the internal pressure chamber 24.

At this time, the external pressure chamber 23 in the box 21 communicates with the external pressure port 28, and the internal pressure chamber 24 communicates with the internal pressure port 29, so that the external pressure chamber 23 is communicated from the outside via the external pressure port 28. The pressure P1 is introduced, and the pressure P2 is introduced into the internal pressure chamber 24 from the outside through the internal pressure port 29.

The pressure difference between the pressure P1 introduced into the external pressure chamber 23 and the pressure P2 introduced into the internal pressure chamber 24 causes the bellows 22 to be displaced in the axial direction thereof.

A displacement sensor 25 is provided inside the bellows 22. The displacement sensor 25 detects the amount of displacement of the bellows 22 in the axial direction as an electric signal, and is connected to a detection amplifier 26 installed outside the box 21.

At this time, it is preferable that a non-contact type sensor that does not contact the bellows 22 is used as the displacement sensor 25 so that the spring constant of the bellows 22 is not affected. What is used is a sensing method such as a laser method or a capacitance method.

The detection amplifier 26 connected to the displacement sensor 25 amplifies the electric signal sent from the displacement sensor 25 and corrects and detects the electric signal by a predetermined calculation process. It becomes possible to measure the amount of displacement as the value of the differential pressure. In this case, in the detection amplifier 26, the differential pressure (P1−P2) = K · L / A is calculated (P1: pressure in the external pressure chamber, P2: pressure in the internal pressure chamber, K: bellows spring constant, L : Displacement of the bellows due to the differential pressure, A: effective area of the bellows).

With the above-described configuration, this differential pressure sensor is configured so that the pressure P1 introduced into the external pressure chamber 23 from the external pressure port 28 of the upper box 21a and the internal pressure chamber 29 from the internal pressure port 29 of the lower box 21b. When a pressure difference (P1 -P2> 0) is generated between the pressure P2 and the pressure P2 introduced into the cylinder, the bellows 22 is displaced so as to contract in the axial direction by the action of the pressure difference, and the displacement amount of the bellows 22 is The displacement sensor 25 detects as an electric signal. Then, the detection signal generated in the displacement sensor 25 is guided to a detection amplifier 26 installed outside the box 21, subjected to amplification and correction processing, and then detected, and thereby generated inside the box 21. The differential pressure will be measured.

However, in the conventional differential pressure sensor as described above, when the electric signal which detects the displacement amount of the bellows 22 is detected, the correction processing of the detection signal becomes difficult or complicated. There was something that happened.

That is, in the above differential pressure sensor, since the initial state of the bellows 22 is set to the free length L0, if the individual free lengths L0 of the bellows 22 used vary, the bellows 22 The initial position may exceed the measurement range that can be detected by the displacement sensor 25, and in such a case, the measurement accuracy becomes unstable.

In particular, the bellows 22 usually causes an error within a predetermined range of the free length L0 depending on the manufacturing conditions and use atmosphere, but generally, the free length L0 is contained within a small tolerance. Since it is very difficult, the variation of the free length L0 of the bellows 22 inevitably occurs.

In this case, if the measurement range that can be detected by the displacement sensor 25 is sufficiently large, there is no problem even if the free length L0 of the bellows 22 varies a little, but the overall size of the box 21 for mounting the bellows 22. When the amount of displacement of the bellows 22 when the differential pressure is applied is very small, the correction of the detection signal in the detection amplifier 26 exceeds the limit of the processing capacity, and the measurement accuracy is reduced. It may decrease.

That is, when the free length L0 of the bellows 22 varies, the reference point of the measurement for the displacement sensor 25 is not determined at a fixed position, so the initial point of the bellows 22 that is the measurement start point. The facing distance (measurement effective length) between the position and the displacement sensor 25 varies from product to product, and the measurement accuracy becomes unstable. Therefore, the detection amplifier 26 corrects the detection signal to stabilize the accuracy, but in this case, since the processing capacity of the detection amplifier 26 for correction is limited, the bellows 22 has a limited capacity. There was a fear that it might not be possible to cope with the variation in the free length L0.

An object of the present invention is to solve the above problems and provide a differential pressure sensor capable of sufficiently dealing with the variation in the free length of the bellows and ensuring the measurement accuracy. And

[0021]

[Means for solving problems]

 In order to solve the above problems, the present invention forms a box with an upper box having an external pressure port and a lower box having an internal pressure port, and divides the external pressure port and the internal pressure port into the box. In this state, a bellows is installed to divide the inside of the box into two chambers, an external pressure chamber and an internal pressure chamber, and the differential pressure between the pressure of the external pressure chamber and the pressure of the internal pressure chamber is measured by a displacement sensor. In the sensor, the box is provided with a stopper that can be brought into contact with and separated from the bellows, and the stopper is used to initialize the bellows.

[0022]

[Action]

 By adopting the above means, the present invention firstly causes a pressure difference between the pressure introduced from the external pressure port of the upper box into the external pressure chamber and the pressure introduced from the internal pressure port of the lower box into the internal pressure chamber. The bellows is displaced by the action of the differential pressure, and the displacement sensor detects the amount of displacement of this bellows to measure the differential pressure generated in the box.

Further, in this invention, the accuracy of measurement can be ensured even when the free length of the bellows varies.

That is, the box is provided with a stopper that can be brought into contact with and separated from the bellows, and the bellows is provided in the box in a state of being slightly compressed by the stopper at the time of initial setting, so that the measurement start point of the bellows is initially set. Is always set to a fixed position.

Therefore, in the past, since the initial setting was made with the bellows in the free length, if there is variation in the free length of the bellows, the amount of displacement of the bellows should be corrected in order to correct the variation. It was necessary to perform a complicated calculation process on the detection signal that detected, and the measurement accuracy was unstable.In this invention, the bellows are initialized by the stopper. Since the measurement start point is always set to a fixed position regardless of the variation in the free length of the measurement signal, it is possible to ensure the measurement accuracy without requiring complicated correction of the detection signal. ing.

That is, in this invention, the gap between the bellows and the displacement sensor facing each other can be made constant at all times, and as a result, the bellows can be used for any application, use condition, and size. On the other hand, it is possible to design a differential pressure sensor using a bellows arbitrarily.

[0027]

【Example】

 Embodiments of the present invention shown in the drawings will be described below.

FIG. 1 is a diagram showing an embodiment of a differential pressure sensor according to the present invention. That is, in the differential pressure sensor shown in FIG. 1, an upper box 1a having an outer pressure port 8 and a lower box 1b having an inner pressure port 9 have a cylindrical shape that is displaced according to the acting pressure and is open to one side. By sandwiching the peripheral edge of the open end of the bellows 2, the inside of the box 1 is divided into two chambers, an external pressure chamber 3 and an internal pressure chamber 4, and is further formed by an upper box 1a and a lower box 1b. The box 1 is provided with a displacement sensor 5 for detecting the amount of displacement of the bellows 2. The box 1 is provided with a stopper 7 that can come in contact with and separate from the bellows 2, so that the bellows 2 can be initially set. Is provided in a state of being slightly compressed by the stopper 7, so that the measurement start point of the bellows 2 is always positioned at a fixed position.

When a pressure difference occurs between the pressure P1 in the external pressure chamber 3 and the pressure P2 in the internal pressure chamber 4, the bellows 2 is displaced by the pressure difference (P1−P2> 0). The resulting differential pressure is detected by the displacement sensor 5, and then the differential pressure is measured by outputting the detection signal generated by the displacement sensor 5 to the outside.

In FIG. 1, a box 1 forms an internal space that is sealed by an upper box 1a and a lower box 1b. An external pressure port 8 is provided in the upper box 1a and an internal pressure port is provided in the lower box 1b. 9 are formed respectively, and the inner space of the box 1 is electrically connected to the outside through the outer pressure port 8 and the inner pressure port 9. Further, on the inner wall of the box 1, there is provided a stopper 7 capable of coming into contact with and separating from a bellows 2 which will be described later.

A bellows 2 having a free length L0 is provided inside the box 1. The bellows 2 is, for example, an electrodeposited bellows or a molded bellows, and has a cylindrical shape made of a metal, one side of which is closed, and is elastic according to the magnitude of pressure applied from the outside. It deforms and expands and contracts, which allows displacement in the axial direction.

The bellows 2 is provided so that the inner space of the box 1 is divided into two chambers by the bellows 2 by sandwiching the peripheral edge portion of the open end between the upper box 1a and the lower box 1b. As a result, in the box 1, the void outside the bellows 2 is formed as the external pressure chamber 3, and the void including the inside portion of the bellows 2 is formed as the internal pressure chamber 4.

At this time, the bellows 2 is provided in the box 1 with its closed end surface in pressure contact with the stopper 7, whereby the length of the bellows 2 is L 1 (L 0> L 0) in a slightly compressed state. L1) and is set as an initial state.

Further, in this case, the external pressure chamber 3 in the box 1 communicates with the external pressure port 8, and the internal pressure chamber 4 communicates with the internal pressure port 9, so that the external pressure chamber 3 is communicated with the external pressure port 8 from the outside. The pressure P1 is introduced into the internal pressure chamber 4, and the pressure P2 is introduced into the internal pressure chamber 4 from the outside through the internal pressure port 9.

The pressure difference between the pressure P 1 introduced into the external pressure chamber 3 and the pressure P 2 introduced into the internal pressure chamber 4 causes the bellows 2 to be displaced in the axial direction thereof.

A displacement sensor 5 is provided inside the bellows 2 so as to face the closed end surface of the bellows 2. The displacement sensor 5 detects the amount of displacement of the bellows 2 in the axial direction as an electric signal, and is connected to a detection amplifier 6 installed outside the box 1.

At this time, the displacement sensor 5 is preferably a non-contact type that does not come into contact with the bellows 2 so that the spring constant of the bellows 2 is not affected. The one that senses by the method, capacitance method, etc. is used.

The detection amplifier 6 connected to the displacement sensor 5 amplifies the electric signal sent from the displacement sensor 5 and corrects and detects it by a predetermined calculation process. It is possible to measure the displacement amount of 2 as the value of the differential pressure. In this case, the differential pressure (P1−P2) = K · L / A is calculated in the detection amplifier 6 (P1: pressure in the external pressure chamber, P2: pressure in the internal pressure chamber, K: bellows spring constant, L: Displacement amount of the bellows due to the differential pressure, A: effective area of the bellows, the same hereinafter).

Next, the operation of the above will be described.

By configuring the differential pressure sensor as described above, the differential pressure generated in the box 1 can be measured. First, the pressure difference (P1-P2>) between the pressure P1 introduced into the external pressure chamber 3 from the external pressure port 8 of the upper box 1a and the pressure P2 introduced into the internal pressure chamber 4 from the internal pressure port 9 of the lower box 1b. When 0) occurs, the bellows 2 is displaced by the action of the differential pressure so as to contract in the axial direction, and the displacement sensor 5 detects the displacement amount of the bellows 2 as an electric signal.

Then, the detection signal generated in the displacement sensor 5 is guided to the detection amplifier 6 installed outside the box 1, subjected to amplification and correction processing, and then detected, whereby the inside of the box 1 is detected. The differential pressure generated at the point will be measured.

Further, in the above-mentioned differential pressure sensor, it is possible to ensure the accuracy of measurement even when the free length L0 of the bellows 2 varies.

That is, in the above-described differential pressure sensor, at the time of initial setting, the bellows 2 is pressed against the stopper 7 and held in the box 1 in a slightly compressed state, so that the initial state of the bellows 2 is less than the free length L0. Even if the individual free length L0 of the bellows 2 used varies, the initial position of the bellows 2 is always within the measurement range that can be detected by the displacement sensor 5. It fits in.

In other words, when the bellows 2 is forcibly compressed to the fixed length L1 by the stopper 7 when setting the initial state, even if the free length L0 of the bellows 2 varies, the bellows 2 for the displacement sensor 5 is When the bellows 2 is in the initial position that is the measurement start point, the reference point for the measurement of is always fixed, so that the closed end face of the bellows 2 and the displacement sensor 5 face each other. The distance (measured effective length) can be made constant at all times without varying for each product.

Therefore, even if the free length L0 of the bellows 2 varies, the detection amplifier 6 does not need to correct the detection signal by a complicated calculation process, and the variation of the bellows 2 can be sufficiently dealt with. As a result, it becomes possible to stabilize the measurement accuracy while simplifying the correction process.

In the above case, since the bellows 2 is provided inside the box 1 in a state of being compressed by the stopper 7 and the total length is set to L1, the length of the bellows 2 is in the range of L0 to L1. Measurement, that is, the differential pressure cannot be detected when the differential pressure is within the range of 0- (L0-L1) K / A, but it is possible to detect the differential pressure higher than that and perform the measurement. Is able to.

[0047]

As described above, according to the present invention, in the differential pressure sensor using the bellows, the box that can be contacted with and separated from the bellows that divides the internal space into the internal pressure chamber and the external pressure chamber. By providing a pad and holding the bellows in a compressed state by the stopper at the time of initial setting, the initial state of the bellows will always be set to a fixed position by the stopper. As a result, even if the free length of the bellows varies, a complicated correction for the detection signal is not required and the measurement accuracy can be ensured.

As described above, since it becomes possible to flexibly deal with the variation in the free length of the bellows, as a result, there are various restrictions such as application, use conditions, and size. In addition, the differential pressure sensor using the bellows can be arbitrarily designed.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a differential pressure sensor according to the present invention.

FIG. 2 is a diagram showing a conventional example.

[Explanation of symbols]

 1, 21 ... Box 1a, 21a ... Upper box 1b, 21b ... Lower box 2, 22 ... Bellows 3, 23 ... External pressure chamber 4, 24 ... Internal pressure chamber 5, 25 ... Displacement sensor 6, 26 ...... Detection amplifier 7 …… Stopper 8, 28 …… External pressure port 9, 29 …… Internal pressure port

Claims (1)

[Scope of utility model registration request] 1. An upper box (1) having an external pressure port (8).
a) and a lower box (1b) having an internal pressure port (9) form a box (1), and the external pressure port (8) and the internal pressure port (9) are defined in the box (1). Box (1) with bellows (2) in place
The interior is divided into two chambers, an external pressure chamber (3) and an internal pressure chamber (4), and the differential pressure between the pressure (P1) of the external pressure chamber (3) and the pressure (P2) of the internal pressure chamber (4) is A differential pressure sensor measured by a displacement sensor (5), wherein the box (1) is provided with a stopper (7) which can freely come into contact with and separate from the bellows (2), and the stopper (7) is used for the bellows (2). A differential pressure sensor characterized by performing initial setting of.