JPH0635157Y2 - Differential pressure transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a differential pressure transmitter which converts a differential pressure into a displacement by a bellows and takes it out by a detection rod.

[Conventional technology]

In general, various types of differential pressure transmitters are known, and among them, there is a pneumatic type differential pressure transmitter that converts a process differential pressure into an air pressure signal.

Conventionally, this type of differential pressure transmitter is constructed as shown in FIG. This will be described with reference to the same figure. In the figure, reference numeral 1 denotes a body which is divided into two chambers by a through hole 2 and a partition wall 3 having two openings and is open on both sides. A high-pressure side sealing diaphragm and a low-pressure side sealing diaphragm, which are respectively attached to the openings and define the inside and outside of the body, 6 are both sealing diaphragms 4, 5
A bellows 9 is provided between the bellows 6 so as to close an opening on one side of the through hole 2 and can be seated on the periphery of the opening through an O-ring 8 on the receiving plate 7. An O-ring 11 is formed on the other side opening edge of the through hole 2.
Plunger 12 which can be seated through is connected to this plunger 9 to move the bellows 6 by means of torque rod 13
Is a torque arm that is transmitted to. Further, the torque rod 13 is connected to a detection rod (not shown) for extracting the rotational force of the torque arm 12 as output torque to the outside. A pressure transmission liquid 14 such as silicone oil is enclosed in the body 1.

In the differential pressure transmitter configured as described above, when high pressure P _H and low pressure P _L are applied to the seal diaphragms 4 and 5, respectively,
A force F corresponding to the pressure difference between the pressures P _H and P _L is transmitted to the seal diaphragms 4 and 5 to the bellows 6 via the pressure transmission liquid 14 in the body 1. This force F is given to the torque rod 13 by the spring 10, the plunger 9 and the torque arm 12, and is taken out as an output torque from the detection rod (not shown) to the outside.

[Problems to be solved by the device]

However, in this type of differential pressure transmitter, the bellows 6
Since the torque arm 12 (plunger 9) and the torque arm 12 are connected by the spring 10, the spring force of the spring 10 always affects the differential pressure measurement. As a result, the linearity of the torque with respect to the differential pressure deteriorates, and there is a problem that accurate measurement cannot be performed. Further, since the spring 10 is fixed to the bellows 6 and the torque arm 12 side by welding, the fatigue strength of each component is lowered by the action of repeated load on these joints,
There was also a problem that the life as an instrument is shortened.

Therefore, a differential pressure transmitter of this type is also provided with a connecting rod (not shown) made of a rigid body instead of the spring 10, but in this case, for example, an excessive pressure acts on the seal diaphragm 4. In addition, when the temperature of the entire body 1 rises, the bellows 6 may be excessively displaced due to the volume expansion of the pressure transmitting liquid 14. That is, when the overpressure acts on the seal diaphragm 4, the O-ring 11 is seated on the opening peripheral edge of the through hole 2, so that the pressure transmission liquid 14 in the compartment surrounded by the plunger 9 and the bellows 6 and the like is generated. This is because the bellows 6 expands and the expanding force acts on the bellows 6. As a result, a phenomenon (stick phenomenon) that does not return to the initial state occurs even if the overpressure on the bellows 6 is released, stable characteristics with respect to the differential pressure cannot be obtained, and the reliability as a meter decreases. There was an inconvenience.

The present invention has been made in view of such circumstances, and can perform accurate pressure measurement, can extend the life of the instrument, and can improve the reliability of the instrument. A differential pressure transmitter is provided.

[Means for Solving the Problems]

The differential pressure transmitter according to the present invention comprises a connecting means provided between a bellows for detecting a differential pressure and a torque arm for transmitting the displacement of the bellows to a torque rod, and for detecting and displacing a pressure. , Two pressure transmission rods which are respectively screwed to the bellows side and the torque arm side and have their respective axes extending in the same direction, and springs in the rod extension direction in which both ends are attached to these pressure transmission rods. A spring having a force is used, and a tension is applied to the spring so that the respective non-fixed end surfaces of the pressure transmitting rod abut against each other in the initial state.

[Action]

In the present invention, when the non-fixed end surfaces of the pressure transmitting rods come into contact with each other, the displacement of the bellows can be transmitted to the torque rod by the pressure transmitting rods during pressure measurement.
Further, even if the pressure transmitting liquid in the body expands in volume and the bellows is excessively displaced, the bellows can be returned to the initial state by the elastic body.

〔Example〕

Hereinafter, the configuration of the present invention will be described in detail with reference to the embodiments shown in the drawings.

FIG. 1 is a cross-sectional view showing a differential pressure transmitter according to the present invention, and FIG. 2 is a front view showing the essential parts of the differential pressure transmitter according to the present invention in an exploded manner. The same reference numerals are given to the members, and detailed description thereof will be omitted. In the figure, reference numeral 21 is a connecting means for sensing and displacing pressure, which is provided between the bellows 6 and the torque arm 12. The connecting means 21 includes two pressure transmitting rods 22 and 23 which are screwed to the receiving plate 7 (on the side of the bellows 6) and the plunger 9 (on the side of the torque arm 12) and have their axes extending in the same direction. , These pressure transmission rods 2
A spring 24 having a spring force (tensile force) in the rod extension direction is mechanically fixed to each of the screwed ends 2 and 23. Of these, tension is applied to the spring 24 so that the non-fixed end surfaces 22a and 23a of the pressure transmission rods 22 and 23 come into contact with each other in the initial state. The initial tension of the spring 24 can be adjusted by changing the screwing amount of each of the pressure transmitting rods 22 and 23 with respect to each screwing portion. Here, assuming that the natural length of the spring 24 and the axial dimension of each of the pressure transmitting rods 22 and 23 are l and a and b, the expression l <a + b is satisfied.

In the differential pressure transmitter configured as described above, when the non-fixed end surfaces 22a, 23a of the pressure transmitting rods 22, 23 come into contact with each other during pressure measurement, the displacement of the bellows 6 is caused by the pressure transmitting rods 22, 23. Coupling means 21, Plunger 9, Torque arm 12
Can be transmitted to the torque rod 13 via. That is, during pressure measurement, the displacement of the bellows 6 is transmitted to the torque rod 13 by the rigid body.

Therefore, in the present invention, since the spring force of the spring 24 does not affect the differential pressure measurement during pressure measurement, the linearity of the torque with respect to the differential pressure can be obtained. This can be understood also from the diagram showing the relationship between the differential pressure P and the spring expansion amount S in FIG. In the figure, reference characters A and B are differential pressure measurement ranges (spring 24
Of the initial tension) and the amount of overload.

Further, in the present invention, since the spring 24 can be mechanically fixed to the pressure transmitting rods 22 and 23, the fatigue strength of each component does not decrease due to the action of repeated load.

Further, in the present invention, the pressure transmitting liquid 14 in the compartment surrounded by the plunger 9 and the bellows 6 expands, and even if this expansion force acts on the bellows 6 and displaces it excessively, the spring 24 is pulled. Since the force acts on the bellows 6, the bellows 6 can be returned to the initial state.

In the present invention, as shown in FIG. 4, the pressure transmitting rods 31, 32 are provided with male screw portions 33, 34, and the root diameters of these male screw portions 33.34 are set to be larger than the spring diameter. The spring 24 can be easily attached to the pressure transmission rods 31, 32. In this case, the initial tension F ₁ (k is the spring constant) of the spring 24 is
If the natural length of the spring and the axial dimensions of the pressure transmission rods 31 and 32 are l ₁ and c, d, then F ₁ = k ・ (c + d-
l ₁ ).

[Effect of device]

As described above, according to the present invention, the connection means is provided between the bellows for detecting the differential pressure and the torque arm for outputting the displacement of the bellows to the torque rod, and the connection means is provided for detecting and displacing the pressure. , Two pressure transmission rods which are respectively screwed to the bellows side and the torque arm side and have their respective axes extending in the same direction, and springs in the rod extension direction in which both ends are attached to these pressure transmission rods. It is composed of a spring having a force, and in this spring, tension is applied to the non-fixed end surfaces of the pressure transmission rods in the initial state so that the non-fixed end surfaces of the pressure transmission rods contact each other at the time of pressure measurement. When the two contact with each other, the bellows displacement can be transmitted to the torque rod by both the pressure transmitting rods. Therefore, since the spring force of the spring does not affect the differential pressure measurement during pressure measurement,
It is possible to obtain linearity of torque with respect to differential pressure,
Accurate pressure measurement can be performed. In addition, even if the bellows is displaced excessively due to volume expansion of the pressure transmitting liquid as in the past, the bellows can be returned to the initial state by the spring, so that not only the reference characteristics but also additional characteristics such as temperature characteristics are stabilized. It is possible to improve the reliability of the instrument. Furthermore, since the spring can be mechanically fixed to the pressure transmission rod,
Since the fatigue strength of each component does not decrease due to the action of repeated loading, it is possible to extend the life of the instrument.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a differential pressure transmitter according to the present invention, FIG. 2 is a front view showing a disassembled main part of the differential pressure transmitter according to the present invention, and FIG. 3 is a differential pressure and a spring expansion amount. 4 is a front view showing a pressure transmitting rod in another embodiment, and FIG. 5 is a sectional view showing a conventional differential pressure transmitter. 1 ... Body, 4 ... High-pressure side sealing diaphragm, 5 ...
… Low-pressure side seal diaphragm, 6 …… Bellows, 7 ……
Back plate, 9 ... Plunger, 12 ... Torque arm, 13 ...
… Torque rod, 14 …… Pressure transmission fluid, 22,23 …… Pressure transmission rod, 22a, 23a …… Non-fixed end face, 24 …… Spring.

Claims (1)

[Scope of utility model registration request] 1. A connecting means provided between a bellows for detecting a differential pressure and a torque arm for transmitting the displacement of the bellows to a torque rod, the connecting means for detecting and displacing the pressure, the connecting means being provided on the bellows side. And two pressure transmitting rods that are respectively screwed to the torque arm side and have their respective axes extending in the same direction, and end portions are attached to these pressure transmitting rods and have a spring force in the rod extending direction. A differential pressure transmitter, wherein a tension is applied to the spring so that the non-fixed end surfaces of the pressure transmitting rod abut against each other in the initial state.