JP3051766B2 - Flow sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a flow sensor for detecting a flow rate in a pipeline using a strain gauge.

[0002]

2. Description of the Related Art A flow rate sensor for detecting the flow rate of a fluid flowing in a pipe is constructed, for example, as shown in FIG.

That is, the pressure receiving plate 4 is provided in the flow path inside the conduit 1.
Is supported by an arm 3 as a support member, and the strain amount of a thin portion 3A formed at the base end of the arm 3 is detected by a strain gauge 8.

The arm 3 has a base end fixed to a large-diameter holder 5, and the holder 5 has a distal end fitted inside a cylindrical sensor housing 2 formed integrally with the conduit 1 in a direction perpendicular to the conduit 1. . Further, a flange 6 formed at the base end of the holder 5 is fixed to an end surface of the sensor housing 2 with a bolt 7.

[0005] The pressure receiving plate 4 in the fluid is displaced downstream by the pressing force of the fluid, deforming the arm 3 and causing the thin portion 3 at the base end to deform.
A causes intensive distortion. Since this strain increases in proportion to the flow rate of the fluid, the strain gauge 8 detects the strain amount and outputs a corresponding signal through the lead wire 9 penetrating the holder 5 to measure the flow rate of the conduit 1. .
Reference numeral 13 denotes an amplifier for amplifying the output of the distortion sensor 8.

The strain gauge 8 is covered with a protective member 20 made of resin or the like to avoid contact with a fluid.
An O-ring 10 that prevents leakage of fluid is interposed between the holder 5 and the sensor housing 2.

[0007]

In the case of this flow sensor, since the strain gauge 8 is provided inside the sensor housing 2, not only the strain gauge 8 but also the take-out portion of the amplifier 13 and the lead wire 9 are fluid. However, it is not easy to sufficiently protect them only by covering with the protection member 20.

Further, there is also a problem that since the arm 3 below the thin portion 3A is long and the pressure receiving plate 4 is heavy, their natural frequencies are small and abnormal phenomena such as resonance are likely to occur.

The present invention has been made to solve the above problems, and has as its object to protect a strain sensor and a lead wire and to prevent resonance of a pressure receiving plate at the time of an excessive flow rate.

[0010]

SUMMARY OF THE INVENTION The present invention provides a pressure receiving plate projecting into a flow of a fluid, a member for supporting the pressure receiving plate on a sensor housing, and detecting a distortion amount of the supporting member caused by displacement of the pressure receiving plate. In a flow sensor provided with a strain gauge and a lead wire for transmitting the output of the strain gauge, a bottomed tubular member that opens the support member from a direction perpendicular to the flow path, and a base end on the bottom surface of the tubular member. The pressure receiving plate is supported by the tip of the arm, and a strain gauge is attached to the back side of the bottom surface of the cylindrical member.

[0011]

Since the strain gauge is attached to the back side of the bottom surface of the cylindrical member supporting the arm, the strain gauge is completely shut off from the fluid. In addition, since the arm is in contact with the cylindrical member, deformation of the arm beyond a certain level is restricted, so that resonance of the arm and the pressure receiving plate due to an excessive flow rate is also prevented.

[0012]

1 to 5 show an embodiment of the present invention.

As shown in FIG. 1, a hole 5A is formed in the center of the holder 5, a bottomed tubular member 11 is fitted into the hole 5A, and the base end of the arm 3 is Bottom 11A
Stick to

A sleeve 12 is formed in the holder 5 so as to extend the hole 5A to the inside of the conduit 1. As shown in FIG. 2, the cylindrical member 11 and the distal ends 11B and 12A of the sleeve 12 are welded or the like. Stick to each other.

The cylindrical member 11 is formed with an inner diameter such that a predetermined gap 15 is secured between the cylindrical member 11 and the outer periphery of the arm 3. The portion of the cylindrical member 11 near the bottom surface 11A is formed to have a larger diameter than this, protrudes above the hole 5A, and is housed inside the holder 5.

The bottom surface 11A of the cylindrical member 11 is formed of a diaphragm-shaped thin metal plate, and four strain gauges 8 are provided on its back surface, that is, on the opposite side of the arm 3 as shown in FIG.
Is attached.

These strain gauges 8 are connected to an amplifier 13 housed inside the holder 5 by a bridge circuit shown in FIG. 4, and lead wires 9 are guided from the amplifier 13 to the outside of the holder 5. In the strain gauges 8 shown in FIGS. 3 and 4, Rb and Rc are dummy resistors, and Re is an adjustment resistor. Temperature and pressure are compensated by these resistors, and the strain amount is detected by Ra and Rd.

The holder 5 is fixed to the sensor housing 2 via a flange 6 by a bolt 7 in the same manner as in the conventional example. Further, between the holder 5 and the sensor housing 2, O
The ring 10 is interposed to prevent fluid from leaking from the sensor housing 2.

Next, the operation will be described. The fluid force f acts on the pressure receiving plate 4 as the fluid flows through the conduit 1, and the arm 3
The thin bottom surface 11A of the cylindrical member 11 is deformed by the moment acting on the base end of the cylindrical member 11 as shown by the broken line in FIG.

The amount of deformation of the bottom surface 11A increases with the flow rate of the fluid, and a strain signal corresponding to the amount of deformation is output from the strain gauge 8 to the lead wire 9. At this time, since the bridge circuit performs temperature compensation and pressure compensation, the output strain signal is accurately proportional to the flow rate of the conduit 1, and the flow rate is measured with high accuracy.

The fluid in the conduit 1 enters the inside of the tubular member 11, but cannot enter between the tubular member 11 and the sleeve 12 due to the welding of the tips 11B and 12A. The inside of 5 is completely isolated from the fluid. For this reason, there is no fear that the strain gauge 8 disposed on the back side of the bottom surface 11A of the cylindrical member 11, the amplifier 14 located above the strain gauge 8, and the lead wire 9 further above will not come into contact with the fluid. It will be highly reliable.

When the amount of displacement of the pressure receiving plate 4 increases due to an excessive flow rate, the arm 3 comes into contact with the cylindrical member 11 and
, The pressure receiving plate 4 does not resonate.

[0023]

As described above, according to the present invention, the base end of the arm supporting the pressure receiving plate is fixed to the bottom surface of the bottomed cylindrical member, and the strain gauge is disposed on the back surface. There is no danger of contact, and the arm abuts on the cylindrical member, so that resonance of the pressure receiving plate against an excessive flow rate can be prevented.

Therefore, there is an effect that reliability and durability of the flow sensor are improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a flow sensor according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is a plan view showing an arrangement of strain gauges.

FIG. 4 is a circuit diagram of a strain gauge.

FIG. 5 is an enlarged sectional view of a main part showing a deformed state of a bottom surface of a tubular member.

FIG. 6 is a longitudinal sectional view of a flow sensor showing a conventional example.

[Explanation of symbols]

 Reference Signs List 1 conduit 2 sensor housing 3 arm 4 pressure receiving plate 8 strain gauge 9 lead wire 11 cylinder member 11A bottom surface

Claims (1)

(57) [Claims] 1. A pressure receiving plate protruding into a flow of a fluid, a member supporting the pressure receiving plate in a sensor housing, a strain gauge for detecting an amount of distortion of the support member due to displacement of the pressure receiving plate, and a strain gauge. In a flow sensor provided with a lead wire for transmitting an output, the support member is formed of a bottomed tubular member that opens from a direction perpendicular to the flow path, and an arm having a base end fixed to the bottom surface of the tubular member, A flow sensor, wherein a pressure receiving plate is supported at a tip of an arm, and a strain gauge is attached to a back side of a bottom surface of a cylindrical member.