JPH0726879B2 - Beam type load cell flameproof structure - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure-resistant explosion-proof structure for a beam-type load cell, in which a pressure-sensitive explosion-proof structure is formed by directly sealing a sensitive portion to which a strain gauge is attached.

[Prior Art] Generally, for load cells used in locations where explosive gas is handled, factors such as heat generation of strain gauges and short-circuit accidents serve as ignition sources, and explosive gas explosives may occur due to safety reasons. Even if it happens, the explosion-proof structure is obligatory so that the explosive force is contained in the load cell, a flame comes out of the load cell, and the explosive gas outside does not catch fire.

And conventionally, as such a pressure-proof explosion-proof structure,
There is known a structure shown in FIG. 5 in which a gap and a depth of the gap which are allowed by the technical guidelines of the National Institute of Industrial Safety are provided.

That is, in FIG. 5, reference numeral 1 is a load cell main body, the right fixing portion 1a is fixed to the fixing base 3 with bolts 2, and the central beam portion 1b is formed with a skewer dumpling-shaped through hole 1b1 in the front-rear direction. A plurality of strain gauges (4 in the figure) 4 are provided on the upper and lower surfaces.
Is attached, and the whole is covered with a thin metal bellows 5 to prevent invasion of moisture, dust, etc., and the left load-bearing portion 1c is provided with a screw 7a at the left end of a facing member 8 described later. A load receiver 9 is fixed to the facing member 8 with a screw 7b.

Further, regarding the flameproof structure, in order to withstand the explosive force, a sturdy cylindrical cover 6 is fixed to the fixing portion 1a of the load cell main body 1 with a screw 7c, and a gap t is held in the opening left end face 6a, in a facing state, The facing member 8 is fixed to the load applying section 1c.

In the above configuration, when the load P is applied to the load receiver 9 during the measurement of the load, the beam portion 1b is bent slightly downward, and the facing member 8 is also rotated slightly to the left. Since the t is provided, the operation is performed without hindrance (no hindrance to the measurement), the amount of bending is detected by the strain gauge 4, and the load value is displayed on a known electric circuit. .

On the other hand, with regard to the counter pressure explosion-proof means, if an explosive gas explosion occurs due to ignition due to the heat generated by the strain gauge 4 or the like,
First, the weak bellows 5 is instantly broken, and at the same time, the explosive gas filling the space A in the tubular cover 6 is also ignited and explodes, but the explosive force is stronger than the sturdy tubular cover 6 and the opposing member. 8 and the flame is provided with the clearance t and the clearance depth (corresponding to the wall thickness of the cylindrical cover 6 in FIG. 5) permitted by the technical guidelines of the National Institute of Industrial Safety. No fire escape to

[Problems to be Solved by the Invention] However, in the conventional pressure-resistant explosion-proof structure shown in FIG.
Since the entire structure of the beam portion (1b) including the bellows 5 where the strain gauge 4 is sealed must be covered, the structure of the cylindrical cover 6 is inevitably large, and the internal volume (A) is large accordingly. Then, since the explosive force of the explosive gas filled there is also large, not only is the wall thickness of the cylindrical cover 6 inevitably increased in order to withstand this explosive force,
Since it is necessary to provide a depth of the numerical gap defined by the pointer so that flame escape does not occur, the wall thickness of the tubular cover 6 becomes large, and the entire structure including the tubular cover 6 and the facing member 8 is large. In addition, the load cell is not restricted in use, and the one sealed with the bellows 5 is further covered with the tubular cover 6, which is complicated in manufacturing.

[Means for Solving the Problems] Therefore, according to the present invention, the beam unit 12 of the beam type load cell 10 is provided.
As a structure in which a hole 12c is formed at a right angle to the flat plate-shaped strain element surfaces 12a and 12b, and a strain gauge is formed on the inner peripheral surface 12d of the hole 12c.
20 is attached, and a pair of cylindrical members 14 and 15 that extend outward from the surfaces 12a and 12b, respectively, are arranged in series with the same inner diameter as the hole 12c,
The base is made relatively thin and the cylindrical members 14, 1
Insert the sealing cylinder 40 into the through hole formed by 5 and the hole 12c,
Both ends of the cylindrical members 14 and 15 in the thick structure and the sealing cylinder 40
Welded the end of the to make a pressure-proof and explosion-proof sealed structure.

[Operation] Even if the explosive gas explodes due to heat generation of the strain gauge 20, the strain gauge 20 attached to the inner peripheral surface 12d of the beam unit 12
However, because it is sealed with a pressure-proof explosion-proof sealed structure (12c, 14, 15, 40), it not only withstands the explosive force, but also the flame generated there does not go outside.

In addition, since the base of the cylindrical member 14 is thin, it does not adversely affect the straining action of the beam portion 12, and conversely, since both ends are thick, welding work is easy to perform.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. In the figure, reference numeral 10 denotes a beam type load cell body, which includes a fixing portion 11, a beam portion 12, a load applying portion 13, and a pair of cylindrical members 14 and 15, which are integrally configured.

Then, the fixed portion 11 has the cut surfaces 11a and 11b vertically except for both ends.
(See FIG. 2) is formed, and a plurality of mounting holes 11c for fixing (four in the figure) are provided on the surface and are fixed to a fixing base (not shown) with bolts.

The beam portion 12 is formed by forming a hole 12c (see FIG. 4) at a right angle with respect to the planes 12a and 12b of the flexure element having a substantially flat plate shape (see FIG. 3), and is indicated by a dotted line of the hole 12c. Beam part 12
A plurality of strain gauges 20 are provided on the inner peripheral surface 12d (of the flat plate portion) of
(See FIGS. 1 and 4) is attached at a proper position, and a lead wire (not shown) connected to the strain gauge 20 penetrates the fixing portion 11 and is located at the right end portion (see FIGS. 2 and 3) of the insertion hole (not shown). It is designed to be connected to the plug-in pin 30 (see).

The load applying section 13 is provided with a hole 13a for connecting a load, and the load application point coincides with the center of the hole 13a.

As can be seen from FIGS. 1 and 4, in particular, the cylindrical members 14 and 15 are formed of a cylinder continuously provided with the same inner diameter as the hole 12c formed in the beam portion 12, and are machined from the load cell body 10 into an annular groove.
It is manufactured integrally with the beam part 12 by cutting 16 and 17, but its thickness is within the range that does not adversely affect the measurement operation (distortion operation) of the beam part 12 and can withstand explosion-proof. Is as thin as possible, and both ends are thick-walled for easy welding.

Here, from the right end portion of the fixed portion 11 and the left end portion of the load applying portion 13, respectively, the convex base portion 11 that projects to the beam portion 12 side.
Although d and 13b are formed when cutting the annular grooves 16 and 17, when attaching a protective cover (not shown) for protecting the beam portion 12 and the entire cylindrical members 14 and 15 portions, It is used as a positioning frame.

A sealing cylinder 40 is inserted into the hole 12c of the beam portion 12 and the cylindrical members 14 and 15 without coming into contact with the strain gauge 20, and both ends 40a and 40b of the sealing cylinder 40 (see FIGS. 3, 4). Are welded in close contact with the end portions 14a, 15a of the indentations of the cylindrical members 14, 15 to form a sealed structure for pressure and explosion proof. In addition, at the time of sealing, an inert gas is filled in for the purpose of protecting the strain gauge 20 if necessary.

In such a configuration, when the load P is applied at the time of measurement, the beam portion 12 bends, and the amount of the deflection is detected by the plurality of strain gauges 20 attached to the inner peripheral surface 12d and measured by a known method. Although the value is displayed, in the case of the present application, the cylindrical members 14 and 15
Since the sealing cylinder 40 and the sealing cylinder 40 are doubly overlapped with each other, as compared with a case in which the end portions 14a and 15a of the cylindrical members 14 and 15 are sealed with a flat plate-like lid, it is more flexible and is given to the beam portion 12 as much. Has little effect and does not adversely affect output characteristics.

Regarding the explosion-proof, when an explosive gas explodes due to the heat generation of the strain gauge 20, etc., the pair of cylindrical members 14 and 15 centering on the beam portion 12 and the sealing cylinder 40 Since the strain gauge 20 is sealed in a large space, the amount of explosive gas that fills up is small, and the relatively weak explosive force is suppressed in this space. There is no worry about leakage.

In the above example, the structure in which the ends of the cylindrical members 14 and 15 that are integrated with the load cell body 10 are sealed by the sealing cylinder 40 has been described above. The sizes do not have to be the same.

[Advantages of the Invention] According to the present invention, since the strain gauge attached to the beam portion of the beam type load cell is directly sealed by the pressure-proof explosion-proof sealing cylinder, the cylindrical member is more easily bent, and the output is increased accordingly. Not only the characteristics are improved, but also the sealing structure can be made compact, and the overall structure is relatively small, not only increasing the number of places to use the beam type load cell, but also the sealing structure, so that the flame is also exposed to the outside. Never leaks.

[Brief description of drawings]

FIG. 1 is a partially developed perspective view showing an embodiment of a beam type load cell according to the present invention, FIG. 2 is a front view of the same embodiment, and FIG.
FIG. 4 is a plan view of the same, FIG. 4 is an enlarged perspective view of an essential part seen from the line BB in FIGS. 1 and 2, and FIG. 1 ... Load cell body, 4 ... Strain gauge, 5 ... Bellows, 6
... Cylindrical cover, 8 ... Opposing member, 9 ... Load receiver, 10 ... Beam type load cell main body, 11 ... Fixed part, 12 ... Beam part, 12a, 1
2b ... surface, 12c ... hole, 12d ... inner peripheral surface, 13 ... load-bearing portion, 14,
15 ... Cylindrical member, 14a, 15a ... End, 16, 17 ... Annular groove, 20 ...
Strain gauge, 30 ... Insertion pin, 40 ... Sealing cylinder, 40a, 40b ...
Ends, A ... space, P ... load, t ... gap.

Claims (1)

[Claims] 1. A beam portion 12 of a beam type load cell 10 is formed by forming a circular hole 12c at a right angle to surfaces 12a, 12b of a substantially flat plate-shaped strain generating element, and the inside of this hole 12c. Attach the strain gauge 20 to the appropriate position on the peripheral surface 12d, and make sure that the surface has the same inner diameter as this hole 12c and that is centered around this hole 12c.
12a, 12b extending outward at right angles, respectively, a pair of cylindrical members 14 and 15 having a thin base and a thick distal end portion are continuously provided, and in the communication space formed by the cylindrical members 14 and 15 and the hole 12c. Through the sealing cylinder 40, both ends 40a, 40b of the sealing cylinder 40 are welded to the ends 14a, 15a of the cylindrical members 14, 15 respectively to seal the strain gauge 20 of the beam type load cell. Explosion-proof structure.