JP4049892B2 - Explosion-proof load cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pressure-resistant explosion-proof load cell in which a strain-generating portion of a load cell is covered with an explosion-proof cover.
[0002]
[Prior art]
In load cells used in locations where explosive gases are handled, heat generated by a strain gauge or a short-circuit accident is usually the ignition source, and even if an explosion accident occurs due to the ignition of an explosive gas, the explosive power is There is a requirement for a flameproof construction that fits within the load cell and does not ignite external explosive gases.
[0003]
As shown in FIG. 7, such a pressure-explosion-proof load cell has a structure in which the entire load cell is covered with a cylindrical cover and a facing member, and an explosion-proof gap t is formed along the radial direction by both. (See Japanese Patent Publication No. 7-26879).
[0004]
[Problems to be solved by the invention]
However, in the explosion-proof structure in which the load cell is simply covered with the cylindrical cover in this way, the cylindrical cover becomes larger, and the internal volume increases accordingly, and the explosive force of the internal explosive gas also increases. In order to withstand such an explosive force, it is necessary to increase the thickness of the cylindrical cover, and it is difficult to reduce the size. Not only that, but the explosion-proof gap is along the radial direction, so explosion-proof standards (for example, Industrial Safety Research Institute technical guidelines, factory electrical equipment explosion-proof guidelines, explosion-proof electrical machinery / equipment type certification) In order to secure the depth of the explosion-proof gap, which is specified in the guide) and prevents the flame from running away, the thickness of the cylindrical cover must be increased, and the overall structure becomes larger. there were.
[0005]
In addition, this type of load cell uses a structure in which the strain-generating part is covered with a flexible cover such as a bellows as a measure against dust, but a cylindrical cover-type explosion-proof structure is used for such a load cell. When applied, the size becomes even larger, and the manufacturing process becomes complicated, resulting in an increase in cost.
[0006]
The present invention has been made in view of such a problem, and the object of the present invention is to provide an inexpensive explosion-proof container by appropriately arranging a position where an explosion-proof gap is allowed in accordance with the standards, and is inexpensive. It is an object of the present invention to provide a pressure and explosion proof load cell that is easy and small in size and has a pressure and explosion proof structure.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the invention according to claim 1 includes a strain-generating body in which a strain-generating portion is formed between the fixed portion and the movable portion, and a strain gauge attached to the strain-generating portion. was in explosion-proof load cell, said respective circular flange is formed in the fixed portion and the movable portion, is fixed a cylindrical tubular cover covering the flange and the strain element in the strain body, the The inner diameter of the cylindrical cover is made larger by a specified explosion-proof gap than the outer shape of the bag.
In the invention according to claim 2, in the explosion-proof explosion-proof load cell according to claim 1, several minute protrusions are provided along the circumferential direction on either the outer peripheral surface of the bag or the inner peripheral surface of the end portion of the cylindrical cover. It is provided.
In the invention according to claim 3, in the explosion-proof explosion-proof load cell including a strain-generating body having a square section in which the strain-generating portion is formed and a strain gauge attached to the strain- generating portion, the strain-generating portion is covered. A rectangular tube cover is composed of an upper cover and a lower cover, and a sill part is provided on the inner surface of the horizontal part of the upper cover and the lower cover to form a recess for accommodating the strain gauge, and the upper surface of the strain body A defined explosion-proof gap is formed between the lower surface and the sill portion, and between the side surface of the strain generating body and the inner surfaces of the side walls of the upper cover and the lower cover.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 1 and 2 show a first embodiment of a pressure-proof explosion-proof load cell according to the present invention. The load cell shown in these drawings has a strain generating body 10 made of a light metal such as aluminum, a metal in general, or a ceramic. The strain generating body 10 includes a strain generating portion 12, a fixed portion 14 and a movable portion 16 in which upper and lower portions are partially cut off from a cylindrical body so that the upper surface and the lower surface are parallel to each other.
[0009]
The strain generating portion 12 is formed by passing a hole 18 having a cross-sectional shape obtained by connecting a pair of round holes with a narrow groove between a pair of opposing side surfaces. Two strain gauges 20 are attached to the upper surface and the lower surface of the strain generating portion 12, respectively. The hole 18 does not need to be a through-hole as in this embodiment, and may be a hole having a bottom. The cross-sectional shape of the hole 18 is not limited to the shape as in this embodiment, and a pair of ellipses. Any shape may be used as long as it forms a strain-generating portion having a thin portion, such as a shape in which holes are connected by narrow grooves.
[0010]
The strain gauge 20 is attached on the vertical plane, one on each of the thinnest and most deformed portions on the upper and lower surfaces of the strain-generating portion 12. Between the hole 18 and the upper surface and the lower surface of the strain generating portion, a cable hole 26 for passing a lead wire from the strain gauge 20 is provided.
[0011]
The fixed portion 14 is provided with a terminal plate storage chamber 22. The terminal board storage chamber 22 has a concave circular shape opened on the upper surface of the fixed portion 14, and communicates with the hole 18 through a cable hole 26. A sealing plug 24 is fixed to the opening of the terminal plate storage chamber 22 with a fixing tool such as a screw, and the terminal plate storage chamber 22 is sealed.
[0012]
Further, the terminal board storage chamber 22 opens on three surfaces of the fixing portion 14 of the strain body 10 (in the case of this embodiment, the end surface of the fixing portion 14 and two side surfaces provided with the holes 18). A cable insertion hole 28 is provided. Any one of the three cable insertion holes 28 is used according to the user's request. For example, the cable is inserted and fixed in the cable insertion hole 28 opened on the end face of the fixing portion 14, and the remaining two cable insertion holes 28 are sealed using a blind plug.
[0013]
One end of the cable is connected to a terminal plate installed in the terminal storage chamber 22. On the other hand, the lead wire of the strain gauge 20 is led out to the terminal board storage chamber 22 through the two cable holes 26 and connected to the same terminal board to constitute a bridge circuit.
[0014]
The load cell configured as described above fixedly supports the fixed portion 14 side, and when a load is applied to the movable portion 16 side, the strain generating portion 12 is deformed, and the strain corresponding to the deformation is configured from the strain gauge 20. The magnitude of the load can be calculated based on the detected value detected by the bridge circuit. The basic configuration of such a load cell is the same as that of a conventional load transducer of this type, but the load cell of this embodiment has the following features that should be noted.
[0015]
That is, the explosion-proof load cell according to the present embodiment obtains a pressure- and explosion-proof structure by effectively utilizing the explosion-proof gap allowed by the standard. This specific configuration is shown in FIGS. Near the boundary between the fixed portion 14 of the strain generating body 10 and the strain generating portion 12 of the movable portion 16, the flanges 42 are left. The strain generating portion 12 and the flange 42 are covered with a cylindrical cover 40. Thus, in order to accommodate the strain gauge 20, a pressure-resistant container portion surrounded by the flange 42 and the cylindrical cover 40 is formed, and the outer peripheral surface of the flange 42 and the inner peripheral surfaces of both ends of the cylindrical cover 40 have a depth L of the explosion-proof gap. A corresponding explosion-proof gap d is also formed. In addition, since the explosion-proof gap always requires a predetermined depth and a dimension less than a specified value, in this specification, it should be correctly called “an explosion-proof gap having a predetermined depth and a dimension less than a specified value”. Is simply described as “explosion-proof gap”.
[0016]
This embodiment will be described in more detail. In this embodiment, the position of the flange 42 is set in the vicinity of the boundary between the strain-generating portion 12 in the fixed portion 14 and the movable portion 16, but is fixed within the range where there is no hindrance to the attachment of a fixing tool such as a bolt. You may provide in the appropriate position of the part 14 and the movable part 16. FIG. The inner diameter of the cylindrical cover 40 is set such that only the explosion-proof gap d is larger than the outer diameter of the flange 42. For this reason, the gap between the outer peripheral surface of the flange 42 and the inner peripheral surfaces of both ends of the cylindrical cover 40 is the explosion-proof gap d at the maximum, and therefore always satisfies the explosion-proof standard. Of course, either end in the circumferential surface of the outer peripheral surface or cylindrical cover 40 of the flange 42, provided with several microprojections along the circumferential direction, is between them, uniform explosion-proof along the entire circumference A gap d may be formed. At the position where the cylindrical cover 40 covers the strain-generating portion 12 and the flange 42, the screw 44 is screwed into the screw hole 48 of the flange 42 through the hole 47 of the cylindrical cover 40, thereby straining one end of the cylindrical cover 40. Secure to body 10.
[0017]
1 to 6 depict the explosion-proof gap d much larger than the actual size so that the present embodiment can be easily understood. Actually, according to the Industrial Safety Institute technical guidelines, in the case of a cylindrical joint surface with an internal volume of 100 cm ³ , the minimum value of the depth L is 6 mm, and when the depth L is between 6 mm and 12.5 mm, As the explosion-proof gap d is determined to be 0.2 mm or less, the explosion-proof gap d is very small. Further, the explosion-proof gap d and the depth L of the gap not only correspond to the provisions of the Industrial Safety Institute Technical Guidelines, Factory Electrical Equipment Explosion-proof Guidelines, and Explosion-proof Electrical Machine Equipment Type Certification Guide, Explosion-proof structural standards, technical standards, IEC standards, and the like have similar regulations, and can be set to conform to these regulations.
[0018]
According to the explosion-proof load cell of the present embodiment, the requirements specified in the explosion-proof standard can be satisfied without substantially reducing the load detection performance of the load cell due to the construction of the explosion-proof construction. Since the explosion-proof gap d is formed by the outer peripheral surface of the flange 42 and the inner peripheral surfaces of both ends of the cylindrical cover 40, which is simple in shape and easy to manufacture, the explosion-proof gap d is along the axial direction of the strain body 10, The cylindrical cover 40 does not require a thickness corresponding to the depth of the explosion-proof gap, and an inexpensive, easy, lightweight and compact pressure-proof explosion-proof structure can be obtained.
[0019]
In the present embodiment, the cylindrical cover 40 has a cylindrical shape that is the most advantageous in terms of strength, but the shape may be arbitrary, and may be, for example, a rectangular tube. In this case, the cross section including the wrinkles of the strain body 10 must also be a square tube.
[0020]
FIG. 3 shows a second embodiment of the flameproof load cell according to the present invention. In the present embodiment, in order to fix the cylindrical cover 40 to the strain body 10, as shown in FIG. 3, a convex edge 43 with which one end of the cylindrical cover 40 abuts is provided on one collar 42, and the other collar A stopper 46 with which the other end of the cylindrical cover 40 abuts is attached to 42, and the cylindrical cover 40 is fixed by the convex edge 43 and the stopper 46. Since the rest is the same as that of the first embodiment, the description thereof is omitted.
[0021]
4 to 6 show a third embodiment of the explosion-proof load cell according to the present invention. The load cell shown in these drawings has a strain body 10 having a square shape with a substantially square cross section. The strain generating body 10 includes a strain generating portion 12 located at the center portion, and a fixed portion 14 and a movable portion 16 located on both sides of the strain generating portion 12. As in the first embodiment, the strain generating body 10 is formed with holes 18, terminal plate storage chambers 22, cable holes 26 and cable insertion holes 28, and the upper and lower surfaces of the strain generating portion 12 are distorted. A gauge 20 is attached, and the terminal board storage chamber 22 is sealed with a sealing plug 24.
[0022]
Even in this embodiment, the point of detecting the load by the output from the strain gauge 20 is the same as in the case of the conventional load transducer, but the load cell of this embodiment is also the same as the explosion-proof load cell of the first embodiment. Similarly, an explosion-proof explosion-proof structure is obtained by effectively utilizing the explosion-proof gap allowed by the standard. As shown in FIGS. 4 to 6, the specific configuration is such that a concave portion 54 is provided on the inner surface of a rectangular tube cover 50 that covers the strain-generating portion 12, and the concave portion 54 and the top and bottom surfaces of the strain-generating body 10 are provided. In addition, a pressure-resistant container portion that accommodates the strain gauge 20 is formed, and a predetermined explosion-proof gap d corresponding to the depth L is formed between the inner surface of the rectangular tube cover 50 and the surface of the strain body 10.
[0023]
Further, this embodiment will be described in detail. The rectangular tube-shaped cover 50 includes an upper cover 51 and a lower cover 52 that are detachable from each other. Both covers 51, 52 have side walls 59 on both sides of the horizontal portion 58 and have a U-shaped cross-sectional shape. A sill portion 55 is provided on the inner surface of each of the horizontal portions 58 of both covers 51, 52, thereby forming a shallow recess 54 that can accommodate the strain gauge 20 over its entire width. Furthermore, on one of the sill portions 55 of the upper cover 51 and one of the sill portions 55 of the lower cover 52, an engagement convex portion 56 with a base 57 that engages with an engagement hole 53 provided in the strain body 10. Is provided. Note that the height of the pedestal 57 is actually only the explosion-proof gap d and is so small that it cannot be displayed in the drawing, but is exaggerated in the drawing. Here, the upper cover 51 and the lower cover 52 are engaged with the engagement hole 53 and the engagement convex portion 56 at a position where the strain generating portion 12 is completely covered, and the screws are passed through the screw holes 60 provided in both covers. Both covers are detachably joined. In this way, a pressure-resistant container portion that accommodates the strain gauge 20 is formed between the upper surface of the strain body 10 and the recess 54 of the upper cover 51 and between the lower surface of the strain body 10 and the recess 54 of the lower cover 52. In addition, between the side surface of the strain body 10 and the side wall inner surface of the rectangular tube cover 50, between the upper and lower surfaces of the strain body and the sill portion 55, that is, the surface of the strain body 10 and the rectangular tube cover. An explosion-proof gap d is formed with the inner surface of 50. At this time, when the square tube cover 50 is fixed to the strain body 10, the pedestal 57 and the surface of the strain body are in contact with each other so that the square tube cover 50 does not wobble.
[0024]
In this embodiment, the upper cover 51 and the lower cover 52 are coupled with screws. However, any detachable fixing tool may be used, and both covers are integrated so as not to be separated by bonding or welding. Also good. In this embodiment, the engaging projection 56 with the pedestal 57 is provided on the sill portion 55, but the height of the sill portion 55 provided with the engaging projection 56 is combined with the upper cover and the lower cover. The pedestal 57 may not be provided as a height at which the entire sill portion 55 and the surface of the strain body 10 come into contact with each other.
[0025]
Furthermore, in this embodiment, the strain gauge 20 is attached to the upper surface and the lower surface of the strain body 12, but the strain gauge 20 may be attached to the inner surface of the hole 18. In this case, since the necessary explosion-proof gap d can be formed only by the side surface of the strain body 10 and the side wall 59 of the rectangular tube cover 50, the shape of the horizontal portion 58 of the rectangular tube cover 50 is not restricted. Also, in this case, the rectangular tube cover 50 is not composed of the upper cover 51 and the lower cover 52, but if it is integrally formed from the beginning, the one end of the rectangular tube cover 50 and the strain body 10 can be fixed to each other arbitrarily. The fixing means can be adopted.
[0026]
Also in the case of the present embodiment, if the size of the explosion-proof gap d is appropriately set according to the internal volume and depth L of the pressure-resistant container portion that houses the strain gauge 20, the explosion-proof gap becomes the side surface of the strain-generating body. In addition, the square cylindrical cover does not require a thickness corresponding to the depth, and a conventional strain generating body having a square cross section that is most often used can be used as it is. A lightweight and compact explosion-proof structure can be easily obtained.
[0027]
【The invention's effect】
According to the first aspect of the present invention, a circular ridge is formed on each of the fixed portion and the movable portion of the strain generating body, and a cylindrical tubular cover covering the strain generating portion and the heel is fixed to the strain generating body. In addition, since the inner diameter of the cylindrical cover is made larger than the outer shape of the bag by a prescribed explosion-proof gap, the explosion-proof standard can always be satisfied. Moreover, because they form the explosion-proof clearance between the inner circumferential surface of the easy cylindrical cover manufactured in a simple shape and a circular Tsubagaishu surface, explosion-proof clearance becomes along Ukoto in the axial direction of the strain body In addition , the cylindrical cover does not require a thickness corresponding to the depth of the explosion-proof gap, and can be easily manufactured from a single thin plate and a single round bar, so that an inexpensive, easy, lightweight and compact pressure-proof structure can be obtained. .
According to the second aspect of the present invention, since several small protrusions are provided along the circumferential direction on either the outer peripheral surface of the ridge or the inner peripheral surface of the end portion of the cylindrical cover, it is uniform along the outer peripheral surface of the ridge. Explosion-proof gaps are formed, and the same effects as the invention according to claim 1 are obtained.
According to the third aspect of the present invention, the rectangular cylindrical cover that covers the strain-generating portion is constituted by the upper cover and the lower cover, and the concave portion that houses the strain gauge is formed on the inner surface of the horizontal portion of the upper cover and the lower cover. Sill portions are provided, and a specified explosion-proof gap is provided between the upper and lower surfaces of the strain-generating body and the sill portion, and between the side surfaces of the strain-generating body and the side walls of the upper and lower covers. Since it is formed, the conventional and most commonly used square strain generating body can be used as it is , and an explosion-proof gap can be formed between the inner surface of the rectangular tube cover and the surface of the strain generating body. The square cylindrical cover does not need a thickness corresponding to the depth of the explosion-proof gap . Thus , similar to the first aspect of the invention, an inexpensive, easy and lightweight and compact pressure-proof structure can be obtained.
[Brief description of the drawings]
FIG. 1 is a perspective view of a strain generating body and a cylindrical cover according to a first embodiment of the present invention.
FIG. 2 is a side view showing a state in which the strain-generating portion of the strain-generating body is covered with a cylindrical cover in the first embodiment. The upper side of the center line is a sectional view, and the lower side of the center line is an outline drawing.
FIG. 3 is a side view showing a state in which a strain generating portion of a strain generating body is covered with a cylindrical cover in a second embodiment according to the present invention. The upper side of the center line is a sectional view, and the lower side of the center line is an outline drawing.
FIG. 4 is a perspective view of a strain generating body and a cylindrical cover according to a third embodiment of the present invention.
FIG. 5 is a side view showing a state in which a strain generating portion of a strain generating body is covered with a cylindrical upper cover in the third embodiment. The upper side of the center line is a sectional view, and the lower side of the center line is an outline drawing.
6 is a cross-sectional view taken along plane AA in FIG.
FIG. 7 is a cross-sectional view of a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Strain body 12 Strain part 14 Fixed part 16 Movable part 18 Hole 20 Strain gauge 40 Cylindrical cover 42 鍔 50 Square cylindrical cover

Claims (3)

In a pressure-proof explosion-proof load cell comprising a strain-generating body in which a strain-generating portion is formed between a fixed portion and a movable portion, and a strain gauge attached to the strain-generating portion,
A circular ridge is formed on each of the fixed portion and the movable portion, and a cylindrical tubular cover that covers the strain generating portion and the ridge is fixed to the strain generating body, and an inner diameter of the cylindrical cover is Explosion-proof load cell characterized by a larger explosion-proof gap than the outer shape of the bag In the explosion-proof explosion-proof load cell according to claim 1,
An explosion-proof explosion-proof load cell characterized in that several minute projections are provided along the circumferential direction on either the outer peripheral surface of the flange or the inner peripheral surface of the end portion of the cylindrical cover . In a pressure-proof explosion-proof load cell comprising a strain-generating body with a square section formed with a strain-generating portion and a strain gauge attached to the strain-generating portion,
A rectangular tube-shaped cover that covers the strain-generating portion is composed of an upper cover and a lower cover, and a sill portion is provided that forms a recess that houses the strain gauge on the inner surface of the horizontal portion of the upper cover and the lower cover, A specified explosion-proof gap is formed between the upper and lower surfaces of the strain generating body and the sill portion, and between the side surface of the strain generating body and the inner surfaces of the side walls of the upper cover and the lower cover. Explosion-proof load cell.

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