JP3288608B2 - Instrument grounding structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grounding structure of an instrument for connecting a conductive casing of the instrument to a ground terminal of an electric circuit component assembled inside the casing.

[0002]

2. Description of the Related Art Conventionally, for example, a differential pressure
In a pressure transmitter, an electric circuit component (hereinafter, referred to as an electric circuit component) including a printed circuit board and a terminal board on which electronic components are mounted is assembled in a conductive housing, and the electric circuit component is provided. This ground terminal is screwed to the inner surface of the housing to form a so-called internal ground structure in which the ground terminal is grounded inside the housing. That is, a screw hole is formed on the inner surface of the housing, and an earth terminal is electrically connected to the inner surface of the housing by an operator screwing a screw for fixing the ground terminal into the screw hole using a screwdriver. Will be. In that case, the worker inserts his hand through the opening of the housing, that is, the opening for assembling the electric circuit component inside the housing, positions the screw for fixing the ground terminal in the screw hole, and inserts the screwdriver. Screws for fixing the ground terminal will be screwed. Generally, the screw hole is formed in the bottom inner surface of the housing facing the opening.

[0003]

Since the conventional grounding structure of an instrument has the above-described structure, especially in the case of a small instrument, a hand is inserted into the inside of the housing of the instrument to form a ground terminal. The connection work is difficult, and the same is true even if the ground wire connected to the ground terminal is lengthened or the ground terminal is directly extended from the electronic component. In addition, if the ground terminal fixing screw is dropped into the housing during the connection of the ground terminal, once the electric circuit component is taken out of the housing, the dropped ground terminal fixing screw is removed. Must be taken out, and the electric circuit component must be assembled again, which greatly reduces the workability of assembling the instrument. Also, if the ground terminal fixing screw is to be formed on the inner surface of the side of the housing, in order to enable the connection of the ground terminal from the opening of the housing, a projecting portion must be formed on the inner surface of the side of the housing. In this case, a screw hole must be formed in the overhanging portion, and the provision of such an overhanging portion restricts the accommodation space inside the housing, and cannot be adopted particularly in a small instrument. further,
Processing a screw hole in such an overhanging part itself causes a complicated manufacturing process of the housing.
On the other hand, once the electric circuit component is once assembled in the housing, it is hardly removed on the user side,
If the user accidentally removes the connection or loosens the connection of the ground terminal, a measurement error may occur in the instrument or an accident may occur.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a grounding terminal can be reliably connected to the inside of a housing even in a small instrument without complicated processing of the housing. In addition, it is possible to prevent the user from inadvertently removing the electric circuit components such as the terminal board and the ground terminal on the user side, and to prevent the occurrence of measurement errors and accidents. The purpose is to obtain a grounding structure.

[0005]

According to a first aspect of the present invention, there is provided an instrument grounding structure provided in an electric circuit structure,
A ground terminal facing the ground connection portion at a predetermined position on the inner peripheral surface of the housing, a fixing screw for fixing the ground terminal to the ground connection portion by being screwed from the inside of the housing to the ground connection portion, A wiring inlet provided on a peripheral portion of the housing opposite to the ground connection portion and positioned on an extension of an axis of the fixing screw screwed to the ground connection portion.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. FIG. 1 and FIG. 2 are views for explaining Embodiment 1 of the present invention. This example is an application example as a grounding structure in a differential pressure / pressure transmitter. In FIG. 1, reference numeral 1 denotes a cylindrical conductive case having a bottom, and 2 denotes a cap screwed to an opening of the case 1. The case 1 and the cap 2 serve as a differential pressure / pressure transmitter as an instrument. A housing 3 is configured. The case 1 is provided with a wiring lead-out opening 1A for drawing out a power supply line and a signal line (not shown). 4 is a printed circuit board on which various electronic components are mounted, 5 is a terminal board to which a power supply terminal 6, a signal terminal 7, a ground terminal 8, and the like are attached,
These substrates 4 and 5 are assembled at fixed positions inside the case 1. The power supply terminal 6 and the signal terminal 7 are connected to a power supply input section and a signal input / output section of the printed circuit board 4 by wiring 9, and the ground terminal 8 is connected to a ground section of the printed circuit board 4 by a ground wire 10. The printed circuit board 4 and the terminal board 5 are used as an electric circuit constituting an electric circuit for a differential pressure / pressure transmitter,
Assembled inside.

[0007] The ground terminal 8 of the present embodiment has a metal plate L
It is configured to be bent in a letter shape, and one side 8A is
The terminal board 5 is fixed to the terminal board 5 by a screw 11 that is screwed to the terminal board 5 through a through hole formed in the side 8A. The ground terminal 8 is attached to the terminal board 5 before being assembled to the case 1 by the screw 11 in advance. The other side 8 </ b> B of the ground terminal 8 faces a fixed position on the inner peripheral surface of the case 1 (hereinafter referred to as a ground connection portion) when the terminal board 5 is assembled at a fixed position in the case 1. A screw hole 1B into which the fixing screw 12 is screwed is formed in the ground connection portion, while a through hole through which the fixing screw 12 passes is formed in a side 8B of the ground terminal 8. Here, the ground connection portion on the inner peripheral surface of the case 1 and the wiring outlet 1A are located on opposite sides of the peripheral portion of the case 1 and are on an extension of the screw hole 1B, that is, a fixing screw 12 screwed into the screw hole 1B. Extension line L of
(Refer to FIG. 2) A wiring outlet 1A is formed at an upper position.

Next, the operation will be described. When assembling the differential pressure / pressure transmitter, first, the printed circuit board 4 and the terminal board 5 are assembled at a fixed position inside the case 1, and the side 8 B of the ground terminal 8 faces the ground connection portion on the inner surface of the case 1. Let it. Then, as shown in FIG.
A. Insert the driver 20 from A, and
The fixing screw 12 positioned in the through hole of B is screwed into the screw hole 1B, and the side 8B of the ground terminal 8 is fixed to the ground connection portion of the case 1. At this time, the driver 20 can be inserted from the wiring outlet 1A along the extension line L of the axis of the fixing screw 12;
Can be securely screwed.

After fixing the ground terminal 8 to the case 1 and electrically connecting the ground terminal 8 to the case 1, a power line and a signal line (not shown) connected to the power terminal 6 and the signal terminal 7 of the terminal board 5 are provided. To the outside from the wiring outlet 1A,
Then, the cap 2 is screwed to the case 1. Therefore, the assembled differential pressure / pressure transmitter has a power supply line and a signal line in the wiring outlet 1A. Therefore, even if the user tries to remove the fixing screw 12, the driver 20 cannot be inserted from the wiring outlet 1 </ b> A, and the removal of the ground terminal 8 and the terminal board 5 is prevented.

As described above, according to the first embodiment, the fixing screw 1 is provided on the inner surface of the case 1 which does not require complicated processing.
2 by screwing the ground terminal 8 to the case 1
The ground terminal 8 can be securely connected to the case 1 with good workability by screwing the fixing screw 12 from the wiring outlet 1A into the small case 1. Further, in the assembled differential pressure / pressure transmitter, since the power supply line and the signal line exist in the wiring outlet 1A, the ground terminal 8 and the terminal board 5 are inadvertently removed on the user side. By restricting this, it is possible to prevent the occurrence of measurement errors and accidents of the instruments. When a tapping screw is used as the fixing screw 12, it is not necessary to form the screw hole 1B in the case 1. Alternatively, a bifurcated connecting portion may be provided on the side 8B of the ground terminal 8, and the fixing screw 12 may be screwed to the case 1 after passing the fixing screw 12 between the bifurcated portions.

Embodiment 2 FIG. 3 is a diagram for explaining Embodiment 2 of the present invention. In this case,
The ground terminal 8 has a U-shaped cross section, and an eaves portion 8C is formed above the side portion 8B. According to the second embodiment, the eaves portion 8C is located above the fixing screw 12, so that it is possible to prevent the driver 20 from removing the fixing screw 12 from above the opening of the case 1.

Embodiment 3 FIG. 4 is a diagram for explaining Embodiment 3 of the present invention. In this case,
Reinforcing ribs 8D are provided on the left and right sides of the ground terminal 8. According to the third embodiment, the circuit component can be firmly fixed inside the case 1 by using the ground terminal 8 as a fixing means of the electric circuit component including the terminal board 5.

[0013]

As described above, according to the first aspect of the present invention, the ground connection portion to which the ground terminal of the electric circuit component is connected is set on the inner peripheral surface of the conductive casing of the instrument. A wiring outlet is provided on the periphery of the housing on the side opposite to the ground connection part, and the wiring outlet is located on the extension of the axis of the fixing screw for connecting the ground terminal screwed to the ground connection part. Therefore, the ground terminal can be securely connected to the inside of the case even with a small instrument by screwing the ground terminal fixing screw through the wiring outlet without complicated processing of the case. It is also possible to prevent the user from inadvertently removing the electric circuit components such as the terminal board and the ground terminal from the user side, thereby avoiding measurement errors and accidents in the instrument. Kill.

[Brief description of the drawings]

FIG. 1 is a perspective view of an instrument provided with a grounding structure according to Embodiment 1 of the present invention.

FIG. 2 is a sectional view of a main part of the instrument of FIG.

FIG. 3 is a side view of a ground terminal used in a ground structure according to a second embodiment of the present invention.

FIG. 4 is a perspective view of a ground terminal used in a ground structure according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Case 1A Wiring outlet 1B Screw hole 2 Cap 3 Housing 4 Printed circuit board 5 Terminal board 8 Ground terminal 12 Fixing screw

──────────────────────────────────────────────────続 き Continuation of the front page (56) References Real opening 57-183678 (JP, U) Real opening 58-106042 (JP, U) Real opening sho 59-108813 (JP, U) Real opening Sho 58- 144772 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01R 4/64

Claims (1)

(57) [Claims] 1. A grounding structure of an instrument for connecting a conductive casing of an instrument and a ground terminal of an electric circuit component assembled inside the casing, wherein the grounding structure is provided on the electric circuit component. A ground terminal facing the ground connection portion at a predetermined position on the inner peripheral surface of the housing, a fixing screw for fixing the ground terminal to the ground connection portion by being screwed from the inside of the housing to the ground connection portion, A wiring inlet provided on a peripheral portion of the housing opposite to the ground connection portion and positioned on an extension of an axis of the fixing screw screwed to the ground connection portion. Grounding structure.