JP2020173490A - Flame sensor - Google Patents

Abstract

To provide a mounting structure of a shield case that can prevent electromagnetic noise from jumping into a lead terminal of a photodetector housed in the case in a state of being mounted on a substrate.SOLUTION: A flame sensor comprises: a body case (11) including a housing unit (11A) and having an aperture formed on one surface of the housing unit; photodetectors (14A, 14B) housed in the housing unit; and a circuit substrate (13) to which lead terminals of the photodetectors are connected. The photodetector is arranged in the housing unit so that a detecting part faces the aperture. The circuit substrate is arranged on the back of a wall opposite to the aperture of the housing unit. A shield case (15) composed of an electromagnetic shield material is arranged so as to surround the lead terminal of the photodetector. The shield case, including a plurality of claws (51a, 51b) that penetrate through the circuit substrate, is configured so that it can be split at either one claw part of the plurality of claws. The plurality of claws are soldered to the circuit substrate.SELECTED DRAWING: Figure 2

Description

The present invention relates to a flame detector, and more particularly to a technique applicable to a flame detector provided with a shield case for blocking electromagnetic noise jumping into a lead terminal of a light receiving element.

Conventionally, as a flame detector, a flame detector having a light receiving element such as an infrared detection element and detecting a flame by detecting light having a predetermined wavelength emitted from the flame is known.
Further, some flame detectors detect a flame by detecting infrared rays in two different wavelength ranges (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 09-91556

In the flame detector, the printed wiring board on which the light receiving element is mounted is housed in a case having a dome-shaped cover, and the light is configured to reach the light receiving element inside the case through the opening provided in the cover. It has a configuration in which the light receiving element inside faces through an opening provided in an object or a cover. Some of the light receiving elements are housed in a metal case, and the substrate on which the elements are mounted is formed with a conductive pattern that serves as a shield to block electromagnetic noise. ..

However, in each sensor, the cover for accommodating the substrate on which the light receiving element is mounted is made of synthetic resin, the lead terminal of the light receiving element is connected to a predetermined part of the printed wiring board by soldering, and the light receiving element is connected from the substrate. It may be implemented in a floating state. In that case, it has been found that there is a problem that electromagnetic noise may jump into the lead terminal of the light receiving element from the outside and cause a malfunction.
The present invention has been made by paying attention to the above problems, and an object of the present invention is to prevent electromagnetic noise from jumping into the lead terminals of a light receiving element housed in a case while being mounted on a substrate. The purpose is to provide a mounting structure for a shield case that can be used.

In order to solve the above problems, the present invention
A main body case having a storage portion and an opening formed on one surface of the storage portion, a light receiving element housed in the storage portion, and a circuit board to which a lead terminal of the light receiving element is connected. In the prepared flame detector
The light receiving element is arranged in the storage portion so that the detection portion faces the opening.
The circuit board is arranged on the back of the wall body opposite to the opening of the storage portion.
A shield case made of an electromagnetic shield material is provided so as to cover the periphery of the lead terminal of the light receiving element.
The shield case is provided with a plurality of claws for penetrating the circuit board and engaging with the circuit board, and is configured to be divisible by any one of the plurality of claws. The plurality of claws are configured so that the circuit board is conductively processed.

According to the above configuration, when the shield case is mounted by inserting the claws into a predetermined portion of the circuit board with both ends abutting against each other, the shield case covers the periphery of the lead terminal of the light receiving element. The electromagnetic wave that jumps into the lead terminal of the light receiving element can be blocked by a shield case made of an electromagnetic shield material, and the detection circuit on the circuit board can be prevented from malfunctioning.
In addition, if the shield case is divided at a part other than the claw part, in order to maintain the desired shape at the time of mounting, both ends may be joined by soldering or the like, or both ends may be fitted into the structure and both ends may be joined before mounting. It is necessary to perform the work of fitting, but the assembling work can be simplified by configuring the claws so that they can be divided.

Here, preferably, the shield case can be abutted at a portion of the plurality of claw portions corresponding to the divisible claw portion, and the abutted end portions are joined to each other.
As a result, it is possible to reliably prevent electromagnetic noise from entering due to a gap formed at the abutted ends. Further, at the same time as the joining process such as soldering the claw portion to the circuit board, the joining process such as soldering to prevent the butt end portion from being formed can be performed, so that the workability is improved.

Further, preferably, the shield case is mounted on the circuit board in a state where the end portions are overlapped with each other at a portion corresponding to the divisible claw portion among the plurality of claw portions.
According to this configuration, a gap is less likely to occur at the ends as compared with the method of butt-butting both ends, and since a soldering process for filling the gap at the butt ends is not required, the time required for assembly is shortened. can do.

Further, preferably, the shield case is provided with a protrusion at one end, a slit into which the protrusion can be fitted is provided at the other end, and the protrusion is fitted into the slit. Is mounted on the circuit board.
According to such a configuration, it is possible to more reliably prevent a failure in which both ends of the shield case are separated from each other.

Further, preferably, a plurality of engaging holes into which the plurality of claws are inserted are formed in the circuit board, and a reference potential can be applied around the plurality of engaging holes. Make sure that a sex land section is provided.
According to this configuration, since the reference potential is applied to the shield case at a plurality of places where the claws are provided, the potential difference between each part of the shield case becomes small, and electromagnetic noise can be blocked more reliably. Can be done.

According to the present invention, in the flame detector, there is an effect that electromagnetic noise can be prevented from jumping into the lead terminal of the light receiving element mounted on the substrate and housed in the case.

An embodiment of the flame detector according to the present invention is shown, where (A) is a plan view and (B) is a front sectional view taken along line BB of (A). The details of the sensing portion inside the flame detector shown in FIG. 1 are shown, and is a cross-sectional view taken along the line II-II of FIG. It is a top view of the sensing part shown in FIG. The details of the shield case in the flame detector according to the present invention are shown, (A) is an enlarged perspective view, and (B) is a side view showing a state before deformation. (A) is a diagram showing a specific example of soldering at the time of mounting the shield case in the flame detector of the embodiment, and (B) is a diagram showing another specific example of soldering at the time of mounting the shield case, (C). ) And (D) are diagrams showing specific examples of the joint portion of the shield case.

Hereinafter, an embodiment of a flame detector to which the present invention is applied will be described with reference to the drawings. FIG. 1 (A) is a plan view showing an embodiment of a flame detector, and FIG. 1 (B) is a front sectional view taken along line BB of (A).
The flame detector (hereinafter, simply referred to as a detector) 10 of the present embodiment is a flame detector having a built-in light receiving element such as an infrared detection element capable of detecting a flame, and is installed on the ceiling surface of a building or the like. It is configured to be used. In the following description, the upper side is the lower side and the lower side is the upper side when the sensor 10 is installed on the ceiling surface of the building.

As shown in FIG. 1, the sensor 10 of the present embodiment is a main body base 10A that holds the circuit board 13 and is fitted and mounted on a sensor mounting base (not shown) provided on the ceiling surface or the like of a building. And an outer cover 10B having a dome shape and covering the entire upper side of the main body base 10A, and the main body base 10A and the outer cover 10B form a main body case as a housing having an internal accommodation space.
Further, an opening is formed in the center of the outer cover 10B so that light can be introduced into the sensing portion housed inside the main body case.

Inside the outer cover 10B, an inner storage case 11 having a storage space for a sensing portion, a disk-shaped flange portion 12 provided on the upper side of the inner storage case 11, and a screw 21 on the main body base 10A are used. A circuit board 13 that is fixed and to which the inner storage case 11 is connected is housed. Further, a connection terminal 22 is provided on the lower surface of the main body base 10A.
2 and 3 show details of the sensing portion inside the main body case of the flame detector 10.
As shown in FIG. 2, the inner storage case 11 includes a storage portion 11A for storing the light receiving element, and a pair of leg portions 11B outside the storage portion 11A for coupling with the circuit board 13. The storage portion 11A has a bottomed tubular shape, and a set of light receiving elements 14A and 14B for detecting light in different wavelength regions are housed in a state where the detection unit is facing upward.

Above the storage portion 11A, a light guide portion 16 that guides light to the light receiving elements 14A and 14B is provided. Further, a transparent protective plate 17 is arranged between the light receiving elements 14A and 14B and the light guide portion 16 to prevent dust from entering.
On the other hand, a rib 11a having a predetermined height is formed on the lower surface of the bottom wall of the storage portion 11A along the edge portion, and the upper surface of the circuit board 13 is in contact with the tip of the rib 11a. Further, a step 11b is formed on the outer periphery of the storage portion 11A at a position substantially the same height as the inner surface of the bottom wall.

The circuit board 13 is composed of a printed circuit board on which electronic components (not shown) such as resistors and capacitances forming a detection circuit and ICs (semiconductor integrated circuits) are mounted on the upper surface and the lower surface.
A pair of engaging holes 13a and 13b are formed in a portion of the inner storage case 11 corresponding to the pair of legs 11B. An elastic locking claw 11c is provided at the tip (lower end in the figure) of the leg portion 11B, and the locking claw 11c engages with the engaging holes 13a and 13b of the circuit board 13 to be inside. The storage case 11 and the circuit board 13 are coupled.

Further, a plurality of insertion holes 11d through which lead terminals 41a and 41b of the light receiving elements 14A and 14B to be mounted are inserted are provided on the bottom wall of the storage portion 11A of the inner storage case 11, and lead terminals 41a are also formed on the circuit board 13. A plurality of insertion holes through which 41b and 41b are inserted are formed, and the tips of the lead terminals 41a and 41b penetrating these insertion holes are welded to a predetermined portion on the back surface of the circuit board 13 with solder.

Further, a shield case 15 for blocking electromagnetic noise is mounted on the outer periphery of the lower portion of the storage portion 11A so that the upper end contacts the step 11b and the lower end contacts the upper surface of the circuit board 13. .. The shield case 15 is formed into a shape (oval shape) corresponding to the outer shape of the storage portion 11A by deforming the surface of an electromagnetic shield material such as brass coated with tin or the like, and faces each other. A pair of engaging claws 51a and 51b are provided at the portion.

Then, the circuit board 13 is formed with an engaging hole at a portion corresponding to the engaging claws 51a and 51b, and the engaging claws 51a and 51b of the shield case 15 are engaged with the engaging hole and engaged with the engaging hole. The tips of the engaging claws 51a and 51b penetrating the joint hole are welded to a predetermined portion on the back surface of the circuit board 13 with solder. A land made of a conductor is formed on the peripheral edge of the engaging hole, and an engaging claw 51a, 51b of the shield case 15 into which a plating layer is formed and inserted inside the engaging hole, and the above land. Is configured to be electrically connected.

Further, the land is connected to a reference potential pattern formed on the substrate, and the tips of the engaging claws 51a and 51b are soldered to the land to apply the reference potential to the shield case 15 via the land. It is designed to exert an electromagnetic shielding effect. Further, a conductive layer pattern (ground pattern) to which a reference potential is applied over a wide range is formed on the circuit board 13, so that electromagnetic noise jumping from the back of the circuit board 13 to the lead terminals 41a and 41b can be blocked. It is configured in.

FIG. 4 shows a specific example of the shield case 15.
As shown in FIG. 4A, engaging claws 51a and 51b are provided at opposite positions of the shield case 15. The shield case 15 is formed so as to have a dividing line at the center of one of the engaging claws 51a. Specifically, the shield case 15 is viewed from above by deforming a strip-shaped, for example, brass plate as shown in FIG. 4 (B) into an annular shape while bending the entire plate so that both ends abut against each other. It is formed to form an oval frame.

In the case of the shield case 15 having the above configuration, if there is a gap in the butt portion, it is not possible to prevent the intrusion of electromagnetic noise, and depending on the structure of the butt portion, a potential difference is generated between each part of the shield plate, and the antenna effect causes. There is a risk that electromagnetic noise will be picked up easily. Therefore, in the shield case 15 of the present embodiment, the following measures are taken. Hereinafter, measures for enhancing the electromagnetic shielding effect will be described with reference to FIG. In FIG. 5, the substrate is not shown.

As shown in FIG. 5A, the first measure is to finish the dimensions of the shield case 15 with high precision by high-precision sheet metal processing so that no gap is generated at the abutting portion and the engaging claw 51a. , 51b is soldered to the land on the substrate side. Further, the size of the engaging hole of the substrate into which the engaging claw 51a on the butt side is inserted is also accurately formed according to the width of the engaging claw 51a so that a gap is not generated in the butt portion. Is good. In FIG. 5, the area where the hatching is attached is the soldered portion.

As shown in FIG. 5B, the second measure is to solder the butt portion as well when soldering the engaging claw 51a so that no gap is formed. Specifically, the size of the engaging hole of the substrate into which the engaging claw 51a on the butt side is inserted is also slightly longer than the width of the engaging claw 51a, and the width of the slit is larger than the thickness of the engaging claw 51a. Make it slightly larger. Then, at the time of soldering, the molten solder is made to enter from the gap between the engaging claw 51a and the engaging hole into the gap of the abutting portion. As a result, the entire butt portion is soldered, there is no gap in the butt portion, and the electromagnetic shielding effect can be enhanced. Further, the butt portion may be closed by not only soldering but also brazing or welding.

As a third measure, as shown in FIG. 5C, the both ends of the shield case 15 are overlapped so that no gap is formed in the abutting portion, and the engaging claw 51a is soldered to the land on the substrate side. It is to be welded to. In this case, by accurately forming the width of the slit of the engaging hole of the substrate into which the engaging claw 51a on the butt side is inserted according to the thickness of the engaging claw 51a, a gap is created in the overlapped portion. It is better not to occur. In addition, after overlapping both ends, the joint surface may be further soldered.

As a fourth measure, as shown in FIG. 5D, a protruding portion 52a is provided at one end of the shield case 15 and a vertical parallel slit 52b is formed at the other end. The engaging claw 51a is welded to the land on the substrate side with solder so that a gap is not generated in the abutting portion due to the fitting structure of the protruding portion 52a and the parallel slit 52b. In this case, by bending the protruding portion 52a so that a step corresponding to the thickness of the shield plate is generated at the base of the protruding portion 52a, the end faces come into contact with each other to prevent a gap, and the end faces come into contact with each other. It may be configured to be electrically conductive.

Although the present invention has been described above based on the embodiment, the present invention is not limited to that of the above embodiment and can be appropriately modified without departing from the gist thereof. For example, in the above embodiment, two engaging claws are provided on the edge of the shield case 15, but three or more engaging claws may be provided.
Further, in the above embodiment, it has been described that the shield case 15 is made of a plate material made of brass, but an electromagnetic shield material other than brass may be used, or a net-like material may be used instead of the plate material.

Further, in the above embodiment, the shield case 15 is formed so as to be divisible by the engaging claws 51a, but it may be formed so as to be divisible by the engaging claws 51a and 51b. Further, when the oval-shaped shield case 15 is housed and interferes with other parts or the like, a notch for preventing interference may be provided in the corresponding portion of the shield case 15.
Further, in the above embodiment, the present invention has been described in which the present invention is applied to a flame detector having a light receiving element, but the present invention is not limited thereto and detects a heat sensitive element such as a thermistor or a harmful gas such as CO. It can also be used for fire detectors equipped with a gas sensor and configured to detect heat or gas.

10 Sensor (flame detector)
10A Main body base 10B Outer cover 11 Inner storage case 11A Storage part 12 Flange part 13 Circuit board 14A, 14B Light receiving elements 41a, 41b Lead terminal 15 Shield case 51a, 51b Engagement claw

Claims (5)

A main body case having a storage portion and an opening formed on one surface of the storage portion, a light receiving element housed in the storage portion, and a circuit board to which a lead terminal of the light receiving element is connected. It ’s a flame detector
The light receiving element is arranged in the storage portion so that the detection portion faces the opening.
The circuit board is arranged on the back of the wall body opposite to the opening of the storage portion.
A shield case made of an electromagnetic shield material is provided so as to cover the periphery of the lead terminal of the light receiving element.
The shield case is provided with a plurality of claws for penetrating the circuit board and engaging with the circuit board, and is configured to be divisible by any one of the plurality of claws. A flame detector characterized in that a plurality of claws are conductively processed on the circuit board. The flame according to claim 1, wherein the shield case can be abutted at a portion of the plurality of claw portions corresponding to the divisible claw portion, and the abutted ends are joined to each other. sensor. The first aspect of the present invention, wherein the shield case is mounted on the circuit board in a state in which the ends of the plurality of claws are overlapped with each other at a portion corresponding to the divisible claw. Flame detector. The shield case is provided with a protrusion at one end, a slit into which the protrusion can be fitted is provided at the other end, and the protrusion is fitted into the slit in the circuit board. The flame detector according to claim 1, wherein the flame detector is mounted. A plurality of engaging holes into which the plurality of claws are inserted are formed in the circuit board, and a conductive land portion configured to be able to apply a reference potential is formed around the plurality of engaging holes. The flame detector according to any one of claims 1 to 4, wherein the flame detector is provided.

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