JP3736035B2 - Pressure sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pressure sensor in which a terminal of a pressure detection unit accommodated in a resin case is exposed to the outside from the resin case, and the resin case is attached to a ground surface.
[0002]
[Problems to be solved by the invention]
Conventionally, a pressure sensor that measures the pressure of LP gas or city gas has a gas to be measured. For example, even if a surge voltage is applied due to a lightning strike, a fire due to gas leakage, etc. Therefore, the resin case is required not to be destroyed so that the secondary disaster of the above will not occur. FIG. 4 shows the configuration of a conventional pressure sensor, in particular, the configuration of lightning protection surge.
[0003]
A pressure detection unit (not shown) is accommodated inside the resin case 2 of the pressure sensor 1, and a part of the terminal (for example, a power supply terminal) 3 of the pressure detection unit extends from the upper surface of the resin case 2. It protrudes upward in FIG. A lead wire 5 is electrically connected to one end 3 a side of the terminal 3 by a terminal 4, and the pressure detection unit is connected to a microcomputer of a gas meter (not shown) via the lead wire 5. Has been.
[0004]
A cylindrical insulating member 6 made of resin is provided between the upper surface portion of the resin case 2 and the terminal 4 on the outer peripheral portion of the terminal 3, and a plurality of insulating members 6 are provided on the surface portion of the insulating member 6. Pleats 6a are formed. And the pressure sensor 1 comprised in this way is attached to the metal housing | casing 7 earth | grounded of the gas meter.
[0005]
According to the pressure sensor 1 having the above configuration, for example, when lightning strikes the gas meter, and a surge voltage is applied to the one end 3a of the terminal 3 via the lead wire 5 along with the lightning, for example, most of the surge current is From 3 to the housing 7, the resistance flows along the surface portion of the insulating member 6 which is relatively smaller than in the air. At this time, since the pleats 6a are formed on the surface portion of the insulating member 6, the creepage distance, that is, the path through which the surge current flows is relatively long. Therefore, the current value of the surge current is reduced by flowing through the relatively long path, that is, the impact due to the surge current is eased, so that the resin case 2 is not destroyed.
[0006]
However, in the above-described conventional one, the insulating member 6 is provided separately from the resin case 2 and the crease 6a is formed on the surface portion of the insulating member 6, thereby making the creepage distance relatively long and the lightning surge configuration. Therefore, there are problems that the number of parts increases and the number of assembly steps increases, resulting in an increase in manufacturing cost. Moreover, in the insulating member 6, it is difficult to manufacture the pleats 6a, which also increases the manufacturing cost.
[0007]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a pressure sensor that can satisfactorily realize a lightning surge-proof configuration without increasing the manufacturing cost.
[0008]
[Means for Solving the Problems]
According to the first and second aspects of the present invention, for example, when a surge voltage is applied to the terminal of the pressure detection unit by a lightning strike, most of the surge current is compared in resistance from the terminal of the pressure detection unit toward the ground plane. It flows along the surface portion of a small resin case. At this time, since the surge current flows along the surface portion of the creeping distance extension integrally provided in the resin case, the path through which the surge current flows is relatively long, and the current value of the surge current is reduced. Shock caused by surge current can be reduced. Therefore, even when a surge voltage is applied due to a lightning strike, the resin case is not destroyed by the impact of the surge current flowing, that is, a lightning surge configuration can be realized well.
[0009]
In this case, the creeping distance extension is integrally provided in the resin case, so there is no increase in the number of parts or assembly man-hours, and it is also necessary to form folds as in the conventional case. Since there is no, the manufacturing cost does not increase. In addition, it is preferable that the creepage distance between the terminal of a pressure detection part and a ground surface is 17 millimeters or more in a resin case.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below with reference to FIGS.
The resin case 12 of the pressure sensor 11 includes a housing 13 made of, for example, PBT (polyvinyl terephthalate) resin, and a cover 14 that covers the housing 13 from above in FIG. The housing 13 includes a base portion 15 and a convex portion 16 projecting downward from the base portion 15 in FIG. 1, and a housing portion 17 is formed in the base portion 15. A pressure sensor main body 18 is accommodated in the accommodating portion 17.
[0011]
The pressure sensor main body 18 is provided with a sensor chip 19 at the upper part, and a diaphragm 20 is formed in a thin film shape by etching on the surface side (lower side in FIG. 1) of the sensor chip 19, and the surface side of the diaphragm 20 A plurality of diffusion resistors (not shown) are bridge-connected to the upper side (in FIG. 1). The resistance values of these diffusion resistors are changed in accordance with the change in pressure acting on the diaphragm 20. The pressure sensor main body 18 is fixed in the housing portion 17 with an adhesive 21.
[0012]
An analog amplification IC chip 22 and a digital arithmetic processing IC chip 23 are respectively fixed to the upper surface of the base 15 by an adhesive. The pressure detector 24 referred to in the present invention is constituted by the pressure sensor main body 18, the analog amplification IC chip 22 and the digital arithmetic processing IC chip 23. At this time, the sensor chip 19 of the pressure sensor body 18 and the analog amplification IC chip 22 are electrically connected by a wire 25, and the analog amplification IC chip 22 and the digital arithmetic processing IC chip 23 are electrically connected by a wire 26. It is connected. The surface portions of the chips 19, 22 and 23 are coated with a resin 27 for protecting the chips 19, 22 and 23.
[0013]
Further, the power supply terminal 28, the ground terminal 29, and the output signal terminal 30 (see FIG. 2) of the pressure detection unit 24 made of phosphor bronze, for example, are bonded to the base portion 15 by welding (in FIG. 1, the power supply terminal). 28). The digital arithmetic processing IC chip 23 of the pressure detection unit 24 and the terminals 28 to 30 are electrically connected by wires 31. Each of the terminals 28 to 30 is bent in a substantially “L” shape, passes through each of the through holes 14 a to 14 c formed in the cover 14, and protrudes upward in FIG. 1 from the upper surface portion of the resin case 12. . At this time, the width dimension of each through-hole 14a-14c is set larger than the width dimension of each terminal 28-30, and there is a gap between the inner wall part of each through-hole 14a-14c and each terminal 28-30. Has occurred.
[0014]
And the one end part 28a-30a side of each terminal 28-30 is connected to the lead wire 35 via the terminals 32-34, respectively, and the lead wire 35 is connected to the microcomputer of a gas meter (not shown). Has been. Note that the other end portions of the terminals 28 to 30 protrude from the left end portion of the base portion 15 in FIG. 1 for convenience of manufacturing (FIG. 1 shows the other end portion 28b of the power supply terminal 28. ing).
[0015]
Here, at the right end portion and the left end portion of the base portion 15 in FIG. 1, wall portions 36 and 37 as creepage distance extension portions are respectively flush with the side surface portion of the base portion 15 in FIG. 1. It is integrally formed so as to extend downward.
[0016]
A pressure introducing hole 38 is formed in the convex portion 16 of the housing 13. The pressure introduction hole 38 communicates with the pressure introduction hole 41 of the pressure sensor main body 18 through holes 39 and 40 formed in the base 15 and having different inner diameters. Thus, the pressure sensor 11 is configured by the housing 13 configured as described above being covered with the cover 14 from above in FIG. 1. At this time, the claw portion 13a formed in the housing 13 is hooked in the hole portion 14d formed in the cover 14, whereby the housing 13 and the cover 14 are fixed (see FIG. 2).
[0017]
The pressure sensor 11 is attached to a metal casing 43 as a grounding surface of the gas meter by screws 42. In the state where the pressure sensor 11 is attached to the housing 43 of the gas meter, the lower portion of the convex portion 16 of the housing 13 is buried in the housing 43, and the space between the convex portion 16 of the housing 13 and the housing 43 is between. Is provided with an O-ring 44 for maintaining hermeticity. Further, the one end portion 28a and the other end portion 28b of the power terminal 28 protrude from the base portion 15 of the housing 13 (indicated by P and Q in FIG. 1, respectively), and the convex portion 16 of the housing 13 is the housing. The creepage distances between the portions projecting from 43 (indicated by R and S in FIG. 1 respectively) are each 17 mm or more.
[0018]
Next, the operation of the above configuration will be described.
In the pressure sensor 11, for example, when the pressure acting on the diaphragm 20 of the pressure sensor body 18 changes due to the pressure of gas such as LP gas or city gas, the resistance value of the diffusion resistance changes, and according to the change in the resistance value. The electrical signal is output from the sensor chip 19 of the pressure sensor body 18 to the analog amplification IC chip 22. The electric signal output to the analog amplification IC chip 22 is amplified by the analog amplification IC chip 22, is output to the digital arithmetic processing IC chip 23, and is subjected to arithmetic processing (for example, correction processing by temperature) by the digital arithmetic processing IC chip 23. . Then, the result of the arithmetic processing is output to the microcomputer of the gas meter via the output signal terminal 30 and the lead wire 35. As a result, the pressure of gas such as LP gas or city gas is measured.
[0019]
Now, let us consider a case where a surge voltage is applied to at least one of the above-described terminals 28 to 30 by, for example, a lightning strike. For example, when lightning strikes the gas meter and a surge voltage is applied to the one end portion 28a of the power supply terminal 28 via the lead wire 35 along with it, most of the surge current is mostly one end portion 28a and the other end portion of the power supply terminal 28. From the part (P and Q) 28b protrudes from the base 15 of the housing 13 to the part (R and S) from which the convex part 16 of the housing 13 protrudes from the housing 43, resistance is in the air. It flows along the surface portion of the housing 13 which is relatively smaller than the above.
[0020]
That is, most of the surge current flows along the wall portions 36 and 37 provided integrally with the base portion 15 of the housing 13 (see arrows X and Y in FIG. 1). At this time, the path through which the surge current flows is 17 mm or more as described above, and is relatively long.
[0021]
As described above, according to the present embodiment, the wall portions 36 and 37 are provided in the housing 13 so that the creepage distance between the terminals 28 to 30 and the gas meter casing 43 is relatively long. Even when a voltage is applied, for example, the housing 13 is not cracked by an impact of surge current flowing, and the resin case 12 is not destroyed. That is, it is possible to satisfactorily realize a lightning surge surge configuration.
[0022]
At this time, since the walls 36 and 37 are integrally provided in the housing 13, the number of parts and the number of assembling steps are not increased, and the walls 36 and 37 are provided with conventional folds. Since it does not need to be formed, the manufacturing cost does not increase.
[0023]
Further, since the walls 36 and 37 are provided inside the resin case 12, the size can be reduced as compared with the conventional case in which a cylindrical insulating member made of resin is provided outside the resin case 12.
[0024]
Now, the inventors measured the relationship between the creepage distance described above and the withstand voltage that the resin case 12 can withstand destruction, and obtained the measurement results shown in FIG. That is, the resin case 12 was destroyed at 9 kV when the creepage distance was set to 9.7 mm, and was destroyed at 19 kV when the creepage distance was set to 14.2 mm. Therefore, when the pressure sensor 11 is commercialized, the creepage distance and Since the withstand voltage is in a substantially directly proportional relationship, it can be seen that the creepage distance may be set to 12.4 mm or more. In consideration of practical problems, the creepage distance is preferably set to 17 mm or more.
[0025]
The present invention is not limited to the above embodiment, and can be modified or expanded as follows.
Each terminal 28-30 may be composed of iron or a copper alloy instead of phosphor bronze, and may be bonded by insert molding instead of welding.
[Brief description of the drawings]
1 is a longitudinal side view showing an embodiment of the present invention. FIG. 2 is a longitudinal front view. FIG. 3 is a diagram showing a relationship between creeping distance and withstand voltage. FIG. 4 is a side view showing a conventional example. Explanation】
In the drawings, 11 is a pressure sensor, 12 is a resin case, 24 is a pressure detector, 28 is a power supply terminal, 29 is a ground terminal, 30 is an output signal terminal, 36 is a wall (creeping distance extension), and 37 is a wall. Reference numeral 43 denotes a creeping distance extension, and reference numeral 43 denotes a housing (grounding surface).

Claims (2)

In the pressure sensor, the pressure detection unit is housed in the resin case, and the terminal of the pressure detection unit is exposed to the outside from the resin case.
A pressure sensor, wherein a creeping distance extension is integrally provided in the resin case so that a creeping distance between a terminal of the pressure detection unit and the grounding surface is a predetermined value or more. The pressure sensor according to claim 1, wherein the predetermined value is 17 millimeters.

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