JPH06201451A - Piezoelectric vibration sensor - Google Patents

Abstract

PURPOSE:To enhance SN ratio by providing a conductive layer through a signal processing circuit board secured to a detecting section and constituting a containing body covering the board and the conductive layer integrally with a containing body for sensor. CONSTITUTION:A piezoelectric vibration sensor 23 comprising a detector 35 and a load body 36 is contained in a recess 22 made in the stainless steel (conductive) containing body 21 a for a package 21. A signal processing circuit board 25 secured to the detecting section 35 is supported by the peripheral edge part 24 around an opening of the containing body 21a and a conductive layer 26 of silver paste is provided above the substrate 25. A containing cover body 21b covering the substrate 25 and the conductive layer 26 is then fit to the opening of the containing body 21a thus realizing an integrated structure. Since the detecting section 25 is double shielded equivalently by means of the conductive layer 26 and the containing cover body 21b made of a conductive material, SN ratio and thereby noise resistance can be enhanced significantly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric vibration sensor device in which a piezoelectric vibration sensor formed by using a piezoelectric body is housed in a package, and particularly, a piezoelectric vibration sensor having improved noise resistance. The present invention relates to a sensor device.

[0002]

2. Description of the Related Art Conventionally, various types of piezoelectric vibration sensors have been developed which are constructed by using a piezoelectric body. For example, the structure of the sensor includes a compression type, a stepped type, a beam type, a film type and the like. In addition, there are materials that use a ceramic material, a plastic material, or a mixture thereof as the material of the piezoelectric body. Then, in order to improve the mass productivity of such a piezoelectric vibration sensor, as a mass production method, an adhesive is applied to both surfaces of the piezoelectric body to fix each electrode, and depending on the intended use, the electrode and the piezoelectric body may be adhered. A piezoelectric vibration sensor excellent in mass productivity is being developed, such as after the support plate is unfastened and then cut into chips by a cutting means such as a dicing saw to mass-produce a large number of detection units. However, since the piezoelectric type sensor as described above has high impedance, it is susceptible to electrical noise. Therefore, conventionally, a piezoelectric vibration sensor device has been constructed in which the sensor is housed in a package having an electromagnetic wave shielding property.

An example of the above piezoelectric vibration sensor device is shown in FIG. Reference numeral 1 in the figure is a piezoelectric vibration sensor. The piezoelectric vibration sensor 1 has a cylindrical shape and includes a pedestal 2, a detection unit 3, and a load body 4. The detection unit 3 is formed by sandwiching both sides of the film-shaped piezoelectric body 5 with electrodes (not shown), and further sandwiching both sides with the support plates 6 and fixing them. The piezoelectric vibration sensor 1 is housed and fixed in a hollow cylindrical hollow package 7 made of a material such as plastic.

The hollow package 7 is integrally provided with an annular sensor mounting portion 8 projecting inward of the hollow package 7 slightly below the center in the longitudinal direction thereof. Further, a disc-shaped mounting portion 9 is provided at the base of the hollow package 7.
Are integrally mounted, and the mounting portion 9 fixes the piezoelectric vibration sensor device to the object to be measured. Further, only the peripheral portion of the pedestal 2 of the piezoelectric vibration sensor 1 is mounted on the sensor mounting portion 8 of the hollow package 7 so as to be laid over and fixed by an appropriate fixing means such as screwing. As a result, the piezoelectric vibration sensor 1 is accommodated and fixed in the hollow package 7 in a floating state,
A void is formed on the lower surface side of the pedestal 2.

On the lower surface of the base 2 of the piezoelectric vibration sensor 1, a signal processing circuit board 17 having an electric circuit including an impedance conversion circuit and an amplification circuit for processing an electric output from the detection section 3 is mounted. Is attached. Further, on the surface of the signal processing circuit board 17 on which the electric circuit is mounted, a temperature assurance element (not shown) for mounting the electric output from the detection unit 3 is mounted. When the plug 13 connected to the connection cable 12 is inserted into the receptacle 11 of the connector attached to the lower portion of the hollow package 7, the piezoelectric vibration sensor 1 is supplied with power by the power supply lines 14 and 15, and the power supply line 14, The signal is output to the outside by 15.

In such a piezoelectric vibration sensor 1, the axis perpendicular to the film-shaped piezoelectric body 5 and passing through the center of the load body 4 is the vibration sensing axis G. In such a piezoelectric sensor 1, by attaching the mounting portion 9 of the hollow package 7 to the object to be measured, it is possible to detect a vibration change in the direction of the sensing axis G of the object to be measured.

[0007]

However, the piezoelectric type vibration sensor device 10 having the above-mentioned structure is often used in an environment susceptible to electrical noise, and its measured vibration level is very low. As described above, there is a problem that the S / N ratio (ratio of signal body noise) is insufficient only by the shield effect obtained by housing the piezoelectric vibration sensor 1 in the electromagnetic wave shielding package 7 or the like.

Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide a piezoelectric vibration sensor device in which the S / N ratio is remarkably improved.

[0009]

In order to solve the above-mentioned problems, a piezoelectric vibration sensor device according to the present invention is designed so that a load is applied to a detection unit having electrodes fixed via adhesive layers provided on both surfaces of a piezoelectric body. In a piezoelectric vibration sensor device in which a piezoelectric vibration sensor having a body attached thereto and a signal processing circuit board fixed to a detection portion of the piezoelectric vibration sensor are accommodated in a package, the package is accommodated. It is composed of a body and a storage cover that covers the upper opening of this storage body,
The storage body and the storage cover are made of a conductive material,
The piezoelectric vibration sensor is housed in the recess provided in the housing, and a conductive layer is provided on the signal processing circuit board through the signal processing circuit board fixed to the piezoelectric vibration sensor. A storage cover that covers the signal processing circuit board and the conductive layer is integrated with the storage body.

[0010]

In the piezoelectric vibration sensor device of the present invention having the above structure, the piezoelectric vibration sensor is accommodated in the concave portion of the container of the conductive package, and the signal is fixed to the detection portion of the piezoelectric vibration sensor. A conductive layer is provided via a processing circuit board, and a storage cover that covers the signal processing circuit board and the conductive layer is integrated with the storage body, and the detection unit of the piezoelectric vibration sensor is The conductive layer provided on the signal processing circuit board and the housing cover made of a conductive material are equivalently doubly shielded.
The / N ratio can be remarkably improved, and the noise resistance can be remarkably improved.

Further, the piezoelectric vibration sensor device of the present invention has a lower center of gravity than the conventional piezoelectric vibration sensor device, so that impact resistance is improved and crosstalk can be reduced. Further, in the piezoelectric type vibration sensor device of the present invention, when the cable outlet is provided in the housing cover of the package, the detection part of the piezoelectric type vibration sensor is a conductive layer provided on the signal processing circuit board. Since it can be doubly covered by the storage cover, reliability of water resistance and oil resistance can be improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the piezoelectric vibration sensor device according to the present invention will be described below with reference to the drawings. As shown in FIG. 1, the piezoelectric vibration sensor device according to the present embodiment has piezoelectric recesses 22 formed in the housing 21a of a conductive package 21 including a housing 21a and a housing cover 21b. The sensor 23 is housed, and the signal processing circuit board 25, to which the piezoelectric vibration sensor 23 is fixed, is supported in the opening peripheral edge portion 24 of the housing 21a, and the conductive layer 26 is provided on the signal processing circuit board 25. Then, the housing cover 21b that covers the signal processing circuit board 25 and the conductive layer 26 is configured to be fitted at the upper opening of the housing 21a. The signal circuit board 2
As shown in FIG. 1, the conductive layer 26 on the storage cover 2
It is preferably electrically connected to 1b.

The upper part of the storage cover 21b is
A cable outlet 27 is provided, a connector is attached to the cable outlet 27, and a power supply line 29 ...
Are connected to the signal processing circuit board 25 through the conduction holes 26a provided in the conductive layer 26.
Therefore, by inserting the plug 31 to which the connection cable 30 is connected to the receptacle 28, the piezoelectric type vibration sensor 23 having the above-described configuration is supplied with power by the power supply line 29. 29 ...
• causes the signal to be output to the outside. In addition, the first embodiment
In the above, the outlet 27 of the cable is provided on the upper portion of the storage cover 21b, but it may be provided not only on the upper portion of the storage cover 21b but also on the side portion or the like depending on the use purpose, which may affect other functions. There is no such thing.

The piezoelectric vibration sensor 23 includes a piezoelectric body 32.
Electrodes (not shown) via adhesive layers (not shown) on both sides of the
Is adhered to the support plate 3 on both sides of the electrode with an adhesive layer interposed therebetween.
3, a detection unit 35 including 34, and the detection unit 3
5, the piezoelectric type vibration sensor 23 has a signal processing circuit board 25 mounted on the surface opposite to the load body 36 provided in the detection unit 35.
Is fixed by. Then, the signal circuit board 2
A temperature compensating element 37 that guarantees the temperature of the output from the detection unit 35 is provided on the surface on which the electric circuit of FIG. Depending on the intended use, the piezoelectric vibration sensor 23 may not be provided with support plates on both the front and back surfaces of the detection unit 35 having the above-mentioned configuration.

The constituent material of the conductive layer 26 provided on the signal processing circuit board 25 is preferably a solder layer or Ag paste, and the conductive layer 26 has a volume resistivity of 5 or less.
It is electrically connected to the storage cover 21b of Ω · cm or less. The storage cover 21b has a volume resistivity of 5 Ω.
If it is not more than cm, either plastic or metal which can be selected as the material can be used.

Therefore, in the piezoelectric vibration sensor device 20 of the present embodiment having the above-mentioned structure, the detecting portion 35 has the conductive layer 26 provided on the upper surface of the signal processing circuit board 25 and the housing cover of the conductive package 21. Since it is equivalently doubly shielded by the body 21a, it is possible to significantly improve the S / N ratio. Further, the piezoelectric vibration sensor device 20 of the present embodiment having the above-mentioned configuration has a lower center of gravity than the conventional piezoelectric vibration sensor device 10 shown in FIG. It is possible to reduce talk. Further, in the piezoelectric type vibration sensor device 20, the cable outlet 27 is provided in the package 2.
By disposing it in the first housing cover 21b, the detecting portion 35 of the piezoelectric vibration sensor 23 is doubly sealed by the conductive layer 26 and the housing cover 21b, thereby improving water resistance and oil resistance. be able to.

In the piezoelectric vibration sensor device 20 as described above, the axis perpendicular to the surface of the piezoelectric body 32 on which the electrodes are formed and passing through the center of the load body 36 is the vibration sensing axis G '. Therefore, in the piezoelectric vibration sensor device 20 as described above, by mounting the measured object on the bottom portion 38 of the housing body 21a of the package 21, it is possible to measure the vibration change of the measured object in the sensing axis G'direction. . Further, when the object to be measured is attached to the upper surface 39 of the storage cover body, it is necessary to provide the cable outlet 27 in a place other than the upper surface of the storage cover body 21b.

Therefore, an example of manufacturing the piezoelectric vibration sensor device of the present embodiment having the above-mentioned structure will be described below. (Production Example) In this production example, 5 mm square, 0.5 mm
Piezoelectric plate 3 made of thick PZT (lead zirconate titanate)
Adhesive made of epoxy resin is applied to both surfaces of No. 2 and a 1 mm thick copper foil is provided therethrough, and this is used as an electrode, and the adhesive made of epoxy resin is further applied to both electrode surfaces. Then, the support plates 33 and 34 made of a glass epoxy plate having a thickness of 1 mm are adhered to each other through the above to form a detection portion 35 of the piezoelectric vibration sensor 23.

An adhesive made of the same material as the above-mentioned adhesive is applied to both surfaces of the detection unit 35, and an impedance conversion circuit and an amplification circuit are previously formed on the surface of one of them through the adhesive. The signal processing circuit board 25 made of the provided ceramic substrate having a thickness of 0.5 mm is provided, the detection unit 35 is fixed, and the detection unit 3 is further provided.
On the other side of 5, the load body 36 made of brass with a weight of 1 g is used.
Are glued together. The piezoelectric vibration sensor 23 including the detection unit 35 and the load body 36 is housed in the recess 22 formed in the housing 21a of the stainless steel package 21 to fix the detection unit 35. 25 is installed so as to be supported by the peripheral edge portion 24 of the housing 21 a, and a conductive layer 26 made of silver paste is provided on the signal circuit board 25. Further, a stainless steel housing cover 21b is provided so as to cover the signal processing board 25 and the conductive layer 26, and the housing cover 21b is fitted and integrated with the upper opening of the housing 21a. Has become.

The upper portion of the storage cover 21b is
A cable outlet 27 is provided, a connector is attached to the cable outlet 27, and a power supply line 29 is pulled out from a receptacle 28 of the connector.
Are connected to the signal processing circuit board 25 through the conductive holes 26a provided in the conductive layer 26. Therefore, by inserting the plug 31 to which the connection cable 30 is connected to the receptacle 28, the piezoelectric vibration sensor 23 having the above-described configuration is supplied with power by the power supply line 29. The signal is output to the outside by.

In the piezoelectric vibration sensor device 20 having the above structure, the axis perpendicular to the surface of the piezoelectric body 32 on which the electrodes are provided and passing through the center of the load body 36 is the vibration sensing axis G '.
Has become. Therefore, in the piezoelectric vibration sensor device 20 of the above-described manufacturing example, the vibration change of the measured object can be detected by attaching the measured object to the bottom portion 38 of the housing 21a.

Then, the following test was conducted to measure the accuracy of the S / N ratio using the piezoelectric vibration sensor device 20 of the above-mentioned manufacturing example. (Test Example) In this test example, in order to compare the accuracy of the S / N ratio with the piezoelectric vibration sensor device 20 of the above-described manufacturing example, the piezoelectric vibration sensors of Comparative Example 1 and Comparative Example 2 shown below. Using the apparatus, an S / N ratio measurement test was conducted under similar conditions. The piezoelectric vibration sensor device of Comparative Example 1 has a structure in which the conductive layer 26 on the signal processing circuit board 25 in the piezoelectric vibration sensor device 20 of the above-described manufacturing example is not provided, and the conductive layer 26 is not formed. Other than the above, the constituent materials of the respective parts are made of the same materials as those in the above-described manufacturing example. As shown in FIG. 2, the piezoelectric vibration sensor device of Comparative Example 2 has a piezoelectric vibration sensor device 20 of the above-described manufacturing example in a peripheral edge portion 24 of an opening of a housing 21a of a package 21 having the same conductivity as that of the manufacturing example. Signal processing circuit board 26 to which the piezoelectric vibration sensor 23 having the same configuration as that of FIG.
And a storage cover 21b similar to that of the above-described manufacturing example, which is provided so as to cover the piezoelectric vibration sensor 23 and the signal processing circuit board 26.

The signal ratio (S) when the piezoelectric type vibration sensor device of each of the manufacturing example, the comparative example 1 and the comparative example 2 having the above-mentioned constitutions was vibrated at 25 Hz and 1 g under the same environmental condition was measured. In addition, the noise level (N) when a motor with an output of 0.75 kW was driven at a distance of 30 cm from the sensor was measured, and the S / N ratio was calculated from the result, and the results are shown in Table 1.

[0024]

[Table 1]

As is apparent from Table 1, the piezoelectric vibration sensor device 20 of the manufacturing example of the present invention can remarkably improve the S / N ratio.

[0026]

According to the piezoelectric vibration sensor device of the present invention having the above structure, the piezoelectric vibration sensor is housed in the concave portion of the housing of the conductive package and is fixed to the detection portion of the piezoelectric vibration sensor. A conductive layer is provided via the signal processing circuit board, and a storage cover that covers the signal processing circuit board and the conductive layer is integrated with the storage body.
The detection part of the piezoelectric vibration sensor is equivalently double shielded by the conductive cover provided on the signal processing circuit board and a storage cover made of a conductive material, so that the S / N ratio is increased. Can be remarkably improved, and noise resistance can be remarkably improved.

Further, the piezoelectric vibration sensor device of the present invention is not limited to a device for measuring vibration, but may be applied to a device formed by using a piezoelectric body such as a piezoelectric acceleration sensor device or a piezoelectric pressure sensor device. Can also be applied and the same effect can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a piezoelectric vibration sensor according to an embodiment and a manufacturing example of the present invention.

FIG. 2 is a schematic configuration diagram of a piezoelectric vibration sensor of Comparative Example 2 used in this test example.

FIG. 3 is a schematic configuration diagram of a conventional piezoelectric vibration sensor.

[Explanation of symbols]

1, 23 ... Piezoelectric vibration sensor 2 ... Pedestal 3, 35 ... Detecting unit 4 ... Load body 5 ... Membrane piezoelectric body 6, 33, 34 ... Support plate 7, 21 ...
Package 10, 20 ... Piezoelectric vibration sensor device 1
7, 25 ... Signal processing circuit board 21a ... Storage body 21b ... Storage cover 22 ... Recessed portion 24 ... Opening peripheral edge portion 2
6 ... Conductive layer 32 ... Piezoelectric body G, G '... Sensing axis

Claims (1)

[Claims] 1. A piezoelectric type vibration sensor in which a load body is attached to a detection section to which electrodes are fixed via adhesive layers provided on both sides of a piezoelectric body, and to the detection section of the piezoelectric type vibration sensor. In a piezoelectric vibration sensor device in which the signal processing circuit board thus formed is housed in a package, the package includes a housing and a housing cover that covers an upper opening of the housing. The cover is made of a conductive material, and the piezoelectric vibration sensor is housed in the recess provided in the housing, and the signal is passed through a signal processing circuit board fixed to the piezoelectric vibration sensor. A piezoelectric vibration sensor device, wherein a conductive layer is provided on an upper part of the processing circuit board, and a housing cover for covering the signal processing circuit board and the conductive layer is integrated with the housing.