JPH0743205A - Piezoelectric vibration sensor device - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain a piezoelectric vibration sensor device in which the sensitivity does not fluctuate due to temperature changes and humidity changes and in which sensitivity aging is small. A piezoelectric type vibration sensor device includes a circuit board 10 having a vibration detecting portion 20 fixed on one surface and a circuit element portion 30 mounted on the other surface, and the circuit element portion 30 has a waterproof resin layer. It is sealed with 40.

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 incorporating a circuit element such as an impedance conversion circuit, and in particular, it suppresses fluctuations in sensitivity due to changes in temperature and humidity as compared with the conventional type vibration sensor device. The present invention relates to a piezoelectric vibration sensor device having a small aging.

[0002]

2. Description of the Related Art Conventionally, as a piezoelectric vibration sensor for measuring vibration of an object, a piezoelectric vibration sensor using a piezoelectric element in which a film-shaped piezoelectric material such as polyvinylidene fluoride is sandwiched between electrode films is widely used. However, since the output impedance from this piezoelectric element does not match the input impedance of a normal electric circuit such as a counting device or a display device as it is, a circuit board mounted with a circuit element part such as an impedance conversion circuit,
Piezoelectric vibration sensor devices having a structure incorporated in a package together with the above piezoelectric element have come to be used.

FIG. 3 shows a conventional example of a piezoelectric vibration sensor device having the above structure. In FIG. 3, the piezoelectric vibration sensor device includes a circuit board 10 on which a vibration detection unit 20 using the above-mentioned piezoelectric element and a circuit element unit 30 for performing impedance conversion of its electrical output are mounted, and this circuit. Board 10
And a pedestal 50 that is fixed to the object to be measured. The pedestal 50 is a seat surface 5 fixed to the object to be measured.
1 and a facing surface 52 parallel thereto, and at the center of the facing surface 52, a concave portion 53 for accommodating the vibration detector 20 in a non-contact manner is formed. The circuit board 10 having the circuit element portion 30 mounted on one surface thereof is fixed to the facing surface 52 so as to cover the concave portion 53 on the other surface. The vibration detection unit 20 extending in a non-contact manner into the recess 53 of the pedestal is fixed to this surface by the surface 28 of the object-side support plate 21. The sensing axis G of the vibration detecting section 20 is configured to be perpendicular to the seat surface 51 of the pedestal.

The vibration detector 20 in this apparatus is shown in FIG.
The structure is as shown in. That is, in FIG. 2, the vibration detection unit 20 includes, in order, the object-side support plate 21 and the object-side electrode film 2 that are fixed to the circuit board 10 at the surface 28.
2, the film-shaped piezoelectric body 23, the load body side electrode film 24, the load body side support plate 25, and the load body 26 acting as an inertial mass are laminated and adhered in parallel by a dielectric adhesive 27 such as an epoxy adhesive. All layers are formed so as to be line-symmetric with respect to the sensing axis G passing through the center of the surface of the film-shaped piezoelectric body 23 perpendicularly. The vibration detection unit 20 is sensitive to the acceleration generated by the vibration of the object to be measured, and the electrodes 22,
A potential difference is generated between 24. Its sensitivity is maximum in the direction of the sensing axis G. The support plates 21 and 25 are
Both are made from rigid bodies such as cloth-phenolic resin laminates and glass fiber-epoxy laminates.

As shown in FIG. 3, the structure composed of the vibration detecting section 20, the circuit board 10 and the pedestal 50 has a pedestal 50.
Is covered with a package 60 that fits on the side surface of the. An end portion 61 of the package 60 is in contact with and fixed to an edge portion 54 extending along the peripheral edge of the seat surface 51 of the pedestal. The seat surface 51 including the edge portion 54 is fixed to the object to be measured. When fixed, the sensing axis G of this piezoelectric vibration sensor device is perpendicular to the mounting surface of the object to be measured.
In the package 60, an output lead wire 71 and a power supply wire 72 are drawn out from the circuit element section 30 and connected to a connection cable 75 outside the package by a receptacle 73 and a plug 74.

[0006]

In the above piezoelectric vibration sensor device, the measurement sensitivity is remarkably changed due to temperature change and humidity change at the time of measurement, and the sensitivity is unstable and stable immediately after the start of measurement. However, there was a problem that it took a long time to perform so-called "aging". 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 sensitivity does not change due to temperature changes and humidity changes and the aging is minute.

[0007]

The above problems can be solved by sealing the circuit element portion on the circuit board with a waterproof resin layer. At this time, a cloth-
The stability of sensitivity is further improved by using the phenol resin laminate.

Here, the waterproof resin is a waterproof and electrically insulating resin that seals the circuit element portion and adheres to the circuit board, and is either a thermoplastic resin or a thermosetting resin. It may be. Examples of the thermoplastic resin include methacrylic resin and polyamide resin, and examples of the thermosetting resin include epoxy resin, phenol resin, polyurethane resin, unsaturated polyester resin and silicone resin. These resins may contain various inorganic or organic fillers, antioxidants, plasticizers, crosslinking agents, radiation blocking agents, colorants and the like. The waterproof resin layer is made by pouring the waterproof resin directly onto the circuit board on which the circuit element part is mounted so that the circuit element part is completely covered, and by encapsulation casting, transfer molding or injection molding. It can be formed by heating and curing if necessary. The thickness of this waterproof resin layer is preferably about 3 to 10 mm, but this thickness changes depending on the bulkiness of the circuit element portion. The point is that the entire circuit element portion should be covered with the waterproof resin layer to the extent that water can be prevented from entering.

A conventional piezoelectric vibration sensor device of the same type is
The problem that the measurement sensitivity fluctuates due to temperature changes and humidity changes during measurement, and that sensitivity is unstable immediately after the start of measurement and aging tends to occur is not clear, but a small amount of water may cause some problems in the electric circuit on the circuit board. It is thought to have an effect. The present inventors have found that these problems can be solved or alleviated by completely sealing the circuit element portion of the circuit board with the waterproof resin layer, and have reached the present invention. Further, the support plate of the vibration detection unit is generally a rigid body made of cloth-phenol resin laminated plate, glass fiber-epoxy resin laminated plate, or the like, but the circuit element unit of the present invention is sealed with a waterproof resin layer. In the piezoelectric vibration sensor device, it has been found that the stability of sensitivity is further improved, although the reason is unknown, particularly when a cloth-phenol resin laminate is used.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of the piezoelectric vibration sensor device of the present invention. In FIG. 1, the piezoelectric vibration sensor device differs from the conventional piezoelectric vibration sensor device shown in FIG. 3 in that the circuit element portion 30 on the circuit board 10 is sealed with a waterproof resin layer 40. . Therefore, the same components as those of the conventional device are designated by the same reference numerals, and the description thereof will be omitted. In this embodiment, the waterproof resin layer 40
Is made of quartz powder-added epoxy resin, and is formed on the circuit board 10 so as to have a thickness of 3 mm or more by completely sealing the circuit element portion 30. The output lead wire 71 and the power supply wire 72 are partially embedded in the waterproof resin layer 40, and
It is derived from 0. A cloth-phenol resin laminated plate was used as the support plate (reference numerals 21 and 25 in FIG. 2) of the vibration detection unit 20.

Next, the operation of this piezoelectric vibration sensor device will be described with reference to FIGS. 1 and 2. In FIG. 1, when a piezoelectric vibration sensor device is fixed to an object to be measured, and vibration in the direction of the sensing axis G occurs in the object to be measured, the acceleration of the vibration is successively increased from the seat surface 51 to the pedestal 50 and the circuit board 10.
Is transmitted to the vibration detection unit 20 via. Then, in FIG. 2, this acceleration is transmitted from the surface 28 to the object-side support plate 21, and further vibrates the film-shaped piezoelectric body 23 through the object-side electrode film 22. However, since the load body 26 resists this acceleration as an inertial mass, the load body side of the film piezoelectric body 23 resists vibration, and as a result, the film piezoelectric body 23 receives a pressure corresponding to the amplitude of vibration. Therefore, a potential difference corresponding to the pressure is generated between the object-side electrode film 22 and the load-side electrode film 24. This potential difference (voltage) is applied to the circuit element unit 30 on the circuit board by a lead wire (not shown).
(FIG. 1). In FIG. 1, the circuit element unit 30
Is operated by the current supplied from the power line 72,
The above voltage is subjected to a process such as impedance matching, and output as a vibration signal to the connection cable 75 via the output lead wire 71, the receptacle 73, and the plug 74.

COMPARATIVE EXAMPLE A conventional piezoelectric vibration sensor device shown in FIG. 3 in which the circuit element portion 30 was not sealed with the waterproof resin layer 40 was used as a comparative example.

With respect to the piezoelectric type vibration sensor devices of the examples and the comparative examples, fluctuations in sensitivity when the environmental temperature or the environmental humidity was changed were measured. Regarding the sensitivity fluctuation corresponding to the temperature change, 80 Hz for the sample (Example or Comparative Example),
The sensitivity was measured by changing the ambient temperature from −30 ° C. to + 100 ° C. while applying a vibration of 1 G, and the maximum fluctuation range of the sensitivity when the sensitivity at 25 ° C. was set to 1 was displayed as ±%. Regarding the sensitivity fluctuation corresponding to the humidity change, the sensitivity is measured by changing the environmental humidity from 0% to 100% while applying the vibration of 80 Hz and 1 G to the sample.
The fluctuation range of the sensitivity when the sensitivity at humidity 0% is set to 1 is shown in%. The above measurement results are shown in Table 1.

[0014]

[Table 1]

From the above results, the piezoelectric vibration sensor device of the embodiment in which the circuit element portion 30 is sealed with the waterproof resin layer 40 has sensitivity fluctuations with respect to changes in temperature and humidity as compared with the comparative example which is not sealed. It is clear that the number has decreased significantly. Further, in the process of measurement, it was confirmed that the piezoelectric vibration sensor device of the example also had improved aging characteristics.

[0016]

In the piezoelectric vibration sensor device of the present invention, since the circuit element portion on the circuit board is sealed with the waterproof resin layer, the sensitivity does not change due to temperature change or humidity change, The sensitivity hysteresis is also reduced, and the sensitivity aging is extremely small. At this time, if the support plate of the vibration detection unit is made of cloth-phenol resin laminated plate,
The sensitivity becomes more stable. Since the sealing with the waterproof resin layer can be performed very easily, the performance of the conventional piezoelectric vibration sensor device can be significantly improved without increasing the price thereof. In addition, since it has high resistance to temperature and humidity, it can be used for vibration measurement even under severe temperature and humidity environments, and can be applied to fields where conventional piezoelectric vibration sensor devices could not be used, increasing versatility. .

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the structure of a vibration detection unit.

FIG. 3 is a sectional view showing a conventional piezoelectric vibration sensor device.

[Explanation of symbols]

10 ... Circuit board, 20 ... Vibration detection part, 30 ... Circuit element part, 40 ... Waterproof resin layer, 50 ... Pedestal.

Claims (1)

[Claims] 1. A piezoelectric type vibration having a circuit board having a vibration detection part fixed on one surface and a circuit element part mounted on the other surface, the circuit element part being sealed with a waterproof resin layer. Sensor device.