JPS6190030A - Piezoelectric oscillator pressure sensor device - Google Patents

Abstract

PURPOSE:To detect pressure which has a wide temperature range and a wide pressure range by providing counter electrodes and three couples of piezoelectric oscillators in an airtight container, connecting an oscillation circuit externally through an electric circuit formed of the counter electrodes and one of the piezoelectric oscillators, and deciding on the frequency of the oscillator. CONSTITUTION:The diaphragm 2 is provided on the top surface of the airtight container 1. The counter electrodes 2a are provided on the reverse surface of the diaphragm 2. The piezoelectric oscillators 3 are provided opposite the electrodes 2a, and oscillation parts 3a, 3b, and 3c are fitted thereto. Then, a pressure difference applied to the diaphragm 2 is converted electrically by the counter electrodes 2a and oscillation part 3a and connected to the external oscillation circuit 7. Then, the electric signal is led to the frequency decision circuit 6 including the oscillation parts 3b and 3c through a buffer 5 to detect variation in frequency and detect the pressure. Then, the plural oscillation parts are provided, so an error caused by variation of temperature charac teristics of a piezoelectric body is eliminated and the pressure is detected with high precision.

Description

[Detailed Description of the Invention] [Field of Application with 1m] The present invention relates to a pressure sensor device using a piezoelectric vibrator, and in particular, utilizes the stability of the frequency of a piezoelectric vibrator, and has a wide range of temperature and pressure. The present invention relates to a piezoelectric vibrator pressure sensor device capable of detecting a pressure within a range of 1C7 using an 1C7 flow.

(Prior art and its problems) Figures i7s9 and :jS1O are explanatory diagrams for explaining an example of a conventional pressure sensor. A plum 21 is provided. On the back side of the diaphragm 21 is an electrode b.
1. b2, and the electrodes b1 and b2 are provided with an internally opposing electrode a, so that when the pressure outside the diaphragm changes, the diaphragm changes, and the distance between the electrodes bl, b2 and the internally opposing electrode a increases. will change, so this change can be expressed as capacitance 41. It is detected as a change in c and used as a pressure sensor. However, this type of pressure sensor is 1! Extreme, b2 and internal facing I
Setting the t-pole a is troublesome, and it is also difficult to make adjustments to widen the pressure range.

On the other hand, piezoelectric vibrators generate strong resonance at their natural frequency (also called electrical resonance frequency) when excitation power is applied, so they have been widely used in dLff machines as a means of obtaining a stable constant frequency. There was a strong desire to learn how to measure pressure using a camera.

(Objective of the Invention) The present invention is a compact pressure sensor that is not affected by the An object of the present invention is to provide a TL vibrator pressure sensor device.

(IN Essentials of the Invention) The present invention is characterized in that three pairs of identical 'Wl pole pairs (vibrating parts) that vibrate through thickness and are formed on the same flat plate-shaped pressure plate are arranged at a predetermined distance apart in an airtight container. , a counter mandrel is provided parallel to the surface of the centrally located electrode pair (rA and B), the diaphragm transmitting the displacement caused by the pressure difference, and this counter electrode and the opposite electrode of the central electrode pair A frequency discrimination circuit in which an oscillation circuit for externally connecting oscillation is connected between the side electrodes, and two one-pole pairs (vibrating portions) other than the central t-pole pair are connected from the oscillation circuit via a buffer. is connected to detect the change in frequency as the f1 output.

(X Example) Hereinafter, an uninvented example will be described in detail with reference to the drawings.

Fig. 1 is a cutaway view of the inside of the piezoelectric vibrator pressure sensor device, and Fig. 2 is a circuit diagram of the piezoelectric vibrator pressure sensor device. 2a is the opposing '@ pole attached to the back side of the diaphragm, 3 is the pressure i
t vibrator piece, 3&~3c a piezoelectric vibrating part, 4 a piezoelectric vibrator piece holder, 5 a constant eyebrow pressure buffer, 6 a frequency discrimination circuit,
7 is an oscillation circuit.

Next, the operation of this piezoelectric vibrator pressure sensor device 2 will be explained. First, the same flat plate-like pressure ? Three pairs of identical electrodes (vibrating parts) formed on the ttM actuator 3 that vibrate through the thickness are separated by a predetermined distance (1 of the wavelength in the piezoelectric material) at which it can be considered that they are not acoustically coupled to each other.
0 times or more). Among these vibrating parts, the diaphragm 2 has a counter electrode 2 corresponding to one surface of the central vibrating part 3b that transmits the displacement caused by the pressure difference.
Provide a. This counter electrode 2a and this central vibrating part 3b
An oscillation circuit 7 for sustaining oscillation from the outside is connected to an electric circuit formed between the cauterizing electrode 2a and the electrode on the opposite side.

On the other hand, from this oscillation circuit 7, three pairs of electrodes (vibration part) 3m, 3
A change in 43 frequencies is detected as a DC output to a frequency discrimination circuit 6 which includes two vibrating parts 3m and 3c, excluding the central vibrating part 3b, among the vibrating parts b and 3c. In addition, in the W4 wave number discrimination circuit 6, the capacitor C5 is a tuning capacitor of the matching transformer T, and the capacitors C2 and C2 are approximately the vibrating portions 2a and 2c.
be equal to the capacitance 'k c o. Resistor R is a detection output load resistance.

The operation of L6 will be explained in more detail.

When the pressure of the diaphragm 2F changes, the pressure difference between it and the atmospheric pressure inside the airtight container l changes, so the diaphragm 2 is displaced in accordance with the change in the pressure difference. Then, the counter electrode 2m#3'11 attached to the diaphragm 2 is placed.

On the other hand, the piezoelectric vibrator piece 3 is held by the holder 4 and is not affected by pressure fluctuations. In other words, the vibrating part 3b formed on the piezoelectric vibrator piece 3 is not displaced even by pressure fluctuations.

Therefore, airtight! ! Due to changes in the external pressure of l, to 4
H
t will change.

The device configured in this manner is connected to an external oscillation circuit 7 shown in FIG. 2 to cause oscillation.

That is, the capacitance C1 formed between the opposing #l pole 2& and the vibrating part 3b is connected in series to the vibrating part 3b, and the oscillation circuit 7 is connected to both ends of the capacitance C1.

Then, when a capacitance CL called a load capacitance is inserted in series with the vibration auxiliary circuit of the vibrating part 3b, this ^)
Depending on the magnitude of the capacitance, the natural frequency f and the series resonant frequency f0 change as follows.The interelectrode electrostatic capacitance 6, c1 is the same. It is a constant determined by the electromechanical coupling coefficient of the piezoelectric material called Co /C+ ) and the structure of the piezoelectric vibrator.

Also, as is clear from FIG. 3, this direct capacitance CL is
Opposite electrode 2 and vibration aB attached to diaphragm 2
3brI! It7) PIA*ttt6t.

CL-/(tXs) -=(2).

Here, is the capacitance IIk calculated constant, and S is the counter electrode 2a.
and represents the effective capacitance area formed by the vibrating portion 3b.

Therefore, as is clear from FIG. 2, when the oscillation circuit 7 is connected to the outside of the pressure sensor and oscillates once, a pressure difference is created between the inert gas pressure inside the pressure sensor container and the external pressure of the diaphragm. The diaphragm 2 moves by an amount approximately proportional to the pressure difference between and the elastic repulsive force of the diaphragm.
The gap t (Fig. 3, 8'!', ) changes. Then, due to this change in the gap t, the static 1
Yong Mutsu CL changes.

The vibrating portion 3b, that is, the center electrode pair, appears as a change tΔf in the circumferential fm dispersion f due to the displacement Δt of the diaphragm 2, which can be expressed by the following equation.

'fe'ACL, ':'l ΔCL--Ct"K"11t, °,
It can be detected as a change in 14 wave numbers proportional to the displacement of the diaphragm 2 by adding 'cte"fs"Δt to Δ+−−.

As is clear from FIG. 2, the signal detected here is guided to the Yarman transformer T via the buffer 5.
The configuration is such that it is detected as a DC voltage V via a frequency discrimination circuit 6 formed by other vibrating parts 2m and 2c of the same structure formed on the same piezoelectric vibrator piece 3. Moreover, as is clear from FIG. 5, the frequencies of the vibrating parts 2m and 2c are changed to
The frequencies are set at approximately equal intervals around the center, but depending on this position, the S characteristic of the frequency discrimination circuit can be selected! a Sensitivity can be set freely. However, here, when the displacement Δt=O,
Adjustment is made in advance so that Δf-0.

Next, this pressure - is the pressure i' of the vibrator pressure sensor device.
T'n4iIll! ! The specific configuration of the m adjustment means will be explained.

:! S5 diagram to iSa diagram are y4! of the pressure sensor. !
In Figure 0, which is an explanatory diagram of one embodiment of the means, 6 is a Y4 commonly used thumbscrew, 7 is a coil spring, and 8 is m! i! This is a bolt, and the other parts are the same as those in the embodiment described above, so a description thereof will be omitted.

Next, the operation of this adjusting means will be explained.

Normally, as shown in Fig. 5, in order to set the adjustment port 8 in the direction that rotates toward the diaphragm, use the coil spring 7 to fully rotate the knob 6 along the anti-rotation groove provided in the adjustment bolt 8. The piezoelectric vibrator 3 is fixed. In order to adjust the bf measurement range of the 0-order pressure which is drawn from the diaphragm counter electrode 2a, the pole 3 & is adjusted by turning the knob 6 of the piezoelectric vibrator 3 and pushing up the adjustment bolt 8 from the state shown in Fig. 8 to set the gap t. Make smaller. 3. By changing the gap t between the pressure itN mover 3 and the diaphragm counter electrode 2 in this way, the capacitance CL can be changed. Therefore, the possible pressure range can be adjusted. In addition, in order to maintain air-tightness between the airtight volume Ml and the adjustment bolt 8, for example, 1.

As shown in FIG. 8, a bellows 7& is provided around the spring 7. In addition, the diaphragm counter electrode 2
By appropriately selecting the angle 0 formed by & and the pressure Ml oscillator 3 in advance, the pressure measurement range can be freely set over a wide range.

Although the case of a single-sided diaphragm is shown here, the pressure IT vibrator can be held on the side of the empty vessel or on the other diaphragm surface 2.
Needless to say, if it is fixed in place, it can be made into a diaphragm.

Furthermore, although the present invention has been described by way of one embodiment, the present invention is not limited to this embodiment.

According to the uninvented ↑ point, various variations are available.

This does not exclude these from the scope of 1 (9
According to RIll, there is a pressure 'N in the airtight container and a lifting force f B
In order to obtain a pressure sensor device, n:
The z oscillator operates stably regardless of atmospheric conditions and has good reproducibility. Moreover, three vibrating parts 2a and 2b are provided on the same piezoelectric vibrator piece.

2c are arranged with the same structure, the conditions of the 6 vibrating parts are the same, and in particular, a compact and highly reliable pressure sensor device that does not cause errors due to changes in the temperature characteristics of the piezoelectric body. can be obtained. Furthermore, by using a part of the output of one oscillation circuit, it is possible to accurately and fillly obtain an output voltage proportional to the differential pressure displacement between the internal pressure of the container and the pressure to be measured.

[Brief explanation of drawings]

FIG. 1 is a perspective view of the inside of the piezoelectric vibrator pressure sensor device according to the present invention, FIG. 2 is a circuit diagram of the pressure sensor device according to the present invention, and FIG. Figure 4 is an explanatory diagram explaining changes in frequency, Figures 5 to 8
The figure is a J'JI diagram that explains the A adjustment function in the eaves side range of pressure.
The ninth factor is a perspective view of a conventional pressure cell, and FIG. 10 is a sectional view of FIG. 9. l...Air heating container, 2...Diaphragm, 2a...
Counter electrode, 3... Piezoelectric vibrator piece, 3m, 3b, 3c.
... Shaking i11 part, 4... Pressure tIi mover holder, 5.
··buffer. 6... Frequency discrimination circuit, 7... Oscillation circuit, 8...
Adjustment knob, 9...Adjustment positioning device, 1G...
・Adjustment lot. Patent applicant: Japan Denpa Kogyo Co., Ltd. Representative: Patent attorney Minoru Tsuji Figure 10

Claims (1)

[Claims] In an airtight container, three pairs of identical electrodes that vibrate in thickness and are formed on the same flat piezoelectric material are arranged at a predetermined distance apart, and a diaphragm is placed parallel to one surface of the central pair of electrodes. An oscillation circuit for sustaining oscillation is connected from the outside between the opposing electrode and the electrode on the opposite side of the opposing electrode of the central pair of electrodes, and the oscillating circuit A piezoelectric vibrator pressure sensor device characterized in that a frequency discrimination circuit including two electrode pairs other than the center electrode pair is connected through a buffer to detect a change in frequency as a DC output.