JPS5845531A - Pressure sensor - Google Patents

Abstract

PURPOSE:To draw out the displacement consisting of the analog quantity changing in response to pressure directly as a change in frequency by displacing a vibration membrane according to the displacement proportional to the pressure of a pressure detecting diaphragm. CONSTITUTION:One side surface of a detecting diaphragm 10 is used as s surface to be acted with external pressure P, and the other side surface is joined to the central projecting part 18 of a permanent magnet 16. A vibration membrane 20 constituted of a flat plate of a ferromagnetic material is disposed in a reference chamber 14. An excitation electrode 24 and a detection electrode 26 are provided by facing the membrane 20 on the top surface of an insulator 22 as a means for exciting said membrane and a means for drawing signals to the outside. When the membrane 20 is excited by the electrostatic force generated by the electrode 24, the natural frequency thereof is detected with the electrode 26. Then the natural frequency of the membrane 20 by the magnetic force of the magnet 16 is changed by the change in the pressure of the diaphragm 10, and said change is drawn out as a frequency signal, and the pressure P is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency transmission type pressure sensor that extracts the pressure difference (differential pressure) between seven fluids to be measured or one different fluid to be measured as a frequency.

Conventionally, various vibrating pressure sensors have been developed that utilize the fact that the resonant frequency of a vibrator, such as a crystal, changes when pressure is applied to the vibrator.

However, this type of conventional pressure sensor does not have a complex structure, does not have linear resonance frequency characteristics with respect to pressure changes, and has multiple functions that can compare pressures and measure absolute pressure. There was a drawback of not having a village.

Therefore, as a result of various studies in order to obtain a pressure sensor that can overcome the above-mentioned problems of the nine conventional pressure sensors and expand its range of application, the present inventor has discovered that the pressure detection dial 7.
A permanent magnet is fixed on one side of the 2mm. - By arranging a vibrating membrane made of a ferromagnetic material that faces a permanent magnet and is displaced by its magnetic force, and causing the vibrating membrane to vibrate once by the required means, the pressure detecting diaphragm The diaphragm is displaced proportionally to the applied pressure, and the permanent magnet is also displaced, changing the magnetic force on the diaphragm.As a result, the diaphragm is displaced and its natural frequency changes, and this natural vibration Succeeded in developing a pressure sensor that can proportionally extract changes in number as changes in pressure.

Therefore, it is an object of the present invention to provide a pressure sensor that can properly extract the displacement consisting of an analog quantity that changes in response to pressure as a direct frequency change without relying on electronic circuit technical means such as a voltage-frequency converter. is to provide.

In order to achieve the above object, the present invention includes a pressure detection diaphragm 72 on which detection pressure acts, a permanent magnet fixed to the center of the other side of the diaphragm, and a permanent magnet arranged opposite to the permanent magnet and driven by its magnetic force. It is equipped with a vibrating membrane to which an initial displacement is applied, and an excitation means which imparts a natural vibration determined by the displacement to this vibrating membrane, which displaces the vibrating membrane based on the displacement proportional to the pressure of the pressure detection diaphragm, and also displaces the vibrating membrane. It is assumed that t-special W is configured to take out proportionally as a change in its natural frequency.

In the above-mentioned pressure sensor, the vibrating membrane is suitably composed of a flat plate of ferromagnetic material.

Further, as the excitation means for the vibrating membrane, electrostatic force, piezoelectric material, or electromagnetic force can be used.

Furthermore, by placing the vibrating membrane in the vacuum reference chamber, absolute pressure can be measured.

Furthermore, in the present invention, two pressure sensors each comprising a pressure detection diaphragm, a permanent magnet, a vibrating membrane, and an excitation means configured as described above are provided symmetrically, and the vibrating membrane is held in a reference chamber at a predetermined pressure. It is possible to provide a differential pressure sensor capable of extracting the differential pressure between two different pressures acting on the pressure detection dial 7 as a change in the natural frequency of the diaphragm.

Next, an embodiment of the pressure sensor according to the present invention will be described in detail below with reference to the accompanying drawings.

1st I5! This is a diagram of the principle of the pressure sensor of the present invention.

FIG. 82 is a sectional view showing an embodiment of the pressure sensor of the present invention. That is, in FIG. #II and FIG.
) The outer periphery of the staff is fixed to a case saw, the - side is used as an external pressure acting surface, and the reference ii/l is attached to both sides on the other side. In addition to the detection diamond 72410, a permanent magnet /l is arranged at the center of the IITrJ, and a central protrusion /r provided on the permanent magnet /r is joined to the detection diamond 72m 10. Criterion i
i/4'tCa, a vibrating membrane λθ made of, for example, a flat plate of ferromagnetic material is disposed below the permanent magnet /4. In this case, the vibration 11F, 20 is fixed to the case 1 parallel to the detection diaphragm 10.

The above is the basic configuration of the pressure sensor of the present invention.
) by an appropriate means, the pressure change of the detection diaphragm 10 changes the natural frequency of the vibrating membrane 0 due to the magnetic force of the permanent surface 10, and this change in natural frequency is used as a frequency signal. By taking it out, the pressure P<2)I can be easily reduced.
It is possible to perform IIJ determination.

However, in this embodiment, the excitation means for the vibrating membrane O and the means for taking out signals to the outside are constructed as follows. That is, as shown in Fig. 2, place the bottom of the reference chamber/F @IIC insulator here, and
A pair of electrodes 244.
26 (excitation electrode, detection electrode) are provided, and lead wires are led out from these electrodes.

30 are taken out to the outside after applying 3 hermetic seals and 3 hermetic seals to each case.

In Fig. 1, reference numeral 3t is a through hole drilled in the case/co for communicating the reference chamber/g with the outside. It has nine holes.

Next, the operation of the pressure sensor constructed in this way and in the nine embodiments will be explained.

First, in the initial state of the vibrating membrane 20, as shown in FIG. 3, the central displacement given by the magnetic force of the magnet 1 is ω. shall be. At this time, the vibrating membrane 20 is excited by the electrostatic force caused by the excitation electrode λ, and maintains the natural frequency f0. In addition, the natural frequency f0 of this diaphragm -〇 is
Detected by detection electrode 2B. The natural frequency f0 of this vibrating membrane is expressed by the following equation.

However, E = Young's modulus of the diaphragm Q, ρ, the specific gravity of the diaphragm - Poisson's ratio, h of the diaphragm O! Film pressure of diaphragm λO 11111 Displacement of island 8 diaphragm -〇 Medium diameter ω3 diaphragm -〇 On the other hand, the attractive force r of the magnet 14 is smaller than the detection diaphragm compared to the gap g between the magnet 14 and the diaphragm KO. When the displacement S of the 72mm 10 is relatively small, it becomes quadratic.

F! -ik @s ・・・・・・・・・・・・
(2) (/ > S/g) On the other hand, the displacement ω of the vibrating membrane λO is given by a quintic equation.

ω=kt・F=ni black・S=ni@P・・・・・・・・・・・・・・・・・・
...(3) However, k2 ~ is 4: Constant P: Input pressure Now, if the membrane displacement ω is sufficiently large compared to the membrane thickness of the vibrating membrane, 20, then the condition in the above formula (1) is satisfied. is as follows.

ω2 / < (0,7+0. to sea 0. stiffness 2) −・・・・
(4)2 Therefore, according to the condition of the above equation (4), the equation (1) is transformed as follows.

ω=fo. （／＋－） ・・・・・・・・・・・・・・・
...(5) ω0 However, ω. : Initial displacement of the vibrating membrane 20 If the above equation (5) is further modified.

IO""'On+Δf ・・・・・・・・・・・・
...(6) Now, the following relationship is required.

If we transform the above equation (7) from the conditions of the above equation (3), we get
It will look like this:

4 Δf=-・fo. ΦP・・・・・・・・・・・・
(8) ω0 From the above relationship, it can be understood that the one frequency change Δf is proportional to the pressure change P. Therefore, according to the present invention, one frequency change 4f is ω/ω with respect to the fundamental frequency f, rl. It is possible to change the frequency on the order of 10%, and an extremely large frequency change (io% to j0%) can be obtained.

As mentioned above, the pressure sensor according to the present invention has excellent frequency characteristics, but other effects obtained by the pressure sensor according to this embodiment are as follows.

(1) Any pressure measurement is possible by changing only the film thickness b and outer diameter dimension a of the detection diaphragm.

(2) By appropriately selecting the material of the detection diaphragm, it is also possible to measure corrosive fluid pressure. In this case, no changes are required to the vibrating membrane or other configurations.

(3) It is possible to measure the pressure of liquids with large specific gravity, which is difficult to measure with conventional pressure sensors.

(4) Absolute pressure can also be measured by closing the hole in the case to form a vacuum reference chamber. Ninth, a vibrating membrane under vacuum conditions is suitable because its mechanical Q is high.

(5) In the pressure sensor of the present invention, since one frequency change is appropriately proportional to pressure, highly accurate pressure measurement is possible.

(6) In addition to using electrostatic force, a piezoelectric material or electromagnetic force can be appropriately used as a means for exciting the vibrating membrane.

(7) When electrostatic force or the like is used as an excitation means for the vibrating membrane, the power required for its operation is approximately several hundred μW;
Power consumption is extremely low.

(8) In addition, the pressure sensor of the present invention has excellent stability and reproducibility, and has good compatibility with computer-based digital equipment due to its two-frequency transmission, making it easy to create a high-precision pressure measuring device. can be produced.

WJ Hirodia is a sectional view of another embodiment of the pressure sensor according to the present invention. The embodiment shown in FIG. 3 differs from the embodiment shown in FIG. 3 only in the arrangement of the detection electrode 2B. That is, in the embodiment shown in FIG. 3, the excitation electrode ≠ and the detection electrode 2t are arranged on the same side of the vibrating membrane 0. On the other hand, in the embodiment shown in Figure 1, the detection electrode 3 is placed on the opposite side of the excitation electrode λda with the diaphragm 〇 in between. in this case.

This detection electrode roller is formed on one surface of the annular insulator 23, and this annular insulator λ3 is fixed to the inner wall of the case saw. The operation is the same as the embodiment shown in FIG.

No.! The figure shows an example of a drive circuit that can be applied to the embodiment shown in FIG. 8841. An excitation voltage is applied to the excitation electrode λ≠ from the oscillator 08C via the capacitor C2 and the lead wire -t. The detection electrode t is connected to the output terminal via the lead wire JO and the capacitor c, and the vibration Jl[-2
A frequency change it of 0 is taken. Note that % Lj l
L2 is a choke coil, and v8 is a DC power supply.

In the above embodiments, the basic configuration of a pressure sensor that measures a single pressure was shown. It can also be suitably implemented as a differential pressure sensor that extracts a signal.

FIG. 6 shows an embodiment of this differential pressure sensor. That is, in one embodiment.

Compared to the embodiment shown in FIG.
A pressure sensor 0 is provided, and this partition wall aO is made axially symmetrical and has a configuration similar to that of the pressure sensor shown in FIG. 2 on the left and right sides respectively. Therefore, the same reference numerals are given to the same components as those shown in FIG. 2, and detailed explanation thereof will be omitted. Note that in this embodiment, each electrode -≠, -
The structure is slightly different in that the lead @iF, 30 derived from 2t is taken out from the case/J via a common hermetic seal JJ. In addition, a through hole 4I-2 is bored in a part of the partition wall po.

The reference chamber/4t is maintained at a predetermined pressure Pa.

In the differential pressure sensor having the configuration described above.

The natural frequency of each vibrating membrane 20.20 is t,, r, and each detection diaphragm 10, 10 is subjected to pressure p,, p from the left and right.
, shall be in effect. In this case, the formula (
In 6), the molecule (T
, t), a linear equation is obtained.

The difference frequency is determined by introducing the frequencies f, , f, obtained in this way into a variable frequency switching circuit and passing them through a low-pass filter.

Now, for simplicity, % each vibrating membrane 20. −4 for the physical constants, shape dimensions, and constants of 〇. ω. If we increase the momentum, the difference frequency if becomes like a linear equation.

ノf=:f, -f, =f, -(P, -P,)...
.....alpha..omega.O As is clear from the above equation a., it can be understood that this is a signal proportional to the one-difference frequency Δf and the pressure differences p and -p2.

It goes without saying that the differential pressure sensor according to the present invention constructed in this way can exhibit exactly the same excellent effects as the pressure sensor of the nine embodiments described above. In particular, the advantages of constructing it as a differential pressure sensor are as follows.

(1) By detecting the difference in two frequencies), changes in the attractive force of the permanent magnet due to temperature changes and changes over time, and the jump between the magnet and the vibrating membrane due to temperature changes! II. It is possible to ignore frequency fluctuations due to disturbances such as changes in the frequency, that is, fluctuations due to these disturbances are all in-phase components and are rounded.

Can be canceled by obtaining the difference between the two frequencies.

(2) In addition, changes other than the pressure of the diaphragm 1, such as changes in Young's modulus (temperature), changes in membrane force (tension), etc. Therefore, h can be canceled out as the in-phase movable component in the same way as above.

FIG. 7 is a sectional view of another embodiment of the differential pressure sensor according to the present invention. This embodiment is a differential pressure sensor based on the idea of the pressure sensor shown in Fig. 3.Therefore, similarly to the pressure sensor shown in Fig. 1, the detection electrodes 4 are each opposed to the excitation electrode 2 with the vibrating membrane -0 in between. It is arranged as follows.

In each of the embodiments described above, the excitation electrode is placed on the opposite side of the diaphragm to the permanent magnet, but it may be placed on the same side as the permanent magnet. An excitation electrode may be disposed at the position of the electrode 24, and a detection electrode may be disposed at the position of the excitation electrode.

As is clear from the various embodiments described above, according to the present invention, displacement consisting of an analogue amount that changes in response to pressure can be directly measured without relying on electronic circuit means such as a frequency-voltage converter. It can be converted into a frequency and extracted, and has numerous advantages over conventional pressure sensors. Therefore, its application is extremely wide.
[*By applying force, it can also be used for force detection.

The preferred embodiments of the present invention have been described above, but it goes without saying that various design changes can be made without departing from the spirit of the present invention.

[Brief explanation of drawings]

FIG. 7 is an explanatory diagram of the basic configuration showing the principle of the pressure sensor of the present invention, FIG. 2 is a sectional view showing an embodiment of the pressure sensor of the present invention, and FIG. 3 is an explanatory diagram of the operation of the sensor shown in FIG. 1. Fig. 3 is a sectional view showing another embodiment of the pressure sensor of the invention, Fig. 3 is a circuit diagram showing an example of a drive circuit applicable to the pressure sensor of the invention, and Fig. 4 is an embodiment of the pressure sensor of the invention. FIG. 7 is a cross-sectional view showing another embodiment of the pressure sensor of the present invention. 10...Detection diameter 72mm Mut...Case ta...
··standard! 16...Permanent magnet/r...Central protrusion -〇...Vibration membrane here...
・Insulator 1-4...Electrode 30・
...Lead wire 3JsJ+...Hermetic seal Jt...Through hole 3t...Through hole 4IO・
...Bulkhead Octopus...Through hole FIG, l
p FIG, 2 FIG, 4 FIG, 5 2 Fl, G, 6

Claims (7)

[Claims] (1) A pressure detection diaphragm on which detection pressure acts, and a permanent magnet fixed to the center of the other side of this diaphragm,
A vibrating membrane that is placed facing a permanent magnet and is given an initial displacement by its magnetic force. The diaphragm is provided with excitation means that gives a natural vibration determined by its displacement, and the diaphragm is displaced based on the displacement proportional to the pressure of the pressure detection diaphragm 72, and the displacement of the diaphragm is proportionally expressed as a change in its natural frequency. A pressure sensor characterized by comprising a 5#I that can be taken out. (2) A pressure sensor according to claim 7, which comprises a flat plate of vibrating wire-extended ferromagnetic material. (3) Claim 8 Rattan Paragraphs 1 and 9 provide a pressure sensor according to claim 1, in which the excitation means of the vibrating membrane utilizes electrostatic force, piezoelectric material, or electromagnetic force. (4) A pressure sensor according to any one of claims 1 to 1sJ, in which a vibrating membrane is disposed within a vacuum reference chamber. (5) A pair of pressure detection diamonds 72^ on which different pressures act respectively, permanent magnets each fixed to the center of the other side of these die books, and a pair of pressure detection diamonds 72^ which are arranged opposite to each permanent magnet and whose initial displacement is determined by their magnetic force. Each vibrating membrane is provided with a given vibrating membrane and an excitation means that gives each vibrating membrane a natural vibration determined by its displacement, each vibrating membrane is held in a reference chamber at a predetermined pressure, and the pressure is proportional to the pressure of each pressure detection diaphragm. A differential pressure centimeter characterized in that the vibrating membranes are respectively displaced based on the displacement, the displacement of each vibrating membrane is treated as a natural frequency change, and the difference is proportionally output. (6) A differential pressure centimeter according to claim 1, which is constituted by a flat plate of a II dynamic ferromagnetic material. (7) In the differential pressure sensor according to claim tsj or claim 6, the vibrating membrane excitation means. A pressure sensor that uses electrostatic force, piezoelectric material, or electromagnetic force.