JPS5935122A - Pressure sensor for gas - Google Patents

Abstract

PURPOSE:To enable the measurement with a high accuracy by detecting changes in the pressure of a gas surrounding a contour piezo-electric vibrator depending on variation in the equivalent series resistance of a vibrator. CONSTITUTION:A tuning fork piezo-electric vibrator 1 is fixed on a sealed tube 2 with the bottom thereof and a lead 3 sticks out from the sealed tube 2 through a cover glass 4. The wall of the sealed tube 2 is provided with gas passage holes 5, 5... while a heating wire 6 is printed thereon with a lead 7 drawn out through the covar glass 4. The tube 2 with the piezo-electric vibrator 1 thus fixed is anchored at a corner in a case 8 and a rubber elastic balloon-like bellows 10 is provided in a hole 9 arranged properly on the wall surface of the case 8 to communiate a gas to be measured in the pressure with the bellows 10. A fluid to be measured is introduced into the bellows 10 so as to be equal to the internal pressure of a pressure sensor case 8 and then, the series equivalent resistance of the vibrator 1 is measured with a meter thereby enabling the reading of the pressure P.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas pressure sensor using a piezoelectric vibrator.

Conventionally, pressure sensors have been proposed that detect gas pressure from changes in vibration frequency caused by minute deformation of a piezoelectric vibrator, such as a crystal, by applying gas pressure directly or using a device that converts it into a suitable transparent displacement. has been done.

However, the conventional pressure sensors as mentioned above have a device that converts pressure into displacement, and have flaws such as a simple structure and susceptibility to external vibrations or shocks, and they do not have very high sensitivity or resolution. Ta.

The present invention was made in order to solve all the deficiencies of the conventional pressure sensors using piezoelectric vibrators as described above. It is an object of the present invention to provide a pressure sensor characterized by detecting the series equivalent resistance of a vibrator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to drawings showing examples using a tuning fork type crystal sensor and experimental results thereof.

FIG. 1 shows a general X-cut tuning fork type crystal resonator that produces a tuning fork vibrating sound, and the tuning fork gap g and plate thickness yt are used as parameters that influence its characteristics. FIG. 2 shows an electrical equivalent circuit of this vibrator.

The number of measurements of such a vibrator fluctuates as shown in Figure 2 depending on the pressure of the surrounding atmosphere, but this phenomenon has long been known as air loading. How to reduce this was an important issue in the design and construction of the vibrator.

The pressure sensor according to the present invention is intended to actively utilize the change in the equivalent series resistance caused by the air loading described above.

No. 31A shows the relationship between the air pressure and the equal series resistance R of a tuning fork type crystal resonator, which is actually measured and plotted for two cases of the tuning fork shape with the ratio t/gk of the tuning fork spacing g and plate thickness t. It is illustrated. Note that the electrode shape was the same when t/gk was changed, and the electrode shape of a commonly used machined tuning fork vibrator was adopted.

As is clear from this figure, it can be seen that with this type of pressure sensor, it is already possible to measure pressures in the range of 10<-3 atmospheres to several atmospheres.

Also, when t/g = 3, the change in equal series resistance with respect to pressure change is several times larger than when t/g = 1, and in both cases, equal series resistance is almost proportional to the logarithm of pressure. This characteristic makes it suitable for pressure measurement over a wide range.

When constructing a pressure sensor using a vibrator having the characteristics described above, the viscosity coefficient of the gas that acts directly on the tuning fork type vibrator generally decreases as the temperature rises, and the tuning fork type piezoelectric vibrator is Since it is known that the equivalent resistance is directly proportional to the viscosity coefficient of the gas, it is necessary to keep the temperature of the gas directly acting on the tuning fork type piezoelectric vibrator constant.

Furthermore, in a pressure sensor using a tuning fork type piezoelectric vibrator according to the present invention, it is necessary to eliminate the effects of sagging, dew condensation, temperature changes, etc. on the vibrator. FIG. 2 is a cross-sectional view showing an example of a sensor.

That is, a tuning fork type piezoelectric vibrator 1 is fixed at its bottom to a sealed tube 2 such as a watch vibrator case, and a lead wire 3 is electrically insulated from the sealed tube 2 via a cover glass 4. protrude to the outside.

Appropriate gas flow holes 5.5 are provided in the wall of the sealing tube 2.・・・
. . . are provided, the heating wire 6 is entirely printed, and its lead wire 7 is also provided outside through the cover glass 4. A tube in which the piezoelectric vibrator as described above is fixed is fixed to one corner of the outer L8 having an appropriate size, and a rubber elastic balloon-shaped bellows 10 is provided in a hole 9 provided at a suitable position on the wall of the outer L8. The inside and outside air or the gas whose pressure is to be measured are made to flow. Similarly, an inert gas such as nitrogen gas is sealed inside the body 8 so that the vibrator 1 vibrates in the gas.

By doing so, when the fluid whose pressure is to be measured is introduced into the bellows 10, it can expand freely, so that its internal pressure P is stabilized to be equal to the internal pressure P of the pressure sensor giant body 8. If the series equivalent resistance of the vibrator 1 in that state is measured using, for example, an 01 meter, the pressure sound can be read from FIG.

Moreover, since the vibrator 1 is housed in the porous sealing body 2, the vibrations are not completely inhibited by contact with the bellows body, and the area around the sealing body 2 is always kept at a constant temperature by the heating wire 6. The pressure of the heat is exchanged with the gas to be measured in the sensor housing 8.
This is done via the inert sealing gas in the oscillator 1 and the bellows 10.
Since the temperature is virtually maintained at a constant temperature, the measurement accuracy is also high and stable.

6- It is clear that the present invention may be modified as shown in FIG. That is, even if the gas whose total pressure is to be measured is directly guided into the sensor holder 8 and the vibrator 1 and its sealing body 2 are housed in the bellows 10, the effect remains the same.

Since the present invention is configured as described above, it is possible to measure gas pressure with extremely high resolution and accuracy, and the measurement is also easy, and the elastic modulus of the bellows can be appropriately selected. For example, the shape of the sensor can be made sufficiently small, making it a sensor suitable for use as an altimeter, a subsonic velocity meter, a gas flow meter, or the like.

Similarly, it goes without saying that the pressure sensor according to the present invention can use not only a tuning fork type vibrator but also other contour vibrating vibrators, and in that case, the method of supporting the nodes may be All you have to do is come up with your own unique ideas.

[Brief explanation of the drawing]

Fig. 1 is an outline drawing of a tuning fork type piezoelectric vibrator used in the pressure sensor of the present invention, Fig. 2 is a diagram showing the electrical equivalent circuit, and Fig. 3 is a diagram showing the peripheral gas pressure and series equivalent resistance of the vibrator. FIG. 4 is a sectional view showing the structure of the pressure bearing part of the present invention, and FIG. 5 is a sectional view showing another embodiment. 1... Tuning fork type piezoelectric vibrator, 10... Bellows patent applicant Toyo Tsushinki Co., Ltd.

Claims (3)

[Claims] (1) A gas pressure sensor characterized in that changes in the pressure of gas surrounding a contour piezoelectric vibrator are detected by changes in the equivalent series resistance of the vibrator. (2) Claim 1 characterized in that the gas surrounding the piezoelectric vibrator is an inert gas, and the piezoelectric vibrator is sealed together with a bellows or a cavity that receives a washing body whose pressure is to be measured. Pressure sensor for barometric pressure. (3) A gas pressure sensor according to claim 1, characterized in that the piezoelectric vibrator is made of a ceramic material together with the inert gas.