JPS5856428B2 - Pressure sensor using a crystal oscillator - Google Patents

Description

Detailed Description of the Invention Technical Field The present invention relates to the structure of a pressure sensor that uses two crystal oscillators to measure pressure, particularly gas pressure, by beat signals of the frequencies of these crystal oscillators. It is something.

BACKGROUND OF THE INVENTION A typical conventional sensor for measuring gas pressure is one that utilizes a strain gauge.

This uses the change in resistance due to the expansion and contraction of the resistance wire to reduce the amount of deformation of the diaphragm and bellows due to changes in the pressure applied to them by 1-11+j. This strain gauge and fixed resistor form a bridge circuit. This type of sensor has the following drawbacks:

(1) Power consumption is large.

(2) Since the magnitude of the output signal depends on the power supply voltage, fluctuations in the power supply voltage directly affect measurement accuracy.

(3) Since the output signal is an analog quantity, when measuring on a remote island, the output voltage will be greatly affected by the length and resistance of the transmission line, the material, the connection condition, etc., and the measurement accuracy will decrease. Subject to various restrictions.

(4) Since the signal output is an analog quantity, special consideration must be given to the transmission of the signal to be measured and data processing when attempting to perform highly accurate measurement.

(5) An A/D converter is often required for signal processing.

(6) For example, in a conventional gas pressure sensor that measures gas pressure via a bellows or diaphragm, the bellows or diaphragm is subject to many changes in the environment (for example, temperature changes).

In addition, there are many types of sensors other than strain gauges that detect measured quantities as analog quantities using changes in resistance, current, and voltage. Generally speaking, many of them have the above-mentioned deficiencies.

OBJECTS OF THE INVENTION It is an object of the present invention to solve the above-mentioned drawbacks of conventional analog output systems and to obtain a pressure sensor with excellent measurement accuracy.

In order to achieve the above objectives, the present invention transmits gas pressure directly to the plate surfaces of two crystal oscillators, and oscillates two crystal oscillators constituted by these two crystal oscillators. The arrangement of two crystal oscillators, the gas pressure transmission mechanism, and A new configuration was obtained for this.

Specifically, two crystal oscillators are bonded to a support member having recesses formed independently from each other so as to cover the recesses in a sealed manner, and the recesses and the two crystal oscillators are formed. The structure is such that a separate system of gas pressure (normally one gas pressure is known and the other is an unknown gas pressure to be measured) can be introduced between two mutually independent systems.

Embodiment of the Invention FIGS. 1A and 1B are a plan view and a side sectional view, respectively, showing an embodiment of the invention.

The meanings of the parts indicated by quotation marks in FIGS. 1A and 1B are as follows.

1...Crystal oscillator (one that is sensitive to the gas pressure to be measured)
2... Crystal oscillator (one that oscillates at a reference frequency) 3... Crystal oscillator holder 4... Space constituted by the crystal oscillator holder 3 and the crystal oscillator 1 (measured gas pressure Space) 5... Space constituted by crystal resonator holder 3 and crystal resonator 2... Ventilation pipe 7 that communicates with space 4... Ventilation hole 8 that communicates with space 5... Reference material Pressure space 9... Ventilation pipe 13 communicating with space 8... Reference gas pressure vessel 14.15... Electrode P1 of crystal oscillators 1, 2...
Gas pressure to be measured PZ...Reference gas pressure In Fig. 1 A and H, the crystal oscillator holder 3 is made of the same material as the crystal oscillator, and is made of, for example, a disk crystal with an H-shaped center longitudinal section. The crystal resonators 1 and 2 are shaped so that the upper and lower parts are hollowed out to have mutually independent circular recesses, and the crystal resonators 1 and 2 are placed in a state in which the recesses are sealed in the symmetrical plane of the crystal resonator holder 3. are joined, thereby forming spaces 4 and 5.

The bonding conditions for the crystal resonators 1 and 2 and the crystal vibrator holder 3 are as follows: (1) The cutting angles of the crystal resonators 1 and 2 with respect to the crystal axes and the cutting angle of the crystal resonator holder 3 with respect to the crystal axes are the same. thing.

(2) When bonding, align the crystal axes of the crystal resonators 1 and 2 and the crystal resonator holder 3, and bond them so that they can be regarded as one crystal body as a whole.

It is. Note that AT cut plates, BT cut plates, etc. are used for the crystal oscillators 1 and 2 buttons and the crystal oscillator holder 3'.

As mentioned above, the crystal resonators 1 and 2 and the crystal resonator holder 3 are made of the same material, that is, crystal, and their cutting angles are the same, and the crystal resonators 1 and 2 and the crystal resonator holder 3 are made of the same material, that is, crystal. Since the crystal axes of the child holders 3 are made to match and the crystal axes of the child holders 3 are aligned so that the whole is made to look like a single crystal, temperature changes at the bonding surfaces of the crystal units 1 and 2 and the crystal unit holder 3 cause the crystal vibration to occur. The strain exerted on the elements 1 and 2 can be reduced to a negligible level, and the temperature characteristics of the pressure sensor are extremely good.

When the crystal resonator 1 is joined to the crystal resonator holder 3, pressure spaces 4 and 8 are formed on the front and back sides of the crystal surface, and the difference between the pressure in the space 4 and the pressure in the space 8 causes the crystal resonator 1 to bend. The bending moment acts as a tension on the entire surface of the crystal resonator 1, and the oscillation frequency of the crystal resonator 1 changes.

When the crystal resonator 2 is joined to the crystal resonator holder 3, pressure spaces 5 and 8 are formed on the front and back sides of the crystal surface, but these spaces 5 and 8 become the same pressure space due to the ventilation hole 7, and the crystal resonator 2 is not subjected to tension.

Therefore, the oscillation frequency of the crystal oscillator 2 does not change, and the crystal oscillator 2 acts as an oscillating element of a reference oscillator (reference frequency oscillator).

When the measured gas pressure P1 is introduced into the space 4 through the ventilation vibro, and the reference gas pressure Pl is introduced into the space 8 through the ventilation vibro 9, the crystal oscillator 1 moves between the spaces 4 and 8.
A frequency change occurs due to the differential pressure between the crystal resonator 2 and the oscillation frequency of the crystal resonator 2, and the frequency change is detected as a beat signal with respect to the oscillation frequency of the crystal resonator 2, thereby making it possible to measure the differential pressure.

If the space 8 is made a vacuum (even if it is a vacuum, the gas pressure can be understood as a value of ``zero'').

) The supply pressure of the measured gas pressure P can be measured, and if the space 8 is set to atmospheric pressure, the gauge pressure of the measured gas pressure P1 can be measured.

The above explanation assumes that the measured gas pressure P1 is introduced into the space 4 and the reference gas pressure P2 is introduced into the space 8. However, it is also possible to introduce the measured gas pressure P1 into the space 8 and the reference gas pressure P2 into the space 4. Similar gas pressure measurements can be made with

In order to measure pressure using the pressure sensor described above, a known measurement circuit is appropriately used.

For example, to obtain the beat signal of the oscillation frequency between the crystal oscillators 1 and 2 as described above, the output signals of two oscillation circuits each using the crystal oscillators 1 and 2 as oscillation elements are mixed by a mixing circuit. Also, the natural oscillation frequencies of crystal oscillators 1 and 2 do not necessarily have to match, and the natural vibration frequencies of crystal oscillators 1 and 2 do not necessarily have to match. If the electrical specifications of crystal oscillators 1 and 2 are known in advance, such as their vibration frequency when there is no vibration, frequency deviation when subjected to stress, etc., the difference in the natural vibration frequencies of crystal oscillators 1 and 2 can be determined. This problem can be handled by a measurement circuit using the pressure sensor.

FIGS. 2A to 2D show other embodiments of the crystal resonator holder 3 shown in FIGS. D) is shown in Figure 2 A, B and C.

These forms include crystal units 1 and 2 and crystal unit holder 3.
It is possible to significantly improve the temperature characteristics of the crystal oscillators 1 and 2 in a state where gas pressure is applied (that is, in a dynamic state) by this joint surface.

Effects of the Invention The present invention completely eliminates the drawbacks of the prior art described above. In particular, as explained above, the pressure sensor according to the present invention has crystal oscillators bonded to two separate spaces, One crystal oscillator is used for reference frequency oscillation, and the other crystal oscillator is used for frequency oscillation based on the gas pressure to be measured. can be measured under the same environment, making it possible to measure with high precision.Furthermore, since the gas pressure to be measured acts directly on the crystal oscillator, which is the sensor, there are no errors caused by the pressure transmission mechanism. The support member (crystal resonator holder) of the crystal resonator is formed from a crystal piece cut at the same angle as the crystal resonator, and when joining the crystal resonator, the crystal axis of the crystal resonator and the crystal of the support member are Since the shaft is aligned with the shaft, errors due to temperature changes, etc. can be suppressed as much as possible.

In addition, the pressure sensor according to the present invention can measure supply pressure and gauge pressure by changing the gas pressure in the space where the crystal oscillator that oscillates the reference frequency is connected.
Another feature is that it has a wide range of applications.

As described above, the pressure sensor according to the present invention has various advantages, and the present invention has extremely significant effects.

[Brief explanation of drawings]

1 and 2 are drawings explaining the present invention in detail, and FIGS. 1A and 2B are a plan view and a side sectional view of a pressure sensor according to an embodiment, respectively, and FIGS. It is a figure which shows the other example of implementation of a part (crystal resonator holder) of the example pressure sensor. Main symbols, 1, 2...Crystal oscillator, 3...
...Supporting member (crystal resonator holder), 4...Measurement gas pressure space, 5, 8...Reference gas pressure space, 13...Reference gas pressure vessel.

Claims (1)

[Claims] It consists of 12 crystal oscillators and a support member made of a quartz crystal with the same cutting angle as the quartz crystal oscillators and having concave portions at two independent locations, and the support member has concave portions at two independent locations. The two crystal oscillators are fixed to the support member so that the crystal axes of the support member are aligned with each other and the two recesses of the support member are tightly covered. A pressure sensor using a crystal oscillator, characterized in that gas pressures of different systems can be introduced into two spaces formed by the recess and the crystal oscillator.