JPS5945932B2 - Pressure sensor using magnet and piezoelectric element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure sensor that converts measured pressure into an electrical signal using a magnet and a piezoelectric element.

Piezoelectric elements such as quartz, Rochelle salt, and barium titanate change their electromotive force or vibration frequency depending on the stress applied to them, so they are used as pressure sensors in pressure gauge vacuum pressure needles, load measuring instruments, flow rate measuring instruments, etc. .

The present invention aims to measure large pressures over a wide range with high accuracy by applying the pressure to be measured to a piezoelectric element through a pressure receiving mechanism in which a pair of magnets with the same polarity are arranged facing each other and a buffer spring. The main purpose is to provide a pressure sensor that enables

FIG. 1 shows an embodiment of the present invention, which is a pressure sensor that directly measures pressure or load.

The pressure receiving mechanism has a structure in which a magnet 3 whose periphery is held down by a spacer 2 is provided at the bottom of a cylinder 1, and a cylinder 4 is inserted into the cylinder 1 using the cylinder 1 as a guide cylinder. 5, and the direction in which the cylinder 4 is inserted into the cylinder 1 corresponds to the direction in which the pressure to be measured is applied.

A pressure-to-electricity converter is provided between the magnet 3 and the bottom magnet 5 of the cylindrical body 4 to sandwich the piezoelectric element 7 with a buffer spring 6 interposed therebetween.

The electromotive force of the piezoelectric element 7 is amplified to an appropriate level by an amplifier 8 and extracted as an electrical signal corresponding to the pressure to be measured.

By using a pressure sensor having such a pressure receiving mechanism and a pressure-electrical converter, the magnets 3 and 5 repel each other with a force inversely proportional to the square of the distance between the poles, and the distance t between the poles and the repulsive force F are The relationship is F=-2, and this can be expressed in a graph as shown in Figure 2.

However, a is a constant determined by the magnets 3 and 5.

Therefore, if the measured pressure (load) applied to the magnet 3 is Wl and the distance between the poles at that time is t, then the load f applied to the spring 6 is expressed by equation (1).

f=W−F=W−1 ・・・・・・・・・(1)2 In addition, the length of the spring 6 in a state where no load is applied to the magnet 3 is t.

Then, f=(to-4)・b, so 1=1
8-become one.

However, b is a spring constant.

Then, by eliminating t from this equation and the previous equation (1), f becomes W
The relationship between is calculated as shown in equation (2).

W=a/(4)2+f=...(2) Here, spring 6
The load f applied to is the pressure applied to the piezoelectric element 7.

Therefore, the pressure f applied to the piezoelectric element 7 and its electromotive force E
If we use a piezoelectric element with a proportional relationship between W and E (!:
The relationship is as shown in equation (3).

However, C is a proportionality constant. E W=a/(to)2+ −・・・(3
) bc C Therefore, the pressure range to be measured relative to the allowable pressure range of the piezoelectric element 7 becomes larger without requiring a pressure receiving mechanism using a lever, and pressure measurement over a wide range becomes possible.

Moreover, when a load is applied to the magnet 3, the buffer spring 6
Since the impact on the piezoelectric element 7 is alleviated, the piezoelectric element 7 will not be damaged.

Further, as for the magnets 3 and 5, it is preferable to use rare earth cobalt magnets because the residual magnetic flux density is stable for a long period of time, the holding force is large, and the magnets can be manufactured easily and inexpensively.

FIG. 3 shows another embodiment of the present invention, which is applied to a vacuum pressure needle.

In the figure, one magnet 3 is provided on the base plate 9, and the base plate 9
The movable plate 111C is guided by a guide rod 10 planted in the other magnet 5, and the movable plate 11 and the base plate 9
are connected to form a pressure receiving mechanism.

A piezoelectric element 7 is provided between the poles of the magnets 3 and 5 with a spring 6 interposed therebetween, as in the case of FIG. 1, and the output of the piezoelectric element 7 is guided to an amplifier 8.

Such a pressure sensor is constructed by interposing a seal 14 in the hole 13A of the vacuum container 13 and covering it with the base plate 9, and guiding the vacuum pressure inside the vacuum container 13 into the bellows 12 through the hole 13A and the introduction of the base plate 9 to the bellows 12. The movable plate 11 is pulled toward the container in accordance with the pressure, and the piezoelectric element 7 is pressurized.

This embodiment also provides the same effects as those described above.

As described above, according to the present invention, pressure is detected using a piezoelectric element, and the piezoelectric element is provided between mutually repelling magnetic poles via a buffer spring, so that large pressure can be detected over a wide range. The piezoelectric element can be measured with high precision over the entire range, and damage to the piezoelectric element can be prevented since a buffer spring is used.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view showing one embodiment of the present invention, FIG. 2 is a characteristic diagram of the distance between magnets with respect to repulsive force, and FIG. 3 is a side sectional view showing another embodiment of the present invention. 3.5... Magnet, 6... Spring, 1... Piezoelectric element,
8... Amplifier, 9... Base plate, 10... Guide rod, 1
1... Movable plate, 12... Bellows, 13... Vacuum container.

Claims (1)

[Claims] 1. A pressure receiving mechanism which arranges a pair of magnets with the same poles facing each other and receives and guides the pressure to be measured in the opposite direction of the magnets, and a piezoelectric element is arranged between the poles of the pair of magnets to apply pressure in the direction between the poles of the magnets. A pressure-electricity converter that obtains an electromotive force from the piezoelectric element according to the force and the pair of magnets is provided so as to sandwich the piezoelectric element and transmit the force applied in the direction between the poles. A pressure sensor characterized by comprising a buffer spring.