JP2001281070A - Physical quantity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a physical quantity sensor which detects physical quantities at a distant position. SOLUTION: A magnetic field is generated in a coil 12 by oscillation of a positive feedback oscillation circuit 1 which contains an amplifier 11 and the coil 12 in a feedback path. A physical quantity detecting part 2 is constituted of a tank circuit comprising a coil 13 and a capacitor 15 connected in parallel with the coil 13, which is wound around magnetic material 14 having temperature sensing characteristic and couples electromagnetically with the coil 12. The detecting part 2 converts an environmental temperature of the coil 13 into a frequency, detects an oscillation frequency of the positive feedback oscillation circuit 1, and measures the physical quantity on the basis of the frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a physical quantity sensor for converting a physical quantity such as temperature, pressure, acceleration and the like into a frequency and detecting the frequency at a remote position.

[0002]

2. Description of the Related Art In the case of a conventional physical quantity sensor, for example, a temperature sensor, a thermometer as a temperature sensor is directly brought into contact with a measured object to measure the temperature of the measured object. However, when the object to be measured is at a remote position and cannot directly contact the temperature sensor, temperature detection becomes difficult.

[0003]

In such a case, the temperature is detected using an infrared sensor or the like. However, this method has a problem that only the surface temperature of the measured object can be detected. For example, there is a problem that it is extremely difficult to detect the temperature of a deep part of a living body or the like. The same applies to detection of pressure, acceleration, and the like, not limited to temperature.

When measuring a physical quantity at a remote location,
Due to the transmission of the detected physical quantity, there is a problem that the physical quantity sensor becomes large and it becomes difficult to detect the temperature in the deep part of the living body.

It is an object of the present invention to provide a physical quantity sensor capable of detecting a physical quantity at a remote position.

[0006]

A physical quantity sensor according to the present invention comprises a positive feedback oscillating section including a first coil in a return path, a second coil and a second coil electromagnetically coupled to the first coil. And a physical quantity detecting means for detecting a physical quantity and converting the frequency to a frequency based on the detected physical quantity, wherein the physical quantity is detected based on the oscillation frequency of the positive feedback oscillation unit. .

According to the physical quantity sensor according to the present invention, the second coil and the second coil which receive the oscillation output from the positive feedback oscillation section and are electromagnetically coupled to the magnetic field generated by the first coil are connected in parallel to the second coil. A current having a resonance frequency based on the inductance of the second coil and the capacitance of the capacitor flows through the physical quantity detecting means including the capacitor, and a magnetic field having the resonance frequency is generated in the second coil. Therefore, the magnetic field generated by the second coil is received by the first coil, and the oscillation frequency of the positive feedback oscillation section is set to the resonance frequency of the physical quantity detection means. As a result, the physical quantity can be measured by measuring the oscillation frequency of the positive feedback oscillation section.

When the physical quantity detected by the physical quantity detecting means changes, the resonance frequency of the physical quantity detecting means changes, and the oscillation frequency of the positive feedback oscillation section becomes the resonance frequency of the physical quantity detecting means, and this frequency is measured. Can measure a physical quantity. That is, the physical quantity is converted into a frequency and measured.

In the physical quantity detecting means, when a coil wound around a magnetic material having a temperature-sensitive characteristic and used to convert an ambient temperature into an inductance based on the ambient temperature is used as the second coil, the characteristic of the magnetic material depends on the temperature. And the inductance of the second coil changes according to the ambient temperature, so that the temperature can be measured based on the frequency of the current flowing through the physical quantity detecting means.

When the physical quantity detecting means is provided with a capacitor using a dielectric material having a temperature characteristic of a dielectric constant, the capacitance of the capacitor changes with temperature, and the oscillation frequency changes with temperature. Temperature can be measured.

When the physical quantity detecting means includes a third coil connected in parallel to the second coil, and the third coil is a magnetostrictive thin film coil which changes the inductance based on the external force when an external force is applied, , Acceleration and the like can be measured.

When the physical quantity detecting means includes an element whose capacitance changes based on the external force when an external force is applied, pressure and stress can be measured.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a physical quantity sensor according to the present invention will be described.

FIG. 1 is a block diagram showing a configuration of a physical quantity sensor according to an embodiment of the present invention, and illustrates a case where temperature is measured as a measured physical quantity.

Reference numeral 1 denotes an oscillation circuit section corresponding to a positive feedback oscillation section, which is constituted by a positive feedback oscillator including an amplifier 11 and a coil 12. The coil 12 is incorporated in a feedback circuit of the amplifier 11, It is configured to oscillate at a frequency at which the impedance indicates an extreme value.

A current based on the oscillation output flows through the coil 12, and a magnetic field is generated by the coil 12 by the current.

Reference numeral 2 denotes a physical quantity detecting section corresponding to the physical quantity detecting means.
3 and a tank circuit composed of a capacitor 15 connected in parallel to the coil 13 so that the inductance L of the coil 13 changes according to the detected physical quantity.

The physical quantity detector 2 may be configured so that the capacitance C of the capacitor 15 changes as described later, instead of the inductance L of the coil 13 based on the detected physical quantity.

In the case of the physical quantity sensor according to the embodiment of the present invention, since the temperature is measured, a soft magnetic material whose magnetic permeability changes with temperature, a temperature-sensitive ferrite used for a temperature switch, etc. A coil 13 is wound around a magnetic material 14 having the above temperature-sensitive characteristics, and a capacitor 15 is connected to the coil 13 in parallel.

Therefore, if the inductance L of the coil 13 changes with the ambient temperature and the capacitance of the capacitor 15 is C, the inductance L of the coil 13
And a capacitance C of the capacitor 15, that is, a resonance frequency frx of the physical quantity detection unit 2,
It changes based on the following equation (1).

Frx = 1 / {2π (LC) ^1/2 } (1) Therefore, the impedance of the tank circuit including the coil 13 and the capacitor 15 shows a minimum value at the resonance frequency, and the current flowing through the coil 13 is the maximum. Value. Therefore, the impedance of the coil 12 electromagnetically coupled to the coil 13 also shows an extreme value at the frequency given by the above equation (1).

Therefore, a magnetic field having a resonance frequency is formed by the coil 13 by the resonance current flowing through the coil 13,
Based on this magnetic field, the oscillation frequency of the oscillation circuit unit 1 configured by incorporating the coil 12 electromagnetically coupled to the coil 13 into the feedback circuit becomes substantially equal to the frequency frx of the equation (1). The oscillation frequency changes depending on the ambient temperature of the coil 12, that is, the ambient temperature of the physical quantity detection unit 2, and the temperature of the physical quantity detection unit 2 can be detected by detecting the oscillation frequency of the oscillation circuit unit 1.

According to the physical quantity sensor according to the embodiment of the present invention configured as described above, it is possible to measure the local temperature at a remote position and in real time.

Next, each element used in the physical quantity sensor according to the embodiment of the present invention will be specifically described.

The coil 12 has, for example, a diameter of 200 m.
An air-core coil having a diameter of 27 μH and a diameter of 16 mm and a length of 16 turns wound with an insulated conductor was used.

As the magnetic material 14 around which the coil 13 is wound, a temperature-sensitive ferrite having a Curie temperature of 55 ° C. was used. Nine disc-shaped temperature-sensitive ferrites each having a diameter of 4 mm and a thickness of 1.6 mm are laminated on this magnetic material, and an insulating conductor is used to surround them.
A coil 13 was formed by applying 88 turns of winding.

In such a configuration, the inductance L of the coil 13 changes with temperature, and in the temperature range of 58 ° C. to 66 ° C., as shown in FIG.
To 2.44 mH.

As the capacitor 15, an 8 nF capacitor was used.

With this configuration, the distance between the coil 12 and the coil 13 was set to 50 mm, and the capability of remote sensing of temperature was measured. As a result, when the temperature around the physical quantity detection unit 2 is changed, the oscillation frequency of the oscillation circuit unit 1 becomes equal to the inductance L of the coil 13.
Changed from 62 kHz to 36 kHz according to the temperature change.

As is apparent from the above results, in this case, the temperature measurement at a remote position is performed at a remote position by measuring the oscillation frequency of the oscillation circuit unit 1 in the temperature range of 58 ° C. to 66 ° C. In addition, the temperature can be measured in real time.

In the physical quantity sensor according to the embodiment of the present invention, since the temperature as the detected physical quantity is converted into a frequency and measured, the position of the physical quantity detecting unit 2 fluctuates during the measurement, and the coil 12 and the coil 13 are changed. One of the major features is that even if the state of the electromagnetic coupling with changes during measurement, there is no problem in the measurement.

In this case, the physical quantity detection unit 2 is several mm.
It can be formed on a corner base, the oscillation circuit unit 1 is provided at a remote position, and the physical quantity detection unit 2 including this base is inserted into the deep part of the living body, whereby the temperature of the deep part of the living body can be detected. .

Further, when two or more physical quantity detectors 2 are arranged, the resonance frequency of the tank circuit formed by the coils 13 and the capacitors 15 of the plurality of physical quantity detectors 2 is changed, and the oscillation circuit A plurality of temperatures can be detected by providing a bandpass filter having a different passband in one feedback circuit and switching the bandwidth as necessary.

In the above-described physical quantity sensor according to one embodiment of the present invention, the case where the temperature is measured using the change in the inductance L of the coil 13 due to the temperature has been exemplified. Alternatively, the capacitance C of the capacitor 15 may be changed according to the temperature by using a capacitor 15 using a dielectric whose dielectric constant changes according to the temperature. FIG. 3 shows an example of a temperature change of the dielectric constant of the dielectric. By configuring the capacitor 15 using this dielectric material, the capacitance C changes with temperature,
The resonance frequency frx changes. Even if this is used, the temperature can be measured by the temperature change of the capacitance C as in the case of the temperature change of the inductance L.

In the above description, the case of temperature detection has been described as an example, but a case where the present invention is applied to acceleration detection instead of temperature detection will be described.

As shown in FIG. 4, in the acceleration sensor 30 having the cantilever 31, the inductance L
Forming a magnetostrictive thin-film coil 32 made of a material which changes due to strain, for example, cobalt, iron, silicon, boron,
By disposing the magnetostrictive thin-film coil 32 at the root of the cantilever 31, it is possible to convert the distortion of the root of the cantilever 31 based on the received acceleration into a change in inductance.

For this reason, in the case of measuring acceleration, a physical quantity detector 2A is used instead of the physical quantity detector 2 as shown in FIG. The physical quantity detection unit 2A is configured by connecting a magnetostrictive thin-film coil 32 in parallel with the air-core coil 13 in the physical quantity detection unit 2. Other configurations are the same as those shown in FIG.

Here, the reason why the magnetostrictive thin-film coil 32 is connected in parallel to the air-core coil 13 is that the magnetostrictive thin-film coil 32 has a small size, so that the efficiency of electromagnetic coupling with the coil 12 is small.
Since the resonance impedance between the magnetostrictive thin-film coil 32 and the capacitor 15 cannot be efficiently transmitted to the coil 12, the air core having a large size for the electromagnetic coupling with the coil 12 and the transmission of the magnetic field to the coil 12 has a large electromagnetic coupling efficiency. The resonance circuit is mainly composed of the magnetostrictive thin-film coil 32 and the capacitor 15.

In this manner, acceleration can be detected by the magnetostrictive thin-film coil 32 and the capacitor 15, electromagnetic coupling with the coil 12 is achieved by the air-core coil 13, and transmission to the coil 12 is attempted. Acceleration at a more remote location can be measured.

Next, the case of pressure measurement will be described.

In the case of pressure measurement, the air-core coil 13
The pressure and stress can also be measured using the physical quantity detection unit 2 composed of a pressure sensor in which the distance between the opposing electrode plates changes due to the received pressure instead of the capacitor 15 and the capacitance C changes.

For example, as the capacitor 15, as shown in FIG. 6, a sensor in which the distance between opposing electrode plates changes due to the pressure received and the capacitance C changes,
Stress can also be measured. In FIG. 6, the polycrystalline S
The case where layers doped with i and n ⁺ are used as electrodes respectively is shown.

In the above, temperature measurement, acceleration measurement,
Although the case of pressure / stress measurement has been exemplified, a physical quantity detection unit that can convert a measured physical quantity into an inductance change, or a capacitance change, even with other physical quantities,
It is applicable to this physical quantity sensor.

[0044]

As described above, according to the physical quantity sensor according to the present invention, the physical quantity is converted into a frequency and detected, and the physical quantity can be detected regardless of the position where the physical quantity sensor is placed. , Miniaturization is possible,
It is possible to detect a physical quantity at a position where measurement was not possible conventionally. Further, since the operating energy of the physical quantity detecting means is magnetically applied from the outside, it is not necessary to provide an energy source inside the physical quantity detecting means, and the physical quantity can be detected at a remote position.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a physical quantity sensor according to one embodiment of the present invention.

FIG. 2 is a temperature characteristic diagram of inductance of a coil in which a winding is formed on a temperature-sensitive magnetic material used in a physical quantity sensor according to one embodiment of the present invention.

FIG. 3 is a temperature characteristic diagram of a dielectric constant of a dielectric of a capacitor used in a physical quantity sensor according to one embodiment of the present invention.

FIG. 4 is a schematic diagram showing an example of an acceleration sensor used for a physical quantity sensor according to one embodiment of the present invention.

FIG. 5 is a block diagram illustrating a configuration example of a physical quantity sensor according to an embodiment of the present invention when an acceleration sensor is used for a physical quantity detection unit.

FIG. 6 is a schematic diagram showing an example of a pressure sensor used for a physical quantity sensor according to one embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Oscillation circuit part 2, 2A ... Physical quantity detection part 11 ... Amplifier 12, 13 ... Coil 14 ... Magnetic material 15 ... Capacitor 30 ... Acceleration sensor 31 ... Cantilever 32 ... Magnetostrictive thin film coil

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) G01L 9/10 G01L 9/12 9/12 G01P 15/11 G01P 15/11 15/125 15/125 G01D 5/24 R (72) Inventor Mitsuteru Inoue 20-8, Jizogairi, Iga-cho, Okazaki City, Aichi Prefecture (72) Inventor Kim Eigaku 4-5, Yagiyama Matsunami-cho, Taishiro-ku, Sendai City, Miyagi Prefecture Tohoku University Yagiyama Hall A301 (72 ) Inventor Atsugaki Itagaki 48, Minamizaiki-cho, Wakabayashi-ku, Sendai City, Miyagi Prefecture Ryowa Electronics Co., Ltd. (72) Inventor Tetsuo Yoshida 6-7-1, Koriyama, Taishiro-ku, Sendai-shi, Miyagi F-term (reference) ) 2F055 AA40 BB20 CC02 DD05 EE21 EE25 FF34 GG31 2F056 SA05 SA07 SB03 SB05 SB06 SB09 2F077 AA49 FF02 FF39 HH03 HH13 TT02 WW08

Claims (5)

[Claims] A positive feedback oscillating section including a first coil in a return path; a second coil electromagnetically coupled to the first coil;
And a physical quantity detecting means for detecting a physical quantity and converting it to a frequency based on the detected physical quantity, wherein the physical quantity is detected based on the oscillation frequency of the positive feedback oscillation unit. Physical quantity sensor. 2. The physical quantity sensor according to claim 1, wherein the second coil is a coil wound around a magnetic material having a temperature-sensitive characteristic and converting the ambient temperature into an inductance based on the ambient temperature. Physical quantity sensor. 3. The physical quantity sensor according to claim 1, wherein the capacitor uses a dielectric having a temperature characteristic as a dielectric and converts an ambient temperature into a capacitance based on the ambient temperature. 4. The physical quantity sensor according to claim 1, wherein the physical quantity detecting means is connected to a third coil connected in parallel to the second coil.
Wherein the third coil is a magnetostrictive thin-film coil that changes inductance based on the external force when an external force is applied. 5. The physical quantity sensor according to claim 1, wherein the physical quantity detecting means includes an element whose capacitance changes based on the external force when an external force is applied.