JPH10267773A - Pressure measuring device and pressure measuring method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure measuring device capable of measuring absolute pressure and the direction of pressure change with high accuracy and a pressure measuring method using the same. SOLUTION: This pressure measuring device has a semiconductor laser 22 which frequency modulates a laser beam in the form of a lamp waveform and emits it as a laser beam LaO; an optical fiber 271 connected at one end to one of the emission ends of an optical fiber coupler 261 ; an optical fiber 272 connected at one end to one of the emission ends of an optical fiber coupler 262 ; a pressure sensor 28 provided inside the compressor of an internal combustion engine; a light power meter 30 by which first and second interference light beams Li1 , Li2 impinging thereon via the respective optical fibers 291 , 292 are converted into first and second electric signals Si1 , Si2 which correspond to the respective beam strengths; and a CPU 32 which calculates the value of pressure to be measured and the direction of change of the pressure to be measured through arithmetic based on the second electric signal Si2 , a trigger signal St, arithmetic data Dc, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure measuring device used for measuring a pressure in a compressor or a combustor of an internal combustion engine and a pressure measuring method using the same.

[0002]

2. Description of the Related Art In recent years, a pressure measuring device excellent in heat resistance, explosion proof property, corrosion resistance and the like has been used for pressure measurement in a compressor of an internal combustion engine. This type of pressure measuring device includes a diaphragm that flexes according to the applied pressure, a semiconductor laser,
This device is composed of an optical fiber or the like and optically measures pressure using the principle of a Fabry-Perot interferometer. This pressure measuring device has an advantage that it is not affected by electromagnetic noise because it uses laser light as a signal source.

FIG. 7 is a block diagram showing a configuration of the above-mentioned conventional pressure measuring device. In this figure, reference numeral 1 denotes a He-Ne laser that generates a laser beam La as coherent light. Reference numeral 2 denotes an optical fiber coupler;
The laser beam La incident through the optical fiber 4 is emitted to the end face of the optical fiber 4, and the interference light Li incident through the optical fiber 4 is emitted to the end face of the optical fiber 5. Details of the interference light Li will be described later.

[0006] Reference numeral 6 denotes a pressure sensor provided in a compressor of the internal combustion engine, and detects a pressure in the compressor. Here, the configuration of the pressure sensor 6 will be described in detail with reference to FIG. In the pressure sensor 6 shown in FIG.
The diaphragm is a substantially disk-shaped diaphragm. The central portion 7a and the peripheral edge portion 7b are formed to be thick, and the annular portion 7c between the central portion 7a and the peripheral edge portion 7b is formed to be thin.
The diaphragm 7 is made of a flexible material and has a measured pressure P applied to a pressure-receiving surface 7d as its surface.
Deflected according to m.

[0005] Reference numeral 8 denotes a substantially columnar support member for supporting the diaphragm 7, and a concave portion 8a is formed in an upper portion thereof. A communication hole 8b communicating from the recess 8a to the lower surface 8c along the axis is formed in the center of the support member 8.
Further, the support member 8 has a communication hole 8d formed near the communication hole 8b so as to communicate from the recess 8a to the lower surface 8c.

That is, an internal space 10 is formed between the support member 8 and the diaphragm 7, and the internal space 10 is open to the atmosphere via a communication hole 8d. That is, the pressure inside the internal space 10 is the atmospheric pressure Pa.

One end of the optical fiber 4 (see FIG. 7)
The end face 4a is inserted and fixed in the communication hole 8b of the support member 8 via an adhesive 9, and the end face 4a is located at an optical distance d from the reflection face 7e which is the back face of the diaphragm 7.

In FIG. 7, reference numeral 11 denotes an optical power meter, which converts the interference light Li incident through the optical fiber 5 into an electric signal Si corresponding to the light intensity. Reference numeral 12 denotes a storage oscilloscope that displays a waveform of the electric signal Si.

Next, the operation of the above-described conventional pressure measuring device will be described. In FIG. 7, a He-Ne laser 1
Is driven, the laser light La is guided to the optical fiber 4 via the optical fiber 3 and the optical fiber coupler 2. Then, a part of the laser light La is transmitted to the optical fiber 4 shown in FIG.
Is reflected by the end surface 4a and propagates in the optical fiber 4 as reference light, while the remaining laser light La is emitted from the end surface 4a, is reflected by the reflection surface 7e of the diaphragm 7, and is incident again on the end surface 4a as reflected light. I do.

Thus, the above-mentioned reference light and reflected light interfere with each other and propagate inside the optical fiber 4 as interference light Li. The interference light Li is generated based on the principle of the Fabry-Perot interferometer due to the existence of the optical path difference 2d (see FIG. 8) between the reference light and the reflected light. Therefore,
The light intensity of the interference light Li changes periodically according to the amount of deflection Δd of the diaphragm 7 shown in FIG. 9, in other words, according to the change in the optical path difference 2d described above. In other words, the light intensity of the interference light Li changes periodically according to the change of the measured pressure Pm. That is, the interference light Li has fringes (interference fringes) that are bright and dark.
Each time the wavelength λ of a changes by a half, the order increases or decreases. The order F of the fringe is proportional to the measured pressure Pm as shown in FIG.

The interference light Li shown in FIG. 7 enters the optical power meter 11 via the optical fiber coupler 2 and the optical fiber 5. As a result, the electric power Si corresponding to the light intensity of the interference light Li is output from the optical power meter 11 to the storage oscilloscope 12, and the waveform of the electric signal Si is displayed on the storage oscilloscope 12.

Assuming that the measured pressure Pm is a certain value Pm1 (see FIG. 11), the amount of deflection Δd of the diaphragm 7 is constant and does not change. Therefore, FIG.
Is constant, the electric signal Si displayed on the storage oscilloscope 12 does not change. At this time, it is not possible to specify the order F of the fringe corresponding to the measured pressure Pm1 shown in FIG. 11 simply by looking at the display of the storage oscilloscope 12.

Now, the measured pressure Pm shown in FIG.
Is increased from Pm1 to Pm2, the level of the electric signal Si displayed on the storage oscilloscope 12 periodically takes a maximum value and a minimum value. The level of the electric signal Si is changed from the maximum value (minimum value) to the minimum value (maximum value)
→ When the period changes by one period, such as the maximum value (minimum value), the order of the order F of the fringe goes up or down by one.

While the level of the electric signal Si is changing, the measurer observes how many periods the level of the electric signal Si has changed, so that the order F () of the fringe corresponding to the measured pressure Pm1 is obtained. An order difference ΔF between an unknown value) and the fringe order F (unknown value) corresponding to the measured pressure Pm2 is determined. Then, the measurer obtains a pressure difference ΔPm between the measured pressure Pm1 and the measured pressure Pm2 from the order difference ΔF.

In the above measurement, the electric signal S
When the level of i is the maximum value or the minimum value, when the direction of the change of the measured pressure Pm is reversed, the conventional pressure measuring device determines whether the measured pressure Pm is increasing or decreasing. Cannot be determined.

[0016]

In the conventional pressure measuring device described above, only the pressure difference ΔPm when the measured pressure Pm changes from one value to another value, that is, only the incremental (change) is measured. However, there was a drawback that absolute pressure could not be measured in principle. Further, in the above-described pressure measuring device, when the measured pressure Pm changes from a certain value to a different value, it is also determined whether the measured pressure Pm has changed in the increasing direction or the decreasing direction. There was a disadvantage that it could not be determined. The present invention has been made under such a background, and an object of the present invention is to provide a pressure measuring device and a pressure measuring method using the same, which can measure the direction of an absolute pressure and a pressure change with high accuracy. .

[0017]

According to a first aspect of the present invention, there is provided the first flexure having first and second portions which flexure with first and second flexures in accordance with a pressure to be measured. Is N times the second deflection amount, and is a diaphragm that reflects the laser light, and when the maximum measured pressure is applied, the second deflection amount is a half of the laser light. A diaphragm that is smaller than one wavelength,
A laser light generating unit that generates the laser light frequency-modulated into a wave shape that changes linearly in a predetermined cycle, a branching unit that branches the laser light into two, and one of the laser lights branched by the branching unit. A first optical fiber for guiding the first portion of the diaphragm to the first portion, and the other laser beam split by the splitting means for the second optical fiber of the diaphragm;
And a first optical fiber in which a part of the one laser light is reflected by an end face of the first optical fiber.
And the remaining part of the one laser light is the first light.
A first converting means for converting a first interference light with a first reflected light reflected on the portion and incident on the end face into a first electric signal; Interference between the second reference light reflected on the end face of the optical fiber and the second reflected light having the remaining part of the other laser light reflected on the second part and incident on the end face. Second conversion means for converting light into a second electric signal, a second phase change amount of the second electric signal is obtained, and a multiplication result obtained by multiplying the second phase change amount by the deflection ratio N Based on the fringe order calculating means for obtaining the fringe order of the first interference light, and calculating the first phase change amount of the first electric signal based on the fringe order calculated by the fringe order calculating means. Determining the phase change amount based on the determined phase change amount calculating means and the first phase change amount; Characterized by comprising a pressure calculating means for determining a constant pressure. The invention according to claim 2 is the pressure measurement device according to claim 1, wherein
Storage means for storing a conversion table representing the relationship between the amount of phase change and the measured pressure, wherein the pressure calculation means applies the obtained first phase change amount to the conversion table. , The measured pressure is obtained. According to a third aspect of the present invention, in the pressure measuring device according to the first or second aspect, each of the tip portions of the first and second optical fibers is supported, and reflection of the tip and the diaphragm is performed. It is characterized by comprising a support member for supporting the diaphragm with a space formed between the diaphragm and the surface open to the atmosphere. According to a fourth aspect of the present invention, in the pressure measuring device according to the first or second aspect, each of the distal end portions of the first and second optical fibers is supported, and reflection of itself and the diaphragm is performed. A support member for supporting the diaphragm by setting a space formed between the diaphragm and the surface to a vacuum state is provided. According to a fifth aspect of the present invention, in the pressure measuring device according to any one of the first to fourth aspects, the laser light generating means generates the laser light frequency-modulated in a ramp waveform. Features. According to a sixth aspect of the present invention, in the pressure measuring device according to any one of the first to fourth aspects, the laser light generating means generates the laser light frequency-modulated into a triangular wave shape. And Further, the invention according to claim 7 has first and second portions which bend with first and second deflection amounts in accordance with a measured pressure, wherein the first deflection amount is equal to the second deflection amount. And a diaphragm that reflects laser light, wherein the second amount of deflection is smaller than half the wavelength of the laser light when a maximum measured pressure is applied. A diaphragm, a laser light generating means for generating the laser light frequency-modulated into a wave shape that changes linearly in a predetermined cycle, a branching means for splitting the laser light into two, and one of the two branched by the branching means. A first optical fiber for guiding laser light to the first portion of the diaphragm, a second optical fiber for guiding the other laser light branched by the branching means to the second portion of the diaphragm, on the other hand The first reference light in which a part of the laser light is reflected on the end face of the first optical fiber and the first reference light in which the remaining part of the one laser light is reflected on the first part and is incident on the end face A first converting means for converting a first interference light with the reflected light into a first electric signal, and a second converting means for reflecting a part of the other laser light on an end face of the second optical fiber. A second interference light for converting a second interference light between the reference light and the second reflected light, the remaining part of the other laser light being reflected by the second part and incident on the end face, into a second electric signal; In a pressure measuring device having a converting means and a display means for displaying the first and second electric signals, a second phase change amount of the second electric signal displayed on the display means is obtained, Based on the result of multiplication of the second phase change amount by the deflection ratio N, the first phase change
A first step of determining the fringe order of the interference light of the following, and based on the fringe order calculated in the first step,
The method comprises a second step of obtaining a first phase change amount of the first electric signal, and a third step of obtaining the measured pressure based on the first phase change amount. .

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a pressure measuring device according to an embodiment of the present invention. FIG.
In FIG. 2, reference numeral 20 denotes a function generator, which outputs a modulation signal Sm and a trigger signal St having a ramp waveform shown in FIG. The modulation signal Sm and the trigger signal St have a period T and a repetition frequency fm. Reference numeral 21 drives the semiconductor laser 22 with a drive current I having a ramp waveform corresponding to the modulation signal Sm. This drive current I has a period T and a frequency f
m.

The semiconductor laser 22 is frequency-modulated by injection of the driving current I with the center frequency ν0, the frequency modulation width Δν, and the modulation frequency fm (period T) shown in FIG. Is emitted as a laser beam La0. An optical fiber 23 has one end connected to the emission end of the semiconductor laser 22 and the other end connected to the incidence end of the optical fiber coupler 24, and guides the laser light La 0 to the incidence end of the optical fiber coupler 24.

The optical fiber coupler 24 includes an optical fiber 23
Is split into a first laser beam La1 and a second laser beam La2. 251
Is an optical fiber, one end of which is at one output end of the optical fiber coupler 24 and the other end of which is an optical fiber coupler 26 to be described later.
1 laser light La1
To the input end of the optical fiber coupler 261. An optical fiber 252 has one end connected to the other output end of the optical fiber coupler 24 and the other end connected to the input end of an optical fiber coupler 262 described later.

The optical fiber coupler 261 is connected to the optical fiber 2
First laser light La1 incident on the incident end via 51
Is emitted from one emission end, and a first
Is emitted from the other emission end. 271 is
It is an optical fiber, and one end is connected to one emission end of the optical fiber coupler 261. This optical fiber 271
Guides the first laser light La1 emitted from one of the emission ends of the optical fiber coupler 261 to a pressure sensor 28 described later.

On the other hand, the optical fiber coupler 262 has the same configuration as the optical fiber coupler 261 described above.
The second laser light La2 incident on the incident end via the optical fiber 252 is emitted from one of the exit ends,
A second interference light Li2 described later is emitted from the other emission end. Reference numeral 272 denotes an optical fiber provided in parallel with the optical fiber 271, one end of which is connected to one output end of the optical fiber coupler 262. The optical fiber 272 guides the second laser light La2 emitted from one of the emission ends of the optical fiber coupler 262 to the pressure sensor.

The pressure sensor 28 is provided in a compressor of the internal combustion engine, and detects a pressure in the compressor. Here, the configuration of the pressure sensor 28 will be described in detail with reference to FIG. In the pressure sensor 28 shown in FIG.
Reference numeral 0 denotes a substantially disk-shaped diaphragm made of a flexible material, which bends in accordance with the measured pressure Pm applied to the pressure receiving surface 40a which is the surface thereof. This diaphragm 40
The center portion 40b has the largest amount of deflection, and the amount of deflection decreases from the center portion 40b toward the edge.

Specifically, as shown in FIG. 6, the deflection ratio between the first deflection amount Δd1 of the central portion 40b of the diaphragm 40 and the second deflection amount Δd2 of the peripheral portion 40c is as follows.
N: 1. The deflection ratio N is obtained by actually applying the measured pressure Pm to the pressure receiving surface 40a of the diaphragm 40, and determining the first deflection Δd1 and the second deflection Δ
d2 is obtained based on data actually measured by a measuring device (not shown).

Here, the peripheral portion 4 of the diaphragm 40
0c means that the second deflection .DELTA.d2 when the maximum measured pressure Pm is applied to the pressure receiving surface 40a is the laser beam La0.
Means a portion having a value smaller than half the wavelength λ.

Reference numeral 41 denotes a substantially columnar support member for supporting the diaphragm 40, and a concave portion 41a is formed at an upper portion thereof. Further, a first communication hole 41b is formed in the center of the support member 41 so as to communicate from the concave portion 41a to the lower surface 41c along the axis.
In the left side of the first communication hole 41b in FIG.
A second communication hole 41d communicating from the concave portion 41a to the lower surface 41c is formed in a portion opposing the portion 0c. In addition, a third communication hole 41e is formed in the support member 41 on the right side of the first communication hole 41b in the figure, and communicates from the recess 41a to the lower surface 41c.

That is, the support member 41 and the diaphragm 4
0, an internal space 42 is formed, and the internal space 42 is open to the atmosphere via a third communication hole 41e. That is, the pressure inside the internal space 42 is
Atmospheric pressure Pa. In this case, the sealing member 43 is
It is not provided.

One end of the optical fiber 271 (see FIG. 1) is fixedly inserted into the first communication hole 41b of the support member 41 via an adhesive (not shown).
Is located at an optical first distance d1 with respect to the reflection surface 40d, which is the back surface of the central portion 40b.

On the other hand, one end of the optical fiber 272 is inserted and fixed in the second communication hole 41d of the support member 41 via an adhesive (not shown), and the end surface 272a is a reflecting surface which is the back surface of the peripheral portion 40c. 40d optical second
Are placed at a distance d2. These first distances d1
And the second distance d2 have the same value when the measured pressure Pm is equal to the atmospheric pressure Pa, in other words, when both the first deflection Δd1 and the second deflection Δd2 are zero.

In FIG. 1, reference numeral 30 denotes an optical power meter having an optical / electrical conversion function, and a first interference light L which enters via an optical fiber 291 and an optical fiber 292.
i1 and the second interference light Li2 are converted to the first light corresponding to each light intensity.
Into an electric signal Si1 and a second electric signal Si2.

FIG. 5 shows the relationship between the respective light intensities of the first interference light Li1 and the second light interference light Li2, the first distance d1 and the second distance d2, and time. As can be seen from this figure, the light intensities of the first electric signal Si1 and the second electric signal Si2 are equal to the first distance d1 and the second distance d1, respectively.
Even if 2 is a constant value, it changes sinusoidally. this is,
This is because the laser light La0 shown in FIG. 1 is frequency-modulated.

Further, as shown in FIG. 5, the first interference light Li1 (first electric signal Si1) and the second interference light Li1
2 (the second electric signal Si2) has the first distance d1
And when the second distance d2 changes in the increasing direction,
The shift is performed in the direction indicated by the arrow indicated by the dashed line in FIG. On the other hand, the first
The first interference signal Li1 (first electrical signal Si1) and the second interference light Li2 (second electrical signal Si2)
And when the second distance d2 changes in a decreasing direction,
The shift is performed in the direction of the arrow shown by the dashed line in FIG. The reason why the first interference light Li1 (first electric signal Si1) and the second interference light Li2 (second electric signal Si2) are shifted in phase will be described later using a theoretical formula.

The reference numeral 31 shown in FIG. 1 denotes the first electric signal Si1 and the second electric signal Si1 shown in FIGS. 2A and 2B, respectively.
Is an oscilloscope displaying each waveform of the electric signal Si2. Each of the waveforms shown by solid lines in FIGS.
This is a case where the measured pressure Pm (see FIG. 4) is zero.

Reference numeral 32 denotes a CPU (central processing unit).
Second electric signal Si2, trigger signal St, operation data D
The value of the measured pressure Pm, the direction of change of the measured pressure Pm, and the like are obtained by calculation based on c and the like, and the calculation result is output as measurement data Dp. Details of the operation of the CPU 32 will be described later.

Here, the calculation data Dc includes the deflection ratio N, the center wavelength λ0 of the laser beam La0, the first initial phase φ1 of the first electric signal Si1, and the second data of the second electric signal Si2. Initial phase φ2, first phase change / measured pressure conversion table. This operation data D
c is known data.

The first initial phase φ1 of the first electric signal Si1 is defined as the pressure receiving surface 40 of the diaphragm 40 shown in FIG.
The phase of the first electric signal Si1 with respect to the trigger signal St shown in FIG. 1 when zero measured pressure Pm is applied to a. Specifically, in the example shown in FIG. 2A, the first electric signal Si1 with respect to the fall of the trigger signal St
, And the first initial phase φ1 is obtained in advance by calibration.

The second initial phase φ2 of the second electric signal Si2 is defined as a value obtained when zero measured pressure Pm is applied to the pressure receiving surface 40a of the diaphragm 40 shown in FIG.
And the phase of the second electric signal Si2 with respect to the trigger signal St shown in FIG. Specifically, in the example shown in FIG. 2B, the phase φ2 of the second electric signal Si2 with respect to the fall of the trigger signal St refers to the second initial phase φ2.
It is obtained in advance by calibration.

The first phase change / measured pressure conversion table shown in FIG. 10 is the first initial phase φ1 of the first electric signal Si1 (see FIG. 2A). Is a table showing the relationship between the first phase change amount Δφ1 and the measured pressure Pm. This first phase change / measured pressure conversion table is obtained in advance by calibration.

The reference numeral 33 shown in FIG.
This is a memory for storing c. 35 is an indicator, C
The measured pressure Pm as a measurement result according to the measurement data Dp input from the PU 32 is displayed. Reference numeral 34 denotes a data input unit operated by the measurer, and is used for inputting the above-described operation data Dc.

Next, the operation of the pressure measuring device according to the above-described embodiment will be described. At the start of pressure measurement, FIG.
It is assumed that the value of the measured pressure Pm applied to the pressure receiving surface 40a of the diaphragm 40 is Pm1 (see FIG. 10). Therefore, in this case, the first deflection amount Δd1 shown in FIG. 4 is N (the deflection ratio N) of the second deflection amount Δd2.
It is twice.

In this state, when power is supplied to each section of the apparatus shown in FIG.
The modulation signal Sm (see FIG. 2B) and the trigger signal St are supplied to the driver 21, the oscilloscope 31, and the CPU
32. As a result, the semiconductor laser 22 emits a laser beam La0 frequency-modulated in a ramp waveform. The frequency ν (t) of the laser beam La0 is
Assuming that the center frequency is νo, the frequency shift is Δν, the frequency of the modulated signal Sm shown in FIG. 2 is fm, and the time is t, it is expressed by the following equation (1).

(Equation 1)

The laser light La0 is incident on the input end of the optical fiber coupler 24 via the optical fiber 23, and the first laser light La1 is emitted by the optical fiber coupler 24.
And the second laser beam La2 is branched into two beams.
The laser light La1 and the second laser light La2 are respectively emitted from the emission ends of the optical fiber coupler 24.

The first laser beam La1 propagates through the optical fiber 251 and is incident on the incident end of the optical fiber coupler 261. The other second laser light La2 propagates through the optical fiber 252 and is incident on the incident end of the optical fiber coupler 262. Then, one of the first laser beams La1
Is emitted from one emission end of the optical fiber coupler 261 and further propagates in the optical fiber 271. And
The first laser beam La1 shown in FIG.
Part of the first reference light Ls is reflected by the end face 271a of the first reference light Ls.
1 as an optical fiber 2 in a direction opposite to the first laser beam La1.
It propagates through 71. The electric field of the first reference light Ls1 is expressed by the following equation (2), where the amplitude is aE0 and the phase is Φ (t).

(Equation 2)

On the other hand, the remaining part of the first laser light La1 is emitted from the end face 271a of the optical fiber 271,
Central part 40b of the diaphragm 40 as the outgoing light Ld1
To the interior space 42. Then, the first outgoing light Ld1 is reflected by the reflecting surface 40d of the central portion 40b of the diaphragm 40, and propagates as a first reflected light Lr1 in the space toward the end surface 271a of the optical fiber 271. The electric field of the first reflected light Lr1 has an amplitude bE0 and a phase Φ.
If (t−τ), it is expressed by the following equation (3).

(Equation 3) In this equation (3), the time difference τ is represented by the following equation (4), where d is the first distance d1 shown in FIG. 4 and c is the speed of light, and the time difference τ is between the end face 271a of the optical fiber 271 and the central portion 40b. This corresponds to the propagation time due to the optical path length (2d1) between itself and the reflection surface 40d.

(Equation 4)

Then, the first reflected light Lr1 is incident from the end face 271a of the optical fiber 271 and is reflected by the optical fiber 271.
Propagate inside. That is, in the optical fiber 271, FIG.
The first reference light Ls1 and the first reflected light Lr1 shown in FIG. Then, the first reference light Ls1 and the first reflected light Lr1
Interferes with the optical fiber 27 as the first interference light Li1.
Propagating in 1. Here, the electric field E (t) of the first interference light Li1 is expressed by the following equation (5) from the above equations (2) and (3).

(Equation 5)

The light intensity I of the first interference light Li1
(T) is expressed by the following equation (6), which is the square of the absolute value of the electric field E (t) shown in equation (5).

(Equation 6) In the above equation (6), the second term on the right side is the first interference light Li1.
Φ (t) −Φ (t−τ)
Is represented by the following equation (7).

(Equation 7) The above equation (7) considers the section [0, T] shown in FIG.

Subsequently, the following equation (8) is derived from the relationship that the time derivative of the phase Φ (t) is the frequency ν (t) of the laser beam La0.

(Equation 8) Further, when the above equation (8) is substituted into the equation (7), the following equation (9) is derived.

(Equation 9)

Here, on the right side of the above equation (9), 2
πf _m Δντ and 2πν ₀ τ are expressed by the following equations (10) and (11), respectively.

(Equation 10)

[Equation 11] Next, by substituting equations (9) to (11) into equation (6),
The light intensity I (t) of the first interference light Li1 is given by the following (12)
It is expressed by an equation.

(Equation 12) Here, the phase φ of the AC component of the light intensity I (t) in the expression (12) is expressed by the following expression (13), where λ0 is the center wavelength of the first interference light Li1.

(Equation 13)

Further, the above-mentioned equations (12) and (13)
As is apparent from the equation, the light intensity I of the first interference light Li1
When the distance d increases, that is, when the measured pressure Pm decreases, the phase φ of (t) shifts in the direction indicated by the dashed arrow in FIG. On the other hand, the phase φ of the light intensity I (t) shifts in a direction indicated by an alternate long and short dash line in FIG. 5 when the distance d decreases, that is, when the measured pressure Pm increases. Therefore,
By measuring the phase φ, the distance d can be obtained as in the following equation (14).

[Equation 14]

On the other hand, the second laser light La shown in FIG.
2 is partially reflected by the end surface 272a of the optical fiber 272 in the same manner as the first laser light La1 described above and serves as the second reference light Ls2 in the opposite direction to the second laser light La2. Propagate inside. On the other hand, the second laser light L
The remaining part of a2 is emitted from the end face 272a of the optical fiber 272 as the second emission light Ld2, and then the periphery 40c is emitted.
Is reflected by the reflecting surface 40d of the optical fiber 272 and enters the end face 272a of the optical fiber 272 as the second reflected light Lr2. And
The second reflected light Lr2 and the second reference light Ls2 interfere with each other and propagate as second interference light Li2 in the optical fiber 272.

The first interference light Li1 and the second interference light Li2 shown in FIG. 1 are transmitted through the optical fibers 271 and 272, the optical fiber couplers 261 and 262, and the optical fibers 291 and 292. Input to the power meter 30.

As a result, the optical power meter 30 has the first
And the second interference light Li2 are converted into a first electric signal Si1 and a second electric signal. The first electric signal Si1 and the second electric signal Si2 are input to the oscilloscope 31 and the CPU 32, respectively.

As a result, the oscilloscope 31 displays the first electric signal Si1 and the second electric signal Si2 indicated by broken lines in FIGS. 2A and 2B, respectively.
That is, the first electric signal Si indicated by a broken line in FIG.
1 has an apparent phase of φ1 ′, and the true phase of the first electric signal Si1 (first initial phase φ1) shown by the solid line is 2Fπ + φ1 ′ in the direction of the arrow + shown in FIG. Is shifting. Note that F is the order of the fringe described above. In other words, the first phase change Δφ1 of the first electric signal Si1 shown by the broken line with respect to the first electric signal Si1 shown by the solid line is 2Fπ + φ1 ', but the fringe can be seen only by looking at the display of the oscilloscope 31. Since the order F cannot be specified, an accurate value cannot be known.

On the other hand, the phase of the second electric signal Si2 indicated by the broken line in FIG. 2B is φ2 ′, and the phase of the second electric signal Si2 indicated by the solid line (second initial phase φ2) is different from that of the second electric signal Si2. Is shifted in the direction of the arrow + shown in FIG. Here, it should be noted that, as described above, the second deflection Δ when the maximum measured pressure Pm is applied to the pressure receiving surface 40a shown in FIG.
Since d2 is smaller than half the wavelength λ of the laser beam La0, the second phase change Δφ2 (| φ2−φ2 '|) of the second electric signal Si2 must exceed 2π. There is no.

Further, the CPU 32 shown in FIG. 1 converts the phases of the input first electric signal Si1 and second electric signal Si2 into φ1 ′ and φ2 ′ as shown in FIGS. 2 (a) and 2 (b). 'And ask. Here, the phase φ1 ′ is an apparent phase. Next, the CPU 32 reads out the second initial phase φ2 stored in the memory 33,
The absolute value of the value obtained by subtracting the previously obtained phase φ2 ′ from the initial phase φ2 is obtained as the above-mentioned second phase change Δφ2.

Next, the CPU 32 reads the deflection ratio N stored in the memory 33, and multiplies this by the second phase change amount Δφ2 to obtain a multiplication result of NΔφ2. Here, (NΔφ2) and (2Fπ +
φ1 ′), there is a relationship that they are almost equal in consideration of the minute error. Therefore, the CPU 32 calculates (N
An integer fringe order F is obtained based on the result of comparing (Δφ2) and (2Fπ + φ1 ′). That is, the CPU 3
2 is (NΔφ) when known N, Δφ2 and φ1 ′ are substituted for (NΔφ2) and (2Fπ + φ1 ′), respectively.
2) An integer fringe order F that minimizes the absolute value of the difference between (2Fπ + φ1 ′) is obtained.

Next, the CPU 32 determines the first
By substituting the apparent phase φ1 ′ of the electric signal Si1 and the fringe order F into the equation 2Fπ + φ1 ′, the first phase change Δφ1 of the first electric signal Si1 is obtained.

Next, the CPU 32 calculates the first phase change Δ obtained previously from the first phase change / measured pressure conversion table (see FIG. 10) stored in the memory 33.
A measured pressure Pm1 corresponding to φ1 is obtained. This allows
The display 35 displays the measured pressure Pm1.

As described above, one embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and a design change within a range not departing from the gist of the present invention. The present invention is also included in the present invention. For example, in the pressure measuring device according to the above-described embodiment, an example in which the frequency modulation is performed on the laser light using the modulation signal Sm having the ramp waveform illustrated in FIG. 1 has been described. The modulation signal Sm may be used. In this case, a function generator that can output a triangular waveform modulation signal Sm may be used as the function generator 20.

Further, in the pressure measuring apparatus according to the above-described embodiment, the description has been given of the differential pressure measurement in which the internal space 42 shown in FIG.
By sealing the opening of e with the sealing member 43,
The internal space 42 may be evacuated to measure the absolute pressure relative to the vacuum pressure.

As described above, according to the pressure measuring device according to the embodiment of the present invention, the first interference is further performed by the two first optical fibers 271 and 272 using the frequency-modulated laser light La. Since the phase changes of the light Li1 and the second interference light Li2 are obtained, it is possible to obtain the effect that the direction of the pressure change can be easily known and the absolute pressure can be measured.

Further, according to the pressure measuring device of one embodiment, the first electric signal Si is obtained based on the value obtained by multiplying the second phase change Δφ 2 of the second interference light Li 2 by the deflection ratio N.
After specifying the fringe order F of 1 (see FIG. 2A),
The first phase change Δφ1 of the first electric signal Si1 is 2Fπ
Since the value is accurately obtained from the equation + φ1 ′, an effect is obtained that the above-described incremental measurement can be performed with high accuracy without accumulation of errors.

Further, according to the pressure measuring device of one embodiment, the first interference light Li1 and the second interference light Li
The pressure is measured based on the first phase change amount Δφ1 and the second phase change amount Δφ2 of the interference light Li2, so that it is hardly affected by the intensity of the light source and the disturbance that the optical fibers 271, 272, etc. receive. Therefore, the effect that the pressure can be measured with high accuracy can be obtained.

[0064]

According to the present invention, the phase change of the first interference light and the second interference light is obtained by the two first and second optical fibers using the frequency-modulated laser light. Therefore, it is possible to obtain the effect that the direction of the pressure change can be easily known and the absolute pressure can be measured.

Further, according to the present invention, since the pressure is measured based on the first phase change amount and the second phase change amount of the first interference light and the second interference light that beat the light, Hardly affected by the intensity of the light source or the disturbance of the first and second optical fibers,
Therefore, the effect that pressure measurement can be performed with high accuracy is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a pressure measuring device according to an embodiment of the present invention.

FIG. 2 shows a first electric signal Si1 and a second electric signal Si1 shown in FIG.
FIG. 7 is a diagram showing each waveform of the electric signal Si2.

FIG. 3 is a diagram showing a change in an optical frequency ν of the laser beam La0 shown in FIG.

FIG. 4 is an enlarged sectional view showing a configuration of the pressure sensor 28 shown in FIG.

FIG. 5 is a diagram 3 illustrating a correlation between a first distance d1 (second distance d2), a first electric signal Si1 (second electric signal Si2), and time in the pressure measurement device according to the embodiment of the present invention. It is a dimensional graph.

FIG. 6 shows a measured pressure Pm and a first flexure Δd1 (second flexure Δd2) in the pressure sensor 28 shown in FIG.
6 is a graph showing a relationship with the graph.

FIG. 7 is a block diagram showing a configuration of a conventional pressure measuring device.

FIG. 8 is a sectional view showing a configuration of the pressure sensor 6 shown in FIG.

FIG. 9 is a three-dimensional graph showing the correlation among the light intensity of the interference light Li, the amount of deflection Δd, and time in a conventional pressure measurement device.

FIG. 10 is a graph showing a relationship between the first phase change Δφ1 of the first electric signal Si1 and the measured pressure Pm in the pressure measuring device according to the embodiment of the present invention.

FIG. 11 shows a measured pressure P in a conventional pressure measuring device.
It is a graph which shows the relationship between m and the order F of a fringe.

[Explanation of symbols]

 Reference Signs List 20 function generator 21 driver 22 semiconductor laser 23 optical fiber 24 optical fiber coupler 251 optical fiber 252 optical fiber 261 optical fiber coupler 262 optical fiber coupler 271 optical fiber 272 optical fiber 28 pressure sensor 291 optical fiber 292 optical fiber 30 optical power meter 31 oscilloscope 32 CPU 33 Memory 34 Data input unit 35 Display 40 Diaphragm 41 Support member La0 Laser light La1 First laser light Ls1 First reference light Ld1 First emission light Lr1 First reflected light Li1 First interference light La2 Second laser light Ls2 Second interference light Ld2 Second emission light Lr2 Second reflected light Li2 Second interference light Δd1 First amount of deflection Δd2 Second amount of deflection d1 First distance d2 Second Distance Si1 First electric signal Si2 No. 2 electric signal Pm measured pressure Δφ1 first phase change amount φ1 first initial phase φ2 second initial phase I drive current Sm modulation signal St trigger signal Dc operation data Dp measurement data

Claims (7)

[Claims] 1. A method according to claim 1, wherein the first and second portions have first and second portions which bend with a first and a second amount of deflection according to a pressure to be measured, and wherein the first amount of deflection is N times the second amount of deflection. A diaphragm that reflects the laser light and has a second deflection amount smaller than a half wavelength of the laser light when a maximum measured pressure is applied; A laser light generating means for generating the laser light frequency-modulated into a wave shape that changes linearly in the laser light, a branching means for splitting the laser light into two, and one of the laser lights branched by the branching means. A first optical fiber for guiding to the first portion, a second optical fiber for guiding the other laser beam branched by the branching means to the second portion of the diaphragm, and one of the one laser beam. Is the first reference light reflected on the end face of the first optical fiber, and the first reflected light is the remaining part of the one laser light is reflected on the first portion and is incident on the end face. A first conversion unit that converts the first interference light into a first electric signal; a second reference light in which a part of the other laser light is reflected by an end face of the second optical fiber; A second conversion unit that converts a second interference light with the second reflected light that is reflected by the second part and that is incident on the end face while the other part of the other laser light is reflected, to a second electric signal; Calculating a second phase change amount of the second electric signal;
Based on a multiplication result obtained by multiplying the amount of phase change by the deflection ratio N, based on the fringe order calculating means for obtaining the fringe order of the first interference light, based on the fringe order calculated by the fringe order calculating means, A phase change amount calculating unit for obtaining a first phase change amount of the first electric signal; and a pressure calculating unit for obtaining the measured pressure based on the first phase change amount. And a pressure measuring device. 2. A storage unit for storing a conversion table representing a relationship between the first phase change amount and the measured pressure, wherein the pressure calculating unit calculates the first phase change amount. The pressure measurement device according to claim 1, wherein the pressure to be measured is obtained by applying the pressure to the conversion table. 3. The optical fiber supports the respective distal end portions of the first and second optical fibers, and supports the diaphragm with a space formed between itself and a reflecting surface of the diaphragm being open to the atmosphere. The pressure measuring device according to claim 1, further comprising a support member. 4. A support for supporting the respective distal end portions of the first and second optical fibers, and for supporting the diaphragm with a space formed between itself and a reflecting surface of the diaphragm being in a vacuum state. The pressure measuring device according to claim 1, comprising a member. 5. The pressure measuring device according to claim 1, wherein said laser light generating means generates said laser light frequency-modulated in a ramp wave shape. 6. The pressure measuring device according to claim 1, wherein the laser light generating means generates the laser light frequency-modulated in a triangular wave shape. 7. A method according to claim 1, further comprising a first portion and a second portion which bend with first and second deflection amounts in accordance with a measured pressure, wherein said first deflection amount is set to N times said second deflection amount. A diaphragm that reflects the laser light, wherein the second amount of deflection is smaller than half the wavelength of the laser light when a maximum measured pressure is applied; A laser light generating means for generating the laser light frequency-modulated to a wave shape that changes linearly, a branching means for branching the laser light into two, and one of the laser lights branched by the branching means to the diaphragm. A first optical fiber for guiding to the first portion, a second optical fiber for guiding the other laser beam branched by the branching means to the second portion of the diaphragm, and one of the one laser beam. Department The first reference light reflected on the end face of the first optical fiber and the first part of the remaining part of the one laser light reflected on the first portion and incident on the end face
A first converting means for converting a first interference light with the reflected light into a first electric signal, and a second converting means for reflecting a part of the other laser light on an end face of the second optical fiber. A second interference light for converting a second interference light between the reference light and the second reflected light, the remaining part of the other laser light being reflected by the second part and incident on the end face, into a second electric signal; Conversion means, and the first
And a display means for displaying a second electric signal, wherein a second phase change amount of the second electric signal displayed on the display means is obtained, and the second phase change amount is calculated. A first step of obtaining a fringe order of the first interference light based on a multiplication result obtained by multiplying the deflection ratio N; and a first electrical operation based on the fringe order calculated in the first step. A second step of obtaining a first phase change amount of the signal; and a third step of obtaining the measured pressure based on the first phase change amount. The pressure measurement method used.