JPH068724B2 - Optical detector - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an optical detection device for optically detecting a physical quantity of pressure and temperature.

[Background of the Invention]

A pressure or temperature measuring device using electric means generally converts the measurement signal into an electric signal and transmits it to a remote place. Therefore, there is a high possibility of receiving electrical induction noise during the transmission of this measurement signal.
In this respect, the pressure or temperature measuring device using optical means enables remote measurement by using an optical fiber in the transmission path, and can realize signal transmission with noise resistance.

The properties of light utilized as optical means include light intensity, phase, frequency and polarization. In particular, a device for measuring a change in light intensity is used in various measuring methods and measuring devices because it is relatively easy to handle and the signal processing is easy. However, in general, in a measurement device that utilizes a change in light intensity, a change in light amount other than a pressure or temperature detection unit, for example, a change in light amount due to a change in transmission loss when an optical fiber is used as a light transmission path causes a measurement error. It becomes a factor. The cause of this transmission loss change is the generation of transmission light having a reflection angle larger than the critical angle due to the bending of the optical fiber, or the generation of microbends due to the vibration of the entire optical fiber. Change the transmission loss of.

For this reason, in an apparatus that uses an optical fiber to measure pressure or temperature by changing the intensity of light, it is necessary to reduce the change in transmission loss or compensate for the change in transmission loss in order to improve the measurement accuracy. . The compensation method for the transmission loss change of the optical fiber is described in the 26th Automatic Control Federation Lecture Meeting, November 1983, p. 435 is discussed in the literature entitled "Improvement of Reference Path Detection Method of Optical Fiber Sensor and Application of Optical Pressure Gauge". FIG. 9 shows an example of application to the compensation circuit of the optical pressure sensor of the transmission loss compensation system described in the above document.

In FIG. 9, the pressure sensor unit is composed of light transmitting fibers 3 and 6.
And the light receiving fibers 8 and 9 and these four optical fibers 3 and
The diaphragm 22 is arranged opposite to the end faces of 6, 8, and 9 and also serves as a reflecting plate, and the housing 23 fixes the positional relationship between them. The light from the light-transmitting fibers 3 and 6 in the pressure sensor unit is received by the light-receiving fibers 8 and 9 at the distance between the optical fiber and the diaphragm 22, that is, the light amount corresponding to the pressure signal. The light emitting diodes 1 and 4 are driven by the drive circuits 7 and 10 controlled by the arithmetic and control circuit 20, and the light 2 and the light of the same wavelength 2,
5 is generated. The photoelectric conversion circuits 17 and 18 to which the light receiving diodes 15 and 16 are connected convert the pressure signals 11, 12, 13 and 14 from the light receiving fibers 8 and 9 into light receiving voltage signals. The arithmetic processing circuit 19 performs later-described arithmetic operations on these received light voltage signals. The calculation result is corrected by the calculation control circuit 20 and displayed on the pressure display circuit 21.

Next, the principle of this compensation method will be described. The light receiving voltage signal of the photoelectric conversion circuits 17 and 18 when the light emitting diode 1 emits light is expressed by the following equation.

V ₁₁ = K ₁₇ · P ₁₁ = K ₁₇ · L ₃ · L _3-9 · L ₉ · P ₂ ……… (1) V ₁₂ = K ₁₈ · P ₁₂ = K ₁₈ · L ₃ · L _{3-8 ·} L 8 · P 2 _......... also (2), receiving the voltage signal when the light emitting diode 4 emits light, the Likewise represented by the following equation.

_{V 13 = K 17 · P 13} = K 17 · L 6 · L 6-9 · L 9 · P 5 ......... (3) V 14 = K 18 · P 14 = K 18 · L 6 · L 6-8 _{· L 8 · P 5 ......... (} 4) However, _{V i;} fiber optic l; pressure signal light i quantity L _l; transform coefficients P _i of the photoelectric conversion circuit j; receiving a voltage signal by the pressure signal i K _j transmission efficiency L _ma; optical fiber m, coupling between n efficiency P _r; amount calculation processing circuit 19 of the light r of the light emitting diode 1 and 4, the equation (1), second (2), second (3) And after storing the received light voltage signals of the formula (4), respectively, the following calculation is performed.

The calculation result of the equation (5) does not include the term of the transmission loss of the light-transmitting fibers 3, 6 or the light-receiving fibers 8, 9, but does not include the light coupling coefficient of the light-transmitting fibers 3, 6 and the light-receiving fibers 8, 9. It is a function, that is, a function of pressure only. Further, in order that the equation (5) does not become a constant, it is necessary that the light coupling coefficients of the light-transmitting fibers 3, 6 and the light-receiving fibers 8, 9 be different. For example, the relationship shown in FIG. 11 can be obtained by symmetrically arranging the detection end faces as shown in FIG. 10, and for example, the range of Z _{1 to} Z ₂ (straight line portion) in FIG. 11 can be used as a pressure sensor. This allows more accurate detection. However, the above compensation method requires four optical fibers as the transmitting and receiving fibers,
The structure of the pressure sensor section becomes complicated.

[Object of the Invention]

The present invention provides an optical detection device capable of reducing the number of optical fibers to be used and simplifying the device structure in the case of measuring a physical quantity such as pressure or temperature by changing the intensity of light using an optical fiber. The purpose is to

[Outline of Invention]

In order to achieve the above object, the present invention makes the types of the optical fiber used for transmitting light and the optical fiber used for receiving light different, and determines the coupling efficiency of light between the transmitting fiber and the receiving fiber depending on the traveling direction of the light. The feature is that the change is compensated for the change of the transmission loss of the optical fiber.

That is, the present invention provides a reflecting plate in which the relative distance between the first light emitting source and the second light emitting source driven in a time division manner and the end face of the optical fiber, which will be described later, changes according to the change in the physical quantity to be measured. A measuring unit having, and arranged between the first and second light emitting sources and the measuring unit,
First and second optical fibers having mutually different optical characteristics, and light from the second light source, which is transmitted through the second optical fiber and reflected by the measurement unit, and then the first optical fiber. Light from the first photoelectric conversion unit that receives the second light transmitted via the first light source and converts the second light into an electric signal, and is transmitted through the first optical fiber in the measurement unit. A second photoelectric conversion unit that receives the first light that has been reflected and then transmitted through the second optical fiber and converts the first light into an electrical signal; and a light from the first light source that is the first optical fiber. Introduced to
The first light branching device for guiding the reflected light from the second light source to the first photoelectric conversion unit and the second light source for the second light source
Second optical branching device that introduces the reflected light from the first light source to the second photoelectric conversion unit, and electricity from the first photoelectric conversion device and the second photoelectric conversion device. An arithmetic unit that calculates the ratio of signals to obtain the measured physical quantity,
It is characterized in that it is equipped with.

In this case, the first and second optical fibers have different optical characteristics by differentiating at least one of the core diameter, the refractive index distribution inside the core, and the numerical aperture. It is characterized by

Example of Invention

 Next, embodiments of the present invention will be described in detail with reference to the drawings.

First Embodiment FIG. 1 shows an embodiment in which the optical detection device according to the present invention is applied to an optical pressure sensor. Light emitting diode 1,
4 is a drive circuit 7 controlled by the drive control circuit 34,
It is driven by 10, and the emitted lights 30 and 32 of the same wavelength are generated. The emitted light 30 from the light emitting diode 1 is transmitted to the pressure sensor unit after being incident on the first optical fiber 28 via the first optical branching device 24 and the rod lens 26.

The pressure sensor unit includes a first optical fiber 28, a second optical fiber 29, and a diaphragm 22 that also serves as a reflection plate and faces the detection end faces of these optical fibers 28, 29.
And a housing 23 for fixing their positional relationship.

The projection light from the first optical fiber 28 in the pressure sensor unit is received by the second optical fiber 29 in the distance between the optical fibers 28 and 29 and the diaphragm 22, that is, the light amount corresponding to the pressure signal. The light received by the second optical fiber 29 is transmitted again, and after passing through the second rod lens 27, the traveling direction of the light is changed by the second optical branching device 25, and the pressure signal light is transmitted to the first light receiving diode 161. The light is irradiated as 31 and is converted into a light reception voltage signal by the first photoelectric conversion circuit 181. Similarly, the outgoing light 32 from the light emitting diode 4 passes through a route opposite to that of the outgoing light 30 from the light emitting diode 1, and the traveling direction of the light is changed by the first optical branching device 24, and the light is emitted to the second light receiving diode 151. It is emitted as the pressure detection signal 33 and converted into a light reception voltage signal by the second photoelectric conversion circuit 171. These received light voltage signals are input to the arithmetic processing circuit 35.

The arithmetic processing circuit 35 executes the arithmetic processing described later, and the arithmetic result is corrected by the microcomputer 36. The microcomputer 36 outputs a control signal to the drive control circuit 34 and indirectly controls the drive circuits 7 and 10. The calculation result corrected by the microcomputer 36 is displayed on the pressure display circuit 37.

Next, the arithmetic processing of the arithmetic processing circuit 35 will be described.
When the light emitting diode 1 emits light, the first photoelectric conversion circuit 1
The light receiving voltage signal of 81 is expressed by the following equation.

_{V 31 = K 181 · P 31} = K 181 · L 28 · L (28-29) · L 29 · P 30 ......... (6) Further, when the light emitting diode 4 emits light, the second photoelectric conversion circuit 171 Similarly, the received light voltage signal of is expressed by the following equation.

V ₃₃ = K ₁₇₁ · P ₃₃ = K ₁₇₁ · L ₂₉ · L _(29-28) · L ₂₈ · P ₃₂ (7) where V _{i is the} received voltage signal K _j by the pressure signal i; photoelectric conversion Conversion coefficient of circuit j P _i ; light quantity of pressure signal light i L _l ; transmission efficiency of optical fiber l L _(ma) ; coupling efficiency when light travels from optical fiber m to n P ₃₀ ; optical fiber 28 Light intensity of incident light 30 P ₃₂ ; Light intensity of incident light 32 to optical fiber 29 The arithmetic processing circuit 35 stores the light receiving voltage signals of the formulas (6) and (7), respectively, and then performs the following calculation. .

here The calculation result of the equation (8) does not include the terms of the transmission loss of the first optical fiber 28 and the transmission loss of the second optical fiber 29, and the calculation result of the first optical fiber 28 and the second optical fiber 29 is not included. It becomes a function of the coupling efficiency between them, that is, a function of only pressure.
Further, in order that the expression (8) does not become a constant, the coupling efficiency L between the optical fibers 28 and 29 depends on the traveling direction of the light.
_(28-29) and L _(29-28) must be different. In order to satisfy this condition, for example, two kinds of optical fibers having different core diameters, refractive index distribution inside the core or numerical aperture may be used as the first optical fiber 28 and the second optical fiber 29.

The emitted light intensity distributions I ₁ and I ₂ from the optical fibers 28 and 29 of different types in the pressure sensor unit to the diaphragm 22 that also serves as the reflection plate are as shown in FIG. 2, for example. That is, the first optical fiber 28 and the second optical fiber 28
By making the type of the optical fiber 29 different from that of the optical fiber 29, the emission light intensity distributions I ₁ and I _{2 at the} diaphragm 22 become different. As a result, the coupling efficiencies L _(28-29) and L _(29-28) between the optical fibers 28 and 29 via the reflection of the diaphragm 22 differ depending on the traveling direction of light, and the required coupling efficiency is obtained. To be Therefore, the first of these different types
By using the optical fiber 28 and the second optical fiber 29, it is possible to obtain an optical pressure sensor having the characteristics shown in FIG.

In this optical pressure sensor, when pressure is applied to the diaphragm 22, the distance between the optical fibers 28 and 29 and the diaphragm 22 changes, and the light coupling efficiency between the optical fibers 28 and 29 changes. This change in coupling efficiency is
As shown in the equation (7), the received light voltage signals V ₃₁ and V ₃₃ change. The received light voltage signals V ₃₁ and V ₃₃ are functions of pressure and transmission loss of the optical fibers 28 and 29. The expression (8), which is the calculation result of the calculation processing circuit 35, shows that the light emitted from the light emitting diodes 1 and 4 is emitted. Is constant, (V ₃₁ / V ₃₃ ) changes only when there is a pressure change. Therefore, the range of, for example, Z _{3 to} Z _{4 in} FIG. ₃ is used as the pressure detection range of the pressure sensor. The microcomputer 36 calculates the pressure and (V _{31 in} FIG. 3 from the calculation result of the calculation processing circuit 35 by the expression (8).
The pressure is determined based on the relationship with / V ₃₃ ).

As described above, in an optical application sensor that uses an optical fiber to measure pressure based on a change in light intensity, two types of high-accuracy pressure measurements can be performed without being affected by transmission loss changes in the optical fiber. This can be realized by using an optical fiber, and along with this, the structure of the pressure sensor unit can be simplified. Further, it can be considered that the change in the transmission loss of the optical fiber also includes the connection loss of the optical connector used when connecting the optical fiber and the optical fiber. Therefore, when laying the optical fiber over a long distance, the pressure sensor unit and the signal processing unit including the light emitting diode, the light receiving diode, and the optical fiber can be separated, and the optical fiber of the signal processing unit and the pressure sensor can be separated. If necessary, it is possible to connect the optical fiber to the optical fiber by using an optical connector. Therefore, the number of connection points by this optical connector is as small as two, and the handling of the optical fiber becomes easy.

Second Embodiment Next, a second embodiment of the present invention is shown in FIG. In this embodiment, the pressure sensor unit comprises a first optical fiber 28,
It comprises a second optical fiber 29, a diaphragm 220 that changes when pressure is applied, a light blocking plate 221 attached to the diaphragm 220, and a housing 230 that fixes the positional relationship between these. In such a configuration, the change in the received light voltage signal output from the photoelectric conversion circuits 171 and 181 with respect to the movement amount of the blocking plate 221, that is, the pressure, has the characteristic shown in FIG. On this characteristic, for example, utilize a range of Z ₅ to Z ₆ as a pressure detection range of the pressure sensor.

The drive circuits 7 and 10 for the light emitting diodes 1 and 4 are controlled by the drive control circuit 34 so that the light emitting diodes 1 and 4 are driven in a time division manner. By making the light emitting diodes 1 and 4 time-division drive, multiple reflected light between the light branching devices 24 and 25 and the rod lenses 26 and 27, or the light branching device 2
It is possible to prevent reflected light generated due to the difference in refractive index between 4, 25 and air from irradiating the light receiving diodes 151 and 161 and becoming an error signal for the light receiving voltage signal due to the pressure signal. That is, for example, when the light emitting diode 1 is driven, multiple reflected light or the like is emitted to the light receiving diode 151, but this multiple reflected light is not used because it is not a pressure sensor signal, and pressure signal light emitted to the light receiving diode 161 is not used. 31 is used to avoid the influence of multiple reflected light.

Third Embodiment Further, the fluctuation of the emitted light amount of the light emitting diodes 1 and 4 is
Even if the pressure signal does not change as shown in the equation (8), the ratio (V ₃₁ / V ₃₃ ) of the received light voltage signals fluctuates, resulting in a measurement error for the pressure signal. Therefore, as shown in FIG. 6, the third light receiving diode 40 and the third light receiving diode 40
The photoelectric conversion circuit 41 is provided, and the light receiving voltage signal from the photoelectric conversion circuit 41 is detected.
It is possible to compensate the influence of the measurement error due to the variation of the outgoing light amount of No. 4. The third embodiment in consideration of the method of processing the received light voltage signal in FIG. 6 will be described below.

When the light emitting diode 1 emits light, the light receiving voltage signal of the third photoelectric conversion circuit 41 has the following expression.

V ₃₈ = K ₄₁ · P ₃₈ (9) Further, when the light emitting diode 4 emits light, the light receiving voltage signal of the third photoelectric conversion circuit 41 similarly becomes the following expression.

V ₃₉ = K ₄₁ · P ₃₉ (10) The following relationships are obtained from the equations (6), (7), (9) and (10).

However, V ₃₈ ; received light voltage signal by the branched light 38 from the first optical branching device V ₃₉ ; received light voltage signal by the branched light 39 from the second optical branching device 25 K ₄₁ ; of the third photoelectric conversion circuit Conversion coefficient P ₃₈ : Light intensity of the branched light 38 from the optical splitter 24 P ₃₉ : Light intensity of the branched light 39 from the optical splitter 25 In the equation (11), the term (P ₃₀ / P ₃₈ ) is the branching ratio of the first optical branching device 24, and the term (P ₃₂ / P ₃₉ ) is the branching ratio of the second optical branching device 25. Because of this, each is a constant.
Therefore, the expression (11) is not affected by the variation in the amount of light emitted from the light emitting diodes 1 and 4.

The configuration of the concrete processing of the calculation of the equation (11) will be described with reference to FIG. When the light emitting diode 1 emits light, the light receiving voltage signals V ₃₁ and V ₃₈ from the first photoelectric conversion circuit 181 and the third photoelectric conversion circuit 41 are input to the division circuit 42. When the light emitting diode 4 emits light, the light receiving voltage signals V ₃₃ and V ₃₉ from the second photoelectric conversion circuit 171 and the third photoelectric conversion circuit 41 are input to the division circuit 42. Since the light emitting diodes 1 and 4 are driven in a time division manner, the outputs of the division circuits 42 and 43 are also obtained in a time division manner, so that the outputs of the division circuits 42 and 43 are held in the sample hold circuits 44 and 45, respectively. . The microcomputer 47 is a drive control circuit 34 for the light emitting diodes 1 and 4.
In addition to outputting a signal for time-division driving, the set and reset signals of the sample and hold circuits 44 and 45 are output, and when the outputs from the divider circuits 42 and 43 are obtained, the sample and hold circuit 46 Control is performed so that signals from 44 and 45 are output. The output from the division circuit 46 is the calculation result of the equation (11), and the microcomputer determines the pressure applied to the diaphragm 22 from the calculation result based on the relation of FIG. Display at.

Fourth Embodiment Next, not only the light coupling between the first optical fiber 28 and the second optical fiber 29, but also the return light 311 from the pressure sensor unit when the light emitting diode 1 is driven, and the light emission. Return light 31 from the pressure sensor unit when the diode 4 is driven
A fourth embodiment in which compensation is performed using 1 will be described with reference to FIG.

The light receiving voltage signal obtained when the light emitting diode 1 emits light is given by the following equation.

V ₃₁₁ = K ₁₇₁ · P ₃₁₁ = K ₁₇₁ · L ^2/28 · L _28-28 · P ₃₀ ……… (12) V ₃₁ = K ₁₈₁ · P ₃₁ = K ₁₈₁ · L ₂₈ · L _{(28-29 )} and receiving a voltage signal obtained when _{L 29 · P 30 ......... (6} ) the similar light emitting diode 4 emits light is represented by the following equation.

V ₃₃₁ = K ₁₈₁・ P ₃₃₁ = K ₁₈₁・ L ^2/29・ L _29-29・ P ₃₂ ……… (13) V ₃₃ = K ₁₇₁・ P ₃₃ = K ₁₇₁・ L ₂₉・ L _{(29-28 ) · L 28 · P 32 .........} (7) calculation processing circuit 35 includes a first (6), first (7) and second (12) and the equation (13) of the light receiving voltage signals respectively stored After that, the following calculation is performed.

Expression (14) is a function of pressure only, without including the terms of the transmission loss of the first optical fiber 28 and the second optical fiber 29. In addition, the first optical fiber 28 and the second optical fiber 2
The coupling coefficient of light with 9 may be the same irrespective of the traveling direction of light. For example, each received voltage signal in this case is as shown in FIG. ₈ , and is in the range of (Z ₇ , Z ₈ ). Is used for the pressure measurement range of the pressure sensor. Therefore, from the calculation result of the formula (14) of the calculation processing circuit 35, the pressure and (V
_The pressure is determined based on the relationship with ₃₁ · V ₃₃ ) / (V ₃₁₁ · V ₃₃₁ ), and is displayed by the pressure display circuit 37.

In the above embodiments, an example in which the present invention is applied to an optical pressure sensor has been described. However, for example, a diaphragm for pressure detection may be a bimetal for temperature detection to provide an optical temperature sensor. Further, it is obvious to those skilled in the art that the present invention can be applied to measurement of displacement, strain and the like.

〔The invention's effect〕

According to the present invention, in an optical sensor that measures pressure, temperature, strain, and the like by changing the intensity of light using an optical fiber, the light coupling efficiency between the optical fibers changes depending on the traveling direction of the light. By using two different types of optical fibers, the measured values of pressure, temperature, strain, etc. are not affected by changes in transmission loss of the optical fibers.
Highly accurate measurement is possible. Further, it is not necessary to use a special configuration for the pressure or temperature sensor section, and the configuration can be simplified.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a characteristic diagram showing an outgoing light intensity distribution of an optical fiber used in the present invention, and FIG. The characteristic diagram shown in FIG. 4, FIG. 4 is a block diagram showing the second embodiment of the present invention, FIG. 5 is a characteristic diagram showing changes in the received light voltage signal in the embodiment of FIG. 4, and FIG. 6 is the present invention. FIG. 7 is a block diagram showing a third embodiment of the present invention, FIG. 7 is a block diagram showing a fourth embodiment of the present invention, and FIG. 8 is a characteristic diagram showing changes in the received light voltage signal in the embodiment of FIG. FIG. 9 is a block diagram showing an example of a conventional optical detection device, FIG. 10 is a diagram showing an example of arrangement of optical fibers in a conventional sensor section, and FIG. 11 is a change of received light voltage signal in FIG. It is a characteristic diagram. 1, 4 ... Light emitting diode, 3, 6, 8, 9, 28, 29
... Optical fiber, 7,10 ... Drive circuit, 15,16,40
... Light receiving diode, 22, 220 ... Diaphragm, 1
7, 18, 171, 181, 41 ... Photoelectric conversion circuit, 20
... arithmetic control circuit 21, 37 ... pressure display circuit 24, 2
5 ... Optical branching device, 34 ... Drive control circuit, 35 ... Arithmetic control circuit, 36 ... Microcomputer, 42, 43, 46 ...
Division circuits, 44, 45 ... Sample and hold circuits.

Claims (2)

[Claims] 1. A first light source and a second light source which are driven in a time division manner, and a reflector whose relative distance to an end face of an optical fiber, which will be described later, changes according to a change in a physical quantity to be measured. A measuring unit, arranged between the first and second light emitting sources and the measuring unit,
First and second optical fibers having mutually different optical characteristics, and light from the second light source, which is transmitted through the second optical fiber and reflected by the measurement unit, and then the first optical fiber. Light from the first photoelectric conversion unit that receives the second light transmitted via the first light source and converts the second light into an electric signal, and is transmitted through the first optical fiber in the measurement unit. A second photoelectric conversion unit that receives the first light that has been reflected and then transmitted through the second optical fiber, and converts the first light into an electrical signal; Introduced to
The first light branching device for guiding the reflected light from the second light source to the first photoelectric conversion unit and the second light source for the second light source
Second optical branching device that introduces the reflected light from the first light source to the second photoelectric conversion unit, and electricity from the first photoelectric conversion device and the second photoelectric conversion device. An arithmetic unit that calculates the ratio of signals to obtain the measured physical quantity,
An optical detection device comprising: 2. The device according to claim 1, wherein the first and second optical fibers each have at least one of a core diameter, a refractive index distribution inside the core, and a numerical aperture. An optical detection device characterized in that the optical characteristics are made different by making the fibers different.