JPS61145403A - Optical detector - Google Patents

Abstract

PURPOSE:To decrease the number of optical fibers employed for measurements of physical quantities, such as pressure, temperature, etc. and to simplify the construction of an apparatus, by using 2 different kinds of optical fiber, the coupling efficiency of the light between the optical fibers changing according to the propagating direction of light. CONSTITUTION:Light emission diodes 1, 4 are driven 7, 10 and generate beams of light 30, 32 of the same wave length respectively. This beam of light 30 is transmitted to a pressure sensor unit consisting of optical fibers 28, 29, diaphragm 22 etc. serving also as a reflecting board positioned opposedly on the detecting end of these optical fibers, after irradiation into the optical fiber 28 through a light divider 24. In this pressure sensor unit, amount of light corresponding to distances between optical fibers 28, 29 and the diaphragm 22 (pressure signal) is received by the fiber 29. This received light is converted to a received light voltage signal V31 after passing through light divider 25 and photoelectric converter 181. Similarly, a beam of light 32 from a diode 4 is divided 24 following the reversed path from the beam of light 30 to become a light-receiving voltage signal V33 after photoelectric conversion 171. A ratio V31/V33 of the signals V31, V33 is calculated by a calculating and processing circuit 35 and by the relation of the result and the specified pressure characteristics, pressure is determined by a computer 36.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical detection device that optically detects physical quantities such as pressure and temperature.

[Background of the invention]

BACKGROUND ART Pressure or temperature measuring devices using electrical means generally convert the measurement signal into an electrical signal and transmit it to a remote location. Therefore, there is a high possibility that electrical induction noise will be received during the transmission of this measurement signal.

In this respect, a pressure or temperature measuring device using optical means can perform remote measurement by using an optical fiber as a transmission path, and can realize signal transmission with noise resistance.

Properties of light used as optical means include light intensity, phase, frequency, and polarization. In particular, devices for measuring changes in light intensity are relatively easy to handle and signal processing is easy, so they are used in a wide variety of measurement methods and devices. However, in general, in measurement devices that utilize changes in the intensity of light, changes in the amount of light due to changes in the amount of light outside of the pressure or temperature detection section, such as changes in the amount of light due to changes in transmission loss when using an optical fiber as the light transmission path, cause measurement errors. It becomes a factor. The causes of this change in transmission loss include the generation of transmitted light with a reflection angle that is larger than the critical angle due to the bending of the optical fiber, or the generation of microbends due to vibration of the entire optical fiber. Changes the transmission loss of optical fiber.

For this reason, in devices that use optical fibers to measure pressure or temperature based on changes in light intensity, it is necessary to reduce changes in transmission loss or compensate for changes in transmission loss in order to improve measurement accuracy. . Regarding the compensation method for transmission loss changes in optical fibers, please refer to @26th Automatic Control Union Lecture, November 1981, p. 435. An example of application of the transmission loss compensation method described in the above-mentioned literature to a compensation circuit for an optical pressure sensor is shown in FIG.

In FIG. 9, the pressure sensor section is connected to the light transmitting fiber 3.6.
and receiving fibers 8 and 9, and these four optical fibers 3,
It is composed of a diaphragm 22, which also serves as a reflecting plate, and a housing 23, which fixes the positional relationship between these parts. The light from the light transmitting fiber 3.6 in the pressure section is received by the light receiving fiber 8.9 in an amount corresponding to the distance between the optical fiber and the diaphragm 22, that is, the pressure signal.

The light emitting diodes 1.4 are driven by a drive circuit 7.10 controlled by the arithmetic control circuit 20 and generate light 2.5 of the same wavelength. The nine photoelectric conversion circuits 17.18 to which the light receiving diodes 15.16 are connected are connected to the light receiving fibers 8.9.
The pressure signals 11, 12, 13 and 14 are converted into light receiving voltage signals.

The arithmetic processing circuit 19 performs arithmetic operations, which will be described later, on these light-receiving voltage signals. The calculation result is corrected by the calculation control circuit 20 and displayed by the pressure display circuit 21.

Next, the principle of this compensation method will be explained.

Photoelectric conversion circuit 17 when the light emitting diode 1 emits light.
The received light voltage signal No. 18 is expressed by the following equation.

Vl, = K,, ・Pt+=to +γ・Ls ・Ls
-9・L9・P2・・・・・・・・・(1) V+z=to+s °P12=KIS IL3 @Ls
-s @Ls°P2 (2) Furthermore, the light receiving voltage signal when the light emitting diode 4 emits light is similarly expressed by the following equation.

Vl5=Kty "PI3=KI7" L
s・Lg-s” L9・Ps...
......(8) Vsi=+s ・P+4=Kts-Ls ・Ls-1
Ls・Ps・・・・・・・・・(4) However, Vll: Light receiving voltage signal Kj due to pressure signal i
;Conversion coefficient P+H of photoelectric conversion circuit j Light intensity LL of pressure signal light i, transmission efficiency Lm of optical fiber t-trajectory j Coupling efficiency between optical fibers m and n Pri Light intensity calculation processing of light r of light emitting diode 1.4 The circuit 19 is based on the equation (1), the equation (2), and the equation (3).
) and (4) are respectively stored, the following calculation is performed.

The calculation result of Equation (5) does not include the term of transmission loss of the light transmitting fibers 3, 6 or the light receiving fibers 8, 9, and the calculation result is the optical coupling coefficient between the light transmitting fibers 3, 6 and the light receiving fibers 8, 9. In other words, it is a function only of pressure.

In addition, in order for Equation (5) to not be a constant, the coupling coefficients of light between the light transmitting fibers 3 and 6 and the light receiving fibers 8 and 9 must be different. For example, by symmetrically arranging the detection end faces as shown in Fig. 10, the relationship shown in Fig. 11 can be obtained, and by using, for example, the range Z+-Zz (straight line part) in Fig. 11 as a pressure sensor, accuracy can be obtained. detection can be performed. however,
The above compensation method requires four optical fibers as transmitting/receiving optical fibers, so the structure of the pressure sensor section becomes complicated.

[Purpose of the invention]

The present invention provides an optical detection device that can reduce the number of optical fibers used and simplify the device structure when measuring physical quantities such as pressure and temperature by changing the intensity of light using optical fibers. The purpose is to provide.

[Summary of the invention]

In order to achieve the above object, the present invention uses different types of optical fibers used for transmitting light and optical fibers used for receiving light, and adjusts the coupling efficiency of light between the transmitting fiber and the receiving fiber according to the traveling direction of the light. The feature is that the change in the transmission loss of the optical fiber is compensated for by changing the transmission loss.

That is, the present invention provides a reflector in which the relative distance between a first light source and a second light source driven in a time-sharing manner and an end face of an optical fiber, which will be described later, changes in accordance with changes in a physical quantity to be measured. a measuring section having a measuring section; disposed between the first and second light emitting sources and the measuring section;
The first one has mutually different optical characteristics. a second optical fiber; and a second light from the second light source that is transmitted through the second optical fiber, reflected at the measurement section, and then transmitted through the first optical fiber. A first photoelectric conversion section that receives the light and converts it into an electrical signal, and the light from the first light source is transmitted through a first optical fiber, reflected by a measurement section, and then sent to a second optical fiber. a second photoelectric conversion unit that receives the first light transmitted through the light source and converts it into an electrical signal;
introducing light from the first light source into a first optical fiber;
and a first optical splitter that guides the reflected light from the second light source to the first photoelectric conversion section;
a second optical splitter that introduces the reflected light from the first light source into the optical fiber and guides the reflected light from the first light source to the second photoelectric converter; and the electricity from the first photoelectric converter and the second photoelectric converter. a calculation unit that calculates the physical quantity to be measured by calculating a ratio of signals;
It is characterized by the following.

In this case - first. The second optical fiber is characterized in that each fiber has different optical characteristics by making at least one of the core diameter, refractive index distribution inside the core, or numerical aperture different.

[Embodiments of the invention]

Next, embodiments of the present invention will be described in detail based on 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 a drive control circuit 34;
10 and generates emitted light 30 and 32 of the same wavelength. The emitted light 30 from the light emitting diode 1 enters the first optical fiber 28 via the first optical splitter 24 and the rod lens 26, and then is transmitted to the pressure sensor section.

The pressure sensor section includes a first optical fiber 28, a second optical fiber 29, and a diaphragm 22 that also serves as a reflector and is placed opposite the detection end faces of these optical fibers 28 and 29.
and a housing 23 that fixes their positional relationship.

The projection light from the first optical fiber 28 in the pressure sensor section is received by the second optical fiber 29 in an amount corresponding to the distance between the optical fiber 28, 29 and the diaphragm 22, that is, the pressure signal.

The light received by the second optical fiber 29 is transmitted again,
After passing through the second rod lens 27, the traveling direction of the light is changed by the optical splitter 25 of the tube 2, and the light is transferred to the first light receiving diode 161.
is irradiated as pressure signal light 31, and is converted into a received light voltage signal by the first photoelectric conversion circuit 181. Similarly,
The emitted light 32 from the light emitting diode 4 passes through a path opposite to the emitted light 30 from the light emitting diode 1, and is changed in the traveling direction of the light by the first light splitter 24, and then sent to the second light receiving diode 1.
51 as a pressure detection signal 33, and is converted into a received light voltage signal by the second photoelectric conversion circuit 171. These light reception voltage signals are input to the arithmetic processing circuit 35.

The arithmetic processing circuit 35 executes arithmetic processing, which will be described later, and the micro combinator 36 corrects the arithmetic results. The microcomputer 36 outputs a control signal to the drive control circuit 34 and indirectly controls the drive circuits 7 and 10. The calculation results corrected by the microcomputer 36 are displayed on the pressure display circuit 37.

Next, the arithmetic processing of the arithmetic processing circuit 35 will be explained.

When the light emitting diode 1 emits light, the first photoelectric conversion circuit 1
The light receiving voltage signal 81 is expressed by the following equation.

Vs+=Ktat 8Ps+=to +st @Lts'
L(ss-xs)aLss 1Ps.

(6) Furthermore, when the light emitting diode 4 emits light, the light reception voltage signal of the second photoelectric conversion circuit 171 is similarly expressed by the following equation.

Vms=Kry BiPm5=Ktyt +Ln +L(w
e-vs) ”L!1111Psz・・・・・・・・・
・(7) However, the received light voltage signal KJ is based on the Vt1 pressure amount;
Conversion coefficient Pl of photoelectric conversion circuit; Light intensity LL of pressure signal light i; Transmission efficiency L of optical fiber L (---)? Coupling efficiency Pso when light travels from optical fiber m to n; light amount P3 of incident light 30 to optical fiber 28! The light amount calculation processing circuit 35 for the incident light 32 on the optical fiber 29 stores the received light voltage signals of equations (6) and (7), respectively, and then performs the following calculation.

(8) Here, the calculation result of equation (8) does not include the terms of the transmission loss of the first optical fiber 2B and the transmission loss of the second optical fiber 29. It is a function of the coupling efficiency between the first optical fiber 2B and the second optical fiber 29, that is, a function only of pressure.

In addition, in order for Equation (8) to not be a constant, the coupling efficiency L (
u −29) * L (28-Snow s) must be different. In order to satisfy this condition, for example, two types of optical fibers with different core diameters, refractive index distributions inside the cores, or numerical apertures must be used as the first optical fiber 28 and the second optical fiber 2.
It can be used as 9.

Output light intensity distribution II from the different types of optical fibers 28 and 29 in the pressure sensor section to the diaphragm 22 which also serves as a reflection plate.

11 is as shown in FIG. 2, for example. That is, by making the first optical fiber 28 and the second optical fiber 29 different in type, the output light intensity distributions Is and It in the diaphragm 22 differ. As a result, depending on the traveling direction of the light, the coupling efficiency L (snow 8 - snow s
), L(!e-zs) are different, the required coupling efficiency can be obtained. Therefore, the first
By using the optical fiber 28 and the second optical fiber 29, an optical pressure sensor having the characteristics shown in FIG. 3 can be obtained.

In the optical pressure sensor, when pressure is applied to the diaphragm 22, the distance between the optical fibers 28, 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 expressed by the received light voltage signal Vst t as shown in equations (6) and (7).
This results in a change in Vss. The light receiving voltage signals VsI and Vss are
Equation (8), which is a function of pressure and transmission loss of the optical fiber 28°29, is the calculation result of the arithmetic processing circuit 35, and when the light emitted from the light emitting diode 1.4 is constant, when there is a change in pressure, Only (Vs1/Vsa) changes.

Therefore, for example, the range from z3 to z4 in FIG. 3 is used as the pressure detection range of the pressure sensor. The microcomputer 36 determines the pressure based on the relationship between the pressure and (V31/Vss) shown in FIG. 3 from the calculation result of equation (8) of the calculation processing circuit 35.

As described above, in optical sensors that use optical fibers to measure pressure based on changes in light intensity, highly accurate pressure measurements can be made without being affected by changes in optical fiber transmission loss. This can be realized by using a real optical fiber, and accordingly the structure of the pressure sensor section can be simplified. Furthermore, the change in transmission loss of optical fibers can be considered to include the connection loss of the optical connector used to connect the optical fibers. Therefore, when laying optical fiber over a long distance, the pressure sensor section and the signal processing section including the light emitting diode, light receiving diode, and optical fiber can be separated, and the optical fiber of the signal processing section and the pressure sensor can be separated. It becomes possible to connect the optical fibers of the parts using optical connectors as necessary. Therefore, the number of connection points using this optical connector can be as small as 2, 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 section includes a first optical fiber 28, a second optical fiber 29, a diaphragm 220 that changes when pressure is applied, a light shielding plate 221 attached to the diaphragm 220, and these. and a housing 230 that fixes the positional relationship. In such a configuration, the change in the received light voltage signal output from the photoelectric conversion circuits 171, 181 with respect to the amount of movement of the shielding plate 221, that is, the pressure, has characteristics as shown in FIG.

Due to this characteristic, for example, the range zs-Z@ is used as the pressure detection range of the pressure sensor.

The drive circuits 7 and 10 for the light emitting diodes 1 and 4 are controlled by a drive control circuit 34 so that the light emitting diodes 1 and 4 are driven in a time-sharing manner. By driving the light emitting diodes 1 and 4 in a time-division manner, multiple reflected light between the light splitters 24 and 25 and the rod lenses 26 and 27, or the light splitter 2
It is possible to prevent reflected light generated due to the difference in refractive index between 4.25 and air from being irradiated onto the light receiving diodes 151 and 161 and becoming an error signal with respect to 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 etc. are irradiated onto the light receiving diode 151, but this multiple reflected light is not used as a pressure sensor signal and is instead used as a pressure signal light irradiated onto the light receiving diode 161. 31 to avoid the effects of multiple reflected light.

Third Embodiment Also, the variation in the amount of light emitted from the light emitting diodes 1 and 4 is
As shown in equation 8), even when the pressure signal does not change, the ratio (Vst/Vss) of the light-receiving voltage signal changes, resulting in a measurement error with respect to the pressure signal.

Therefore, as shown in FIG.
By providing a third photoelectric conversion circuit 41 and detecting the light reception voltage signal from this photoelectric conversion circuit 41, it is possible to compensate for the influence of measurement errors due to fluctuations in the amount of light emitted from the light emitting diodes 1 and 4. A third embodiment will be described below, which takes into account the method of processing the received light voltage signal in FIG.

When the light emitting diode 1 emits light, the light receiving voltage signal of the third photoelectric conversion circuit 41 is expressed by the following equation.

Vsa = K41 ・Pss −”・
・(9) Also, when the light emitting diode 4 emits light, the third
Similarly, the light receiving voltage signal of the photoelectric conversion circuit 41 is expressed by the following equation.

Vs meeting = K41 work Ps * ・・・・・・
...The following relationship is obtained from αO equations (6), (7), (6), and 61st equations.

However, Vss: Branched light 38 from the first optical splitter 24
Received light voltage signal v39: Received voltage signal due to branched light 39 from second optical splitter 25 41: Conversion coefficient P38 of third photoelectric conversion circuit; Light amount Ps*+ of branched light 3B from optical splitter 24 In the light quantity αυ equation of the branched light 39 from the optical splitter 25, the term (Pso/Pss) is the branching ratio of the first optical splitter 24, and (Psi/Pss)
Since the terms are the branching ratios of the second optical splitter 25, they are constants. Therefore, the αυ equation is not affected by fluctuations in the amount of light emitted from the light emitting diodes 1 and 4.

The configuration of a specific process for calculating the αυth expression will be explained with reference to FIG. When the light emitting diode 1 emits light, the respective light receiving voltage signals Valev, from the first photoelectric conversion circuit 181 and the third photoelectric conversion circuit 41.

is input to the division circuit 42. Further, when the light emitting diode 4 emits light, the respective light receiving voltage signals Vss from the second photoelectric conversion circuit 171 and the third photoelectric conversion circuit 41
, VB are input to the division circuit 43. Since the light emitting diodes 1 and 4 are driven in a time division manner, the division circuits 42 and 43
Since the output of the division circuit 42. is also obtained in a time-division manner, the division circuit 42.
The outputs of 43 are held in sample and hold circuits 44 and 45, respectively. The microcomputer 47 outputs a signal for time-division driving to the drive control circuit 34 of the light emitting diode 1.4, and also outputs a set signal and a reset signal for the sample and hold circuit 44.45, and also outputs a set signal and a reset signal for the division circuit 42.4.
When the output from sample and hold circuits 44 and 45 is obtained, the division circuit 46 is controlled so that the signals from the sample and hold circuits 44 and 45 are outputted. The output from the division circuit 46 is the calculation result of the αυ expression, and the microcomputer calculates from this calculation result,
The pressure applied to the diaphragm 22 is determined based on the relationship shown in FIG. 3, and is displayed on the pressure display circuit 48.

Fourth Embodiment Next, not only the coupling of light between the t-th optical fiber 28 and the second optical fiber 29 but also the return light 311. Return light 3 from the pressure sensor section when the light emitting diode 4 is driven
A fourth embodiment in which compensation is performed using 31 will be described with reference to FIG.

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

V311=Kl? 1-PS11=KI71 ・Lmu°L
ss-ss-Ps.

・・・・・・・・・a2 v3I:' to 11IHP3 to +g+'Lzs e
L(u-we) 1lLz*°ps.

(6) Similarly, the light receiving voltage signal obtained when the light emitting diode 4 emits light is expressed by the following equation.

Vss+=to+st'P3st=to+shiLe°L
B-B・p: +z・・・・・・α rise Vss=KIy+ °Pss°to +yhiL29 eL
(e-3m) 0L21°P32・・・・・・・・・
(7) The arithmetic processing circuit 35 calculates the equation (6), the equation (7), and the equation (1).
After storing the received light voltage signals of the second formula and the αth formula, the following calculation is performed.

......Q4 The α-th equation does not include the term of transmission loss of the first optical fiber 28 and the second optical fiber 29, and is a function only of pressure. In addition, the first optical fiber 28 and the second optical fiber 2
9 may be the same regardless of the direction in which the light travels. For example, each light receiving voltage signal in this case is as shown in FIG. 8, for example (Zy, Za).
The range is used as the pressure measurement range of the pressure sensor. Therefore, from the calculation result of equation (14) of the calculation processing circuit 35, the pressure in FIG. 8 and (Vs+-Vss) / (Vss
The pressure is determined based on the relationship with +-V 5st) and is displayed on 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, by using a diaphragm for detecting pressure as a pi-metal for detecting temperature, it can be used as an optical temperature sensor.

Furthermore, the present invention can be applied to measurements of displacement, strain, etc.
It will be clear to those skilled in the art. ′ [Effects of the Invention] According to the present invention, in an optical sensor that uses optical fibers to measure pressure, temperature, strain, etc. based on changes in the intensity of light, the coupling efficiency of light between optical fibers is By using two different types of optical fibers that change depending on the direction of light propagation, measurements of pressure, temperature, strain, etc. are not affected by changes in optical fiber transmission loss, resulting in highly accurate measurements. becomes possible. Further, it is not necessary to use a special configuration for the sensor section for pressure, temperature, etc., and the configuration can be simplified.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a characteristic diagram showing the output light intensity distribution of the optical fiber used in the invention, and Fig. 3 shows the change in the received light voltage signal in Fig. 1. The characteristic diagram shown, diagram K4, 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. 7 is a block diagram showing the fourth embodiment of the present invention. FIG. 8 is a characteristic diagram showing changes in the received light voltage signal in the embodiment of FIG. 7. FIG. 9 is a block diagram showing an example of a conventional optical detection device, FIG. 10 is a diagram showing an example of the arrangement of optical fibers in a conventional sensor section, and FIG. 11 is a characteristic showing changes in the received light voltage signal in FIG. 9. It is a 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, 17, 18, 171, 181.41・
...Photoelectric conversion circuit, 20... Arithmetic control circuit, 21゜3
7... Pressure display circuit, 24.25... Optical splitter, 3
4... Drive control circuit, 35... Arithmetic control circuit, 36
... Micro Combiator, 42, 43, 46...
Division circuit, 44.45...sample hold circuit.

Claims (1)

[Claims] 1. Reflection in which the relative distance between a first light emitting source and a second light emitting source driven in a time-sharing manner and an end face of an optical fiber, which will be described later, changes in accordance with changes in a physical quantity to be measured. a measuring section having a plate; disposed between the first and second light emitting sources and the measuring section;
first and second optical fibers having mutually different optical characteristics; and the light from the second light source is transmitted through the second optical fiber and reflected at the measuring section, and then transmitted to the first optical fiber. a first photoelectric conversion section that receives the second light transmitted through the first light source and converts it into an electrical signal; and a measurement section that receives the second light transmitted through the first optical fiber and converts it into an electrical signal; a second photoelectric conversion unit that receives the first light transmitted through the second optical fiber after being reflected and converts it into an electrical signal;
introducing light from the first light source into a first optical fiber;
and a first optical splitter that guides the reflected light from the second light source to the first photoelectric conversion section;
a second optical splitter that introduces the reflected light from the first light source into the optical fiber and guides the reflected light from the first light source to the second photoelectric converter; and the electricity from the first photoelectric converter and the second photoelectric converter. a calculation unit that calculates the physical quantity to be measured by calculating a ratio of signals;
An optical detection device characterized by comprising: 2. In the device according to claim 1, the first,
Optical detection characterized in that the second optical fiber has different optical characteristics by making at least one of the core diameter, the refractive index distribution inside the core, or the numerical aperture different for each optical fiber. Device.