JPH0439896B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention optically measures flow rates such as pressure and temperature.
Still further, the present invention relates to a digital output fiber optic sensor for digital detection.

[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 regard, pressure or temperature measuring devices using optical means can perform remote measurements by using optical fibers in the 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 that measure changes in light intensity are relatively easy to handle and signal processing is easy.
It is used in a wide variety of measurement methods and measurement devices. However, in general, in measurement devices that utilize changes in the intensity of light, measurement errors occur due to changes in the amount of light outside of the pressure or temperature detection section, such as changes in transmission loss when an optical fiber is used as the light transmission path. It becomes a factor. The cause of this change in transmission loss is the generation of transmitted light with a reflection angle larger than the critical angle due to the bending of the optical fiber.
Alternatively, microbends may occur due to vibration of the entire optical fiber, and these changes the transmission loss of the optical fiber.

For this reason, in devices that use optical fibers to measure pressure or temperature by changing the intensity of light, in order to improve measurement accuracy, it is necessary to reduce changes in transmission loss, compensate for changes in transmission loss, or Either a digital output that is less susceptible to changes in transmission loss is required. Regarding this digital output optical fiber sensor, there is ``Optical Pulse Output Pressure Sensor'' in Japanese Patent Application Laid-Open No. 57-131032. FIG. 15 shows the configuration of the optical pulse output sensor described in the above-mentioned document.

In FIG. 15, the pressure detection unit includes a light transmitting bundle fiber 25n and a light receiving band fiber 26n.
, a reflecting plate 61 that is disposed to face the end faces of these bundle fibers 25n and 26 and is displaced by the application of pressure, and a pressure chamber 11 that fixes their positional relationship. Light from a light source 24 including a drive circuit is transmitted through a bundle fiber 25 for light transmission.
The light is sequentially incident on each of the n optical fibers 251, 252, . . . 25n constituting n. The incident light passes through the light transmitting band fiber 25.
n, and is projected onto the reflecting plate 61. The projected light is reflected by the reflection plate 61, a part of which is received by the light-receiving bundle fiber 26, and is irradiated onto the light-receiving diode 27. This emitted light is
It is converted into an electrical signal by the optical-electrical conversion circuit 28, and converted into a binary level signal of "L" and "H" according to the absolute value of the amount of light received by the threshold circuit 29, and pulse counting is performed. The number of "H" level signals is counted in the circuit 30, and a pressure value is converted from the counted value.

In other words, the pressure measurement range is determined by the number n of optical fibers constituting the light transmitting bundle fiber 25n.
When the light is sent sequentially to the n optical fibers, the light receiving bundle fiber 26 becomes "H".
The pressure value is calculated based on how many times the amount of light received, which can be considered as a level, is received.

Therefore, by adopting the configuration as shown in FIG. 15, the amount of light received by the light receiving optical fiber 26 can be digitized into a binary level signal by the threshold circuit 29. Therefore, the influence of transmission loss fluctuations of the optical fiber or light intensity fluctuations of the light source is reduced by digitization, and the pressure can be measured by counting pulses from the threshold circuit 29.

However, in this example, the measurement resolution of the pressure sensor is clearly
depends on the number n of optical fibers, and an attempt to increase the resolution will result in an increase in the number of optical fibers. In addition, along with this, the bundle fiber for light transmission 25n
This makes it difficult to couple the light with the light source 24.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a digital output optical fiber that can accurately measure the displacement of a reflector even when the reflector is displaced in a direction perpendicular to the surface on which the code is attached.

[Summary of the invention]

The features of the present invention include a first slab lens that is connected to a light transmitting optical fiber and projects the light transmitted by the light transmitting optical fiber onto a coded surface of a reflector; and is connected to each light receiving optical fiber and whose longitudinal direction is the first one.
The present invention includes a second slab lens arranged in a direction perpendicular to the longitudinal direction of the slab lens.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 1 shows an embodiment of the detection section of the digital output optical fiber sensor of the present invention.

In FIG. 1, a unidirectional refractive index gradient type slab lens 2 is attached to one end of a light transmitting optical fiber 1. As shown in FIG. Due to the action of the slab lens 2, the light emitted from the light transmitting optical fiber 1 becomes linear and is projected onto the reflecting plate 6. The reflecting plate 6 is displaced in the Z _a and Z _b directions as pressure or temperature changes. Further, a reflecting mirror 5n coded according to a specific rule is arranged on the reflecting plate 6 at a portion where the projection light from the slab lens 2 hits. Here, light is not reflected by anything other than the reflecting mirror 5n. Therefore, the light reflected from the coated reflecting mirror 5n is similarly coded, and the coded light enters the n unidirectional refractive index gradient slab lenses 3n. The incident light is collected by the slab lens 3n, and each slab lens 31,
The light is received by light-receiving optical fibers 41, 42, 43, . The longitudinal direction of each slab lens 3n is arranged so as to face the direction (Y direction) orthogonal to the longitudinal direction (X direction) of the slab lens 2.

The relationship between the light reflected by the reflecting mirror 5n and the reflecting plate 6 will be described with reference to FIG. FIG. 2 shows a part of the reflector plate 6 on which the coded reflector 5n is arranged. Z _a of the reflector 6 in FIG. 1,
Due to the displacement in the Z _b direction, the relative distance between the reflector 6 and the slab lens 2 changes, so the slab lens 2
The position where the projection light 7 projected from the reflection plate 6 is reflected moves in the Y _a and Y _b directions. The reflecting mirror 5n is
They are not uniformly arranged on the reflector plate 6, but are arranged in a coded manner according to a certain specific rule. That is, the reflector 5n based on a specific rule
A plurality of codes differ depending on the arrangement of the reflector plate 5.
It is marked on one side in the Y _a and Y _b directions. For this reason,
When the reflection plate 5 is displaced in the Z direction due to a change in pressure or temperature, the reflection position of the projection light 7 projected from the slab lens 2 shifts in the Y _a and Y _b directions as described above, so that each slab lens 3n receives the reflected light from the reflecting mirror 5n which is arranged differently than before. FIG. 2 shows an example of arrangement of reflecting mirrors 5n coded according to a certain specific rule based on a binary code. That is,
The lowest row of the reflecting mirror 5n has ²⁰ bits, the next row has 21 bits, the next row has ²² bits, etc. with respect to the distance ^of the reflecting mirror 5n in the X direction. Also, at this time, 0, 1, 2, 3, . . . , n are shown for the reflecting mirror 5n in the Y direction.
Therefore, in the Y direction of the reflecting mirror 5n, the projected light 7
The position of is n, and a binary-coded reflecting mirror 5n corresponding to the value of n is arranged in the X direction.

The coded reflected light from the reflecting mirror 5n differs depending on the position of the projected light 7 on the reflecting plate. Therefore, in the example shown in FIG. 2, in order to receive reflected light corresponding to each bit, a plurality of slab lenses 3n are arranged in the X direction of the reflecting mirror 5n as shown in FIG. That is, the slab lens 31 receives the reflected light from the reflecting mirror 5n corresponding to ²⁰ bits,
2 receives the reflected light from the reflecting mirror 5n corresponding to ²¹ bits, and transmits the light to the light receiving optical fiber 4n connected to each slab lens 3n. Therefore, the displacement of the reflection plate 6 can be detected from the presence or absence of light to the light-receiving optical fiber 4n.

In this embodiment, the longitudinal direction of the light-receiving slab lens 3n is oriented perpendicular to the longitudinal direction of the light-emitting slab lens 2, so that the reflection plate 6 may change due to changes in temperature or pressure. Even if the reflector is displaced in a direction perpendicular to the surface to which the code is attached, the displacement of the reflector can be measured with high accuracy. This makes it possible to accurately measure the temperature or pressure after the change. Further, in this embodiment, as shown in FIG. 1 of Japanese Utility Model Application Publication No. 60-15642, the case where the reflector 6 is displaced in the direction parallel to the surface with the code (Y direction in this embodiment) Also, the displacement of the reflection plate 6 can be measured with high precision. Therefore, this embodiment has a sensor structure that makes it easy to install an optical fiber etc. in consideration of the surrounding conditions of the temperature or pressure measurement location.
It is possible to arbitrarily select (1) a structure in which the reflector 6 is displaced perpendicularly to the surface to which the code is attached, and (2) a structure in which the reflector 6 is displaced parallel to the surface to which the code is attached.

Further, in this embodiment, the number of optical fibers can be reduced.

The effects of this embodiment described above also occur in other embodiments of the present invention described below.

FIG. 3 shows a configuration diagram when the digital output optical fiber sensor having the reflecting mirror 5n shown in FIGS. 1 and 2 is applied to a pressure sensor.

In FIG. 3, light from a light emitting diode 9 driven by a drive circuit 8 enters a light transmitting optical fiber 1. In FIG. The light incident on the light transmitting optical fiber 1 is
Emitted from the unidirectional gradient index slab lens 2,
It is projected onto a reflector plate 6 having a coded reflector. The reflected light from the reflecting mirror is received again by the plurality of unidirectional refractive index gradient type slab lenses 3n, and is transmitted by the light receiving optical fiber 4n connected to each slab lens 3n. Further, the reflection plate 6 is attached to a bellows 10 that deforms due to pressure changes, and is attached to a bellows 10 that deforms due to pressure changes.
In order to set the positional relationship between the light receiving fibers 4n and the reflecting plate 6, these are fixed in the housing 11. This is a bit signal that represents the displacement of the reflector 6 in binary code.
These optical signals are applied to the photodiode array 12 as light corresponding to each bit. The optical signal corresponding to each bit from the photodiode 12 is input to an amplifier circuit 13, and then waveform-shaped and becomes an input signal 14 of a decoder. Decoder 14
For example, the input binary code signal is 10
Convert to base number. The calculation and pressure display circuit 15 performs calculations to make the converted signal correspond to an actual pressure value, and displays the result as a pressure value.

FIG. 4 shows an amplifier circuit 13 for the decoder 14.
An example of an input signal from is shown below. Since the binary-coded reflected light from the reflecting mirror changes depending on the displacement of the reflecting plate 6, the input signal to the decoder 14 changes depending on the pressure change. Furthermore, the pressure measurement resolution of this pressure sensor is determined by the number of bits of the binary code. For example, if the resolution for the pressure measurement range is 1/64, 6 bits are required. Therefore, the binary-coded reflecting mirror of the reflecting plate 6, the unidirectional refractive index distribution type slab lens 3n, the light-receiving optical fiber 4n, and the photodiodes of the photodiode array 12 need only correspond to this number of bits. good.

FIG. 5 shows another embodiment of the detection section of the digital output optical fiber sensor of the present invention.

The difference between FIG. 5 and FIG. 1 is that a destination optical fiber 1a and a unidirectional gradient index slab lens 2a are added to FIG.

In FIG. 5, the displacement of the reflector 6 in the Z _a and Z _b directions causes the reflector 6 to move from the slab lenses 2 and 2a.
The coded linear projection light onto the reflecting mirror 5n moves in the Y _a and Y _b directions. Here, a case where the reflection plate 6 is displaced in the Z _a direction will be described. At this time, it is assumed that only the light transmitting optical fiber 1 is in the light transmitting state, and the light indicated by the broken line is received by the unidirectional refractive index gradient type slab lens 3n. Reflector 6
Due to the displacement in the _Zb direction, the linear projected light on the reflecting mirror 5n moves in the _Yb direction, and when the displacement exceeds a certain level, the coded reflected light is no longer received by the slab lens 3n. For this reason, transmission to the light transmission optical fiber 1a is started before the reflected light is no longer received. Reflector 5n from slab lens 2a
The projected light becomes the light shown by the solid line, and is again received by the slab lens 3n. With such a configuration, the code of the same reflecting mirror 5n is used twice in the case of FIG. 5 for the same measurement range as in FIG. It becomes possible to reduce the number of 4n.

FIG. 6 shows a configuration diagram when the digital output optical fiber sensor shown in FIG. 5 is applied to a pressure sensor.

In FIG. 6, the light emitting diodes 9, 9a are
It is driven by a drive circuit 8, and the drive circuit 8 is controlled by a sensor control circuit 16. The light from the light receiving optical fiber 4n is transmitted to the photodiode array 12.
1, the light-to-electricity conversion is performed. The photodiode array 121 is sequentially scanned by a scanning signal (clock signal) φ from the sensor control circuit 16, and transmits its output to the amplifier circuit 18. The counting circuit 17 is
A reset signal for scanning of the photodiode array 121 is generated. The output from the amplifier circuit 18 is converted by a signal conversion circuit 19 into a signal corresponding to an actual pressure value, and is displayed by a pressure display circuit 20.
Further, the output from the signal conversion circuit 19 is transmitted to the sensor control circuit 16. Based on this signal, the sensor control circuit 16 determines which of the light emitting diodes 9 and 9a is to be driven. Furthermore, the method of conversion into a pressure value by the signal conversion circuit 19 differs depending on which of the destination optical fibers 1 and 1a the light is being sent to. That is, for example, the signal conversion circuit 1 obtained when transmitting to the destination optical fiber 1a
The output from the light emitting diode 9 is obtained when the light emitting diode 9 is switched to the light emitting diode 9a, but the output from the signal conversion circuit 19 obtained when the light is transmitted to the light transmitting optical fiber 1 is , the pressure is biased by a certain value, and the result of applying the bias is displayed on the pressure display circuit 20.

As an embodiment of the present invention, an example in which a binary-coded reflector is provided on a reflector plate has been described above. It is clear that it is also possible to arrange a reflector.

The digital output optical fiber sensor described above can be considered to be weighted with respect to the amount of light received by the plurality of light receiving optical fibers. On the other hand, a case will be described in which the same weighting is applied to the amount of light received by the plurality of light receiving optical fibers.

FIG. 7 shows another embodiment of the detection section of the digital output optical fiber sensor of the present invention. It has a structure in which the end faces of the light transmitting optical fiber 1 and the light receiving optical fiber 4n face each other and a reflecting plate 61 that is displaced by an optimum amount change such as pressure or temperature, and their positional relationship is shown in the housing 11.
It is fixed at. At this time, the light transmission optical fiber 1
and light receiving optical fibers 41, 42, 43,..., 4n
They are arranged at different distances from each other.

In FIG. 7, light emitted from the light transmitting optical fiber 1 is reflected by the reflecting plate 61 and received by the light receiving optical fiber 4n. The _amount of light received by each of the light-receiving optical fibers 41, 42, 43, .
The relationship among S ₂ , S _{3 .} . . , and _So is shown in Figure 8.

That is, as the distances between the optical fibers 1, 4n and the reflecting plate 61 become Z ₁ , Z ₂ , Z ₃ .
1, 42, 43, . . . , the received light amounts S ₁ , S ₂ , S ₃ , . . . are sequentially received. Therefore, the threshold amount of light received
The amount of displacement of the reflection plate 61 can be determined by determining the light-receiving optical fiber 4n that receives more than S _{th of} light.

FIG. 9 shows a configuration for processing signals from the detection section 21 of the digital output optical fiber sensor shown in FIG.

In FIG. 9, the light emitting diode 9 is driven by a drive circuit 8, and the drive circuit 8 is controlled by a sensor control circuit 16. The light from the light receiving optical fiber 4n is sent to the photodiode array 121.
converted into electricity. This photodiode array 1
21 is sequentially scanned by the clock signal φ of the sensor control circuit 16 and transmits its output to the amplifier circuit 18. What is the output of the amplifier circuit 18 and the clock signal φ?
It passes through the AND gate 23, is sent to the signal conversion circuit 22, and is converted into a value of a measured physical quantity such as pressure or temperature corresponding to the number of input pulses to the signal conversion circuit 22. The display circuit 20 displays the converted value based on the converted value. Further, the counting circuit 17 counts the clock signal φ, and the photodiode array 121,
A reset signal R for the signal conversion circuit 22 is generated.

FIG. 10 shows an example of an input signal to the signal conversion circuit 22.
Corresponding to the scanning signal (clock signal) φ of 21,
An input to the signal conversion circuit 22 is obtained according to the displacement of the reflection plate of the detection section 21. In other words, when the measurement range of the digital output optical fiber sensor is divided into n by the light-receiving optical fiber 4n, the amount of displacement of the reflector due to pressure, temperature, etc. is determined by the number of pulses obtained when the photodiode array 121 is scanned once. can be found.

FIG. 11 shows a method for reducing the number of light receiving optical fibers 4n. In FIG. 11, the light transmitting optical fiber 1a and the light receiving optical fiber 4n are arranged at different distances from each other, and the light transmitting optical fiber 1a and the light receiving optical fiber 4n are arranged at different distances from each other. With such a configuration, as shown in FIG. 12, in addition to the characteristics shown in FIG.
By newly adding the light transmitting optical fiber 1a, S _1a and S _2a are obtained. Therefore, the same reflector 6
Since the resolution of the displacement is improved for a displacement of 1, the number of light receiving fibers 4n can be reduced if the sensor resolution is the same as that in FIG.

FIG. 13 shows a configuration for processing the signal from the detection section 21 of the digital output optical fiber sensor shown in FIG. 11. In FIG. The difference from FIG. 9 is that light-emitting diodes 9, 9a are provided to send light to the light-transmitting optical fibers 1, 1a in a time-sharing manner. An example of the input signal to the signal conversion circuit 22 at this time is shown in FIG. 14. Since the light emitting diodes 9 and 9a are time-divisionally driven,
21 scanning is T ₁ and T ₂ for one displacement measurement due to changes in physical quantities such as pressure or temperature of the reflecting plate.
It is necessary to do this twice. That is, from the number of pulses obtained by scanning the photodiode array 121 twice, the value of the measured physical quantity such as pressure or temperature can be determined.

Although we have described an example in which a coded reflecting mirror is placed on the reflecting plate of the detection section, by giving wavelength selectivity to the reflecting mirror and making it a multilayer structure, the number of optical fibers can be reduced. A further reduced digital output optical fiber sensor can be realized.

That is, the light from two light emitting diodes having different emission wavelengths is time-divisionally driven and projected onto a reflecting plate by a light transmission fiber. On the reflecting plate, reflecting mirrors each having a different code are arranged in a two-layer configuration, and the reflecting mirrors in each layer have wavelength selectivity to selectively reflect each wavelength of the projected light. At this time, the light-receiving optical fiber receives the reflected light from each reflecting mirror in a time-divisional manner, and the displacement of the reflecting plate can be determined from this received light signal. In comparison, the number of optical fibers can be reduced to about 1/2. Also,
The light emitting diodes can be driven simultaneously by adding a wavelength separation function to the light receiving signal on the light receiving side.

〔Effect of the invention〕

According to the present invention, even when the reflector is displaced perpendicularly to the surface to which the code is attached, the displacement of the reflector can be measured with high accuracy.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention,
Fig. 2 is a diagram showing an example of encoding of a reflecting mirror on a reflector plate used in the present invention, Fig. 3 is a block diagram in which the present invention is applied to a pressure sensor, and Fig. 4 is a diagram showing the decoder input signal of Fig. 3. FIG. 5 is a block diagram showing a second embodiment of the present invention, FIG. 6 is a block diagram in which the embodiment of FIG. 5 is applied to a pressure sensor, and FIG. 7 is a block diagram showing a second embodiment of the present invention. 8 is a diagram showing the light receiving characteristics in the embodiment of FIG. 7, FIG. 9 is a diagram showing the configuration of an optical fiber sensor to which the embodiment of FIG. 7 is applied,
Figure 0 is a diagram showing an example of the input signal of the counting circuit in Figure 9;
FIG. 11 is a diagram showing the fourth embodiment, FIG. 12 is a diagram showing the light receiving characteristics in the embodiment of FIG. 11, and FIG.
Fig. 3 is a configuration diagram of an optical fiber sensor to which the embodiment of Fig. 11 is applied, Fig. 14 is a diagram showing an example of input signals to the counting circuit of Fig. 13, and Fig. 15 is a configuration diagram of a conventional digital output optical fiber sensor. It is a diagram. 1, 1a... Optical fiber for light transmission, 2, 2a, 3
n...unidirectional refractive index gradient slab lens, 4n...
...Receiving fiber, 5n...Reflector, 6,61...
... Reflection plate, 8 ... Drive circuit, 9, 9a ... Light emitting diode, 12, 121 ... Photo diode array, 13, 18 ... Amplification circuit, 14 ... Decoder, 15, 20 ... Display circuit, 16 ... ...Sensor control circuit, 17...Counting circuit, 19, 22...Signal conversion circuit.

Claims (1)

[Claims] 1 A reflector plate having a code expressing a numerical value on its surface and displaced by pressure or temperature, a light transmitting optical fiber, a plurality of light receiving optical fibers, connected to the light transmitting optical fiber, and connected to the light transmitting optical fiber. a first slab lens that projects the light sent by the optical fiber onto a surface of the reflector to which an electrical cord is attached; and a first slab lens that receives the light reflected from the reflector and sends it to each of the light receiving optical fibers. a second slab lens which is connected to the second slab lens and whose longitudinal direction is orthogonal to the longitudinal direction of the first slab lens; 1. A digital output optical fiber sensor characterized by comprising means for determining the amount of displacement.