JPS6160200A - Light-applied measuring apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (a) Technical Field The present invention relates to an optical applied measurement device, and more specifically, to a measurement device using an optical waveguide and a physical quantity/optical converter, which compensates for measurement errors due to fluctuations in loss of signal light. This invention relates to an optical application measurement device.

(b) Conventional technology The optical waveguide of the optical applied measurement device uses an optical fiber as the waveguide, and fluctuations in transmission characteristics due to temperature changes and bending stress cause incorrect output, so it is necessary to compensate for this.

FIG. 2 shows an example of a method for compensating for loss fluctuations in a conventionally used optical application measuring device. In this example, signal light emitted from a light emitting unit 1 is guided to a detection unit 3 via an optical fiber 2, and the signal light changed in accordance with the physical quantity to be measured in the detection unit 3 is transmitted via an optical fiber 4 to a light receiving unit. 5, the detection unit 3 receives pressure, which is a physical quantity to be measured, through an optical fiber, and detects this physical quantity from the loss of signal light due to deformation of the optical fiber. Further, a part of the signal light guided to the detection section 3 via the optical fiber 2 is transmitted to the optical fiber 6 which is under the same environment as the detection section 3 and is not affected by the physical quantity to be measured, and under the same conditions as the optical fiber 4. It is guided to the light receiving section 5 via an optical fiber 7 located at the center. The light emitting section 1, the detecting section 3, the light receiving section 5, and the optical fibers 2.4, . 6 and 7 are connected by optical connectors 8, respectively.

In such a configuration, if the spectral ratio between the detection unit 3 and the optical fiber 6 is known, the light intensity of the signal light guided through the optical fiber 4 can be compared to the signal light guided through the optical fiber 7. The light passage rate of the detection unit 3 can be calculated by dividing by the amount of light. Therefore, the physical quantity to be measured is detected while canceling the transmission loss of the optical fiber.

However, in this device, it is necessary to attach and detach the optical connector 8 for convenience of handling, and there is a problem in that the loss fluctuation of the signal light due to the attachment error that occurs at that time has a large effect on the measurement.

Another method for compensating for loss fluctuations, such as temperature measurement, is to monitor loss fluctuations using two light waves with different wavelengths, and perform signal processing using an arithmetic circuit.

That is, for example, in a time-division manner, each light wave is sent to a detection section made of an optical semiconductor, each light wave is received from the detection section, and the physical quantity to be measured is detected from the ratio of the received intensities. This method utilizes the property that an optical semiconductor has a steep optical fundamental absorption edge wavelength λg and absorbs almost all light waves having a wavelength shorter than this wavelength λg. Therefore, one of the wavelengths of the two light waves is selected near the absorption edge of the optical semiconductor, and this wavelength is used as signal light, and movement of the absorption edge due to the physical quantity to be measured is detected as a change in the intensity of the signal light. The other wavelength is set to be sufficiently longer than this absorption edge wavelength, and this is used as the reference light. The reference light is
Since the intensity does not change depending on the physical quantity to be measured, the intensity change of the detected reference light is due to loss variation. Therefore, this amount of loss can be removed by taking the ratio of the signal light and the reference light.

However, in this method, since the signal light and the reference light pass through the same detection section, the detection method is naturally subject to limitations.

Furthermore, as another conventional method, Japanese Patent Application Laid-Open No. 58-62799
There is a two-wavelength method disclosed in No. In this method, signal light and reference light with different wavelengths are supplied to the detection section via a reference light reflection filter, and the signal light reflected within the detection section and the reference light reflected by the filter are received at the light receiving section. The physical quantity is detected by determining the amount of change in the signal light from the intensity ratio.

However, this method is limited to those with a reflective detection section, and its range of application is narrow.Also, in order to find the ratio of the intensity of the reference light and the signal light, a calculation unit that performs division is required. However, the overall configuration has become complicated, leading to an increase in costs.

(c) Purpose The present invention has been made in view of the above-mentioned problems,
It is an object of the present invention to provide an optical measurement device that can effectively compensate for measurement errors caused by loss fluctuations in the leading wavepath connecting the light emitting part and the light receiving part, the coupling part thereof, etc.

(d) Configuration In order to achieve the above object, the optical application measurement device according to the present invention includes a light emitting section that emits a signal light and a reference light having a wavelength different from that of the signal light, and a light emitting section that emits a signal light and a reference light having a different wavelength from the signal light. a first light receiving section that simultaneously or selectively receives the reference light via a first optical waveguide and converts it into an electrical signal; a storage means for temporarily holding an electric signal; a separation means for receiving the signal light and the reference light emitted from the light emitting section through a second optical waveguide and separating the signal light and the reference light; A physical quantity/optical converter that receives the signal light separated by the separation means and converts the magnitude of the physical quantity to be measured into light intensity, and this physical quantity/optical converter have the same environmental conditions other than the physical quantity to be measured. a third leading waveguide that conducts the reference light separated by the separation means; the reference light emitted through the third optical waveguide; and the signal light emitted via the physical quantity/light converter. The fourth
a second light-receiving section that receives the signals and converts them into electrical signals; a first control means for controlling the amount of light emitted by the reference light; a second control means for controlling the amount of the signal light emitted by the light emitting section so that the amount of the signal light received by the first light receiving section is constant; The present invention is characterized in that the physical quantity to be measured is detected from the amount of received light of the signal.

Hereinafter, the present invention will be explained in detail based on Examples.

FIG. 1 is a block diagram showing the overall configuration of an optical application measurement device that is an embodiment of the present invention.

In the figure, α means the control side, and β means the detection side. Among these, on the control side α, a reference light emitting diode LEDI and a signal light emitting diode LED2, which are light emitting parts, are caused to emit light alternately by a pulse generator 9, an inverter 10, and a light emitting diode drive circuit 11.12. These two light waves having different wavelengths are guided to a light receiving diode PDI, which is a first light receiving section, through optical fibers 13 and 14, which are first optical waveguides, respectively. Here, the optical fiber 13.14
are shown by broken lines, and splitters 15a, 15b, 15e and couplers 16a, 16b, 16c are provided at the branching points and merging points of the light waves, respectively. The light wave received by the photodetector diode PDI is transmitted to the amplifier 1.
After being amplified in step 7, the sample and hold circuit 18, which is a storage means, holds the light in the form of an electrical quantity (for example, voltage) corresponding to the amount of light received. This sample and hold circuit 18 is controlled by the output signal of the pulse generator 9, and holds only information on the amount of reference light received from the reference light emitting diode LEDI. Light emitting diode LEDI
, the light waves emitted from the LEDs 2 are sent to the splitter 15, respectively.
a, 15b and optical fibers 19, 20, are combined at the coupler 16b, and sent to the detection side β from the optical connector 21a. The control side α and the detection side β are connected by an optical fiber 22, which is a second optical waveguide.

The light wave guided from the optical connector 21b on the detection side β is branched by a splitter 15c, and then passed through a filter 2 which is a separating means.
3 and 24. The filter 23 transmits only the reference light of wavelength λ1 from the light emitting diode LEDI, and the filter 24 transmits only the reference light of wavelength λ1 from the light emitting diode LEDI.
It allows only the signal light of wavelength λ2 from D2 to pass through. The reference light that has passed through the filter 23 is guided to the coupler 1.6c via the optical fiber 25, which is the third leading wavepath. On the other hand, the signal light transmitted through the filter 24 is guided to the coupler 16c via the sensor 26, which is a physical quantity/light converter. Here, the sensor 26 changes the passage rate of the signal light according to the physical quantity to be measured, for example, the pressure to be measured. The light wave from coupler 16c is guided to optical connector 21c via optical fiber 27.

The light wave sent out from the optical connector 21c is guided to the optical connector cover 21d on the control side α via the optical fiber 28, and is converted into an amount of electricity (for example, voltage) by the light receiving diode PD2, which is the second light receiving section. It is amplified by an amplifier 29. The light emitting diode drive circuit 1 for the reference light is controlled so that the amount of light received by the reference light measured by the light receiving diode PD2 becomes a constant value by the control circuit 30 which is the first control means.
1 is controlled. Further, the amount of signal light emitted is set to be a constant magnification of the amount of reference light previously held by the sample and hold circuit 18 and received by the light receiving diode PDI.

The signal light light emitting diode drive circuit 12 is controlled by a control circuit 31 which is a second control means.

Next, a method of compensating for loss fluctuations in the optical measurement device configured as described above will be explained in order.

■ Reference light light emitting diode LEDI (hereinafter simply referred to as LE)
(denoted as DI) lights up. At this time, the signal light emitting diode LED2 (hereinafter simply referred to as LED2) is turned off. The reference light with wavelength λ1 is connected to optical fiber 19.22.
and is emitted to the branching device 15c on the detection side β via the optical connectors 21a and 21b, passes through the filter 23 that passes only the light wave of wavelength λ1, and is connected to the optical fiber 25°27.28 and the optical connector 21. The light receiving diode PD2 (hereinafter simply referred to as PD2) on the control side α is irradiated via the light receiving diode PD2 (hereinafter simply referred to as PD2) through the light receiving diode PD2 (hereinafter simply referred to as PD2). At this time, the output of the LED 1 is controlled by the control circuit 30 so that the amount of received reference light becomes a constant value A.

The output Q1 of this controlled LEDl is P from LEDl.
If the passage rate of the reference light up to D2 is T1, then Q + = A / T +
(1,).

(2) A part of the reference light from the LEDI irradiates the light receiving diode PDI (hereinafter simply referred to as PDI) via the optical fiber 13. The amount of reference light received by PDl B+ is L
If the passage rate of the reference light from EDI to PD' 1 is T2, then B+ = Q+ ・T2 = (A/T+) ・T
2 (2). The received light amount B1 is electrically held at the value immediately before the LEDI is turned off by the sample bold circuit 18.

■ Next, turn off LEDI and turn on LED2.

The signal light having the wavelength λ2 is emitted to the PDI via the optical fiber 14. At this time, the amount of received signal light is the amount of received reference light B1 held by the sample and hold circuit 18.
The output of the LED 2 is controlled by the control circuit 31 so as to have a constant magnification C relative to the output voltage. The output Q2 of this controlled LED2 is Qz=B+ ・C/T1, where Ts is the passing rate of the signal light from the LED2 to the PDI.
1 (3).

■ The remaining part of the signal light (wavelength λ2) from LED 2 is transmitted through optical fiber 20.22 and optical connectors 21a and 21.
b to the branching device 15c on the detection side β, and the wavelength λ
PD 2 on the control side α passes through a filter 24 that passes only the light waves of
is injected into the Here, the sensor 26 has a light wave passage rate η that changes depending on the physical quantity to be measured. At this time, P
The amount of light received by D2, X, is calculated as follows from the relationship of equation (3), where T4 is the passage rate of the signal light from LED2 to PD2 that is independent of the physical quantity to be measured. ) ・T4・η=A−T2
・C-T4・η/ T + ・T3 (4).

In this equation (4), A and C are constants, and T2/T
The value of 11 can be measured in advance on the control side α or can be known under the same conditions. Also, T+.

The value of T4 constantly fluctuates due to transmission loss due to the optical fiber or loss due to the optical connector, etc., but since both indicate the passage rate under the same conditions, the ratio T 4 /T I is It can be regarded as constant. Therefore, equation (4) can be expressed as X=K·η −(4)′, where K is a constant. Here, each optical fiber has a somewhat different transmission rate depending on the wavelength, but the difference can be measured in advance and made into a constant.

(2) Repeat steps (1) to (2) above by turning off LED2 and turning on LED1 again.

FIGS. 3(a) and 3(b) show timing charts of input signals or output signals of each part of the embodiment shown in FIG.

To explain based on the same figure (a), first, L E D 1
The reference light emitted by the PD 2 and containing an initial error or noise is received by the PD 2 and immediately brought to a constant level by the control circuit 30. The reference light at this level emitted from the LED 1 is received by the PDI and held by the sample and hold circuit 18 until the next reference light is emitted. Next, although the signal light emitted from the LED 2 initially contains an error or noise, it is immediately corrected by the hold value by the sample and hold circuit 18. Then, from the PD 2, a signal output proportional to the physical quantity to be measured is obtained as shown in equation (4). Figure 3(b) shows each output when the loss variation due to optical fibers, optical connectors, etc. is large.The outputs of LEDI and LED2 are increased by the amount of loss, but P
The amount of reference light detected by D2 is always the same value (A
), the signal output is always detected at the same level.

As described above, according to the above embodiment, the transmission characteristics of the optical fiber that connects the control side α and the detection side β are affected by temperature during the route, or are bent by external force, etc., and the transmission characteristics thereof change. However, the detected signal output is not affected in any way. Further, even if the connection state of the optical connector connecting the control side α and the detection side β changes due to differences in the measurement location or the connection work, the signal output is always kept constant. Furthermore, even if the outputs of the light emitting units LEDI and LED2 are disturbed due to fluctuations in the external environment or power supply voltage, it is possible to obtain signal output without the influence.

In the above-mentioned embodiment, an apparatus was shown in which the loss fluctuation of one signal light is compensated for using two reference lights by time division, but this can also be done in the following manner.

For example, FIG. 4 shows a method for compensating loss fluctuations of a plurality of signal lights in a non-time division manner, and only the main part thereof is shown in FIG. On the control side α, light waves from an LED 3 that emits a reference light with a wavelength λ1, an LED 4 that emits a signal light with a wavelength λ2, and an LED 5 that emits a signal light with a wavelength λ3 are transmitted to PD3. PD4. The light is simultaneously received by the PD5. Furthermore, these light waves are branched by a splitter 15 on the detection side β and passed through filters 23 and 24a, respectively.
, 24b and are separated by a filter 23 that passes only the wavelength λ1, a filter 24a that passes only the wavelength λ2, and a filter 24b that passes only the wavelength λ3.
to the control side α via the optical fiber 25 under the same conditions as wavelength λ2 . The signal light of λ3 is transmitted to the control side α via sensors 26a and 26b, respectively. Control side α
At , these light waves are again filtered through filter 32a.

Branched at 32b and 32c, respectively PD6°PD7.
Irradiate with PD8. Here, the broken line indicates an optical fiber.

In this example, the reference light emitted from the LED 3, which is monitored by the PD 6 and set to a constant value (A), is held by a sample and hold circuit (not shown) as the amount of light received by the PD 3, but the held value is held by the PD 4. The difference from the time-sharing case is that the outputs of LED4 and LED5 detected by PD5 are continuously controlled. Therefore, it is possible to compensate for loss fluctuations more precisely than in the case of time division.

In FIG. 5, PD3 to PD5 shown in FIG. 4 are made into one light receiving diode PD9, and PD6 to PD8 are made into one light receiving diode PDIO. In this case, PD9
and scanning filter 3 placed just before P D i O
3.34 is sequentially scanned from one that only allows light from LED 3 to pass to one that allows light from LED 5 to pass. Therefore, in this example, it is possible to compensate for loss fluctuations of a plurality of signal lights and to measure physical quantities without increasing the number of light receiving diodes.

As described in detail above, in any of the embodiments, it is possible to compensate for loss fluctuations caused by optical fibers, optical connectors, etc., and to measure physical quantities with high precision. Furthermore, since there is no need to calculate the ratio between the reference light and the signal light as in the conventional compensation method, there is no need for an arithmetic unit for this purpose. Further, the sensor may be any sensor as long as it converts the physical quantity to be measured into light intensity; for example, it may be a reflective sensor.

Note that the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the scope of the invention.

For example, when performing time division, a single light emitting diode that can oscillate light waves of various wavelengths may be used. Then, loss fluctuations can be compensated for in the same way by sequentially changing the wavelength and emitting light. In that case, for example, the optical fibers 13 and 1.4 leading to T''DI in FIG. 1 can be made common.

Further, as a means for separating light waves, a diffraction grating may be used instead of using a filter. In that case, for example, a predetermined light receiving diode, optical fiber, sensor, etc. is arranged in the direction of a predetermined diffraction angle that has passed through the diffraction grating. Furthermore, when a diffraction grating is used instead of the scanning filters 33 and 34, the inclination of the axis of the diffraction grating may be changed.

(e) Effects As described in detail in 2, according to the present invention, by controlling the intensity of the signal light applied to the physical quantity/optical converter so that it is always constant using the reference light, We provide an optical applied measurement device that can compensate for loss fluctuations in signal light at the connection parts, etc. with high precision, and can always accurately measure the physical quantity to be measured under any environment.
− I can do things.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention, FIG. 2 is a schematic diagram for explaining the principle of a conventional example,
FIGS. 3(a) and 3(b) are timing charts showing the input and output of each part of the embodiment shown in FIG. 1, and FIGS. 4 and 5 show the configurations of other different embodiments of the present invention. FIG. 13, 14.19', 20°22.25, 27.28...Optical fiber,]
5a, 15b, 15c --- Turnout,]
Ga, 16b, 16c - coupler, 18...
...sample hold circuit, 2], a~2]d...
...Optical connector, 23.24, 24a, '24b 32a-32c, 33,34...Filter,
26, 26a, 26b - sensor, 30.31...
...Control circuit, LED'l~LED5...Light emitting diode, 2O- PDI~PDIO...Light receiving diode, α...
...Control side, β...Detection side. Figure 3 (a) (b) 4th Figure 2326a25 ・・"Transfer indicator LED 3→-E----1-P-Collection-16°°°'Ko-shi♀7-Me-no 11 LED5→ -Sunichi Ozulight-i l 24b 26
b io-fly 16

Claims (1)

[Claims] (1) A light emitting unit that emits a signal light and a reference light having a different wavelength from the signal light; and a light emitting unit that simultaneously or selectively transmits the signal light and the reference light from the light emitting unit through a first optical waveguide. a first light-receiving section that converts the received electrical signal into an electrical signal; a storage means that temporarily stores an electrical signal corresponding to the amount of the reference light received by the first light-receiving section; a separating means for receiving the signal light and the reference light through a second optical waveguide and separating the signal light and the reference light; a physical quantity/light converter that converts into intensity; a third optical waveguide that conducts the reference light separated by the separation means, the physical quantity/light converter having the same environmental conditions other than the physical quantity to be measured; a second light receiving section that receives the reference light emitted via the third optical waveguide and the signal light emitted via the physical quantity/optical converter and converts it into an electrical signal; a first control means for controlling the amount of the reference light emitted by the light emitting section so that the amount of the reference light received by the light receiving section is constant; The amount of the signal light emitted by the light emitting section is adjusted so that the amount of the signal light received by the first light receiving section is constant with respect to the amount of the reference light received after being converted into an electric signal in a storage means. and a second control means for controlling the second light receiving section, and detects a physical quantity to be measured from the amount of the signal light received by the second light receiving section.