JPH0131580B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature measuring device in which an optical signal emitted from an optical temperature sensor is transmitted via an optical fiber or the like.

When transmitting an analog quantity from an optical temperature sensor via an optical transmission line, the transmission characteristics of the optical transmission line fluctuate due to temperature changes and bending stress, making accurate temperature measurement difficult. It is necessary to improve measurement accuracy.

Figure 1 shows an example of a temperature measuring device that compensates for such transmission characteristic fluctuations. For example, light emitted from a light source 1 using a halogen lamp is converted into a parallel beam by a lens 2, and then passed through a filter 3 and a dichroic composite mirror. 4,5,
Visible light is removed by lens 6, and only ultraviolet light is filtered through lens 7.
is focused onto the end face core of the optical fiber 8. The ultraviolet rays irradiate the fluorescent substance of the sensor 9 attached to the tip of the optical fiber 8. The fluorescent substance is excited by ultraviolet light and consists of, for example, gadolinium oxide ions and europium which activates them. This fluorescent material emits visible light having a spectrum indicated by the emission wavelength on the right side in response to ultraviolet light having a spectrum indicated by the excitation wavelength on the left side of FIG. 2A. This visible light passes through the optical fiber 8 again, is split into two by the beam splitter 10, one is reflected by the mirror 11, and is filtered through interference filters 12 and 13, respectively, to extract only the visible light at emission wavelengths a and c shown in FIG. 2A. , these two visible light rays reach photodetectors 16 and 17 through lenses 14 and 15, respectively. The optical signal is converted into an electric signal by photodetectors 16 and 17, and further passed through preamplifiers 18 and 19 and A/D converted by an A/D converter multiplexer 20, and then converted to Ic/Ia.
(Ic: light intensity of wavelength c, Ia: light intensity of wavelength a) is calculated and input to the microcomputer 21. The read-only memory (ROM) 22 includes
Relative intensity Ic/Ia of temperature and radiation wavelength shown in Figure 2B
The relationship between the
It will be displayed after 4. Here, by taking the relative intensities Ic/Ia of wavelengths a and c, fluctuations in the transmission characteristics of the optical fiber etc. are compensated for. Because Ia and
Ic varies depending on the fluctuation of transmission characteristics, but
This is because Ic/Ia does not change.

FIG. 3 shows another temperature measuring device, in which a pulse generator 31 and a light emitting diode driver 32 cause two light emitting diodes 33 and 34 to alternately emit light at wavelengths λ ₁ and λ ₂ . Both lights are optical fibers 35, 36
The light of wavelengths λ ₁ and λ ₂ enter the same optical fiber 38 at a multiplexer 37 through the optical connector 39 and reach the temperature detection section 40 . The detection unit 40 includes
A semiconductor such as GaAs, CdTe, etc. is placed, and light passes through this semiconductor and enters a photodetector 42 through an optical fiber, an optical connector 41, and is converted into an electrical signal. After passing through the light receiving circuit 43 and being amplified by the sample and hold amplifier 44, it is then amplified by the dividing circuit 45.
Find the ratio _{Iλ 1 /} Iλ ₂ of the light intensities Iλ ₁ and Iλ ₂ of λ 1 and λ ₂ . Here, semiconductors such as GaAs, CdTe, etc.
The wavelength range in which light is absorbed is temperature dependent. In other words, as shown by curve P in FIG. The light intensity has temperature dependence as shown in FIG. 4B. Therefore, the wavelength of λ ₁ is set to a wavelength at which the intensity of transmitted light changes with temperature fluctuation, and λ ₂ is set to a wavelength at which the intensity of transmitted light at a wavelength longer than λ ₁ does not have temperature dependence. Iλ ₁ changes due to changes in temperature and optical transmission characteristics, and Iλ ₂ changes due to changes only in optical transmission characteristics. Then,
By determining Iλ ₁ /Iλ ₂ , variations in transmission characteristics of the optical fiber, etc. are reduced and eliminated by the numerator and denominator, making it possible to accurately measure temperature without being affected by variations in transmission characteristics.

However, the compensation methods used in these devices cannot be applied to temperature measuring devices using optical temperature sensors based on other principles. The compensation method in the device shown in FIG. 1 is applicable only to optical temperature sensors that utilize temperature changes in the emission spectrum of fluorescent substances, and the compensation method in the device shown in FIG. It is applicable only to optical temperature sensors based on the principle of using wavelengths whose intensity is temperature-dependent and wavelengths whose intensity is not temperature-dependent. However, such a compensation method cannot be applied to an optical temperature sensor using the principle of natural birefringence or multiwave interference because there is no wavelength range in which the transmitted light intensity does not have temperature dependence.

The present invention is intended to eliminate the above-mentioned drawbacks,
It is an object of the present invention to provide a temperature measuring device that can compensate for fluctuations in optical transmission path characteristics even when an optical temperature sensor based on another principle is used.

The purpose of this is to use a temperature measuring device equipped with an optical temperature sensor whose optical properties at two different wavelengths are temperature-dependent, to separate the two light sources into two parts, and to separate the two lights into two parts. the optical temperature sensor, which is provided with a splitter and a means for guiding the light of the one portion and guiding the light of one wavelength to the inside, so that only the intensity of the light of the one wavelength is changed depending on the temperature; By comprising means for calculating the ratio of the intensity of the light in one part and the light in the other part that have passed through the optical temperature sensor, and further calculating the temperature by comparing the respective ratios for the light of both wavelengths. achieved.

Embodiments of the present invention will be described below with reference to the drawings. In each figure, parts common to the previously cited figures are given the same reference numerals. In FIG. 5, light emitting elements 33 and 34 having different wavelengths λ ₁ and λ ₂ are caused to emit light by a driving section 32. In FIG. Light emitting element drive section 3
An example of 2 is shown in FIG. A pulse is generated by a pulse generator 31, and the pulse is directly applied to one light emitting element drive circuit 51, but the pulse is applied to the other light emitting element drive circuit 52 after passing through an inverter 53. As a result, the circuit 51 for driving the light emitting element 33 and the circuit 52 for driving the light emitting element 34 are operated alternately, causing the light emitting elements 33 and 34 to emit light alternately. The light emitted from the light emitting elements 33 and 34 enters into optical fibers 35 and 36 and enters into one optical fiber 38 at an optical multiplexer 37. Next, the optical splitter 54 outputs λ ₁
A part of the light with wavelengths λ 2 and λ ₂ is branched, and the branched light passes through the optical fiber 56 and enters the light receiving element 60 for monitoring the light source, where it is converted into an electrical signal. The other light emitted from the optical splitter 54 enters the temperature sensor 57 through the optical fiber 55, passes through the inside of the temperature sensor, and exits from the temperature sensor 57. The emitted light enters an optical fiber 58 different from the optical fiber 55 at the time of input, enters a light receiving element 59, and is converted into an electrical signal by a signal processing section 61. FIG. 7 shows an example of a signal processing section. The electric signals for the light of λ ₁ and λ ₂ received by the light receiving element 59 are respectively defined as V ₁ λ ₁ and V ₁ λ ₂ ,
The electric signals for the lights of λ ₁ and λ ₂ received by the light-receiving element 60 for monitoring the light source are assumed to be V ₂ λ ₁ and V ₂ λ ₂ , respectively.
After the electrical signal is amplified by the amplifier 62, the divider 4
5, and divides V ₁ λ ₁ /V ₂ λ ₁ and V ₁ λ ₂ /V ₂ λ ₂ alternately. This is because the lights of λ ₁ and λ ₂ are alternately incident on the light receiving element 59 and the light receiving element 60 for monitoring the light source. The results of both divisions are held in sample-and-hold amplifiers 44, 44', and the results of both divisions are input again to the second divider 45'. The holding of the division result is performed by a signal from the light emitting element driving section 32. As a result, (V ₁ λ ₁ /V ₂ λ ₁ )/
The value (V ₁ λ ₂ /V ₂ λ ₂ ) is output from the divider 45'. This output is amplified by an amplifier 63 and displayed on a display section 64.
to display the temperature.

Next, a specific example of the optical temperature sensor 57 will be described. FIG. 8 shows an example of an optical temperature sensor based on the principle of multiwave interference, in which light is converted into a parallel beam by a lens 65 connected to the ends of optical fibers 55 and 58, and is emitted from the lens 65. The emitted light passes through the beam splitter 10, the light of λ ₁ passes through the filter 66,
The light is incident on a transparent solid 67 with optically parallel planes. On the other hand, the light of λ ₂ is reflected by the filter 66.
That is, the filter 66 has a characteristic of transmitting light of λ ₁ and reflecting light of λ ₂ . The light of λ ₁ incident on the transparent solid body 67 (having an optically parallel plane) causes multiwave interference, and a part of the incident light becomes reflected light and exits from the transparent solid body 67 . The intensity of this emitted light changes depending on the temperature of the optical parallel plane solid 67. The reflected lights λ ₁ and λ ₂ have their optical paths bent by the beam splitter 10, pass through the mirror 11 and the lens 65, and then pass through the detection end 57.
It enters into a different optical fiber 58 than when it entered.

FIG. 9 is an example of an optical temperature sensor based on the principle of natural birefringence. In FIG. 9, a parallel beam emitted from a lens 65 passes through a polarizing beam splitter 68 to become linearly polarized light, and then passes through a wave plate 69 to be given a phase difference. After this, the light of λ ₂ passes through the filter 6
6. The light of λ ₁ passes through the filter 66, enters the optically anisotropic crystal 70, travels through it, is reflected by the reflective film 71, and passes through the optically anisotropic crystal 70 again as the incident light. travels in the opposite direction and passes through the filter 66. At this time, the light of λ ₁ is further given a phase difference in the optically anisotropic crystal. The reflected lights of λ ₁ and λ ₂ pass through the wavelength plate 69 again, and are further subjected to a phase difference to become elliptically polarized light. Thereafter, the vibration component (S component) of the light in a certain direction is extracted by the polarizing beam splitter 68, passes through the mirror 11 and the lens 65, and enters the optical fiber 58 different from the one used when entering the detection end 57.
At this time, the phase difference provided by the wave plate 69 has almost no temperature dependence, but the phase difference provided by the optically anisotropic crystal 70 has temperature dependence. In other words, the phase difference given to the light of λ ₁ has temperature dependence, but the phase difference given to the light of λ ₂ has almost no temperature dependence. For this reason, the S component of λ ₁ taken out by the polarizing beam splitter 68 has temperature dependence, but the S component of λ ₂ has almost no temperature dependence.

By employing the above-described configuration, it is possible to compensate for measurement errors due to variations in the output of the light emitting element, variations in the optical loss characteristics of the optical fiber, and the like. The reason for this is explained below. In FIG. 5, if the intensity of the light of λ ₁ emitted from the light emitting element 33 is Iλ ₁ and the intensity of the light of λ ₁ received by the light receiving element 59 is I ₁ λ ₁ , then I ₁ λ ₁ is I ₁ λ ₁ =M(T)Bλ ₁ Dλ ₁ Iλ ₁ (1). Here, Bλ ₁ is the optical loss when the light of λ ₁ of Dλ 1 passes through the optical fiber 35, the optical multiplexer 37, the optical fiber 38, and the optical splitter 54, and Bλ ₁
4, then the optical fiber 55 and the sensor 5
7. Light loss M(T) from passing through the optical fiber 58 to entering the light receiving element 59 represents the temperature dependence of the light intensity at the temperature sensor 57. Bλ ₁ , Dλ ₁ ,
Each Iλ ₁ has time dependence. On the other hand, the intensity of the light of λ ₁ received by the light receiving element 60 for monitoring the light source is
I ₂ λ ₁ is given by I _{2 λ 1 = Cλ 1 Dλ 1} Iλ ₁ (2). Here, Cλ ₁ is the optical loss from outputting the optical splitter 54 to passing through the optical fiber 56 and entering the light receiving element 60 for monitoring the light source.
Similarly, the intensity of the light with wavelength λ ₂ emitted from the light emitting element 34 is Iλ ₂ , the intensity of the light with wavelength λ ₂ received by the light receiving element 59 and the light receiving element 60 for light source monitoring is respectively I ₁ λ ₂ ,
If I ₂ λ ₂ , it is given by I ₁ λ ₂ =Bλ ₂ Dλ ₂ Iλ ₂ (3) I ₂ λ ₂ =Cλ ₂ Dλ ₂ Iλ ₂ (4). Here, Bλ ₂ , Cλ ₂ , and Dλ ₂ represent the loss of the optical transmission path for the light of λ ₂ , as in the case of λ ₁ .

From equations (1), (2), (3), and (4), I ₁ λ ₁ /I ₂ λ ₁ /I ₁ λ ₂ /I ₂ λ ₂ =M(T)Bλ ₁ /C
λ ₁ /Bλ ₂ /Cλ ₂ . Since there is almost no wavelength dependence of loss in the optical transmission line, Bλ ₁ = Bλ ₂ , Cλ ₁ = Cλ ₂ (5) holds, and I ₁ λ ₁ /I ₂ λ ₁ /I ₁ λ ₂ /I ₂ λ ₂ =M(T) (6). The right side of equation (6) represents the temperature dependence of the temperature detection end, and light source fluctuations and optical transmission line loss fluctuations are eliminated. From this, it can be seen that by adopting this configuration, accurate temperature measurement is possible regardless of variations in the light source and variations in loss in the optical transmission line.

Next, a modification of FIG. 5 will be described. FIG. 10 shows an example in which the lights of λ ₁ and λ ₂ are not emitted alternately, but are emitted simultaneously. The difference from FIG. 5 is that the light is transmitted to the light receiving element 59 and the light receiving element 6 for monitoring the light source.
0, the light of λ ₁ and λ ₂ are separated by an optical demultiplexer 72, and different light receiving elements 59, 59' for λ ₁ and λ ₂ are used.
This is the point where light enters the light receiving elements 60, 60' for monitoring the light source. Accordingly, the signal processing section 61 changes, an example of which is shown in FIG. That is, I ₁ λ ₁ /
Two dividers 45 are provided separately for calculating I ₂ λ ₁ and I ₁ λ ₂ /I ₂ λ ₂ , and the quotient is further divided by another divider 45'. do. Further, the light receiving element driving section 73 also includes the light emitting elements 33 with wavelengths λ ₁ and λ ₂ ,
This has been modified so that 34 motors can be driven at the same time.

FIG. 12 is similar to FIG. 10, but has a configuration in which light with wavelengths λ ₁ and λ ₂ are emitted simultaneously, but before the light enters the optical multiplexer 54, the light is split by the optical splitter 54 and is received for light source monitoring. This is a method in which the light enters the light receiving elements 60, 60' for light source monitoring.
There is no need for an optical demultiplexer 72 in front of the optical demultiplexer 72. FIG. 13 shows a system in which light of λ ₁ and λ ₂ are emitted alternately, but the configuration is such that the light incident on the detection end 57 and the light emitted from the detection end 57 are transmitted through the same optical fiber. light emitting element 33,
The light emitted from the optical fiber 34 passes through the optical fibers 35 and 36, the optical multiplexer 37, and the optical fiber 38, and enters the optical directional coupler 74. Here, part of the light is split,
The branched light passes through the optical fiber 56 and enters the light receiving element 60 for monitoring the light source. Optical directional coupler 74
The other light emitted passes through the optical fiber 55, enters the temperature detection end 57, is reflected therein, enters the optical fiber 55 into which it entered again, and reaches the optical directional coupler 74. Here, the light is branched in a direction different from the direction toward the light receiving element 60 for monitoring the light source, passes through the optical fiber 56', and enters the light receiving element 59. In this configuration, both the light emitting element driving section 32 and the signal processing section 61 are the same as the configuration shown in FIG. FIG. 14 shows a combination of the method shown in FIG. 13 and the method shown in FIG. 10 so that it can be applied to simultaneously emitted light. Examples of temperature sensors using the methods shown in FIGS. 13 and 14 are shown in FIGS. 15 and 16. FIG. 15 uses the principle of natural birefringence, and FIG. 16 uses the principle of multiwave interference. In both figures, the light of λ ₂ is reflected by the filter 66,
The light of λ 1 does not enter the optically anisotropic crystal 70 or the transparent solid 67 having optically parallel planes but returns, but the light of λ ₁ passes through the filter 66, enters the anisotropic crystal 70 or the transparent solid 67, and passes through the reflective film. 71 or the end face of the transparent solid 67 and returns.

As described above, the present invention uses two lights of different wavelengths, passes them through the same optical transmission path, changes only the intensity of the light of one wavelength at the temperature sensor depending on the temperature, and then inputs the light into the temperature sensor. Before doing so, calculate the ratio of the light intensity of each branched wavelength,
Furthermore, the temperature is measured by comparing their quotients, thereby compensating for fluctuations in the optical transmission characteristics of the optical temperature sensor based on principles such as temperature changes in natural birefringence or temperature dependence of multiwave interference. can do. Furthermore, even if the light source fluctuates, highly accurate temperature measurements can be obtained, and temperature measurement devices that use an optical temperature sensor that produces a temperature-dependent intensity change for only one of two wavelengths. It is widely applicable and extremely effective.

[Brief explanation of drawings]

Fig. 1 is a system diagram of an example of a temperature measuring device using a conventional optical temperature sensor, Fig. 2A is a spectrum diagram of excitation ultraviolet rays and emitted light showing the characteristics of the fluorescent substance used in it, Fig. 2 B is a diagram of the relationship between the light intensity of wavelengths a and c of the synchrotron radiation and their ratio and temperature, Figure 3 is a systematic diagram of another conventional example, and Figure 4A is a diagram of the absorption edge characteristics of the semiconductor used for it. Temperature dependence, Figure 4B
5 is a diagram showing the dependence of the light intensity of light passing through a semiconductor based on the above, FIG. 5 is a block diagram of an embodiment of the temperature measuring device according to the present invention, and FIG. 6 is a system diagram of the light emitting element driving section thereof. , Fig. 7 is a system diagram of the signal processing section, Fig. 8 is a system diagram showing one embodiment of the optical temperature sensor, Fig. 9 is a system diagram showing another embodiment, and Fig. 10 is the temperature measuring device. FIG. 11 is a system diagram showing another embodiment of the temperature measuring device, FIG. 11 is a system diagram of the signal processing section in the modified example, and FIGS.
5 and 16 are system diagrams showing two embodiments of the optical temperature sensor used in the apparatus shown in FIGS. 13 and 14, respectively. 33, 34... Light emitting element, 35, 36, 38,
55, 56, 56'... Optical fiber, 37... Optical multiplexer, 54... Optical splitter, 57... Optical temperature sensor, 59, 59'... Light receiving element, 60, 60'...
Light receiving element for light source monitor, 61...Signal processing section, 6
4... Display portion, 67... Transparent solid having optically parallel planes, 70... Optically anisotropic crystal, 74...
Optical directional coupler.

Claims (1)

[Scope of Claims] 1. A temperature measuring device equipped with an optical temperature sensor whose optical characteristics at two different wavelengths exhibit temperature dependence, including a light emitting source of two light having different wavelengths, and two light emitting sources for each of the two lights. The light temperature is provided with a splitter that divides the light into parts, and a means for guiding the light of the one part and guiding the light of one wavelength to the inside, so that only the intensity of the light of the one wavelength is changed depending on the temperature. A sensor, and means for calculating the ratio of the intensity of the light in one part and the light in the other part that have passed through the light temperature sensor, and further calculating the temperature by comparing the respective ratios for the light of both wavelengths. A temperature measuring device characterized by: 2. In the device according to claim 1,
A temperature measuring device characterized in that the optical temperature sensor utilizes the temperature dependence of natural birefringence. 3. In the device according to claim 1,
A temperature measuring device characterized in that the optical temperature sensor utilizes the temperature dependence of multiwave interference.