JPS60164227A - Temperature detecting method - Google Patents

Abstract

PURPOSE:To make the restriction on a fluorescent material generous and to make it possible to use a long optical fiber, by exciting the fluorescent material in a pulsating mode, determining the life of the fluorescent light from the fluorescent material based on the time waveform of the generated fluorescent light, and measuring temperature from the temperature dependence of the life of the fluorescent light. CONSTITUTION:A light pulse, which has the pulse width equivalent to the life of the fluorescent light from a fluorescent material 1, is outputted from an excited light source 6. The fluorescent material 1 is excited through a lens 3 and an optical fiber 2. The fluorescent light, which is generated by the excitation, is inputted to a light detector through the fiber 2 and the lens 3. The output of the light detector 9 is inputted to a measuring unit 13 for the life of the fluorescent light. The life of the fluorescent light is determined by a least square method based on the waveform of an attenuation curve of the fluorescent light. Temperature is obtained based on the temperature dependence of the life of the fluorescent light by a temperature converting circuit 14.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention provides a method for accurately measuring temperature even under adverse environmental conditions.
This invention relates to a temperature detection method using an optical fiber.

(Prior art and its problems) In recent years, temperature measurement methods have been developed that make use of the non-inductive nature, flexibility, and environmental resistance of optical fibers to enable remote measurement under adverse environmental conditions that would be difficult to measure using other methods. is proposed. FIG. 4 is a block diagram of a conventional method using a fiber for measuring temperature from the temperature dependence of the radiation intensity of a fluorescent substance. In FIG. 1, the fluorescent substance 1 is connected to the sixteenth beam splitter 4. Lens 3. It is excited by the excitation light from the excitation light source 6 via the optical fiber 2. The fluorescence generated by excitation is
Return the optical fiber 2 in the opposite direction, and turn the optical fiber 2 back to the first beam spiriter 4.
The light is then separated from the optical path of the excitation light source 6 and is incident on the second beam spiriter 5.

The fluorescent light is further branched into two by the second beam spiriter 5, and the fluorescent light component whose radiation intensity is less temperature-dependent and the fluorescent light component whose radiation intensity is significantly temperature-dependent are divided into the first and second fluorescent light components, respectively. The light is selected by the two interference filters 7 and 8 and received by the first and second photodetectors. The fluorescent substance 1 temperature can be measured. In this method, by measuring the intensity ratio of two fluorescent components whose radiation intensity differs in temperature dependence, errors due to fluctuations in the intensity of the excitation light, bending loss of the optical fiber 2, and loss fluctuations at the optical fiber coupling part are detected. It has the advantage of being able to measure temperature while suppressing
There are also significant drawbacks, as listed below.

First, since two fluorescent components with different temperature dependencies of radiation intensity are required, the fluorescent substances 1 that can be used are extremely limited. Conventionally, as this fluorescent substance 1, (Gdal19
Euo, o+ )20z S only has been reported.

This fluorescent substance 1 has an excitation band in the ultraviolet region, and fluorescent light is generated in the visible region. However, in this wavelength range, the loss in the optical fiber is large and it is difficult to use a long fiber.The loss of the optical fiber 2 at the two fluorescence wavelengths to be detected is different.
This method has disadvantages such as the relationship between the intensity ratio of the fluorescent light and the temperature changes depending on the length of the optical fiber.

Secondly, in order to separate the two fluorescent wavelengths, narrow band filters such as interference filters 7.8 are ineffective, and losses in these filters cause the photodetectors 9,1 to
00 light receiving efficiency is reduced, making it difficult to obtain a high 8/N ratio, and the shift filter center wavelength shifts due to changes in the interference filter 7.8 over time, which tends to cause errors in the measured temperature. was also occurring.

(Objective of the Invention) The object of the present invention is to eliminate the above-mentioned drawbacks, to ease the restrictions on the usable fluorescent substance 1, to allow the use of long fibers, to reduce changes over time, and to achieve a high 8/N ratio. An object of the present invention is to provide a temperature detection method that can receive fluorescent light.

(Structure of the Invention) The temperature detection method of the present invention optically excites a fluorescent substance in a pulsed manner, detects the time waveform of fluorescence emitted from the fluorescent substance, and detects the time waveform of the fluorescent light from the time waveform of the fluorescent substance. The present invention is characterized in that the temperature in the vicinity of the fluorescent substance is remotely detected based on the temperature dependence of the fluorescent life.

(Operations and Effects of the Invention) Next, embodiments of the temperature detection method of the present invention will be described in detail with reference to the drawings. FIG. 2 is a configuration diagram of an embodiment according to the present invention in which the excitation optical fiber and the detection optical fiber are the same optical fiber, and the configuration and names are the same as in FIG. 1 except for the following points. It is. In FIG. 2, the photodetector 9
The output is connected to a fluorescence life measuring unit 13, and a temperature conversion circuit 14 calculates the temperature from the temperature dependence of the fluorescence life. On the other hand, the excitation light source 6 outputs a light pulse having a pulse width comparable to the fluorescence lifetime of the fluorescent substance 1.

FIG. 3 is a diagram showing temporal changes in the excitation pulse and fluorescence intensity. Figure 3 shows the excitation pulse waveform, and Figure 3B shows the fluorescence time waveform. The fluorescence rises at the beginning of the excitation light and decreases exponentially after the excitation pulse ends. The decay curve of fluorescence when the fluorescence lifetime is expressed as τ is (1)
It can be expressed by the formula -1 A = AOe 1 (1) In the formula (1), A is the fluorescence intensity, t is the time, and A
O is a constant. The simplest way to measure the fluorescence lifetime τ is to calculate the fluorescence intensity A at time t1 and Δ from the fluorescence intensity A after the elapse of time.
You can find out by comparing the .

Ru. In addition, for even more precise measurements, it is possible to memorize the waveform of the fluorescence attenuation curve and calculate the fluorescence lifetime using the least squares method from that waveform or a logarithmically transformed waveform of the waveform.

Since the determined fluorescence lifetime is temperature dependent as shown in FIG. 4, the temperature around the fluorescent substance can be determined from this fluorescence lifetime.

Next, the temperature dependence of the fluorescence lifetime will be explained in detail. Figure 4 shows alexandrite (BeAl*Oa: Cr”+), which has recently been put into practical use as a wavelength tunable solid-state laser.
shows the temperature dependence of the fluorescence lifetime.

Solid-state laser materials usually have a high melting point, high hardness, high thermal conductivity, and are chemically stable, so they satisfy the characteristics necessary as a temperature sensing material. Furthermore, it has the advantage that the fluorescence lifetime is long, ranging from several hundred to several milliseconds, and the fluorescence lifetime can be easily measured. However, there was not much interest in the temperature dependence of the fluorescence lifetime before the appearance of alexandrite because its changes do not have a large effect on the laser oscillation characteristics near room temperature. Alexandrite has a characteristic that the amplification factor as a laser increases as the temperature increases, and the temperature dependence of fluorescence over a wide temperature range as shown in FIG. 4 has been measured.

The figure shows that the fluorescence lifetime decreases exponentially with temperature from around 150 to around 500. In other words, it can be seen that by measuring the fluorescence lifetime, the temperature can be determined uniquely and accurately. The lifetime of fluorescence is determined by two energy dissipation processes: a non-emission process due to interaction with phonons at the emission level of the fluorescence, and a fluorescence emission process. Of these, the fluorescence emission process has little temperature dependence, but the probability of a non-emission process due to interaction with the 7-onone is higher than that of the thermally excited 7-onone.
Since it is proportional to the number of onons, it includes temperature dependence approximately expressed as e1〒.

E is the phonon energy, k is the Portzmann constant, and T is the absolute temperature. This dependence is well applicable in the case of alexandrite, and is essentially the same in the case of other fluorescent materials. Crystals and glass materials containing rare earth ions, known as solid-state laser materials, are also used in the present invention. Can be used as a fluorescent material. These fluorescent substances have different energies at their emission levels, so by combining these fluorescent substances, it is possible to detect temperature over a wide temperature range.

The above example uses a solid-state laser material, but in order to further improve the temperature dependence of the fluorescence lifetime and improve the characteristics, it is possible to increase the concentration of fluorescent ions and quench the fluorescence. In some cases, ions with functions may be added.

By increasing the temperature dependence of the fluorescence lifetime, it is possible to obtain even higher temperature accuracy.

The fluorescence lifetime measuring unit 13 measures the time t after the end of the excitation pulse.
, and 1. The fluorescence intensities A1 and A at +Δt are sampled by A/D conversion and input into a microcomputer, and Δt·In-' (Al /A ) is calculated and the result is output. The above equation is the fluorescence lifetime τ claimed by equation (1).
It shows. The temperature conversion circuit 14 is composed of a microcomputer, and its operation is as follows.

It is shi. The temperature corresponding to the output of the fluorescent life measuring unit 13 is determined and output according to the pre-stored relationship between the fluorescent life and temperature.

One advantage of the present invention is that a variety of fluorophores can be used. For example, even when using a long fiber, if a crystal containing Nd ions is used as the fluorescent material 1, the excitation wavelength can be set to 0.8 μm and the fluorescence wavelength to 1 μm, thereby reducing transmission loss in the optical fiber.

Further, in this case, a GaAlAs semiconductor laser having a long light source life and capable of increasing the excitation light intensity can be used as the excitation light source 6, so there is an advantage that a high 87N ratio can be obtained at the time of detection. In addition, the interference filters 7 and 8, which caused temperature accuracy deterioration in the conventional method, are not required, and at the same time, the interference filters 7 and 8, which caused temperature accuracy deterioration in the conventional method, are not required. There is also the advantage that there are no errors.

Another advantage of the present invention is that one temperature measurement can be carried out in a short time comparable to the fluorescence lifetime of the fluorescent substance 1. By using a chemically stable fluorescent material with high thermal conductivity in the detection part, this method eliminates protective tubes and other materials that are difficult to wipe off with conventional methods, and allows the temperature to be measured between the object and the fluorescent material. This is possible by reducing the thermal resistance between

This is especially useful when you want to know the temperature fluctuations of fluids with high flow rates.

As another embodiment of the present invention, if the optical fiber 2 and the detection section are integrated by doping the tip of the optical fiber 2 with fluorescent ions such as rare earth ions, the structure is strong and simple. As a result, it is possible to provide a temperature detection method with fewer failures.

As another embodiment according to the present invention, a pumping optical fiber;
It is conceivable to separate the detection fiber. In this case, by increasing the NA of the detection optical fiber, it becomes possible to guide the fluorescent light to the photodetector 10 with high efficiency, and it becomes possible to obtain even higher temperature accuracy.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an example of a conventional method, FIG. 2 is a configuration diagram of an embodiment according to the present invention, and FIGS. 3A and 3B are timing diagrams of operations in the configuration shown in FIG. 2. FIG. FIG. 3A shows the excitation light intensity, and B shows the fluorescence intensity over time. FIG. 4 is a diagram showing the temperature dependence of the fluorescent life of alexandrite. In the figure, 1 is a fluorescent material, 2 is an optical fiber, 3 is a lens, 4 is a first beam splitter, 15 is a second beam splitter, 16 is an excitation light source, 7 and 8 are first and second beam splitters, respectively. an interference filter; 9 and 10 are first and second photodetectors, respectively; 11 is a division circuit; 12 is a temperature conversion circuit;
13 is a fluorescent life measuring unit, and 14 is a temperature conversion circuit. Representative Patent Attorney Uchihara Den';Ivt Figure 72 Figure l'jI;J) (No change in content) Figure 3 Time Time (1) O 4 Figure Temperature (K) Procedural Amendment (Method) 1. Indication of the case 1982 Patent Application No. 19606 2, Title of the invention Temperature detection method 3, Person making the amendment Relationship to the case Applicant 5-33-1 Shiba, Minato-ku, Tokyo (423) NEC Corporation Representative: Tadahiro Sekimoto 4, Agent telephone: Tokyo (03) 456-3111 (main representative) (Contact information: NEC Corporation Patent Department) 5. Date of amendment order: April 24, 1980 (shipment date)
6. Drawing to be amended 7. Contents of the amendment Figure 3 of the drawings attached to this application will be amended as shown in the attached drawing. Agent Patent Attorney Oto Uchihara

Claims (1)

[Claims] A process of photo-exciting a fluorescent substance in a pulsed manner, a process of detecting a temporal waveform of the fluorescent light emitted from the fluorescent substance, and a process of detecting the temporal waveform of the fluorescent light, and adding a light divine light to the temporal waveform of the fluorescent light. A temperature detection method characterized by comprising the steps of: