JPH05288613A - Optical fiber temperature sensor - Google Patents

Abstract

PURPOSE:To achieve a highly accurate measurement of the temperature of a part to be measured with a simple construction and a smaller size. CONSTITUTION:A filter 7 for measurement is provided at a part to be measured and a filter 4 for reference in the main body 1 of the apparatus having the same temperature characteristic. Emission light with a single wavelength emitted from a light emitting element 2 is supplied to a photodetector 10 for measurement through an optical fiber 6 while being detected with a photodetector 12 for reference. Detection signals are computed with an arithmetic section 15. This enables the computation and outputting of the temperature of the part to be inspected depending on a difference in transmittance of the filter 7 for measurement from the filter 4 for reference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber temperature sensor for measuring the temperature of a measuring point using an optical fiber.

[0002]

2. Description of the Related Art An optical fiber temperature sensor shown in FIG. 4 is known as an apparatus for measuring the temperature at a measured point. This optical fiber temperature sensor has a light source 30 in the main body of the apparatus, and guides the light of the light source 30 to a measurement point via a lens 31 and an optical fiber 32. A temperature-sensing section 33 made of a substance such as a semiconductor whose transmittance changes with temperature is provided at the measurement location.

The reflected light of the temperature sensing portion 33 or the transmitted light as shown in the figure is again guided to the main body of the apparatus through the optical fiber 34, the lens 35, and the filter 3 having a different transmission wavelength.
The color is divided into two colors by the turntable 37 having 6a and 36b, detected by the detector 38, and the temperature is calculated and output by the calculator 39 based on the radiant energy ratio of each wavelength. still,
The temperature measurement method using two colors has two wavelengths: a wavelength at which the transmittance does not change with temperature and a wavelength at which the transmittance changes with temperature.
The wavelength is used to calculate and output the temperature based on the transmittance ratio of the two wavelengths.

[0004]

However, the conventional optical fiber temperature sensor has a problem in that the size of the main body of the apparatus becomes large. That is, the light source 30 needs to be a white light source that obtains a light emission wavelength in a high band including wavelengths of two colors, and thus the size is increased. Furthermore, a rotating disk 37 having two-color filters 36a and 36b, and a structure for obtaining a synchronous output of the rotating mechanism and each filter are required, which causes a problem that the device becomes large and complicated. Further, since the white light source is used, there is a problem that the output for each wavelength cannot be made constant, and the output fluctuates depending on the temperature so that stable temperature measurement cannot be performed.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical fiber temperature sensor capable of highly accurately measuring the temperature of a measurement point with a simple structure. There is.

[0006]

In order to achieve the above object, the optical fiber temperature sensor of the present invention comprises a light emitting element 2 which emits light of a predetermined wavelength as a light source, and the light emitting element 2 which has a temperature-dependent transmittance. Filter 4 for transmitting the emitted light of
A reference photodetector 12 that receives the transmitted light of the reference filter 4, an optical fiber 6 that guides the light emitted from the light emitting element 2 to an external measurement site, and the reference filter 4. An optical fiber 6 made of the same material, which is the measured point
Detected by the measurement filter 7 provided at the end of the measurement light, the measurement photodetector 9 that receives the transmitted light of the measurement filter 7, the reference photodetector 12, and the measurement photodetector 9. It is characterized by including a calculation unit 15 that calculates and outputs the temperature of the measured point based on the difference in transmitted light.

[0007]

[Function] A measurement filter 7 is provided at the measured point,
The light emitted from the light emitting element 2 is supplied to the measuring filter 7 through the optical fiber 6. Since the measuring filter 7 has a temperature characteristic, the transmittance changes according to the temperature change. This transmitted light is detected by the measuring photodetector 9. The light emitted from the light emitting element 2 is detected by the reference photodetector 12 via the reference filter 4 made of the same material as the measuring filter 7. The calculation unit 15 can obtain the temperature of the measurement site by subtracting the output of the measurement photodetector 9 with the output of the reference photodetector 12 as a reference.

[0008]

1 is a schematic diagram showing the configuration of a first embodiment of an optical fiber temperature sensor of the present invention. In the device body 1,
A light emitting element (hereinafter, referred to as LD) 2 such as a laser diode that emits light having a predetermined wavelength is provided as a light source. The light of the LD 2 is emitted to the outside and the reference filter 4 via the half mirror 3. An optical fiber 6 is provided on the outside through a condenser lens 5, and an end portion of the optical fiber 6 is led out to a measured position. A measurement filter 7 that transmits the light having the predetermined wavelength is provided at the measured position.

The measuring filter 7 is composed of the same member as the reference filter 4 and transmits the same predetermined wavelength as the reference filter 4. The transmittances of the reference filter 4 and the measurement filter 7 similarly change depending on the temperature. The transmitted light of the measurement filter 7 is
It is introduced into the inside of the apparatus main body 1 through the optical fiber 8.

At the end of the optical fiber 8, a condenser lens 9 is provided, and a measuring photodetector 10 is provided. The detection signal f (t) of the photodetector 10 for measurement is output to the calculating means 15. Further, the transmitted light of the reference filter 4 is input to the reference photodetector 12, and the detection signal f (tr) of the reference photodetector 12 is also output to the calculating means 15. Further, the reference filter 4 is provided with a temperature sensor 13 composed of a Pt resistance temperature detector or the like, and this temperature signal g (tr) is also output to the computing means 15.

Explaining the configuration of the calculating means 15, the subtracting section 16 to which the detection signals of the measuring photodetector 10 and the reference photodetector 12 are input calculates the difference between these detection signals, and then the adding section. 17 is input. The adding unit 17 adds the temperature signals of the temperature sensor 13 and outputs the result as a temperature signal.

Next, the temperature measuring operation of the measured portion having the above structure will be described. When the LD 2 is driven to emit light at a predetermined wavelength, this light is emitted from the reference filter 4 and the optical fiber 6.
The light is emitted to each of the measurement filters 7 via. here,
The reference filter 4 is set as a reference temperature. Further, the measurement filter 7 provided at the measured position is an LD
Since the transmittance changes according to the temperature change at the predetermined wavelength of 2 emitted, the light is transmitted at the transmittance corresponding to the temperature of the measurement point, and is detected by the measuring photodetector 10 via the optical fiber 8. It

The subtracting section 16 of the calculating means 15 calculates the difference f (t) -f (tr) between these detection signals. By this calculation,
The difference between the measurement filter 7 and the reference filter 4 that serves as a temperature reference is calculated. This enables temperature measurement. Further, the actual temperature of the reference filter 4 is measured by the temperature sensor 13, and f (t) -f for temperature compensation of the reference filter 4 is used to set the reference filter 4 as a temperature reference.
The operation (tr) + g (tr) is performed. As a result, it is possible to measure the temperature with higher accuracy.

As described above, the reference filter 4 and the measurement filter 7 are configured in the same manner, and the difference in the transmittance between the reference filter 4 and the measurement filter 7 can be obtained only by using a single wavelength. It has become possible to obtain the temperature at the measured point with a simple configuration for performing the above calculation based on Further, since the temperature of the reference filter 4 is measured by the temperature sensor 13, the accuracy of the measurement does not decrease even if the temperature of the inside of the apparatus main body that serves as the reference of the temperature measurement changes. Incidentally, L
Even if the emission wavelength of D2 changes, the reference filter 4 and the measurement filter 7 are filters having the same transmission wavelength, and the measurement calculation is performed using a single wavelength. The effect can be minimized.

By the way, as shown in FIG. 1, in order to stabilize the output wavelength of the LD 2, the detection signal of the reference photodetector 10 is input to the light source driving unit 20, and the light source driving unit 20 causes L
With the configuration in which the output of D2 is driven in a stable manner, it is possible to easily prevent the variation of the emission wavelength and the variation of the optical power due to the temperature variation of the environment of the LD2.

Next, FIG. 2 is a schematic view showing a second embodiment of the optical fiber temperature sensor of the present invention. In this embodiment, the same parts as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. As shown in the figure, in this embodiment, the measurement filter 7 at the measurement site has a reflection type configuration. Therefore, a mirror 25 for total reflection is provided on the back of the measurement filter 5 as shown in the figure. Further, as shown in the side view of FIG. 3, the back portion of the measuring filter 7 may be processed into a spherical surface 7a.

Further, the optical fiber 8 is unnecessary and only one optical fiber 6 is used. The reflected light is configured to be incident from the optical fiber 6 through the half mirror 3 to the measuring photodetector 10 on the back of the half mirror 3. With this configuration as well, it is possible to obtain the same effects as the first embodiment.

[0018]

According to the present invention, two filters having similar temperature characteristics that transmit the wavelength emitted by the light source are provided for the measurement point and the reference, and the temperature of the measurement point is obtained by the difference in the transmittances. Therefore, the temperature can be measured with only a single wavelength, and the device body can be downsized. In addition, since the light emitting element is used as the light source, there is little variation in the emission wavelength, and highly accurate measurement can be performed.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of a first embodiment of an optical fiber temperature sensor of the present invention.

FIG. 2 is a schematic view showing a second embodiment of the same optical fiber temperature sensor.

FIG. 3 is a side view showing another example of the measurement filter.

FIG. 4 is a diagram showing a conventional optical fiber temperature sensor.

[Explanation of symbols]

1 ... Device body, 2 ... Light emitting element, 3 ... Half mirror, 4 ...
Reference filter, 6, 8 ... Optical fiber, 10 ... Measurement photodetector, 12 ... Reference photodetector, 13 ... Temperature sensor, 1
5 ... Calculation unit.

Front Page Continuation (72) Inventor Kiyotaka Sugiyama 32-8 Kumano-cho, Itabashi-ku, Tokyo Chino Co., Ltd.

Claims (1)

[Claims] 1. A light emitting element (2) for emitting light of a predetermined wavelength as a light source, a reference filter (4) having a temperature-dependent transmittance and transmitting the emitted light of the light emitting element, and the reference. Photodetector (12) for receiving the transmitted light from the filter, an optical fiber (6) for guiding the light emitted from the light emitting element to an external measurement site, and the same material as the reference filter. A measuring filter (7) that is configured and is provided at the end of the optical fiber that is the measurement point, a measuring photodetector (9) that receives the transmitted light of the measuring filter, and the reference photodetector. And an arithmetic unit (15) for arithmetically outputting the temperature of the measurement site based on the difference between the transmitted light detected by the measurement photodetector, and the optical fiber temperature sensor.