JP2000046655A - Radiation thermometer having light receiving loss compensation function and temperature measuring method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compensate for the transmission loss of an optical fiber in a service condition, and thereby provide a transmission loss compensation function capable of continuous measurements over a long time. SOLUTION: A partially reflective coating 2a is preliminarily applied to the reverse side of a condenser lens 2 and the preset light quantity P of pulse light having wavelength reflected due to the coating 2a at the time of using a radiation thermometer is inputted from the outside via an optical fiber for introduction to the condenser lens 2. As a result, light reflected from the reverse side of the condenser lens 2 sustains a transmission loss corresponding to back- and-forth across the optical fiber, and is measured after addition to ordinary measurement light. According to this construction, the light quantity ΔS of reflected light after sustaining the transmission loss corresponding to the back- and-forth of pulse light can be found from the changes S1 and S2 of the light receiving quantity due to the existence and non-existence of the pulse light. The transmission factor Tr of the optical fiber can be calculated from the value of ΔS for making compensation for the transmission loss.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation thermometer having a transmission loss compensating function and a method for measuring the temperature.

[0002]

2. Description of the Related Art Radiation thermometers that measure the temperature of the surface of an object in a non-contact manner by using the phenomenon that the amount of radiation light (radiation light) changes in accordance with a change in the temperature of the object have been used. For example, in temperature measurement of a turbine blade such as a gas turbine, there is an advantage that a large number of turbine blades rotating at a high temperature can be measured by one sensor in a non-contact manner.

Further, there has been developed an apparatus capable of precisely measuring the temperature of a minute portion by combining such a radiation thermometer with an optical fiber and transmitting the emitted light through the optical fiber. In this radiation thermometer using an optical fiber, as schematically shown in FIG. 4, a condenser lens 2 is installed near a measurement point 1 (for example, a turbine blade), and light collected by the condenser lens is It is led to the light receiving element 4 via the optical fiber 3,
The temperature is calculated from the output. In addition,
In this figure, 5 is a light receiving circuit, 6 is an arithmetic circuit, and 7 is an output device.

[0004]

In a radiation thermometer using an optical fiber, the transmission loss of the optical fiber changes due to a change in temperature, bending and aging. Therefore, even with a radiation thermometer that has been precisely calibrated (corrected) at the time of manufacture, if it undergoes temperature changes, bending, and changes over time, accurate measurements cannot be made, and disassembly or the like is performed again to recalibrate. There is a problem that it is necessary and cannot be applied to long-time continuous measurement.

The present invention has been made to solve such a problem. That is, an object of the present invention is to compensate for the transmission loss of an optical fiber in use.
Accordingly, it is an object of the present invention to provide a radiation thermometer having a transmission loss compensating function that enables continuous measurement for a long time, and a method of measuring the temperature.

[0006]

A partial reflection coating is applied to the back surface of the condenser lens (2) in advance, and when a radiation thermometer is used, a predetermined amount of pulse light of a wavelength P reflected by the coating is externally transmitted via an optical fiber. The light reflected by the back surface of the lens receives the transmission loss of the round trip of the optical fiber, and is added to the normal measurement light and measured. Therefore, from the changes S1 and S2 of the received light amount depending on the presence or absence of the pulse light, the light amount ΔS of the reflected light having received the transmission loss for the reciprocation of the pulse light can be calculated. From this, the transmittance Tr of the optical fiber is calculated to compensate the transmission loss. be able to. The present invention is based on such a new principle.

According to the present invention, a condensing lens (2) having a partially reflective coating on the back surface for condensing light emitted from a high-temperature object (1), and an optical fiber for transmitting the condensed light And (3) a photoelectric conversion device (1) that converts the transmitted light amount into an electric signal and calculates the temperature T of the high-temperature object from the electric signal.
0), wherein the photoelectric conversion device comprises: a light receiving element (4) for converting transmitted light into a current signal; a light receiving circuit (5) for converting the current signal into a voltage signal; Light-emitting element (12) that emits a predetermined amount of light P at a desired wavelength, a driving circuit (13) that causes the light-emitting element to emit light in pulses, and an optical coupling element (14) that couples the light-emitting element and the light-receiving element to an optical fiber. And a sampling circuit (15) for acquiring a light receiving signal in synchronization with ON / OFF of the light emitting element
And the voltage signal S1, from the light receiving circuit at each timing.
A radiation thermometer having a transmission loss compensating function, comprising: an arithmetic circuit (16) for compensating transmission loss from S2.

According to a preferred embodiment of the present invention, the partial reflection coating is a coating which selectively reflects a specific wavelength λ 1, and the light of the light emitting element (12) is a pulse light of a wavelength λ 1. .

Further, according to the present invention, a condenser lens (2) is provided in the vicinity of the high-temperature object (1), and light condensed by the condenser lens is received by a light receiving element (3) via an optical fiber (3). In the temperature measurement method for calculating the temperature T of the high-temperature object from the received light amount according to 4), a partial reflection coating is applied to the back surface of the condenser lens, and a pulse light of a predetermined light amount P having a wavelength reflected by the partial reflection coating is applied. There is provided a temperature measurement method characterized in that the light is incident on an optical fiber so as to be guided to a condenser lens (2), and transmission loss is compensated from changes S1 and S2 of a received light amount depending on the presence or absence of pulsed light.

According to the apparatus and method of the present invention, the light emitting element (12), the driving circuit (13) and the optical coupling element (14).
As a result, a pulse light having a predetermined light amount P having a wavelength reflected by the coating when the radiation thermometer is used is guided to the back surface of the condenser lens (2) via the optical fiber, and the optical coupling element (14), the sampling circuit (15), The light receiving element (4) and the light receiving circuit (5) add the reflected light from the back surface of the lens to the transmitted light amount S2 of the condenser lens, measure the amount, and calculate the arithmetic circuit ( According to 16), the transmission loss ΔS for the reciprocation of the pulse light can be calculated. From this, the transmittance Tr of the optical fiber can be calculated to compensate for the transmission loss.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. In the drawings, common members are denoted by the same reference numerals, and redundant description is omitted. FIG. 1 is an overall configuration diagram of a radiation thermometer according to the present invention. As shown in the figure, the radiation thermometer of the present invention comprises a condenser lens 2, an optical fiber 3, and a photoelectric conversion device 10 that converts a transmitted light amount into an electric signal and calculates a temperature T of a high-temperature object from the electric signal. Is done. The condenser lens 2 is installed near the hot object 1 (for example, a turbine blade).
The light emitted from the optical fiber 3 is focused on the end face of the optical fiber 3. Although the condensing lens 2 is shown as a single convex lens in this figure, it may be a compound lens composed of two or more lenses. Further, although the protective glass of the condenser lens 2 is not shown in this figure, such a protective glass may be used. Further, according to the present invention, the partial reflection coating 2a is applied to the back surface (the right surface in the figure) of the condenser lens 2. It is preferable that the partial reflection coating 2a selectively reflects a specific wavelength λ1. However, the present invention is not limited to this, and may reflect a wide range of wavelengths. The optical fiber 3 transmits the light condensed by the condenser lens 2 to the photoelectric conversion device 10.
The optical fiber 3 is configured by bundling a plurality of (for example, three) ultrafine fiber wires having a diameter of about 0.4 mm, for example, and has flexibility.

As shown in FIG. 1, the photoelectric conversion device 10 includes a light receiving element 4, a light receiving circuit 5, a light emitting element 12, a driving circuit 13,
Optical coupling element 14, sampling circuit 15, and arithmetic circuit 1
Consists of six. The light receiving element 4 converts the light transmitted through the optical fiber 3 into a current signal. The light receiving circuit 5 converts the current signal converted by the light receiving element 4 into a voltage signal. Therefore, the combination of the light receiving element 4 and the light receiving circuit 5 allows the optical fiber 3
Can be converted into a voltage signal (voltage level), and the voltage signal is processed by an appropriate arithmetic circuit to calculate the temperature of the high-temperature object 1 as in the related art. it can.

The light emitting element 12 has a partially reflective coating 2
A light having a predetermined light amount P having a wavelength reflected by a is emitted. If the partial reflection coating 2a selectively reflects a specific wavelength λ1, the same wavelength λ1
However, when the partial reflection coating 2a reflects a wide range of wavelengths, any wavelength may be used as long as it is in a narrow wavelength range. The drive circuit 13 causes the light emitting element 12 to emit light in a pulse shape. Further, the optical coupling element 14
Connects the light emitting element 12 and the light receiving element 4 to the optical fiber 3. With this configuration, it is possible to irradiate the condenser lens 2 with pulsed light from the light emitting element 12 via the optical fiber 3 and simultaneously receive the reflected light and the transmitted light together, and measure the amount of light received by the light receiving element 4 can do.

The sampling circuit 15 acquires a light receiving signal from the light receiving element 4 in synchronization with ON / OFF of the light emitting element 12. Further, the arithmetic circuit 16 determines whether the light emitting element 12 is ON / OFF.
The transmission loss is compensated from the voltage signals S1 and S2 from the light receiving circuit at each OFF timing.

FIG. 2 shows the principle of the present invention. In (A), if the transmittance of the partial reflection coating 2a is Tr2 with respect to the light amount S0 of the radiated light from the high temperature object 1, the light amount of the radiated light input to the optical fiber 3 is Tr2 * S0. Further, assuming that the transmittance of the optical fiber 3 is Tr, the light amount S2 measured by the light receiving element 4 is Tr2 × S0 × Tr, and S0 = S2 / (Tr2 × Tr). . (Equation 1) holds. That is, since the transmittance Tr2 of the partial reflection coating 2a is known by measurement at the time of manufacturing, if the transmittance Tr of the optical fiber 3 is known, it is possible to calculate the light amount S0 of the emitted light and compensate for the transmission loss. Understand.

In FIG. 2B, the radiation thermometer (light emitting element 12, drive circuit 13, optical coupling element 14) is used to collect a pulse light of a predetermined light amount P having a wavelength reflected by the partial reflection coating 2a. 2 leads to an optical fiber 3
If the light quantity of P × Tr multiplied by the transmittance Tr of the light enters the partial reflection coating 2a and the reflectance of the partial reflection coating 2a is Fr, the light quantity of P × Tr × Fr is reflected, and the transmission of the optical fiber 3 is further performed. P × Tr ² × Fr multiplied by the rate Tr
= ΔS. . The light amount of (Equation 2) is added to the transmitted light amount S2 of (A), and is measured by the light receiving element 4 as the light amount S1. Therefore, S2 + ΔS = S1. . (Equation 3) holds. Here, S2, S1, and P are known or measurable, respectively, and the reflectance Fr of the partial reflection coating 2a is also known by measurement at the time of manufacturing. Therefore, the transmittance Tr of the optical fiber 3 is actually measured from Expression 2. Can be.

By using the above-mentioned FIG. 2 and (Equation 1) to (Equation 3), the pulse light of the predetermined light amount P is
The transmission loss can be compensated from the changes S1 and S2 in the amount of received light depending on the presence or absence of pulsed light. That is, the light emitting element 12, the driving circuit 13, and the optical coupling element 14 guide the pulse light of a predetermined light amount P having a wavelength reflected by the coating when the radiation thermometer is used to the back surface of the condensing lens 2 via the optical fiber. Coupling element 1
4, sampling circuit 15, light receiving element 4, and light receiving circuit 5
, The reflected light from the back surface of the lens is added to the transmitted light amount S2 of the condenser lens, and measured. Can be calculated (Equation 3), the transmittance Tr of the optical fiber can be calculated from this (Equation 2), and the transmission loss can be compensated (Equation 1), and this can be displayed on a CRT or the like by the output device 7, or otherwise. Can be output to a control device or the like.

FIG. 3 is a diagram showing the relationship between input wavelength and intensity (light quantity) in the radiation thermometer of the present invention. In this figure, (A) shows a case where the partial reflection coating 2a is a coating that selectively reflects a specific wavelength λ1, and the light emitting partial element 12 emits light of a predetermined light amount P of the wavelength λ1. . In this case, the light amount S0 of the radiated light from the high-temperature object 1 is usually, for example, from 750 nm to 1550 n.
Although the light is distributed over a wide range up to m, light having a specific wavelength λ1 (for example, about 1300 nm) is reflected by the coating 2a, resulting in a loss. However, since the loss area due to the coating 2a is very narrow as compared with the entire wavelength region, there is almost no influence on the radiation thermometer, and the loss in the entire wavelength region is small, so that highly accurate temperature measurement can be performed. In addition, since the coating 2a affects only the specific wavelength λ1, the coating 2a is used when another wavelength (for example, λ2) is used for another purpose or when high precision is required in a wavelength portion other than the wavelength λ1. Can be reduced to a negligible or almost negligible level.

FIG. 3B shows a partial reflection coating 2a.
Is a coating that uniformly reflects a wide range of wavelengths, and shows a case where the light emitting sub-element 12 emits light of a predetermined light amount P of wavelength λ1. In this case, the light amount S0 of the radiated light from the high-temperature object 1 is lost because light of a wide range of wavelengths (for example, a wavelength of 750 nm to 1550 nm) is reflected by the coating 2a. However, if the reflectance (transmittance Tr) of the coating 2a is measured in advance, the temperature can be similarly measured by the above-described method. In the above description, the conversion gain η in the photoelectric conversion of the light receiving element 4 and the light emitting element 12 is ignored (assumed to be 100%). However, in an actual apparatus, such a conversion gain η is known and included. It is good to apply an expression.

The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention. For example, the present invention can be applied to surface temperature measurement of general high-temperature objects other than gas turbine blades.

[0021]

As described above, the radiation thermometer having the transmission loss compensating function and the temperature measuring method according to the present invention can compensate for the transmission loss due to the attachment on the lens surface.
And so on.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a radiation thermometer according to the present invention.

FIG. 2 is a principle diagram of the present invention.

FIG. 3 is a diagram showing the relationship between input wavelength and intensity (light quantity) in the radiation thermometer of the present invention.

FIG. 4 is a schematic diagram of a conventional radiation thermometer using an optical fiber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 High temperature object 2 Condensing lens 2a Partial reflection coating 3 Optical fiber 4 Light receiving element 5 Light receiving circuit 6 Arithmetic circuit 7 Output device 10 Photoelectric converter 12 Light emitting element 13 Drive circuit 14 Optical coupling element 15 Sampling circuit 16 Arithmetic circuit

Claims (3)

[Claims] 1. A partially reflective coating is applied to the back surface,
And a condenser lens (2) for condensing light emitted from the high-temperature object (1), and an optical fiber (3) for transmitting the condensed light
And a photoelectric conversion device (10) that converts the transmitted light amount into an electric signal and calculates the temperature T of the high-temperature object from the electric signal. The photoelectric conversion device converts the transmitted light into a current signal. ), A light receiving circuit (5) for converting the current signal into a voltage signal, a light emitting element (12) for emitting a predetermined amount of light P having a wavelength reflected by the partial reflection coating, and a light emitting element for emitting the pulsed light. A driving circuit (13), an optical coupling element (14) for coupling the light emitting element and the light receiving element to the optical fiber, a sampling circuit (15) for acquiring a light receiving signal in synchronization with ON / OFF of the light emitting element, A radiation thermometer having a transmission loss compensating function, comprising: an arithmetic circuit (16) for compensating transmission loss from voltage signals S1 and S2 from the light receiving circuit at the timing. 2. The method according to claim 1, wherein the partial reflection coating is a coating that selectively reflects a specific wavelength λ1, and the light of the light emitting element is pulsed light having a wavelength of λ1. 2. The radiation thermometer according to 1. 3. A condensing lens (2) near the hot object (1), and the light condensed by the condensing lens is guided to a light receiving element (4) via an optical fiber (3). In a temperature measuring method for calculating a temperature T of a high-temperature object from an amount of received light, a partial reflection coating is applied to a back surface of a condenser lens, and a pulse light of a predetermined light amount P having a wavelength reflected by the partial reflection coating is collected. A temperature measurement method characterized in that the transmission loss is compensated from changes S1 and S2 in the amount of received light depending on the presence or absence of pulsed light.