JPS6029622A - Detecting method of temperature - Google Patents

Abstract

PURPOSE:To detect a temperature even if an emissivity of an object is unknown by installing a reference radiator to an incident end of an optical fiber. CONSTITUTION:A reference radiator 3 is made to approach a temperature measuring object 10, a radiated heat energy is received by the reference radiator 3, and the reference radiator 3 which has received it radiates a heat energy of a temperature corresponding to the received energy. This energy is transmitted from an incident end 2 of an optical fiber 1 to an emitting end 4 and emitted from the emitting end 4. Subsequently, this energy is devided into an energy which is made incident on a filter 6 of a center wavelength lambda1 and an energy which is made incident on a filter 7 of a center wavelength lambda2 by a half mirror 5, and signals which have transmitted through the respective filters 6, 7 are inputted separately to optical-electric transducers 8, 9, and converted to electric signals V1, V2. Both of these signals are operated by a two color operating device, a ratio of both signals is derived, and from this ratio, a temperature of the measuring object is derived.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature measurement method using an optical fiber, and provides a temperature measurement method that has high measurement accuracy, allows remote measurement, and is non-electromagnetic inductive.

There are various methods for measuring the temperature of solids, liquids, and gases, and electrical methods and optical methods are used in the industrial field.

The main electrical methods include thermocouple thermometers and resistance thermometers. The main optical methods include radiation thermometers and optical pyrometers.

Thermocouple thermometers or resistance thermometers have been put into practical use as thermometers, and there are no particular problems, but thermocouple thermometers do have the following drawbacks.

(a) The length of the detection element is several meters at most, and a cold junction is required to accurately measure temperature. Therefore, in order to send thermoelectromotive force to a distant place and display the temperature, it is usually necessary to use a compensating conductor.

(b) Since the detection element and compensation conductor are metal, they are subject to electromagnetic induction.

(c) Some types of thermocouples cannot be used depending on the atmosphere of the measurement location, and the range that can be stably measured industrially is limited to 1600°C at most.

Optical measurement methods detect the emitted light energy and measure the temperature, so they are suitable for measuring the surface temperature of solids, but are not suitable for measuring the ambient temperature of gases or fluids. Not suitable.

Also, with this method, the temperature cannot be determined unless the emissivity of the object is known.

The energy radiated from a certain object depends on the temperature of that object, and the spectral radiance of an ideal object called a perfect black body is expressed by the following equation.

Lo(λ1T)=2C1/input 5(e■■/λT-1)-
1 (1) Input = wavelength, T - temperature of object, C1, C2 are constants In an actual object, the spectral radiance varies depending on the material and surface condition, L (input 1T) = ε (λ) Lo (λ1T) (2 ). Here, ε(λ) is called emissivity.

The temperature of an object can be determined by obtaining information about this spectral radiance in some way.

This is the principle of a radiation thermometer.

In the optical fiber radiation thermometer shown in FIG. 2, the output electrical signal V is empirically given by the following equation.

V(T)=C■■■■Z(λ1)ε(λ)Lo(λT)
Sf(NA)2e-α(λ)z. D(λ)dλ(3) Here, τ(λ) = Spectral transmittance of lens etc. Sf = Core area of fiber NA = NA of fiber α(λ) = Spectral attenuation rate of fiber Z = Length of fiber D (λ) = O/E photoelectric conversion sensitivity C = unknown constant measured by measurement In reality, these parameters are not known accurately, so
For the entire system, a blackbody furnace (ε(λ)≈1) is used to calibrate the relationship between temperature T and voltage V (T), and a thermometer is provided with a scale.

When actually using a radiation thermometer based on the above principle, the emissivity ε(λ) of the actual object is different from that of a blackbody furnace, and ε(
λ)=1, but ε(λ)<1, and there is some error.

The present invention solves the above-mentioned difficulties of the electrical method and the optical method, and also makes it possible to detect the temperature without knowing the emissivity of the object.

The present invention will be explained below based on the drawings from FIG. 3 onwards. In Fig. 3, 1 is an optical fiber, 2 is an input end of the optical fiber, and 3 is an optical fiber.
is a reference radiator placed on the input end of the optical fiber, 4 is the output end of the optical fiber, 5 is a half mirror placed on the output end side of the optical fiber, 6 and 7 are filters, and 8.9 is an optical/electrical converter. It is.

The reference radiator 3 is made of heat-resistant metal, ceramics, or the like and is formed into a cylindrical shape or in any other suitable shape.

Among the two filters 6.7, one filter 6 has a center wavelength of λ1, and the other filter 7 has a center wavelength of λ2. The interval between the wavelength inputs 1λ2 is appropriately selected.

In the present invention, the reference radiator 3 is brought close to the temperature measurement object 10, and the reference radiator 3 receives the thermal energy radiated from the temperature measurement object 10, and the reference radiator 3 that has received the thermal energy absorbs the received energy. Make it radiate thermal energy at the corresponding temperature. Then, this energy is transmitted from the input end 2 of the optical fiber 1 to the output end 4 and is emitted from the output end 4.

Next, this energy is transferred to the center wavelength λ by a half mirror 5.
The energy incident on the filter 6 of 1 and the center wavelength input 2
The energy incident on the filters 7 and the signals transmitted through the respective filters 6.
．． 9 and convert it into electrical signals V1 and V2. These two signals are processed by a two-color arithmetic unit to determine the ratio of both signals, and the temperature of the object to be measured is determined from this ratio.

In this case, the output signals 1 and V2 of the optical-to-electrical converters 8 and 9 are expressed by the following equations.

■1=C1τ(λ)ε(λ1)Lo(λ1T)Sf(N
A) 2e-α(λ1)z. D(λ1)・dλ1(4)V
2=(1■(λ2)ε(λ2)Lo(λ2T)Sf(N
A) 2e-α(λ2)z. D(λ2). dλ2 (5) Taking this ratio gives the following equation.

C1 and C2 are constants, ε(λ1) and ε(λ2) are constants because they are known radiators, D(λ1) and D(λ2) are also constants specific to O/E, dλ1 and dλ2 are also filter constants, τ (λ1
), τ(λ2) is the transmittance of a half mirror, filter, etc. Although these are originally constant, they may fluctuate over a long period of time due to dust, misalignment of the optical axis, etc.

However, even if it fluctuates, the transmittance changes at a constant rate, so the ratio τ(λ1)/τ(λ2) remains constant. Similarly, even if the optical fiber losses α(λ1) and α(input 2) vary by the same amount, the ratio e−α(λ2)z/e−α(λ1)z does not vary. That is, the parameter C becomes a constant specific to the measurement system.

The transmission cloths dλ1 and dλ2 of the filter are usually narrow, 0.05μ or 0.1μ, and the resulting electrical signals V1, V
2 is small and difficult to measure low temperatures.

When the transmission width of the filter is widened, V=C2■λ'iλ'i■(λ)ε(λ)Lo(λ1T
)Sf(NA)2e-a(λ)z. Dα1dλ(8) Here, i corresponds to 1 or 2, λi and λi' are the wavelengths that define the filter's transmission range, and V1 and V2 are large values, so that a signal of sufficient size can be obtained and the electric circuit (amplifier, etc.) ) design becomes easier.

In a normal two-color thermometer, the wavelength dependence of ε (in) differs depending on the object, so λ must be able to detect the wavelength of radiation from any object. Therefore, ε(λ1)≒ε(λ2)
The wavelength is chosen to be λ1=in2 so that it can be approximated as follows. Therefore, it is inevitable that dλ1. dλ2 must be very close.

However, in the present invention, the reference radiator 3 is attached to the input end 2 of the optical fiber.
There is no such restriction because it is installed.

Since the present invention is constructed as described above, it has various effects as described below.

(a) Energy from the object to be measured is received by the reference radiator 3 attached to the input end 2 of the optical fiber 1, energy at a temperature corresponding to the radiant energy is radiated from the reference radiator 3, and this energy is transferred to the optical fiber. Since the temperature is transmitted from the input end 2 to the output end 3 of the sensor, accurate temperature measurement can be performed without being affected by the properties of the object to be measured. Furthermore, temperature measurement becomes possible even without knowing the thermal emissivity of the object.

(b) Although it loses the advantage of non-contact measurement compared to a normal radiation thermometer, it can measure the ambient temperature of gases and liquids.

(c) Since the light emitted from the emission end 3 is divided into two or more optical energies having different wavelength ranges, the ratio of these is determined, and the temperature of the measurement object 10 is detected based on the ratio. Highly reliable temperature measurement is possible without being affected by loss changes in optical fibers, etc.

(d) Since it uses optical fiber, there is no electromagnetic induction, and signals can be transmitted over long distances.

(e) By selecting materials for the reference radiator 3, optical fiber 1, etc., measurements at temperatures of 2000° C. or higher are possible.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the energy radiation state of an ideal object, Figure 2
The figure is an explanatory diagram of a conventional optical fiber radiation thermometer, and FIG. 3 is an explanatory diagram of the present invention. 1 is the optical fiber 2 is the input end of the optical fiber 3 is the reference radiator 4 is the output end of the optical fiber

Claims (4)

[Claims] (1) Radiant energy from the temperature measurement target is received by a reference radiator attached to the input end of the optical fiber, energy with a temperature corresponding to the radiant energy is radiated from the reference radiator, and this energy is transmitted from the input end of the optical fiber. The light is transmitted to the output end, the light emitted from the output end is divided into two or more optical energies with different wavelength ranges, the ratio of these is determined, and the temperature of the object to be measured is detected based on the ratio. temperature detection method. (2) The temperature detection method according to claim 1, characterized in that the wavelength interval between two or more optical energies having different wavelength regions is narrowed. (3) The temperature detection method according to claim 1, characterized in that the wavelength interval between two or more optical energies having different wavelength regions is widened. (4) The temperature according to claim 1, characterized in that the light emitted from the emission end is divided into light energy in the entire wavelength range and light energy in a part of the wavelength range within that range. Detection method.