JPS62118227A - Optical fiber temperature sensor - Google Patents

Abstract

PURPOSE:To measure exactly a temperature by a simple constitution, by exciting optically a phosphor whose light emitting intensity is varied by a temperature through an optical fiber, receiving a reflected light from the phosphor, and an excited light emitting light, and bringing a projector to a negative feedback control by a reflected light receiving output. CONSTITUTION:The light of a projector 5 is propagated through optical fibers 2, 4, and the phosphor 1 whose light emitting intensity is varied by a temperature is excited optically. Also, through the optical fibers 4, 3, a reflected light from the phosphor 1, and an excited light emitting light of the phosphor 1 are received by light receivers 10, 9, respectively. The output of this photodetector 10 is supplied through a negative feedback circuit 8 and the projector 5 is controlled, and the influences of a loss, a variation, etc., of an optical transmission line are prevented. In this way, a temperature is measured exactly by a light receiver 6 by a simple constitution, by which it is unnecessary to calculate, etc., a two wavelength output ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an optical fiber temperature sensor used to detect the temperature in a certain atmosphere, the temperature of the surface of an object, etc.

<Summary of the Invention> In this invention, in addition to the light receiver for detecting the light emitted by the phosphor due to excitation, a second light receiver is provided for detecting the excitation light reflected by the phosphor. , the amount of light received by this second receiver is negatively fed back to the emitter, so that even if the transmission efficiency of the optical transmission line fluctuates, it will not be affected by the temperature measurement value, and the configuration can be simplified and complicated. The present invention provides an optical fiber temperature sensor that does not require any complicated calculations.

<Background of the Invention> For example, when a phosphor that emits phosphorescence or a phosphor that emits fluorescence (hereinafter collectively referred to as "phosphor phosphor") is irradiated with excitation light, the phosphor becomes phosphor due to the excitation. It emits nine fluorescent lights, and the intensity of this phosphorescent light changes depending on the temperature of the surrounding environment in which it is placed. Therefore, it is possible to measure the ambient temperature by utilizing changes in the intensity of phosphor light due to temperature. Conventionally, this type of temperature measurement device uses optical fibers to propagate excitation light and phosphor light. A fiber temperature sensor was used. However, with this optical temperature sensor, for example, if the optical fiber is bent or stressed beyond a specified value,
There is a drawback that the loss in the transmission path of the excitation light and phosphorescent light increases and the transmission efficiency changes, making accurate temperature measurement difficult.

Therefore, as a method that does not affect the temperature measurement value even if the transmission efficiency changes, a two-wavelength measurement method has been proposed in which temperature is measured using light of two different wavelengths.

FIG. 5 shows one method. The illustrated device example is a floodlight 2
This is a method in which the ultraviolet rays generated in step 1 are irradiated to the phosphor 23 via an optical fiber 22, and the phosphor 23 generates two types of fluorescent light with different wavelengths by excitation, and each fluorescent light is generated separately. The light is received by the light receivers 24 and 25, and the signal processing unit 26
After determining the ratio of the respective amounts of received light, the temperature is calculated using a characteristic curve l as shown in FIG. In the figure, 27 to 29 are half mirrors.

FIG. 6 shows another method. The illustrated device example includes a first light projector 30 that emits excitation light of a certain specific wavelength involved in temperature measurement, and a second light projector 31 that emits reference light of another wavelength for monitoring fluctuations in transmission efficiency. configured using
The light from each floodlight 30, 31 is alternately connected to the optical fiber 32~
The phosphor 36 is irradiated through the phosphor 35 and the phosphor 36 is excited.
In this method, the light emitted from each of the optical fibers 6 and 6 is received by a light receiver 39 via optical fibers 37 and 38. After calculating the ratio between the amount of received excitation light and the amount of received reference light using the divider 40, the temperature is calculated using the same characteristic curve as described above. In the figure, 41 is a coupler, 42.43 is an optical connector, and 44.45 is a sample/hold circuit.

FIG. 7 shows yet another method. The illustrated example of the device is
The excitation light generated by the projector 46 is transmitted through optical fibers 47 and 48.
The phosphor 49 is irradiated through the phosphor 49 through excitation.
The fluorescent light (including afterglow) emitted by the phosphor 49 and the reflected light from the phosphor 49 of the excitation light are each received by the light receivers 50 and 51. After determining the ratio of the amount of received light, the temperature is calculated using the same characteristic curve as described above. In addition, in the figure, 53.54
is a filter.

In each of the above method examples, the temperature measurement value is not affected even if the loss in the transmission path fluctuates.The reason for this will be explained below, using the method shown in Figure 7 as an example, and Figure 9. Refer to and explain.

FIG. 9(1) shows that by bending the optical fiber 48,
FIG. 9 (2) shows a state where transmission loss α has occurred, and FIG.
The optical circuit in this state is represented by an equivalent circuit 55 similar to an electric circuit.

When the total amount of excitation light is expressed as EX, the amount of light when this excitation light reaches the surface of the phosphor 49 is (1-α)EX. Also, the absorbance of this phosphor 49 is a (where a<<
l), the excitation light contributing to the light emission of the phosphor 49 is a
(1-α)Ex, and the excitation light reflected by the phosphor 49 becomes (1a)(111M)Ex. Furthermore, l-a>
>a.

The phosphor 49 that has absorbed light emits light with a constant luminous efficiency η, and if the amount of light emitted is El, it is given by the following equation.

EII=η・a・(1−α)EX The light reflected by the phosphor 49 further suffers a loss α on the return trip, so the amount of light received by the light receiver 51 is (1a
)(1-α)” Ex.

Further, the fluorescent light emitted by the fluorescent body 49 also suffers a similar loss α on the return trip, and the amount of light received by the light receiver 50 is η·a·(1−α)2Ex. Therefore, due to the loss α caused by bending the optical fiber 48, η・a
- The amount of received fluorescent light fluctuates by twice (1-α), resulting in an error when converting this amount of received light into temperature.

In this way, the reflected light N (1
a) (1-α)” Ex and the amount of fluorescent light η・a・(1-α)2EX received by the optical receiver 50, it is related to the transmission loss α as shown in the following equation. The value is temperature-dependent.

(1-a) (1-α)”Ex 1-a 1η-
a-C1-α)”Ex 77・a 1・a However, in the above, the luminous efficiency η is a function of 0 to 2nd order,
There is a problem that such order calculations and furthermore, calculations of division thereof are extremely complicated processes, and moreover, in the case of the method example shown in FIG. 6, two projectors 30 and 31 are required.
This has drawbacks such as the circuit configuration becoming more complicated.

<Object of the invention> This invention is intended to solve the above problems,
It is an object of the present invention to provide an optical fiber temperature sensor that has a simple configuration that is not affected by temperature measurement values even if the transmission efficiency of an optical transmission line changes, and does not require any complicated calculations.

<Configuration and Effects of the Invention> In order to achieve the above object, the optical fiber temperature sensor of the present invention includes a phosphor whose emission intensity changes depending on the temperature, and irradiation of excitation light to this phosphor. and a first light source for detecting the light emitted by the phosphor upon excitation.
a second light receiver for detecting the excitation light reflected by the phosphor, and a light provided between the emitter and the phosphor and between the phosphor and both receivers. It was decided to provide an optical fiber for propagating the light, and a negative feedback circuit for feeding back the amount of light received by the second light receiver to the projector.

According to this invention, since the amount of light emitted by the projector is negatively fed back according to the increase or decrease of the excitation light reflected by the phosphor, the phosphor can be irradiated without being affected by fluctuations in loss in the transmission path. The amount of excitation light can be kept constant, allowing accurate temperature measurement. In addition, since the temperature is determined from the output of the first light receiver (one wavelength output), there is no need for calculations such as calculating the ratio of two wavelength outputs as in the conventional example, which greatly simplifies the calculation process. Since only one is required, it is possible to prevent the circuit from becoming complicated, and has a remarkable effect of achieving the purpose of the invention.

<Description of an Embodiment> FIG. 1 shows an embodiment of an optical fiber temperature sensor according to the present invention.

The illustrated example shows the temperature inside the atmosphere or on the surface of the object (
In the figure, the phosphor 1 is placed at a point (indicated by a broken line), and the phosphor 1 is fixedly attached to the distal end, and two branch parts 2.3 are formed at the proximal end in a roughly Y shape. a shaped optical fiber 4, and a light projector 5 comprising a light emitting diode disposed with its light projecting surface facing the proximal end surface of one branch 2 of the optical fiber 4;
The amount of light received by the first and second light receivers 6.7 consisting of photodiodes arranged with their light receiving surfaces on the proximal end surface of the other branch 3 of the optical fiber 4, and the second light receiver 7 is determined by the projector. 5, and a negative feedback circuit 8 for providing negative feedback to the
Light is propagated through the optical fiber 4 between the light emitter 5 and the phosphor 1, and between the phosphor 1 and both light receivers 6.7.

The phosphor 1 has a characteristic that the luminescence intensity changes depending on the temperature, and various types can be used regardless of the type. For example, in ultraviolet light excitation, Y, O□
S: Rare earth metal oxysulfide such as Eu, ZnS
: Ln (Ln is a general term for rare earth elements), SrS:Ln
For infrared light excitation, LnFz
: (Yb, Er), LnOF : (Yb
.

'F3. r ) , L i N d P a O+
z: Yb, etc. are used.

The light projector 5 is for irradiating the fluorescent body 1 with excitation light, and is, for example, a light emitting diode such as GaAs:Si.

The first photoreceiver 6 receives fluorescent light (
The second light receiver 7 is for detecting the excitation light reflected by the phosphor 1, and the light receiving surface of each of the light receivers 6 and 7 is provided with a filter 9. , 10 are deployed. The light reception signal from the first light receiver 7 is sent to a signal processing unit (not shown) such as a computer circuit, where the received light intensity-temperature characteristic curve is referred to and temperature conversion is performed, and the result is displayed on a display unit, etc. Output to. The light reception signal from the second light receiver 7 is sent to a negative feedback circuit 8, where negative feedback is applied to the amount of light emitted from the light projector 5 in accordance with fluctuations in the light reception signal, thereby compensating for losses in the transmission line.

FIG. 2 shows one embodiment of the negative feedback circuit 8.

The illustrated example circuit includes an amplifier 11 that amplifies the light reception signal of the second photoreceiver 7, a sample-and-hold circuit 12 that samples and holds the amplified output, and generates a monitor voltage ■ from the sampled and held output value. a variable resistor 13,
A variable resistor 14 that generates a constant voltage V0 and a monitor voltage Vm
and a constant voltage v0, an adder 15 generates a feedback voltage VFI from the following equation, and this feedback voltage VFR and a reference voltage V R
It includes a comparator 16 that compares the EF and determines the deviation.

■1. =α■6+βv0 (However, α, β<1.α+β=1) The deviation determined by the comparator 16 is input to the voltage-current conversion circuit 17, and this voltage-current conversion circuit 17 determines that the deviation is zero. The drive circuit 18 of the light projector 5 is controlled so that this occurs. According to this embodiment, the light emitter 5 by the negative feedback circuit 8
This has the effect of reducing the effect of self-heating, and this effect can be further enhanced by adjusting the capacitance of the capacitor 19 of the sample-and-hold circuit 12. In addition, in the figure, CPU (Central Process
The sampling unit 20 controls the operation of the negative feedback circuit 8 by providing a sampling pulse to the sample/hold circuit 12 and a drive pulse for the light projector 5 to the drive circuit 18 .

FIG. 3 is a timing chart of the negative feedback circuit 8, in which (1) is the waveform of the excitation light, (2) is the waveform of the reflected light of the excitation light, (3) is the sample position of the reflected light, (4) shows a waveform of fluorescent light (the attenuated portion indicates afterglow), and (5) shows a sample of fluorescent light. Note that the sample position of the reflected light can be set arbitrarily, but when the second light receiver 7 is sensitive to fluorescent light, the position tl in the figure is more desirable than t2, and the self-heating amount of the projector 5 is When is large, t2
The position of t2 is more desirable.

The light projector 5 is then pulse-driven, and the excitation light (see Fig. 3) is activated.
When the phosphor 1 is irradiated with light (see 1) through the optical fiber 4, the phosphor 1 is excited and emits fluorescent light (see FIG. 3 (4)), and further this fluorescent light and The excitation light reflected by the phosphor 1 (see FIG. 3 (2)) passes through the optical fiber 4 and is received by the light receiver 6.7. In this case, when there is a loss in the optical transmission path and the amount of light received by the second optical receiver 7 fluctuates, the negative feedback circuit 8 adjusts the amount of negative feedback corresponding to the fluctuation to the emitter based on the sampled and held value. 5, the above-mentioned loss is compensated. As a result, the first photoreceiver 6 receives an amount of fluorescent light that depends only on temperature without being affected by loss. ) over)
' After calculating the residual integrated light amount by integrating, by comparing this with the preset temperature characteristics of the remaining integrated light amount (shown in Figure 4), the temperature of the atmosphere in which the phosphor 1 is placed can be determined. is calculated.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an optical fiber temperature sensor according to an embodiment of the present invention, FIG. 2 is a block diagram showing an example of the circuit configuration of a negative feedback circuit, and FIG. 3 is a timing chart of the circuit in FIG. 2. , Figure 4 is a characteristic diagram used for temperature measurement, and Figure 5 is a characteristic diagram used for temperature measurement.
Figures 7 to 7 are diagrams showing the configuration of the conventional example, Figure 8 is a characteristic diagram used for temperature measurement for the conventional example shown in Figure 5, and Figure 9 is a diagram for explaining loss compensation in the optical transmission line. be. 1... Fluorescent material 4... Optical fiber 5.
...Emitter 6,7...Receiver 8...
・Negative feedback circuit Applicant: Tateishi Electric Co., Ltd.
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Claims (1)

[Scope of Claims] A phosphor whose emission intensity changes depending on temperature; a floodlight for irradiating the phosphor with excitation light; and a device for detecting light emitted by the phosphor upon excitation. a first light receiver, a second light receiver for detecting the excitation light reflected by the phosphor, and a second light receiver provided between the emitter and the phosphor and between the phosphor and both light receivers. An optical fiber temperature sensor comprising: an optical fiber for propagating the received light; and a negative feedback circuit for negatively feeding back the amount of light received by a second light receiver to a light emitter.