CA1158888A - Optical fiber temperature sensor - Google Patents
Optical fiber temperature sensorInfo
- Publication number
- CA1158888A CA1158888A CA000386591A CA386591A CA1158888A CA 1158888 A CA1158888 A CA 1158888A CA 000386591 A CA000386591 A CA 000386591A CA 386591 A CA386591 A CA 386591A CA 1158888 A CA1158888 A CA 1158888A
- Authority
- CA
- Canada
- Prior art keywords
- optical fiber
- fiber element
- temperature
- thermal radiation
- self
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K3/00—Thermometers giving results other than momentary value of temperature
Abstract
21 49,191 ABSTRACT OF THE DISCLOSURE
The self-generating thermal radiation properties of an optical fiber element are employed to determine the temperature, location and length of a hot spot, or region, of an object.
The self-generating thermal radiation properties of an optical fiber element are employed to determine the temperature, location and length of a hot spot, or region, of an object.
Description
1 49,191 OPTICAL FIBER TEMPERATURE SENSOR
BACKGROUND OF THE INVENTION
While it is a critical requirement in the opera-tion of electrical machinery, such as generators and transformers, to monitor the development of hot spots, or regions, in order to avoid equipment failure, measuring techniques employed to date have suffered due to their sensitivity to ambient, thermal and magnetic conditions, as well as the difficulty in gaining access to the equip-ment by conventional methods.
SUMMARY OF THE INVENTION
There is disclosed herein with reference to the accompanying drawing a novel technique employing an opti-cal fiber made of conventional fiber materials to deter-mine the location, length and temperature of a hot region anywhere along the length of the fiber.
The technique is based on the observation that all materials, when heated, will emit thermal radiation, in an amount dependent on the temperature, emissivity of the fiber material, and the spectral range of wavelength being observed. For perfectly transparent material, the emissivity is zero, and no thermal radiation is produced.
However, even highly transparent materials, such as glass-es that are used to make optical fibers, have a finite emissivity in the near infrared, where thermal radiation for the temperature range from about 100C to 1000C is relatively pronounced. Furthermore, glasses such as silica transmit relatively well to wavelengths near 4 ....
:
- ~ . ~ ..
: , ; ~ , ,&~8
BACKGROUND OF THE INVENTION
While it is a critical requirement in the opera-tion of electrical machinery, such as generators and transformers, to monitor the development of hot spots, or regions, in order to avoid equipment failure, measuring techniques employed to date have suffered due to their sensitivity to ambient, thermal and magnetic conditions, as well as the difficulty in gaining access to the equip-ment by conventional methods.
SUMMARY OF THE INVENTION
There is disclosed herein with reference to the accompanying drawing a novel technique employing an opti-cal fiber made of conventional fiber materials to deter-mine the location, length and temperature of a hot region anywhere along the length of the fiber.
The technique is based on the observation that all materials, when heated, will emit thermal radiation, in an amount dependent on the temperature, emissivity of the fiber material, and the spectral range of wavelength being observed. For perfectly transparent material, the emissivity is zero, and no thermal radiation is produced.
However, even highly transparent materials, such as glass-es that are used to make optical fibers, have a finite emissivity in the near infrared, where thermal radiation for the temperature range from about 100C to 1000C is relatively pronounced. Furthermore, glasses such as silica transmit relatively well to wavelengths near 4 ....
:
- ~ . ~ ..
: , ; ~ , ,&~8
2 49,191 microns, thus rendering the materlal re~pon~ive to rela-tlvely low temperatures, wherein the response can be detected at the end of the flber.
The use of optical fibers in te~perature senslng appllcatlons are described in U.S. Patent~ 4,151,747 and 4,203,326 which were ls~ued to the preæent inventors.
In the conventlonal application of optical fibers to pyrometry the ~unct$on of the fiber 18 simply to transmit an optical signal which is lntroduced into one end of the fiber to the other end. In the technique disclosed hereln, thermal radiation is selr-generated wlthin the ~iber itseli, 80 that if the fiber is ln ther-mal equilibrium with its surroundings, determining the ~iber temperature from its radiation characteristics will serve to determine the temperature o~ the surroundings as well. For a relatlvely long length o~ a ~iber element, thermal radiation will emanate ~rom all portions o~ the riber, which may be at widely dif~erent temperatures, and therefore emit radiation of greatly dif~erent spectral composition. However, the total power radiated at all wavelengths increases very dramatically with in¢reasing temperature 80 the ~pectral composition detected at the end Or the fiber element will be essentially determined by the highest temperature along the riber, and will be largely independent Or the length Or the hot reglon.
mus, this ~iber element conflguration is well suited for hot-spot, or r~egion, detection o~ an ob~ect where it may be o~ little importance to know where along the ~iber the hot region o~ the obJect has occurred. While the speciric embodiment discussed derlnes the monitored obJect to be electrical machlnery, the obJect belng monitored by the elongated optlcal ~iber temperature sensor may be gas or nuid environment.
Numerous materlal selectlon~ are avallable, and numerous physlcal con~lguratlons can be employed to meet a gi~en appllcation. The material selection for the fiber ~ ~ J
~, ., .
.;~
. . . .
.
. -
The use of optical fibers in te~perature senslng appllcatlons are described in U.S. Patent~ 4,151,747 and 4,203,326 which were ls~ued to the preæent inventors.
In the conventlonal application of optical fibers to pyrometry the ~unct$on of the fiber 18 simply to transmit an optical signal which is lntroduced into one end of the fiber to the other end. In the technique disclosed hereln, thermal radiation is selr-generated wlthin the ~iber itseli, 80 that if the fiber is ln ther-mal equilibrium with its surroundings, determining the ~iber temperature from its radiation characteristics will serve to determine the temperature o~ the surroundings as well. For a relatlvely long length o~ a ~iber element, thermal radiation will emanate ~rom all portions o~ the riber, which may be at widely dif~erent temperatures, and therefore emit radiation of greatly dif~erent spectral composition. However, the total power radiated at all wavelengths increases very dramatically with in¢reasing temperature 80 the ~pectral composition detected at the end Or the fiber element will be essentially determined by the highest temperature along the riber, and will be largely independent Or the length Or the hot reglon.
mus, this ~iber element conflguration is well suited for hot-spot, or r~egion, detection o~ an ob~ect where it may be o~ little importance to know where along the ~iber the hot region o~ the obJect has occurred. While the speciric embodiment discussed derlnes the monitored obJect to be electrical machlnery, the obJect belng monitored by the elongated optlcal ~iber temperature sensor may be gas or nuid environment.
Numerous materlal selectlon~ are avallable, and numerous physlcal con~lguratlons can be employed to meet a gi~en appllcation. The material selection for the fiber ~ ~ J
~, ., .
.;~
. . . .
.
. -
3 49,191 can be such that the spectral transmission of the material will provide optimum performance of the hot spot detector for a preferred temperature range and fiber length.
DESCRIPTION OF THE DRAWINGS
The invention will become more readily apparent from the following exemplary description in connection with the accompanying drawings:
Figures lA-~F are schematic illustrations of an optical fiber hot spot detector embodiments employing the inventiOn;
Figs. 2-7 are graphical illustrations of the operation of the detector concept of Figs. lA-~E.
DESCRIPTION OF THE PREFERRED INVENTION
An analysis of the operation of a temperature sensing fiber device TS in accordance with this invention can be made on the basis of the well-known theory of black body radiation and the light guiding properties of optical fibers. A schematic of an optical fiber F in which there is a high temperature region HR emitting thermal radiation in response to a corresponding hot region HS of an adja-cent object EM, i.e. electrical machinery, is shown in Fig lA. As indicated above, the optical fiber F does not merely transmit radiation from a glowing, opaque surface, but rather the fiber F becomes, in effect, a black body cavity whose temperature can be determined. Among the advantages of this type of sensor, are the distributed sensitivity of the optical fiber F, i.e., the temperature of a hot spot, or region, located anywhere along the optical fiber F can be determined. No light source is required since only thermal radiation is detected.
The total power density radiated from the sur-face of a heated body, between the wavelengths ~O and Af is: p = ~ ~(A.T) A1 [eAT _ ~ dA watts/cm2 (1) . ~ ~
., .
.: , ' , .:
: :-
DESCRIPTION OF THE DRAWINGS
The invention will become more readily apparent from the following exemplary description in connection with the accompanying drawings:
Figures lA-~F are schematic illustrations of an optical fiber hot spot detector embodiments employing the inventiOn;
Figs. 2-7 are graphical illustrations of the operation of the detector concept of Figs. lA-~E.
DESCRIPTION OF THE PREFERRED INVENTION
An analysis of the operation of a temperature sensing fiber device TS in accordance with this invention can be made on the basis of the well-known theory of black body radiation and the light guiding properties of optical fibers. A schematic of an optical fiber F in which there is a high temperature region HR emitting thermal radiation in response to a corresponding hot region HS of an adja-cent object EM, i.e. electrical machinery, is shown in Fig lA. As indicated above, the optical fiber F does not merely transmit radiation from a glowing, opaque surface, but rather the fiber F becomes, in effect, a black body cavity whose temperature can be determined. Among the advantages of this type of sensor, are the distributed sensitivity of the optical fiber F, i.e., the temperature of a hot spot, or region, located anywhere along the optical fiber F can be determined. No light source is required since only thermal radiation is detected.
The total power density radiated from the sur-face of a heated body, between the wavelengths ~O and Af is: p = ~ ~(A.T) A1 [eAT _ ~ dA watts/cm2 (1) . ~ ~
., .
.: , ' , .:
: :-
4 49,191 where the emissivity, ~, may be a function of both wave-length,A, and temperature, T, and Cl = 3.741 x lO 12 watts/cm2 C2 = 1.439 cm K.
S The emissivity, and the fraction of total emit-ted radiation guided down the optical fiber F is readily determined by a commercially available microprocessor circuit MP in accordance with equation (l) above.
The optical fiber F of Fig. lA consists of a fiber core CR surrounded by a fiber clad CL. Typically, the fiber core CR may be quartz or borosilicate glass while the cladding CL may typically be plastic or air.
The temperature of the ambient environment E
surrounding the optical fiber F results in thermal radia-tion emanating from all portions of the fiber F. Only theradiation that is emitted in such a direction that strikes the boundary B of the core CR of the fiber F at angles greater than the critical angle, ~c' will be guided by the fiber F to an optical detector DE, located at one end of the fiber F. The optical detector DE, which may typically be a silicon or germanium photodiode, converts the optical thermal radiation energy into an equivalent electrical signal. Radiation incident at smaller angles than the critical angle will escape from the fiber F. The output signal of the detector DE can be used for display or control purposes or can be supplied to the microprocessor circuit MP for processing in accordance with a predeter-mined mathematical expression.
THEORY OF OPERATION
The contribution to the radiation power from a thin slab of material of a thickness d~', of Fig. lA, is:
,. . .
, :. . ;
. ~ , - -49,191 dP =aWDd~' where a is the absorption, or loss, constant and W is the integral of the planck function, Cl LeAT ~ ~ dA.
If this radiation must travel a distance D' to the end of the hot region HR, then some of this radiation will be absorbed, and remaining radiation will be represented as follows:
dP =awe~a~ d~.
The total power density from the entire hot region HR of length ~ is P = I We~ae dQ~ = W(l-e-a~ (2) The emissivity is, by definition, the factor by which the planck integral is multiplied to get the total radiated power density, ~ (1 -a) (3) In the usual optical fiber situation, with a localized hot region, a ~ < ~1 ( 4) and ~ae, so that the emissivity increases linearly with the length of the hot region HR. In the other extreme, where aQ~> 1, ,~1, ., ..... . .. .
6 49,191 and the total radiation is independent of the extent of the hot region HR, the optical fiber behaves essentially as a black-body cavity. Since the absorption constant must be non-negligible, i.e., relatively high loss, in S order for thermal radiation to be generated, the signal will be attenuated in the cool length KL of the optical fiber F between the hot spot HR and the detector DE, by the factor e-aL
where L is the distance between the hot spot HR and the detector DE. Thus, the choice of the absorption constant will be dictated by a selected combination of the above factors. Only the radiation that is emitted in such a direction that strikes the boundary B of the core CR of the fiber F at angles greater than the critical angle, ~c' will be guided by the optical fiber F to the detector DE.
Radiation incident at angles smaller than the critical angle will escape from the optical fiber F. The critical angle, determined by the refractive indices n of the core CR and the cladding CL, is -1 nclad (5) c ncore and the fraction of the total radiation that falls within the angular aperture of the fiber F is shown to be equal ;
to:
1 - s~n ~c = 1 - ~ (6) core Taking into account all the above factors, -assuming an optical fiber F wherein the diameter D of the core CR corresponds with core diameter CD, the total radiant power propagated down the fiber F in the wave-length interval Ao to Af is . ,... ~ . . .. . . . , .. , . ,.. , ,- ~. , . ,. ,. ,. ..... , , , -:
7 49,191 (77,D2) ~ nC1ad) (1 -a~) - a,e ~ C1 [AT ~ dA tt (7) where for simplicity, it is assumed that a is not a func-tion of wavelength over the range Ao to Af, and is thus removed from the integral expression above. The wave-length range will depend upon the detector DE employed, and to be more precise, the integrand should be multiplied by the spectral response function of the detector DE. For the purposes of discussion, it will be assumed that the spectral response is flat. The detector DE can be conven-iently implemented through the use of a silicon or german-ium photodiode, with long wavelength cut-offs of 1.0 micron and 1.8 microns, respectively. For low temperature applications, a lead sulfide detector can be employed, which has a long wavelength cut-off of 2.9 microns. The significant effects of temperature and long wavelength cut-off, A c' on the black body radiation function where the above typical detector materials are employed is apparent from Table 1.
. ~ . ' ~, . .
~r;~
8 49,191 TABLE I
BLACK BODY RADIATION POWER
T P~c = 1~m) w/cm P(A = 1 8~m)h'/Cm P(A = 2.9,~m) /
100C 2.8 x 10 14 1.17 x 10 9.33 x 10 5 200 1.16 x 10 10 1.3$ x 10 5 2.04 x 10 3 300 2.72 x 10 8 3.18 x 10 1.61 x 10 400 1.31 x 10 6 3.01 x 10 3 7.26 x 10 2 500 2.36 x 10 1.64 x 10 2 2.29 x 10 600 2.24 x 10 4 6.24 x 10 2 5.73 x 10 1 700 1.36 x 10 3 1.84 x 10 1 1.25 In order to evaluate the expected signal from the combination of the optical fiber F and the detector DE
it is necessary to assign values to the remaining para-meters in equation 7 above. The most critical fiber parameter is the absorption constant, which is determined by maximizing the term F = (1 e~a~ e~
The result of this maximization is am ' ~ ~ e n ~ (8) 20 which is a relatively insensitive function of ~ and L over the range of values of interest for monitoring temperature in electrical machinery. Typical values for ~ and L are about 10 centimeters and 3 meters, respectively, which result in ',.; :
': . . ~ , , . . .
.
fY~3 9 49,191 am = 3.28 x lO cm , or 1423 db/km, and F = 1.21 x lO 2.
The measured signal increases linearly with the cross-sectional area of the core CR of the fiber element F, so it is advantageous to use as large a diameter fiber F as possible. The largest diameter standard communications quartz fiber is 1 mm., corresponding to an area of -3 2 For an air clad (nClad core (nCOre = 1.4g), having a critical angle ~c of 42, the calculated output signal power from the fiber F corre-sponds to:
P(T) = 3 08 X 10 5 ~ A1 LAT ~ dA watts (9) The minimum detectable temperature will be set by the noise equivalent power NEP of the particular detector used, and this will, in general, scale with the area of the detector DE. For optimized detection, the sensitive area of the detector DE should approximate the cross-sectional area of the core CR of the fiber F and be in direct contact so as to minimize transmittal losses.
Table II below, shows the NEP for several 1 mm. diameter detectors operating at room temperature, and the minimum detectable temperatures for each as calculated in accord-ance with equation 9 above. Both lead sulfide and lead selenide photodiodes are capable of responding to tempera-tures below room temperature, but this would require t~etemperature of the surroundings to be at a significantly lower temperature in order not to mask the hot region HR.
:
.
49,191 TABLE II
MINIMUM DETECTABLE TEMPERATURES FOR
SEVERAL TYPES OF DETECTORS WITH
Minimum Detectable TypeA cutoff (~m) NEP (I~/Hz ) Temperature Silicon 1.0 5 x 10 14 240C
Germanium1.8 1o~l2 80C
Lead Sulfide 2.9 10 11 <room temp.
Lead Selenide 4.5 10-1 <room temp.
The choice of a loss constant ~ to optimize response of the fiber F for any particular application will depend upon the expected range of values of ~, L and T. Operation at high temperatures, i.e., in excess of 300C, can be readily implemented with relatively low loss fibers because the value of the planck integral is large.
For low temperatures, i.e., below 300C, a must be chosen more carefully. A summary of the values of the function F
(a, ~, L) is shown in Fig. 2 which is a plot of signal variation with absorption, or ioss, consthnt a for several values of L, and a hot region HR having a length of 10 cm.
It is noted from Fig. 2 that for a values approaching about 10 2cm 1, F is a fairly linear function of , for~
values up to about 50 cm. These curves illustrate that for a range of L from about 1 meter to 5 meters, the optimum a is about 3 x 10 3cm 1 (or about 1000 db/km).
This corresponds to a very lossy communications fiber, the loss constant of low loss fiber typically lies in the range of about 1 to 10 db/km. For distances of less than one meter, greater sensitivity can be achieved by using fibers of even higher loss, i.e., 2 x 10 2cm l. Quartz fiber of such high loss corresponds to that used in glass-blowing operations.
. ~
~; ~
: , , -B
11 49,191 The optical signal from such a high loss fiberlength HLF can be transmitted over a long distance by coupling the high loss fiber length HLF to a low loss fiber length LLF outside of the environmental region ER to be monitored via a suitable fiber coupler FC. This com-bined fiber length FL is schematically illustrated in Fig.
lB. An advantage of employing a fiber of a relatively small a is that the response is essentially independent of L as can be seen in Fig. 3. In this illustration, it is apparent that for a < lo cm 1, F varies only a few percent between zero and 5 meters. Clearly, it may be advantageous to use the lower loss fiber if the tempera-tures are sufficiently high to produce an adequate signal so that variations of F and L can be ignored. A potential high temperature optical fiber material is sapphire. Low temperature applications can employ plastic fibers or chalcognide qlasses, i.e., As2S3, which transmit into the far infrared.
If a fiber element F', as illustrated in Fig.
lC, having a high value of loss constant and disposed adjacent to the object EM, is chosen to give high sensi-tivity, it is possible to determine the distance from the hot region HR, corresponding to a heated region of the object EM, to the end of the fiber element F' by making a measurement of the optical signal at both ends of the fiber element F'. Assuming the location of a hot region HR' at a distance Ll from one end of the fiber and a distance L2 from the other end o the fiber, the known fiber total length is L = Ll + L2. The signals Sl and S2 measured by two identical detectors DEl and DE2, respec-tively, located at either end of the fiber element F' are as follows:
12 49,191 Sl = e aLlll _ e-a~ (G) (planck integral) (10) S2 = e aL2~1 - e aS (G) (planck integral) where G contains the fiber geometry factors. From the ratio of the two signals Sl and S2 Sl = e~ a (Ll-L2) (11) the distance Ll is easily shown to be:
Ll = ~L ~ 2a ~n (S-2) (12) The ratio of equation (11) and the computation of the hot region location of equation (12) is readily accomplished by the microprocessor MP. Thus, if it is desired to know the location of a hot region HR' along a fiber element F', it will be advantageous to use a high loss fiber material in order to generate a large difference between the sig-nals Sl and S2. The relationship between the signal ratio and the fiber loss constant for a 500 cm. long fiber element is illustrated in Fig. 4 for values of Ll ranging from L/2 to L.
It is possible to make an estimate of the tem-perature, even with limited knowledge of the length ~ of the hot spot HR due to the fact that the radiated power increases exponentially with temperature, but only linear-ly with the length factor ~. The relative radiated powers for hot spots having lengths ranging over a factor of 8 are shown in Fig. 5. For temperatures below 300C, the uncertainty in temperature is about + 25C, and this uncertainty increases with increasing temperature. If only an approximation of temperature is required, then a single indication of total power by the detector DE of Fig. lA is adequate.
.. ~ ~ . , - ~ ; . , - :
- : , . .. , :. , ,. ~ , . , ,. ,. . ~ ~ "
, . :~ - . -. ~ ., .
: .... ... ... , ~ :, :. .. . . . . .
,~
, . .. ~ . ; . : ~ ~ . . . : .. .. .
13 49,191 If a more accurate determination of temperature is required, and there is no established information as to the length ~ of the hot region, then a second detector measurement must also be made. The rnost straightforward method of eliminating the dependence on the hot region length ~ and the detector distance L is to measure the ratio of radiated power for two different values of long - wavelength cut-offs, i.e., Af1 and Af2, in accordance with the following expression:
~Af2 r c2 ~ -1
S The emissivity, and the fraction of total emit-ted radiation guided down the optical fiber F is readily determined by a commercially available microprocessor circuit MP in accordance with equation (l) above.
The optical fiber F of Fig. lA consists of a fiber core CR surrounded by a fiber clad CL. Typically, the fiber core CR may be quartz or borosilicate glass while the cladding CL may typically be plastic or air.
The temperature of the ambient environment E
surrounding the optical fiber F results in thermal radia-tion emanating from all portions of the fiber F. Only theradiation that is emitted in such a direction that strikes the boundary B of the core CR of the fiber F at angles greater than the critical angle, ~c' will be guided by the fiber F to an optical detector DE, located at one end of the fiber F. The optical detector DE, which may typically be a silicon or germanium photodiode, converts the optical thermal radiation energy into an equivalent electrical signal. Radiation incident at smaller angles than the critical angle will escape from the fiber F. The output signal of the detector DE can be used for display or control purposes or can be supplied to the microprocessor circuit MP for processing in accordance with a predeter-mined mathematical expression.
THEORY OF OPERATION
The contribution to the radiation power from a thin slab of material of a thickness d~', of Fig. lA, is:
,. . .
, :. . ;
. ~ , - -49,191 dP =aWDd~' where a is the absorption, or loss, constant and W is the integral of the planck function, Cl LeAT ~ ~ dA.
If this radiation must travel a distance D' to the end of the hot region HR, then some of this radiation will be absorbed, and remaining radiation will be represented as follows:
dP =awe~a~ d~.
The total power density from the entire hot region HR of length ~ is P = I We~ae dQ~ = W(l-e-a~ (2) The emissivity is, by definition, the factor by which the planck integral is multiplied to get the total radiated power density, ~ (1 -a) (3) In the usual optical fiber situation, with a localized hot region, a ~ < ~1 ( 4) and ~ae, so that the emissivity increases linearly with the length of the hot region HR. In the other extreme, where aQ~> 1, ,~1, ., ..... . .. .
6 49,191 and the total radiation is independent of the extent of the hot region HR, the optical fiber behaves essentially as a black-body cavity. Since the absorption constant must be non-negligible, i.e., relatively high loss, in S order for thermal radiation to be generated, the signal will be attenuated in the cool length KL of the optical fiber F between the hot spot HR and the detector DE, by the factor e-aL
where L is the distance between the hot spot HR and the detector DE. Thus, the choice of the absorption constant will be dictated by a selected combination of the above factors. Only the radiation that is emitted in such a direction that strikes the boundary B of the core CR of the fiber F at angles greater than the critical angle, ~c' will be guided by the optical fiber F to the detector DE.
Radiation incident at angles smaller than the critical angle will escape from the optical fiber F. The critical angle, determined by the refractive indices n of the core CR and the cladding CL, is -1 nclad (5) c ncore and the fraction of the total radiation that falls within the angular aperture of the fiber F is shown to be equal ;
to:
1 - s~n ~c = 1 - ~ (6) core Taking into account all the above factors, -assuming an optical fiber F wherein the diameter D of the core CR corresponds with core diameter CD, the total radiant power propagated down the fiber F in the wave-length interval Ao to Af is . ,... ~ . . .. . . . , .. , . ,.. , ,- ~. , . ,. ,. ,. ..... , , , -:
7 49,191 (77,D2) ~ nC1ad) (1 -a~) - a,e ~ C1 [AT ~ dA tt (7) where for simplicity, it is assumed that a is not a func-tion of wavelength over the range Ao to Af, and is thus removed from the integral expression above. The wave-length range will depend upon the detector DE employed, and to be more precise, the integrand should be multiplied by the spectral response function of the detector DE. For the purposes of discussion, it will be assumed that the spectral response is flat. The detector DE can be conven-iently implemented through the use of a silicon or german-ium photodiode, with long wavelength cut-offs of 1.0 micron and 1.8 microns, respectively. For low temperature applications, a lead sulfide detector can be employed, which has a long wavelength cut-off of 2.9 microns. The significant effects of temperature and long wavelength cut-off, A c' on the black body radiation function where the above typical detector materials are employed is apparent from Table 1.
. ~ . ' ~, . .
~r;~
8 49,191 TABLE I
BLACK BODY RADIATION POWER
T P~c = 1~m) w/cm P(A = 1 8~m)h'/Cm P(A = 2.9,~m) /
100C 2.8 x 10 14 1.17 x 10 9.33 x 10 5 200 1.16 x 10 10 1.3$ x 10 5 2.04 x 10 3 300 2.72 x 10 8 3.18 x 10 1.61 x 10 400 1.31 x 10 6 3.01 x 10 3 7.26 x 10 2 500 2.36 x 10 1.64 x 10 2 2.29 x 10 600 2.24 x 10 4 6.24 x 10 2 5.73 x 10 1 700 1.36 x 10 3 1.84 x 10 1 1.25 In order to evaluate the expected signal from the combination of the optical fiber F and the detector DE
it is necessary to assign values to the remaining para-meters in equation 7 above. The most critical fiber parameter is the absorption constant, which is determined by maximizing the term F = (1 e~a~ e~
The result of this maximization is am ' ~ ~ e n ~ (8) 20 which is a relatively insensitive function of ~ and L over the range of values of interest for monitoring temperature in electrical machinery. Typical values for ~ and L are about 10 centimeters and 3 meters, respectively, which result in ',.; :
': . . ~ , , . . .
.
fY~3 9 49,191 am = 3.28 x lO cm , or 1423 db/km, and F = 1.21 x lO 2.
The measured signal increases linearly with the cross-sectional area of the core CR of the fiber element F, so it is advantageous to use as large a diameter fiber F as possible. The largest diameter standard communications quartz fiber is 1 mm., corresponding to an area of -3 2 For an air clad (nClad core (nCOre = 1.4g), having a critical angle ~c of 42, the calculated output signal power from the fiber F corre-sponds to:
P(T) = 3 08 X 10 5 ~ A1 LAT ~ dA watts (9) The minimum detectable temperature will be set by the noise equivalent power NEP of the particular detector used, and this will, in general, scale with the area of the detector DE. For optimized detection, the sensitive area of the detector DE should approximate the cross-sectional area of the core CR of the fiber F and be in direct contact so as to minimize transmittal losses.
Table II below, shows the NEP for several 1 mm. diameter detectors operating at room temperature, and the minimum detectable temperatures for each as calculated in accord-ance with equation 9 above. Both lead sulfide and lead selenide photodiodes are capable of responding to tempera-tures below room temperature, but this would require t~etemperature of the surroundings to be at a significantly lower temperature in order not to mask the hot region HR.
:
.
49,191 TABLE II
MINIMUM DETECTABLE TEMPERATURES FOR
SEVERAL TYPES OF DETECTORS WITH
Minimum Detectable TypeA cutoff (~m) NEP (I~/Hz ) Temperature Silicon 1.0 5 x 10 14 240C
Germanium1.8 1o~l2 80C
Lead Sulfide 2.9 10 11 <room temp.
Lead Selenide 4.5 10-1 <room temp.
The choice of a loss constant ~ to optimize response of the fiber F for any particular application will depend upon the expected range of values of ~, L and T. Operation at high temperatures, i.e., in excess of 300C, can be readily implemented with relatively low loss fibers because the value of the planck integral is large.
For low temperatures, i.e., below 300C, a must be chosen more carefully. A summary of the values of the function F
(a, ~, L) is shown in Fig. 2 which is a plot of signal variation with absorption, or ioss, consthnt a for several values of L, and a hot region HR having a length of 10 cm.
It is noted from Fig. 2 that for a values approaching about 10 2cm 1, F is a fairly linear function of , for~
values up to about 50 cm. These curves illustrate that for a range of L from about 1 meter to 5 meters, the optimum a is about 3 x 10 3cm 1 (or about 1000 db/km).
This corresponds to a very lossy communications fiber, the loss constant of low loss fiber typically lies in the range of about 1 to 10 db/km. For distances of less than one meter, greater sensitivity can be achieved by using fibers of even higher loss, i.e., 2 x 10 2cm l. Quartz fiber of such high loss corresponds to that used in glass-blowing operations.
. ~
~; ~
: , , -B
11 49,191 The optical signal from such a high loss fiberlength HLF can be transmitted over a long distance by coupling the high loss fiber length HLF to a low loss fiber length LLF outside of the environmental region ER to be monitored via a suitable fiber coupler FC. This com-bined fiber length FL is schematically illustrated in Fig.
lB. An advantage of employing a fiber of a relatively small a is that the response is essentially independent of L as can be seen in Fig. 3. In this illustration, it is apparent that for a < lo cm 1, F varies only a few percent between zero and 5 meters. Clearly, it may be advantageous to use the lower loss fiber if the tempera-tures are sufficiently high to produce an adequate signal so that variations of F and L can be ignored. A potential high temperature optical fiber material is sapphire. Low temperature applications can employ plastic fibers or chalcognide qlasses, i.e., As2S3, which transmit into the far infrared.
If a fiber element F', as illustrated in Fig.
lC, having a high value of loss constant and disposed adjacent to the object EM, is chosen to give high sensi-tivity, it is possible to determine the distance from the hot region HR, corresponding to a heated region of the object EM, to the end of the fiber element F' by making a measurement of the optical signal at both ends of the fiber element F'. Assuming the location of a hot region HR' at a distance Ll from one end of the fiber and a distance L2 from the other end o the fiber, the known fiber total length is L = Ll + L2. The signals Sl and S2 measured by two identical detectors DEl and DE2, respec-tively, located at either end of the fiber element F' are as follows:
12 49,191 Sl = e aLlll _ e-a~ (G) (planck integral) (10) S2 = e aL2~1 - e aS (G) (planck integral) where G contains the fiber geometry factors. From the ratio of the two signals Sl and S2 Sl = e~ a (Ll-L2) (11) the distance Ll is easily shown to be:
Ll = ~L ~ 2a ~n (S-2) (12) The ratio of equation (11) and the computation of the hot region location of equation (12) is readily accomplished by the microprocessor MP. Thus, if it is desired to know the location of a hot region HR' along a fiber element F', it will be advantageous to use a high loss fiber material in order to generate a large difference between the sig-nals Sl and S2. The relationship between the signal ratio and the fiber loss constant for a 500 cm. long fiber element is illustrated in Fig. 4 for values of Ll ranging from L/2 to L.
It is possible to make an estimate of the tem-perature, even with limited knowledge of the length ~ of the hot spot HR due to the fact that the radiated power increases exponentially with temperature, but only linear-ly with the length factor ~. The relative radiated powers for hot spots having lengths ranging over a factor of 8 are shown in Fig. 5. For temperatures below 300C, the uncertainty in temperature is about + 25C, and this uncertainty increases with increasing temperature. If only an approximation of temperature is required, then a single indication of total power by the detector DE of Fig. lA is adequate.
.. ~ ~ . , - ~ ; . , - :
- : , . .. , :. , ,. ~ , . , ,. ,. . ~ ~ "
, . :~ - . -. ~ ., .
: .... ... ... , ~ :, :. .. . . . . .
,~
, . .. ~ . ; . : ~ ~ . . . : .. .. .
13 49,191 If a more accurate determination of temperature is required, and there is no established information as to the length ~ of the hot region, then a second detector measurement must also be made. The rnost straightforward method of eliminating the dependence on the hot region length ~ and the detector distance L is to measure the ratio of radiated power for two different values of long - wavelength cut-offs, i.e., Af1 and Af2, in accordance with the following expression:
~Af2 r c2 ~ -1
5(Af2) Afl Cl/A5 LeAT _ ~ dA
s(Afl, Afl r c2 - j -1 (13) AoJ Cl/A5 eAT ~ 1 dA
This measurement is accomplished through the use of a two element, or "two color", detector, such as that illus-trated in Fig. lD, which consists of a short wavelength cutoff detector DS, such as silicon, which detects essen-tially all thermal radiation up to approximately 1 micron,and a long wavelength cutoff detector DL, such as german-ium, which detects the remaining radiation between approx-imately 1 micron and 1.8 microns. The selection of the various detector candidates for the two element combina-tion is a matter of design preference. Any of thoseillustrated in Table II above can be packaged into a single detector unit. The dependence of the signal ratio at any temperature will depend upon the combination of detector elements employed. This ratio is shown in Fig. 6 as calculated from equation 13 above for a 1 micron and 1.8 micron pair of cut-off wavelengths, and for a 1.8 micron and 2.9 micron pair. These pairs correspond to a silicon-germanium dual element detector, and a germanium-lead sulfide dual element detector, respectively. These detectors are commercially available from Infrared Indus-tries. It is evident from Fig. 6 that the actual value of the signal ratio will depend upon the sensitivity of each .
. .
' 14 49,191 of the detectors, kut the relative change with temperature is determined only by the black body radiation character-istics.
It is noted from Table II above that any two element, two wavelength, detector combination has the greatest sensitivity at lower temperatures, i.e., exhibits the greatest rate of change with respect to temperature.
In accordance with the above discussion, the silicon-germanium photodiode combination would be most suitable for temperatures above approximately 240C, which corresponds to the minimum detectable temperature for silicon, while the germanium-lead sulfide combination can be used for temperatures in the range of about 80C to about 600C, where the rate of change of signal ratio with temperature decreases rapidly. Various combinations of detector elements can be chosen to give high sensitivity within desired temperature ranges.
If the temperature has been determined by a two element measurement, and if the hot region location has also been determined by use of equation 12, then it is possible to evaluate the length ,~of the hot region from a measurement of the signal power P1(Af1) at one end of the fiber. The result is:
Pl ~fl) a (~D2)( nclad~ e 1 f Cl/A [e ~ ~ A (14) OPERATIONAL EVALUATION
The practical implementation and operation of the fiber optic black-body radiation temperature sensor concept described above has been documented by measuring the optical signal produced by heating a 10 cm. section of moderate loss, 1 mm. diameter, standard communication optical fiber. The signal measurements for the optical fiber temperature sensing device TS were made with silicon and germanium photodiodes, operating in the photovoltaic t~j~
49,191 mode, employing a microvoltmeter to measure the DC signal.
The temperature response of the optical fiber element F, which for evaluation purposes consisted of a Quartz Pro-ducts QSF-lOOOC fiber with an attenuation constant of 50 db-km, is graphically illustrated in Fig. 7. The minimum detectable temperature for this configuration is 125C.
This measurement limitation is the result of non-optimized coupling between the fiber element F and the detector DE, and further by the low value of the fiber loss constant.
It is clear from the above discussion that the basic concept disclosed and documented herein can be implemented through the use of various combinations of detectors and fiber compositions and configurations to satisfy temperature monitoring requirements over a prede-termined temperature range beginning at temperatures approximating room temperature. The high temperature limit is generally set by the softening or melting point of the fiber material. If commonly available quartz fiber is used, this upper limit is approximately 1000C.
In order to assure the operational integrity of a fiber, or fibers, of a temperature measuring configura-tion, it may be desirable to locate a light source LS, as shown in Fig. lE, at one end of the fiber element F, with the detector DE located at the opposite end of the fiber element responding to the presence or absence of light to provide an indication of the operational integrity of the fiber. This light could be periodically pulsed so as not to interfere with the determination of a hot spot HR along the fiber F.
While the above discussion, for the purposes of simplicity, has been directed to an optical fiber tempera-ture sensing device TS employing a single fiber, it is apparent that many fibers Fl, F2...Fn can be joined at their ends and brought to a common detector, CD as illus-trated in Fig. lF so that only one detector is used to monitor many individual fiber elements. An optical si~nal multiplexing device SM can be applied if it is desired to monitor hot regions along the individual fibers.
.
,
s(Afl, Afl r c2 - j -1 (13) AoJ Cl/A5 eAT ~ 1 dA
This measurement is accomplished through the use of a two element, or "two color", detector, such as that illus-trated in Fig. lD, which consists of a short wavelength cutoff detector DS, such as silicon, which detects essen-tially all thermal radiation up to approximately 1 micron,and a long wavelength cutoff detector DL, such as german-ium, which detects the remaining radiation between approx-imately 1 micron and 1.8 microns. The selection of the various detector candidates for the two element combina-tion is a matter of design preference. Any of thoseillustrated in Table II above can be packaged into a single detector unit. The dependence of the signal ratio at any temperature will depend upon the combination of detector elements employed. This ratio is shown in Fig. 6 as calculated from equation 13 above for a 1 micron and 1.8 micron pair of cut-off wavelengths, and for a 1.8 micron and 2.9 micron pair. These pairs correspond to a silicon-germanium dual element detector, and a germanium-lead sulfide dual element detector, respectively. These detectors are commercially available from Infrared Indus-tries. It is evident from Fig. 6 that the actual value of the signal ratio will depend upon the sensitivity of each .
. .
' 14 49,191 of the detectors, kut the relative change with temperature is determined only by the black body radiation character-istics.
It is noted from Table II above that any two element, two wavelength, detector combination has the greatest sensitivity at lower temperatures, i.e., exhibits the greatest rate of change with respect to temperature.
In accordance with the above discussion, the silicon-germanium photodiode combination would be most suitable for temperatures above approximately 240C, which corresponds to the minimum detectable temperature for silicon, while the germanium-lead sulfide combination can be used for temperatures in the range of about 80C to about 600C, where the rate of change of signal ratio with temperature decreases rapidly. Various combinations of detector elements can be chosen to give high sensitivity within desired temperature ranges.
If the temperature has been determined by a two element measurement, and if the hot region location has also been determined by use of equation 12, then it is possible to evaluate the length ,~of the hot region from a measurement of the signal power P1(Af1) at one end of the fiber. The result is:
Pl ~fl) a (~D2)( nclad~ e 1 f Cl/A [e ~ ~ A (14) OPERATIONAL EVALUATION
The practical implementation and operation of the fiber optic black-body radiation temperature sensor concept described above has been documented by measuring the optical signal produced by heating a 10 cm. section of moderate loss, 1 mm. diameter, standard communication optical fiber. The signal measurements for the optical fiber temperature sensing device TS were made with silicon and germanium photodiodes, operating in the photovoltaic t~j~
49,191 mode, employing a microvoltmeter to measure the DC signal.
The temperature response of the optical fiber element F, which for evaluation purposes consisted of a Quartz Pro-ducts QSF-lOOOC fiber with an attenuation constant of 50 db-km, is graphically illustrated in Fig. 7. The minimum detectable temperature for this configuration is 125C.
This measurement limitation is the result of non-optimized coupling between the fiber element F and the detector DE, and further by the low value of the fiber loss constant.
It is clear from the above discussion that the basic concept disclosed and documented herein can be implemented through the use of various combinations of detectors and fiber compositions and configurations to satisfy temperature monitoring requirements over a prede-termined temperature range beginning at temperatures approximating room temperature. The high temperature limit is generally set by the softening or melting point of the fiber material. If commonly available quartz fiber is used, this upper limit is approximately 1000C.
In order to assure the operational integrity of a fiber, or fibers, of a temperature measuring configura-tion, it may be desirable to locate a light source LS, as shown in Fig. lE, at one end of the fiber element F, with the detector DE located at the opposite end of the fiber element responding to the presence or absence of light to provide an indication of the operational integrity of the fiber. This light could be periodically pulsed so as not to interfere with the determination of a hot spot HR along the fiber F.
While the above discussion, for the purposes of simplicity, has been directed to an optical fiber tempera-ture sensing device TS employing a single fiber, it is apparent that many fibers Fl, F2...Fn can be joined at their ends and brought to a common detector, CD as illus-trated in Fig. lF so that only one detector is used to monitor many individual fiber elements. An optical si~nal multiplexing device SM can be applied if it is desired to monitor hot regions along the individual fibers.
.
,
Claims (7)
1. Apparatus for determining the presence of a hot region associated with an object, comprising, an elongated optical fiber element disposed in proximity to said object and within the temperature environment produced by said object, said optical fiber element responding to said temperature environment by self-generating thermal radiation within the optical fiber element, the wavelengths of the spectral composition of the self-generated thermal radiation varying along the length of said optical fiber length as a function of the variations in the temperature of the object along the length of the optical fiber element, the total radiation varying exponentially with temperature such that the spectral composition of the self-generated thermal radia-tion transmitted to an end of the optical fiber element is determined substantially by the highest temperature region along the optical fiber element, and a thermal radiation detector means operatively coupled to an end of said elongated optical fiber element to provide an indication of the hottest region of said object.
2. Apparatus as claimed in claim 1 wherein the material composition of the optical fiber element is selected on the basis of an absorption constant which will optimize the self-generating thermfal radiation character-istic of the optical fiber element in a preferred temperature range.
17 49,191
17 49,191
3. Apparatus for determining the presence and temperature of a hot region associated with an object, comprising, an elongated optical fiber element disposed in proximity to said object and within the temperature en-vironment produced by said object, said optical fiber element responding to said temperature environment by self-generating thermal radiation within the optical fiber element, the wavelengths of the spectral composition of the self-generated thermal radiation varying along the length of said elongated optical fiber element as a func-tion of the variation in the temperature of the object along the length of the elongated optical fiber element, the total thermal radiation at all wavelengths increases exponentially with increasing temperature such that the spectral composition of the thermal radiation transmitted within the optical fiber element is essentially determined by the temperature of the hottest region of said object, detector means operatively coupled to an end of said elongated optical fiber element and responding to said transmitted thermal radiation by identifying the presence of a hot region, said detector means including a first detector having a short wavelength cutoff responding to said thermal radiation by generating a first output signal and a second detector having a long wavelength cutoff responding to said thermal radiation by generating a second output signal, and a means for taking the ratio of said first and second output signal as an indication of the temperature of the hot region.
4. Apparatus for determining the presence of a hot region associated with an object, comprising, an elongated optical fiber element disposed in proximity to said object and within the temperature environment produced by said object, said optical fiber element responding to said temperature environment by self-18 49,191 generating thermal radiation within the optical fiber element, the wavelengths of the spectral composition of the self-generated thermal radiation varying along the length of said optical fiber length as a function of the variations in the temperature of the object along the length of the optical fiber element, the total radiation varying exponentially with temperature such that the spectral composition of the self-generated thermal radia-tion transmitted to the ends of the optical fiber element is determined substantially by the highest temperature region along the optical fiber element, and a first and second thermal radiation detector means operatively coupled to either end of said elongated optical fiber element for converting the self-generated thermal radiation transmitted to either end into a first and second output signal respectively, and means for taking the ratio of said first and second output signals and developing an indication of the location of the hot region of said object along said elongated optical fiber element.
5. Apparatus for determining the presence of a hot region associated with an object, comprising, an elongated high loss optical fiber element disposed in proximity to said object and within the tem-perature environment produced by said object, said optical fiber element responding to said temperature environment by self-generating thermal radiation within the optical fiber element, the wavelengths of the spectral composition of the self-generated thermal radiation varying along the length of said optical fiber length as a function of the variations in the temperature of the object along the length of the optical fiber element, the total radiation varying exponentially with temperature such that the spectral composition of the self-generated thermal radia-tion transmitted to an end of the optical fiber element is 19 49,191 determined substantially by the highest temperature region along the optical fiber element, an elongated low loss optical fiber element having one end optically coupled to an end of said elongat-ed high loss optical fiber element and extending beyond the temperature environment produced by said object, and means operatively connected to the opposite end of said elongated low loss optical fiber element and responding to said self-generated thermal radiation of said elongated high loss optical fiber element and trans-mitted by said elongated low loss optical fiber by provid-ing an indication of the hottest region of said object.
6. Apparatus for determining the presence of a hot region associated with an object, comprising, an elongated optical fiber element disposed in proximity to said object and within the temperature environment produced by said object, said optical fiber element responding to said temperature environment by self-generating thermal radiation within the optical fiber element, the wavelengths of the spectral composition of the self-generated thermal radiation varying along the length of said optical fiber length as a function of the variations in the temperature of the object along the length of the optical fiber element, the total radiation varying exponentially with temperature such that the total power of the self-generated thermal radiation transmitted to an end of the optical fiber element is determined substantially by the highest temperature region along the optical fiber element, and means operatively coupled to an end or said elongated optical fiber element to respond to said total power of the self generated thermal radiation transmitted to said end by providing an indication or the temperature of the hottest region of said object.
7. Apparatus for determining the presence of a hot region associated with an object, comprising, 49,191 an elongated optical fiber element disposed in proximity to said object and within the temperature environ-ment produced by said object, said optical fiber element responding to said temperature environment by self-generating thermal radiation within the optical fiber element, the wavelengths of the spectral composition of the self-generated thermal radiation varying along the length of said optical fiber length as a function of the variations in the tempera-ture of the object along the length of the optical fiber element, the total radiation varying exponentially with temperature such that the spectral composition of the self-generated thermal radiation transmitted to an end of the optical fiber element is determined substantially by the highest temperature region along the optical fiber element, a thermal radiation detector means operatively coupled to an end of said elongated optical fiber element to provide an indication of the hottest region of said object, and means for monitoring the operational integrity of said elongated optical fiber element in combination with said detector means, said means for monitoring the operational integrity including a periodically activated radiation source operatively coupled to the end of said elongated optical fiber element opposite said detector means, said means for monitoring the operational integrity periodically introducing a radiation energy input signal into said elongated optical fiber element for transmission through said fiber element for detection by said detector means.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/195,911 US4362057A (en) | 1980-10-10 | 1980-10-10 | Optical fiber temperature sensor |
| US195,911 | 1988-05-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1158888A true CA1158888A (en) | 1983-12-20 |
Family
ID=22723324
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000386591A Expired CA1158888A (en) | 1980-10-10 | 1981-09-24 | Optical fiber temperature sensor |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4362057A (en) |
| EP (1) | EP0049866A3 (en) |
| JP (1) | JPS5791422A (en) |
| KR (1) | KR830008157A (en) |
| CA (1) | CA1158888A (en) |
| ES (1) | ES506177A0 (en) |
| IL (1) | IL63829A0 (en) |
Families Citing this family (33)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4508461A (en) * | 1981-09-22 | 1985-04-02 | Westinghouse Electric Corp. | Distributed fiber optic temperature monitoring apparatus and method |
| US5696863A (en) * | 1982-08-06 | 1997-12-09 | Kleinerman; Marcos Y. | Distributed fiber optic temperature sensors and systems |
| US5363463A (en) * | 1982-08-06 | 1994-11-08 | Kleinerman Marcos Y | Remote sensing of physical variables with fiber optic systems |
| SE451409B (en) * | 1983-01-13 | 1987-10-05 | Lars Stenmark | DEVICE FOR DETERMINING THE TEMPERATURE OF A METOBJECT BY DETECTING THE ELECTROMAGNETIC RADIATION EMITTED BY THE METOBJECT |
| US4576485A (en) * | 1983-04-29 | 1986-03-18 | Westinghouse Electric Corp. | Method and apparatus for measuring temperature profile with a single optical fiber |
| US4621929A (en) * | 1983-10-12 | 1986-11-11 | Luxtron Corporation | Fiber optic thermal anemometer |
| IT1196701B (en) * | 1984-05-24 | 1988-11-25 | Fiat Auto Spa | PROCEDURE AND DEVICE FOR THE NON-DESTRUCTIVE CONTROL OF A JOINT BETWEEN SHEETS MADE BY ELECTRIC POINT WELDING |
| US4679934A (en) * | 1985-08-08 | 1987-07-14 | The United States Of America As Represented By The Secretary Of The Air Force | Fiber optic pyrometry with large dynamic range |
| FR2599838B1 (en) * | 1986-06-06 | 1988-08-26 | Charbonnages De France | FIRE OPTIC HEATING AND FIRE DETECTOR |
| GB2192984B (en) * | 1986-07-25 | 1990-07-18 | Plessey Co Plc | Optical sensing arrangements |
| US4794619A (en) * | 1986-12-05 | 1988-12-27 | Conax Buffalo Corporation | Optical fiber temperature sensor |
| US4827487A (en) * | 1987-12-11 | 1989-05-02 | Westinghouse Electric Corp. | Distributed temperature sensing system for stator windings |
| US5324200A (en) * | 1988-08-25 | 1994-06-28 | American Dental Technologies, Inc. | Method for enlarging and shaping a root canal |
| US5180304A (en) * | 1988-08-25 | 1993-01-19 | American Dental Laser, Inc. | Method for apical fusion of the foramina |
| US5277496A (en) * | 1990-10-17 | 1994-01-11 | Ametek, Inc. | High temperature optical probe |
| US5310344A (en) * | 1990-11-01 | 1994-05-10 | Arthur Vassiliadis | Dental laser system |
| CA2089223C (en) * | 1992-02-13 | 1999-06-01 | Kazuo Amano | Temperature abnormality detecting structure for fluid pipe |
| US5330136A (en) * | 1992-09-25 | 1994-07-19 | Union Switch & Signal Inc. | Railway coded track circuit apparatus and method utilizing fiber optic sensing |
| WO1994022241A1 (en) * | 1993-03-18 | 1994-09-29 | Telstra Corporation Limited | A method and apparatus for inducing a temporary localised transmission loss in a telecommunications cable |
| US5455551A (en) * | 1993-05-11 | 1995-10-03 | Abb Power T&D Company Inc. | Integrated temperature sensing duct spacer unit and method of forming |
| US5529267A (en) * | 1995-07-21 | 1996-06-25 | Union Switch & Signal Inc. | Railway structure hazard predictor |
| DE19541142A1 (en) * | 1995-10-27 | 1997-04-30 | Siemens Ag | Industrial temp. monitoring system using light pipe as temp. sensor, esp. for long pipe-like structure |
| DE10143222C1 (en) * | 2001-09-04 | 2003-04-17 | Siemens Linear Motor Systems G | Temperature measuring device for an electric motor |
| US6748129B2 (en) * | 2002-02-22 | 2004-06-08 | Lucent Technologies Inc. | Method and apparatus of monitoring optical power level in waveguiding structures |
| US6811307B2 (en) * | 2002-07-10 | 2004-11-02 | Kenneth J. Crowe | DTS measurement of HV cable temperature profile |
| AT500141B1 (en) * | 2004-04-28 | 2008-03-15 | W & H Dentalwerk Buermoos Gmbh | DENTAL LASER TREATMENT DEVICE |
| US20060251147A1 (en) * | 2005-05-06 | 2006-11-09 | Qualitrol Corporation | Transformer temperature monitoring and control |
| US7377689B2 (en) * | 2005-05-06 | 2008-05-27 | Qualitrol Corporation | Transformer temperature monitoring and control |
| EP2973930B1 (en) | 2011-02-01 | 2019-10-23 | S & C Electric Co. | Distributed energy storage system and method of distributing energy |
| GB2509153B (en) | 2012-12-21 | 2016-07-13 | Kidde Tech Inc | Heat detector with shape metal alloy element |
| GB2509530B (en) | 2013-01-07 | 2015-11-11 | Kidde Tech Inc | Optical fibre distributed LHD with SMA element for discrete alarm |
| US10539465B2 (en) * | 2017-03-29 | 2020-01-21 | Eaton Intelligent Power Limited | Systems, devices, and apparatus for monitoring temperature at remote locations using infrared light |
| US11959811B2 (en) * | 2019-12-20 | 2024-04-16 | SSAB Enterprises, LLC | Temperature sensors |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE7808169L (en) * | 1977-08-10 | 1979-02-11 | Graviner Ltd | TEMPERATURE SENSOR SENSOR |
| US4151747A (en) * | 1978-06-21 | 1979-05-01 | Electric Power Research Institute, Inc. | Monitoring arrangement utilizing fiber optics |
| SE418997B (en) * | 1978-06-26 | 1981-07-06 | Asea Ab | FIBEROPTICAL TEMPERATURE SENSOR BASED ON THE MEASUREMENT OF THE TEMPERATURE-DEPENDENT SPECTRAL ABSORPTION FORM OF A MATERIAL |
| US4201446A (en) * | 1978-10-20 | 1980-05-06 | Honeywell Inc. | Fiber optic temperature sensor using liquid component fiber |
| SE420769B (en) * | 1978-12-05 | 1981-10-26 | Asea Ab | FIBEROPTICAL TEMPERATURE METHOD OF PYROMETER TYPE |
| JPS5599033A (en) * | 1979-01-24 | 1980-07-28 | Mitsubishi Electric Corp | Measuring device for temperature |
| US4203326A (en) * | 1979-01-26 | 1980-05-20 | Electric Power Research Institute, Inc. | Method and means for improved optical temperature sensor |
| US4302970A (en) * | 1980-05-09 | 1981-12-01 | United Technologies Corporation | Optical temperature probe employing rare earth absorption |
-
1980
- 1980-10-10 US US06/195,911 patent/US4362057A/en not_active Expired - Lifetime
-
1981
- 1981-09-14 IL IL63829A patent/IL63829A0/en unknown
- 1981-09-24 CA CA000386591A patent/CA1158888A/en not_active Expired
- 1981-10-07 EP EP81108051A patent/EP0049866A3/en not_active Withdrawn
- 1981-10-09 ES ES506177A patent/ES506177A0/en active Granted
- 1981-10-09 JP JP56160378A patent/JPS5791422A/en active Pending
- 1981-10-10 KR KR1019810003833A patent/KR830008157A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| ES8302907A1 (en) | 1983-01-16 |
| US4362057A (en) | 1982-12-07 |
| JPS5791422A (en) | 1982-06-07 |
| EP0049866A2 (en) | 1982-04-21 |
| ES506177A0 (en) | 1983-01-16 |
| IL63829A0 (en) | 1981-12-31 |
| KR830008157A (en) | 1983-11-16 |
| EP0049866A3 (en) | 1983-10-19 |
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