JPH0146809B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a temperature detection device. In particular, the present invention relates to a temperature sensing device for measuring the temperature of an electromechanical device with a temperature sensing probe using an optical fiber. A current problem facing the power generation industry is that equipment is being operated increasingly near its maximum current and voltage ratings. Such operating conditions increase the degree to which the components are heated to an undesirable degree. reliability of electrical equipment;
Maintenance and operating life are directly affected by its operating temperature. If this temperature exceeds a certain value for a significant period of time, the life of the device is rapidly reduced. Information regarding the existence of "hot spot" and "overtemperature" conditions in equipment may indicate improper operation, defective parts, poor insulation, or potential failure. It can show that something is true. However, gathering such information can be difficult. Conductors and equipment are often at high potential with respect to ground.
Because of these high voltages or their associated electromagnetic interference, direct temperature measurements on conductors are not possible and the use of metal probes is unsuccessful. One reason for this is that insulation containing metal conductors is susceptible to dangerous flashover. Also, the current induced in the metal temperature sensor by the high potential prevents accurate temperature measurements. Therefore, a device incorporating an insulating probe that can be inserted into an electromechanical device is desirable.
This device is capable of continuously measuring temperature during operation of an electromechanical device and is capable of effectively detecting the location of superheat temperatures within the electromechanical device, known as "hot spots." It should be something. This type of insulating probe should be vibration-insensitive in order to be most widely used. Furthermore, devices of this type must be reusable without repair, apart from the fuses, in order to minimize costs and service requirements. Measuring temperature is only the first step in the problem. That measurement information must then be communicated to the operator or control center for that particular machine. The area to be measured whose temperature is to be measured is most often located inside a complex of electrical and mechanical components. The area to be measured is
It may be located in the deepest, most difficult-to-access location of the machine. In the past, many techniques have been used to measure temperature. However, these conventional techniques are becoming unsuitable under severe conditions such as industrial high potentials. One conventional thermometer used a common thermocouple to measure temperature changes within a generator. This thermometer required the thermocouple lead to be routed through the generator housing. Therefore, high potential conductors and their associated bushings and insulation were required just to monitor temperature. One way to solve this problem was to use a wireless transmitter. However, connecting a wireless transmitter to a temperature sensor requires processing of the electromagnetic field. The electromagnetic field is
Interfere with signal transmission. Non-metallic, non-magnetic temperature sensors have been studied in the past. One of the methods investigated was the use of optical fibers. For example, US Pat. No. 3,960,017 discloses the use of optical fibers to optically read thermometers and transmit information from transformer windings. The temperature sensitivity is scaled linearly with temperature across opposing openings of the juxtaposed light pipes. Therefore, optical transmission that makes the optical intensity proportional to the temperature is partially blocked. Another solution involves the use of optical fibers in conjunction with liquid crystals. This method has been proposed for measuring temperature in biological studies of living tissues. As the temperature changes, the liquid crystal becomes opaque and partially blocks the transmitted light. The opacity is first calibrated against a standard thermometer and, in use, the liquid crystal containing probe is illuminated and read by a separate fiber optic light guide. Certain properties of the light guide itself are affected by changes in temperature. As will be explained below, one of these properties, the ratio of the refractive indices of the materials forming the light guide, is important for transmission and is temperature dependent. A temperature detection device according to the invention that utilizes a light guide to indicate temperature changes comprises at least one light guide, a light source, and a photodetector. The light guide has a cladding extending concentrically around the core. The core and cladding materials are selected such that their respective refractive indices vary with temperature over a predetermined temperature range. Light is transmitted through the light guide only while the refractive index of the cladding is less than the refractive index of the core. Therefore, by detecting changes in transmitted light, heating or cooling within a certain temperature range can be determined. A portion of the light guide is placed in thermally conductive relationship with a predetermined region whose temperature is to be measured. This area to be measured can be within electrical equipment such as a motor, generator or transformer. The light guide may remain inserted within the machine to measure temperature during design, testing, or operation. A light source provides a predetermined conditioned light to one end of the light guide for transmission to the other end. When the light reaches the other end of the light guide, its transmission is detected by a photodetector. The light source may provide, for example, white light, visible light, monochromatic light, ultraviolet light, or infrared light. The photodetector may be capable of visually detecting the transmitted light or may be capable of measuring a predetermined characteristic such as the intensity of the light. For example, if the transmitted light reaching the photodetector has an intensity detectably different from that of the supplied light, then the temperature of the region to be measured is equal to or equal to the critical temperature of that particular light guide. Is it possible to surpass that? Next, the present invention will be described in detail with reference to embodiments of the present invention based on the accompanying drawings. FIG. 1 shows the basic structure of a light guide 10. FIG. An axial section of a light guide 10 of the type used in the present invention is shown. As shown, light guide 10
includes a core 12 and a cladding 14 concentrically surrounding it. Core 12 and Clad 1
4 are constructed of selected glass, plastic and liquid, for example. Individual light guides or bundles of light guides are housed within a light jacket 16 to prevent cutting and wear of the core 12 and cladding 14 to maintain the integrity of light transmission. The light guide 10, also known as a fiber pipe or optic guide, essentially consists of:
It is a tube capable of optical transmission. Here, transmission means propagation or guiding of light. The transmitted light can be continuous or in the form of a pulsed signal. A light beam is transmitted only when the refractive index of core 12 is greater than the refractive index of cladding 14. The materials of core 12 and cladding 14 are selected such that their temperature dependent refractive indices change at different rates as temperature changes. In other words, the refractive index of each material is selected to have a relatively large and different temperature coefficient. Figure 2 shows the refraction versus temperature of a set of commercially available Schott glasses that can be used as core and cladding materials in the optical wavelength band of approximately 643 nm.

Table 1 Known commercially available light guides are typically constructed of core and cladding materials whose critical temperatures, if any, are well outside industrially possible temperatures. FIG. 3 schematically depicts a temperature sensing device constructed in accordance with the present invention, which can be best understood by concurrently referring to FIG. A light source 20 provides light to a first end of the plurality of light guides 10. The light source 20 may be of any conventional type capable of providing a preselected light, for example a light emitting diode (coherent or non-coherent), a tungsten lamp or a monochromatic light source. As discussed below, the index of refraction is a function of the wavelength of the transmitted light. Therefore, the light source 20 must provide light in a predetermined wavelength band. Furthermore, each light guide 10 only has a second refractive index when the refractive index of its core 12 is greater than the refractive index of its cladding 14.
light can be transmitted to the edge of the Although it is not necessary to do so, the second
Materials having the refractive index shown can be used for both core 12 and cladding 14. In the first of two possible options, the material of curve A is used for the core 12 and the material of curve B is used for the cladding 14. Since light is transmitted only when the refractive index of the core 12 exceeds the refractive index of the cladding 14, this selection of materials will result in a temperature below the critical temperature for this wavelength of light, i.e. in the region indicated by Greek numerals. Transmission takes place only at If any point along the light guide 10 is above a critical temperature, very little light will reach the photodetector 22. In the second material selection, the material of curve B is used for the core 12 and the material of curve A is used for the cladding 14. In this case, light is transmitted only in the area indicated by the Greek numerals. To reiterate, the temperature sensing device of FIG. 3 is capable of (1) detecting whether the hottest point along the fiber guide exceeds a critical temperature;
Also, (2) by choosing a different combination of materials,
It is possible to detect whether the coldest point has fallen below a critical temperature. At this point in the discussion of the drawings, it may be best to continue the description of the embodiment of FIG. 3 with respect to one of its possible industrial applications. In this example of use, at least a portion of one light guide 10 is placed in thermally conductive relationship with at least one region 26 to be measured. This region to be measured may be located within the electromechanical device 24, such as a motor, generator, or transformer. This temperature detection device, for example,
The temperature of the hottest part of that particular light guide 10
It shows when the critical temperature of is exceeded. light guide 10
should be selected to have a predetermined critical temperature equal to or a safety factor below the maximum temperature rating of the electromechanical device 24. Light is introduced into the first end of the light guide 10 from a predetermined light source 20 . A photodetector 22 disposed in optically conductive relationship with the second end of the light guide 10 monitors or detects certain characteristics of the light, such as intensity in a preselected wavelength band. A number of different photodetectors can be used, such as those shown at 22A and 22B in FIG. The photodetector 22A has an aperture 25 that allows the transmitted light to be visually inspected. Instead of or in addition to such inspection capabilities, metrology capabilities may be desired. Photodetector 22B includes a photosensor 28, such as a photodiode, phototransistor, or photomultiplier, that converts the light transmitted thereto into an electrical signal proportional to it. This light sensor 28 is electrically connected to measuring means 30 and, if necessary, to recording means 34 for permanent recording of the temperature. The measuring means 30 can indicate changes in the intensity of the transmitted light or indicate the amplitude of a pre-calibrated electrical signal and read out a quantitative value of the intensity. The temperature detection device described above is unsuitable if the temperature-dependent light guide has to pass through a point of higher temperature than the region to be measured in order to reach the region to be measured in the machine. Light loss occurs in these areas of high temperature, so the amount of light that reaches the photodetector is not indicative of the temperature of the area being measured. Therefore, a temperature detection probe that is not affected by high temperatures outside the measurement area is desired. This type of probe is called a point temperature sensor to distinguish it from a line temperature sensor. The point temperature probe, as shown in FIG. , the light guide 10 and the data link 36
A coupling ring 38 is provided to connect the two to form an optical path. For example, coupling 3
8 may be a mechanical fastener or an adhesive.
Data link 36 may be any optical transmitter that is relatively lossless (or capable of providing a given transmission) over the temperatures encountered. In operation, light guide 10 is placed in thermally conductive relationship with region 26 to be measured. The light is transmitted from the light source 20 to the first
data link 36 , then through the light guide 10 and then through the second data link 36 to the photodetector 22 . If several measurement areas are to be measured, the data link-light guide-data link connection should be repeated, with each measurement area in thermal conductive relationship with one light guide. Can be done. As mentioned above, the refractive index is related to wavelength. Since the critical temperature is determined by the relative refractive indices of the core and cladding materials, changes in the refractive index of each material shift the critical temperature. FIG. 4 is a graph showing critical temperature ranges corresponding to light of various wavelengths. The particular light guide used to generate the data for this graph and the graphs of FIGS. 5 and 6 consisted of a benzene liquid core and a polycyclohexyl methacrylate cladding. This light guide shows that for these wavelengths, a 50 nanometer change in the wavelength of the light changes the critical temperature by about 13 degrees. FIG. 5 further illustrates the interrelationship of intensity, wavelength and temperature. The vertical axis represents the percentage loss of transmitted light intensity. The wavelength of the supplied light is 200nm
It was hot. As can be seen from this graph, the intensity changed by 27% at this wavelength over the same temperature range as in Figure 4. This change in intensity is
It can be visually observed by the photodetector 22A. Quantitative measurements of the temperature of the region to be measured can be made by utilizing such changes in critical temperature. A white light source (eg, a uniform intensity light source from 400 nm to 700 nm) or a monochromatic light source can be used. Referring again to FIG. 3, while the light source 20 provides white light to the light guide 10, a light means 32 is disposed between the light guide 10 and the photodetector 22 in optical communication therewith. Should. This optical means 32 should pass, for example, a wavelength band smaller than 10 nm wide. This optical means 32 may be, for example, a filter or a beam splitter. If a beam splitter is used, a photodetector 22 is required for each beam to be detected. If light of one preselected wavelength or a narrow band of wavelengths, such as narrower than 10 nm wide, is provided by the light source 20, its intensity can be applied to the photodetector 22 without optical means. Therefore, it can be measured. In FIG. 6, light intensity is plotted against wavelength at two temperatures. The light supplied from the light source has a predetermined intensity, designated as I _p for purposes of explanation. Further, for ease of understanding, possible usage examples will be described with reference to FIGS. 3 and 6. In this example, the light source 20 provides white light and the light means 32 is capable of passing wavelengths of 436 nm or 486 nm. At 9.3° C., 436 nm light is no longer transmitted by the light guide. (Light means 32
The photodetector 22 without Io shows a decrease in the total intensity Io. ) If any of the regions 26 to be measured are further heated, light at other frequencies will be lost. At 22°C, 486nm light is no longer transmitted. Therefore,
using a suitable filter to examine the light
If it is found that 486 nm light is being transmitted but 436 nm light is not being transmitted, the area to be measured 26
It can be seen that the maximum temperature of is between 9.3℃ and 22℃. When photodetector 22A is used to provide white light between 400nm and 600nm, the light emitted through the aperture appears blue at 9.3°C and changes in visible color as the area being measured heats up. changes and other frequencies are removed. If, instead of white light, a tunable monochromatic light source is used, only the desired frequencies need to be provided. As temperature increases, it is expected that certain frequencies will no longer be transmitted. Using a single guide cannot indicate the size and location of hot spots within electromechanical device 24, nor can it indicate the thermal state of other portions of electromechanical device 24. Information about these can be provided by using more than one light guide. Two or more light guides 10, each having a different critical temperature, can be placed in thermally conductive relationship with the same region to be measured 26. These light guides may e.g.
Although these light guides can be housed within and driven by a common light source 20, they are separated by separate photodetectors 22.
must be connected to. At this time, the photodetector 22
indicates which critical temperature has been exceeded. By arranging at least two light guides 10 in thermally conductive relationship with juxtaposed but different regions 26 to be measured, the temperature within the electromechanical device 24 can be monitored independently of each other and the high temperature Temperature information is provided about the location of the point and its size. The present invention has the following effects. (1) A single light guide can be used to warn which point in an electrical device and when the temperature is higher than a predetermined temperature. (2) The light guide is insensitive to high potentials, magnetic fields and vibrations. (3) In contrast to fuses, the device is reusable in that the light is retransmitted through the glass once the temperature returns to normal.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway, enlarged perspective view of a light guide of the type used in the present invention; FIG. 2 is a graph showing the temperature dependence of the refractive index of certain core and cladding materials; and FIG. A schematic diagram of a temperature detection device as an embodiment of the invention; FIG. 4 is a graph showing critical temperature ranges corresponding to different wavelengths of light; FIG. 5 is a graph showing temperature vs. percentage loss of transmitted light intensity for one specific wavelength; FIG. 6 is a graph showing wavelength versus transmitted light intensity for two temperatures, and FIG. 7 is a schematic diagram of a point temperature probe as an embodiment of the present invention. DESCRIPTION OF SYMBOLS 10... Light guide, 12... Core, 14... Clad, 20... Light source, 22... Photodetector, 26
...Measurement area.

Claims (1)

Claims: 1. at least one light guide including a core and a cladding extending cylindrically around the core;
a light source for providing a predetermined light to a first end of the light guide and a temperature to which the light guide is exposed for detecting the presence or absence of light transmitted to a second end of the light guide; means for indicating that the material is in a first portion or a second portion, respectively, of a temperature range; the first core material is made of two materials;
the first of said temperature ranges in which said light guide transmits light;
having a refractive index greater than the second cladding material over a portion thereof and having a refractive index equal to or less than the second cladding material over a second portion of the temperature range in which the light guide does not transmit light; a temperature sensing device, wherein the sensing means includes a light sensor responsive to the transmitted light and converting the light into an electrical signal correlated with the measuring means. 2 The at least two light guides each have a different core material and cladding material, a light source provides light to a first end of each light guide, and a detection means is transmitted to a second end of each light guide. 2. The temperature detection device according to claim 1, wherein the temperature detection device detects the light separately. 3. The light source supplies a predetermined white light of the same intensity, and the detection means includes a light sensor for converting the transmitted light into an electrical signal proportional to the intensity thereof, and a second end of the light guide and the said light. 2. The temperature detection device according to claim 1, further comprising optical means placed in optical communication between the sensors and means for measuring electrical signals from the optical sensors. 4. The temperature detection device according to claim 3, wherein the optical means passes light in a wavelength band smaller than 10 nm, and the measuring means measures changes in the electrical signal. 5. The optical means passes light in a wavelength band less than 10 nm wide, and the measuring means measures the amplitude of the pre-calibrated electrical signal, thereby providing the intensity of the light transmitted to the light sensor. Temperature detection device described in section. 6. a first data link optically disposed between the light source and the first end of the light guide and capable of selectively transmitting the provided light over both the first and second portions of the temperature range; , means for mechanically coupling the first data link to a first end of the light guide; and means optically disposed between the second end of the light guide and a light sensor; a second data link capable of predetermined transmission of the provided light over both the first and second portions of the temperature range; and mechanically connecting the second end of the light guide to the second data link. 6. The temperature detection device according to claim 1, further comprising means for coupling. 7. A method for obtaining temperature information of a target area at a first location and retrieving such temperature information at a second location that may be remote from the first location, the method comprising: a light source and a light source at the second location; a first end that is near the light source and receives light from the light source and a second end that is near the photodetector and supplies light to the photodetector, in the optical path between the detector and the photodetector; and arranging a light guide having predetermined temperature dependent properties to pass through the target area; providing light from the light source to a first end of the light guide; and passing a preselected wavelength. By shining light, the light passes through the light guide to the second
detecting with the photodetector whether the transmitted light is transmitted to an end of the temperature range to indicate whether the temperature zone is in a first part or a second part of the temperature range; converting the predetermined temperature-dependent characteristic of the light guide into an electrical signal proportional to the intensity of the light guide and indicative of the temperature of the temperature zone, the predetermined temperature dependent property of the light guide being determined by the relative values of the refractive indices of the core material and the cladding material of the light guide. A method for obtaining temperature information which is reusably optically transparent in a first part thereof in a certain temperature range, but optically non-transmissive in a second part of said temperature range, depending on the temperature range.