JPH0127071Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field) The present invention relates to the structure of an optical cable that can continuously detect low temperatures in the longitudinal direction over a wide temperature range.

(Prior art and its problems) Low-temperature detection optical cables can rapidly and accurately continuously detect the outflow of low-temperature media in the longitudinal direction, and are used in fuel storage facilities, etc., by taking advantage of the complete insulation properties of optical fibers to provide explosion-proof protection. It is attracting attention as a product with excellent safety. A method for detecting low temperatures using optical fibers was considered to be the BS method, which measures the backscattering of the light propagating through the optical fibers to measure changes in the transmission loss of the optical fibers due to temperature changes. The principles of changing the transmission loss of an optical fiber according to temperature changes include changing the refractive index difference between the core and cladding according to the temperature difference, and causing the optical fiber to meander by shrinking the optical fiber coating material due to temperature changes. There are some things that can cause this. In order to improve the low temperature detection sensitivity of low temperature detection sensors, it is necessary to increase the change in transmission loss with respect to temperature changes within the required temperature range, but the normally used loss variation range has a lower limit on the required amount of light propagation. , several 10dB/Km
Naturally, the operating temperature range is also limited. For this reason, with a normal detection fiber, it is difficult to detect in a wide temperature range, and it is conceivable that it may malfunction.

(Structure of the invention) The present invention is a low-temperature detection optical cable that eliminates the above-mentioned drawbacks and can accurately measure over a wide temperature range.The feature is that various optical fibers are inserted into the grooves of the core body, which has multiple spiral grooves on the outer periphery. The core material is made of a metal such as aluminum or copper that has a low coefficient of linear expansion and has excellent thermal conductivity, and each optical fiber has a different temperature range for low temperature detection. There is a particular thing.

(Example and Effects) An example of the present invention will be described with reference to FIG.
A silicone resin-coated optical fiber 3, an optical fiber 4 in which the fiber 3 is coated with Teflon, and an acrylic resin-coated optical fiber 5 are housed one by one in an aluminum spacer 2 having a spiral groove on the outer periphery, and an aluminum pipe is formed. 6 is applied to its outer periphery.

The cable of the present invention has been improved so that low temperature detection can be performed over a wide temperature range by creating a cable using optical fibers with different low temperature detection areas, which were conventionally used individually.

FIG. 2 shows the low temperature detection characteristics of the optical cable according to the embodiment of the present invention. Curves A, B, and C indicate the temperature characteristics of the optical fibers 3, 4, and 5, respectively;
For individual fibers, the temperature at which the transmission loss begins to increase until it suddenly increases is limited, and the detection temperature range is naturally limited, but by making the individual applicable detection temperature ranges continuous, it is possible to Can be used in a wide temperature range of ℃.

Furthermore, in the present invention, the spacer accommodates each type of optical fiber one by one in each groove, so that individual low temperature detection is not impaired by cable formation, and the influence of external forces is also blocked.

Furthermore, by using a metal with excellent thermal conductivity and a lower coefficient of linear expansion than the coating resin of the optical fiber for the spacer and pipe, the time delay in temperature detection is reduced, the effect of shrinkage of the spacer is reduced, and the optical fiber is The characteristics of the system were made to appear as they are.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment of the low temperature detection optical cable of the present invention, and FIG. 2 is a diagram showing the temperature detection characteristics of the cable of the present invention. DESCRIPTION OF SYMBOLS 1...Spiral groove, 2...Spacer, 3...Silicone resin coated fiber, 4...3 fiber coated with Teflon, 5...Acrylic resin coated optical fiber, 6...Metal pipe.

Claims (1)

[Scope of utility model registration request] In a cable core in which an optical fiber is housed in the groove of a core body having a plurality of spiral grooves on the outer periphery, the core body is made of a metal such as aluminum or copper that has a low coefficient of linear expansion and excellent thermal conductivity; A low-temperature detection optical cable characterized in that a plurality of optical fibers each having a different covering structure are housed in a groove in a manner that the operating temperature range for low-temperature detection is different.