JPS57113328A - Low-temperature detecting system by optical fiber - Google Patents

Abstract

PURPOSE:To enable to perform a simple detection of a temperature change occurring position within a wide measurement region, by a method wherein an optical fiber, which is sharply increased in an optical transmission loss at a low temperature, is mounted to measure a delay time corresponding to a rapid change in a back scatter light against an incident light. CONSTITUTION:An optical fiber 1, which shows a steep increase in an optical transmission loss at a low-temperature region, is mounted at a scope to be measured of temperature, and the photo incident terminal is connected to a luminous source 3 to measure a quantity of a back scatter light against an incident light at the incident terminal. A temperature change occurring position lx is detected from a delay time corresponding to a steep change in the quantity of the back scatter light. Further, a differential characteristic dPl/dl against a position l of a quantity Pl of said back scatter light is found, a producing section X of a temperature change is detected from the differential characteristic, or temperature at an abnormal cooling occurring section is detected from said temperature characteristic and the temperature characteristic of the optical transmission loss per unit length measured beforehand.