| 摘要 |
<p>PURPOSE:To detect the abnormality of low temperature in a short time with high precision by wiring one cable close to a body whose temperature should be detected and wiring the other in the same route so that it is not affected by the variance of temperature, and detecting the difference of optical transmission loss between them. CONSTITUTION:If a liquid leak of LNG or the like occurs in a pipeline 4, an optical fiber cable 31 wired close to the line in a sensor part A is cooled to increase the optical transmission loss quickly. A fiber cable 32 separated from the line 4 is not cooled and the optical transmission loss is not changed, and the output value of a differential amplifier 53 becomes larger than the set value of an optical lever setter 54, and a comparator 55 is operated to send an alarm signal 56. Thus, the unnecessary change of optical transmission loss is eliminated by the combination of cables 31 and 32, and the difference between the output value of the amplifier 53 and the set value of the setter 54 is reduced because the output value of the amplifier 53 is not changed in the state of no liquid leak, and liquid leak is detected with good response.</p> |
