Abstract: A liquid leakage detector line is provided with a coating layer having at least liquid-absorbent properties and disposed at the outer periphery of a core which contains a pair of wiry electrodes disposed nearly parallel with each other, wherein the wiry electrodes comprise conductors which are extrusion coated with a polyester elastomer as an insulator. The liquid leakage detector line has excellent mechanical strength, rubber elasticity, resistance to fatigue from flexing and crack propagation resistance, and is free from the occurrence of pinholes, crazings, etc. inside the insulator during production and laying due to external forces applied to the wiry electrodes, such as pressure, tensile force, bending, and the like. As a result, erroneous actuation due to rainfall, etc. does not occur, and the time required to detect the sulfuric acid or other liquid to be detected has little dependence on the temperature, and short detection times for leaking liquid are possible even at low temperatures.

Abstract: An optical liquid sensor comprises an optical fiber folded back in two, a light-emitting element disposed at one end of the optical fiber, a light-receiving element disposed at the other end, and a detection means comprising a pair of units of a rod lens and/or large-diameter glass optical fiber with a narrow gap interposed therebetween in a linear segment of a folded-back portion of the optical fiber, the folded-back portion being hermetically sealed except at an aperture portion for admitting a liquid into the narrow gap. In this sensor, the loss of light at the narrow gap is minimized. In the manufacture of the sensor, a special jig is used for insuring that a rod lens or the like is accommodated in a metal sheath in such a manner that its forward end is flush with the end face of the sheath or projects slightly beyond the end face.

Abstract: The present invention relates to a liquid leakage detector line for detecting the leakage, if occurs, of a liquid such as sulfuric acid or strong alkali from a transportion pipe line or a storage tank. The liquid leakage detector line comprises: a pair of wiry electrodes each including a conductor covered with an insulator layer made of macromolecular material including an ester bond, the wiry electrodes being disposed substantially in parallel with each other; and a liquid-absorbent material covering these wiry electrodes. The liquid-absorbent material may be a braided body layer made of liquid-absorbent yarn which is disposed outside of the pair of wiry electrodes, or may be a braided body layer similar to the first-mentioned braided body layer which is disposed at the outer periphery of each of the wiry electrodes. If a sulfuric acid or alkali liquid leaks, the liquid-absorbent material covering the wiry electrodes absorbs such leakage liquid.