光ファイバを用いた液体識別センサの試作

抄録

An optical fiber liquid sensor for the remote detection of very small amount of liquid leak was developed. The sensor consists of an optical prism and focusing lenses and has the following features.
(a) long distance, maltiple point detection for more than 10km
(b) insensitive to water
(c) safety in explosive or high voltage environment
In this sensor, the optical signal from the input fiber is collimated by a Selfoc lens, and the incident angle to the detection surface of the prism is adjusted to a specific angle which is determined by the refractive indices of the prism and the liquid to be detected. The sensitivity of the sensor was 5dB against a differnce in refactive indics of 0.02, according to the experiment using various kind of liquids. The resulting data of the expriment were well matched to the theoretical value, and indicated that the sensor can discreminate liquids of differnt refractive indices. The sensitivity against the liquid quantity is also very high as to detect a small spot of kerosine on cloth. An experimental system for long distance leak detection was evaluated using an optical fiber of 1.6km long. The system works by the same principle to optical fiber fault locator (OTDR), with a range gate circuit controlled by a digital delay circuit to detect sensor distance. A 10km leak detection system with 17 liquid sensors was estimated to be possible using 1.3μm wavelength and such system will be suitable for pipe-line or plant maintenance application in chemical industry.