| 摘要 |
<p>Conducting cable, glass fibre or tubing is embedded in the wall of eg a dike bounding a canal bank over a distance of some kilometres. It is anchored at intervals. Signals, pulsed or continuous wave, are transmitted along it. A reflected signal indicates a disturbance; timing is a function of distance. Electrical, light or fluid pressure signals may be used. A transmitter at each end allows continued operation if the conductor breaks. Nuisance alarms are avoided by setting a threshold level. The sensitivity can be compensated for gradual settling.</p> |
