ASL400 is designed for marine and on-land applications for liquid detection, pump control, water ingress alarm systems, for high and low alarm level, overfilling protection on liquids with or without foam. ASL400 works on the principle of distributed acoustic waves in a metal rod. If the rod is not covered by the liquid the sound waves are dispersed freely without any interference. If liquid covers the rod the emission of sound waves is muffled and this interference is picked up by the piezoelectric sensor and converted into a current signal in the current loop (on-off). These instruments have no moving parts, no vibration, no optical or capacitive detectors. They are pure static sensors offering the maximum reliability.