Analyser for determining composition of sea-, river- or canal-bed

摘要

A dredger lowers a probe that sinks under gravity into the silt on the sea bed. The probe is effectively a tuning fork (4) with one tine (5) excited by piezo-electric means. The other tine (6) receives the signal, whose frequency and amplitude are functions of the density of the silt between the tines. The received signal is amplified (7,8) and fed via a low-pass filter for computer processing. A phase-lock loop (13,14) between receiver chain and the flip-flop (15) maintains the piezo-electric frequency at resonance. The flip-flop output (16) also goes to the computer.