Instrument: Tilt Current Meter

Tilt current meters are based upon the property that a tethered object will experience drag inside a current flow. If a restoring force perpendicular to the drag is introduced, the tethered object will tilt until the system of forces is balanced. Therefore, measuring the tilt allows calculation of drag force, from which current speed can be obtained. Measuring the direction of tilt gives current heading.

Tilt current meters operate under the drag-tilt principle and are designed to either float or sink depending on the type. A floating tilt current meter typically consists of a sub-surface buoyant housing that is anchored to the sea floor with a flexible line or tether. A sinking tilt current is similar, but the housing is designed such that the meter hangs from the attachment point. In either case, the housing tilts as a function of its shape, buoyancy (negative or positive) and the water velocity. Once the characteristics of a housing is known, the velocity can be determined by measuring the angle of the housing and direction of tilt.