Rotor current meter

Many RCMs have been replaced by instruments measuring the flow by hydroacoustics, the so-called Acoustic Doppler Current Profilers.

However, for instance in Fram Strait, the Alfred Wegener Institute still uses RCMs for long-term monitoring the inflow into the Arctic Ocean.

[1] A RCM usually consists of the recording unit, a propeller to detect the water velocity and vane to determine the direction of the flow.

The recording unit houses a battery pack for energy supply, the Analog-to-digital converter, possible additional sensors for other variables (like the standard parameters conductivity, temperature, depth, CTD) and a micro-controller.

Small velocities are difficult to detect because the vane shows a lot of inertia and the rotor needs to overcome friction before starting to rotate.

Rotor current meter RCM 8 with red vane and Savonius -rotor.
Data storage unit of an RCM-8.
The movement of Earth's north magnetic pole across the Canadian arctic, 1831–2007.