Load cells under water.

The EPICTidal Team consisting of Lab-Sea-Systems Dr Florent Trarieux, Cranfield University’s Dr Joao Amaral-Teixeira and Nick Barlow, Managing Director of Designcraft Ltd (Blade designer and manufacturer) wanted to know the performance implications of employing lower cost methods for the manufacture of large scale tidal turbine rotors. Lowering the cost of rotor blade manufacture would make this renewable energy more economical to use and widely accessible, benefiting all tidal energy markets throughout the world.

To assess the rotor blade performance they developed a submersible tidal turbine test rig incorporating 2 x DDEN load cells from Applied Measurements. The rotor blade design to be tested was coupled to the tidal turbine test rig and placed in a state-of-the-art test tank, where the team were able to increase the size, flow rate and turbulence levels within the tank. The first DDEN load cell measured the torque and the other measured the thrust of the tidal rotor design.

“The DDEN were ideal to use in this application as they are fully submersible up to 10 metres” explained Bob Davies, Applied Measurements’ Production Director.

The DDEN in-line submersible load cells are low profile and very compact and designed to measure both tension and compression underwater. They come with an IP68 rating and are sealed using ‘O’ rings to guarantee integrity during long term submersion. Their IP68 rating and ‘O’ ring sealing makes them ideal to use underwater or in areas at risk of flooding. The DDEN submersible load cell comes in capacities from 0-250N up to 50kN with customised capacities, threads and dimensions on request, as well as versions rated to greater submersion depths in seawater, oil and other more aggressive media.

For this submersible application the DDEN load cells were fitted with 10 metres of submersible 4-core screened polyurethane cable for complete submersible protection underwater. They have a guaranteed accuracy to <±0.15% of the rated capacity (0.05% typical) enabling precise thrust and torque blade measurements which was crucial to this renewable energy application.

A small ICA6H amplifier was fitted within the bodies of both the DDEN submersible load cells. At only 19mm diameter this amplifier is ideal for fitting inside the body of a load cell. An ICA6H amplifier was used in this application so it could easily fit within the load cell, maintaining the submersible protection needed for underwater testing. The ICA6H load cell amplifier delivered a high-level ±10Vdc analogue output, for use with their data acquisition and control systems.

Other outputs are available for the DDEN including 0-5Vdc, 0-10Vdc or 4-20mA, which can be used with many data acquisition and control systems. For a digital output, a DCell load cell digitiser can be used instead of an ICA to deliver a RS485 digital output.

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