An insulated gold electrode terminates 0.1mm from the tip of the rotating blades and detects the change in electrical impedance as each blade passes. The sensing head consists of a 5-bladed propeller that runs in jewelled bearings. As there is no physical contact between the electrode and blade, the propeller can rotate freely and respond to low velocity of the surrounding fluid. The propeller is able to rotate freely within a protective shrouded cage.
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