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Sensor dragging -- Anemometer problem
1 February 2009
A fix for a minor measurement inconsistency detected in commonly used anemometers has been found by NRG Systems, a US supplier of wind measuring equipment to the wind industry. The inconsistency had been noted on its #40 anemometer supplied from 2006 to the present. NRG, working with customers and wind consultants, found a tendency in many of the anemometer cups to sometimes succumb to vibrations that resulted in recordings of wind speeds slightly lower than they should have been. After several months of research, NRG says it understands the root cause for vibration and has the information needed to resolve the issue. More wind farms have been built throughout the world based on the NRG #40 sensor than any other, says the company's Barton Merle-Smith, but he points out that underestimation of wind speeds at a potential project site is better than over-reporting them. NRG has not been alone with the problem, according to Clint Johnson of wind consultancy Garrad Hassan. He says the C3 anemometer from American Second Wind has suffered a similar problem, which he describes as "sensor dragging," though the root causes may differ. Merle-Smith says the level of error for the #40 is small and generally within the margins of noise error that an anemometer might experience. "Certainly [NRG] can't fix all the anemometers in the field, but we hope once the problem is resolved, this issue will become a thing of the past," says Johnson.
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