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Wind NI | Instrumentation

Advice Section

Instrumentation

Posted on: December 3rd, 2011

Sensors:

A crucial factor for precise measuring is the correct choice of sensors. For wind measurement, only anemometers according to IEC 61400 – recommended: category – should be used. The anemometers must be calibrated by a specialised institute in accordance with national and international standards and regulations (MEASNET)

If the client is relying upon data generated by an insufficient or incorrectly-installed wind measurement system, this could lead to big miscalculations and builds up the risk of economically non-viable operation of the planned investment. Small deviations could be caused simply by the use of non-calibrated anemometers

Anemometer producers guarantee a certain accuracy for their products, for example ± 0.3 to 0.5 m/s (or 3 to 5 % for speeds above 15 m/s). The measurements usually remain well within this tolerance range and this is sufficient for all needs in weather forecast and in industrial processes. For a reliable prognosis in wind energy, this tolerance is not acceptable. When using a non-calibrated anemometer, it is necessary to reckon with a reduced accuracy for the predictions. This is a risk and we recommend using only anemometers which are individually calibrated.

The anemometer should be calibrated by a specialised institute in accordance with national and international standards and regulations, which should also provide an official certificate of compliance (ISO 3966 1977, IEA-guidelines, uniform measuring process of the MEASNET-Group). The members of the MEASNET Group (www.measnet.com) are independent, international institutes which have specialised on applications in the field of wind energy. The development of standard measuring processes and the continuous flow of experience and information makes sure that the calibration of anemometers will be handled according to the strictest guidelines.

The results of each anemometer calibration are presented in a calibration report, which describes precisely which aspects of the performance of the anemometer have been measured. In addition, the measurement equipment should be described in each report, including the reference tools and their last check-up.