Wind sensors: anemometers, wind vanes, barometers

Anemometers measure the horizontal wind speed (velocity). This parameter is crucial for any wind site assessment. Cup anemometers are the general standard type of anemometer. They are robust and resistant to turbulence and skew winds caused by masts and traverses. Each anemometer should be individually calibrated and equipped with a certified calibration report, according to international standards (e.g. MEASNET). The number of anemometers applied at one mast can vary from a minimum of 2 sensors up to 6 sensors (using Ammonit data logger Meteo-32X). Most anemometers can be equipped with electronically regulated heating.
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Ultrasonic anemometers measure the horizontal wind speed and direction as well as the acoustic virtual temperature. However, because of their high power consumption, a connection to mains power supply is required and their application at self-contained, solar-powered measurement systems is not feasible. Ultrasonics offer excellent performance ratings at well-powered measuring stations. At present they are not accredited according to the internationally valid MEASNET regulations. Ultrasonics are applied for wind park monitoring, on wind turbines and on offshore projects. Most ultrasonic anemometers can be fitted with electronically regulated heating.
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Propeller anemometers measure the air flow from any vertical and horizontal wind direction. They are usually applied in wind park monitoring by showing how the turbines react to airflow. A propeller anemometer utilises a fast-response helicoid propeller and high-quality tach-generator transducer to produce a DC voltage that is linearly proportional to air velocity. Airflow from any direction may be measured, but the propeller responds only to the component of the airflow that is parallel to its axis of rotation. Off-axis response closely approximates a cosine curve with appropriate polarity; with perpendicular air flow, the propeller does not rotate. The output signal of propeller anemometers is suitable for a wide range of signal translators and data logging devices.
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Wind vanes determine wind direction. Evaluation of the wind direction enables the best possible positioning of wind turbines. Ammonit wind vanes offer an excellent, fine resolution of 1°, while having very low energy consumption. It is essential that a wind vane covers an entire 360° degree radius, without a north gap. Cheaper wind vanes often have lower quality internal electro-mechanic fittings, which limit their life span, and a considerable north gap. Most wind vanes can be equipped with electronically regulated heating. Analog or potentiometric wind vanes are available.

Ammonit will soon add the Thies TMR wind vane to the product range.

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Thermal sensors measure air temperature, while hygro-sensors measure air humidity. Both sensors are often applied in combination to reduce cost. The calculation of the air humidity does not directly influence a wind site assessment, but knowing this parameter helps assessing the potential danger of ice build-up at the measuring location. The temperature sensor should always be mounted at a height of at least 10m to ensure sufficient distance from heat radiating from the earth.
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Barometric pressure sensors (barometers) measure the air pressure. Air pressure and air temperature should be evaluated for an accurate wind site assessment, however, because this data could be obtained from nearby weather stations, they are not considered an essential part of a measuring system. Even so, barometers are worth consideration, taking into account the savings made on the expense of supply, analysis and incorporation of external data over the course of a measuring campaign (at least 12 months). We generally would recommend the inclusion of an air pressure sensor as part of a measuring system.
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Precipitation sensors are designed to measure the quantity and intensity of precipitation striking the earth’s surface. Precipitation is best measured with a tipping bucket device. Precipitation, collected over a surface of 200 cm2, is conducted through an inflow sieve into a tipping bucket. When the bucket has collected 2 cm2 = 0.1 mm of precipitation, it tips over. This measurement principle is based on the “Guide to Meteorological Instruments No 8, WMO”. Precipitation sensors are typically applied for meteorological assessments. This robust device can be equipped with heating when appropriate to the climatic conditions.
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Pyranometers (global radiation sensors) measure global radiation. They are also used as reference instruments due to their measurement precision. The use of this sensor is crucial for measurements with solar-powered applications. It is advisable to use only classified and calibrated pyranometers to ensure accurate results. Adjustable feet and a level allow easy horizontal adjustment.
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Appropriate high-quality cables are essential to connect the sensors with the data logger. Corrupted measurement data can occur when connection cables are too long or when the cable resistant is compensated in the supply. It is crucial that cables are carefully installed within the lattice tower to avoid cable damage.