Anemometers and how they work!
|In the August 2015 Newsletter we covered choosing an anemometer for your application. In this month’s newsletter we will cover how anemometers work. The anemometers we will cover include cup anemometers, vane anemometers, hot wire anemometers and we will also cover ultrasonic anemometers which are becoming more popular due to the fact they have no moving parts.
The cup anemometer is the most common type of anemometer and generally has three or four cups attached to horizontal arms. The arms are then connected to a vertical rod. The cups rotate as the wind blows which in turn then makes the rod spin. A reed switch or a Hall effect sensor is generally used to measure this rotation. The number of times the rod spins over a certain period of time is then converted into a wind speed. This is then usually displayed on a digital display so that user can view the reading. Alternatively it may output a signal so that it can be sent back to a PLC, data logger or building management system.
These units operate in a similar manner to the cup anemometer, however, instead of operating horizontally using cups it uses a vane propeller. Some of the fan blades on the propeller have tiny magnets mounted on them and, each time they make a single rotation, they move past a magnetic detector called a reed switch. When a magnet is nearby, the reed switch closes and generates a brief pulse of electric current, before opening again when the magnet goes away. This kind of anemometer effectively makes a series of electric pulses at a rate that is proportional to the wind speed.
Figure 2: Our most popular vane anemometer for HVAC Professionals the LV110S.
Hot Wire Anemometers:
The principal of a hot wire anemometer is based on a heated element from which heat is extracted by the colder impact airflow. The temperature of the hot wire is kept constant via a regulating switch, and the current (amp draw measured internally) is directly proportional to the air velocity. They then measure how much current is required to keep it at a constant temperature, or measure how much the temperature changes under constant current. The heat loss is then converted into an air velocity reading.
Measures wind speed based on the time of flight of sonic pulses between pairs of transducers. Measurements from pairs of transducers can be combined to yield a measurement of velocity in 1-, 2-, or 3-dimensional flow. The lack of moving parts makes them appropriate for long-term use in exposed automated weather stations the accuracy and reliability of traditional cup-and-vane anemometers are adversely affected by salty air or dust.
Figure 4: Our Orion Station, utilises a Ultrasonic sensor, meaning it contains no moving parts.
If you would like to discuss this article further please feel free to contact one of our friendly Scientists via email or phone on 1300 737 871.