Cup anemometers measure the rotation induced by the wind on three or more cups mounted on a central axis. This rotation is then converted into an electrical signal via an encoder. The electrical signal is related to the horizontal wind speed around the cup via a calibration function. Cups must be installed carefully to avoid the effects of the surrounding structure on the measurement. Cups do not always measure off-horizontal winds accurately. This capability is known as a cosine response and is often limited to flows with inclinations of less than 10°. The IEC 61400-12-1 (2005) wind turbine power performance standard can be used as a starting point for literature related to making accurate cup anemometer measurements. Cup anemometers have TRL >8. The history of cup anemometers is outlined by Pindado et al. (2014). One example of a cup anemometer is shown in Figure 4.
The accuracy of a cup compared to a reference device (usually a pitot-static tube) can be better than 1%, but this depends on cleanliness, service period, turbulence, and other factors.
Cup Anemometers are generally considered to have a TRL greater than 8.