I average this speed over 30 seconds before reporting it to HA. You could chose anything or convert it later in a HA template. So I had to calibrate f_a manually, by comparing with another calibrated anemometer. Of course, since this is an old scrap part, I have nil info on that. Typically higher end anemometers specify an anemometer factor (f a) which depends on things like size, shape of the cups, shaft bearing friction, etc. But that would heavily underestimate the real wind, because it doesn’t account for friction losses in the anemometer mechanics. Now you could use basic math to derive the wind speed from the angular speed if you measure the length of the arms from the shaft to the center of the cups. That is the time the cups take to do a 90° turn. I measure the time (in microseconds) that a pulse is high. I still have to do some more field testing on how well that works with very short pulses on high winds. The shorter the pulse, the higher the speed. So I decided to measure the pulse width instead and derive the rotation speed from that. That works pretty well for higher wind speeds, but it’s not very precise for low wind speeds when the cups rotate very slowly. The easiest way to convert this to wind speed is to count the pulses over a set amount of time.
#ANEMOMETER UNIT OF MEASUREMENT FULL#
So the signal goes high and low twice per full rotation (two magnets).
So I just hooked up my scope on its output while blowing on the cups to make them turn:Īh ! Nice digital signal with a convenient amplitude for an MCU ! The signal goes high if one of the two magnets is within 45° of either side of the hall sensor.
The references printed on the chip were cryptic and partially unreadable. According to one report, reacting to oncoming wind before it reaches a turbine improves power production by about 10%.I wasn’t able to find any information about the type of sensor used. The base unit, housed in a separate assembly, can be mounted inside the turbine’s nacelle. The system is comprised of a base laser and a remote lens. It transmits that data to the controls in time (20 sec of lead time for a 35-mph wind) to reorient the turbine. This sensor looks 300m ahead of the turbine to measure wind speed and direction as it approaches the turbine rotor. One laser wind sensor mounts atop the turbine nacelle (pointing through the rotor) to measure real-time horizontal and vertical wind speed and directions in front of the turbine. Laser-based wind sensors use laser Doppler velocimetry – an optical remote-sensing technique similar to Doppler radar – to measure minute frequency changes of light reflected by microscopic air particles moving with the wind, which precisely determines wind speed and direction. Sodar units are reported to have performed well in tests. Sodar uses short-wavelength sound waves to measure the Doppler shift of emitted sound and calculate wind speeds. Users can often access data in real time from a computer over a satellite wind-data service. Readings from these devices look like anemometry results and so need no expert analysis. One model runs on as little as 7 W from a battery recharged by a solar panel, and it can be relocated by one man with a truck. The unit is said to work unattended to capture accurate wind data at turbine heights in any weather and location. This latter device, also called a sonic wind profiler or a sodar (sound detection and ranging) unit, detects wind speeds and directions at several levels up to about 300 m. Larger, ground-mounted sonic instruments, however, can take the place of a met tower and measure wind speed and direction at several elevations. In the cases above, the instruments are small enough to mount on a nacelle. Without moving parts, measurement is said to be immediate and precise. Measurement times are affected by the wind speed and direction blowing along the line between the transducers. The wind speed is calculated from the time it takes the ultrasound to travel to the opposite transducer. A microprocessor measures the time it takes to travel to a ‘South’ transducer. On a typical sonic anemometer, a transducer sends a pulse of ultrasonic sound from a ‘North’ facing side of the sensor. Ultrasonic sensors function without moving parts. Second Wind’s Triton wind profiler uses sodar to collect wind data.