How our superbly reliable wind sensor works: A reed switch is a long-lived, hermetically sealed switch that actuates when a magnet is brought near it. The anemometer reed switch is normally open, whereas the centered vane reed switch is normally held closed by the strong vane magnet, regardless of wind direction. During each revolution of the cups:

• The anemometer reed switch closes briefly as the anemometer magnet approaches, then reopens when the anemometer magnet has passed. This actuation always occurs at the same angular position of the cups.

• The vane reed switch opens briefly, then closes again as the magnetic shield passes between it and the vane magnet, absorbing the magnetic field. The timing of the vane reed switch is determined by the angular position of the vane magnet, which is in turn determined by wind direction.

Wind direction is calculated (with a resolution of 1.4 degrees) by comparing the relative timing between operation of the two reed switches.