Wind Speed & Direction Meter with A Clever Touch （1）

Published:2011/7/25 3:04:00 Author:Amy From:SeekIC

By G.Samblancat

This ingeniously designed circuit may be just the ticket for those interested in weather observations, in particular, wind speed and direction. The clever bit about the instrument is that both wind speed and wind direction are measured with a single sensor: a rotational speed meter with three blades, one fitted with a small vane.

One advantage of the specific design of the combined sensor is that the mechanical construction of the anemometer is far simpler than that of traditional meters while also reducing the risk of wear and tear as well as breakdowns. The instrument readout showing wind speed and direction is on an LCD as well as via a serial out­put that allows a PC or an (NMEA compatible) navigation instrument to be connected.

Even if mounted in a single enclosure, wind speed and wind direction meters typically employ two different sensors. Several solutions have become commonplace for the wind speed (anemometer) function, includ­ing optical sensors, generators and reed contacts. However, the classic design comprising a rotor with three half spheres causing a magnet to pass across a Hall sensor has the smallest number of disadvantages. The sensor type UGN3503 used in this project supplies a voltage of the order of 1 mV per gauss. These sen­sors, which are discussed in some detail, in the inset are impervious to dirt ingress and may be totally encap­sulated. They consume little energy and unlike reed switches cause hardly any electrical noise.

Wind direction meters are usually realized using potentiometers and optical Gray encoders, but here, too, the linear Hall sensor is a good choice. The circuit presented in this article is a simplified version of the Rotavecta system whose main advantage lies in the total absence of mechanical parts

The principle

The crux of the system is the little vane on one of the half spheres on the rotor. The vane causes a small acceleration or deceleration of the rotor, depending on its position relative to the wind direction. If we assume an angle refer­ence point relative to the wind (on the fixed part) then it has to be possible to determine the wind direction using two sensors fitted at an angle of 90 degrees. The calculation method con­sists of first measuring the average value (of each sensor) over a couple of revolutions. Each change in the wind direction will result in a small variation of these two average values. Next, using an angular reference table with two inputs, the microprocessor is able to figure out a ’wind vane’ angle expressed in degrees. Hence in our wind speed and direction meter, only two Hall sensors are used supplying voltages proportional to their magnetic field. Each sensor supplies a sinewave-like voltage (Figure 1) whose frequency increases with wind speed while the average value is an indirect indicator for the wind direction.

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