Riding the wave

Anemometer

The anemometer is used to measure the wind speed, that is measured, like the other speeds, in meters per second or kilometers per hour.

It consists of two parts:

1. The receiver, namely the external device which receives the action of wind.

2. The counter, which is the device that counts the number of kilometers traveled by the wind.

Receiver

The outer element consists of a windmill called a Robinson windmill, formed by four copper cups fastened at the ends of two rods forming a cross. The hemispherical cups, of equal size, are all facing the same direction.

The mill is attached to a vertical rotating shaft that, penetrating the enclosure of cast iron "A" rests at the lower end on a hollow bronze support. This hollow support contains oil that can last several days.

The container "A", very strong and closed on each side, serves to protect the components it houses. The mill always turns in the same direction, whatever the wind direction, as the wind, acting on the concave face of each cup with more strength than on the convex side, gives the mill a circular motion.

The shaft "FR" is equipped in its lower part with a worm gear, which engages the vertical wheel "H". An eccentric "I" at every turn slowly lowers the end "I" of the lever "IL" pinned in "K", while the other end "L "is goes up.

The lever "IL" can slide on the pivot "K", and can be fastened with a screw, to adjust the range of movement of end "L". The latter pulls a wire going into the meter below.

A cap under the center "F" of the cross protects from the rain the bearing, that is provided with a groove to introduce oil into it.

The diameter of the mill, ie the distance from the center of two opposite cups, is 2.9 feet, while the number of teeth in the wheel is 120. Therefore, according to the formula of Robinson, the wind speed "V", corresponding to a complete revolution of the wheel, will be 1000 meters, as it is known that the wind speed is three times the circumferential speed of a cup of the mill. In other words, while the cup travels while turning, the wind travels three times that.

Anemometer

Counter

The counter has three wheels connected with each other - displaying the units, tens and hundreds - located in a small box (bottom left in the figure). The box is on a flat below the receiver, and has a glass window on the upper face, through which values are read.

A lever "M" engages with one end in the teeth of the first wheel - the one for units - and each time the other end is lifted by means of the wire connected to lever "ON" the wheel advances one step.

Then every ten turns of the wheel H, the first wheel makes a complete turn and moves one step the second wheel. The same for the third wheel, that makes a turn every thousand rotations of the wheel H.

Hence the meter counts up to a thousand kilometers, which occurs when the in the three zeros are shown.

An anemoscope is placed on one side of the anemometer. The rod "DE" that supports the vane "B", passing through two bearings, moves an index on the dial "E" next to the counter.


Portable anemometer


The portable anemometer provides an immediate reading of the instantaneous velocity of the wind. When shipping it is related to the apparent wind which results from the combination of the motion of the ship with the real wind. The latter is determined with a graphic construction.
The instrument shown here belongs to the collection of the Hydrographic Institute of the Navy.

By Paola Presciuttini
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