1. Anemometer Laboratori
2. Venturi anemometer principle

1. Anemometer Laboratori
Anemometer Laboratori
Fig 1. Schematics

Built several years ago, with 100% reused materials. Cost: zero euros!

- Butter pot
- Vu-meter from old HI-FI
- A variable resistance of 100 K of old radio equipment
- Old radio cassette motor
- Aluminum disc (from Coke)

The working principle is as follows:

- With the box of coca-cola, you get a disc of aluminum to build the propeller.
- The helix drives the radio cassette motor on variable speed, according to the wind.
- Electricity generated (motor running as a dynamo) is measured at the vu-meter.
- The variable resistance allows to adjust the device.
- Finally you must change the internal scale of the vu-meter or make a conversion table, adjusted to the actual wind in km/h or m/s
- Batteries are not necessary

1. Compact and transportable design

2. Front view

3. Aluminum helix front view

4. You can see the helix, the motor, the
vu-meter, and variable resistance
(in black) on the left.

Fig 2. Photos

2. Venturi anemometer principle

The principle is simple:

The device consists of a transparent cone-shaped tube, open at both ends. The lower opening is rotated 90 degrees to face the wind. Inside the tube there is a disc, very light, balanced by the wind pressure and selfweight.

Due to the conical shape of the tube, the flow of air circulating inside the tube has variable speed. In its most narrow section (bottom) air runs faster than in the wider section (up) due to the conservation of the air flow between the two extremes.

When the external wind speed increases, the dynamic pressure on the disc increases (in proportion to the square of wind speed). The pressure on the disc is greater than its own weight, then the disk moves upwards. But, simultaneously decreases the wind speed inside the tube, and pressure re-balance the weight of the disc in its new position.

Similarly, when the external wind speed decreases, decreases the pressure on the disc, which is not enough to balance its own weight. Then the internal disc moves downward, and simultaneously increases the wind speed inside the tube, until its pressure balances the disk in the new position.

All this is a simplified description of other effects that occur. But for practical purposes, can be used to make a functional anemometer, experimenting with different tubes and disks of various sizes and weights.