Anemometer: principle of operation and types of instruments

In the first half of the 16th century, the Italian mathematician L.B. Alberti invented a device that measures the speed of air movement. The device was called an anemometer (from the Greek anemo — wind, meter — to measure). The design was improved by the Irishman D. Robinson in 1846. And at the end of the 20th century, the device was able to determine the direction of the wind.

Where and how are anemometers used?

Currently, the device measures the speed and direction of movement of gases and liquids. The device has found its application in the following areas of human activity:

• meteorological service. Meteorological stations record a set of physical phenomena in the atmosphere that determine the weather. One of them is the strength and direction of the wind near the ground and at a height. Based on the analysis of indicators, a weather forecast is compiled.
• Airport Ground Service. Using an anemometer, airport ground services receive information about the actual and expected weather at aerodromes and aircraft flight routes (strength and direction of wind, dangerous phenomena).
• During construction work. Used in the design of ventilation and air conditioning systems in rooms for various purposes. Tower, cable and gantry cranes are equipped with devices to signal the driver, since strong wind poses a threat to this type of equipment.
• In agriculture. A modern anemometer not only determines the strength and direction of the wind. It also determines the temperature difference, weather harshness factor, dew point and air humidity. These are the main indicators that affect the work of the farmer.
• In energy. Based on observations of the «behavior» of the air, the installation site, height and model of the windmill are determined with an alternative use of wind. After installation, analyzing the data of the installed anemometers, determine the efficiency of the windmill.
• in the mining industry. At mining enterprises, an anemometer is used for depression surveys, monitoring and determining the actual values ​​of the air flow velocity in tunnels, mines and ventilation networks.
• Sport. Sports in which the strength and direction of the wind play a decisive role: parachuting and sailing, high diving, kitesurfing, surfing, etc.

General principle of operation of anemometers

Measurement of the speed of movement of air masses, gases, etc. and the transformation of the information received into «specific units» occurs in three main parts of the anemometer:

• measuring parts, in which the air flow creates a «disturbance» directed to a physical quantity that determines the principle of operation of the device (ultrasound, radiation, metal cooling, pressure, etc.);
• transformative a part that transforms a given physical quantity into some kind of energy;
• fixing a part that displays the result using various counters, displays, scales and indicators.

Types and device of anemometers

The design and principle of operation of the device determines the type of anemometer. They are mechanical and electronic.

Mechanical

Mechanical anemometers include:

• Cup device. The simplest and most common. It is an axis on which four hemispheres (cups) are cruciformly fixed. Under the pressure of the air flow, the cups rotate around their axis in a vertical plane. The axis, in turn, is connected to a three-scale dial, which counts the number of cup rotations in a certain time interval. A flag attached to the cup allows you to know the direction of the wind.
  

  This device makes it possible to measure wind strength from 1 to 20 m/s. The resistance of the anemometer to turbulent flows allows it to be used on open surfaces.

• Wing device. It works similarly to a cup, but instead of an axis with cups, the wind rotates a paddle impeller. The mechanical counter is located next to the blades, since the impeller rotates parallel to the air flow. This factor limits the ability to measure wind force from 0.3 to 5 m/s. Unlike cup devices, bladed determines the direction of the wind by changing its position.
  

  The impeller is used in the design of air duct systems of buildings and structures. Devices with a flexible connection of the impeller and mechanical counter are excellent for working in hard-to-reach places.

Electronic

Less common — electronic — include such devices:

• Ultrasonic anemometer (acoustic) measures the strength of the sound transmitted from the transmitter to the receiver and determines the wind speed using the dependence of the sound speed on the direction of the air masses.
  

  The design of an acoustic anemometer is rather complicated. Measurements take place in two-, three- or four-dimensional space. Along each axis, there are two pairs of receiving and transmitting devices that send/receive ultrasonic waves. The speed at which an ultrasonic wave travels from the transmitter to the receiver determines the wind speed.

  The 2D ultrasonic instrument shows how fast the air is moving and in which direction. Three-dimensional additionally — air humidity, four-dimensional — temperature.

  Since the device has no moving parts, it can record wind speeds up to 60 m/s. Devices of this type are used to measure the microclimate at workplaces of industrial enterprises.

• Thermal anemometer (thermal). It fixes the heat loss of a thread made of metal, in which the temperature resistance coefficient has a “+” sign, during the movement of air masses.
  

  The principle of operation is as follows: a current is passed through the filament, the moving air flow lowers the temperature of the filament, and the electronic device calculates the speed of gusts. A thermal anemometer measures slow air currents.

  This device is not used as an independent unit. Most often it is part of some system. For example, a thermocouple is present in every car and controls the engine cooling system.

• Dynamometric anemometer. Comparing the excessive internal and external pressure in the L-shaped glass tube (Pitot tube), the device determines the speed of air movement. It is used in ventilation systems and mines to determine the volume of flow and the speed of the air flow.
  
• Laser Doppler anemometer. This is a complex optical-electronic system that measures the linear velocity using the Doppler method. The operating principle of the system is as follows: a beam of laser radiation from a stationary receiving device irradiates a moving object. The radiation reflected from the object is registered by the receiving device. The radiation frequency of the moving object and the receiving device are compared. The values ​​differ by an amount proportional to the speed of the object relative to the receiving device.
  

  This type is used in wind tunnels in the modeling and design of aircraft, submarines, cars, trains, as well as to determine the load of wind and blast waves on structures for various purposes.

This article lists only some areas of human activity where an anemometer is used. In fact, this device solves a wider range of tasks. If it is necessary to use anemometers, the purpose of the application and the conditions must be clearly defined.