Anemometers

anemometers
Anemometers:
a - hand wing (ventilation);
b - hand Cup;
in - induction manual

Anemometers are instruments to measure the speed of air movement. In sanitary-hygienic reasons, the most commonly used are the following types of anemometers.
Manual wing (ventilation) anemometer is designed to measure the speed directional air flow in pipes and channels of the air handling units. The threshold sensitivity of the device 0.2 m/s. Measuring range 0,3-0,5 m/sec. The reception part of the device - a light wind wheel (impeller) (Fig., a, 1), enclosed with a metal ring for protection against mechanical damage. The motion of the axis of the propeller is transferred to the system of gears, driving arrow meter (Fig., and, 2).
Manual Cup anemometer is used to determine average wind speeds. The reception part of the device - the chopper (Fig., b, 1) of the four hollow hemispheres, facing convex surfaces in the same direction. The counting mechanism (Fig., b, 2) enclosed in a plastic box. Turntable mounted on metal the axis of the lower end of which is connected with counting mechanism; wire handles (Fig., b, 3) serves to protect the pinwheel from accidental damage. Three arrows on the dial of the device show the speed of the hemispheres axis: a large number of units and tens, and two small number of the hundreds and thousands. A limit of measurement of air speed from 1 to 20,0 m/s; the threshold of sensitivity of 0.8 m/sec.
Except as described anemometers with mechanical counter, industry produces devices with electric meter. These include handheld anemometer induction ARI-49 (Fig. in).
Rules of work with the anemometer: device raise at arm's length (or fixed on a pole), orienting the current wind. Observation are within 10 minutes. When using the first two anemometers with mechanical counters, speed of air movement is determined by calibration certificate that came with the device; while using the ARI-49 translated calculation is required, wind speed (m/s) indicated on the scale of the anemometer.

Anemometers (from the Greek. anemos - wind and metred " measure") is of meteorological instruments for measuring elements of the wind. Air flows are characterized by speed and direction. The anemometer is possible to define one of these elements (usually speed), or both. In the medical-sanitary practice anemometers are used for observing the movement of air flows in an open atmosphere; but more often they are used in the closed premises: in laboratory and industrial conditions for measuring the air velocity in the suction and air supply openings of mechanical and natural ventilation to determine its effectiveness, the study of meteorological conditions in the working premises of industrial enterprises, public buildings and other Instrument to measure average speed flows for a certain period of time (usually expressed in m/s). The principle of the most anemometers is based on the phenomenon of power (dynamic) pressure exerted by the air flow into the oncoming obstacle; the speed is determined by the force of pressure on a moving rigid system of the device (wind anemometers). There are devices for definition of speed of air flow so-called gauge way; their receptor part of the tube is a pita (retaining, or pneumometric, snorkel). Finally, the air flow speed can be identified and the largest cooling of preliminary heated body under the action of the measured air flow (see Cattermole).
The direction of movement of air flows are determined most often by fluharty - plate wedge-shaped with a counterweight; meets flyugarka of two plates, placed at an angle of 20 degrees, such flygare more sensitive. Wind direction indicated by the name of the country of light, where it blows; the point of the horizon, where the wind blows, called Rumba; the horizon is divided into 8 or 16 points (Fig. 1). In practice usually take into account the prevailing (predominant) wind direction in this area; they are determined by long-term (usually within a year) daily observations. On this basis, the schedule or the so-called rose of winds (Fig. 2)expressing the percentage for the year number of cases of winds for each day on each Rumba and days of calm. The direction of the prevailing winds is important hygienic value: they must take into account in the planning of residential areas(see), in the construction of medical institutions (hospitals, health centers and others), as well as the placement of industrial facilities and sports facilities.
In practice enjoy the following types of anemometers. Handheld anemometer (Cup, Fusca) (Fig. 3) - portable, easy to use, widely used in sanitation practices device. Reception part represents the chopper from 4 hollow hemispheres (cups), fixed on the metal the axis of the lower end of which is linked to the registration mechanism. The arrow on the dial of the device show the speed of the hemispheres axis: a large number of units and tens, and two small number of the hundreds and thousands. For switching on and off of the counter of revolutions on the box of the device, there are the lever, and two rings. The screw attached to the anemometer below, is designed for installation of the unit on a pole height of 2 meters Measurement of wind speed: recording the readings of all the arrows (on small dials take into account only the integer division), place the device on a pole vertically (in an open atmosphere is best to keep the device in a stretched up her hand, making her face against the wind (scale anemometer facing the observer), wait 1-2 minutes, until the full speed of rotation of a vane, then cord include anemometer (Fig. 4) while the stopwatch; surveillance is conducted within 10 minutes by Calculating the difference between two counter (original and after 10 minutes of work of the anemometer) and dividing this value by the time of observation expressed in seconds, receive revolutions per 1 sec. This value approximates the desired speed of the air flow; to obtain more precise values are table for translation speed in speed (attached to each device). The device serves for determination of average wind speeds in the range of 1.0 to 20.0 m/sec.
Vane anemometers with grinder (ventilation). The receiving part is the impeller (grinder) of light metal blades attached connected with the counter of revolutions the horizontal axis. The devices are particularly sensitive and apply therefore to measure the velocities of the air flows in channels of ventilation systems.
Manual vane anemometer (ventilation) (Fig.5). When operating the unit focuses on the thread so that the counting mechanism was behind the thread concerning the impeller; to overcome the inertia of the resistance of the device rather the impeller is rotating idle only 0.5 minutes; the duration of observations is limited to 2 minutes; the procedure for calculating average speed of the flow is the same as the previous type of anemometer; beyond measure air velocity of 0.3 - 5.0 m/sec.
Ventilation differential anemometer (Fig. 6) equipped with a small blower fan, leading the grinder in motion. This device is designed to overcome the inertia of the resistance of the device and thus significantly increases its sensitivity: you can measure the speed ranging from 0.02 m/sec.
Work with the anemometer so: having the key of the fan mechanism (outside the scope of air flow)include counter, recording speed of rotation of the impeller under the influence only of the fan. Then again start the spring fan and put anemometer so that air is directed to the side of the impeller, again celebrate the counter; the difference between the first and the second readings will show the speed of the air flow.


Electrical anemometers. For devices with electric tachometers (mechanisms for determining the number of turns) include: induction anemometer and contact anemometer. Reception of the manual for induction anemometer (Fig. 7) - three Cup spinner, the axis of which is connected with the magnetic system (generator of electric current); the scale of the instrument graduated in m/s; the outside measurements of the flow velocity of 0.2-30.0 m/sec. Work with the device, as with conventional manual anemometer (Fuss). To improve accuracy, you should spend a few measurements at intervals of 0.5 minutes and take an average.
Anemorumbometer - devices that are used to determine the speed and direction of the wind. The simplest of them is the weathervane wild (Fig. 8), used primarily in medical institutions, on the beaches, sites for air baths, etc. During the rotation of a vane Board always takes a position perpendicular to the wind direction, and under pressure last deviates from the vertical position on a particular angle. Position rejected by the Board, including bars using pointers, determine the wind speed; the instrument has two boards: a lightweight (200g) to measure velocities not exceeding 20 m/s, and heavy (800 g) for speeds up to 40 m/sec. Close the wind speed can be defined, multiply the number of brad 2 (when using light Board) or 4 (when using heavy boards). Weathervane for observations set in an open place at the dry smooth pole height of 8-10 m brad with the letter S (N) must be installed on the North (the compass or the Meridian line, i.e. along the Meridian of this place).
Electric anemorumbometer (Fig. 9) - the Cup device type. Its principle of operation is based on transformation of mechanical energy, developed by the rotation of a vane in electric; power generator is a permanent magnet (located at the top of a fixed part of the device); voltage resulting current is measured by a voltmeter with a scale graduated in m/sec. The wind direction indicator in the instrument is flyugarka.
Manometric method of measuring wind speed. The method is quite easy to determine the speed of air movement in the pipelines and, in particular, in mechanical ventilation ducts to calculate its efficiency. Devices directly measured the pressure of the air flow, the basis for calculation of the speed of its movement. For definition of pressure are Prandtl tube (Fig. 10)to be included in liquid manometer.
It consists of two metal tubes are soldered one another. The receiving end of the device (i.e. one that is introduced into the lumen of the duct) are organized as follows: the internal tube is one hole (Fig. in point 1), a few holes(2, 2', 2", 2"'), located radially (on the picture in place of section a-b); the lower ends of the tubes with the help of short rubber hoses attached to the liquid manometer; it is easiest to use a U-shaped glass tube filled to half the height of the water and fixed on a scale with millimetric divisions (Fig. 11). Having measured the altitude difference of water in both knees, expressed in mm of water. senior calculate (approximately) the air flow rate by the formula: v = 4 & Radic; h m/s, where h is the value of pressure in mm of water. Art. (gauge; usually taken the average of several measurements at different points of the duct). For precise measurements using micromanometer.

Fig. 1. The scheme of points.
Fig. 2. Wind rose with the prevailing North-Western winds.
Fig. 3. Manual Cup anemometer.
Fig. 4. Switching on and off of the anemometer cable. Fig. 5. Manual wing (ventilation) anemometer.
Fig. 6. Ventilation differential anemometer. Right - scheme of actions of the air flow generated under the action of the fan.
Fig. 7. Manual induction anemometer.
Fig. 8. Vane wild: 1 - flyugarka; 2 - the vertical bar; 3 - tube wind vanes; 4 - contrast; 5 - coupling for twigs pointer points; 6-8-pointer speed, metal plate, frame and arc with numbered by including bars from 0 to 7.
Fig. 9. Electric anemorumbometer (scheme): 1 turntable; 2 - magnet; 3 - connecting wires; 4 - button; 5 - speed indicator.
Fig. 10. Tube Prandtl.
Fig. 11. The gauge of the U-tube with water.