In the seventeenth century, the fact that air has a certain weight became known and proven to humanity. The assumption of its pressure on various objects was proven using a special device - a barometer. It will be discussed in this article.

A device that determines air pressure

First, let's give a definition. A barometer is a device for measuring a certain air pressure on objects. Its inventor was E. Torricelli. In 1644, the barometer was a tube containing mercury and a measuring scale. On the day when the barometer was tested, the mercury level was at 760 mm, which was the reason to consider the mark at this level to be normal pressure. Such instruments are still used by meteorological stations.

Two centuries later, after the invention of the mercury barometer, as a result of many studies, Lucien Vidy constructed a fundamentally new liquid-free type. Subsequently called the aneroid barometer. Throughout their existence, aneroids have gained great popularity among many users, because they are small in size, lightweight and accurate. Compared to mercury barometers, aneroids are completely safe to use.

Types of barometers

Mercury is a device that measures pressure. The principle of operation is the movement of mercury relative to the applied scale.

Liquid - a device with which the pressure level is measured by balancing the weight of a liquid column with atmospheric pressure.

Aneroid barometer - the principle of operation and display of indicators is based on changing the size of a sealed metal box, filled with rarefied air, under the action of its surface atmospheric pressure.

Electronic is modern look a device that converts the linear indicators of a classic aneroid into an electronic signal. The signals processed by the microprocessor are displayed on the liquid crystal screen.

Aneroid barometer is the most common of the above instruments, due to its small sizes and lack of fluid in the mechanism. Let's look at it in more detail.

The structure of the atmospheric barometer

• Round silver-nickel plate.
• Box with ribbed bases.
• Transmission mechanism.
• Return spring.
• Index arrow.

Atmospheric barometer - operating principle

When assembled, the aneroid is a box with various mechanisms. When a certain amount of air is pumped out of it, it creates a strong vacuum return spring, index arrow and transmission mechanism between them. Under the influence of pressure, the walls of the “pressure chamber” contract or increase in size, and the index arrow begins to move relative to the measuring scale in the direction of increasing or decreasing pressure, respectively. At rest, the needle will be at 760 mm.

Self-recording barometer

Used to record meteorological data regarding fluctuations in atmospheric pressure. In other words, this is an improved aneroid barometer, with the addition of a clock mechanism to the pressure chamber, an apparatus that holds graduated paper, and a drive needle that applies an ink line to the paper.

The depicted “drawing” on the paper of the device is called a barogram. During the operation of the barograph, in accordance with hourly indicators, the mechanism winds special paper on its base, along the surface of which an attached arrow with ink slides and marks the indicators of deviations in atmospheric pressure.

Indicators of pressure discrepancies are recorded continuously. For meteorologists this is the main documentary fact weather changes in the near future. Depending on the size of the drum, the duration of recording can range from several hours to one week. The special design allows you to take readings and monitor atmospheric indicators at any time.

Barometer on your phone - what is it?

Technology does not stand still, and now you can measure atmospheric pressure using mobile device. Many users of modern gadgets, faced with a new function, wonder: what is a barometer on their phone? A modern miniature weather station allows the phone user to constantly electronically check the level of atmospheric pressure. By tracking pressure indicators over a certain time, you can find out whether a cyclone or anticyclone is approaching. These indicators will be useful for people with hypersensitivity to sudden changes pressure.

The capabilities of a mobile device don’t stop there. In electronic form, it shows altitude, geographic width and longitude, which, in turn, facilitates quick search of the device and determination exact location his location. Thanks to GPS satellites the process is fast and accurate. Mobile barometer is an accurate altimeter. The accuracy of determining the user's location is reduced to a radius of 3 meters. These are the devices that climbers use in the mountains. But they have gained great popularity in the aviation sector.

Barometer built into the watch

Appeared relatively recently. Few know what this device is for, and most are wondering - a barometer in a watch, what is it?

Let's try to figure it out. The barometer in certain types of watches is presented in electronic or mechanical form. Electronic view- is no different from supplying atmospheric pressure data and displaying it on the screen, like on a phone. A watch with a mechanical pressure display is a perfectly accurate mini-copy of an aneroid. The only difference is in the simplified display scale. The cost of barometer watches is quite high, but, as a rule, they are shockproof and waterproof.

"Non-standard barometer"

Thanks to its founders it is called Harvard. The economic barometer underlies the formation of econometrics. Predicts changes in market conditions, dynamics of supply and demand, etc. The Harvard Barometer is a description of empirical patterns and extrapolations from recent months of observation. They are based on a study of the dynamics of development of various economic indicators.

The development forecast was displayed graphically. Each curved line plotted on the graph displayed one or another indicator. For example, curve “A” displayed changes in average exchange rates (stock market); curve “B” displayed the index of wholesale prices and changes in trade turnover (production); curve “C” - reflected the rise or fall in the price of securities on the money market. IN perfect condition graphics - indicators “A” and “C” must coincide at the level of the maximum of the first unit and the minimum of the curve of the second unit.

Thanks to the leadership of W. Persons and W. Mitchell, the United States used this type of device until 1925. The Harvard Mitchell Barometer is the first powerful regulator and indicator of factors in national economy countries. Considering the popularity and effectiveness of such construction and display of facts, this method has been adopted by many countries around the world. to the globe. But the prospect of development of many countries according to this ratio of indicators in the economy did not last long, because before and after the Second World War - in percentage they have become irrelevant. The economies of all the countries that took part in the war were in complete decline, and to solve the problem of getting up from their knees, each country used its own methods to stabilize its own monetary currency. The old methods of raising indicators (getting out of the crisis) were not used at all, but the foundations laid by Mitchell became a precedent for the world economy.

Pressure gauge

It is worth noting another device that also measures pressure, not of air, but of gases and liquids - this device is called a pressure gauge. These two devices are very interconnected. The sum of the readings of the manometer and barometer is the absolute pressure, which has a higher value than atmospheric pressure.

Conclusion

IN modern world A barometer is one of the main instruments of meteorology. The marked indicators on paper help many people learn about upcoming changes in atmospheric pressure and, accordingly, prepare for them. This applies to a greater extent to hypertensive patients. A barometer is an optional item in the house, but as a auxiliary element or in addition to the interior - desirable. Modern framing is so the required device allows it to fit into any interior design.

One of the most accurate instruments used to measure atmospheric pressure in all weather stations, is the so-called station cup barometer. It is a glass tube about 80 cm long, with a cross section of 1 cm2. Its upper end is sealed, and the lower open end is lowered into a cup of mercury. The tube is filled with mercury; in the unfilled part of the tube there is airless (or rather extremely rarefied) space.

To protect the tube from mechanical damage it is enclosed in a metal frame. Schematic diagram of the design of a marine cup barometer: two longitudinal slits are made on both sides, one opposite the other, necessary to determine the height of the mercury column in the tube. On the left side of the front slit there is a scale: in old barometers - in millimeters, in new ones - in millibars. To read the pressure on a scale, a movable ring with a vernier is used. The vernier is moved along the slot using a screw located on right side frames Before counting, the lower cut of the vernier is brought to the upper point of the visible meniscus of mercury, and then the pressure is read out in tenths: wholes are counted along the lower cut of the vernier, and tenths - according to the divisions of the vernier (from 0 to 9). Tenths (mm or mb) are judged by the vernier division that exactly coincides with any division on the scale. To allow air to enter the cup with mercury, a small hole is made in it, loosely closed with a screw stopper.

The station cup barometer is installed in the weather station room in a special cabinet in a vertical position.

A marine mercury barometer, as its name suggests, is designed to measure atmospheric pressure on sea vessels. In principle, it is designed in the same way as a station cup barometer, and differs from it in its smaller size and narrower barometric tube with extensions at its ends. The narrowing of the middle part of the tube to the thickness of the capillary is done to reduce the fluctuation of mercury in the tube during the rocking of the ship and to protect against penetration air bubbles into mercury. The cup with mercury is made narrower than in the station barometer. This also significantly eliminates the influence of the ship's pitching on the condition and barometer readings.

A marine barometer is suspended indoors on a ship using a gimbal.

An aneroid barometer, or simply aneroid, is a simple and easy-to-use instrument widely used for measuring atmospheric pressure on ships.

The operating principle of the aneroid is based on measuring the degree of deformation of the walls of a hollow flat metal pressure box under the influence of atmospheric pressure.

The aneroid box, being the sensing part of the device, reacts very sensitively to changes in atmospheric pressure. The sensitivity of the pressure box is achieved by the fact that the air in it is very highly discharged. When pressure increases, the box contracts, and when pressure decreases, it expands. To avoid complete deformation of the box, which is possible under the influence of atmospheric pressure, an arc-shaped spring is attached to it, which, by stretching the box, balances the atmospheric pressure acting on it.

The compression and tension of the box is transmitted to the barometer pointer through a system of rods and levers. The aneroid scale is graduated in either millimeters or millimeters of mercury. The aneroid is calibrated under the condition that the temperature of the pressure box at all pressure values ​​is 0°. Therefore, to determine the correction for the aneroid reading, which depends on temperature, when reading the pressure, the temperature of the device itself is determined each time. The latter is determined by a thermometer mounted in an arcuate slot on the front surface of the aneroid.

The aneroid mechanism is enclosed in a round metal or plastic box, glazed with front side. The device is always stored in a special case with an opening lid.

An aneroid barometer, compared to a mercury barometer, is a less accurate instrument, but it is almost insensitive to the rocking of the ship. This makes it more convenient to use and store in ship conditions. The main disadvantage of aneroids is the gradual decrease in their sensitivity and accuracy of indication due to the residual deformation of the aneroid box and spring that occurs over time. To eliminate these shortcomings, aneroids must be periodically checked in special institutions of the Hydrometeorological Service - in the verification bureau. Aneroids must be checked every six months.

The barograph is designed to continuously record changes in atmospheric pressure. Its structure is similar to that of a thermograph. It also consists of two main parts: receiving and writing. Several (5-10) aneron boxes connected to each other by metal gaskets serve as a pressure receiver. To avoid complete deformation of the boxes, which is possible under the influence of atmospheric pressure, a spring-type spring is built inside each of them.

Partial total deformation in the form of small vertical displacements of the entire series of pressure boxes, arising under the influence of changing atmospheric pressure, is transmitted through a system of levers to an arrow, at the end of which a feather is mounted.

The pressure is recorded in the form of a curve on a drum that rotates slowly using a clock mechanism. A paper tape is placed on the drum, marked with horizontal lines (pressure in mb) and vertical arcs (time in hours and minutes.

Depending on the time of full rotation of the drum, baroriffs are divided into “daily” and “weekly”.

Using a barograph, you can determine not only the specific value of atmospheric pressure at any time, but also the magnitude and nature of its change over any time interval.

Since the change in atmospheric pressure is very closely related to the current and upcoming weather, to predict it in sailing conditions it is important to know not so much the absolute value of the pressure as the magnitude and nature of its change over the past few hours.

The barograph on the ship is installed in indoors from springy braces or attached to a special shelf or table.

The device for measuring pressure is called pressure gauge. Pressure gauges can be siphon or cupped types

A siphon type pressure gauge is a U-shaped glass tube filled with water or mercury (Figure 2.1).

One of the ends of the pressure gauge is sealed and does not have air access; open end connected to atmospheric air. The difference in liquid levels in the two bends of the tube is calibrated in pressure units.

A cup-type pressure gauge contains a vertical glass tube, sealed at the top and filled with liquid (Fig. 2.2).

The lower end of the tube is immersed in a reservoir partially filled with liquid. The pressure generated by the liquid column in the tube is balanced by atmospheric pressure. The high measurement accuracy of the cup-type pressure gauge (0.1 mm Hg) allows it to be used as a standard device for checking aneroid barometers and altimeters.

Rice. 2.1. Siphon type pressure gauge

Rice. 2.2.

Mercury barometer is classic example cup type pressure gauge. Atmospheric pressure, measured by a mercury barometer, is equal to:

where is the density of mercury, 13600 kg/m3; g- free fall acceleration, m/s2; h- height of the mercury column, m.

The appearance of the mercury manometer is shown in Fig. 2.3.

The barometer contains a glass tube filled with mercury and immersed in a reservoir of mercury.

The level of mercury in the reservoir is controlled using a cone bone.

The mercury manometer is characterized by high sensitivity. The pressure measurement accuracy of a mercury barometer is 0.1 hPa. Its disadvantage is the toxicity of mercury.

In accordance with the European Union Directive of June 5, 2007, a restriction on the sale of mercury was adopted, practically stopping the production of new mercury barometers in Europe.

Contains an aneroid capsule consisting of two thin (0.2 mm thick) metal corrugated membranes (Fig. 2.4). In the middle of the capsule, the air is pumped out (pressure is 10-2 hPa) or the capsule is filled with inert gas at a pressure of 65 mbar.

The advantage of an aneroid barometer is its compactness, mechanical strength, and ability to be transported. These devices can be used in automatic pressure measurement systems, since the mechanical movements of aneroid capsules can be easily converted into an electrical signal. The disadvantage of an aneroid barometer is that the measurement accuracy is less than that of a mercury barometer.

Rice. 2.3. Mercury manometer

Rice. 2.4.

Bourdon tube It is a flat, distorted tube that straightens when atmospheric pressure changes (Fig. 2.5).

This elliptical tube is the sensing element deformation type. One end of the tube is open to record pressure and is measured, while the other is rigidly attached to the body.

Determination of pressure by deformation tubular spring was patented in 1849 by the French watchmaker Eugene Bourdon, after whose name this pipe is named

The Bourdon tube is used to measure pressures exceeding 10-2 torr (approximately 1 Pa); the measurement accuracy is ± 2%.

Rice. 2.5. Bourdon tube

Methods automated measurement atmospheric pressure

An instrument used to continuously record air pressure. It consists of a column of aneroid boxes connected to a self-recording arrow (Fig. 2.6).

Rice. 2.6.

Each aneroid capsule consists of two thin (0.2 mm thick) metal corrugated membranes. Inside the capsule, the air pressure is 10"2 hPa. Sometimes the capsule is filled with inert gas at a pressure of 65 mbar. The number of capsules in modern devices can reach 14. The membranes are in a tense state due to the corrugated surface and the action of the spring.

It is known that the natural frequency of a stretched string increases with tension. Mathematically, the relationship between the resonant frequency of the string and the tension force of the string is determined by the formula:

Where F- main resonant frequency strings, Hz; L- string length, m; Г string tension force, Η; μ - mass per unit length of string, kg/m.

Mechanical movements of the diaphragm 1 of such a device under the influence of variable pressure are converted into electromagnetic oscillations of the inductor 2 due to the movement of magnet C connected to wire 4. Electromagnetic oscillations are recorded by recording system 5 (Fig. 2.7). For sensors of this type, tungsten, indium or highly elastic steel, as well as alloys such as Elinvar, are used.

Rice. 2.7.

The design of one of these sensors is shown in Fig. 2.8. Increasing the pressure on the diaphragm reduces the tension on the wire, which leads to a decrease in the resonant frequency.

Rice. 2.8.

Consists of a thin diaphragm made of metal or quartz with sputtered metal surfaces. The diaphragm forms two capacitors with metal surfaces, which, together with two more capacitors C1 and C2, form an electrical bridge (Fig. 2.9).

Rice. 2.9. Capacitive pressure sensor

The diaphragm is subject to atmospheric pressure on one side and support pressure on the other. Changes in external pressure cause the diaphragm to bend and corresponding changes in the capacitance of the capacitors formed by the diaphragm and the plates located on either side of the diaphragm. These changes in capacity (which can reach several percent of the initial capacity) lead to a change in the frequency of the recording system signal, the scale of which is graduated in units of pressure.

Capacitive pressure sensors are characterized by high sensitivity, small size, and the ability to provide readings at temperatures up to 250 ° C.

This device, the production of which was made possible thanks to modern technologies, consists of two silicon alloy wafers connected to each other by a layer of silicon dioxide (Fig. 2.10).

Silicon alloys serve as capacitor plates, in which the thickness of silicon dioxide and, accordingly, the capacitance of the capacitor depend on the applied atmospheric pressure.

The capacitance of the capacitor C depends on the distance d between the plates (), which in turn depends on atmospheric pressure.

Rice. 2.10.

Pressure measurement range with barometric pressure sensor PTB210 from Vaisala (Finland) - 500-1100 hPa; temperature range from -40 ° C to + 60 ° C; overall accuracy ± 0.15 - 0.35 hPa; weight 110 g dimensions 122 mm.

Piezoelectric pressure sensor. Crystalline substance, in which, when compressed or stretched in certain directions, electrical polarization occurs even in the absence electric field, are called P " ezoelectricams. The phenomenon of the appearance of charges on the surface of a piezoelectric under the influence of mechanical deformations is called direct piezoelectric effect, and the appearance of mechanical deformations under the influence of an electric field - reverse piezoelectric effect. Piezoelectrics include quartz, ammonium dihydrogen phosphate (ADP), lithium sulfate, Rochelle salt, barium titanate, etc.

Charge amount q, appearing on the surface of the crystal, is determined by the expression:

Where F- force applied to the crystal, N; R - pressure, N/m2; S- crystal surface area, m2; k- piezoelectric constant, C/N.

The voltage, which is measured on the surfaces of the crystal due to the piezoelectric effect, is defined as follows:

where U - voltage, V; v is the sensitivity of the crystal, V-m/N; d- crystal thickness, m; R pressure, N/m2.

example

The quarium crystal has a thickness of 0.25 cm. Determine the stress arising on the surfaces of the crystal due to the action of a pressure of 345 N/m2 if the sensitivity of the crystal is 0.055 V m N-1.

solution

Using equations (2.4), we obtain:

test task

Determine the piezoelectric constant of quartz if, under a pressure of 345 N/m2, a crystal with an area of ​​1 cm2 creates a charge Cl.

answer:

Scheme piezoelectric sensor pressures are shown in Fig. 2.11.

Rice. 2.11.

The advantage of piezoelectric sensors is their compactness, linear dependence electrical signal from mechanical load, the ability to have high stability over a wide temperature range(up to 1000 ° C).

In hygienic studies, two types are used barometers:

- liquid barometers;

- metal barometers - aneroid.

The operating principle of various modifications of liquid barometers is based on the fact that Atmosphere pressure balances a column of liquid of a certain height in a tube sealed at one end (top). The less specific gravity liquid, the higher the column of the latter, balanced by atmospheric pressure.

They are most widespread, since the high specific gravity of liquid mercury makes it possible to make the device more compact, which is explained by balancing the atmospheric pressure with a lower column of mercury in the tube.

Three systems of mercury barometers are used:

- cup;

- siphon;

- siphon-cup.

The indicated systems of mercury barometers are schematically presented in Figure 35.

In some modifications there are two scales - in mm Hg. Art. and mb. Tenths of mm Hg. Art. or mb are counted on a moving scale - vernier. To do this, you need to use a screw to set the zero division of the vernier scale on the same line with the top of the meniscus of the mercury column, count the number of whole divisions of millimeters of mercury on the barometer scale and the number of tenths of a millimeter of mercury to the first mark vernier scales, coinciding with the division of the main scale.

Example. Zero division The vernier scale is between 760 and 761 mm Hg. Art. main scale. Therefore, the number of whole divisions is 760 mm Hg. Art. To this figure it is necessary to add the number of tenths of a millimeter of mercury, measured on a vernier scale. The first division of the main scale coincides with the 4th division of the vernier scale. Barometric pressure is 760 + 0.4 = 760.4 mmHg. Art.

As a rule, cup barometers have a built-in thermometer (mercury or alcohol, depending on the expected air temperature range during research), since in order to obtain the final result it is necessary to bring the pressure to standard conditions temperature (0°C) and barometric pressure (760 mm Hg).

IN cup expeditionary barometers Before observation, first use a special screw located at the bottom of the device to set the mercury level in the cup to zero.

Siphon and siphon-cup barometers(Figure 35). In these barometers, the amount of atmospheric pressure is measured by the difference in the heights of the mercury column in the long (sealed) and short (open) bends of the tube. This barometer allows you to measure pressure with an accuracy of 0.05 mmHg st. Using a screw at the bottom of the instruments, the mercury level in the short (open) bend of the tube is brought to the zero point, and then the barometer readings are taken.

Siphon-cup inspector barometer. This device has two scales: on the left in mb and on the right in mmHg. Art. To determine tenths of mmHg. Art. serves as a vernier. The found values ​​of atmospheric pressure, as when working with other liquid barometers, must be brought to 0°C using calculations or special tables.

At meteorological stations, not only a temperature correction is introduced into barometer readings, but also a so-called constant correction: instrumental and gravity correction.

Barometers should be installed away from or isolated from sources of thermal radiation ( solar radiation, heating devices), and also away from doors and windows.

Metal aneroid barometer(Figure 36). This device is especially convenient when conducting research in expeditionary conditions. However, this barometer must be calibrated against a more accurate mercury barometer before use.

Rice. 36.Aneroid barometer

Rice. 37. Barograph

The principle of the design and operation of an aneroid barometer is very simple. A metal pad (box) with corrugated (for greater elasticity) walls, from which air has been removed to a residual pressure of 50-60 mm Hg. Art., under the influence of air pressure changes its volume and as a result is deformed. The deformation is transmitted through a system of levers to an arrow, which indicates atmospheric pressure on the dial. A curved thermometer is mounted on the dial of the aneroid barometer due to the need, as mentioned above, to bring the measurement results to 0°C. The dial graduation can be in mb or mmHg. Art. Some modifications of the aneroid barometer have two scales - both in mb and in mmHg. Art.

Aneroid altimeter (altimeter). In measuring altitude by the level of atmospheric pressure, there is a pattern according to which there is a relationship between air pressure and altitude that is very close to linear. That is, as you rise to a height, the atmospheric pressure decreases proportionally.

This device is designed to measure atmospheric pressure at altitude and has two scales. One of them shows pressure values ​​in mm Hg. Art. or mb, on the other - height in meters. On aircraft altimeters are used with a dial on which the flight altitude is determined on a scale.

Barograph (barometer-recorder). This device is designed for continuous recording of atmospheric pressure. In hygienic practice, metal (aneroid) barographs are used (Figure 37). Under the influence of changes in atmospheric pressure, a package of aneroid boxes connected together, as a result of deformation, affects the system of levers, and through them, a special pen with non-drying special ink. As atmospheric pressure increases, the aneroid boxes compress and the lever with the feather rises upward.

When the pressure decreases, the aneroid boxes expand with the help of springs placed inside them and the pen draws a line downward. A record of pressure in the form of a continuous line is drawn with a pen on a graduated line in mmHg. Art. or MB paper tape placed on a cylindrical mechanically rotating drum. Barographs with weekly or daily winding with appropriate graduated tapes are used, depending on the purpose, objectives and nature of the research. Barographs are produced with an electric drive that rotates the drum.

However, in practice this modification The device is less convenient, since its use in expeditionary conditions is limited. To eliminate temperature influences on barograph readings, bimetallic compensators are inserted into them, which automatically correct (correct) the movement of the levers depending on the air temperature. Before starting work, the lever with the pen is installed in the initial position, corresponding to the time indicated on the tape and to the pressure level measured by an accurate mercury barometer.

Ink for recording barograms can be prepared according to the following recipe:

Bringing the air volume to normal conditions (760 mmHg, 0°C). This aspect of barometric pressure measurement is very important when measuring the concentrations of pollutants in the air. Ignoring this aspect can lead to significant errors in concentration calculations harmful substances, which can reach 30 percent or more.

Bringing the volume of air to normal conditions is carried out according to the formula:

(39)

Example . To measure the dust concentration in the air, 200 liters of air were passed through a paper filter using an electric aspirator. The air temperature during the period of aspiration was - +26 ° C, barometric pressure - 752 mm Hg. Art. It is necessary to bring the air volume to normal conditions, that is, to 0 ° C and 760 mm Hg. Art.

We substitute the values ​​of the corresponding parameters of the example into the formula X and calculate the required volume of air at normal conditions:

Thus, when calculating the concentration of dust in the air, it is necessary to take into account the air volume of exactly 180.69 l, not 200 l.

To simplify calculations of air volume under normal conditions, you can use correction factors for temperature and pressure (Table 25) or calculated ready-made values ​​​​of formula 39 and (Table 26).

Basic terms and units of measurement

Atmosphere pressure is the pressure of a column of air extending from the ground to the upper boundary of the atmosphere per unit of the earth's surface.

Pressure units:

1 bar = 1 million dynes/cm2; 1/1000 bar = 10 mb

In the SI system 1Pa = 1N/m2 = 10-5 = 0.01 mb.

For practical purposes, the following units of measurement are used:

1 hPa = 100 PA = 1 mb = 0.75 mmHg.

1 mmHg = 1.33 hPa

A pressure of 1012 hPa corresponding to a mass of mercury column of 760 mm at t = 0ºС at a latitude of 45º and at sea level is called normal atmospheric pressure.

by the wind is called the horizontal movement of air relative to the earth's surface. Wind is characterized by speed and direction. Wind speed is measured in m/s, less often in km/h or points. The direction of the wind is determined by the rhumb or azimuth of the point on the horizon from which the wind is blowing. When measuring wind, 8 main directions are used.

Aneroid barometer BAAM(Figure 6.1) – used to measure atmospheric pressure in stationary and expeditionary conditions.

The receiving part of the aneroid is a thick-walled metal box, inside of which the air is highly discharged. When the pressure increases, the box compresses, and when it decreases, it is stretched by a spring. These changes, using a system of levers and a chain, are transmitted to a pointer moving along a circular aneroid scale, divided by 0.5 mmHg. On the dial of the aneroid there is a thermometer with a scale of 1ºC. The entire aneroid mechanism is enclosed in a plastic case.

Figure 6.1 – Aneroid barometer BAMM

Pressure measurement produced in a place where there are no sudden changes in air temperature. By tapping the glass with your finger, a reading is taken from the position of the end of the arrow relative to the scale with an accuracy of a tenth of a division (0.1 mmHg or 0.1 hPa). A temperature correction is introduced into the readings by first measuring the temperature on the thermometer scale of the device.

Barograph(Figure 6.2) serves for continuous recording of changes in atmospheric pressure.

The barograph is housed in a plastic case. A metal plug is attached to the lower frame of the case, on which the entire mechanism of the device is mounted.

The sensitive element of the device is a bar block, which is connected to the pen arrow by a system of levers. The position of the movable screw, which has a hinge in the bracket, is focused from above by the screw, and from below by a thrust spring. Marks on the barograph tape can be made by pressing a button.

Figure 6.2 – Barograph

Installation of the device is carried out on a separate shelf of the weather station away from heating devices, window openings and places where direct Sun rays.

Processing and installation of barograph tapes is done in the same way as with a thermograph. Barograph tapes are laid out at equal horizontal intervals every 2 mb and marked every 10 mb. On the vertical time scale, divisions between adjacent arcs are 15 minutes for daily and 2 hours for weekly winding of the clock mechanism.