What is the instrument used to measure atmospheric pressure. Atmospheric pressure units. Height Adjustment
The force of the weight of an air column 10 km high, acting on a unit of the earth's surface, is called atmospheric pressure. In the SI system, the unit of pressure is Pascal (Pa)
However, 1 Pa is a very small pressure value, therefore, when measuring atmospheric pressure, multiple units are used: kPa = 1000 Pa and MPa = 10 6 Pa = 1000 kPa.
In addition to Pascal, non-systemic units are also used to measure atmospheric pressure - millimeters of mercury (water) column and bars, and
1 bar = 101.3 kPa = 760 mm. rt. Art.,
This is what atmospheric pressure at sea level means.
An instrument for measuring atmospheric pressure is called a barometer. The most common type is the metal aneroid barometer, the construction of which is shown in Fig. 1.2. The basis of the aneroid is a cylindrical chamber To from which air has been evacuated. The chamber is hermetically sealed with a thin corrugated (wavy) membrane M. To prevent atmospheric pressure from flattening the membrane, it T connected to a spring P attached to the body of the device. The lower end of the arrow is hinged to the spring FROM, which can rotate around an axis O. A scale is used to measure instrument readings. W. When atmospheric pressure changes, the membrane bends inward or outward and moves the arrow along the scale, showing the pressure value (the aneroid barometer scale is calibrated and verified according to the readings of a mercury barometer).
Rice. 1.2 - Schematic diagram of an aneroid barometer
Aneroids are very easy to use, durable, small in size, but less accurate than mercury barometers. The appearance of the aneroid barometer is shown in fig. 1.3.
Instruments for measuring atmospheric pressure
Atmospheric pressure is measured using barometers. Οʜᴎ are mercury e and aneroids.
Mercury barometers are essentially scales, where the pressure of a column of air, a unit section, extending through the entire atmosphere, equalizes a column of mercury enclosed in a glass tube from which air is pumped out.
A scale is attached to the glass tube, on which the pressure value is read (mm Hg or mb). Mercury barometers require correction for temperature (its changes affect the height of the mercury column). Typically, barometer readings are reduced to a mercury temperature of 0 ° C. At the same time, a correction for gravity is introduced, which depends on geographic latitude (gravity is greatest at the pole, least at the equator). Barometer readings are usually reduced to normal gravity at a latitude of 45°. There is also an instrumental correction that occurs during the manufacture of a barometer. All corrections are usually summarized in special tables available at the weather station for each barometer.
An example of a mercury barometer is stationary cup barometer.
Aneroid barometers designed primarily for pressure measurement in the field. The receiver of atmospheric pressure in the aneroid is a metal wavy cylindrical box, from which air is pumped out. The box at one end (lower) is attached to a fixed base, a spring is attached to its upper part. When atmospheric pressure increases, the box contracts, and when it decreases, under the action of a spring, it straightens. These changes are transmitted by a system of levers to an arrow, which moves along a scale with marked divisions corresponding to pressure in millimeters of mercury or millibars.
The aneroid barometer is installed indoors. It is equipped with a thermometer. Aneroid barometer readings need temperature correction (they are reduced to 0 o C). At the same time, scale and additional corrections are introduced. All corrections are given in the certificate (certificate) of the device.
For continuous registration atmospheric pressure and its changes, a device (recorder) is used barograph. It consists of a receiving part (several aneroid boxes), a transmitting device (a system of levers with a pen) and a drum with a clockwork, on which a tape is put on, marked vertically with lines indicating the time, horizontally with lines indicating the magnitude of the pressure.
There are barographs daily and weekly watch factory.
As atmospheric pressure increases, the aneroid capsules shrink and the line drawn by the pen on the drum rises. When the pressure decreases, the opposite happens. With the help of a graphic representation of the pressure trend on the tape, the baric tendency is determined.
The barograph is installed indoors and is one of the most indicative instruments that allows you to visually and continuously monitor the course of atmospheric pressure. Change in pressure is one of the signs of a change in the weather (a decrease in pressure indicates the approach of a cyclone - an area with relatively bad weather, an increase in pressure indicates the approach of an anticyclone - an area with relatively good weather).
In the absence of a barograph and a barometer, a change in pressure (its decrease or increase) can be judged from the readings of the barometric altimeter available on each aircraft. The principle of operation of the device is based on the measurement of atmospheric pressure, for which an aneroid box is enclosed in the body of the device.
Instruments for measuring atmospheric pressure - concept and types. Classification and features of the category "Instruments for measuring atmospheric pressure" 2017, 2018.
A device for accounting for fluctuations in atmospheric pressure. The above-ground layer of our planet has a thickness of tens of kilometers. The concentration of mixed gases in it is distinguished by a small mass, but in such significant volumes it exerts a significant load on the surface. In fact, a person rarely feels it, as he has an adaptability to the effects of this factor. However, this value is quite realistic to measure.
The principle of operation of the simplest devices
The simplest device for measuring atmospheric pressure (BP) is a simple device consisting of a thin-walled glass tube and mercury filler. One of the standard sizes of such a device: a tube 1 millimeter thick and a hundred centimeters long.
If you turn the container with the closed end up and the open part down, then a certain amount of mercury will be removed, and a certain part will remain inside. The liquid metal content will decrease until the internal and external pressure stabilizes.
Aneroid and mercury device
Aneroid barometer, what is it? The principle of operation of this device takes into account vibrations through a round metal case with wavy walls, from which air is pumped out.
The elastic sidewalls of the box bend with an increase in pressure, and bulge out with a decrease. By a special mechanism, the working chambers are connected with the arrow. It indicates the value of atmospheric pressure on a scale graduated in millimeters of mercury.
The instrument for measuring atmospheric pressure is a U-shaped bent glass flask filled with mercury. Indications are determined by the difference between the contents in the enlarged and small segment of the flask.
With the help of barographs, BP variations are recorded on a tape located in an operating drum-type unit. Measured values are recorded in millimeters (mmHg) or millibars (mbar).
Barograph
The following is a bargraph. To the question - a barometer, what it is in this configuration, you can answer - this is a recorder unit for constantly fixing atmospheric pressure. Its action is based on fluctuations in blood pressure. As a result, the deformation is transferred by the system to the device. When the readings increase, the boxes are compressed, the lever with the pen goes up, and in the case of a decrease in pressure, the chambers become wider under the action of the control spring, and the recorder draws the bottom line. Fixed pressure readings are subtracted on a special graduated paper tape, which is placed on a rotating drum.
To eliminate temperature fluctuations that affect the accuracy of the readings, bimetal capacitors are mounted in the devices. Devices are installed away from heating devices and must be protected from direct exposure to sunlight. The winding mechanism is designed for a day or a weekly regime.
Features of use
Barometer readings are fixed taking into account changes in climatic conditions in different regions, since air pressure is a variable value, which has been known since school lessons in natural history.
In good, warm and calm weather, a wall or table barometer shows high values. Accordingly, with a decrease in data, cooling or precipitation is expected in the near future.
A device located inside the house works exactly the same as in a space not limited by fences, walls and fences. The height of the building slightly modifies the readings of the device, since the pressure will be lower on the 9th floor and higher than at lower levels of the same building.
Height Adjustment
The higher the rise, the lower the pressure of the atmospheric column. The revealed pattern is used in aircraft instruments that determine the flight altitude. Such devices are called altimeters.
Of course, the results of the first, not quite perfect devices, varied significantly from weather factors, because negative weather conditions were accompanied by a pressure drop, respectively, the readings of the device highlighted data that were objectively greater than the real mark. To take the correct readings, an adjustment of the outgoing parameters is required. The principle of operation of modern altimeters is different - they do not use atmospheric pressure to measure altitude.
How to use?
A watch with a barometer and other types of devices is a pointer device with a round or oval scale, on which there are divisions. The measurement value is taken in millimeters of mercury.
At values of 750-760 mm Hg. Art. in the future, a wonderful fine day is expected, which will not interfere with a walk, a trip to nature, a summer house. If the barometer pointer drops below 750, there is a possibility of a further fall, which means that we should expect inclement weather, a sudden cold snap and heavy rainfall.
Monitoring blood pressure is vital for those who suffer from high blood pressure. During periods of critical change in this indicator, such people are subject to deterioration in their health. Information about weather changes is essential for them because of the timely taking of the medicine, maintaining their working capacity and health.
Modern specimens
Now the most commonly used barometers are cup-type or siphon types. In stationary devices that are equipped with a compensated scale, the atmospheric pressure is calculated directly from the position of the mercury in the glass container.
In specimens for expeditions, before the start of observations, the mercury level in the cup is preliminarily corrected at the zero mark using the adjusting screw. In siphon-cup devices, the value of blood pressure is measured by the difference in the heights of the column in a long and open section. Such a device counts readings with an accuracy of five hundredths. To determine the tenths of the column, a movable metal template is used.
The obtained numerical results of atmospheric pressure are given according to a special table to zero degrees Celsius. Temperature adjustments to readings can be quite significant. Regardless of the types of barometers, they are installed away from heat sources (stoves, heaters, direct sunlight), as well as away from door and window openings.
Peculiarities
The considered device can be used in a convenient and compact design. For example, a watch with a barometer has the following functionality:
- Impervious to water, up to 50-100 meters.
- Resistance to impacts and mechanical stress, which is important for fishermen, hunters and lovers of extreme recreation.
- The barometer allows you to predict changes in atmospheric pressure and weather in general.
- In addition, the watch can be equipped with a thermometer, backlight, compass and even a navigator, which makes it much easier to stay in an unfamiliar area.
To the question "Barometer, what is it?" You can definitely answer - the device is especially important for travelers, fishermen, hunters and sailors. In addition, this thing in domestic use allows you to fairly accurately predict weather fluctuations, which is important for people with diseases of the cardiovascular and nervous systems.
Barometer - a device that measures the readings of air pressure on surrounding objects, was invented in the 17th century by the outstanding Italian scientist E. Torricelli. Initially, it looked like a glass tube with marks, inside it was filled with mercury. At the time of the study, the mercury column was at 760 mm, now this indicator is considered to be the level of normal pressure, by which it is judged whether the pressure rises or vice versa decreases. A device of this type, due to its high degree of accuracy, is now used at various meteorological stations and in scientific laboratories.
After 2 centuries, having conducted a huge number of tests and using the achievements of the outstanding German scientist Jacob Leibniz, the engineer-inventor from France, Lucien Vidi, revealed to the world his "brainchild" - an improved aneroid barometer (from the Greek "aneros" - "without moisture"), which was much safer to use and had a lighter weight.
To date, there are such varieties:
- Liquid barometers;
- mercury;
- Barometers - aneroids;
- Electronic.
The principle of operation of the barometer
Externally, a liquid barometer has the form of glass tubes interacting with each other as communicating vessels in accordance with hydrostatic laws. Fill them with mercury or other light weight liquids (glycerin, oil).
cup barometer
Cup - a glass tube with a closed end and a cup, pressure readings are determined by measuring the height of the column of liquid, which starts from the level of the cup and ends with the mark of the upper meniscus.
Siphon barometer
Siphon - a tube with a closed long end, siphon-cup - two tubes, one open, the other closed + cup, in which air pressure readings are set by determining the difference in the levels of the liquid column in the first and second tube.
mercury barometer
A mercury barometer is a pair of communicating vessels, inside is mercury, the top of one glass tube, about 90 cm long, is closed, there is no air. Depending on changes in pressure, mercury rises or falls in the glass tube under the influence of air, and a small float shows the movement of the mercury mass and stops at a mark showing its level in millimeters. The norm is mercury at around 760 mm Hg. Art., readings above this value - there is a process of increasing pressure, below - lowering. Barometers of this type are practically not used in everyday life, because mercury is a dangerous toxic substance, the design of the barometer is rather cumbersome and requires careful handling. Therefore, they are widely used only in laboratory conditions, at various scientific meteorological stations and in industry, where the absolute accuracy of data transmission is important.
Classic aneroid barometer
(1 - body; 2 - corrugated hollow metal box; 3 - glass; 4 - scale; 5- metal flat spring; 6 - spiral spring; 7 - thread; 8 - transmission mechanism; 9 - pointer arrow)
The system of operation of a mechanical aneroid barometer, in which there is no liquid, is based on the principle of the effect of air pressure on metal. In the middle of the device there is a box with thin corrugated metal walls, under the force of air the walls are compressed or unclenched, the lever turns the arrow in one direction or another. There are wall and desktop types, they are very convenient and practical to use, so they are very often used at home, in offices and various institutions.
Electronic barometer
An electronic (or digital) barometer is a modern version of this device, the linear indicators of a conventional aneroid barometer are converted into an electronic signal, which is processed by a microprocessor and displayed on a liquid crystal screen. It has compact dimensions, is simple and convenient to use, for example, for fishing, tourism or as a country option.
At the moment, there is already a digital version of barometers, which are built-in as an additional function in a mobile device or in barometer watches.
Basic terms and units of measurement
Atmosphere pressure is the pressure of a column of air extending from the earth to the upper boundary of the atmosphere per unit of 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.
blown by the wind 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 bearing or azimuth of the point on the horizon from which the wind is blowing. When measuring wind, 8 main points are used.
Aneroid barometer BAAM(Figure 6.1) - serves to measure atmospheric pressure in stationary and expeditionary conditions.
The receptive part of the aneroid is a thick-walled metal box, inside which the air is highly discharged. When the pressure increases, the box is compressed, and when it decreases, it is stretched by a spring. These changes are transmitted by means of a system of levers and a chain to an arrow moving along a circular scale of the aneroid, divided by 0.5 mm Hg. A thermometer with a scale of 1ºС is mounted on the aneroid dial. The entire mechanism of the aneroid 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 a finger on the glass, 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 mm Hg or 0.1 hPa). A temperature correction is introduced into the readings, having previously measured the temperature on the instrument's thermometer scale.
Barograph(Figure 6.2) is used to continuously record changes in atmospheric pressure.
The barograph is housed in a plastic housing. A metal plug is attached to the lower frame of the case, on which the entire mechanism of the device is mounted.
The sensing element of the device is a baroblock, which is connected by a system of levers to the pen pointer. 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. Markings on the barograph tape can be made by pressing the button.
Figure 6.2 - Barograph
Installing the instrument produced on a separate shelf of the weather station away from heaters, window openings and places where direct sunlight can penetrate.
Processing and installation of barograph tapes is done in the same way as with a thermograph. The barograph tapes are divided into equal intervals horizontally every 2 mb and are official every 10 mb. On the vertical time scale, the divisions between adjacent arcs are 15 minutes for a daily winding and 2 hours for a weekly winding of the watch mechanism.