The liquid thermometer is an instrument for measuring the temperature of technological processes using a fluid that responds to a change in temperature. Liquid thermometers are well known to everyone: for measuring room temperature or human body temperature.
Liquid thermometers consist of five fundamental parts, it is: the thermometer ball, liquid, capillary tube, bypass chamber, and scale.
The thermometer ball is a part where the liquid is placed. The liquid reacts to the temperature change lifting or dropping along the capillary tube. The capillary tube is a narrow cylinder according to which fluid moves. Often the capillary tube is equipped with a bypass chamber, which represents the cavity where excess fluid flows. If there is no bypass chamber, then after the capillary tube is filled, a sufficient pressure will be created in order to destroy the tube if the temperature continues to rise. Scale is a part of a liquid thermometer with which the readings are removed. The scale is calibrated in degrees. The scale can be fixed on the capillary tube, or it can be mobile. Mobile scale makes it possible to adjust it.
The principle of operation of liquid thermometers is based on the property of the liquids to shrink and expand. When the liquid is heated, it is usually expanding; The fluid in the thermometer ball expands and moves up the capillary tube, thereby showing the temperature rise. And, on the contrary, when the liquid is cooled, it is usually compressed; The liquid in the capillary tube of the liquid thermometer decreases and thereby shows a decrease in temperature. In the case when there is a change in the measured temperature of the substance, the warmth is transferred: first from the substance whose temperature is measured, to the thermometer ball, and then from the ball to the liquid. The fluid reacts to the temperature change moving up or down the capillary tube.
The type of liquid used in the liquid thermometer depends on the range of temperature-measured temperature.
Mercury, -39-600 ° C (-38-1100 ° F);
Alloys mercury, -60-120 ° C (-76-250 ° F);
Alcohol, -80-100 ° C (-112-212 ° F).
The design of many liquid thermometers suggests that they will hang on the wall, and the entire surface of the thermometer enters into contact with the substance, the temperature of which is measured. However, some types of industrial and laboratory fluid thermometers are constructed and calibrated in such a way that they suggest their immersion into the liquid.
Thermometers used in this way are most widely used thermometers with partial immersion. In order to obtain accurate readings using a partial immersion thermometer, it is immersed by its ball and capillary tube only before this line.
Partial immersion thermometers are immersed before the mark in order to compensate for the changes in ambient temperature, which can be on the liquid inside the capillary tube. If the ambient air temperature changes (changes in air temperature around the thermometer) are likely, they can cause an expansion or compression of fluid inside the capillary tube. As a result, the testimony will affect not only the temperature of the substance that is measured, but also the ambient temperature. The immersion of the capillary tube to the marked line removes the effect of ambient temperature to accuracy of indications.
In industrial production, it is often necessary to measure the temperatures of substances passing through pipes or in containers. Measuring Temperature Under these conditions, creates two problems for the sborkors: how to measure the temperature of the substance, if there is no direct access to this substance or liquid, and how to remove the liquid thermometer to inspect, check or replace without stopping the process. Both of these problems are eliminated if applying measuring channels for inputing thermometers.
The measuring channel for entering the thermometer is a channel in the form of a pipe, which is closed from one end and is open to another. The measuring channel is designed to put a liquid thermometer ball into it and thus protect it from substances that can cause corrosion, poisoning substances, or high pressure. When measuring channels are used to enter thermometers, the heat exchange occurs in the form of indirect contact (through the measuring channel) of the substance whose temperature is measured, and the thermometer ball. The measuring channels are a seal for increased pressure and prevent the output of the fluid, the temperature that is measured.
Measuring channels are made standard sizesSo they can be used with different types of thermometers. When the thermometer is installed in the measuring channel, its ball is inserted into the channel, and the nut is screwed over the thermometer to secure the thermometer.
Principle of operation
The principle of operation of the pressure gauge is based on the equilibration of the measured pressure by the force of the elastic deformation of the tubular spring or a more sensitive two-bedned membrane, one end of which is smeared into the holder, and the other through the thrust is associated with the tribe-sectoral mechanism converting a linear movement of the elastic sensory element into the circular motion of the showing arrow.
Varieties
In the instrument group of measuring overpressure:
Pressure gauges - instruments with a measurement of 0.06 to 1000 MPa (measured overpressure - a positive difference between absolute and barometric pressure)
Vacuummers - instruments measuring discharge (pressure below atmospheric) (up to minus 100 kPa).
Manovacummeters - manometers measuring both excessive (from 60 to 240,000 kPa) and vacuum (up to minus 100 kPa) pressure.
Power meters of small overpressure up to 40 kPa
Tighomera -Vacummeters with limit up to minus 40 kPa
TAGONPOROMERS -MANAKUMMETERS with extreme limits not exceeding ± 20 kPa
The data are given according to GOST 2405-88
Most domestic and imported manometers are manufactured in accordance with generally accepted standards, in connection with this, the pressure gauges of various brands replace each other. When choosing a pressure gauge, you need to know: measurement limit, body diameter, instrument accuracy class. Also important is the location and carving of the fitting. These data are the same for all devices manufactured in our country and Europe.
Also there are pressure gauges measuring absolute pressure, that is, overpressure + atmospheric
Device measuring atmosphere pressure, called barometer.
Types of manometer
Depending on the design, the sensitivity of the element differ liquid pressure gauges, freight, deformation (with a tubular spring or membrane). Pressure gauges are divided into accuracy classes: 0.15; 0.25; 0.4; 0.6; 1.0; 1.5; 2.5; 4.0 (the smaller the number, the more accurate the device).
Types of manometer
According to the appointments, the pressure gauges can be divided into technical - general, electrocontact, special, self-resistant, rail, vibration-resistant (glycerol-free), ship and reference (exemplary).
General: Designed for measuring non-aggressive copper liquids, gases and vapors.
Electrocontact: have the ability to adjust the measured medium, due to the presence of an electrocontact mechanism. A particularly popular instrument of this group can be called ECM 1U, although it has long been removed from production.
Special: oxygen- should be degreased, since even a minor contamination of the mechanism when contact with pure oxygen can lead to an explosion. Often produced in blue housings with the designation on the O2 dial (oxygen); Acetylene -not are allowed in the manufacture of the measuring mechanism of copper alloys, since in contact with acetylene there is a risk of formation of explosive acetyline copper; Ammonia-should be corrosive.
References: Having a higher accuracy class (0.15; 0.25; 0.4) These devices serve to verify other pressure gauges. Such instruments are installed in most cases on freight pressure gauges or any other installations capable of developing the right pressure.
Ship manometers are designed for operation on a river and sea fleet.
Railway: Designed for use on railway transport.
Summary: Pressure gauges in the case, with a mechanism that allows you to reproduce a chart of the pressure gauge on the diagram paper.
Thermal conductivity
Thermal conductivity gauges are based on a reduction in thermal conductivity of gas with pressure. In such pressure gauges, the intensity of the heat is built, which heats up when the current is passed through it. Thermocouple or temperature determination sensor through resistance (DOTS) can be used to measure the temperature thread temperature. This temperature depends on the speed with which the heat thread gives the heat to the surrounding gas and, thus, from thermal conductivity. It is often used Piran a pressure gauge, which uses a single thread of the heat from platinum at the same time as a heating element and as DOTS. These manometers give accurate readings in the interval between 10 and 10-3 mm Hg. art. but they are quite sensitive to chemical composition Measured gases.
[edit] Two incandescent threads
One wire coil is used as a heater, the other is used to measure temperature through convection.
Pirani Manometer (one thread)
Pirani manometer consists of a metal wire, open to the measured pressure. The wire is heated through the current flowing through it and is cooled by the surrounding gas. When the gas pressure decreases, the cooling effect also decreases and the equilibrium temperature of the wire increases. Wire resistance is a temperature function: measuring wire voltage and current current, resistance (and thus gas pressure) can be defined. This type of pressure gauge was first constructed by Marcello Pirani.
Thermal and thermistor manometers work in a similar way. The difference is that the thermocouple and thermistor are used to measure the incandescent thread temperature.
Measuring range: 10-3 - 10 mm RT. Art. (Rough 10-1 - 1000 Pa)
Ionizing manometer
Ionization manometers - the most sensitive measuring instruments for very low pressures. They measure the pressure indirectly through the measurement of ions of electrons generated during gas bombardment. The less gas density, the less ions will be formed. The calibration of the ionic pressure gauge is unstable and depends on the nature of the measured gases, which is not always known. They can be calibrated through a comparison with the testimony of the pressure gauge of the pop-up, which are significantly more stable and independent of chemistry.
Thermoelectrons are construed with gas atoms and generate ions. The ions are attracted to the electrode under the appropriate voltage known as the collector. The current in the collector is proportional to the rate of ionization, which is a function of pressure in the system. Thus, the measurement of the collector current allows you to determine the gas pressure. There are several subtypes of ionization gauges.
Measuring Range: 10-10 - 10-3 mm RT. Art. (Rough 10-8 - 10-1 Pa)
Most ionic pressure gauges are divided into two types: hot cathode and cold cathode. The third look is a pressure gauge with a rotating rotor more sensitive and roads than the first two and is not discussed here. In the case of a hot cathode, the electric heating thread creates an electronic beam. Electrons pass through the pressure gauge and ionize gas molecules around themselves. The formed ions are assembled on a negatively charged electrode. The current depends on the number of ions, which, in turn, depends on the pressure of the gas. Hot cathode gauges gently measure pressure in the range of 10-3 mm Hg. Art. up to 10-10 mm Hg. Art. The principle of a pressure gauge with a cold cathode is the same, excluding that electrons are formed in the discharge created by a high-voltage electric discharge. Pressure gauges with a cold cathode gently measure the pressure in the range of 10-2 mm Hg. Art. up to 10-9 mm RT. Art. Calibration of ionizing gauges is very sensitive to structural geometry, chemical composition of measured gases, corrosion and surface spraying. Their calibration can be unsuitable when turned on at atmospheric and very low pressure. The composition of the vacuum at low pressures is usually unpredictable, so the mass spectrometer should be used simultaneously with the ionizing pressure gauge for accurate measurements.
Hot cathode
The ionizing pressure gauge with the hot cathode of the bayard alpert usually consists of three electrodes working in trigger mode, where the cathode is a thread of the heat. Three electrodes are a collector, a gas thread and a grid. The collector current is measured in the picoamper by the electrometer. The potential difference between the heat and land thread is usually 30 V, while the grid voltage under constant recreation is 180-210 volts, if there is no optional electron bombardment, through the grid heating, which can have a high potential of approximately 565 volts. The most common ionic pressure gauge is a hot cathode of bayard alpert with a small ionic collector inside the grid. The glass casing with a hole to the vacuum can surround the electrodes, but usually it is not used and the pressure gauge is embedded in the vacuum device directly and contacts are displayed through a ceramic fee in the wall of the vaccinal device. Ionization gauges with a hot cathode may be damaged or losing calibration if they are turned on at atmospheric pressure or even with a low vacuum. Measurements of ionizing gauges with a hot cathode are always logarithm.
Electrons emitted by the thread of the heat move several times in the direct and reverse direction around the grid until they fall into it. With these movements, part of the electrons faces gas molecules and forms electron-ion pairs (electronic ionization). The number of such ions is proportional to the density of the gas molecules multiplied to the thermoelectronic current, and these ions fly to the collector, forming the ion current. Since the density of gas molecules is proportional to pressure, the pressure is estimated through the ion current measurement.
Sensitivity K. low pressure Pressure gauges with a hot cathode is limited to a photoelectric effect. Electrons hitting into the grid produce X-rays that produce photovoltaic noise in the ionic manifold. It limits the range of old pressure gauges with a hot cathode to 10-8 mm Hg. Art. and bayard alpert approximately 10-10 mm Hg. Art. Additional wires under the potential of the cathode in the ray of view between the ionic collector and the grid prevent this effect. In the type of extraction, the ions are not attracted by a wire, but an open cone. Because ions cannot solve what part of the cone to hit, they pass through the hole and form an ion beam. This ion beam can be transferred to the Faraday mug.
Forkarne burner
Forkarne burner - a device consisting of a gas collector with holes for the gas output, a monoblock with channels and a ceramic refractory forkamera, located above the collector, in which gas mixture occur with air and burning gas-air mixture. The burner Forkarne is designed for burning natural gas in the furnaces of sectional cast iron boilers, dryers and other heat plants working with a vacuum 10-30 Pa. Forkamer burners are located on the couch, thereby creating good conditions for the uniform distribution of thermal flows along the length of the furnace. Forkaround burners can operate at low and medium gas pressure. The forkarm burner consists of a gas collector (steel pipe) with one side of the gas outlet holes. Depending on the thermal power, the burner may have 1.2 or 3 collectors. Over the gas collector, a ceramic monoblock is installed on the steel frame forming a series of channels (mixers). Each gas hole has its own ceramic mixer. Gas jets, expired from the reservoir holes, ejected 50-70% of the air, the required length of burning, the rest of the air comes from the cut in the furnace. As a result of ejection, mixing formation is intensified. In the channels, the mixture is heated, and when its burning begins. From the channels, the burning mixture enters the forcamation, in which 90-95% gas is combustion. The fork meter is made of chammed brick; It has a gap. Gas burning occurs in the furnace. The height of the torch is 0.6-0.9 m, an excess of air is an excess of air a - 1,1 ... 1,15.
Compensators are designed to mitigate (compensation) of temperature elongations of gas pipelines, to avoid breaking of pipes, for the convenience of mounting and dismantling fittings (flange, valves).
The gas pipeline with a length of 1 km of averaged diameter when heated by 1 ° C is lengthened by 12 mm.
Compensators are:
· Lenzovy;
· P-shaped;
· Laruned.
Lens compensator It has a wavy surface that changes its length, depending on the temperature of the gas pipeline. The lens compensator is made from stamped welding semilation.
To reduce the hydraulic resistance and prevent clogging inside the compensator, a guide nozzle is installed, welded to the inner surface of the compensator from the gas entry side.
The lower part is filled with bitumen to prevent water accumulation.
When installing the compensator in winter timeIt is necessary to stretch a little, and in the summer - on the contrary, squeeze with tie nuts.
 |
P-shaped shaped
compensator. Compensator.
Changes in the temperature of the medium surrounding the gas pipeline cause changes in the length of the gas pipeline. For the straight line of the steel gas pipeline, the length of 100 m lengthening or shortening when the temperature changes by 1 ° is about 1.2 mm. Therefore, on all gas pipelines after valves, considering the lenzovtors (Fig. 3). In addition, during operation, the presence of a lens compensator facilitates installation and disassembling valves.
When designing and building gas pipelines, tend to reduce the number of compensators installed by maximum use Self-compensation of rude - by changing the direction of the route, both in terms of and in the profile.
Fig. 3. Lens compensator 1 - flange; 2-nozzle; 3-hand; 4 - semilia; 5 -lapa; 6 - edge; 7 - traction; 8 - Naka
The principle of the liquid pressure gauge
In the initial position, water in the tubes will be on the same level. If the rubber film will be pressure, then the level of fluid in one knee of the pressure gauge will decrease, and in the other, therefore will increase.
This is shown in the figure above. We daw on the film with your finger.
When we press the film, the air pressure, which is in the box, increases. The pressure is transmitted through the tube and reaches the fluid, with it. When lowering the level in this knee, the fluid level in the other knee of the tube will increase.
In terms of fluid levels, it will be possible to judge the difference in atmospheric pressure and that pressure, which turns out to be on the film.
The following figure shows how using a liquid pressure gauge measure the pressure in the liquid at different depths.
Membrane manometer
In the membrane pressure gauge, the elastic element is a membrane, which is a corrugated metal plate. The deflection of the plate under pressure of the fluid is transmitted through the transmitting mechanism of the arrow of the device, moving on the scale. Membrane devices are used to measure pressure to 2.5 MPa, as well as to measure vacuum. Sometimes use electrical output devices, which have an electrical signal, proportional to the pressure of the pressure gauge.
The pressure is called uniformly distributed force acting perpendicular to the unit area. It may be atmospheric (the pressure of the near-earth atmosphere), excessive (exceeding atmospheric) and absolute (amount of atmospheric and redundant). The absolute pressure below atmospheric is called rarefied, and a deep discharge - vacuum.
The pressure unit in the international system of units (C) is Pascal (PA). One Pascal is the pressure created by the force of one Newton on the square one square meter. Since this unit is very small, the units of multiples are also used: kilopascal (kPa) \u003d PA; Megapascal (MPa) \u003d PA et al. In view of the complexity of the task of transition from the previously used pressure units to a unit of Pascal, a unit is temporarily allowed to use: kilogram-force per square centimeter (kgf / cm) \u003d 980665 Pa; kilogram-force per square meter (kgf / m) or a millimeter of water column (mm water) \u003d 9,80665 Pa; Millimeter mercury pillar (mm Hg) \u003d 133,332 Pa.
Pressure control devices are classified depending on the measurement method used in them, as well as by the nature of the measured value.
According to the measurement method, which determines the principle of operation, these devices are divided into the following groups:
Liquid, in which pressure measurement occurs by balancing its fluid post, the height of which determines the pressure value;
Spring (deformation), in which the pressure value is measured by determining the measure of the deformation of the elastic elements;
Trucks based on the equilibration of the forces created on the one hand measured by pressure, and on the other hand, calibrated loads of the piston placed in the cylinder.
Electrical, in which pressure measurement is carried out by converting its value to an electrical value, and by measuring the electrical properties of material depending on the pressure value.
In the form of the measured pressure, the devices are divided into the following:
Manometers intended for measurement overpressure;
Vacuummers that serve to measure the vacuum (vacuum);
Manovakuumometers measuring excessive pressure and vacuum;
The outfielders used to measure small overpressure;
Tighometers used to measure small resolutions;
TAGONPORMERS, intended for measurement of small pressures and permission;
Differential pressure gauges (diffmanenometers), with the help of which measure the pressure difference;
Barometers used to measure barometric pressure.
Spring or deformation pressure gauges are most often used. The main types of sensitive elements of these devices are presented in Fig. one.
Fig. 1. Types of sensitive elements of deformation pressure gauges
a) - with a single tube spring (Bourdon tube)
b) - with a multi-burglar spring
c) - with elastic membranes
d) - bellows.
The principle of operation of these devices is based on the properties of the curved tube (tubular spring) of a non-circular cross section to change its curvature when the pressure is changed inside the tube.
Depending on the form of the spring, the springs are different (Fig. 1a) and multiple (Fig. 1b). The advantage of multiple tubular springs is greater than that of the atomic movement of the free end with the same change. input pressure. The disadvantage is essential dimensions with such springs.
Pressure gauges with a single tubular spring - one of the most common types of spring appliances. A sensitive element of such devices is bent along the circle arc, beaten from one end, tube 1 (Fig. 2) of an elliptical or oval section. The open end tube through the holder 2 and nipple 3 joins the source of the measured pressure. The free (walled) end of the tube 4 through the transmission mechanism is connected to the axis of the arrow moving on the instrument scale.
Tubes of pressure gauges designed for pressure up to 50 kg / cm are made of copper, and the tubes of pressure gauges designed for greater pressure from steel.
The property of the curved tube of the nonlaring cross section to change the value of bending with a change in pressure in its cavity is a consequence of changes in the shape of the section. Under the action of pressure inside the tube, an elliptical or plane cross section, deforming, is approaching a circular cross section (the small axis of the ellipse or oval increases, and the large decreases).
The movement of the free end of the tube during its deformation under certain limits is proportional to the measured pressure. For pressures emerging from the specified limit, residual deformations arise in the tube, which make it unsuitable for measurement. Therefore, the maximum working pressure of the pressure gauge should be below the limit of proportionality with a certain margin of strength.
Fig. 2. Spring pressure gauge
The movement of the free end of the tube under the action of pressure is very small, so to increase the accuracy and clarity of the instrument readings, the transmitter mechanism is introduced, which increases the scale of moving the end of the tube. It consists (Fig. 2) from the gear sector 6, gears 7, which adhesive with the sector, and the spiral spring (hairs) 8. On the axis of the gear 7, the indicating step of the pressure gauge 9 is fixed. The spring 8 is attached by one end to the axis of the gear, and the other fixed point of the fee of the mechanism. Spring assignment - eliminate the backlash, choosing gaps in the grip and hinge connections of the mechanism.
The sensitive element of membrane pressure gauges may be tough (elastic) or sluggish membrane.
Elastic membranes are copper or brass discs with corrugations. Corrugations increase the rigidity of the membrane and its ability to deformation. From such membranes, membrane boxes are manufactured (see Fig. 1B), and from boxes - blocks.
Slisp membranes are made of rubber on a tissue basis in the form of single-channel disks. They are used to measure small overpressure and discharge.
Membrane pressure gauges and can be with local testimony, with electrical or pneumatic transmission of indications for secondary instruments.
For example, we consider the DM membrane dm, which is a germ sensor of a membrane type (Fig. 3) with a differential transformer transformation system of the measured value of the measured value to the secondary instrument of the KSD type.
Fig. 3 DM DM MEMBRAN DIFMANOMETER
The sensitive element of the diffmanemeter is a membrane block consisting of two membrane boxes 1 and 3 filled with a silicon fluid located in two separate chambers separated by partition 2.
The iron core 4 of the differential transformer converter 5 is attached to the center of the upper membrane 5.
A larger (positive) measured pressure is supplied to the lower chamber, in the upper one (minus) pressure. The force of the measured pressure drop is balanced at the expense of other forces arising during the deformation of the membrane boxes 1 and 3.
With an increase in the pressure drop, the membrane box 3 is compressed, the liquid flows into the box 1, which expands and moves the core of the 4 differential transformer converter. When the pressure drop decreases, the membrane box 1 is compressed and the liquid is supplanted from it into the box 3. The core 4 is moved down. Thus, the position of the core, i.e. The output voltage of the differential transformer circuit uniquely depends on the pressure difference value.
To work in control systems, regulating and controlling technological processes by continuously converting the pressure of the medium to a standard current output signal with transmission to secondary instruments or executive mechanisms The Sapphire-type transducers are used.
Pressure converters for this type are: to measure absolute pressure ("sapphire-22d"), measurements of overpressure (Sapphire-22Di), measuring vacuum (Sapphire-22DV), pressure measurements - discharge ("Sapphire-22Div") , hydrostatic pressure ("sapphire-22dg").
The device of the Sapphire-22 TG transducer is shown in Fig. 4. They are used to measure hydrostatic pressures (levels) of neutral and aggressive media at temperatures from -50 to 120 ° C. Upper measurement limit - 4 MPa.
Fig. 4 Sapphire -22DG transducer device
The membrane-lever tensacement agent 4 is placed inside the base 8 in a closed cavity 10 filled with silicone liquid, and is separated from the measured medium with metal corrugated membranes 7. The sensitive elements of the strain agent are film tesorons 11 of silicon plates plates 10 from sapphire.
The membranes 7 are welded along the outer contour to base 8 and interconnected by the central stem 6, which is associated with the end of the lever of the strain converter 4 using the thrust 5. Flanges 9 are sealed with gaskets 3. The positive flange with an open membrane serves to mount the converter directly on the process capacity. The impact of the measured pressure causes the deflection of the membrane 7, the bending of the membrane of the strain processor 4 and the change in the resistance of the strainers. The electric signal from the strain converter is transmitted from the measuring unit on the wires through the Hermovate 2 to the electronic device 1, converting the change in the resistance of the strainers to change the current output signal in one of the ranges (0-5) MA, (0-20) MA, (4-20) Ma
The measuring unit withstands without destroying the effect of one-sided overload of working overpressure. This is ensured that with such an overload, one of the membranes 7 lies on the profiled surface of the base 8.
A similar device has the above modifications of Sapphire-22 converters.
Measuring converters of hydrostatic and absolute pressure "Sapphire-22K-DG" and "Sapphire-22K-yes" have an output current signal (0-5) Ma or (0-20) Ma or (4-20) Ma, as well as an electric code The RS-485 interface signal.
Sensitive element silphon pressure gauges and diffmanematers There are bellows - harmonic membranes (metal corrugated tubes). The measured pressure causes elastic deformation of the bellows. The pressure measure can be either moving the free end of the bellows, or the force arising during deformation.
Schematic scheme The silt diffum meter type DS is shown in Fig.5. A sensitive element of such an instrument is one or two bellows. Sylphons 1 and 2 are fixed in one end on a fixed base, and the other are connected via the movable rod 3. The internal cavities of the bellows are filled with a liquid (water-grained mixture, silicon-organic liquid) and are connected to each other. When the pressure drop changes, one of the bellows is compressed, distilling liquid into another bellows and moving the boding of the bellows block. Moving the rod is converted to the movement of the pen, the arrow, the integrator pattern or the remote signal signal proportional to the measured pressure drop.
The nominal pressure drop defines the screw cylindrical springs block 4.
With pressure drops above the nominal cup 5 overlap the channel 6, stopping the fluid flow and preventing the bellows from destruction.
Fig. 5 Circuit diagram of the bellows diffmanenometer
To obtain reliable information about the value of any parameter, it is necessary to accurately know the error of the measuring device. Determining the main error of the device at various points of the scale at certain intervals of time produce by its calibration, i.e. Compare the readings of the operated device with the readings of a more accurate, exemplary instrument. As a rule, the calibration of the instruments is carried out first with the increasing value of the measured value (direct move), and then at a decreasing value (reverse).
Pressure gauges believe in the following three ways: the calibration of the zero point, the working point and complete verification. At the same time, the two first calibises are made directly in the workplace using a three-way crane (Fig. 6).
The operating point is covered by attaching the control manometer to the working gauge and comparing their testimony.
Full verification of pressure gauges is carried out in the laboratory at the calibration or piston pressure gauge, after removing the pressure gauge from the workplace.
The principle of operation of the carbon installation for the verification of pressure gauges is based on the equilibration of the forces created on the one hand measured by pressure, and on the other hand, acting on the piston placed in the cylinder.
Fig. 6. Schemes for the calibration of zero and working points of the pressure gauge using a three-way crane.
The positions of the three-way crane: 1 - working; 2 - calibration of the zero point; 3 - verification of the working point; 4 - purge of the pulse line.
Instruments for measuring overpressure are called pressure gauges, vacuum (pressure below atmospheric) - vacuum, excess pressure and vacuum - manicommers, pressure differences (drop) - differential pressure gauges.
The main serial produced instruments for measuring pressure on the principle of operation are divided into the following groups:
Liquid - the measured pressure is equalized by the pressure of the fluid column;
Spring - the measured pressure is equalized by the force of elastic deformation of the tubular spring, membrane, a bellows, etc.;
Piston - the measured pressure is equilibrated by the force acting on the piston of a certain cross section.
Depending on the conditions of application and appointment, the following types of pressure measurement devices are available:
Technical - general purpose instruments for equipment operation;
Control - for verification of technical devices at the site of their installation;
Exemplary - to verify control and technical devices and measurements requiring increased accuracy.
Spring manometers
Purpose. To measure overpressure, a widespread application was found, the work of which is based on the use of deformation of the elastic sensory element, which occurs under the action of the measured pressure. The value of this deformation is transmitted to the counting device of the measuring instrument, graded in pressure units.
As a sensitive element of the pressure gauge, the single-handed tube spring (Bourdon tube) is most often used. Other types of sensitive elements are: a multi-burglar spring, a flat corrugated membrane, a harmonic membrane - a bellows.
Device. Pressure gauges with a single tubular spring are widely used to measure overpressure in the range of 0.6 - 1600 kgf / cm². The working body of such pressure gauges is the hollow tube of the elip-or oval cross section, curved around the circle by 270 °.
The device of a pressure gauge with a single tube spring is shown in Figure 2.64. The tubular spring - 2 open end is rigidly connected to the holder - 6, reinforced in the housing - 1 pressure gauge. The holder passes through the fitting - 7 with a thread that serves to connect to the gas pipeline in which the pressure is measured. The free end of the spring is closed by a plug with a hinge axis and the smeared. By means of a leash- 5, it is associated with a gear ratio consisting of a gear sector - 4, linked with a gear - 10, sitting motionless on the axis along with the index arrow - 3. Near the gear is a flat spiral spring (hairs) - 9, one end of which Connected with a gear, and the other is fixed still on the rack. The hairs constantly presses the tube to one side of the sector's teeth, thereby eliminating the dead stroke (backlash) in the gear gear and ensures the smoothness of the arrows.
Fig. 2.64. Showing a pressure gauge with a single tubular spring
Electro-contact pressure gauges
Purpose. Pressure gauges, vacuum letters and manovakuumetra Electro-contact types of ECM EKV, ECMD and VE-16RB are designed to measure, signaling or two-position control of pressure (discharge) neutral with respect to brass and steel of gases and liquids. The VE-16RB type measuring instruments are performed in an explosion-proof case and can be installed in fire-hazardous and explosive rooms. Operating voltage of electrical contact devices up to 380V or up to 220V DC.
DeviceThe device. Defecting electrocontact pressure gauges is similar to spring, with the only difference that the gauge body has large geometric dimensions due to the installation of contact groups. The device and list of the main elements of electrocontact pressure gauges are presented in Fig. 2.65 ..
Manometers exemplary.
Purpose. Pressure gauges and vacuum letters of the MO and are designed to test pressure gauges, vacuum meters and manovacuumometers for measurements in laboratory conditions of pressure and discharge of non-aggressive liquids and gases.
Mac Maineners and Vacuum Letters of the ICRA are designed to check the operation of working pressure gauges at the site of their installation and for control measurements of overpressure and discharge.
Fig. 2.65. Electro contact pressure gauges: A - type ECM; EKMW; Eq;
B - type VE - 16 RB main parts: tubular spring; scale; mobile
Mechanism; Group of mobile contacts; entrance fitting
Electric pressure gauges
Purpose. Electric MAN gauges type MAD are designed for continuous transformation of excess or vacuum pressure into a unified AC output signal. These devices are used to work complete with secondary differential transformer devices, centralized control machines and other receivers of information capable of receiving a standard signal in mutual inductance.
Device and principle of operation. The principle of the operation of the device, as well as in pressure gauges with a single tubular spring, is based on the use of deformation of the elastic sensory element when exposed to a measured pressure. The device of an electric pressure gauge type MED is shown in Fig. 2.65. (B). The elastic sensitive element of the device is the tubular spring - 1, which is mounted in the holder - 5. Plank - 6 is brought to the holder, on which the coil is fixed - 7 of the differential transformer. Permanent and variable resistance are mounted on the holder. The coil is closed by the screen. The measured pressure is supplied to the holder. The holder is attached to the body - 2 screws - 4. The housing of the aluminum alloy is closed with a lid on which the plug connector is strengthened - 3. The core - 8 of the differential transformer is associated with the movable end of the tubular spring with a special screw - 9. When the pressure is applied to the pressure device, the tubular spring is deformed. which causes proportional to the measured pressure, moving the moving end of the spring and the associated core of the differential transformer.
Operational requirements for pressure gauges:
· When installing a pressure gauge, the tilt dial from the vertical should not exceed 15 °;
· In idle position, the arrow of the measuring instrument must be in a zero position;
· Pressure gauge passed verification and has a stigma and a seal indicating the duty of calibration;
· There are no mechanical damage to the body of the pressure gauge, the threaded part of the fitting, etc.;
· Digital scale is clearly visible to service personnel;
· When measuring the pressure of a wet gaseous medium (gas, air), the tube is performed in the form of a loop in which the moisture is condensed;
· At the site of the selection of the measured pressure (before the pressure gauge), a crane or valve must be installed;
· To compact the place of joining the fittings of the pressure gauge, gaskets made of leather, lead, annealed red copper, fluoroplast should be used. The use of packles and suice is not allowed.
The instruments for measuring pressure are used in many industries and are classified, depending on their purpose, as follows:
· Barometers - measure atmospheric pressure.
· Vacuum meters - measure vacuum pressure.
· Pressure gauges - measure excess pressure.
· Manicuummeters - measuring vacuum and overpressure.
· Barocummeters - measure absolute pressure.
· Differential pressure gauges - measure pressure difference.
On the principle of operation, the instruments for measuring pressure may be of the following types:
· Liquid device (pressure is balanced using a liquid column weight).
· Trucking devices (measured pressure is balanced by force, which is created by the calibrated loads).
· Devices with remote transmission of indications (changes of various electrical characteristics of the substance under the influence of the measured pressure).
· The spring device (the measured pressure is equalized by the elasticity of the spring, the deformation of which serves as a pressure measure).
For pressure Measurements Apply Various Devices , which can be divided into two main groups: liquid and mechanical.
The simplest device is piezometer,
measuring pressure in the fluid, the height of the same liquid column. It is a glass tube, open from one end (tube in Fig. 14a). The piezometer is a very sensitive and accurate device, however it is convenient only when measuring small pressures, otherwise the tube is very long, which complicates its use. 
To reduce the length of the measuring tube, appliances with a larger density liquid (for example, mercury) are used. Mercury manometer it is a U-shaped tube, the curved knee of which is filled with mercury (Fig. 14b). Under the action of pressure in the vessel, the level of mercury in the left knee of the pressure gauge decreases, and in the right - rises.
Differential manometerapply in cases where it is necessary to measure non-pressure in the vessel, but the pressure difference in two vessels or two points of one vessel (Fig. 14 V).
The use of liquid devices is limited to the area of \u200b\u200brelatively small pressures. If necessary measure high pressure, apply the devices of the second type-module.
Spring manometerit is the most common from mechanical instruments. It consists (Fig.15a) from a hollow thin-brown bent brass or steel tube (spring) 1, one end of which is smeared and connected by a drive device 2 with a gear mechanism 3. On the axis of the gear, the arrow is located 4. The second end of the tube is open and connected to the vessel. in which pressure is measured. Under the action of the pressure of the spring, it is deformed (straightens) and through the drive device drives an arrow to the deviation of which determine the pressure value on the scale 5.
Membrane manometersalso refer to mechanical (Fig. 15b). Instead of the spring, a thin plate-membrane 1 (metallic or from rubberized matter) is installed. The deformation of the membrane by means of the drive device is transmitted by an arrow indicating the pressure value.
Mechanical manometers have compared to liquid some benefits: portability, versatility, ease of device and operation, a large range of measured pressures.
For measuring pressures, there is less atmospheric and mechanical vacuum, the principle of operation of which is the same as pressure gauges.
Principle of reporting vessels .
Communicating vessels
Reporting 
Called vessels with a channel filled with a liquid. Observations show that in the reporting vessels of any form, homogeneous fluid is always installed at one level.
Otherwise, heterogeneous fluids behave even in the same in the form and dimensions of the reporting vessels. Take two cylindrical communicative vessels of the same diameter (Fig. 51), on their bottom of the mercury layer (shaded), and on top of it into the cylinders with a nallem liquid with different densities, for example R 2 H 1).
Mentally highlight inside the tube connecting the communicative vessels and the mercury filled, the area S, perpendicular to the horizontal surface. Since the fluids rest, the pressure on this platform on the left and right is the same, that. P 1 \u003d P 2. According to formula (5.2), the hydrostatic pressure P 1 \u003d 1 GH 1 and P 2 \u003d 2 GH 2. Equating these expressions, we obtain R 1 H 1 \u003d R 2 H 2, from where
h 1 / H 2 \u003d R 2 / R 1. (5.4)
Hence , heterogeneous liquids at rest are installed in the reporting vessels in such a way that the heights of their columns are inversely proportional to the densities of these liquids.
If R 1 \u003d R 2, then from formula (5.4) it follows that H 1 \u003d H 2, i.e. Uniform fluids are installed in the communicative vessels at the same level.
The kettle and its spout are communicating vessels: water is in them at one level. So, the aids of the kettle must 
Water supply device.
A large tank with water is installed on the tower (water tower). From the tank there are pipes with a variety of branches introduced into the house. The ends of the pipes are closed with cranes. In the crane, the pressure of water filling pipes is equal to the pressure of the water column having a height, equal to the difference between the heights between the crane and the free surface of the water in the tank. Since the tank is installed at the height of tens of meters, the pressure of the crane can reach several atmospheres. Obviously, water pressure on the upper floors is less than the pressure on the lower floors.
Water to the water tank tank is served by pumps
Water tube.
On the principle of reporting vessels, water tubes for water tanks are arranged. Such tubes, for example, are available on tanks in railway cars. In the open glass tube attached to Baku, water is always worth at the same level as in the tank itself. If the water tube is installed on a steam boiler, the upper end of the tube is connected to the upper part of the boiler filled with steam.
This is done so that pressure over the free surface of the water in the boiler T in the tube was the same.
Peterhof is a magnificent parking ensemble, palaces and fountains. This is the only ensemble in the world, whose fountains work without pumps and complex water treatment facilities. These fountains use the principle of reporting vessels - the levels of fountains and storage ponds are taken into account.
The pressure characteristic is the force that evenly affects the unit of the body surface area. This force affects various technological processes. Pressure is measured in Pascals. One Pascal is equal to the pressure of the force in one Newton on the surface area in 1 m 2.
Atmospheric The pressure is formed by the atmosphere of the Earth.
Vacuummetric Pressure is a pressure that does not reach the amount of atmospheric pressure.
Excessive Pressure is a pressure value that is superior to atmospheric pressure.
Absolute The pressure is determined from the magnitude of the absolute zero (vacuum).
Instruments measuring pressure are called pressure gauges. The technique most often has to determine overpressure. The considerable interval of the measured pressure values, the special conditions for measuring them in all kinds of technological processes causes a variety of types of pressure gauges, which have their differences in constructive features and on the principle of operation. Consider the main types of applied species.
The barometer is called the device measuring air pressure in the atmosphere. There are several types of barometers.
Mercury The barometer acts on the basis of mercury movement in the tube on a specific scale.
Liquid The barometer works on the principle of equilibrating the fluid with pressure of the atmosphere.
Barometer aneroid It works on changing the size of a metal hermetic box with vacuum inside, under the action of the pressure of the atmosphere.
Electronic Barometer is more modern device. It converts the parameters of a conventional aneroid into a digital signal displayed on a liquid crystal display.
In these models, the pressure is determined by the height of the fluid column, which lines this pressure. Liquid devices are most often performed in the form of 2 glass vesselsinterconnected in which the liquid is filled (water, mercury, alcohol).
Rice-1
One end of the tank is connected to the measured medium, and the second is open. Under the pressure of the medium, the liquid flows from one vessel to another until the pressure leveling. The difference in fluid levels determines overpressure. Such instruments measure the pressure difference and vacuum.
Figure 1A shows a 2-pipe pressure gauge, measuring vacuum, excess and atmospheric pressure. The disadvantage is a significant error in measuring pressures having pulsation. For such cases, 1-pipe pressure gauges are used (Figure 1B). They are in them one edge of a larger vessel. A cup is connected to the measured cavity, the pressure of which moves the liquid into a narrow part of the vessel.
When measuring, only the height of the fluid in a narrow knee is taken into account, since the liquid changes its level in a cup slightly, and they neglected. To perform measurements of small overpressure use 1-pipe micromanometers with a tube inclined at an angle (Figure 1B). The more the tilt of the tube, the more precisely the instrument's readings, due to the increase in the length of the fluid level.
A special group is considered to be instruments for measuring pressure, in which the movement of the liquid in the container acts on the sensing element - the float (1) in Figure 2a, the ring (3) (Figure 2B) or the bell (2), which are associated with the arrow, which is a pressure pointer.
Rice-2
The advantages of such devices are remote transmission and their registration of values.
In the technical field, deformation devices for pressure measurement have become popular. Their principle of operation lies in the deformation of the sensing element. This deformation appears under pressure. The elastic component is associated with a reader having a scale with a graduation of pressure units. Deformation pressure gauges are divided into:
Rice-3.
In these devices, the sensitive element is a spring connected to the arrow by the gear ratio. The pressure is affected inside the tube, the cross section is trying to take a round shape, the spring (1) is trying to unwind, as a result, the arrow moves on the scale (Figure 3a).
In these devices, the elastic component is the membrane (2). It begins under pressure, and affects the arrow using the transfer mechanism. The membrane is manufactured by the type of box (3). This increases the accuracy and sensitivity of the device due to greater deflection at an equal pressure (Figure 3B).
In the devices of the bellows type (Figure 3B), the elastic element is the bellows (4), which is made in the form of a corrugated thin-walled tube. Pressure is affected in this tube. In this case, the bellows increases in length and with the help of the transmission mechanism moves the pressure gauge arrow.
Silphon and membrane types of pressure gauges are used for measurements of minor overpressure and vacuum, since the elastic component has a small rigidity. When applying such devices for measuring vacuum they got a name taigomerov . The device measuring overpressure is powermers To measure overpressure and vacuum serve tyagonorizers .
The instruments for measuring the pressure of the deformation type have an advantage in comparison with liquid models. They allow you to transmit readings to remotely and write them in automatic mode.
This is due to the transformation of the deformation of the elastic component in the output signal of the electric current. The signal is fixed by measurement devices that have grades on pressure units. Such devices are called deformation and electric pressure gauges. Widespread use was tensometric, differential transformer and magnetomodulation converters.
Rice-4.
The principle of operation of such a converter is the change in the power of the induction current depending on the pressure value.
The instruments with the presence of such a converter have a tubular spring (1), which moves the steel core (2) of the transformer, and not an arrow. As a result, the power of the induction current is changed through the amplifier (4) to the measuring device (3).
In such devices, the force is converted into an electrical current signal due to the movement of the magnet associated with the elastic component. When moving, the magnet affects the magnetomodulation converter.
The electrical signal is enhanced in the semiconductor amplifier and enters the secondary electrical measuring devices.
Converters based on a strain gauge sensor operate based on the dependence of the electrical resistance of the strainer from the deformation value.
Rice-5.
Tenzodators (1) (Figure 5) are fixed on an elastic element of the device. The output electrical signal occurs due to a change in the resistance of the strainer, and is fixed by secondary measurement devices.
Rice-6.
The elastic component in the device is a tubular atomic spring. Contacts (1) and (2) are performed for any instrument scale marks, rotating the screw in the head (3), which is on the outside of the glass.
With a decrease in pressure and reaching its lower limit, the arrow (4) using the contact (5) will turn on the lamp chain of the corresponding color. With an increase in pressure to the upper limit, which is set by contact (2), the arrow closes the chain of the red lamp contact (5).
Exemplary devices define the error of testimony of work appliances that participate in the production technology.
The class of accuracy is interrelated with a permissible error, which is the magnitude of the deviation of the pressure gauge from real values. The accuracy of the device is determined by the percentage ratio from the maximum permissible error to the nominal value. The more percentage, the less the accuracy of the device.
Exemplary gauges have accuracy much higher working models, as they serve to assess the conformity of the readings of the working models of the instruments. Exemplary gauges are used mainly in the laboratory conditions, so they are manufactured without additional protection from the external environment.
Spring pressure gauges have 3 accuracy class: 0.16, 0.25 and 0.4. Working model working models have such accuracy classes from 0.5 to 4.
Instruments for measuring pressure The most popular devices in various industries when working with liquid or gaseous raw materials.
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