Physical basis of measurements - Laboratory
Laboratory work No. 6
CHECKING TECHNICAL PRESSURE GAUGES
Purpose of the work: familiarization with technical pressure gauges and methods for their verification.
DESCRIPTION OF PRESSURE GAUGES
Pressure measuring instruments are classified depending on the type of pressure being measured, principle of operation and purpose.
Based on the type of pressure being measured, instruments are divided into absolute pressure gauges, barometers, pressure gauges, vacuum gauges, pressure and vacuum gauges, and differential pressure gauges.
Barometers are designed to measure atmospheric pressure, excess pressure gauges, differential pressure gauges.
All devices for measuring pressure, regardless of its type, can be divided according to the principle of operation into liquid, spring, cargo, electric and others.
According to their purpose, pressure gauges are divided into pressure gauges for oil, gasoline or other liquid fuel, water, steam, air, oxygen, acetylene, etc.
Among the wide variety of instruments used to measure pressure, the simplest and at the same time the most accurate are U-shaped liquid pressure gauges, the main varieties of which are presented in Fig. 1.
The upper limit of the pressure difference (P1-P2) measured by U-shaped pressure gauges with visual reading is considered to be 1.96·105 N/m2 (2 kg/cm2).
This value is determined by the strength of the glass tubes and the conditions for obtaining tightness in connections between glass and metal or rubber.
A U-shaped pressure gauge (Fig. 1a) consists of two communicating tubes filled to half with a barrier fluid (water, mercury, alcohol, transformer oil). The reading is made on a scale that has a zero mark in the equilibrium state. The level difference H determines the measured excess pressure P1.
where, j - specific gravity barrier fluid. The main disadvantage of U-shaped pressure gauges is the need to take two readings for each measurement. This drawback is partially eliminated in a cup pressure gauge (Fig. 1b), consisting of vessels of different diameters. The measured pressure is applied to a wide vessel, and a thin tube communicates with the atmosphere.
The difference in H2 levels in a cup gauge is mainly determined by the movement of the meniscus in the thin tube. Really difference in levels
(1)
where h1 and h2 are the movement of the menisci in the wide and narrow knees, respectively.
Considering that , where S1 and S2 are the cross-sectional areas of the wide and narrow elbows, respectively, expression (1) can be written in the form
Since , then (2a). This allows measurements to be limited to only one reading along a thin (measuring) tube.
For accurate measurements of small excess pressures and vacuums, special cup pressure gauges with an inclined measuring tube are used (Fig. 1c). The linear movement of the meniscus in the measuring tube of such a pressure gauge is related to the value h by the relation:
where is the angle of inclination of the measuring tube. Since, then, due to which the accuracy of the count increases. The minimum angle of inclination of the tube is 8-10°.
The operation of spring devices is based on balancing the pressure of the medium with forces arising during elastic deformation of special elements. Spring pressure gauges and vacuum gauges are distinguished by their simplicity of design, reliable operation, wide measuring range and fairly high accuracy.
Spring pressure devices can be classified by the type of spring that converts pressure or force into movement. On this basis, spring pressure devices can be divided into the following groups:
1. Devices with a tubular manometric spring (Fig. 2a; 2b).
2. Membrane devices in which the conversion of pressure into displacement is carried out by an elastic membrane (Fig. 2c), an aneroid or manometric membrane box (Fig. 2d, 2e), a block of aneroid or manometric boxes (Fig. 2f, 2g).
3. Bellows devices, where the mentioned transformation is carried out by a bellows (Fig. 2h).
4. Devices in which pulse pressure is converted into a force acting on a rod spring of one type or another. Common devices in this group include:
a) spring-piston (Fig. 2i);
b) spring-membrane devices with a flexible membrane (Fig. 6.2k);
c) spring-bell (Fig. 2k),
d) spring-bellows devices (Fig. 2m).
In single-turn and multi-turn spring pressure gauges, the measured pressure is supplied to the internal cavity of the spring. One end of the spring, connected to the nipple, is motionless, and the other, sealed, is free and connected to the indicating system. Springs are made of brass and other copper alloys, and for high pressures - of steel. The cross section of the spring is an ellipse, the major axis “a” of which is perpendicular to the plane of the spring coil. As the pressure increases, the cross-section of the spring is “rounded” and at the same time the minor axis “b” of the ellipse increases, and the angle of twist of the spring decreases. Changes in these quantities are related to each other by the relation
Thus, the change in the angle of twist of the spring is proportional to the initial value of the angle and the deformation of the minor axis of the tube cross-section. 
The scale of a spring pressure gauge is uniform, since the spring operates in a zone of proportionality between stress and deformation.
The movement of the free end of a single-turn spring is small (less than 5-8 mm), therefore, to increase the angle of rotation of the pressure gauge needle, transmission mechanisms are used - lever or gear (sector).
Pressure gauges with a single-turn spring are manufactured as standard, control and technical ones; accuracy classes from 0.2 to 4. They are placed in housings with a diameter of 60, 80, 100, 150, 200 and 500 mm. Measurement limits from 1 to 10,000 kg/cm2. Vacuum gauges and pressure-vacuum gauges are produced on the basis of single-turn spring pressure gauges.
The multi-turn tubular spring is serial connection 6-9 single-turn springs, due to which it has a relatively large movement of the free end and develops significant force. In this regard, multi-turn springs are widely used in self-recording pressure gauges.
In laboratory pressure gauges, the elastic element is an elastic metal membrane, a soft membrane (for example, rubber) with an additional spring. Diaphragm pressure gauges are used to measure the pressure of aggressive and viscous media; In this case, the elastic membrane is protected by a gasket.
The disadvantages of membrane pressure gauges are the low sensitivity of the system, the difficulty of adjustment, and changes in characteristics over time due to “fatigue” of the membrane.
The harmonic-shaped membrane has high sensitivity, and therefore it is widely used in technical instruments (bellows pressure gauges of the MS type, secondary instruments in the pneumatic aggregate system of the AUS). MS type bellows pressure gauges are used for measuring pressures up to 5 kg/cm2, accuracy class 1.5 for pressure gauges and 2.5 for vacuum gauges and pressure-vacuum gauges.
The operating principle of piston pressure gauges is based on balancing the measured pressure with a calibrated weight.
They are used to measure high pressures (up to 10000 kg/cm2 and as reference and control devices, instrument accuracy classes 0.02; 0.05; 0.2. The use of piston pressure gauges for technical measurements is extremely limited.
The design of a standard nanometer with a simple unsealed piston is shown in Fig. 3. In the cylindrical channel of the column 1 there is a steel piston 2, at the upper end of which there is a platform 3 for removable loads 4. The column channel communicates with the cavity of the cylinder of the screw press 8 and with two fittings 6. The column channel and the fitting are equipped with shut-off carbon valves 7. Drain the channel is closed by valve 9. The pressure gauge channels are filled with working fluid, usually transformer or petroleum jelly oil.
The working pressure in the vessel is determined by the choice of the size of the load 4:
where, G is the weight of the load and the piston
S is the sum of the piston area and half the clearance area.
The described methods and instruments are suitable for measuring rapidly changing and very high pressures and vacuums. In this case, they mainly resort to using electrical appliances, whose operation is based on the dependence of electrical characteristics sensitive element from pressure. Such devices include piezoelectric pressure gauges, capacitive and inductive ionization pressure gauges and electric vacuum gauges with thermal resistance.
With a piezoelectric pressure gauge, when pressure is applied to metal plates in contact with quartz plates (or with plates of Roselle salt or tourmaline), a charge q arises, the value of which is related to the pressure P by the relation:
Ude, S is the area of the plate;
K - piezoelectric constant, for quartz K = 2.1. 10-11k/kg.
The measuring device is connected to the terminals of the piezoelectric pressure gauge through an electronic amplifier. The advantage of a piezoelectric pressure gauge is its low inertia
The operation of an electric resistance pressure gauge is based on the dependence of the electrical conductivity of some alloys on the pressure of the medium surrounding the conductor. Manganin is usually used as a conductor material. The resistance of the conductor, depending on the pressure, changes according to a linear law:
where is the resistance of the conductor at normal atmospheric pressure;
Conductor resistance at excess pressure P;
K - piezoelectric coefficient, for manganin ranging from to cm2/kg.
The frequency of calibration of technical pressure gauges with a single-turn tubular spring is once a year, membrane, bellows - once every two years. Verification must be carried out at an ambient temperature of 30˚C.
Measurement results (Table 1)
Table 1
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Indications of the standard device kg/cm2 |
Indications of the device being tested kg/cm2 |
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straight stroke |
reverse stroke |
|
We build a calibration graph for forward and reverse motion in one coordinate system.
Pressure gauges are special devices that measure pressure. Today there are a large number of them. There are low pressure gauges, as well as high pressure. Models with a temperature scale are classified as thermometers. These devices are used in many areas. First of all, they are intended to study various natural processes. They also help in determining the pressure of technical instruments. Each model has its own accuracy class.
Device of deformation pressure gauges
In the center there is a deformation pressure gauge overpressure has a tubular spring. Nearby there are silons that interact with it. The device also has membranes. They happen various types. The most common are flat and corrugated membranes. There is a special box for them in the pressure gauge. The sensitivity of the device depends on in this case The housing of pressure gauges can be made of different materials.
What does a mechanical pressure gauge consist of?
The design of mechanical pressure gauges is quite simple. The spring in this device is single-turn. It interacts with the holder, which is located under it. There is also a small-diameter leash installed in the pressure gauge. It is necessary to secure the gear sector. It is attached to an arrow that shows actual pressure readings.
The difference between electrical contact pressure gauges
Electric contact pressure gauges have a special lead inside. It interacts with the arrow of the device. Electrical contacts are located at the bottom and top of the device. When the pressure is high, the circuit is open. If the indicator is within the operating range of the pressure gauge, then the alarm system shows the deviation through an arrow. For position control, a special relay is provided in the network.
Bellows type pressure gauges
A block is hidden under the body of the bellows pressure gauge. Above it there is silicon organic liquid. A working bellows is installed under the block, which is in contact with the glass. He is always in a motionless state. Additionally, the pressure gauge has a lever that is connected to the central axis. Rubber rings are located on the corrugation. The internal rod operates in the device using valves. There are two types (shut-off and equalizer).
Diaphragm pressure gauges
In the center of diaphragm pressure gauges there is a very a complex system levers. In this case, an axis is provided at the bottom of the device. It is connected to an arrow that shows pressure. There is a membrane box at the top of the pressure gauge. Additionally, under the fitting there is a corrector, which is hidden behind a profile scale.
Devices "DM2010"
These pressure gauges have the following: accuracy class - 1.5, reading range is from 0 to 0.25 MPa, voltage in the AC circuit is 27 A. Working temperature is in the range from -50 to +60 degrees. The average weight of the pressure gauge is 0.8 kg. The DC circuit indicator fluctuates around 110 A.
Characteristics of pressure gauges "MP50"
Data is used to determine excess water pressure. They can only be used in a non-crystallizing environment. These devices come in different diameters. They are mainly produced in sizes from 50 to 160 mm. The accuracy class for them is 2.5. The measurement limits range from 0.1 to 25 MPa. They have a standard design with a fitting.
Water pressure gauges are produced exclusively from brass with a diameter of 1.5 mm. The measuring element consists of a copper alloy. There are two types of springs used in these pressure gauges (Bourdon and multi-turn). The dial of this device is made of polystyrene. However, some manufacturers produce it from a copper alloy. As a rule, the scale is black and the arrow is white. The body of the device is made of steel. Polymer glass. The rim of this pressure gauge (electronic) has a steel rim, which is painted black.
Pressure gauges "MP63"
These pressure gauges specifications have the following: device diameter - 50 mm, accuracy class 1.5, and measurement limits range from 0.1 to 40 MPa. Its design is standard and includes a fitting. As a rule, it is installed of the radial type. However, in some cases the device contains an axial fitting. It consists entirely of brass. The spring in the pressure gauge is made of copper. The dial, in turn, is made of aluminum. It is always painted only black. The arrow is standard white. The pressure gauge body is completely steel. In this case, polymer glass is installed. The rim of this pressure gauge is made of plastic and painted black.
Models "MP2-UV"
This water is intended. It has an accuracy class of 2.5. Degree of protection - series "IP40". The case diameter is 60 mm. This pressure gauge can last 10 years. Its mass is 0.15 kg. The body of the device consists of steel. It can be used at temperatures from -50 to +60 degrees. The glass in this model is organic.
The fitting in the pressure gauge is made of bronze. The spring is installed in a tubular type. The tribco-sector mechanism is made of bronze. In some cases, brass is used or stainless steel. The dial is made of aluminum and is painted White color. The fitting is usually installed of the radial type. Moreover, in some cases it stands without a flange. The central-axial fitting can also be installed without it.
Pressure gauges "MPV3-UF"
These pressure gauges have the following technical characteristics: the fitting thread is 1.5 mm, the accuracy class is 2, and the degree of protection is set to the “IP40” series. The mass of this device is 0.5 kg. This model can last approximately 10 years. The case diameter is 100 mm. This device can be used at temperatures ranging from -50 to +50 degrees. The housing is very durable and can withstand heavy loads. It is produced entirely from steel.
Technical glass is installed. The fitting in the pressure gauge is made of bronze. The spring is mainly produced in a tubular type. It also consists entirely of bronze. Trib-sector mechanisms are made of steel or brass. The dials are made of aluminum alloy. Their color is always white. The fittings are only of the radial type. In some cases they are available without a rear flange.
Characteristics of the "VP4-UF" model
This model is intended for measuring excess air pressure in the range from 0 to 40 MPa. Accuracy class - 1.5. In this case, the standard degree of protection is “IP40”. These air pressure gauges can be used at temperatures environment from -50 to +60 degrees. The case diameter is as much as 150 mm. The average service life of a pressure gauge is 10 years. Its body is made of steel and is very durable.
Additionally, it should be noted technical glass in the device. The tubular spring and fitting are made of bronze. Dials are only available in white. They are made from aluminum alloy. Eccentric-axial fittings are always installed without a flange.
Parameters of the pressure gauge "DV2030"
This model is intended for measuring fuel pressure in the range from - 30 to 30 MPa. The thread of the fitting is 1.5 mm. The pressure gauge can be used at a temperature of -50 degrees. The accuracy class is 2. The degree of protection is “IP30” series. The body of this device is exactly 100 mm in diameter. The service life of the pressure gauge is 8 years. Moreover, its mass is 0.6 kg.
Separately, it is worth mentioning the durable case, which is made of steel. Manufacturers make glass organic. The spring is only available in the tubular type. It is made, just like the fittings, from bronze. The dial is white. The sector mechanism is entirely made of bronze. In some cases, brass and steel are used. There are standard contact groups. Moreover, this fuel pressure gauge is equipped with magnetic pressure. Fittings are used only of the radial type. All of them are installed in a device without a flange.
Model "DM2005"
These signaling pressure gauges are intended for measuring gas pressure. At the same time, they are equipped with connecting fittings. Their size is exactly 10 mm. Device accuracy class 1.5. Pressure gauges are available with a body diameter of 150 mm. The protection system is installed in the IP30 series. These devices weigh 0.9 kg. Moreover, they can last about 9 years. In general, their body is quite durable.
Glass is available in organic type. The fitting and spring in the device are made of bronze. The dial of these gas pressure gauges is made of aluminum alloy. It is painted white. Radial fittings, as a rule, are not equipped with flanges. However, there are models with them. The contact group is provided as standard. In this case, there is magnetic compression.
What is the difference between "DA2005"?
The thread in this pressure gauge is metric by default. The maximum pressure the device can withstand is 30 MPa. The model can be operated even at a temperature of -60 degrees. The accuracy class is quite high and is 1.5. The protection system is provided as standard. The case is available with a diameter of no more than 150 mm.
The average service life is 10 years. The pressure gauge weighs as much as 0.9 kg. The body itself is made of steel and is not afraid of minor mechanical damage. The fitting in this model is of a radial type. There are devices with and without a flange. Only standard contact groups are installed. Magnetic compression is usually present. Dial material - Aluminium alloy. Separate mention should be made of the tribic-sector mechanism. It is made of bronze in the pressure gauge. Steel and brass counterparts are rare. Glass is produced only of organic type.
Characteristics of "DA8010"
This high pressure gauge is available with a special scale. In this case, the limit values are maintained at 10 MPa. Additionally, it should be noted that the device has a damper. The rim of the device is made of steel. It is usually painted black. Only technical glass is installed. The entire pressure gauge body is painted black. The dial is made of polystyrene. The arrow is white and the scale is black. The measuring element is a Bourdon spring. It consists entirely of brass. In some cases, pressure gauges are made with a multi-turn spring. The fittings come in radial and central-axial types. All of them are made of brass. The accuracy class of this pressure gauge is 1.5.
Pressure gauge "DM2020"
These pressure gauges have the following technical characteristics: the reading range ranges from 0 to 20 MPa, in the AC circuit the voltage is 110 A. The operating temperature of the device is from -50 to +50 degrees. The mass of the pressure gauge is 0.7 kg. Accuracy class is provided for 2. The system maintains a voltage of 36 A. The degree of protection is available in the IP40 series.
This pressure gauge will last about 10 years. The spring is installed in a fitting type. It is made of bronze. The sector mechanism is made entirely of brass. Among other things, it is worth noting the convenient dial. It is painted black and the arrow is white. The model has technical glass. The fitting is installed with a special 1.5 thread. Pressure gauge options are available with or without a flange.
Federal Agency for Technical Regulation and Metrology
Federal State Autonomous educational institution additional vocational education
"ACADEMY OF STANDARDIZATION, METROLOGY AND CERTIFICATION (educational)"
Department Metrology
Group No.
COURSE WORK
Topic Verification and calibration
(SI name)
Listener
(place of work)
Supervisor
Saint Petersburg
Verification - technical pressure gauges
includes an external examination, as well as determination of the main error and variation of readings. To determine the error of readings, standard spring and piston pressure gauges are used. Devices should be checked in working position. Checking of technical pressure gauges, vacuum gauges and pressure-vacuum gauges must be carried out at five marks evenly distributed along the scale. The error of the device during a gradual increase and decrease in pressure should not exceed the values specified by the standards. For , and also for measuring pressure in laboratory conditions, standard pressure gauges with a conventional scale divided into 100 or 250 divisions are used. To convert scale divisions into pressure values, use the conversion table provided in the device certificate. For calibration of technical pressure gauges, installed on the reduction heads and upper trims of group tank installations, serve as control pressure gauges. Verification of control pressure gauges with sealing or branding and issuance of a verification certificate must be carried out at least once every 12 months.
| Diaphragm draft meter diagram. |
For calibration of technical pressure gauges Piston pressure gauges are used. The principle of their operation is based on balancing the force created by the pressure on one side of the piston with the force of gravity of the loads. At calibration of technical pressure gauges and pressure and vacuum gauges, an external inspection is carried out, the tightness of the device is checked and the error of the readings is determined. During the external inspection, the presence of a seal is checked, the date of the next check of the pressure gauge, the absence of mechanical damage, the return of the needle to zero when the pressure gauge is turned off. How to do it calibration of technical pressure gauges.Control pressure gauges serve for verification of working technical pressure gauges at the place of their installation. Model piston pressure gauge MOP, designed for calibration of technical pressure gauges with an upper limit of up to 500 kgf/cm2, permissible error 0 2% of the measured pressure. Model piston pressure gauge MOP, designed for calibration of technical pressure gauges with an upper limit of up to 500 kgf/cm2, permissible error 0 2% of the measured pressure.
 | Deadweight piston standard pressure gauge. |
Deadweight piston standard pressure gauge MP-60, designed for calibration of technical pressure gauges with a single-turn tubular spring, shown in Fig. 1.13. It consists of a vertical cylinder 8 with a carefully fitted steel piston 5, at the upper end of which a plate 7 is attached for placing sample weights 6, shaped like disks. Funnel 4 is used to fill the device with mineral oil. The device has a piston press / lip seal. Needle valves 2, 9 and / / are used to shut off the channels, valve 12 is used to drain the oil.
Reference instruments are used for precise measurements and for calibration of technical pressure gauges. The accuracy class is understood as the magnitude of the instrument’s error as a percentage of the upper limit of its scale. High-pressure control pressure gauges of the MKV type are intended for calibration of technical pressure gauges at the place of their installation. Exemplary pressure gauges are devices of the 3rd category and are intended for verification of control and technical pressure gauges, as well as for precise measurements. Standard pressure gauges type OMV GOST 6521 - 53 are intended for calibration of technical pressure gauges and are used for accurate pressure measurement in laboratory installations. The exemplary deadweight pressure-vacuum gauge MVP-25 of the 2nd category (class 0 05) is intended for verification of standard and technical pressure gauges, vacuum gauges and pressure and vacuum gauges of accuracy classes from 0 2 to 0 5 inclusive. The upper limit for measuring vacuum (vacuum pressure) is determined by the value of atmospheric pressure and the set of weights used. High pressure control manometers of the MKD type (GOST 6400 - 52) are intended for calibration of technical pressure gauges at the place of their installation. Model pressure gauges of the MOV-180 type, which were manufactured before the publication of GOST 6521 - 53, are intended for calibration of technical pressure gauges and are used for accurate pressure measurement in laboratory installations.
MKD control pressure gauges are portable and serve for periodic, more accurate pressure measurements, as well as for calibration of technical pressure gauges directly at the place of their installation. They have two independent measuring systems. To connect to the technical pressure gauge during its verification, the control pressure gauge has a flange with a needle valve, which is connected to the flange of the three-way valve of the technical pressure gauge using a clamp. Control pressure gauges of the MKD type are portable devices used for periodic, more accurate pressure measurements, as well as for calibration of technical pressure gauges at the place of their installation. In order to increase the reliability of readings, the springs of control pressure gauges are made from materials High Quality. These pressure gauges are available with two independent measuring systems located in one housing. The device has two single-turn tubular springs, soldered into a common holder and attached to one fitting, two sector transmission mechanisms, two arrows and two arc scales. If such a pressure gauge is in good condition, the readings of both of its springs (arrows) must match (taking into account the magnitude of the main error of each system), otherwise the pressure gauge is unsuitable for measurements.
Pressure gauges of class 0 05 are intended for checking standard and other pressure gauges for precise measurements, pressure gauges of class 0 2 are for calibration of technical pressure gauges.
Deadweight piston standard pressure gauges of the MP type (Fig. 180) are produced for a maximum pressure of 60, 600 2500 kgf/cm2, class III (error no higher than 0 2%) for and class II (error no higher than 0 05%) for checking standard spring pressure gauges. Deadweight piston standard pressure gauges type MP (Fig. 179) are produced for maximum pressures of 60 kgf/cm2, 600 kgf/cm2, 2500 kgf/cm2, class III (error no higher than 0 2%) for calibration of technical pressure gauges for general use and class II (error no higher than 0 05%) for checking standard spring pressure gauges.
 | Diagram of a piston pressure gauge with weights. |
One calibrated and one reference pressure gauge is connected to holes 1 and different pressures are created in the channels of the device using a worm press. Checking the technical pressure gauge consists in comparing its readings with the readings of a standard device. For calibration of technical pressure gauges With a single-turn tubular spring, a deadweight piston pressure gauge is usually used. Deadweight piston pressure gauges are designed for checking pressure gauges; they are stationary devices. Pressure gauges of class 0 05 are intended for checking standard and other pressure gauges for precise measurements, pressure gauges of class 0 2 are for calibration of technical pressure gauges.
 | Diagram of a pressure gauge with a single-turn tubular spring. |
Spring pressure gauges are manufactured in three types: technical, control and standard. Technical pressure gauges are produced for a wide range of pressures, in housings with a diameter of 40 to 400 mm. Control pressure gauges are portable and serve for periodic, more accurate pressure measurements, as well as for calibration of technical pressure gauges directly at the place of their installation. They have two independent measuring systems. The use of certain standard instruments depends on the measurement limit of the device being verified. Thus, to verify devices for measuring low pressures and vacuums (draft gauges, pressure gauges), compensation micromanometers, micromanometers with an inclined tube, U-shaped, and pressure-vacuum gauges with water filling are used. To check vacuum gauges and pressure gauges with measurement limits up to 2 kg/cm, a mercury U-shaped mano-vacuum gauge with a mirror scale is usually used. Verification of technical pressure gauges with various measurement limits (up to 10,000 kg/cm2 inclusive) is carried out using spring standard and piston pressure gauges. The use of certain standard instruments depends on the measurement limit of the device being verified. Thus, to verify devices for measuring low pressures and vacuums (draft gauges, pressure gauges), compensation micromanometers, micromanometers with an inclined tube, U-shaped, and pressure-vacuum gauges with water filling are used. To check vacuum gauges and pressure gauges with measurement limits up to 2 kg/cm, a mercury U-shaped mano-vacuum gauge with a mirror scale is usually used. Verification of technical pressure gauges with various measurement limits (up to 10,000 kg/cm2 inclusive) is carried out using spring standard and piston pressure gauges. The use of certain standard instruments depends on the measurement limit of the device being verified. Thus, to verify devices for measuring low pressures and vacuums (draft gauges, pressure gauges), compensation micromanometers, micromanometers with an inclined tube, U-shaped, and pressure-vacuum gauges with water filling are used. To check vacuum gauges and pressure gauges with measurement limits up to 2 kg/cm2, a mercury U-shaped mano-vacuum gauge with a mirror scale is usually used. Verification of technical pressure gauges with various measurement limits (up to 10,000 kg/cm2 inclusive) is carried out using spring standard and piston pressure gauges. Verification of technical pressure gauges includes an external examination, as well as determination of the main error and variation of readings. To determine the error of readings, standard spring and piston pressure gauges are used. Devices should be checked in working position. Verification of technical pressure gauges, vacuum gauges and pressure-vacuum gauges should be performed at five marks, evenly distributed on the scale. The error of the device during a gradual increase and decrease in pressure should not exceed the values specified by the standards.
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