7.3. Basic rules for verification and calibration

(from the KIPinfo website) 1. Article 1, paragraph 3 of the Federal Law on Ensuring the Uniformity of Measurements No. 102-F3 of June 26, 2008 (Article 13 of the Law of the Russian Federation No. 4871-1 of April 27, 2003) defines the scope of state regulation of ensuring the uniformity of measurements. All S.I. those included in this area must be certified as a type of measuring instruments, and, with a certain frequency, undergo verification carried out by accredited legal entities and individual entrepreneurs. The list of measuring instruments, verification of which is carried out only by state regional centers, is determined by the Government of the Russian Federation. 2. Measuring instruments that do not fall under paragraph 3 of Article 1 of this law may be voluntarily calibrated using standards traceable to state primary standards. Legal entities and individual entrepreneurs performing calibration can be voluntarily accredited in the field of ensuring the uniformity of measurements. 3. The scope of state regulation of the uniformity of measurements is determined by the metrological service of an enterprise, organization, legal entity in agreement with the state metrological supervision, Rostechnadzor and the regional metrological center. 4. Measuring instruments entered into the state register of S.I. can be used both in the field of state regulation of the uniformity of measurements, and outside the scope of state regulation of the uniformity of measurements at any enterprise, organization, individual entrepreneur, legal entity or individual. Everything is determined by technical and technological necessity.

According to point 1: All SI can be divided and “legalized” by the corresponding lists: a—participating in commercial, trading and accounting operations; b— related to ensuring the safe conduct of the technological process and safety; c—related to environmental protection and ensuring environmental safety; d—related to ensuring the quality of products; d—standard and standard measuring instruments; All these measuring instruments must be certified and must undergo State Verification. e—all other measuring instruments can be calibrated, or can be classified as measuring instruments used in the “Control” (“Indication”) mode, without assessing their normalized accuracy, which are not subject to verification and calibration. According to the new guidelines, these devices are marked “K” (“I”).

According to paragraph 2: They can, but are not obliged to. And your organization can carry out calibration for itself, using those SIs for which it has standards and reference instruments. To calibrate “for yourself” you do not need any rights or licenses; it is enough to have sufficient (you determine) qualifications of the employee, and to maintain the appropriate accounting document for this work. Naturally, it is better to establish this work with appropriate orders and instructions.

According to clause 3: Your organization determines by creating and approving the appropriate lists and lists of SI, and is also fully RESPONSIBLE for their correctness and sufficiency. They may not be verified or calibrated, but used in the “Control” mode, only naturally ending up in your compiled “List of measuring instruments used to monitor the measurement of quantities, without assessing their normalized accuracy, not subject to verification and calibration.” For the composition of which your organization bears 100% RESPONSIBILITY.

Source: www.pkf-orgcervic.ru

Various measuring instruments can be installed in a compressed air injection system; a pressure gauge has become widespread. Like many other devices, this one must undergo periodic maintenance. Only in this case can you be sure that it will last for a long period, and the readings obtained will be accurate. Let's consider all the features of the pressure gauge checking procedure in more detail.

Frequency of checking pressure gauges

A pressure gauge is a device that measures pressure in a device or container in a certain section of the pipeline. Periodic checking helps avoid major problems. It is worth considering that verification of pressure gauges should be carried out exclusively taking into account the type of device:

In order for the calibration of pressure gauges to be carried out with high efficiency, attention should be paid to their design features. Spirals are characterized by the following features:

1. Inside the housing there is a spiral, which is connected to the transmitting elements. It is made using a special metal with high elasticity.
2. The dial is connected to a spiral, due to which the position of the arrow changes. The dial operates on a mechanical principle and is represented by a scale with an arrow. Typically, units of measurement and other more important information are displayed on the surface.
3. As the pressure increases, the spiral unwinds, causing the needle to deflect to a greater extent. The size of this element determines the range over which measurements can be taken.

Membrane versions operate due to a flat plate that is connected to the transmitting element. As the pressure increases, the membrane bends to a greater extent, causing the needle to move.

The frequency of verification depends on a variety of factors, including the area of ​​application of the device. In some cases it is necessary to carry out the procedure once a year, in others for 5 years. Incoming inspection is carried out by many organizations with an on-site visit, since in some cases the procedure must be carried out by a certified specialist and taking into account the requirements for processing.

Calibration of the pressure gauge and other procedures used to be carried out once a year, but due to the use of modern technologies in production, the period has been doubled.

Due to this, the accuracy of the pressure gauge readings is at a high level.

Today, state verification is carried out when monitoring the condition of measuring instruments of critical systems. The received data is decrypted in a variety of ways, so the procedure is carried out exclusively by a specialist.

Where is the mistake?

First thought: the standard pressure gauges are lying. To check them, a splitter was connected to the compressor hose. One of its sleeves was connected to a standard pressure gauge, and the second to an inflated tire.

Indeed, they all lied, but the pressure in the inflated tire still did not meet the required pressure. A sample pressure gauge connected to a running compressor showed 2.0 bar, but as soon as the electric motor stopped, the pressure decreased to 1.8 bar. The model pressure gauge showed the same thing when connected directly to the wheel valve. How to explain this fact?

The fact is that approximately 0.2 bar is lost when overcoming the narrow bottle neck - the channels in the spool. As soon as the compressor turns off and the air flow becomes zero, the pressure in the entire system immediately equalizes - then you can estimate the error of the compressor pressure gauge.

Understanding came when they thought of connecting a valve turned out of the wheel to a running compressor. It would seem that the pressure gauge should show zero: after all, there is no back pressure. However, the first experiment showed an excess of 0.4 bar! Having looked through several valves from different manufacturers, we determined the range of “overstatement” - from 0.4 to 0.6 bar.

The spread of readings depends on how much the spool rod moves when the compressor hose nozzle presses on it. Just don’t think that we didn’t put or screw the pump tip onto the valve tightly enough. If the tip does not press the spool rod at all, the valve will open under a pressure of at least 5 bar. And a regular car compressor develops this with great difficulty.

Installation diagram for checking compressor pressure gauges

1 - wheel, 2 - valve, 3 - standard pressure gauge, 4 - tested compressor with built-in pressure gauge.

Methodology for checking pressure gauges

There are quite a large number of different technologies that allow you to determine the condition of a measuring device. Checking of technical pressure gauges should be carried out exclusively by professionals, since mistakes made can cause a decrease in the accuracy of the readings. Services should only be provided by specialists who have received appropriate permission.

There are several most common verification technologies:

1. When using a hydraulic press. In this case, the measuring device is installed between two elements of the device. It is worth considering that this measurement technology is characterized by low error. There are quite a large number of different types of hydraulic presses, all of them are characterized by their own specific features. This design is found exclusively in specialized stores; to use it you must have certain skills and knowledge.
2. When using a metrological stand. In this case, the main indicators are taken with a minimum error at the established control points. Such a device creates the required pressure in the system. Among the features of using a metrological stand, we note that the measurement errors are quite high. However, the design features make it possible to significantly expand the scope of application of the device, for example, in the case of high pressure in the system.
3. When using a special calibrator. This device can be purchased today in a specialized store for independent verification of the device. When choosing a calibrator, attention is paid to the range of indicators it can be used in. Most of the models work according to the same scheme.

Content:

Pressure gauges are instruments that are used to measure excess gas pressure.
In the case of gas-flame processing of metal surfaces, this device is indispensable, since only with its help can one obtain information about exactly what gas pressure is maintained in the cylinder. The use of pressure gauges is necessary in order to maintain ideal pressure in the system, which is why gas reducers are equipped with pressure gauges. Since a pressure gauge for a gas reducer is required to measure high pressures, it has an unusual type of sensing element. This is a copper tube, the peculiarity of which is that it not only has a significantly narrower cross-section, but also has a large number of turns, around the axis of which the tube moves when pressure is applied to the gearbox itself. In addition to the conversion function, the copper tube plays the function of a damper, and therefore it is the main part of the pressure gauge.

Under gas pressure, the tube straightens, therefore, the greater the gas pressure, the more the tube straightens. The tube itself is connected to the arrow, which allows the movement of the tube to be transmitted to the arrow. The arrow itself displays the real pressure value.

Since pressure gauges are designed for a certain pressure, each pressure gauge has a red line marking it, corresponding to the maximum permitted pressure. Loading pressure gauges with pressure exceeding their upper limit of measurement is strictly prohibited.

Spring pressure gauges are installed on oxygen and acetylene gearboxes. The pressure gauge for the gas reducer is connected to the high and working pressure chambers with a wrench; fiber and leather gaskets are used to seal the connection.

Checking pressure gauges: rules

Pressure gauges must be checked exclusively taking into account the basic rules and recommendations, since mistakes made can lead to a decrease in the accuracy of the product. The basic rules are as follows:

1. First, the pressure gauge is inspected to determine the condition of the mechanism. Damage to the device may indicate that verification is not worthwhile. Some of the defects can be eliminated, for example, by replacing the protective glass, it all depends on the features of the specific pressure gauge model.
2. The conditions closest to operational ones are created. An example is the indicator of air humidity, atmospheric pressure and temperature in the room.
3. At the beginning of the test, the needle must be at zero. Due to this, the possibility of an error at the time of measurement is eliminated.

If it is not possible to set the needle to zero, then the device is adjusted using a special bolt.

Pressure gauges checking proper operation - Chemist's Handbook 21

Metal pressure gauges are simple in design and quite reliable in operation. For periodic monitoring of the serviceability of pressure gauges, proven control pressure gauges are used. The pressure gauge in use on the device must have a seal with the date of inspection and testing. [p.44]
Each autoclave must be equipped with a working, sealed pressure gauge. Each pressure gauge must be checked and sealed at least once every six months (regardless of the period of operation). A red line should be drawn on the pressure gauge scale or, instead of it, a metal plate painted red should be strengthened (soldered), tightly adjacent to the glass of the pressure gauge and installed on the division corresponding to the maximum permissible pressure in the autoclave. [p.764]

Flushing of main air pipelines Major cleaning of a piston compressor Major cleaning of a rotary compressor during single-shift operation Major cleaning of a rotary compressor during two-shift operation Cleaning of intermediate refrigerators Checking the serviceability of pressure gauges Checking the presence of water in the sealing box of a rotary compressor Changing the oil in the sealing box and washing it
[p.130]
Pressure gauges and thermometers must be in good working order - with intact glass and a body without dents. The operating pressure range of the oil pump should be in the first half of the pressure gauge scale. If, for example, a centrifuge oil unit operates in the pressure range of 5-20 kgf/cm2, then the pressure gauge scale should be designed for 40 kgf/cm2. The body of the pressure gauge and thermometer must have a seal and a sign of a state inspector, indicating that the device has passed an annual test. [p.158]

The procedure for working on the test bench is as follows.
After checking the serviceability of the stand and preparing it for work, a safety valve 8 is installed on one of the workplaces. Air is pumped into the receiver with a compressor to the operating pressure of the safety valve. Slowly open the valve in front of the valve and check the tightness of the seal between the valve and the seat. If there is a lack of tightness, the necessary repairs to the valve are made (changing the sealing ring, cleaning the surfaces, adjusting the spring force, etc.). After repair, adjust the valve to the required pressure by tightening or loosening the spring adjusting screw. The response pressure is determined by control pressure gauge 3 at the moment of the characteristic pop of the valve with a gradual increase in air pressure in the receiver. In this case, the receiver is necessary to generate a pop that makes it easier to adjust the valve. Receiver capacity is recommended to be at least 40 liters. After adjusting the valve, the adjusting screw is secured with a locknut. [p.55]
After completing the listed work, they begin to check the operation of instrumentation.
For spring pressure gauges, the return of the needle to zero is checked after communicating it with the atmosphere and releasing the gas pressure through a three-way valve. If the pressure gauge readings are inaccurate, a control pressure gauge is installed on the three-way valve and, using the three-way valve, pressure is simultaneously measured with the control and working pressure gauges. If the readings of the pressure gauges turn out to be different, then the working pressure gauge is replaced with a working one. Next, they begin to check the readings of the pressure gauge, which measures the pressure drop across the filter. If the pressure drop across the filter is higher than the permissible 100 mm water. Art. (1000 Pa), then the filter must be cleaned. [p.146]
The entire territory of the installation, as well as the sites of the reactor unit, are cleared of oil products and foreign objects, which ensures normal working conditions for the operating personnel at the installation.
The serviceability of the steam extinguishing system is checked (steam risers in the twin chambers of furnaces, in pump rooms), the serviceability of the risers, the presence of fire extinguishers, fire blankets, sand, etc. The fans of all ventilation devices in production pump rooms and rooms must be tested and brought into working condition blowers and compressors. Pressure gauges are checked, as well as safety valves installed in devices operating under pressure above 0.7 ati. Safety valves that have defects (the lever does not move, or the seal is broken), or that have expired are not allowed to be used. [p.137]
When setting up instruments and assessing the quality of operation of the installation, they are guided by the general methods outlined above for determining the condition and serviceability of the installations and their individual elements.
Pressure and boiling and condensation temperatures are determined by pressure gauges, which are installed during testing on special tees of the compressor discharge and suction valves. Techniques for installing pressure gauges, methods for controlling temperature conditions and setting up automation devices are outlined in the description of the start-up of small installations after installation. [p.197]
After removing the valves, check the condition of the working surfaces of the cylinders through the valve seats. If there are scratches and burrs, disassemble the piston group, clean the cylinder bore with a thin sanding cloth, and clean the rings and grooves on the piston. Then connect all the pipelines and devices that were disconnected for purging, clean the filters on the lubrication system, and check the tightness of the threaded connections on the compressor. Replace the pressure gauges used during purging with permanent ones, check the serviceability of the safety valves and prepare the compressor for load tests. Load tests are used to check the performance of all components and systems of the compressor under operating conditions. After starting, they begin to load the compressor, making sure that all components are operating normally at idle. At first

www.chem21.info

Requirements for calibration of pressure gauges

To verify the basic parameters of the measuring device, attention should be paid to the basic requirements that apply to the procedure in question. These include the following points:

1. Before the actual inspection, you should provide documents that confirm that you have completed this procedure previously. The results that were obtained earlier may also be required during the next verification. Some companies do not carry out the procedure in question if the appropriate document is not available.
2. If the device is part of a critical mechanism, then it must have a seal. Otherwise, the mechanism cannot be used for its intended purpose.
3. Depending on the pressure in the system, the most suitable equipment is selected. The most important parameters are the measurement range and the scope of application of the device.
4. The data from the device used must be easily readable. For this purpose, the most optimal working conditions are selected.
5. The installation of a pressure gauge must be carried out exclusively in compliance with all safety measures. A fairly common mistake is reducing the strength of the connection. If high pressure is applied, a leak may occur, which will reduce the pressure in the system.

All established standards are taken into account by the specialist who verifies the device. If the requirement is not taken into account, the condition of the structure cannot be verified with high accuracy.

What is the accuracy class of a pressure gauge?

The accuracy class of a pressure gauge is one of the main values ​​characterizing the device. This is a percentage expression of the maximum permissible error of the meter, reduced to its measurement range. ... It is with this value that the accuracy class is associated. There are two types of pressure meters - working and standard.

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Time limits for checking pressure gauges

Most attention is paid to deadlines. The purpose of calibration is to increase the accuracy of the readings taken. Among the features we note the following points:

1. When submitting a pressure gauge for verification, you need to be prepared for the fact that it will be in the company for 14 working days. Some companies complete the task much faster. Do not forget that verification requires quite a lot of time, which eliminates the possibility of making an error.
2. For reference devices, the period is reduced to 7 working days. When contacting a company that provides the services in question, you can find out how long the work will be completed.
3. You can reduce the timeframe by submitting documents in advance. Many companies allow you to call and order verification, as well as send documents electronically for their preliminary verification.
4. The measuring device can only be removed from the device by calling a specialist who provides the appropriate services. Do not forget that making mistakes at the time of installation can compromise the integrity of the highway.
5. The tests carried out must last for a certain period. Manufacturers often add instructions for using calibration devices to the package.

You can carry out the procedure in question yourself only if the device is installed as an element of non-critical mechanisms.

Why do pressure gauges have different markings?

The same pressure gauge can be used to measure liquid and gas pressure. This becomes acceptable only if each of its structural elements is resistant to these types of environments. When a pressure gauge can be used in limited conditions, specialized symbols are applied to the scale of the device, which notify about the intricacies of operating a particular device. Detailed information about the influence of which particular environment can be measured by the device is indicated in the manufacturer’s data sheet.

When measuring small indicators, a membrane is used as a sensitive element. Due to the large area of ​​the membrane, even a small influence on it provokes a clear transformation of the membrane. Such a change is communicated using the thrust of the rotary switch mechanism, and the device demonstrates exactly the pressure that actually exists at any given moment in time. To connect the pressure gauge to an aggressive environment, specialized membranes are used. The bodies of devices are often painted in different colors, and this is no coincidence: blue devices are used to measure oxygen pressure, yellow ones are used for ammonia pressure gauges, white ones are for acetylene pressure gauges, dark green ones are used for hydrogen, grayish-green ones are used for chlorine.

The body of products designed for propane and other flammable gases is painted red. The black color of the body is for pressure gauges designed for the use of non-flammable gases. Oxygen-type devices must be degreased, since sometimes minor contamination of the fitting, when connected to oxygen, can cause a flame and even an explosion. In pressure gauges for acetylene, the presence of copper alloys in the measuring device is not allowed, due to the fact that during contact with acetylene there is a risk of formation of explosive acetylene copper.

Is it necessary to check pressure gauges?

The initial verification of the device is carried out to determine the nominal pressure indicator. In the future, control eliminates the possibility of a decrease in accuracy.

Periodic checking of the pressure gauge is required in order to eliminate the possibility of its failure.

Some systems cannot be operated without the use of a pressure gauge.

If the procedure in question is not carried out in a timely manner, you may encounter the following problems:

1. Error when taking measurements. In some cases, a slight error does not reduce the efficiency of the compressor; in others, pressure accuracy is important.
2. The service life of the pressure gauge is significantly reduced. Some damage to the mechanism during long-term use can lead to rapid wear. The cost of high-precision pressure gauges is very high.
3. There is a possibility of a medium leak, which will cause a decrease in pressure in the system.

In conclusion, we note that if it is necessary to verify the compressor measuring instrument, you can carry out similar work yourself. To do this, you can purchase a special device in a specialized store. Other mechanisms that have higher requirements must be checked exclusively by a specialist. After the procedure, a filling must be placed.

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Source: stankiexpert.ru

How to check a blood pressure monitor at home?

Such a check, unlike verification at a government agency, may turn out to be inaccurate, but in most cases it allows you to identify possible malfunctions in the operation of the device.

When purchasing a tonometer, you can check the device directly in the store. To do this, the consultant will check the integrity and tightness of the joints of the tubes, bulb, cuff and make sure that the pressure gauge needle coincides with the o. He will carry out a control measurement with a device tested according to all the rules and measure blood pressure with a purchased device. If they match, then the device you purchase works accurately and can be used.

How to check the accuracy of an electronic blood pressure monitor

? To do this, the consultant checks the integrity of all components and, just as when purchasing a mechanical device, checks the blood pressure readings on the certified tonometer in accordance with all the rules and the purchased tonometer.

The same algorithm for checking a tonometer can be carried out at home, but for this you will need another tonometer, which has been verified by organizations that have been accredited for the right to verify measuring instruments or in standardization, metrology and testing centers (TSM). This is also not always possible and it would be better to contact specialists.

How to check your home blood pressure monitor

, if you do not have the opportunity to check the readings with a device certified by specialists? To do this, you can use the following rules:

We have already found out how to check the accuracy of a tonometer at home, now we will look at how to set up a tonometer.

Which pressure gauges are subject to verification?

In accordance with Article 13 of the Federal Law “On Ensuring the Uniformity of Measurements”, the Government of the Russian Federation decides:

1.

Approve the attached list of measuring instruments, verification of which is carried out only by state regional metrology centers accredited in the established manner in the field of ensuring the uniformity of measurements.

2.

Verification marks applied to measuring instruments or verification certificates issued for them before the date of entry into force of this Resolution are valid until the expiration of their validity period.

3.

This Resolution does not apply to relations arising during verification of measuring instruments:

A)

applied by federal executive authorities, the Armed Forces of the Russian Federation, other troops, military formations and bodies when carrying out activities in the field of defense and state security in accordance with the Federal Law “On Defense” and the Law of the Russian Federation “On Security”;

b)

belonging to organizations of the State Atomic Energy Corporation "Rosatom";

V)

located in the form of stocks of material and technical means in storage or used for civil defense purposes;

G)

used at the Baikonur complex.

4.

This Resolution comes into force on January 1, 2012.

Measuring instruments by types of activities related to the sphere of state regulation of ensuring the uniformity of measurements

Carrying out activities in the field of healthcare

1.

Instruments for measuring human body temperature

2.

Instruments for measuring human mass

3.

Instruments for measuring strength and power used in diagnosing the performance of human muscle groups

4.

Length measuring instruments used to determine human height

5.

Blood pressure measuring equipment

6.

Instruments for measuring volume, flow rate, gas concentration

Schrader valve

1 - sealing sleeve; 2 - seal; 3 - threaded bushing; 4 — spool rod; 5 — valve body; 6 - valve body; 7 - conical spring; 8 — valve cup. The spools of the old (a) and new (b) samples are completely interchangeable. The air resistance is approximately the same.

If you have looked into the hole in the wheel valve, you have probably seen a spool there. This device, standardized throughout the world, is used not only in the wheels of cars, motorcycles and bicycles, but also in air conditioners, scuba gear and other elements of pneumatic equipment.

It is the Schrader valve that creates the main resistance to the air flow. Because of its influence, no pressure gauge will show the correct pressure while the compressor is inflating the tire.

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Frequency of checking pressure gauges

A pressure gauge is a device that measures pressure in a device, container, or pipeline. There are several types:

Spiral pressure gauges consist of a metal spiral that is connected by a transmitting element connected to a pointer on a dial. The higher the pressure, the more the spiral unwinds and pulls the arrow along with it. Which is reflected in an increase in pressure readings on the instrument scale.

The diaphragm pressure gauge provides readings due to a clamped flat plate, which is connected to the transmitting element. When exposed to pressure, the membrane bends and the transmitting element presses on the dial arrow. This is how blood pressure increases.

To check the compliance of the accuracy parameters of the meter declared by the manufacturer and to monitor the metrological serviceability of the device, without which the pressure gauge cannot be used in areas falling under GROEI (state regulation for ensuring the uniformity of measurements), and also to ensure that the device serves the established period and operation is safe, it should be periodically carried out checking the pressure gauge. The rules set by the state state that, depending on the technical characteristics of the device and the manufacturer's instructions, the reconciliation period ranges from 12 months to 5 years.

Regular inspection of the device after a year was considered the most common, but now manufacturers are improving the characteristics of the equipment, and devices with a verification period of 2 years are increasingly found. It is worth remembering that the pressure gauge must undergo inspection and verification after a certain period from the date of production, and not from the moment it is put into operation.

The service life of a pressure gauge is set by manufacturers; on average, it is 8-10 years. It is necessary to keep a log of pressure gauge checks in order to check the device on time.

How to pump up correctly

It remains to admit the obvious: it is impossible to accurately set the pressure using compressor pressure gauges. After all, any valve is an obstacle to the air flow. And any obstacle creates the same back pressure. For this reason, in all compressors the pressure generated always exceeds that which we later measure directly at the wheel. Therefore, even the most accurate built-in device will always show a pressure higher than in the tire. And accordingly, the compressor will turn off earlier than necessary.

It is better to overinflate the tire, measure the pressure with an accurate pressure gauge and bring it back to normal by bleeding excess air from the tire.

You can set the pressure with some anticipation. If you need to get 2.0 bar, you should inflate the wheel to 2.2 bar. However, different valves create different back pressure, the magnitude of which is unknown in advance. And even on one car it can walk from wheel to wheel. We encountered this phenomenon in the examination of electronic pressure gauges (we will publish it in the September issue of the magazine). By the way, in most cases their accuracy is higher than that of the devices built into compressors. Therefore, we advise everyone to acquire such a pressure gauge in addition to the compressor.

Methodology for checking pressure gauges

To check the operation of the measuring device, you should contact specialists who have received accreditation of a sufficient level (in accordance with the type of pressure gauge you have); these organizations are registered in the state register. The service must be provided by trained employees. Verification is also carried out by state metrological control bodies. You will then be provided with a protocol, which should be kept until your next follow-up visit.

The pressure gauge can be checked in several ways using:

• metrological stand;
• hydraulic press;
• calibrator.

Checking the pressure gauge using a metrological stand allows you to check the pressure at the installed control points with minimal error. The process is carried out using two pressure standards and comparing their indicators. The device creates special pressure using a pump. Deadweight piston devices are used more often.

Verification using a hydraulic press takes place on a device that includes several weights, a standard meter and a device that sets the pressure, a press. A calibrated pressure gauge is installed between the parts of the apparatus. The final data of the pressure gauge under study must coincide at the control points of the scale. These devices are highly accurate and allow a minimum error (0.04 psi).

The first two methods of verifying measuring instruments are provided for when sealing and installing a stamp on the device being verified and require clear, normatively recorded actions on the part of the service provider (issuance of a protocol or certificate of work performed).

Verification using a calibrator does not apply to measuring instruments that require control and supervision by the state. This device is mobile, it allows you to conduct research at the location of the device.

4.4. Basic rules for verification and calibration

Verification methods by which verification and calibration of standard pressure gauge instruments are carried out are presented in /4-19,4-20,4-15, etc./. For devices of special designs, there must be individual verification methods approved by the relevant body (usually VNIIMS), such as /4-21/.

Verification of measuring instruments can only be carried out by metrological services of legal entities accredited by the Federal Accreditation Service (Rosaccreditation). Rosakcreditation was created in 2011 in accordance with Decree of the President of the Russian Federation dated January 24, 2011 No. 86 “On a unified national accreditation system” / 4-22 / and operates on the basis of Federal Law of the Russian Federation N 412-FZ “On accreditation in the national system” accreditation" dated December 28, 2013/4-23/ and by Decree of the Government of the Russian Federation No. 845 dated November 17, 2011/4-24/.

Accreditation of metrological services for the right to carry out verification and calibration work is carried out by the relevant commissions created by the Federal State Unitary Enterprise "RosAccreditation" of experts with the appropriate qualifications.

Accreditation can be carried out both by the metrological service and its structural unit - the verification and/or calibration laboratory.

If the decision is positive, the Federal Accreditation Service issues an accreditation certificate for the right of verification with the annex “Scope of Accreditation”, which indicates the type and type of measuring instruments that can be verified by an accredited person. The scope of accreditation for verification rights also determines the measurement range of the instruments being verified and their errors.

According to the requirements of Law No. 412-FZ/4-23/, an accredited person is obliged to undergo the procedure for confirming competence within the following time frames:

• during the first year from the date of accreditation;
• at least once every two years, starting from the date of completion of the previous procedure for confirming competence;
• every five years from the date of accreditation.

It should be noted that “the decision to carry out the procedure for confirming the competence of an accredited person is made on the basis of an application from the accredited person” / 4-23 / i.e. the accredited person must independently apply for confirmation of competence. In the absence of such an application within the time limits specified in /4-23/, accreditation for verification rights is suspended. The forms of documents for interaction with Rosakkreditatsiya are determined by order of the Ministry of Economic Development of the Russian Federation No. 288 dated May 23, 2014/4-25/.

When organizing verification and calibration, special attention must first of all be paid to the following factors: the professional preparedness of verifiers and calibrators, the technical condition of working standards and auxiliary equipment, the conditions for verification or calibration.

Professional preparedness of verifiers and calibrators . Verification can be carried out only by specialists who have completed a special training course, successfully completed it and received the appropriate certificate or certificate, followed by certification of verification specialists to work with a certain list of measuring instruments, which is carried out by the State Metrological Service, for which a corresponding certificate is also issued.

Each verifier has a personal mark, which he can use only within the limits of his competence.

Technical condition of working standards. Metrological services carrying out verification or calibration must have the entire set of standards and other measuring instruments, as well as auxiliary equipment necessary for verification or calibration of measuring instruments defined by the scope of accreditation.

Standards, which mean means of comparison (see above for more details), intended for verification of pressure gauge instruments, in accordance with the requirements /4-4,4-3,4-26/ must undergo primary certification and must be included in the Database of Approved standards/4-27,4-28/. To undergo the initial certification procedure, documentation for the standard is developed: passport, rules of content and application, including the section “Methodology for periodic certification of the standard” or “Calibration Methodology”. A verification certificate indicating the category of the standard according to the state verification scheme and the above documentation are sent to Rosstandart. If the submitted technical characteristics and accompanying documents are positively assessed, Rosstandart issues a certificate of certification of the standard and includes it in the appropriate database. After receiving the certification certificates, the owner of the standards issues an order at the enterprise to put them into operation.

Standards must be verified in accordance with the established methodology and with an established inter-verification period for verification or calibration and must have valid verification certificates, as well as verification protocols. A state verification certificate of the established form is issued for pressure standards. On the reverse side of the certificate, the regulatory documents against which this pressure standard was verified are indicated.

Auxiliary equipment must be subject to performance monitoring in accordance with the requirements of technical documentation.

Each standard and each piece of auxiliary equipment must be affixed with one of the labels reflecting their condition:

• serviceable; fit with limitations; - subject to repair.

The label must be attached to the packaging or storage unit for standards or equipment.

When choosing a standard, the following requirements /4-3/ must be met:

• the upper measurement limit of the standard must be no less than the upper measurement limit of the device being verified;
• The limits of the permissible basic absolute error of the standard must be no more than 0.25 of the limit of the permissible basic error of the pressure gauge being verified (for class from 0.04 to 0.4).

Conditions for verification or calibration. For verification or calibration, the parameters of normal environmental conditions are adopted. Normal conditions for determining the basic error of a verified measuring instrument according to GOST 8.395–80 /4-29/ should be those under which the component of the error of the verified instrument from the actions of various influencing parameters in total does not exceed 35% of the limit of the permissible basic error of the verified meter. Specific data for normal environmental conditions when calibrating measuring instruments are presented in Table 4.1.

Table 4.1

Normal values ​​of environmental parameters during verification/4-29/

The standard procedure for checking indicating pressure gauge instruments /4-19/ determines that the ambient air temperature (tamb) in the room where verification is carried out must be 20 or 23 ºС with a permissible deviation: ±2 °С - for instruments of accuracy classes 0.6 and 1; ±5 °С - for instruments of accuracy classes 1.5; 2.5 and 4.

• pressures, which are subject to higher precision due to their high accuracy, are intended, depending on the design and manufacturer, to operate at tambient = 10...35 °C and relative humidity up to 80%. When organizing verification under environmental conditions different from those given in table. 4.1, it is necessary to enter corrections Рt , determined according to the method given in /4-3/:

Рt = Kte ( t2 - t1 ) P/ 100,

where P is the measured pressure; t2 —real temperature; t1 —nominal temperature; Ktе - temperature coefficient.

The temperature coefficient must be installed in each metal from which the elastic sensing element is made.

The author is not aware of any work on the experimental study of the effect of temperature on the elastic properties of modern metals used in reference manometry. This determines the purpose of experimental studies conducted at NPO YUMAS to determine the effect of temperature on the metrological characteristics of pressure standards.

For research, deformation pressure standards with an elastic sensitive element made of beryllium bronze were used.

For research, temperatures from 5 to 60 °C were accepted with fluctuations in the relative humidity of the surrounding air within the range of 70-80%.

The experimental setup and measurement methodology are presented in more detail in /4-30, 4-31/ and section 2.5. Its main elements are shown in Fig. 4.21.

Fig.4.21. Scheme of the experimental setup for determining the operating modes of pressure gauge instruments with ECE depending on the ambient temperature: 1 – pressure gauge under study; 2 - hand press to create pressure; 3 – weight piston column; 4 – air thermostat; 5 – dynamic air heater; 6 – thermometer; 7, 8 – shut-off valves.

• Control of the heating temperature is organized according to the temperature of the metal of the holder and the metal of the UChE at the soldering site

An MP-60 deadweight column with an accuracy class of 0.05, previously verified at a metrological center, was used as a standard device.

For testing, indicating pressure standards with a stainless steel case diameter of 250 mm, with a straight mirror reading scale, accuracy class 0.25, with a square brass holder 22x22mm, connecting thread M20x1.5, a coiling diameter of a tubular spring of 104 mm and a measurement limit of 2 were adopted. .5 MPa. In order to activate heat transfer and reduce the time to reach a stable temperature regime, pressure gauges with a dismantled housing were used in the studies.

The studies were carried out in accordance with /4-19, 4-21/ with forward and reverse stroke. For a more qualitative experiment, recording of readings at 21 (twenty-one) manometric points was adopted.

• Each temperature point was given the time required to set the values ​​on the device under study and take readings from the reference pressure gauge. The optimal mode was accepted when the temperature of the metal of the end of the UCHE at the soldering point of the tip was compared, as a less metal-intensive section of the device, and the temperature of the metal of the holder, which, relative to the tube, represents a thick-walled massive structure.

As a result of the experiment, data was obtained and processed, on the basis of which a dependence was constructed (Fig. 4.22) of the difference between the readings of the test standard and the working pressure standard in the pressure range from 0 to 2.5 MPa during forward and reverse stroke.

Fig.4.22. Dependence of the error of a deformation pressure standard with a beryllium bronze sensing element on the ambient temperature.

1. The data obtained as a result of the experiment was processed in accordance with GOST 8.906-2015/4-3/, which is the main regulatory document for indicating pressure standards and calculating the error from the influence of ambient temperature. The calculation is based on the temperature coefficient (K).

Analysis of calculated and experimental data shows that at a temperature of 7°C there is a peak value of the total maximum permissible error equal to 0.014 MPa with a calculated value of 0.03025 MPa. When the temperature increases to 24.7 °C, a smoother dependence is observed, adhering to the X axis, which is quite logical, because The normal temperature for devices with a high accuracy class is 20+2°C. The peak error observed at this temperature is 0.008 MPa with a calculated value of 0.0088. At a temperature of 31.9 o

C there is a pronounced behavior of the dependence with a peak value of 0.012 MPa with a calculated value of 0.0196 MPa. In the temperature range from 42 to 53°C there is a smooth increase in the dependence of the error on temperature. Thus, at a temperature of 42°C the peak value is 0.02 MPa with a calculated value of 0.0347 MPa, at a temperature of 53°C the peak value is 0.03 MPa with a calculated value of 0.0512 MPa.

Calculated errors of the deformation standard of pressure with class.t. 0.25 s Beryllium bronze UCE at different temperature coefficients

Table 4.2

Thus, it follows that the temperature coefficient is equal to 0.06%/оС for deformation pressure standards with CL.T. 0.25 s UCHE made of beryllium bronze produced by NPO YUMAS is overestimated.

To select the most optimal temperature coefficient value for deformation pressure standards with class.t. 0.25 s ECE made of beryllium bronze, Table 4.2 shows calculations of the values ​​of the total permissible errors with different Kte.

As a result, based on the data obtained experimentally and computationally (Table 4.2), it is possible to determine the optimal temperature coefficient for CL devices. 0.25 of this series of experiments. At an ambient temperature of 7°C, the experimental value is 0.014 MPa, while the minimum value of the calculated total maximum permissible error is 0.01425 MPa, obtained using a temperature coefficient of 0.02%/°C. For a temperature of 24.7 °C, the experimental value is 0.008 MPa, and the most optimal value of the calculated permissible error is 0.00795 MPa, which, although it is on the border of the experimental value, when rounded, a value equal to the experimental one is obtained, with a temperature coefficient of 0.04% /oC.

Subsequent analysis of the data shows that at an ambient temperature of 31.9 °C the most acceptable temperature coefficient is 0.03%/ °C, at 42 °C - 0.03%/ °C, at 53 °C - 0.04%/ °C.

Thus, from the experimental studies carried out it follows that for deformation pressure standards with cl.t. 0.25 s of beryllium bronze ECE, a temperature coefficient of 0.03%/оC can be applied, which satisfies most points of the experiment, but corresponds to all points of the experiment with a significant margin of coefficient equal to 0.04%/оC.

The basic rules for conducting verification are regulated in detail by MI 2124-90/4-19/. The first stage of verification is an external inspection, as a result of which pressure gauges with mechanical damage to the body, connecting fitting (preventing connection and not ensuring the tightness and strength of the connection), needles, glass, dials that affect the operational properties are rejected.

At the second stage, each device is checked for tightness and the quality of the seal between the connecting fitting and the socket of the device for creating pressure. A pressure corresponding to the upper measurement limit of the device being verified is created in the system, and the valves for supplying the working medium are closed. The device and seals are considered airtight if its readings after establishing pressure within 1...2 minutes. and the next 3 minutes. does not decrease by more than 2% of the steady-state pressure.

The devices must first be kept for 5 minutes. under pressure equal to the value of the upper limit of measurement, then, reducing the pressure to zero, adjust the zero position of the arrow. It is allowed to withstand vacuum gauges under pressure less than the upper measurement limit, but not less than 0.95 atmospheric pressure during verification.

Verification of pressure gauges with additional scales, such as freon gauges with a temperature scale, should be carried out only on the pressure scale. The verification of pressure gauges that do not have a scale graduated in pressure units is verified only if there is a ratio between the units shown on the scale and the pressure units.

The pressure gauge can be checked in one of the following ways:

• certain pressure values ​​are set according to the standard, and the reading is carried out according to what is being verified;
• using a press, certain pressure values ​​are set according to the pressure gauge being verified, and the reading is made according to the standard.

The readings of the indicating pressure gauge during verification must be carried out with an accuracy of 0.1 division. The operator's direction of vision when taking readings should pass through the end of the index arrow, perpendicular to the surface of the dial. At the knife end of the index arrow, the direction of vision should be in the plane of the knife blade (see section 4.2).

Checking the pressure gauge is carried out by smoothly increasing the pressure, stopping at each of the specified points, reaching the maximum scale value, holding for 5 minutes and smoothly decreasing, recording the readings at the same pressure values ​​as when the pressure increases. The rate of pressure change should not exceed 10% of the reading range per second.

The main absolute error of the device is defined as the difference between the readings of the calibrated and reference pressure gauges. This error, as well as the difference in the readings of the forward and reverse strokes, should not exceed the value corresponding to the accuracy class for the instruments being verified from the operational system. For both new devices and repaired ones, the value of the basic absolute error must correspond to 0.8.

The result of verification is confirmation of the suitability or unsuitability of the measuring device for use. If suitable, as a rule, a verification mark is applied to the glass of the pressure gauge. For numbered devices, the verification stamp can be printed on the accompanying documentation (passport). A verification certificate is required for standard instruments and, in some cases, high-precision pressure gauge instruments.

If the verification results do not correspond to the declared accuracy class of the measuring device, a corresponding note is made in the accompanying documentation for this device.

The verification results, both positive and negative, must be recorded in the accounting journal of the accredited unit.

In the rooms where verification or calibration is carried out, all kinds of vibrations and shaking are excluded. It is not allowed to subject the devices, both standards and pressure gauges, to shocks or even minor mechanical influences. The maximum permissible mechanical impact on pressure gauge instruments should not exceed the maximum permissible values ​​both in frequency (within 0.01...30 Hz) and in amplitudes of vibration displacements (up to 0.075 mm) and acceleration (up to 0.2 m/s2).

There should be no heating devices, open windows, cold air installations, etc. near the devices.

When checking and calibrating pressure gauges, depending on their design and accuracy class, certain requirements must be observed. Let's consider the features of verification of the most common models of pressure gauges.

Pressure gauges with a tubular spring are checked at a temperature of 20 or 23 °C. The permissible temperature deviation depends on the accuracy class of the indicating pressure gauge and is: for accuracy class 0.4 and 0.6 - ± 2 °C, with accuracy class 1.0 - ± 3 °C. For devices with accuracy classes 1.5; 2.5 and 4 temperature deviations should be ± 5 °C. For standard pressure gauges with a tubular spring, the temperature specified in the device passport is taken as normal.

The devices are kept in a non-operating state at the temperature noted above for 1 to 12 hours. Depending on the difference in air temperature in the room for verification and the place from which the device is brought.

For technical pressure gauges, verification is carried out, as noted in paragraph 1.3, using eight pressure values ​​for accuracy classes 0.4 and 0.6 and at least five scale points for accuracy classes 1.0; 1.5; 2.5 and 4.0 with inclusion of lower and upper pressure limits. Pressure standards, depending on the range, are checked at 8-13 points (Table 4.3). The scale points to be verified must be evenly distributed throughout the entire measuring range of the device. The readings of the device being verified are taken after holding under pressure at each verified point of the scale for at least 5 s. The metrological characteristics of the verified working pressure standards are determined on the basis of two series of observations for instruments of accuracy classes 0.25 and 0.4 and three series of observations when calibrating a device with an accuracy class of 0.15.

Recommended number of scale points to be verified for spring pressure standards

Table 4.3

* The number n can be negative, positive or zero.

An external pressure generating device can be used to test spring pressure gauges. The main requirement for it is the ability to smoothly increase and decrease pressure, as well as to maintain it stably both at intermediate points and at the limit value.

In Fig. Figure 4.23 shows a diagram of the installation for checking spring, (reference and technical) pressure gauges complete with two socket clamps and a GPM measuring column. Such an installation can operate both on the basis of a deadweight piston pressure gauge press, and on the basis of presses, the descriptions of which are presented in the section

4.3.

The pressure creation device consists of a press 1, a reservoir 2, clamps of the calibrated 3 and standard 4 pressure gauges, valves 5, 6, 7, 8 and 9, a measuring column 10, and connecting pipelines.

The reservoir contains the required volume of working fluid for the operation of the system, which, with valve 5 open and drain valve 6 closed, is pumped into the hydraulic system of the installation by a press. After it is filled, valve 5 of the reservoir closes, and the pressure in the installation rises with the press when valves 7, 8 and 9 are open. With the measuring column 10 removed and clamps 3 and 4 open, air is removed from the installation hydraulic system. At the next stage, the piston of the measuring column is returned to its original operating state, and the pressure gauge to be verified is installed in clamp 3. Valve 7 of the reference pressure gauge clamp is closed. The verification scheme by comparing two indicating instruments, as well as using a GMF measuring column, is ready for operation. When checking a spring reference pressure gauge, it is installed in clamp 4, valve 7 opens, and valve

8 connection of the measuring column is closed.

Rice. 4.23. Installation diagram for checking spring pressure gauges: 1 – press; 2 – working fluid reservoir; 3 – clamp of the pressure gauge being verified; 4 – standard pressure gauge clamp; 5, 6, 7, 8, 9 – valves; 10 – measuring column.

The working fluid can be either various oils or water-based solutions. Some installations use water without additives. In this case, problems arise with corrosion of internal surfaces, as well as with the performance of press seals.

If it is necessary to fill the internal cavity of the sensitive element of a pressure gauge device with liquid, use the installation, the diagram of which is given in section 4.2 (Fig. 4.14).

When checking deformation pressure standards of accuracy class 0.15, it is allowed, in agreement with the State Metrological Service (as an exception), to use a deadweight pressure gauge of accuracy class 0.05.

Before testing, differential pressure gauges are checked for leaks by supplying an excess pressure equal to the maximum nominal differential to the “plus” chamber. The “minus” chamber communicates with the atmosphere. Exposure duration –

10 minutes, after which the pressure supply is stopped and also maintained for 15 minutes. Verification is carried out at a smoothly increasing and then at a smoothly decreasing pressure at at least five points evenly spaced from each other, including marks of 30 and 100% of the limit value. Excess pressure standards can be used as standards when checking differential pressure gauges.

Electrical contact pressure gauges are checked for the error of operation of the signaling device, for electrical strength and electrical insulation resistance.

The operating error of the signal device of an electric contact pressure gauge is established as the difference between the readings of the signal arrow and the value at which the electric contact system is triggered - the electrical circuit is closed or opened.

The strength of electrical insulation is tested by a voltage source with a power of at least 250 V • A, connected between the electrical circuit under test and the device body.

A deadweight piston pressure gauge can be divided into two parts: a device for creating pressure and a device for measuring and reading the measured value, called a measuring column. For verification, devices without pressure creation devices are presented, i.e., measuring columns complete with weights /4-28/. In Fig. Figure 4.24 shows the verification diagram. The diagram shows a reference pressure-creating device, which differs from the technical one in that increased requirements are placed on its installation and operating conditions, and a reference measuring column 1. The pressure-creating device consists of a working fluid tank 2, a press 3 and a drain valve 4. The measuring column being verified 5 is mounted on the same horizontal level as the reference one.

The scheme works as follows. With valve 6 open and valve 4 closed, the press pumps the working fluid into the pressure creation system. After it is filled, the working fluid supply valve 6 is closed. To eliminate air from the system, the pistons of the reference and verified columns are removed from the cylinders and the liquid level in the system is raised with a press until the cylinders are completely filled. The pistons are installed in their sockets, the levels of their ring marks relative to the marks are checked. The loads are gradually installed on the standard and verified load-receiving plates.

Rice. 4.24. Scheme for checking the deadweight piston pressure gauge: 1 – standard column; 2 – working fluid reservoir; 3 – press; 4 – drain valve; 5 – column being verified; 6 – valve for supplying working fluid

Before verification, the measuring column being verified must be dismantled and disassembled into its component elements, which are washed in a “nefras” type solvent. Parts working in contact with castor oil are washed with alcohol.

The device intended for verification must be in the room being verified for at least 10 hours to equalize it with the temperature of the reference products.

Before the start of verification, an external inspection is carried out and devices in which there are pistons in the cylinder, as well as loads that, when placed on top of each other, as well as on the load receiving plate, jam or are deformed to such a state that the parallelism of their supporting planes are not maintained are rejected. The maximum deviation should not exceed 0.05 mm.

The load receiving plate must have the serial number of the manufacturer. Each load is also marked with this number and the normalized pressure value that it provides in the pressure gauge system when installed on the load receptor.

The following basic parameters are checked in the deadweight piston pressure gauge:

• horizontal position of the level of the supporting plane of the load receiving plate;
• duration of free rotation of the piston;
• piston lowering speed;
• sensitivity threshold.

The position of the load receiving plate relative to the horizontal plane is checked in several stages. Pre-install the piston of the measuring head in a vertical position. This is achieved by adjusting the adjusting screws of the deadweight piston pressure gauge frame. At the next stage, the horizontal level meter is placed on the load receiving plate, which is successively rotated 90° in four positions. In this case, it is allowed to move the level indicator (bubble) by no more than one division (1').

You can check the horizontal position of the supporting plane of the load receiving plate in another way. To do this, it is necessary to rigidly fasten the tip of the linear displacement indicator to the plane of the load receiving plate and slowly turn it one turn. This is ensured when the working fluid supply valve is closed.

The duration of free rotation of the piston is checked when installing half the maximum weight of the loads. The duration of rotation is taken as the time interval from the initial angular speed of the load receiving plate of 120±10 rpm to its complete stop. For each type of pressure gauge, according to GOST 8291–83/4-32/, the value of this parameter is determined. So, for MP-60 with a load diameter of 220 mm, the duration of free rotation should be at least 3 minutes.

The lowering speed of the piston is controlled as follows. A quantity of weights is installed on the plate that provides the upper pressure limit of the device, and the shut-off valve for the supply of working fluid is closed. The lowering of the piston is monitored by a ruler with millimeter divisions and correlated with time controlled by a stopwatch.

To check the sensitivity threshold at the upper limit of measurement of the device being verified, the positions of the pistons of the pressure gauges being compared are balanced. Then a load is placed on the load receiving plate of the pressure gauge being verified, the weight of which is strictly defined. Thus, the position of the piston of an MP-6 pressure gauge with an accuracy class of 0.05 must change with a load weighing 0.12 g. Otherwise, the device is considered unsuitable for further use.

Pressure measuring transducers with upper measurement limits of up to 0.25 MPa are verified in gas media /4-33/. At higher pressures, the type of working medium does not affect the measurement result, and therefore verification is allowed on both gas and liquid.

When calibrated complexes operate on gas, and pressure standards operate on liquids, a circuit with a gas-liquid separation vessel is used (Fig. 4.25).

Rice. 4.25. Scheme for testing a pressure measuring transducer using a deadweight pressure gauge and a gas-liquid separation vessel: 1 – gas-liquid separation vessel; 2 – outlet shut-off valve; 3 – measuring column; 4 – complex being verified; 5 – connection valve; 6 – compressed nitrogen cylinder; 7 – gas reducer; 8 – supply valve

A measuring column 3 is installed along the liquid outlet line from the gas-liquid separation vessel 1 through the outlet shut-off valve 2. The complex 4 under test is connected to the separation vessel through connection valve 5. The circuit uses a cylinder 6 with compressed nitrogen as a pressure source, which enters the supply line through gas reducer 7 and supply valve 8.

The liquid level in the separation vessel, the horizontal pressure supply to the complex being verified and the lower plane of the measuring column fitting must be in the same horizontal plane. If this condition is not met, the measurement result must take into account the influence of the hydrostatic liquid column.

When checking devices with an electrical output signal, special requirements are placed on the characteristics of the external magnetic field. Both the magnetic induction of a constant magnetic field (up to 1 • 10–6 T) and its strength (up to 16 A/m) are normalized.

Domestic pressure measuring transducers must be kept with the power on for at least one hour before verification. Modern converters from many of the world's leading manufacturers do not require such temperature adaptation.

More detailed recommendations for testing pressure measuring transducers are set out in MI 1997-89/4-33/.

oxygen pressure gauges must be shaken with the connecting fitting down over a clean sheet of paper (blotting paper). After drying, the presence of oil residues on the internal surfaces of the sensitive element of the device is monitored. If grease stains are detected, the device is rejected and all equipment used in testing oxygen pressure gauges is inspected.

Checking pressure gauges - rules

To accurately examine a measuring device, it is necessary to follow some rules for calibrating pressure gauges:

• inspect for external defects (for example, broken glass);
• it is necessary to create conditions close to normal when carrying out verification (atmospheric pressure 760 mm Hg, air humidity up to 65%, room temperature 20◦ C);
• set the dial hand to zero;
• compare the readings of the reference device and the one being tested.

The last two points, if it is impossible to set the arrow to zero and differences appear between the reference and the device being tested, should be adjusted using bolts. If the nominal parameters are not set, it may be easier to replace the pressure gauge with a new one, given the low cost of the device.

Description

The operating principle of the devices is based on balancing the measured pressure by the forces of elastic deformation of a manometric spring.

Pressure readings in the lines are taken using the instrument dial scale; The pressure difference is measured on the scale of the rotating disk.

The devices have the following modifications: MP, MP-2, MP-2 with disk, MVP. Pressure gauges and pressure-vacuum gauges MP and MVP (freon) are designed to measure the excess and vacuum continuously varying pressure of freons of brands 12, 13, 22, 134a, 142, 404a and 502 (including freons with oils) in refrigeration machines installed in railway cars - refrigerators.

MP pressure gauges (single pointer) and MP-2 pressure gauges (double pointer) are designed to measure the pressure of liquid and gaseous media (water, fuel, oil, air) that are non-aggressive towards copper alloys in power and braking systems and installations of rolling stock of railways, subways and tram cars.

MP-2 pressure gauges with a rotating disk are designed for measuring the pressure of non-aggressive media in installations for general industrial purposes, as well as for measuring the pressure difference.

To measure pressure in places where there is pulsation of the measured medium (with an upper value of the reading range of 1 MPa), the devices should only be used in conjunction with a damping device DV.

To improve performance characteristics, the devices are equipped with electric backlighting of the dial.

Devices can be manufactured either with or without electric dial illumination.

The devices are manufactured in a 100 mm housing, with a rear mounting flange and a radial or axial pressure tap.

Source

Requirements for calibration of pressure gauges

To verify pressure meters you must:

• provide documents confirming the completion of the previous verification;
• presence of a seal, stamp;
• use devices of class 1.5 or 2.5 (depending on operating pressure);
• the pressure gauge data must be clearly readable by the person conducting the verification (if the pressure gauge is installed at a height of 2 m, then the diameter of the dial must be at least 100 mm, if at a height of 3 m - 160 mm);
• The pressure gauge must be installed in compliance with all safety rules (if it is a gas cylinder measuring device, then it should be installed in a well-ventilated, separate room, protected from unexpected fire).
• The owner, in addition to annual verification, must record data in a log when using a reference device.

Do not operate devices that have not been verified on time.

Cases when using a pressure gauge is prohibited.

If the pressure gauge does not have a seal or stamp, the verification period has expired, or the gearbox pointer does not return to the initial mark, by an amount greater than half the permissible error when turned on, then it is prohibited to use such a pressure gauge.

In addition, it is not allowed to use a device that has broken glass or other damage that could affect the accuracy of the readings.

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In conclusion, we note that a working pressure gauge can serve as a guarantee of safety when working with gas welding equipment.

Measuring instruments and tools require control using metric meters. Pressure gauges that analyze the pressure of liquids and gases are installed on heating boilers, gas cylinders, and used on production units. To obtain correct readings from the device and to protect company employees, pressure gauges should be checked periodically.

Time limits for checking pressure gauges

If you have submitted a pressure gauge for verification, be prepared for the fact that it will be returned to you only after 14 working days. For reference devices, reconciliation is carried out within 7 working days. You must submit or fill out an application in advance to ensure verification is completed on time. Also, if you are going to bring a device that has been sealed or branded for verification, you should call the specialist who performed the services and remove the measuring device. If you can call a specialist to the site to calibrate the pressure gauge, it will take a whole working day.