Reprint--Should the pressure gauge be verified or calibrated?

Source: Thermal Control Circle

As a kind of pressure measuring instrument with elastic elements as sensitive elements, pressure gauge has been widely used in the industrial field since its development and application, with its technical advantages of high accuracy, convenient detection and simple operation. Since the pressure gauge is mainly used for the detection of important links in the industrial field, once the problem of inaccurate measurement and verification of the pressure gauge occurs, it will inevitably have a great impact on the stability and safety of production in the industrial field. Under the further application and promotion of pressure gauges, the accuracy of pressure gauge measurement verification has received extensive attention, and how to carry out correct measurement verification and calibration of pressure gauges is a very prominent problem in the development process of pressure gauges.

01 Selection and use of pressure gauges

The pressure gauge uses the elastic line element as a sensitive element for sensing, which can measure and indicate the instrument higher than the ambient pressure, so that the surveyor can know the pressure value of the measuring instrument through the display of pressure change. According to the classification of the use of the pressure gauge, the pressure gauge can be divided into ordinary pressure gauge, ammonia pressure gauge, oxygen pressure gauge, seismic pressure gauge, electric contact pressure gauge, digital compact pressure gauge and double needle pressure gauge, etc. Under normal circumstances, the maximum range scale of the pressure gauge is 1.5-3.0 times of the maximum working pressure of the container, but in order to ensure the accuracy and safety of the pressure gauge pressure detection, the actual measurement needs to control the multiple at about 2 times, and the diameter of the pressure gauge cannot exceed the range of 100 mm.

02 Installation and setting of the pressure gauge

When installing the pressure gauge, it is necessary to conduct a comprehensive analysis of the installation environment, so as to carry out the reasonable installation of the pressure gauge according to the actual installation environment and ensure that the pressure gauge is in a stable and safe environment. According to the installation specification of the pressure gauge, the following aspects need to be paid attention to during installation:

The pressure gauge needs to be installed in a location that is easy to observe

When choosing the installation location of the pressure gauge, it is necessary to choose a position that is easy to observe as much as possible, so that the pressure gauge can be fully observed and dirt treated. In order to improve the accuracy of the pressure gauge, it is necessary to install the pressure gauge in a location that is not in direct sunlight and has a high temperature to avoid radiant heat, freezing and vibration of the pressure gauge due to external factors.

The gauge body needs to be in a vertical orientation

When installing the pressure gauge body, it is necessary to control the pressure gauge body in the vertical direction so that the staff can read the displayed value of the pressure gauge. If the pressure gauge needs to be installed in a higher position, it can be adjusted vertically by tilting forward, but the tilt angle should not exceed 30 degrees.

Install the buffer tube in front of the pressure gauge

After the installation of the pressure gauge is completed, a buffer pipe needs to be installed in front of the pressure gauge to avoid the pressure gauge being affected by external gases. As the guarantee facility of the pressure gauge, the buffer tube can alleviate the gas in the spring tube, and the buffer tube has a certain condensate collection effect, which can prevent the pressure gauge from having too much gas.

Install a three-way or type valve

In the bending part of the pressure gauge buffer pipe, it is necessary to install the three-way or type valve in a suitable intermediate position, so that the three-way plug or type valve can ensure the safety of the pressure gauge work.

03 Measurement and verification operation steps of pressure gauge

Before the installation of the pressure gauge, it needs to be inspected by the relevant national measurement unit, and the relevant inspection certificate will be presented after passing the inspection. To ensure the qualification and accuracy of the pressure gauge, it can be determined according to the frequency of use, and the measurement verification of the pressure gauge is generally carried out once every 6 months, and the verification operation steps need to comply with the following operations:

Metrological verification operations are carried out in accordance with the specifications

Inspectors can carry out the measurement and verification of pressure gauges through the regulations and specifications of elastic element type general pressure gauges, pressure vacuum gauges and vacuum gauges JJG52-2013. According to the range of the pressure gauge to be tested, the verification personnel need to select the calibration instrument corresponding to the range, and at the same time, according to the specified inspection operation, check the validity period of the label of the standard gauge, so that the inspection work of the pressure gauge meets the verification requirements.

Calibration instrument installation is carried out according to the type of pressure gauge

When carrying out pressure gauge measurement and testing, it is necessary to install the standard gauge and the tested pressure gauge on the calibration instrument. If the tested pressure gauge belongs to the oil-free pressure gauge of the oxygen type, it is necessary to install the tested pressure gauge on the oil-free joint that is connected to the oil-water separator, and adjust the calibrator after the installation operation, so that each part can be in a good verification state.

Observe the temperature and humidity of the test room

To ensure the accuracy of the pressure gauge measurement verification, it is necessary to measure the temperature and humidity of the verification room before the measurement verification of the pressure gauge to check whether the room temperature and humidity meet the limit range of the specified operation.

Check whether the pressure gauge meets the operating requirements

In the process of metrological verification of the pressure gauge, the appearance and internal parts of the pressure gauge should be tested to see if they meet the operational requirements of the metrological verification, and after the test is completed, the corresponding test results should be recorded.

Reasonable verification of the display value of the pressure gauge

In the process of metrological verification of the pressure gauge, the appearance and internal parts of the pressure gauge should be tested to see if they meet the operational requirements of the metrological verification, and after the test is completed, the corresponding test results should be recorded.

Metrological verification is carried out in a standardized way

The indication value of the pressure gauge should be verified according to the 5/1 index value, and in the verification process, the standard gauge shall be verified according to the way of line reading, and the inspected gauge shall be verified according to the way of estimating the reading. For the error generated in the verification process, it is necessary to carry out the error according to the specification, and make relevant records after the error verification operation.

04 Solutions to pressure gauge measurement verification faults

The pressure elevated hand cannot be turned

The pointer of the pressure gauge cannot be rotated, mainly because the of the pressure gauge is not opened, or the pointer is stuck due to the blockage between the and the pressure gauge. For the measurement verification fault that the pressure rise pointer cannot be rotated, it is necessary to install the pointer repeatedly at the position of the first measurement verification to make relevant corrections to the measurement verification value of the pressure gauge.

The pressure gauge pointer shakes when it is working

After the hairspring of the pressure gauge is damaged, the pointer will continue to shake in the process of measurement and verification, and the connection of the central shaft of the pressure gauge will be bent, which will also cause the corresponding duty shaking. After the needle of the pressure gauge shakes, it is necessary to check the pressure gauge and solve the damaged parts in time to avoid the pressure gauge from shaking again.

The gauge needle cannot be reset to zero when there is no pressure

Cause the pressure gauge pointer to be unable to zero when there is no pressure, there are many reasons, the frequent reasons are the pointer and the central shaft connection is loose, the spring elbow loses elasticity, the pointer is stuck and the water storage elbow is blocked, etc., once these types of faults appear, it will cause the pressure gauge to appear can not be zeroed verification fault. For the failure of this type of lane, it is necessary to repair the damaged part, and if the pointer is damaged, the pointer needs to be replaced, so that the pointer can be zeroed when there is no pressure.

The gauge needle cannot be reset to zero when there is no pressure

After the wear of the wheel shaft of the pressure gauge gear, the pressure gauge is very easy to have the corresponding inaccurate display value due to improper operation of the gear. When the balance spring and of the pressure gauge are measured and verified, it is easy to cause the corresponding flocculation and blockage due to improper operation, which leads to the inaccurate display value of the pressure gauge. This kind of fault needs to repair the wear and tear, and remove the plug to ensure that there is no fault in each part of the pressure gauge, and the fault problem that the display value of the pressure gauge is not accurate enough can be solved.

In order to effectively meet the demand for high accuracy of pressure gauge in the industrial field, it is necessary to carry out reasonable fault solving and scientific verification of the pressure gauge to promote the further optimization of the detection level of the pressure gauge. In this regard, when using the pressure gauge for pressure verification, it is necessary to select a reasonable pressure gauge type according to the use and scope of the pressure verification, and after the selection is completed, the pressure gauge is installed in accordance with the requirements of the specification. To implement the measurement verification of pressure gauges, it is necessary to use professional staff to adjust the measurement, so that they can complete various types of pressure gauge testing according to the requirements of standard operating steps and processes, so as to minimize the occurrence of pressure gauge failures.