[Abstract]At present, with the continuous improvement of China's economic level and productivity, pressure gauges, as a testing instrument and equipment, arePlays a crucial role in actual production work, providing a wealth of valuable reference information for production activities, making production and science more efficientThe quality and efficiency of research activities have been substantially improved. However, based on the current application status, for the measurement of pressure gaugesA series of problems often arise during the relevant testing of the pressure gauge, resulting in abnormal working conditions and seriously affecting production and scientific research activities

Normal operation of the movement. Given this situation, in this article, the author will approach the calibration of pressure gauges from a technical perspective and combine it with practical situationsProvide a detailed analysis and discussion of common problems and their solutions.

Introduction

Instrumentation equipment requires periodic metrological calibration during production and use, which is also one of the core processes of instrumentation in production and use. However, the metrological calibration of pressure gauges is relatively complex, the calibration process is cumbersome, and the technical standards are high. At the same time, some metrological calibration personnel have certain deficiencies in professional skills, which leads to various problems encountered in the process of pressure gauge metrological calibration. In addition, with the continuous development of social productivity, the relevant standards for pressure gauge calibration have also been raised to adapt to the trend of refined production. Therefore, how to effectively solve the problems in pressure gauge calibration through appropriate technical measures is the focus of research by relevant departments and staff in the near future.

1 The specific content of pressure gauge calibration

1.1 Appearance and internal structure verification of pressure gauge

Before starting the verification work, the staff should first inspect the appearance of the pressure gauge, paying attention to whether its shape has changed, whether there are any signs of damage on the outside, whether there are broken or cracked glass surfaces, whether the pressure gauge pointer is loose, and the smoothness of the external coating, etc. After the appearance inspection is completed, the staff also need to inspect the internal structure of the pressure gauge to see if there are any problems with its structure, with a focus on checking the safety hole and anti dust device of the pressure gauge. By inspecting the appearance and internal structure of the pressure gauge, the staff can detect any apparent problems in the gauge over time and promptly address them.

1.2 Zero position calibration of pressure gauge

Under normal circumstances, the pressure gauge pointer will always stop at the stop pin position and maintain a high degree of tightness with the joint, without any gaps in the middle. If the pressure gauge does not have a stop pin, in the absence of pressure, the pointer of the pressure gauge will stay in the center position of zero[1]And maintain a stationary state. Therefore, the staff is conducting zero position calibration of the pressure gauge

At that time, it is necessary to conduct a detailed inspection of the zero position of the pressure gauge and judge whether there is a problem with the pressure gauge from a comprehensive perspective.

1.3 Calibration of pressure gauge readings

The calibration of pressure gauge readings is the core part of the entire calibration workIt is the part of the verification work that is difficult and requires high precision. During the verification process, the increase and decrease of pressure must always be maintained at a constant speed, and the pressure gauge pointer should be observed in detail to see if it shows a constant motion state. When the pointer reaches the limit value mark, the calibration personnel need to perform a three minute pressure resistance treatment to finally determine the performance status of the pressure gauge. When the reading of the pressure gauge reaches the detection point, the calibration personnel need to compare and analyze the reading of the pressure gauge with that of the standard instrument, accurately grasp the difference between the two, and ensure that the error is within the standard value range. Subsequently, the calibration personnel need to perform a light tapping displacement measurement of the pressure gauge, and the displacement should be controlled within half of the error. In addition, during the process of calibrating the return error of the pressure gauge, the calibration personnel need to steadily reduce the pressure at a certain rate, ultimately reducing the pressure to0The return error should be controlled below the error value.

image1 Pressure gauge calibration document

2 Typical problems and solutions in pressure gauge calibration

2.1 Pressure gauge pointer lightly tapping displacement

Lightly tap the pressure gauge at the calibration point, and if the gauge needle in the pressure gaugeIf displacement occurs, it can be determined that the table has a tapping displacement fault. The main reasons for the displacement caused by tapping are as follows: poor fixation of the pressure gauge spring, excessive tightening or excessive expansion; Insufficient transmission clearance of the pressure gauge leads to abnormal friction, resulting in delayed reaction of the connecting rod and shaft rotationabnormal[2]The tightness of the relevant screws in the pressure gauge is insufficient, and the gears are bitingThere are problems with the engagement, which can lead to meshing failure or obstruction.

In response to the phenomenon of excessive displacement caused by tapping lightly, when it exceeds the allowable error of half a value, the staff should calibrate it in time, remove the back cover of the pressure gauge, and then calibrate the balance spring. If the balance springWhen abnormal situations occur at both ends, adjustments should be made. If there is a malfunction in the transmission components, the surface dirt should be removed in a timely manner, and a certain degree of lubrication treatment should be carried out to resolve unnecessary friction and restore the normal working state of the transmission parts, ultimately eliminating the phenomenon of light tapping displacement in the pressure gauge. If the tapping displacement is within the allowable error range after processing, it can also be considered as achieving the verification target. After the calibration work is completed, the staff need to conduct a pressure tapping test again until the calibration results meet the relevant standards.

image2 Lightly tapping displacement of pressure gauge pointer

2.2 Stagnation and jumping of pressure gauge pointer

The stagnation and jumping of a pressure gauge refer to the non-uniform numerical changes that occur during the measurement process, as the pressure rises and falls, causing the pressure gauge pointer to shake, fluctuate rapidly or slowly, or remain stationary. In this case, if the actual pressure value changes, it is difficult to maintain the accuracy of the pressure gauge reading, which has a very serious impact on production activities.

Given the situation of needle sticking and jumping on the pressure gauge pointer, in generalIt is all caused by the accumulation of dirt in the pressure gauge. Under the influence of dirt, the internal teeth of the pressure gauge may be damaged or the smoothness between teeth may decrease. Over time, this will lead to excessive wear on the shaft holes and increased friction between the shaft wallsIntensify the intensity[3]The friction force in the connecting rod increases, causing the pointer to become unstablePhenomenon. Therefore, the staff should clean and polish the foreign objects inside the pressure gauge during the problem handling process. If the internal components are excessively worn, they need to be replaced in time, which can eliminate themEnsure the accuracy of pressure gauge measurement in case of needle sticking and jumping faults.

2.3 Fixed increase or decrease in pressure gauge error

In the calibration of pressure gauges, the following situations often occur: whether the pressure gauge is pressurized or depressurized, the error between the pressure gauge and the standard pressure value is always a constant value. The reason for this problem is ultimately due to certain issues during the installation of the pressure gauge pointer, which resulted in the error value in the pointer remaining fixed.

Given the nature of this malfunction, the staff can place the problematic pressure gauge and standard gauge in the same pressure environment during the handling process. When the indicated value of the standard gauge meets the predetermined requirements, the staff can remove the pointer from the problematic pressure gauge,

Install it at normal values[4]This can effectively solve such problems. If the fixed value of this error is very small, then there is no need to disassemble the pressure gauge. The staff can make subtle adjustments to the error through calibration equipment to ultimately meet the qualified standards.

2.4 Nonlinear error in pressure gauge

The nonlinear error in the pressure gauge will show a positive and negative trend with the rise and fall of pressure, which may gradually change from positive to negative, or from negative to positive[7]The adjustment method for nonlinear errors is also relatively simple. The staff only need to adjust the angle between the connecting rod and the teeth to eliminate this nonlinear error or control it within a reasonable range. If the degree of the angle is too large, the pressure gauge will exhibit a slow front and fast back characteristic; If the degree of the angle is too small, it will exhibit a fast front and slow back characteristic. The staff only need to grasp the variation law of nonlinear errors and then make reverse adjustments to them. In addition, the staff should also note that the rotation direction of the pressure gauge pointer movement is directly related to the angle between the connecting rod and the teeth[5]If the pointer movement rotates clockwise, the angle will show an increasing trend. If the pointer movement rotates counterclockwise, the angle will show a decreasing trend. At this time, the staff can adjust the pointer movement to adjust the nonlinear error.

2.5 The pressure gauge pointer does not return to zero or the full degree does not meet the standard

The position control of the pointer in the pressure gauge depends on the tightness of the pointer spring. If the spring spring is too tight or too loose, it will cause the pressure gauge pointer to not return to zero or fail to meet the full degree standard. The tightness problem of the balance spring is mostly concentrated in new pressure gauges. If such problems occur after a period of use, it is mostly caused by the aging of the balance spring, which in turn leads to excessive wear of the connecting rod. The transmission part cannot receive information, and thus cannot bring the pointer into its normal position. If the transmission ratio decreases, the pressure gauge pointer cannot reach the full movement state. At this time, the staff needs to reduce the length of the fan-shaped gear arm to eliminate the fault. If the angle between the connecting rod and the teeth is too small, the staff needs to readjust the movement. They can also slowly increase the number of teeth on the pressure gauge to restore the accuracy of the pressure gauge measurement.

2.6 Estimation of pressure readings

The readings in the pressure gauge have a certain pattern, including the divisionMarkings, ranges, and indication markings all have certain standards and have different patterns at different levels of accuracy. If the staff have insufficient understanding of the pressure gauge, there may be deviations in the estimation of pressure readings. Therefore, in actual calibration work, staff can use one-fifth of the decimal places of the small division value as a reference for estimating and retaining decimal places. When conducting indication estimation, staff must strictly follow theFollow this standard to ensure the accuracy of the estimation.

3 summary

In summary, in the process of calibrating a pressure gauge, the first step should beTo eliminate its faults and ensure that its readings meet normal standards, only then can the calibration work of the pressure gauge reach a satisfactory level. ExcludingDuring the process of malfunction, comprehensive consideration must be given and one-sided decisions cannot be madeOtherwise, the quality inspection of the pressure gauge will not meet the qualified standards. If the malfunction of the pressure gauge during the calibration process can no longer be carried outCalibration, then this pressure gauge will be discontinued as scrap.