Analysis of Natural Gas Flowmeter Category and Influence Metering Accuracy
1 Natural gas flow meter type 2 Analysis of factors affecting measurement accuracy 3.2 Volumetric Flowmeter Measurement Accuracy Analysis When selecting the flowmeter, attention should be paid to checking the gap parameters of the instrument components to ensure that the parameters are within the allowable range of accuracy in order to meet the error measurement requirements. 4 Conclusion
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Based on the current development of natural gas measurement instruments, from the point of view of the measurement principle, natural gas flowmeters can be divided into 5 categories, namely ultrasonic flowmeters, turbine flowmeters, waist flowmeters, orifice flowmeters, and skin membranes. ]. The specific working principle and characteristics of various types of flowmeters are shown in Table 1. 
2.1 pressure, temperature
The state of natural gas is very sensitive to the changes of pressure and temperature. Under the standard state of measurement, according to the temperature and pressure of the medium material, combined with the actual operation of natural gas, the natural gas standard range can be reasonably adjusted, which can effectively reduce the measurement deviation. In the north, the temperature difference between winter and summer is large, and the flow measurement error of natural gas ranges from 3% to 8%. If the pressure and temperature measurement specifications are not established, the gas company will suffer a certain degree of loss [1-4].
2.2 Measurement Environment Temperature
The measurement accuracy of natural gas is also subject to changes in the ambient temperature. When the ambient temperature changes, the measurement accuracy decreases. A long time in an unstable state of temperature can cause problems in the instrument. One of the metering devices is a flow sensor, which is made of a thermally expandable material. The flow sensor is sensitive to changes in the temperature of the working environment. When the measurement ambient temperature is very low, the measurement of natural gas will be slower and the measurement error will be larger, which is generally 2.6 to 3.9 times of the normal measurement value, indicating that the temperature difference of the working environment has a greater impact on the measurement accuracy of the meter [5].
2.3 Skills and Training
Instrument operators' knowledge of measurement specifications and the improvement of their skills will help reduce human measurement deviations. For personnel engaged in flow measurement work, it is necessary to strengthen skills training and learning, and improve the overall level of the measurement team. First of all, to understand the performance of the meter, to measure the instrument flow under different pressures and temperature differences, according to the work environment to select the model, suitable measurement instruments Second, the installation training for operators, in particular, to understand the working principle of the meter, to avoid improper installation of measuring instruments caused by improper operation, causing greater measurement deviations. In order to solve the above problems, it is necessary to strengthen the skills training of staff, popularize the knowledge of natural gas flow metering errors, and master the working principle of metering devices so as to effectively ensure the safety of gas companies' natural gas transmission operation.
3 Analysis of Factors Affecting the Accuracy of Different Types of Flowmeters
3.1 Speed ​​Meter Measurement Accuracy Analysis
Ultrasonic flowmeters are the most widely used in speed flowmeters. Velocity flowmeters also include turbine flowmeters, vortex flowmeters , and precessional vortex flowmeters . The major factors affecting the measurement accuracy of speed flowmeters are:
(1) Fluid density, viscosity. The greater the density and viscosity, the greater the measurement resistance and the lowering of the measurement accuracy. Only when the fluid velocity and flow state are relatively stable can the measurement accuracy be improved.
(2) Turbine flowmeter installation requirements. Measuring instrument installation deflection can also cause measurement errors.
(3) Mechanical parts. The size of the instrument components will also have an impact on the metering results of the turbine. Contaminants in the fluid or long-term operation of the meter will wear out the bearing pressure and reduce the accuracy of the measurement.
The most typical volumetric flowmeter is a waist wheel flowmeter. The formula for calculating the flow rate is as follows:
q =?n·V
Where: q is the volumetric flow, m3/s; n is the number of revolutions, weekly/s; V is the volume of discharge flow for a certain time, m3/time.
The leakage rate has a great influence on the measurement accuracy. The amount of leakage is related to the clearance of the components of the flowmeter. The larger the gap between the components, the greater the measurement error. The formula for calculating the flow rate error caused by the leakage is as follows: 
3.3 Differential pressure flowmeter measurement accuracy analysis
The differential pressure flowmeter is mainly an orifice flowmeter. The influence of the measurement accuracy of the instrument on the fluid characteristics of natural gas, the performance of the instrument itself, and the installation and use conditions are as follows:
(1) Pressure and temperature. Changes in ambient temperature and pressure can have an impact on natural gas density, compressibility, and viscosity. Measurement of fluids with impurities can cause erosion and corrosion of parts at corners and bends.
(2) Instrument performance. The thickness of the orifice plate, the flatness of the end face of the flowmeter, the axiality of the component, the pressure position, the position of the pressure tube, and the length of the lead tube all affect the volumetric fluid, which reduces the accuracy of the measurement results.
(3) Working conditions. The rationality of the installation pipeline is directly related to the deviation of the flowmeter from the center and the accuracy of the straight pipe segment measurement. At the same time, ambient temperature, humidity, electromagnetic interference, etc. have an effect on the measuring instrument.
Correctly selecting the type of flowmeter and understanding the requirements of various flowmeters is very important for improving the measurement accuracy of natural gas and reducing the measurement deviation. Operators should improve their professional skills and knowledge, be familiar with the technical characteristics of instrumentation, reduce operational errors, increase the accuracy of measurement, and ensure the safe operation of equipment.