|信息来源： 压力变送器 | 2019-05-20 点击量： 2112|
The orifice plate flowmeter is a high range ratio differential pressure flowmeter consisting of standard orifice plate and multi-parameter differential pressure transmitter(or differential pressure transmitter,temperature transmitter and pressure transmitter),which can measure the flow of gas,steam,liquid and natural gas.It is widely used in petroleum,chemical,metallurgical,electric power,etc.Process control and measurement in heating,water supply and other fields.
1.The influence of measured fluid characteristics:
Because of the nature of natural gas itself,complex changes will occur with the change of ambient temperature,thus affecting the measurement accuracy of flowmeters.For the measurement of natural gas,we must first determine the working temperature and pressure of natural gas,because the change of external temperature will change the pressure and temperature of natural gas itself,which may result in excessive density change and compression coefficient change.Low density gas is difficult for some measurement methods.At this time,it is necessary to change the selected measurement methods,or make temperature and/or pressure correction to ensure the accuracy of measurement.
The main reasons for the errors caused by orifice flowmeter itself are:the right angle sharpness of orifice plate entrance;the size of pipe diameter is not consistent with the calculation;the thickness of orifice plate is mistaken;the appendages of orifice plate produce step and eccentricity;the flatness of upstream end face of orifice plate;the size of annular chamber produce step and eccentricity;the position of pressure taking;the welding and welding seam are prominent;the processing of pressure taking hole is not standardized or blocked;the different axes of orifice parts,etc These factors may affect the repeatability of orifice plate.The repeatability is determined by the principle of the instrument itself and the manufacturing quality.It is an important indicator in the process control application.Besides the repeatability,the accuracy is also related to the calibration system.In practical application,the excellent repeatability of the instrument is disturbed by many factors,including fluid viscosity,density and other changes,which will affect the measurement accuracy.If the output characteristic of the instrument is non-linear,the influence will be more prominent.
3 Influences of Flowmeter Installation:
The installation error caused by the deviation of pipeline layout is universal,and the main reason is that the site can not meet the requirements of the length of straight pipeline section.
4.Impact of environmental conditions:
The orifice plate flowmeter designed,manufactured and calibrated according to the national standard does not need real-flow calibration.It has high accuracy,simple structure and low manufacturing cost.However,the pressure loss is the largest in all standard throttling devices,and it is not suitable for situations requiring low pressure loss.The standard orifice plate is widely used in petroleum,chemical,metallurgical,power and other industries.
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