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被測流體特性的影響：

　　由于天然氣本身的性質(zhì)，會隨著外界環(huán)境溫度的變化而發(fā)生復(fù)雜的變化，從而影響流量計的測量精度。對于天然氣的測量，必須首先確定天然氣的工作溫度和壓力，因為外界溫度的變化，會使天然氣本身的壓力和溫度也發(fā)生變化，都有可能造成過大的密度變化和壓縮系數(shù)變化。低密度氣體對某些測量方法呈現(xiàn)困難，此時就要改變所選擇的測量方法，或者作溫度和(或)壓力修正，以保證測量準確準確度。

 

　　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.

 

　　2儀表性能的影響：

　　孔板流量計本身引起的誤差原因主要有：孔板入口直角銳利度;管徑尺寸與計算不符;孔板厚度誤羞;節(jié)流件附件產(chǎn)生臺階、偏心;孔板上游端面平度;環(huán)室尺寸產(chǎn)生臺階、偏心;取壓位置;焊接、焊縫突出;取壓孔加工不規(guī)范或堵塞;節(jié)流件不同軸度等等。這些因素都有可能影響孔板的重復(fù)性，重復(fù)性是由儀器本身原理與制造質(zhì)量所決定，它在過程控制應(yīng)用中是重要的指標。而精確度除取決于重復(fù)性外，尚與量值標定系統(tǒng)有關(guān)。在實際應(yīng)用中，儀表優(yōu)良的重復(fù)性被許多因素包括流體粘度、密度等變化所干擾，都會影響測量精度。若儀表輸出特性是非線性的，則這種影響更為突出。

 

　　2.Instrument performance:

　　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流量計安裝的影響：

　　管線布置的偏離造成的安裝誤差是普遍性的，其產(chǎn)生的主要原因是現(xiàn)場不能滿足直管段要求的長度。

 

　　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環(huán)境條件方面的影響：

　　孔板流量計按國標規(guī)定進行設(shè)計、制造和檢定的標準孔板無需實流標定，精度高、結(jié)構(gòu)簡單、制造成本低，但壓力損失在所有標準節(jié)流裝置中最大，不適用于要求壓力損失小的情況，標準孔板廣泛用于石油、化工、冶金、電力等行業(yè)。

 

　　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.

 

PS：天津壓力變送器性能，孔板流量計存在的問題及解決途徑！

PS:Tianjin pressure transmitter performance,orifice plate flowmeter problems and solutions!