# Level and Flow Measurement

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# Skill analysis of calculation formula for orifice flowmeter

##### Author:Source:Date: 2021-05-27 15:08:47
Orifice flowmeter can be widely used in petroleum, chemical, natural gas, metallurgy, electric power, pharmaceutical and other industries to continuously measure the volume flow or mass flow of various liquids, gases, natural gas and steam. But many people do not know how to calculate orifice flow meters. Today I will discuss with you the calculation formula of orifice flowmeter
In short, the differential pressure value must be a square output to correspond to the flow rate
In practical applications, the calculation is more complicated. Under normal circumstances, it is rarely calculated by yourself. This is calculated by software. Give an example
1. Overview of flow compensation
The measuring principle of the differential pressure flowmeter is based on the mutual conversion principle of fluid mechanical energy. The fluid flowing in the horizontal tube has dynamic pressure energy and static pressure energy (the potential energy is equal). Under certain conditions, the two forms of energy can be converted to each other, but the sum of energy is constant. Take the volume flow formula as an example
Q v=C&;ε;&;Alpha;/sqr(2&; Delta; P/(1-&;β;＾4) /&;ρ;1)
Among them: C outflow coefficient
&; ε; Expansion coefficient; Alpha; the cross-sectional area of the orifice of the throttle member, m 2
And; Delta; P differential pressure output by throttling device, PA
&; Beta; Diameter ratio; ρ; Density of the measured fluid at 1 I-I, kg/m3
QV volume flow, m3/h
According to the compensation requirements, temperature and pressure compensation should be added. According to the calculation book, the calculation idea is based on the process parameters at 50°C to calculate the flow rate at any temperature and pressure. In fact, the most important thing is the conversion of density. Calculated as follows:
Q=0.004714187*d＾2*&;ε;*@sqr(&A); delta; P/ and; ρ;) Nm3/h 0C101.325kPa
That is, the standard atmospheric pressure that needs to be displayed on the screen at 0℃
According to the density formula:
&;Ρ;=P*T50/(P50*T)*&;ρ;50
Among them: &; ρ第. T is the value at any temperature and pressure
&; ρ; 50, P50, T50 are 50 degrees gauge pressure 0.04MPa
The process reference point below, combined with these two formulas, can complete the program
2. Program analysis
1. Instantaneous amount
Temperature: must be converted to absolute Celsius; that is +273.15
Pressure: Must be converted to absolute pressure for calculation. I.e. gauge pressure + atmospheric pressure
Compensation calculation, according to the calculation formula, the data is stored in the PLC register. At the same time, on the touch screen
2 to monitor. Cumulative amount
Use the scanning rising edge trigger within 2 seconds for accumulation, that is, convert the compensated flow value (Nm3/h) into a flow value every 2 seconds, and perform the accumulation. The screen has reset and clear functions.

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