The orifice flowmeter is a kind of differential pressure flowmeter. Like other differential pressure flowmeters, it needs to be matched with the transmitter for data measurement. The classification and respective characteristics can be seen in the table below.
The orifice flowmeter is a kind of differential pressure flowmeter. Like other differential pressure flowmeters, it needs to be matched with the transmitter for data measurement. The classification and respective characteristics can be seen in the table below.



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Orifice flowmeters can be widely used in petroleum, chemical, natural gas, metallurgy, electric power, pharmaceutical and other industries, continuous measurement of volume flow or mass flow of various liquids, gases, natural gas and steam. However, many people don't know how to calculate the orifice flowmeter. Today I will discuss with you the calculation formula of the orifice flowmeter. Simply speaking, the differential pressure value must be the output of the outlet to correspond to the flow.
In practical applications, the calculation is more complicated. Generally, this is calculated by software. This is a practical example. Let's take a look at it.
one. Flow compensation overview
The measurement principle of the differential pressure flowmeter is based on the principle that the mechanical energy of the fluid is converted to each other. The fluid flowing in the horizontal pipe has dynamic pressure energy and static pressure energy (bit energy 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 = CεΑ/sqr(2ΔP/(1-β^4)/ρ1)
Where: C outflow coefficient;
ε swell coefficient
Α Throttle cross-sectional area of ​​the throttle, M^2
The differential pressure output by the ΔP throttling device, Pa;
直径 diameter ratio
Ρ1 density of the measured fluid at II, kg/m3;
Qv volume flow, m3/h
According to the compensation requirements, it is necessary to add the compensation of temperature and pressure. According to the calculation book, the calculation idea is to calculate the flow rate at any temperature at any temperature based on the process parameters at 50 degrees. In fact, it is important to convert density. Calculated as follows:
Q = 0.004714187 *d^2*ε*@sqr(ΔP/ρ) Nm3/h 0C101.325kPa
That is, the volume flow rate at 0 degree standard atmospheric pressure required for the screen display.
In accordance with the density formula:
ρ= P*T50/(P50*T)* ρ50
Where: ρ, P, T represent values ​​at any temperature and pressure
Ρ50, P50, T50 denote the process reference point at 50° gauge pressure of 0.04 MPa
Combine these two formulas to complete the compilation in the program.

two. Orifice flowmeter program analysis
Instantaneous amount
Temperature: must be converted to absolute Celsius; ie +273.15
The amount of pressure: must be converted to absolute pressure for calculation. Gauge pressure + atmospheric pressure
Compensation calculation According to the calculation formula, the data is stored in the register of the PLC. At the same time, monitor on the intouch screen.
Cumulative amount
The accumulation is triggered by a rising edge of one scan in 2 seconds, that is, the compensation flow value (Nm3/h) is converted into the flow value per 2S from the upper 1800 units, and the cumulative sum is performed, and the screen is reset and cleared.


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