Integrated orifice flow meter calculation formula

Orifice flowmeters can be widely used in the petroleum, chemical, natural gas, metallurgy, electricity, pharmaceutical and other industries to continuously measure the volume flow or mass flow of various liquids, gases, natural gas and steam. However, many people do not know how the orifice flowmeter is calculated. Today, I will discuss with you the calculation formula of the orifice flowmeter. Simply put,

the differential pressure value must be squared to output to correspond to the flow.

The calculation in actual application is relatively complicated. Generally, it is rarely calculated by oneself. This is calculated using software. Here is a practical example for you to see.

1. Overview of flow compensation

The measurement principle of the differential pressure flowmeter is based on the principle of mutual conversion of mechanical energy of the fluid. The fluid flowing in the horizontal pipeline has dynamic pressure energy and static pressure energy (potential energy is equal). Under certain conditions, these two forms of energy can be converted into each other, but the total energy remains unchanged. Take the volume flow formula as an example:

Qv = CεΑ/sqr (2ΔP/(1-β＾4)/ρ1)

Where: C outflow coefficient;
ε expansion coefficient
Α throttling device opening cross-sectional area, M＾2
ΔP throttling device output differential pressure, Pa;
β diameter ratio
ρ1 measured fluid density at II, kg/m3;
Qv volume flow, m3/h

According to the compensation requirements, temperature and pressure compensation need to be added. According to the calculation book, the calculation idea is based on the process parameters at 50 degrees, and calculate the flow at any temperature and pressure. In fact, the important thing is the conversion of density. The calculation formula is as follows:

Q = 0.004714187 *d＾2*ε*＠sqr (ΔP/ρ) Nm3/h 0C101.325kPa

is the volume flow at 0 degrees standard atmospheric pressure required to be displayed on the screen.

According to the density formula:

ρ= P*T50/（P50*T）* ρ50

Where: ρ, P, T represent the values ​​at any temperature and pressure
ρ50, P50, T50 represent the process reference points at 50 degrees and 0.04MPa gauge pressure.
Combining these two formulas can complete the compilation in the program.

2. Program Analysis

1. Instantaneous

temperature: must be converted into absolute Celsius temperature; that is, +273.15
pressure: must be converted into absolute pressure for calculation. That is, gauge pressure + atmospheric pressure
compensation calculation is based on the calculation formula, and the data is saved in the PLC register. At the same time, it is monitored on the intouch screen.

2. The cumulative amount

is accumulated by triggering a scan rising edge in 2 seconds, that is, the compensated flow value (Nm3/h) is converted into a flow value every 2S by dividing it by 1800 units, and the cumulative sum is performed. The screen has a reset and clear function. (end)