1、 Principles for selecting flow meters

The principle of choosing an Atrier flowmeter is first to have a deep understanding of the structural principles and fluid characteristics of various flowmeters, and to choose based on the specific situation on site and the surrounding environmental conditions. We also need to consider economic factors. In general, the selection should be made from the following five aspects:

① Performance requirements for flow meters;

② Fluid characteristics;

③ Installation requirements;

④ Environmental conditions;

⑤ The price of the flow meter.

1. Performance requirements for flow meters

The performance of flow meters mainly includes: measuring flow rate (instantaneous flow rate) or total flow rate (cumulative flow rate); Accuracy requirements; Repeatability; Linearity; Flow range and range degree; Pressure loss; Output signal characteristics and response time of flow meter, etc.

(1) Measuring traffic or total volume

Flow measurement includes two types, namely instantaneous flow and cumulative flow. For example, measuring the total amount of crude oil in distribution station pipelines for trade transfer or continuous proportioning production or process control in petrochemical pipelines, or occasionally supplemented by observation of instantaneous flow. In some workplaces, instantaneous flow measurement is required to control flow. Therefore, the selection should be based on the needs of on-site measurement. Some flow meters, such as volumetric flow meters and turbine flow meters, use mechanical counting or pulse frequency output to directly obtain the total amount. They have high accuracy and are suitable for measuring the total amount. If equipped with corresponding signaling devices, they can also output the flow rate. Electromagnetic flow meters, ultrasonic flow meters, etc. are used to measure fluid flow velocity and derive flow rate. They have fast response and are suitable for process control. If equipped with an accumulation function, the total amount can also be obtained.

(2) Accuracy

The specification for the accuracy level of a flowmeter is within a certain flow range. If it is used under a specific condition or within a relatively narrow flow range, such as only changing within a small range, its measurement accuracy will be higher than the specified accuracy level. If a turbine flowmeter is used to measure the distribution of oil in barrels, with the valve fully open, the flow rate remains relatively constant, and its accuracy may increase from level 0.5 to level 0.25.

When high measurement accuracy is required for trade accounting, storage and transportation handover, and material balance, the durability of accuracy measurement should be considered. Generally used for flow meters in the above situations, the accuracy level requirement is 0.2. In such workplaces, standard measuring equipment (such as volumetric tubes) is usually equipped on-site to perform online testing on the flow meters used. In recent years, due to the increasing tension of crude oil and the high requirements of various units for crude oil measurement, it has been proposed to implement coefficient handover for crude oil measurement. That is, in addition to conducting periodic testing of flow meters every six months, the two parties of trade handover negotiate to calibrate flow meters every one or two months to determine the flow coefficient. Every day, the data measured by the flow meter is handed over based on the flow coefficient calculation of the flow meter to improve the accuracy of the flow meter, also known as zero error handover.

The accuracy level is generally determined based on the maximum allowable error of the flowmeter. The flow meter instructions provided by each manufacturer will be included. It is important to note whether the percentage of error refers to relative error or citation error. Relative error is the percentage of the measured value, commonly expressed as "% R". Reference error refers to the percentage of the upper limit or range of the measurement, commonly used as "% FS". Many manufacturing manuals do not specify this. For example, float flowmeters generally use reference error, and some models of electromagnetic flowmeters also use reference error.