For small factories or new factories, because the process personnel does not know much about the instrument, they often think that the flow can be measured as long as the flow meter is installed on the processing pipeline. Because the craftsmen do not understand the complexities of flowmeter applications.

1. You should understand the flow state of the fluid

The flow state of the fluid directly affects the velocity distribution, because the flow measurement is related to the velocity distribution. Fluid flow states include laminar flow, transitional flow, and turbulent flow. For example, differential pressure flow meters are only used for stable turbulent flow, and thermal flow meters only require that the fluid state is laminar flow. Without knowing the flow state of the fluid, it is impossible to determine what flow measurement method to use. Therefore, before deciding which flowmeter to choose, the Reynolds number of the fluid must be calculated first, that is, the Reynolds number when the minimum flow rate is accurately measured.

2, should understand the properties of the fluid

The properties of fluids include physical properties such as temperature, pressure, density, and viscosity; as well as chemical properties such as medium composition, toxic and harmful, and corrosive. Because each type of flowmeter has regulations on the properties of the fluid medium it measures, it is necessary to understand the properties of the fluid before selecting a flowmeter. If the temperature of the medium to be measured is high, only the throttling device can be selected for measurement. For high-viscosity media, only positive displacement flowmeters can be selected, and electromagnetic flowmeters can be considered for conductive fluids.

3. You should understand the flow measurement range and related issues

Some technicians only provide an approximate flow measurement range, but cannot provide an accurate maximum flow. Of course, it can be determined by experiences, such as estimated by the design capacity of production and the operating data of the number of pumps. It is best not to use the diameter of the process pipe to estimate flow because sometimes the diameter of the process pipe is too large. The author has experienced the calculation of the opening size of the orifice plate according to the data provided by the process. For a pipe with an inner diameter of 150mm, the diameter opening of the orifice plate is only about 30mm. Obviously, the diameter of the process pipe is too large. It is also possible that the process is considered in the future. development needs. Fortunately, the current differential pressure transmitter and flow totalizer have a large range adjustment ratio, and it is very convenient to reset the adjustment if the range is found to be wrong in the application.

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