【Design Institute】The parameters of the gas flow meters supplied for process control instruments are all in standard cubic feet; how do the flow meter manufacturers select the appropriate models?

In such cases, flow meter manufacturers usually choose instruments with a wide range of flow rates to ensure that they can cover various flow variations that may occur in the process parameters. In addition, the manufacturer will also make the selection based on factors such as the properties of the gas provided by the user and the process requirements. If a vortex flow meter without temperature and pressure compensation is chosen, the flow rate displayed on the gauge is the actual flow rate, rather than the standard cubic flow rate. It should be noted, however, that vortex flowmeters lack temperature and pressure compensation, which can affect the measurement results; therefore, temperature and pressure compensation calculations must be performed within the system to obtain more accurate flow values. .

For process condition optimization, three operating conditions are generally specified: minimum, normal, and maximum. The operating pressure and temperature will also increase accordingly; with these conditions, cubic and standard volumes can be directly converted.

Vortex flowmeters measure the flow rate of steam and gases under operating conditions, unless they have built-in temperature and pressure compensation. Generally, when purchasing instruments, the parameters specified by the manufacturing process differ little from the actual values, so the error is not significant. However, for accurate measurements, temperature and pressure compensation is still necessary. Vortex flowmeters with temperature and pressure compensation are more expensive; if pressure and temperature sensors are already installed in the pipeline, it is recommended to use them within the DCS system.

The last edit to this post was made by Wind’s Sorrow on 2023-6-15 at 08:56. The conditions specified for the process also include parameters such as operating temperature and pressure, as well as the viscosity and density of the medium; these are sufficient for manufacturers to make a selection (the flow rate under operating conditions can be determined based on the operating temperature and pressure). Vortex flowmeters can measure the volume flow rate under the actual operating conditions, and the transmitter can convert this value to a standard condition flow rate based on the operating temperature and pressure specified during design (some transmitters do not have this function). However, the operating temperature and pressure specified during design cannot exactly match those in the actual operating conditions; therefore, temperature and pressure compensation is necessary to ensure accuracy.

Because you are converting flow rate using the differential pressure principle, the square of the flow rate is proportional to the differential pressure; therefore, the differential pressure must be taken to the power of one half in order to obtain the flow rate value. The range is selected based on the design flow rate, and it has nothing to do with whether square roots are taken or not!

Whatever you want, the manufacturer will make it for you

It is possible to output cubic meters directly; confirm this with the manufacturer, as cubic meters are generally used for gases