The feeding requires a precision of two thousandths

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Gentlemen, we currently have a continuous feeding system, and the mass flow rate needs to be controlled with an accuracy of within 0.2 percent. Pipe with diameter DN25, temperature: normal temperature, pressure: 3.0-4.0 MPa. At the front end, a metering pump is used to deliver material into the storage tank, which is pressurized with nitrogen to a level of 4.0 MPa; the required accuracy is 5 parts per ten thousand. A Rosemount pressure transmitter was selected, as it can achieve an accuracy of 2.5 parts per ten thousand. I consulted the manufacturer of the control valve; they said that the highest precision indicated on the nameplate is 0.3%, but in practice it can be controlled at around 0.1%. Due to the very stable pressure, using manual valves on-site can meet a precision requirement of 0.05%, whereas when automation is employed, the precision drops to just over 1%. At this stage, I am considering whether the precision errors in automatic operation are caused by the accuracy of the PLC on site If this is indeed the problem, and it’s not possible to switch to automatic mode when the control system is disconnected, I hope those who are interested can offer their suggestions. Additionally, the material discharged from the storage tank maintains a very stable flow rate of 150 kg/h, as pressure control is in place at this stage. The required accuracy for flow measurement is within 0.2 percent; currently, relatively inexpensive flow meters are being used. Soon, mass flow meters with an accuracy of 1.8 percent will be employed (to avoid any appearance of advertising, the brand name will not be mentioned, but this level of accuracy can certainly be ensured). Communication via 485 is used for data transmission, which also helps to reduce errors in the accuracy of analog input cards; however, the accuracy of analog outputs generally only reaches 0.2 percent. There are similar issues with pressure control as well; it is necessary to control the flow rate with precision. How should one consider the precision of the valves and that of the system?