Regarding the instrument specification sheet

Perform temperature and pressure correction calculations in DCS.

There is a dedicated compensation module for ideal gases on the DCS, which can be used directly

Purchase the orifice plate and differential pressure transmitter in accordance with the requirements specified in the instrument specification sheet. Perform temperature and pressure compensation during DCS configuration, and set the range based on the flow units and range specified in the orifice plate calculation sheet.

In the orifice plate calculation sheet, the gas is generally expressed in standard cubic units, and the full-scale measurement range is also in standard cubic units. Steam, generally in terms of mass flow rate. Liquids are generally classified into mass flow rate and volume flow rate; the volume flow rate refers to the volume flow under specific operating conditions, and it depends on the calculations provided.

As for where to take the square root, it depends on the regulations.

I would like to ask whether there are any relevant design specifications for this. In practical applications, no temperature and pressure compensation is applied at that point in the PID diagram; in such cases, how should the DCS range be set? Moreover, in practical applications, a problem has arisen: for example, if the actual pressure is 10 MPa but only 6 MPa is measured in practice, then the range setting might be too large, resulting in the instrument failing to give any indication when it is put into use.

Thank you for your reply. I would like to ask that since the steam flow is calculated based on mass flow rate in the orifice plate calculation sheet, how should the unit for steam flow be set during DCS configuration? Additionally, no temperature and pressure compensation has been applied at this point. Aptite plates are used to measure volumetric flow rate, so why is mass flow rate used for calculation?

The DCS configuration can be used for temperature and pressure compensation; otherwise, the volume will be incorrect after changes in the on-site process

　　The use of standard conditions rather than actual conditions in measurement is for the sake of operational convenience. Otherwise, it will be very troublesome to match the materials from the previous and subsequent processes. For example, if the compressor takes in several hundred cubic feet of air but only outputs a dozen cubic feet, it’s very difficult to calculate how much air is lost in between. So, unless there are special requirements in the process, measurements are taken under standard conditions ； 　　Using volumetric flow rate or mass flow rate is also primarily for practical reasons; generally, the measurement method applicable under normal conditions of the medium is adopted. For gases, it is difficult to determine the mass under normal conditions, while it is much easier to determine the volume ； It is more convenient to determine the mass of a liquid. Orifice plates, and in fact almost all flowmeters, are designed (for measurement) based on operating conditions, and then the readings are displayed under standard conditions. Since the output of the flow meter represents standard conditions, no further conversion is necessary when displaying it. The differential pressure value output by the differential pressure cumulative flow meter, after being taken to the square root, is directly proportional to the volume or mass. 　　Except for Coriolis flowmeters and thermal flowmeters, the mass flow rate indicated by most flowmeters is calculated based on a manually specified density of the fluid. Therefore, when the actual operating conditions deviate from those specified in the design, measurement errors will occur to some extent. If this error exceeds the acceptable level, measures must be taken: either the measured data must be corrected (such as through temperature and pressure compensation), or the flow meter must be redesigned (such as by recalculating the range based on the actual operating conditions)