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How do you understand the flow unit of the mass flow meter / mass flow controller?

Gas mass flow units are typically expressed in sccm (Standard Cubic Centimeter per Minute) and slm (Standard Liter per Minute, standard liters per minute). This means that under the conditions of use of this instrument, the indicated flow rate is the flow under standard conditions. The standard state is defined as: Pressure - 101325 Pa (760 mm Hg); Temperature - 0 °C (273.15K). This is an important difference between this type of meter and other flow meters. It is also where sccm and slm differ from mL/min and L/min.
For most users, the volumetric flow rate representation is very consistent and easy to use, but there are also users who need to know the mass of media flowing through the unit of time (eg, g/min). This requirement is easily achieved. Because the density of the gas in the standard state is a constant and can be easily found, it is simple to do a multiplication (by multiplying the density by several slm). Therefore, the volume flow in the standard state is equivalent to the mass flow.
It should be noted that the mass flow unit sccm/slm used by mass flow controller manufacturers worldwide does not comply with the international unit of mass flow (Kg/min) that is commonly used in domestic measurement standards, but it conforms to the International Semiconductor Association. Formulated SEMI international standards.

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