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Principle of Mass Flow Instruments
- 3. Measuring Unit of Flow Rate
- A mass flow meter measures the mass flow irrespective of pressure and temperature. When representing mass by the flow, it is necessary to use units such as g/min and kg/min which are different from the familiar units used for general fluid measurement.
Therefore, it is common to use volume fl ow under predetermined standard conditions of pressure and temperature. At present, Pa·m3/s is used in conformance with the SI units, but SCCM and SLM which have long been used for mass flow instruments are still used as principal units.
With respect to the definition of the standard unit, KOFLOC adopted the definition based on the SEMI standard in October 1998.
SCCM is an abbreviation of Standard Cubic Centimeter per Minute, indicating cc/min at 0°C at 1 atmospheric ressure, while SLM is an abbreviation of Standard Liter per Minute, indicating L/min under the same conditions. Other units of fl ow, if they are recognized as units of measurement at present, can be used for calibration and manufacture of our products.
In some industries other than the semiconductor industry, SCCM and SLM are defi ned as the units at 20°C at 1 atmospheric pressure and NCCM and NLM as the units at 0°C at 1 atmospheric pressure.
Concerning the flow indication of our mass flow instruments, the standard temperature and pressure in units of SCCM (0°C, 1 atm) and NLM (0°C, 1 atm) are shown on our products and in test reports.
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