As a manufacturer of thermal mass flow meters, we are often asked, “What is the thermal mass flow meter correction factor? Why do we need to measure mass flow? What is the difference between ACFM and SCFM? Is pressure or temperature correction needed for thermal mass flow meters?
ACFM vs. SCFM
Many gas flow meters measure the actual flow rate (ACFM) at operating conditions rather than the desired mass flow rate. Volumetric flow is the actual volume flow of gas leaving the flow meter.
Standard flow rate (SCFM) is the corresponding flow rate the gas would be flowing if the temperature and pressure were at standard operating conditions. It is usually the most useful measure of gas flow because it defines the mass flow, the number of molecules, and the heat delivery capacity of the gas.
Pressure and Temperature Correction
To obtain the mass flow measurement of gas, it is necessary to correct for pressure and temperature. The most common device used to measure the flow rate is a differential pressure flow meter. In this case, the differential pressure device is measured to arrive at the actual flow rate, which is then corrected for pressure and temperature. Unfortunately, to do this requires the differential flow meter as well as a temperature and pressure device. All three signals are sent to the flow computer which determines the mass flow rate of the gas. In this case, four separate devices are used.
Is pressure or temperature correction needed for thermal mass flow meters? No. Thermal mass flow meters replace all of this with one instrument that directly measures the mass flow rate of the gas.
Should you want more information, visit Thermal Flow Working Principle and Theory.