Normal reference, European style
Following the ‘European’ definition, a temperature of 0°C and a pressure of 1,013 bar are selected as ‘normal’ reference conditions, indicated by the underlying letter “n” in the unit of volume used (mln/min or m3n/h). The direct thermal mass flow measurement method is always based on these reference conditions unless otherwise requested.
An example conversion to volumetric units using Normal reference conditions: The mass flow meter indicates 100 g/h of Air flow. • Density Air (@ 0°C) = 1.293 kg/m3 • X ln/m Air = 100 g/h / (60 minutes x 1.293 kg/m3) • Flow = 1.29 ln/m Air
Standard reference, European style
Alternatively, a temperature of 20°C and a pressure of 1,013 bar are used to refer to
‘standard’ reference conditions, indicated by the underlying letter
‘s’ in the unit of volume used (mls/min or m3s/h).
An example conversion to volumetric units using Standard conditions: The mass flow meter indicates 100 g/h Air flow. • Density Air (@ 20°C): 1.205 kg/m3 • X ls/m Air = 100 g/h / (60 minutes x 1.205 kg/m3) • Flow = 1.38 ls/m Air
If the prefix
‘s’ has been used, it refers to the
American style.
Standard reference, American style
According to the ‘American’ definition the prefix ‘s’ in
sccm, slm or
scfh refers to
‘standard’ conditions, 101.325 kPa absolute (14.6959 psia) and temperature of 0°C (32°F).
Please be aware of the reference conditions when ordering an instrument. ‘Normal’ and ‘Standard’ can be relative to each customer.
Why is this important? Because mixing up these reference conditions causes an offset in what the customer expects to see by greater than 7%!