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User Manual MAS-100 Regulus en.docx, Version: 4.0
ANNEX B – CONVERSION FORMULA FOR
FLOW CALCULATION
The mass of air contained in a specific volume varies upon pressure and temperature. To
create a defined reference, standard conditions were defined at 20 °C and 1013.25 mbar.
Any volume normalized to these conditions keeps the mass constant. Hence, the term
«Mass flow» is commonly used to describe a standardized volume flow and the unit used is
SLPM (Standard Liter Per Minute).
B.1 CALCULATION FORMULA
Standard volume flow («Mass flow») will be calculated from the following formula:
V
N
=
V
∙ p ∙ T
N
p
N
∙ T
p mbar Measured air pressure
T K Measured air temperature
V
L/min Measured volume flow
p
N
mbar Standard air pressure 1013.25 mbar
T
N
K Standard temperature 293.15 K (+20 °C)
V
SLPM
Volume flow at standard conditions («Mass flow»)
Hazard of wrong sampling results
The temperature values in flow conversion formulas must be inserted as Kel-
vin.
Hazard of wrong adjustment/calibration
A temperature sensor is integrated into the aluminum housing of the MAS-100
Regulus. Before calibration, the air sampler and the anemometer must be brought
to ambient temperature.
B.2 CALCULATION EXAMPLES
EXAMPLE 1
An MAS-100 NT air sampler delivers a volume flow of 102.9 L/min on the anemometer. The
ambient temperature is 22 °C and the ambient pressure 980 mbar. Calculate the equivalent
standard (mass) flow.
V
N
=
V
∙ p ∙ T
N
p
N
∙ T
=
102.9 L/min ∙ 980mbar ∙ 293.15K
1013.25 mbar ∙ 295.15 K
= 98.85 SLPM
The calculated value above deviates by 1.15% from 100 SLPM, thus it is within the specified
maximum tolerance of ±2.5% stipulated for the MAS-100 NT.
EXAMPLE 2
For various reasons, it may be desirable to do an inverse calculation (transform standard
flow to volume flow). For example, a MAS-100 NT air sampler delivers a standard flow of
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