This technical note explains the following:
How mass flow is measured with volumetric units at standard conditions.
How to convert between volumetric units at standard conditions of 0ºC, 1
atm, and nonstandard temperature and pressure conditions.
How to convert between volumetric units at standard conditions of 0ºC, 1
atm, and an alternative standard temperature and pressure conditions.
How to convert from volumetric units to mass units.Honeywell mass flowsensors use a silicon sense die construction known as a microbridge to measure
the rate of mass transfer in a fluid.
Mass flow is a dynamic mass/time unit measured in grams per minute. It is
common in the industry to specify mass flow in terms of volumetric flow units
at standard (reference)
conditions. By referencing a volumetric flow to a standard temperature and
pressure, an exact mass flow (g/min) can be calculated from volumetric flow.
The temperature and pressure reference conditions of the volumetric unit
do not imply nor do
they require the pressure and temperature conditions of the measured fluid
to be the same; they are simply part of the volumetric unit that is required to
specify mass from a measured volume.
Honeywell mass flow sensors are generally specified as having volumetric
flow units at standard reference conditions of 0°C and 1 atm. This is indicated
on volumetric units with the "
S" prefix. For example: SCCM "Standard Cubic Centimeters (per)
Minute"
Reference Conditions: 0°C, 1 atm SLPM "Standard Liters (per)
Minute" Reference Conditions: 0°C, 1 atm If a certain application requires
nonstandard reference conditions, the units will be specified in the device
datasheet without the “S” prefix and the reference conditions will be
called out. The “@” symbol will be used to indicate the volumetric unit
reference conditions for temperature and flow.
For example:
CCM@ 21°C, 101.325 kPa
LPM @ 20°C, 1013.25 mbar
When designing an application around a mass flow sensor, it is critical to
use consistent refere
nce conditions for volumetric units throughout the system. There is no
industry standard for
the reference conditions indicated by “SCCM” or “SLPM”, they must be
explicitly determined.
Consider a Honeywell mass low sensor which has output calibrated for a
full scale of 1000
SCCM. If this sensor is used in a system with a mass flow controller that
has a Full Scale of
1000 SCCM(defined by the manufacturer as using a reference condition of
25°C, 1 atm), then without converting units, the system error will be more than
9% of reading.
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