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Manual 111-082010_Nall Mass Flowmeters Page 12 of 23
Actual flow = meter reading X (KHe)
= 50 SCCM X 1.382
= 69.1 SCCM of Helium
5.5.2 Flowmeter Factory Calibrated for a Special Gas
If the Hastings Linear Mass Flowmeter is calibrated for a gas other than air, it may also be used to measure
the flow rate of many other gases. The flow rate will be equal to the meter reading multiplied by the ratio of
the gas conversion factors.
Example: What is the actual flow rate of Carbon Dioxide through a flowmeter calibrated for Helium, if
the meter reading is 96 SCCM?
Solution: Flow of CO2‚ = (meter reading) (K for CO2)
K for He
= (96 SCCM) * .6933
1.3820
= 48.2 SCCM
5.5.3 Gas Mixtures
If a mixture of gases is used and the percentage by volume of each gas is reasonable constant, a conversion
factor for the gas mixture can be obtained.
K (mix) = _____________________________1__________________
__ __ __
Va + Vb + Vc + ….
Ka Kb Kc
Where
V (a, b, ….) = percent of gas a, b ….)
K = conversion factor
K can be obtained from the table beginning on page 35 for many gases.
Example: What is the conversion factor for a mixture of 20% Hydrogen, 40% Argon, and 40%
Oxygen?
Solution: = _________________________1______________
__ __ __
Va + Vb + Vc + ….
Ka Kb Kc
=__________________________1______________
.2 + .4 + .4
1.01 1.41 .96
= 1.11
5.6 Output Signal:
The two output terminals on the back of the power supply provide a 0-5 VDC signal for recording or
operating auxiliary equipment such as flow controllers or converters. The output signal is linear with respect
to mass flow and has sensitivity equal to the rated full-scale flow rate divided by 5.00 VDC.