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301/303/305/306/307 Flowmeters and Controllers Instruction Manual
4. Gas Conversion Factors
Gas conversion factors (GCFs) for gases metered using Hastings Instruments products, can be found by visiting
the Hastings Instruments web site. The web address can be found at the end of this document. The GCFs
provided by Hastings Instruments have accuracies dependent on the method by which they are found
(empirical, NIST data, independent researcher data).
Most Hastings flow meters and controllers are calibrated using nitrogen and the GCF is calculated to convert
from nitrogen to another process gas. To apply the GCF's, simply multiply the gas flow reading and the GCF for
the process gas in use. For example, to calculate the actual flow of argon passing through a nitrogen-
calibrated meter that reads 20 sccm, multiply the reading and the GCF for argon.
20 sccm N
x 1.4047 = 28.094 sccm Ar
2
Conversely, to determine what reading to set a nitrogen-calibrated meter to get a desired flow rate of a
process gas other than nitrogen, you divide the desired rate by the GCF. For example, to get a desired flow of
20 sccm of argon flowing through the meter, divide 20 sccm by 1.4047.
20 sccm Ar / 1.4047 = 14.238 sccm N
2
That is, you set the Nitrogen calibrated meter to read 14.238 sccm.
Some meters, specifically the high flow meters, are calibrated in air. The flow readings must be corrected for
the case where a gas other than air is flowing through the meter. In addition, there must be a correction for
the difference in the GCF from nitrogen to air. In this case, multiply the reading by the ratio of the process
gas' GCF to the GCF of the calibration gas. For example, a meter calibrated in air is being used to measure the
flow of propane. The reading from the meter is multiplied by the GCF for propane divided by the GCF of air.
20 slm Air * (0.3499/1.0015) = 6.9875 slm C
H
3
8
To calculate a target setting (20 slm) to achieve a desired flow rate of propane using a meter calibrated to air,
invert the ratio above and multiply.
20 slm C
H
* (1.0015/0.3499) = 57.2449 slm Air
3
8
Gas conversion factors can be found at the Hastings Instruments web site.
http://www.teledyne-hi.com
Follow the link to Mass Flow Products and then to Gas Conversion Factors.
EAR99 Technology Subject to Restrictions Contained on the Cover Page
Page 26 of 32
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