MKS P9B, Instruction Manual, Page: 35 / 112

Operation of the MFC with Gases other than Nitrogen Chapter Two: Overview
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When a gas other than the calibration gas is selected by the user, the MFC automatically pulls up the correct
functions that calculate the flow of that gas with respect to the original calibration. This allows the MFC to
report the gas flow for the gas in use immediately and with better accuracy than has previously been available.
In comparison, the typical MFC uses Gas Correction factors for converting the calibration gas flow into the
flow of the gas being used. This may lead to inaccuracy in the flow reported to levels as high as 6-10% (of
FS) depending on the gas used.
The P9B, by using these functions for the various gases, actually reports the flow within the stated accuracy
of the flow controller, but for non-calibration gases. The reported flow from a MFC using Helium as the
process gas, but not calibrated for Helium, will have the same accuracy for the Helium as it does for Nitrogen,
the calibration gas. Traditional flow controllers and meters using a Gas Correction Factor for Helium
typically have an error in the flow output of as much as 5% of FS or more.