MKS 247D - Scaling Control Factor; Gauge Factor; Gas Correction Factor (GCF)

Chapter Three: Overview Scalin
g
Controls
47
Scaling Control Factor
The Scaling Control Factor is the
product
of the Gauge Factor for the MFC in use and the Gas
Correction Factor for the gas in use:
S
CALING
C
ONTROL
F
ACTOR
=G
AUGE
F
ACTOR
x G
AS
C
ORRECTION
F
ACTOR
Gauge Factor
The Gauge Factor is a factory set value which scales the +5 VDC output signal to the appropriate
full scale range for the MFC, so that the digital panel meter reads 1000 counts. The gauge
factors for various flow ranges are listed in Table 10.
MFC Gauge Factors
MFC Flow Range (sccm) Gauge Factor
1, 10, 100, 1000, 10K 100
2, 20, 200, 2000, 2K 200
5, 50, 500, 5000, 50K 50
Table 10: MFC Gauge Factors
Gas Correction Factor
A Gas Correction Factor (GCF) is used to indicate the ratio of flow rates of different gases which
will produce the same output voltage from a mass flow controller. The GCF is a function of
specific heat, density, and the molecular structure of the gases. Since flow controllers are usually
calibrated with nitrogen, nitrogen is used as the baseline gas (GCF = 1).
Refer to Table 17, page 83, for a list of GCFs for commonly used pure gases. If the pure gas you
are using is not listed in Table 17, page 83, or you are using a gas mixture, you must calculate its
GCF. Refer to
How To Calculate the GCF for Pure Gases
, page 50, and
How To Calculate the
GCF for Gas Mixtures
, page 51, for more information.
Note
Refer to
How To Setup the System
, step 6, page 56, for more information
and an example Scaling Control Factor calculation.