MKS 246C - Scaling Control Factor; Table 9: MFC Gauge Factors

Chapter Three: Overview Gau
g
e Factor Scalin
g
Control
45
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 9.
MFC Gauge Factors
5 V Full Scale Input (sccm) Gauge Factor Display at Full Scale
10
100 10.00 sccm
20
200 19.99 sccm
50
50 50.0 sccm
100 100 100.0 sccm
200 200 199.9 sccm
500 50 500 sccm
1000 100 1000 sccm
2000 200 1999 sccm
5000 50 5.00 slm
10000 100 10.00 slm
20000 200 19.99 slm
50000 50 50.0 slm
Table 9: 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 12, page 77, for a list of GCFs for commonly used pure gases.
If the pure gas you are using is not listed in Table 12, page 77, or you are using a gas mixture,
you must calculate its GCF. Refer to
Gas Correction Factor
, page 47, for more information.
Note
Refer to
How To Setup the System
, step 6, page 54, for an example
Scaling Control Factor calculation.