How To Setup the System Cha
ter Four: O
eration
54
5. Connect the MFCs to connector J8 on the rear panel of the 246 units in use and, if
necessary, connect multiple units together using the proper interface cables.
Refer to
System Configurations
, page 26, for setup information.
Note
If you are using a 1259A/2259A MFC,
do not connect
the 2-pin
connector to the control valve at this time. If the 1259A/2259A MFC has
the control valve connector plugged in, separate the plug to break the
connection.
6. Calculate the SCALING CONTROL FACTOR for each MFC in use.
The Scaling Control Factor specifies how much the +5 VDC output signal from the MFC
will be scaled down so that the flow rate can be read directly from the digital panel
meter, which reads 1 VDC as 1000 counts full scale.
Note
It is
critical
for
ro
er s
stem o
eration that the Scalin
Control Factors
are calculated properly. Refer to
Gauge Factor Scaling Control,
page
44, for more information.
a. 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
b. The
Gauge Factor
is a factory set value which scales the 5 VDC 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, page 45.
c. The
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.
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