How To Setup the System Cha
ter Four: O
eration
58
Example 2:
Calculate the Set Point Control setting for a 500 sccm MFC which is flowing pure argon
(Ar), if the flow must be maintained at 375 sccm.
a. Calculate the desired set point as a
percentage
of full scale
.
% F
ULL
S
CALE
= 375 sccm
500
sccm
=0.75
= 75%
b. Calculate the Set Point Control setting.
S
ET
P
OINT
C
ONTROL
S
ETTING
= 75% x 10
1.39 (GCF for argon)
= 540
The GCF for argon is 1.39 (refer to Table 12, page 77). In this case, the SET POINT
CONTROL should be set to “5/40”; that is, an “5” should appear in the window and
the dial should be set to “40.”
9. Reconnect the AC LINE CORD to power the 246 unit; allow it to warm up and stabilize
for at least 15 minutes.
Caution
The 246 unit uses the AC line cord as its power switch, that is, the
unit is
ALWAYS ON
when connected to a line source.
Note
Allow a minimum of 1½ hours for the MFC to reach control temperature
and stabilize. Refer to the appropriate MFC Instruction Manual for
information concerning turn-on drift characteristics.
10. Set the DECIMAL POINT for the digital panel meter to the appropriate location for the
MFC being used by adjusting the dipswitches on the side of the 246 unit.
The position of the decimal point is determined by the full scale range of the MFC in
use. For example, a 100 sccm mass flow controller requires the decimal point to be
positioned as “100.0” (display at full rated flow).
The correct display at full scale for various flow ranges are listed in Table 9, page 45.
Refer to
Decimal Point Selector Dipswitches
, page 43, for more information.
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