MKS 246C, Instruction Manual

Page: 67 / 92

Chapter Four: Operation How To Setup the System
57
8. Calculate and adjust the SET POINT CONTROL setting for each 246 unit in use.
Note
The Set Point Control is bypassed when using an external set point
voltage for individual gas flow control. If you are using this type of
operation, this step is not required. Proceed to step 9, page 58.
Refer to How To Control Individual Gas Flows with an External Set
Point, page 62,for more information.
The Set Point Control allows gross adjustment of the set point voltage. Fine adjustment
is done under actual operating conditions by watching the front panel readout and
adjusting the Set Point Control for the desired flow reading.
The SET POINT CONTROL setting is calculated as follows, based on the desired set
point level as a percentage of full scale, and the GCF for the gas in use:
S
ET
P
OINT
C
ONTROL
S
ETTING
= % of FS x 10
G
AS
C
ORRECTION
F
ACTOR
Example 1:
Calculate the Set Point Control setting for a 100 sccm MFC which is flowing pure
nitrogen (N
2
), if the desired set point value is 85 sccm.
a. Calculate the desired set point as a percentage of full scale.
% F
ULL
S
CALE
= 85 sccm
100
sccm
= 0.85
= 85%
b. Calculate the Set Point Control setting.
S
ET
P
OINT
C
ONTROL
S
ETTING
= 85% x 10
1.0 (GCF for N
2
)
= 850
Since N
2
has a correction factor of 1.00 ( refer to Table 12, page 77), the rear panel
Gauge Factor Scaling Control is set to “1/00”, and the set point is directly applied
without needing any gas correction. In this case, the front panel SET POINT
CONTROL should be set to “8/50”; that is, an “8” should appear in the window and
the dial should be set to “50.”