VAT 642 Series - Page 44

INSTALLATION Series
642
44/119 Edition 2017-11-24 742280ED
Gasflow calculation for LEARN:
Do not apply a different gasflow for learn than determined below. Otherwise pressure
control performance may be insufficient.
Required pressure / flow regime must be known to calculate the most suitable learn
gas flow for a specific application.
1. At first it is necessary to find out about the required control range respectively its conductance values.
Each working point (pressure / flow) must be calculated with one following formulas.
Choose the applicable formula depending on units you are familiar with.
C
WP
required conductance of working point [l/s]
q
WP
gasflow of working point [Pa m3/s]
p
WP
pressure of working point [Pa]
C
WP
required conductance of working point [l/s]
q
WP
gasflow of working point [mbar l/s]
p
WP
pressure of working point [mbar]
C
WP
required conductance of working point [l/s]
q
WP
gasflow of working point [sccm]
p
WP
pressure of working point [Torr]
2. Out of these calculated conductance values choose the lowest.
C
R
required lower conductance [l/s]
C
WPx
required conductance of working points [l/s]
To make sure that the valve is capable to control the most extreme working point verify
that C
R
≥ C
min
of the valve (refer to «Technical data»).
3. Calculate gasflow for learn. Choose the applicable formula depending on units you are familiar with.
q
L
gasflow for learn [
Pa m
3
/s
]
p
SFS
sensor full scale pressure [Pa]
C
min
min. controllable conductance of valve [l/s], (refer to
«Technical data»)
q
L
gasflow for learn [
mbar l/s
]
p
SFS
sensor full scale pressure [mbar]
C
min
min. controllable conductance of valve [l/s], (refer to
«Technical data»)
q
L
gasflow for learn [
sccm
]
p
SFS
sensor full scale pressure [Torr]
C
min
min. controllable conductance of valve [l/s], (refer to
«Technical data»)
1000
•
q
WP
C
WP
=
p
WP
q
WP
C
WP
=
p
WP
q
WP
C
WP
=
78.7
•
p
WP
C
R
= min(C
WP1,
C
WP2, . . . ,
C
WPn
)
p
SFS
•
C
min
q
L
=
1100
p
SFS
•
C
min
q
L
=
1.1
q
L
= 71
•
p
SFS
•
C
min