VAT 612 Series User Manual

Series 612 DESIGN AND FUNCTION
605262EE Edition 2018-08-20 13/
116
3.2.1 Pressure control system overview and function
Vacuum pressures are always absolute pressures unless explicitly specified as pressure differences.
Example: Downstream control
1 Valve
2 Process chamber
3 Gas inlet
4 Pressure sensor(s)
5 Sensor cable
6 Controller and actuator
7 Cable to remote control unit
8 Cable to power supply
9 HV Pump
S
eff
Q / p
S
eff
effective pump speed (ls
-1
)
Q Gas flow (mbar)
p Pressure (mbar)
or units used in USA
S
eff
= 12.7 • Q / p
S
eff
effective pump speed (ls
-1
)
Q Gas flow (sccm)
p Pressure (mTorr)
3.2.1.1 Way of operation
The controller compares the actual pressure in the process chamber given by the pressure sensor
with the preset pressure. The controller uses the difference between actual and set pressure to
calculate the correct position of the control valve. The controller drives the control valve into the
correct position and the actual pressure again equals the set pressure.
This control operation is performed continuously. Pressure changes in the process chamber due to
leaks, desorption, and gas flow, reaction products, variations in pumping speed etc. are always
corrected at once.
3.2.1.2 Pressure control
In a vacuum system which is pumped and into which gas is admitted at the same time, the pressure
can be controlled in two ways:
1. Downstream control (standard):
The pressure is controlled by changing the conductance of a control valve between pump and
process chamber. This changes the effective pumping speed at the process chamber. Pressure
and gas flow can be independently controlled over a wide range.
2. Upstream control:
The pressure is controlled by changing the gas flow into the process chamber, while the pumping
speed remains constant.
M
3
4
5
7
8
2
1
9
Q
p
V
Seff
6

VAT 612 Series Specifications

General

Brand	VAT
Model	612 Series
Category	Control Unit
Language	English