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3000-Watt
Impedance Matching Networks Manual and Automatic Coaxial
Power Systems Ltd manufacture two styles of impedance matching network to link
the load to the RF generator. The purpose of the network is to adjust the
input impedance of the load to 50 Ohms so that maximum power is transferred
from the generator, whose output impedance is 50 Ohms, to the load. The
network must be installed as close a possible to the load. The best possible
position, in a plasma application for example, would be to mount the network
directly on the vacuum chamber with a direct connection to the electrode or
magnetron. Coaxial
Power Systems Ltd. manufacture two types of network - Manual and Automatic Manual Matching Network The
manual matching network consists of two adjustable vacuum capacitors and a
fixed inductor, which are usually arranged as an ”L” network. (The
arrangement can be simply converted to a “Pi” network if required).
Cranked knobs with built in turns counters are used to adjust the capacitors
for minimum reflected power as displayed on the generator reflected power
meter. When the reflected power is zero, the system is “tuned” and all of
the power output of the generator is being fed to the load. The inductor is
water cooled.
Automatic Matching Network The
automatic matching network is similar to the manual version except that
servomotors drive the capacitors. At
the input of the network, a phase and magnitude detector determines the
position of the capacitors. This information is transferred to the separate
controller. The controller then drives the servomotors to the positions, which
give zero, or minimum reflected power. The
controller is ½ rack, 4U high and is usually fitted in the same enclosure as
the generator.
Alternatively
the controller may be fitted within a generator - the readouts and controls on
the generator front panel. The
position of each variable capacitor is shown on a 31/2 digit LED meter.
Automatic or Manual mode is switch selectable - in manual mode the servomotors
are controlled by spring loaded switches. The
start position of the capacitors can be individually adjusted. When RF power
is detected, the capacitors automatically adjust for minimum reflected power.
When the RF is turned off, the motors drive the capacitors back to heir
original position. The start positions are adjusted using potentiometers
accessible via the controller front panel Option:
Model DCP-1 : Dark Space Bias Voltage Measurement and Control A
probe, installed inside the network, measures the d.c voltage (0 to 1999V)
developed across the dark space in plasma applications such as sputtering and
reactive ion etching. The voltage is converted to a 0 to 5V signal which can
be fed back to the generator control system. The voltage is displayed on the
loading capacitor position meter. Includes all necessary cables to link to any
generator in the low power range manufactured by Coaxial Power Systems Ltd. Note:
This option not available on manual networks (07.06.2007) |
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