ELECTRICAL NOISE
Electrical noise refers to stray electrical signals in the
atmosphere at various signal strengths and frequencies
that can affect the operation of equipment. One of the
best ways to prevent this is to shield the equipment and
cables within a
continuous
ground envelope, such that
any incident noise will be conducted to earth ground
before it can affect the circuit conductors.
For conductors inside the control unit or Controller, the
grounded enclosures provide this envelope. For the
cables that connect the applicator to the control unit
or Controller, a shielded cable has been used. The
shield consists of an overall foil shield in combination
with an overall braided shield. This provides the most
effective shielding, as the foil covers the “holes” in the
braid, and the braid allows for practical 360° termination
at both ends of the cable.
The AC input cord is not shielded, but is directed to
an AC line filter as soon as it enters the cabinet. This
method filters out most of the noise that comes in on
the AC line. For maximum noise immunity, if the AC
line is wired using conduit instead of the provided AC
line cord, it should connect to the filter as soon as it
enters the cabinet with as short of leads as possible.
Additional noise protection can be provided by running
the AC input line to the control panel in grounded conduit.
For maximum noise protection any user supply input/
output (I/O) wiring should be made using shielded
cable (or conduit) which is connected to earth ground
in a continuous 360° fashion at both ends. The best
way to do this is to use a connector (conduit fitting) at
each end of the cable (conduit) that makes contact
to the shield (conduit) in a full 360° circle around the
cable (conduit) and makes contact to the grounded
enclosure in the same fashion. Connecting the drain
wire of a shield to a ground point on or in the cabinet
(usually referred to as pigtailing) is not an effective
method of shielding and actually makes things worse
(see Figure 6).
It is recommended that all AC I/O (interlocks) be run
in conduit. If desired and codes permit, cabling may
be used for these signals, but for maximum noise
immunity the cabling must contain overall foil and
braided shields and be terminated as described in the
preceding paragraph.
Cable is recommended for all of the analog and digital
Figure 6: Pigtailing Connection
remote I/O control signals including the relay controlled
DC I/O (high voltage output signal, fault output signal).
Again, for maximum noise immunity the cabling
must contain overall foil and braided shields and be
terminated in a continuous 360° manner as described
in the preceding paragraph. Special fittings have
been provided on the control panel for termination of
these cables at that point. The use of these fittings is
described in the corresponding sections of this manual.
Using the methods previously described, the 9060
Controller have been successfully tested to the stringent
standards of the Electromagnetic Compatibility Directive
of the European Union. The results conclude that
these units are neither a source of electrical noise nor
affected by electrical noise when the above methods
are utilized.
PIGTAILS (POOR SHIELDING)
360° TERMANATION TO GROUND
(GOOD SHIELDING)
CP-17-02
13
9060 Classic High Voltage Controller -
INSTALLATION
