Ransburg MicroPak Controller A11789 - Manual (Page 18)

MICROPAK GROUNDING
THEORY
Electrical noise refers to stray electrical signals in
the atmosphere at various signal strengths and
frequencies that can affect the operation of elec-
trical equipment. One of the best ways to prevent
this is to shield the equipment and cables with
a continous ground envelope, such that any in-
cident noise will be conducted to earth ground
before it can affect the circuit conductors.
For conductors inside the Evolver MicroPak
Controller, the grounded enclosure provides this
envelope. For the low voltage cable(s) that run
from the controller to the Evolver spray guns, a
shielded cable has been used. The shield con-
sists of an overall foiled 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 prac-
tical 360° termination at both ends of the cable.
The AC input cord is not shielded, but instead is
directed to an AC line filter in the 24VDC power
supply as soon as it enters the cabinet. This filter
filters out any noise that comes in on the AC line.
For maximum noise immunity the AC line should
connect to the filter as soon as possible after it
enters the cabinet. Additional noise protection
can be provided by running the AC input line to
the controller in grounded conduit, which is the
recommended method and is required by most
codes.
For maximum noise protection any user supplied
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
conductive connector/fitting at each end of the
cable/conduit that makes contact to the shield/
conduit in a full 360° circle around the shield/
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 can ac-
tually make things worse (see Figure 7).
Figure 7: Cable Connection Examples
A special cable grommet fitting has been provid-
ed for I/O connector P3 of the controller (see Fig-
ure 4). When the nut is tightened, the spring in
the grommet compresses and makes 360° con-
tact with the braid of the cable. This electrically
connects the cable braid to ground via the con-
nector housing and controller back panel.
MicroPak Controller - Installation
16
Ransburg
CP-06-01.1