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OM-530 Page 30
L. High Frequency
High frequency is radio frequency energy, either con-
tinuous or pulsed, used to start or stabilize a welding arc.
M. High-Frequency Assisted Arc Welding
High-frequency assisted arc welding refers to any of the
arc welding processes requiring high frequency.
N. Interference
Interference is the unwanted and problematic reception
of high-frequency energy.
O. Radiation
Radiation is the transmission of high-frequency energy
through space.
8-3. HIGH-FREQUENCY RADIATION
Installations using high frequency, either as an integral
part of the power source or as an accessory unit, will
produce some high-frequency radiation. Such radiation,
if the signal strength is sufficient at the receiving device,
can cause an inconvenience or disruption of communi-
cations or can cause malfunction in sensitive electronic
controls and systems. The four major causes of high-
frequency radiation are as follows:
A. Direct Radiation From The Power Source Or
High-Frequency Accessory Unit
Direct radiation is that radiation emanating directly from
the power source or accessory unit. Radiation from the
power line and welding power source accessories is not
considered to be direct radiation from the power source
or accessory unit.
B. Direct Radiation From The Welding Circuit
Any attachment to the output terminals of the high-fre-
quency source is capable of acting as an antenna and
radiating high-frequency energy. Attachments include
weld cables, torches, worktables, etc. Since direct ra-
diation from the welding circuit is the major source of ra-
diation, it is important to keep attachments to a mini-
mum.
C. Conduction And Radiation From The Power
Line
Most power lines are capable of conducting high-fre-
quency energy which may cause interference directly or
by reradiation from these power lines. Normally such ra-
diation is small when compared to that caused by radia-
tion from the weld cables.
D. Reradiation
Radiation from the welding circuit can be picked up by
ungrounded metal objects or unshielded wiring in the
immediate vicinity, conducted some distance, and
reradiated. This can be a troublesome source of inter-
ference.
8-4. LOCATION
Locate the high-frequency power source as close to the
welding process as possible. Also consider the near-
ness of a suitable ground connection when selecting a
site for the installation of the power source. Ideally, the
high-frequency power source should be located in an
area where there is a limited amount of miscellaneous
wiring (lighting, power, telephone, communications, and
other unshielded conductors) located within the welding
zone. Ungrounded, metallic conductors in the welding
zone can act as antennas which will pick up, conduct, or
reradiate the high-frequency energy transmitted by the
welding circuit. All miscellaneous wiring in the welding
zone should be enclosed in grounded, rigid metallic con-
duit, copper braid, or some other material having an
equivalent shielding efficiency, and grounded at 50 ft.
(15 m) intervals (see Figure 8-1).
S-0017
High-Frequency
Welding
Power Source
Shielded Wire
Ground At 50ft.
(15 m) Intervals
50 ft.
(15 m)
Work Clamp
Ground
Keep all unshielded and ungrounded
wires out of the welding zone.
Holder
Electrode
Figure 8-1. Requirements To Minimize Reradia-
tion Pickup In The Vicinity Of The Welding Zone
8-5. GENERAL INSTALLATION PROCEDURES
A. Weld Cables
Keep the weld cables as short as possible and do not
exceed 25 ft. (8 m) in length. Position the cables as
close together and as close to the floor or ground plane
as possible.
If the welding operation must be carried out at a point
farther than 25 ft. (8 m) from the welding power source,
use a portable high-frequency source and locate the
portable unit within 25 ft. (8 m) of the welding electrode.
B. High-Frequency Assisted Arc Welding Power
Sources
When the high-frequency assisted arc welding power
source is in operation, all service doors and covers must
be closed, securely fastened, and adequately bonded to
ensure good contact around the entire perimeter of the
opening. Except for changes and adjustments allowed
by the manufacturer, the high-frequency assisted arc
welding power source should not be modified.