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OEM-AT6400 Installation Guide
signal wiring, especially when they are tied in the same
wiring bundle or conduit.
When this kind of problem occurs, you should consider
shielding signal cables or isolating the signals. A proper
shield surrounds the signal wires to intercept electrical
fields, but this shield must be tied to Earth to drain the
induced voltages. At the very least, wires should be run
in twisted pairs to limit straight line antenna effects.
Even the worst noise problems in environments near 600
amp welders and 25kW transmitters have been solved
using enclosures, conduit, optical isolation, and single-
point ground techniques.
Ground Loops
Ground Loops are the most mysterious noise problems.
Symptoms like garbled transmissions and intermittent
operation are typical.
The problem occurs in systems where multiple Earth
ground connections exist, particularly when these
connections are far apart.
The way to test for and ultimately eliminate a ground loop
is to lift or
cheat Earth ground connections in the system
until the symptoms disappear.
Defeating Noise
The best time to handle electrical noise problems is before
they occur. When a motion system is in the design
process, the designer should consider the following set of
guidelines for system wiring (in order of importance):
➀
Put surge suppression components on all electrical
coils: Resistor/capacitor filters, MOVs, Zener and
clamping diodes.
➁
Shield all remote connections, use twisted pairs.
Shields should be tied to Earth at one end.
➂
Put all microelectronic components in an enclosure.
Keep noisy devices outside. Watch internal
temperature.
➃
Ground signal common wiring at one point. Float this
ground from Earth if possible.
➄
Tie all mechanical grounds to Earth at one point. Run
chassis and motor grounds to the frame, and the
frame to Earth.
➅
Isolate remote signals. Solid state relays or opto
isolators are recommended.
➆
Filter the power line. Use common RF filters, and use
an isolation transformer for worst case.
A noise problem must be identified before it can be
solved. The obvious way to approach a problem situation
is to eliminate potential noise sources until the symptoms
disappear, as in the case of ground loops. When this is
not practical, use the above guidelines to make the
installation as robust as possible.
R e f e r e n c e s
Information about the equipment referred to may be
obtained by calling the numbers listed below.
•
Corcom line filters, (214) 386-5515
•
Opto-22 optically isolated relays, (408) 496-6611
•
Crydom optically isolated relays, (415) 463-2250
•
Potter Brumfield optically isolated relays, (812) 386-
1000
•
Teal power line isolation filters, (800) 888-8325
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