96 UDC3300 Limit Controller Product Manual 1/01
9.2 Potential Noise Sources
Overview
Noise can enter electronic equipment via three methods of coupling,
namely:
• Capacitive (or electrostatic)
• Inductive (or magnetic)
• Impedance.
Capacitive and
inductive coupling
Capacitive and inductive coupling have the same essential effect — they
couple current or voltage, without any actual connection of the two
circuits. Impedance coupling requires a connection between the two
circuits. Typical noise-generating sources that could affect electronic
equipment through capacitive and inductive coupling include:
• Relay coils
• Solenoids
• AC power wires — particularly at or above 100 Vac
• Current carrying cables
• Thyristor field exciters
• Radio frequency transmissions.
Impedance coupled
noise
Impedance-coupled noise may enter by way of the lines used to power the
digital equipment or by way of improper grounding. Most power lines, at
typical industrial locations, are far from noise-free. The noise on them can
be generated in many ways, but are nearly always associated with
switching circuits of some nature.
These include:
• Large relays
• Contactors
• Motor starters
• Business and industrial machines
• Power tools
• HID (high intensity discharge) lights
• Silicon controlled rectifiers (SCRs) that are phase-angled fired.
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