Potential Noise Sources; Overview - Honeywell VPR100 User Manual

Appendix B
B.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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