Rockwell Automation System Design for the Control of Electrical Noise - Manual (Page 15)

Publication GMC-RM001A-EN-P — July 2001
Electrical Noise Control Overview 1-5
Capacitance
At radio frequencies (RF) the capacitance between two adjacent wires
is significant. Two insulated wires touching each other and only 1.0
meter (39.0 in.) long form a capacitance of approximately 100 pF
(Pico Farads). At 10 MHz the impedance is only 200 ohms.
Fortunately, the effect reduces as the square of the separation
distance. Refer to Figure 1.4 for an example of capacitive coupling.
Figure 1.4
Capacitive Coupling
Mutual Inductance
At radio frequencies (RF) the inductance of a straight wire is
significant. A length of wire 1.0 meter (39 in.) has an inductance of
approximately 1.0
µ
H (Micro Henry). At 10 MHz the impedance is 60
ohms.
Two adjacent wires have mutual inductance forming a transformer.
Fortunately, the effect reduces as the square of the separation
distance. Refer to Figure 1.5 for an example of inductive coupling.
Figure 1.5
Inductive Coupling
Circuit A
Circuit B
Stray
capacitance Separation distance
Circuit A
Circuit B
Stray
inductance
Separation distance Magnetic coupling