Rockwell Automation System Design for the Control of Electrical Noise - Manual (Page 14)

Publication GMC-RM001A-EN-P — July 2001
1-4 Electrical Noise Control Overview
Noise Victims
Typical noise victims include the following:
• Microprocessor controlled devices
• Analog devices
• Encoder and registration interfaces
Refer to Figure 1.3 for an example of a typical victim.
Figure 1.3
A victim TTL gate is easily triggered
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Refer to the section Capacitance below for an explanation of the 200 ohm impedance. Generally, most potential
victims are better protected than this.
The source noise level and the victim’s sensitivity are normally outside
the control of the system designer so that it is necessary to concentrate
on the transmission of noise between them.
Coupling Mechanisms The coupling mechanism is the means by which electrical noise
interferes with the routine operation of equipment. This section
describes the four common coupling mechanisms for electrical noise
transmission.
Conducted Noise
Noise is conducted directly by system power wiring. A common route
for conducted noise is the 24V dc distribution wiring.
5V TTL gate
Signal Source
(zero impedance)
50
Ω
Noisy circuit carrying 6V spikes
comprising mainly 10 MHz
Victim TTL gate receives 1.2V spikes
100 pF = 200 Ω
@ 10 MHz
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