Rockwell Automation System Design for the Control of Electrical Noise - Manual (Page 13)

Publication GMC-RM001A-EN-P — July 2001
Electrical Noise Control Overview 1-3
• Microprocessor clocks can generate high levels of noise at the
clock frequency and its harmonics.
• Contact switching.
Of the noise sources listed above, only contact switching noise can be
reduced at the source by the system builder.
Refer to the figure below for an example of a typical noise source.
Figure 1.1
Switch-Mode Power Supply Noise Measurement
Refer to Figure 1.2 for an example of six volt noise spikes from a
typical 24V dc power supply. The spikes usually contain frequencies
above 10 MHz.
Figure 1.2
Switch-Mode Power Supply Noise
+24V
Noise voltage
measured here
No load connected
AC
Line
Filter
24V dc PSU
DC common
Ground Plane - conductive metal panel
6.0V pk
Sitop Power 20 with 3 phase input - no load
Common Mode Noise +24 Volts to Backplane
10V
8
6
4
2
0
-2
-4
-6
-8
-10V
ms -1 0 1 2 3 4 5 6 7 8 9