Rockwell Automation System Design for the Control of Electrical Noise - Manual (Page 67)

Publication GMC-RM001A-EN-P — July 2001
Power Distribution 7-9
Linear PSU
The linear PSU does not generate noise on its AC terminals, as does a
switch-mode supply, however, some noise reduction provisions are
still recommended.
Linear PSU Mounted in Clean Zone
In the figure below, the linear power supply is mounted in the clean
zone, but the AC line feeding it requires filtering. The AC line filter is
positioned between zones and attenuates line noise which may
otherwise be passed through to the DC circuit.
Figure 7.8
Linear PSU mounted in Clean Zone
24V dc Linear PSU
AC
Filter
+24V 24V com
Dirty Zone
Clean Zone
Clean Load
Segregation
De-coupling
capacitor