Rockwell Automation System Design for the Control of Electrical Noise - Manual (Page 55)

Publication GMC-RM001A-EN-P — July 2001
Contact Suppression 6-3
The suppressor across the contact (as shown below, lower) reduces
the noise from the wiring inductance as well as the coil inductance.
Figure 6.3
RC suppressor in circuit
Understanding Contact
Suppression for 24V dc
Circuits Examples of DC devices requiring contact suppression include:
• Solenoid coils
• Contactor coils
• Relay coils
Methods of DC Contact Suppression
First choice for DC circuit suppression is a flywheel diode (shown in
the figure below), but this does increase the release time which may
not be acceptable in all applications. For the transient absorber
method, refer to Figure 6.5.
Figure 6.4
Flywheel diode
L
Line
N
RC suppressor
Better Solution
Good Solution
Line
N
L
Load
Load
Flywheel diode
Flywheel diode
+24V dc
+24V dc
Common
Common
Good Solution
Better Solution