ADLINK cPCI-7252 - Manual (Page 49)

Appendix 39
Appendix
Relay Contact Protection Circuits
The contacts are the most important elements of a relay construc-
tion, Contact performance conspicuously influenced by contact
material, and voltage and current values applied to the contacts.
Another important issue is contact protection; the right contact pro-
tection circuit can suppress the counter EMF to a low level. How-
ever, note that incorrect use will result in an adverse effect. Typical
contact protection circuits are given below:
RC Circuit
This circuit is suitable for DC applications. If the load is a timer,
leakage current flow through the RC circuit may cause faulty oper-
ation.
The circuit below is suitable for both DC and AC applications. If
the load is a relay or solenoid, the release time is lengthened.
Effective when connected to both contacts if the power supply volt-
age is 24V or 48V and the voltage cross the load is 100 to 200V.
Contact
Inductive
Load
R C
Contact
Inductive
Load
R
C