ADLINK PCI-7256 - Manual (Page 44)

36 • Appendix A Relay Contact Protection Circuits
Appendix A. Relay Contact Protection
Circuits
The contacts are the most important elements of relay constructions, Contact
performance is conspicuously influenced by contact material, voltage and
current values applied to the contacts.
Another important issue is contact protection, a right contact protection circuit
can suppress the counter EMF to a low level. However, note that incorrect
use will result in an adverse effect. Typical contact protection circuits are
given below :
1. RC Circuit
This circuit is suitable for DC application. If the load is a timer, leakage
current flows through the RC circuit causing faulting operation.
Contact
Inductive
Load
R C
The below circuit is suitable for both AC and DC applications. If the load is a
relay or solenoid, the release time lengthens. It’s effective when connected to
both contacts if the power supply voltage is 24V or 48V and the voltage cross
the load is 100 to 200V.
Contact
Inductive
Load
R
C