ADLINK PCI-7256 - Manual (Page 46)

38 • Appendix A Relay Contact Protection Circuits
Device Selection:
Use a zener diode with a zener voltage about the same as the power supply
voltage.
4. Varistor Circuit
This circuit is also suitable for both AC & DC applications. Using the stable
voltage characteristics of the varistor, this circuit prevents excessively high
voltages from being applied across the contacts. This circuit also slightly
delays the release time. Effective when connected to both contacts of the
power supply voltage is 24 or 48V and the voltage across the load is 100 to
200 V.
Contact
Inductive
Load
Diode