ADLINK PCI-7251 - Manual (Page 47)

Appendix 39
Diode & Zener diode Circuit
This circuit is also suitable for DC application. Effective when the
release time i in the diode circuit is too long.
Device Selection:
Use a zener diode with a zener voltage about the same as the
power supply voltage.
Varistor Circuit
This circuit is also suitable for both AC & DC applications. Using
the stable voltage characteristics of the varistor, this circuit pre-
vents excessively high voltages from being applied across the
contacts. This circuit also slightly delays the release time. 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
Diode
Contact
Inductive
Load
Diode