ADLINK PCI-7260 - Manual (Page 63)

Appendix 53
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 of the power supply voltage is 24
or 48V and the voltage across the load is 100 to 200 V.
Contact
Inductive
Load
Diode