FP-RLY-420 6 www.natinst.com
In addition, the FP-RLY-420 contains its own internal protection
MOV to prevent excessively high voltage from being applied
across the contacts. The MOV is located between the N.O. and I.C.
contacts of each relay, but National Instruments still recommends
the use of a protection circuit across your inductive load.
Guidelines for Selecting Contact Protection Circuits1
Proper selection is critical as the use of a contact-protection device
can extend contact life. When mounting the protection device,
always locate it near the immediate area of the load or contact.
Typically you should mount a protective device within 18 in. of the
load or contact.
Typically, contact-protection circuits are provided for an overview,
but you should thoroughly examine the circuit you are planning to
use. For more specific information on any of these circuits, contact
the Technical Services Department at American Zettler, Inc.
Diode and Zener Diode Circuit
1 This section has been reprinted with permission from American Zettler, Inc.
Diagram Notes
Use in DC applications only.
Use when diode circuit causes too long
release time.
Use zener diode with zener voltage about
equal to power supply voltage.
Load