National Instruments cFP-RLY-423 Relay Output Module for Compact FieldPoint

The NI cFP-FLY-423 (Part Number: 777318-423) has four single-pole double-throw (SPDT) relay channels, LED relay status indicators, 250 VRMS maximum isolation voltage, 2,300 VRMS transient overvoltage protection, and is hot swappable. This Relay Output Module is created to be mounted on a cFP-BP-x Compact FieldPoint Backplane to bring power to the module. The four relay channels on the cFP-RLY-423 module each have four terminals: one normally open (NO), one normally closed (NC), and two isolated common (IC). The relays are break-before-make. Upon power-up, the relays are in the NC state. When the user turns on the relay channel, it breaks the NC-IC link and results in the NO-IC link. Every relay can be controlled individually, or the user can modify all relays at the same time.

If inductive loads are linked to the relays on the cFP-RLY-423 Relay Output Module, then a massive counter-electromotive force can take place at relay switching time. This is a result of the energy saved in the inductive load. The flyback voltages can greatly harm the relay contacts and reduce the life of the relay. The user can minimize flyback voltages by installing a flyback diode across an inductive DC load or a metal oxide varistor (MOV) across an inductive AC load. Also, the NI cFP-RLY-423 module has internal protection MOVs to deter extremely high voltage from being applied across the contacts. Each channel has two MOVs. One is between NC and IC and the other between NO and IC.