©
National Instruments Corp.
5
FP-RLY-422
The maximum switching capacity of each relay is 3 A up to
250 VAC or 35 VDC. To switch greater DC voltages, refer to
Figure 4.
Figure 4.
Maximum Current vs. DC Volts
Contact Protection for Inductive Loads
When inductive loads are connected to the relays, a large
counter-electromotive force may occur at relay switching time
because of the energy stored in the inductive load. These flyback
voltages can severely damage the relay contacts and greatly
shorten the life of the relay.
It is best to limit these flyback voltages at your inductive load by
installing, across your inductive load, a flyback diode for DC loads
or a metal oxide varistor (MOV) for AC loads. Refer to the next
section,
Guidelines for Selecting Contact Protection Circuits
, for
more information.
In addition, the FP-RLY-422 contains its own internal protection
MOV to prevent excessively high voltage from being applied
across the contacts. Each channel contains two MOVs: one
between N.Closed and I.Com and one between N.Open and I.Com.
However, National Instruments still recommends the use of a
protection circuit across your inductive load.
20
0
40
60
DC Volts
Current
(Amps)
80
100 120
.5
1
1.5
2
2.5
3
Safe Operating
Region
