Mechanical Relays; Relay Forms; Non-Latching Relays; Relay Power Ratings - National Instruments NI 6521 User Manual

Mechanical Relays

Relay Forms

Table 4 describes the relay forms available on the NI 6520/6521.
Form Symbol
Form A
Form C

Non-Latching Relays

The relays on the NI 6520/6521 are non-latching. A non-latching relay has
an initial position of normally closed (NC). This position is maintained by
the force of a spring or permanent magnet while no current flows. The
normally open (NO) contact is closed by the force of a magnetic field while
current flows through the coil. When the current stops, the relay reverts
back to its initial NC position.
Non-latching armature relays are useful in control applications when the
switch must return to a known state if power is lost.

Relay Power Ratings

Caution The maximum switching current is limited by the maximum switching power, the
maximum voltage, and must not exceed 60 W, 60 VA.
(NI PCI-6520 Only)
60 W or 60 VA, with a maximum current of 2 A for all channels from 0 to
55 °C, external PC ambient.
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Table 4. NI 6520/6521 Relay Forms
Single-pole single-throw (SPST) relays with a default state of
normally open.
Single-pole double-throw (SPDT) relays that break the
NC
connection with one throw before making contact with the other
NO
(break-before-make).
NC
COM
NO
NC Position
Figure 8. Non-Latching Relay States
The maximum power rating for the NI PCI-6520 relays is
15
Description
NC
COM
NO
NO Position
NI 6520/6521 User Guide