Low-Cost Industrial Digital I/O – 60 V, Channel-to-Channel Isolated

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Relay Forms

Relays are classified by number of poles and number of throws. The

pole of a relay is the terminal common to every path. Each position

where the pole can connect is called a throw. A relay can be made of

n poles and m throws. A single-pole single-throw (SPST) relay has one

pole and one throw. A single-pole double-throw (SPDT) relay has one

pole and two throws.

Nonlatching Relays

A nonlatching relay has a power-off 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

maintained 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. Nonlatching relays return to the default NC position in case of a

fault or power failure. This is particularly useful when controlling a motor

or value where the motor or valve needs to be turned off in case of

power failure or fault.

Software

NI-DAQmx Software Technology

The PCI-6520 requires and is shipped with NI-DAQmx driver software,

version 7.5 or higher. NI-DAQmx software is also available for download

from ni.com/downloads. With NI-DAQmx, you can use your NI digital I/O

device in NI LabVIEW, ANSI C, Microsoft Visual C++, and the Microsoft

.NET languages C# and Visual Basic .NET.

Using NI-DAQmx technology, you can access the full functionality and

state-of-the-art hardware technology of your PCI-6520 digital I/O board.

NI-DAQmx technology speeds up your development with many features

such as automatic code generation to make configuration and

programming easy. The PCI-6520 takes full advantage of key NI-DAQmx

software technologies such as multithreaded streaming technology for

dramatic improvements in I/O performance and ease of use.

• Use DAQ Assistant to guide you to fast, accurate measurements with

no programming.

• Use automatic code generation to create your application in LabVIEW,

C, Visual Basic .NET, or C#.

• Take advantage of multithreaded streaming technology for 1,000X

performance improvements.

• Use automatic timing, triggering, and synchronization technology

to make advanced applications easy.

jump-start your project.

• Use the NI-DAQmx functions for jumper-free software configuration

of all digital I/O features without hardware switches/jumpers

• Develop your application with easy and open programming in

LabVIEW, ANSI C, Microsoft Visual C++, C#, and Visual Basic .NET.

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P1.0NO

P1.0COM

P1.0NC

P1.2NO

P1.2COM

P1.2NC

P1.4NO

P1.4COM

P1.6NO

P1.6COM

NO CONNECT

P0.0+

P0.0-

P0.2+

P0.2-

P0.4+

P0.4-

P0.6+

P0.6-

P1.1NO

P1.1COM

P1.1NC

P1.3NO

P1.3COM

P1.5NO

P1.5COM

P1.7NO

P1.7COM

NO CONNECT

P0.1+

P0.1-

P0.3+

P0.3-

P0.5+

P0.5-

P0.7+

P0.7-

Digital Input: P0.0 – P0.7

Form C relays: P1.0 – P1.2

Form A relays: P1.3 – P1.7

Figure 3. NI 6520, 37-Pin D-Sub I/O Connector

Single-Pole Single-Throw (SPST) Relay

Single-Pole Double-Throw (SPDT) Relay

Form

Symbol

Description

Form A

SPST relays with a normally open default state

Form C

SPDT relays that break the connection

with one throw before making contact with

the other (break-before-make)

Table 1. Form A and Form C Relays

Figure 2. Types of Relays