National Instruments NI 9421 Getting Started Manual

GETTING STARTED GUIDE

NI 9421

8-Channel Sinking Digital Input Module

This document explains how to connect to the NI 9421. In this
document, the NI 9421 with screw terminal, NI 9421 with spring
terminal, and NI 9421 with DSUB are referred to inclusively as
the NI 9421.

Note Before you begin, complete the software and

hardware installation procedures in your chassis
documentation.

Note The guidelines in this document are specific to

the NI 9421. The other components in the system might
not meet the same safety ratings. Refer to the
documentation for each component in the system to
determine the safety and EMC ratings for the entire
system.

Safety Guidelines

Operate the NI 9421 only as described in this document.

Caution Do not operate the NI 9421 in a manner not

specified in this document. Product misuse can result in
a hazard. You can compromise the safety protection
built into the product if the product is damaged in any

2 | ni.com | NI 9421 Getting Started Guide

way. If the product is damaged, return it to NI for
repair.

Safety Guidelines for Hazardous Voltages

If hazardous voltages are connected to the device, take the
following precautions. A hazardous voltage is a voltage greater
than 42.4 Vpk voltage or 60 VDC to earth ground.

You can connect hazardous voltages only to the NI 9421 with
screw terminal and the NI 9421 with spring terminal. Do not
connect hazardous voltages to the NI 9421 with DSUB.

Caution Ensure that hazardous voltage wiring is

performed only by qualified personnel adhering to local
electrical standards.

Caution Do not mix hazardous voltage circuits and

human-accessible circuits on the same module.

Caution Ensure that devices and circuits connected to

the module are properly insulated from human contact.

Caution When module terminals are hazardous

voltage LIVE (>42.4 Vpk/60 VDC), you must ensure
that devices and circuits connected to the module are

NI 9421 Getting Started Guide | © National Instruments | 3

properly insulated from human contact. You must use
the NI 9932 connector backshell kit to ensure that the
terminals are not accessible.

NI 9421 with Screw/Spring Terminal Safety
Voltages

Connect only voltages that are within the following limits:

...........................................................Channel-to-COM 30 V max

Isolation

...................................................Channel-to-channel None

Channel-to-earth ground

...........................................Continuous 250 Vrms,

Measurement Category II

...........................................Withstand 2,300 Vrms, verified by a

5 s dielectric withstand test

Measurement Category II is for measurements performed on
circuits directly connected to the electrical distribution system.
This category refers to local-level electrical distribution, such as
that provided by a standard wall outlet, for example, 115 V for
U.S. or 230 V for Europe.

4 | ni.com | NI 9421 Getting Started Guide

Caution Do not connect the NI 9421 with screw

terminal or NI 9421 with spring terminal to signals or
use for measurements within Measurement
Categories III or IV.

NI 9421 with DSUB Safety Voltages

Connect only voltages that are within the following limits:

...........................................................Channel-to-COM 30 V max

Isolation

...................................................Channel-to-channel None

Channel-to-earth ground

...........................................Continuous 60 VDC,

Measurement Category I

...........................................Withstand 1,000 Vrms, verified by a

5 s dielectric withstand test

Measurement Category I is for measurements performed on
circuits not directly connected to the electrical distribution system
referred to as MAINS voltage. MAINS is a hazardous live
electrical supply system that powers equipment. This category is
for measurements of voltages from specially protected secondary
circuits. Such voltage measurements include signal levels, special

NI 9421 Getting Started Guide | © National Instruments | 5

equipment, limited-energy parts of equipment, circuits powered
by regulated low-voltage sources, and electronics.

Caution Do not connect the NI 9421 with DSUB to

signals or use for measurements within Measurement
Categories II, III, or IV.

Note Measurement Categories CAT I and CAT O are

equivalent. These test and measurement circuits are not
intended for direct connection to the MAINS building
installations of Measurement Categories CAT II,
CAT III, or CAT IV.

Safety Guidelines for Hazardous Locations

The NI 9421 is suitable for use in Class I, Division 2, Groups A,
B, C, D, T4 hazardous locations; Class I, Zone 2, AEx nA IIC T4
and Ex nA IIC T4 hazardous locations; and nonhazardous
locations only. Follow these guidelines if you are installing the
NI 9421 in a potentially explosive environment. Not following
these guidelines may result in serious injury or death.

Caution Do not disconnect I/O-side wires or

connectors unless power has been switched off or the
area is known to be nonhazardous.

6 | ni.com | NI 9421 Getting Started Guide

Caution Do not remove modules unless power has

been switched off or the area is known to be
nonhazardous.

Caution Substitution of components may impair

suitability for Class I, Division 2.

Caution For Division 2 and Zone 2 applications,

install the system in an enclosure rated to at least IP54
as defined by IEC/EN 60079-15.

Caution For Division 2 and Zone 2 applications,

connected signals must be within the following limits.

...........................................................Capacitance 0.2 µF max

Special Conditions for Hazardous Locations Use in
Europe and Internationally

The NI 9421 has been evaluated as Ex nA IIC T4 Gc equipment
under DEMKO Certificate No. 03 ATEX 0324020X and is
IECEx 14.0089X certified. Each NI 9421 is marked

II 3G and
is suitable for use in Zone 2 hazardous locations, in ambient
temperatures of -40 °C ≤ Ta ≤ 70 °C. If you are using the NI 9421
in Gas Group IIC hazardous locations, you must use the device in

NI 9421 Getting Started Guide | © National Instruments | 7

an NI chassis that has been evaluated as Ex nC IIC T4, Ex IIC
T4, Ex nA IIC T4, or Ex nL IIC T4 equipment.

Caution You must make sure that transient

disturbances do not exceed 140% of the rated voltage.

Caution The system shall only be used in an area of

not more than Pollution Degree 2, as defined in
IEC 60664-1.

Caution The system shall be mounted in an

ATEX/IECEx-certified enclosure with a minimum
ingress protection rating of at least IP54 as defined in
IEC/EN 60079-15.

Caution The enclosure must have a door or cover

accessible only by the use of a tool.

Electromagnetic Compatibility Guidelines

This product was tested and complies with the regulatory
requirements and limits for electromagnetic compatibility (EMC)
stated in the product specifications. These requirements and
limits provide reasonable protection against harmful interference

8 | ni.com | NI 9421 Getting Started Guide

when the product is operated in the intended operational
electromagnetic environment.

This product is intended for use in industrial locations. However,
harmful interference may occur in some installations, when the
product is connected to a peripheral device or test object, or if the
product is used in residential or commercial areas. To minimize
interference with radio and television reception and prevent
unacceptable performance degradation, install and use this
product in strict accordance with the instructions in the product
documentation.

Furthermore, any changes or modifications to the product not
expressly approved by National Instruments could void your
authority to operate it under your local regulatory rules.

Special Conditions for Marine Applications

Some products are Lloyd’s Register (LR) Type Approved for
marine (shipboard) applications. To verify Lloyd’s Register
certification for a product, visit ni.com/certification and search
for the LR certificate, or look for the Lloyd’s Register mark on
the product.

NI 9421 Getting Started Guide | © National Instruments | 9

Caution In order to meet the EMC requirements for

marine applications, install the product in a shielded
enclosure with shielded and/or filtered power and
input/output ports. In addition, take precautions when
designing, selecting, and installing measurement probes
and cables to ensure that the desired EMC performance
is attained.

Preparing the Environment

Ensure that the environment in which you are using the NI 9421
meets the following specifications.

...........................................................Operating temperature

(IEC 60068-2-1, IEC 60068-2-2)

-40 °C to 70 °C

...........................................................Operating humidity

(IEC 60068-2-78)

10% RH to 90% RH,
noncondensing

...........................................................Pollution Degree 2

...........................................................Maximum altitude 2,000 m

Indoor use only.

10 | ni.com | NI 9421 Getting Started Guide

Note Refer to the device datasheet on ni.com/manuals

for complete specifications.

Connecting the NI 9421

The NI 9421 provides connections for eight digital input
channels.

NI 9421 Getting Started Guide | © National Instruments | 11

Figure 1. NI 9421 Pinout

DI0
DI1
DI2
DI3
DI4
DI5
DI6
DI7
NC
COM

DI0
DI1
DI2
DI3
DI4
DI5
DI6
DI7
NC
COM

0

4

3

2

1

5

6

9

8

7

3

7

0
1
2
3
4
5
6
7
8
9

0

4

COM
NC
COM
COM
NC
COM
COM
NC
COM
COM
NC
COM
COM

DI0
NC
DI1
DI2
NC
DI3
DI4
NC
DI5
DI6
NC
DI7

1
2
3
4
5
6
7
8

9
10
11
12
13

14
15
16
17
18
19
20
21
22
23
24
25

0 3

4 7

Note You must use 2-wire ferrules to create a secure

connection when connecting more than one wire to a
single terminal on the NI 9421 with screw terminal or
NI 9421 with spring terminal.

12 | ni.com | NI 9421 Getting Started Guide

NI 9421 Signals

Each channel of the NI 9421 has a DI terminal or pin to which
you can connect voltage or current signals. The NI 9421 also has
COM, a common terminal or pin that is internally connected to
the isolated ground reference of the module.

The NI 9421 has sinking inputs, meaning that when the external
device drives current or applies voltage to the DI terminal or pin,
DI provides a path to COM for the current or voltage. The
NI 9421 internally limits current signals connected to DI.

Connecting Sourcing-Output Devices

You can connect 2-, 3-, and 4-wire sourcing-output devices to the
NI 9421. A sourcing-output device drives current or applies
voltage to DI. An example of a sourcing-output device is an open
collector PNP.

Connect the output of the sourcing-output device to DI on the
NI 9421. Connect the common of the external device to the COM
terminal or pin.

NI 9421 Getting Started Guide | © National Instruments | 13

Figure 2. Connecting a Device to the NI 9421 (3-Wire Device Shown)

NI 9421

+

–

Sourcing-Output

Device

COM

DI

External

Power

Supply

The NI 9421 channel registers as ON when the sourcing-output
device applies a voltage or drives a current that is in the input ON
range to DI. The channel registers as OFF when the device
applies a voltage or drives a current that is in the input OFF range
to DI. If no device is connected to DI, the channel registers as
OFF.

LED Indications

Each channel has an LED that indicates the state of the channel,
as the following table describes. The LEDs are disabled when the
chassis is in sleep mode.

14 | ni.com | NI 9421 Getting Started Guide

Table 1. LED Indications

LED State Indication

Illuminated Channel is on

Not illuminated Channel is off

High-Vibration Application Connections

If your application is subject to high vibration, NI recommends
that you follow these guidelines to protect connections to the
NI 9421:

• Use ferrules to terminate wires to the detachable connector.

• Use the NI 9927 backshell kit with the NI 9421 with screw
terminal or the NI 9981 backshell kit with the NI 9421 with
spring terminal.

NI 9421 Getting Started Guide | © National Instruments | 15

Where to Go Next

Located at ni.com/manuals Installs with the software

CompactRIO

NI CompactDAQ

RELATED INFORMATION

C Series Documentation
& Resources

ni.com/info cseriesdoc

Services

ni.com/services

NI 9421 Datasheet

NI-RIO Help

LabVIEW FPGA Help

NI 9421 Datasheet

NI-DAQmx Help

LabVIEW Help

16 | ni.com | NI 9421 Getting Started Guide

Worldwide Support and Services

The National Instruments website is your complete resource for
technical support. At ni.com/support, you have access to
everything from troubleshooting and application development
self-help resources to email and phone assistance from NI
Application Engineers.

Visit ni.com/services for NI Factory Installation Services, repairs,
extended warranty, and other services.

Visit ni.com/register to register your National Instruments
product. Product registration facilitates technical support and
ensures that you receive important information updates from NI.

A Declaration of Conformity (DoC) is our claim of compliance
with the Council of the European Communities using the
manufacturer’s declaration of conformity. This system affords the
user protection for electromagnetic compatibility (EMC) and
product safety. You can obtain the DoC for your product by
visiting ni.com/certification. If your product supports calibration,
you can obtain the calibration certificate for your product at

ni.com/calibration.

NI 9421 Getting Started Guide | © National Instruments | 17

National Instruments corporate headquarters is located at
11500 North Mopac Expressway, Austin, Texas, 78759-3504.
National Instruments also has offices located around the world.
For telephone support in the United States, create your service
request at ni.com/support or dial 1 866 ASK MYNI (275 6964).
For telephone support outside the United States, visit the
Worldwide Offices section of ni.com/niglobal to access the branch
office websites, which provide up-to-date contact information,
support phone numbers, email addresses, and current events.

Refer to the NI Trademarks and Logo Guidelines at ni.com/trademarks for information on
National Instruments trademarks. Other product and company names mentioned herein are
trademarks or trade names of their respective companies. For patents covering National
Instruments products/technology, refer to the appropriate location: Help»Patents in your software,
the patents.txt file on your media, or the National Instruments Patent Notice at ni.com/

patents. You can find information about end-user license agreements (EULAs) and third-party

legal notices in the readme file for your NI product. Refer to the Export Compliance Information at

ni.com/legal/export-compliance for the National Instruments global trade compliance policy

and how to obtain relevant HTS codes, ECCNs, and other import/export data. NI MAKES NO
EXPRESS OR IMPLIED WARRANTIES AS TO THE ACCURACY OF THE INFORMATION
CONTAINED HEREIN AND SHALL NOT BE LIABLE FOR ANY ERRORS. U.S. Government
Customers: The data contained in this manual was developed at private expense and is subject to
the applicable limited rights and restricted data rights as set forth in FAR 52.227-14, DFAR

252.227-7014, and DFAR 252.227-7015.

© 2003—2015 National Instruments. All rights reserved.

373504G-01 May15