National Instruments USB-9421 User manual

USER GUIDE AND SPECIFICATIONS
NI USB-9421
8-Channel, 24 V Logic, Sinking Digital Input Device
This user guide describes how to use the National Instruments USB-9421
and lists the device specifications. In this user guide, the NI USB-9421 with
screw terminal and the NI USB-9421 with D-SUB are referred to
inclusively as the NI USB-9421.
Introduction
The NI USB-9421 data acquisition device provides a USB interface with
connections for eight digital input channels. The NI USB-9421 consists
of two components: an NI 9421 module and an NI USB-9162 carrier,
as shown in Figure 1.
Figure 1. NI USB-9421 Components
NI 9421
NI USB-9162
NI USB-9421
Hi-SPeed USB Carrier
NI USB-9162
Hi-Speed USB Carrier
NI USB-9162

NI USB-9421 User Guide and Specifications 2 ni.com
Dimensions
Figures 2 and 3 show the NI USB-9421 device dimensions.
Figure 2. NI USB-9421 (Screw Terminal) Device in Millimeters (Inches)
Figure 3. NI USB-9421 (D-SUB) Device in Millimeters (Inches)
Hi-Speed USB Carrier
NI USB-9162
140.23 mm
(5.521 in.)
137.82 mm
(5.426 in.)
120.68 mm
(4.751 in.)
118.26 mm
(4.656 in.)
88.12 mm
(3.469 in.)
25.34 mm
(0.998 in.)
Hi-Speed USB Carrier
NI USB-9162
125.76 mm
(4.951 in.)
123.38 mm
(4.857 in.)
120.68 mm
(4.751 in.)
118.26 mm
(4.656 in.)
88.12 mm
(3.469 in.)
25.34 mm
(0.998 in.)

©National Instruments Corporation 3 NI USB-9421 User Guide and Specifications
Safety Guidelines
Operate the NI USB-9421 only as described in these operating instructions.
Note Although the NI 9421 module may have more stringent certification standards than
the NI USB-9421, when used with the NI USB-9162 carrier, the combined system may be
limited. Refer to the Specifications section for more details.
Hot Surface This icon denotes that the component may be hot. Touching this component
may result in bodily injury.
Caution Do not disconnect I/O-side wires or connectors unless power has been switched
off or the area is known to be nonhazardous.
Caution Do not remove modules unless power has been switched off or the area is known
to be nonhazardous.
Caution The NI USB-9421 is not certified for use in hazardous locations.
Safety Guidelines for Hazardous Voltages
If hazardous voltages are connected to the module, take the following
precautions. A hazardous voltage is a voltage greater than 42.4 Vpk or
60 VDC to earth ground.
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 Make sure that devices and circuits connected to the module are properly
insulated from human contact.
Caution When module terminals are live with hazardous voltages, make sure that the
terminals are not accessible by using the high voltage screw terminal backshell. Refer to
the Assembling the High Voltage Screw Terminal Backshell section for more information.

NI USB-9421 User Guide and Specifications 4 ni.com
Related Documentation
Each application software package and driver includes information about
writing applications for taking measurements and controlling measurement
devices. The following references to documents assume you have
NI-DAQmx 8.7 or later, and where applicable, version 7.1 or later of the
NI application software.
NI-DAQmx for Windows
The DAQ Getting Started Guide describes how to install your NI-DAQmx
for Windows software, your NI-DAQmx-supported DAQ device, and how
to confirm that your device is operating properly. Select Start»All
Programs»National Instruments»NI-DAQ»DAQ Getting Started
Guide.
The NI-DAQ Readme lists which devices are supported by this version of
NI-DAQ. Select Start»All Programs»National Instruments»NI-DAQ»
NI-DAQ Readme.
The NI-DAQmx Help contains general information about measurement
concepts, key NI-DAQmx concepts, and common applications that are
applicable to all programming environments. Select Start»All
Programs»National Instruments»NI-DAQ»NI-DAQmx Help.
LabVIEW
If you are a new user, use the Getting Started with LabVIEW manual to
familiarize yourself with the LabVIEW graphical programming
environment and the basic LabVIEW features you use to build data
acquisition and instrument control applications. Open the Getting Started
with LabVIEW manual by selecting Start»All Programs»National
Instruments»LabVIEW»LabVIEW Manuals or by navigating to the
labview\manuals directory and opening LV_Getting_Started.pdf.
Use the LabVIEW Help, available by selecting Help»Search the
LabVIEW Help in LabVIEW, to access information about LabVIEW
programming concepts, step-by-step instructions for using LabVIEW, and
reference information about LabVIEW VIs, functions, palettes, menus, and
tools. Refer to the following locations on the Contents tab of the LabVIEW
Help for information about NI-DAQmx:
•Getting Started»Getting Started with DAQ—Includes overview
information and a tutorial to learn how to take an NI-DAQmx
measurement in LabVIEW using the DAQ Assistant.
•VI and Function Reference»Measurement I/O VIs and
Functions—Describes the LabVIEW NI-DAQmx VIs and properties.

©National Instruments Corporation 5 NI USB-9421 User Guide and Specifications
•Taking Measurements—Contains the conceptual and how-to
information you need to acquire and analyze measurement data in
LabVIEW, including common measurements, measurement
fundamentals, NI-DAQmx key concepts, and device considerations.
LabWindows/CVI
The Data Acquisition book of the LabWindows/CVI Help contains
measurement concepts for NI-DAQmx. This book also contains Taking
an NI-DAQmx Measurement in LabWindows/CVI, which includes
step-by-step instructions about creating a measurement task using the DAQ
Assistant. In LabWindows™/CVI™, select Help»Contents, then select
Using LabWindows/CVI»Data Acquisition.
The NI-DAQmx Library book of the LabWindows/CVI Help contains
API overviews and function reference for NI-DAQmx. Select Library
Reference»NI-DAQmx Library in the LabWindows/CVI Help.
Measurement Studio
If you program your NI-DAQmx-supported device in Measurement Studio
using Visual C++, Visual C#, or Visual Basic .NET, you can interactively
create channels and tasks by launching the DAQ Assistant from MAX or
from within Visual Studio .NET. You can generate the configuration code
based on your task or channel in Measurement Studio. Refer to the DAQ
Assistant Help for additional information about generating code. You also
can create channels and tasks, and write your own applications in your
ADE using the NI-DAQmx API.
For help with NI-DAQmx methods and properties, refer to the NI-DAQmx
.NET Class Library or the NI-DAQmx Visual C++ Class Library included
in the NI Measurement Studio Help. For general help with programming in
Measurement Studio, refer to the NI Measurement Studio Help, which is
fully integrated with the Microsoft Visual Studio .NET help. To view
this help file in Visual Studio. NET, select Measurement Studio»
NI Measurement Studio Help.
To create an application in Visual C++, Visual C#, or Visual Basic .NET,
follow these general steps:
1. In Visual Studio .NET, select File»New»Project to launch the New
Project dialog box.
2. Find the Measurement Studio folder for the language you want to
create a program in.
3. Choose a project type. You add DAQ tasks as a part of this step.

NI USB-9421 User Guide and Specifications 6 ni.com
ANSI C without NI Application Software
The NI-DAQmx Help contains API overviews and general information
about measurement concepts. Select Start»All Programs»National
Instruments»NI-DAQ»NI-DAQmx Help.
The NI-DAQmx C Reference Help describes the NI-DAQmx Library
functions, which you can use with National Instruments data acquisition
devices to develop instrumentation, acquisition, and control applications.
Select Start»All Programs»National Instruments»NI-DAQ»
NI-DAQmx C Reference Help.
.NET Languages without NI Application Software
With the Microsoft .NET Framework version 1.1 or later, you can use
NI-DAQmx to create applications using Visual C# and Visual Basic
.NET without Measurement Studio. You need Microsoft Visual Studio
.NET 2003 or Microsoft Visual Studio 2005 for the API documentation
to be installed.
The installed documentation contains the NI-DAQmx API overview,
measurement tasks and concepts, and function reference. This help is fully
integrated into the Visual Studio .NET documentation. To view the
NI-DAQmx .NET documentation, go to Start»Programs»National
Instruments»NI-DAQ»NI-DAQmx .NET Reference Help. Expand
NI Measurement Studio Help»NI Measurement Studio .NET Class
Library»Reference to view the function reference. Expand NI
Measurement Studio Help»NI Measurement Studio .NET Class
Library»Using the Measurement Studio .NET Class Libraries to view
conceptual topics for using NI-DAQmx with Visual C# and Visual Basic
.NET.
To get to the same help topics from within Visual Studio, go to
Help»Contents. Select Measurement Studio from the Filtered By
drop-down list and follow the previous instructions.
Device Documentation and Specifications
NI-DAQmx includes the Device Document Browser, which contains
online documentation for supported DAQ, SCXI, and switch devices, such
as help files describing device pinouts, features, and operation, and PDF
files of the printed device documents. You can find, view, and/or print the
documents for each device using the Device Document Browser at any
time by inserting the CD. After installing the Device Document Browser,
device documents are accessible from Start»All Programs»National
Instruments»NI-DAQ»Browse Device Documentation.
Note You can download these documents at ni.com/manuals.

©National Instruments Corporation 7 NI USB-9421 User Guide and Specifications
Training Courses
If you need more help getting started developing an application with NI
products, NI offers training courses. To enroll in a course or obtain a
detailed course outline, refer to ni.com/training.
Technical Support on the Web
For additional support, refer to ni.com/support or zone.ni.com.
Installing the Software
Software support for the NI USB-9421 for Windows Vista/XP/2000 is
provided by NI-DAQmx. The DAQ Getting Started Guide, which you can
download at ni.com/manuals, offers NI-DAQmx users step-by-step
instructions for installing software and hardware, configuring channels and
tasks, and getting started developing an application.
Installing Other Software
If you are using other software, refer to the installation instructions that
accompany your software.
Example Programs
The NI-DAQmx CD contains example programs that you can use to get
started programming with the NI USB-9421. Refer to the NI-DAQmx for
USB Devices Getting Started Guide that shipped with your device, and
is also accessible from Start»All Programs»National Instruments»
NI-DAQ,for more information.
Installing the NI USB-9421 Device
Before installing the device, you must install the software you plan to use
with the device. Refer to the Installing the Software section of this guide
and the documentation included with the software for more information.
Installing the NI 9421 in the NI USB-9162 Carrier
The NI 9421 module and NI USB-9162 carrier are packaged separately.
Refer to Figure 4, while completing the following assembly steps:
1. Make sure that no signals are connected to the NI 9421 module.
2. Remove the protective cover from the 15-pin D-SUB connector.

NI USB-9421 User Guide and Specifications 8 ni.com
3. Align the I/O module with the carrier, as shown in Figure 4.
Figure 4. Module Installation
4. Squeeze the latches and insert the NI 9421 module into the
NI USB-9162 carrier.
5. Press firmly on the connector side of the NI 9421 module until the
latches lock the module into place, as shown in Figure 5.
Figure 5. Locking Module into Place
1 High Voltage Screw Terminal Backshell
1

©National Instruments Corporation 9 NI USB-9421 User Guide and Specifications
Mounting the NI USB-9421 to a Panel
Threaded inserts are located in the NI USB-9421 for mounting it to a panel.
Refer to Figure 6 for dimensions.
Figure 6. Module Dimensions in Millimeters (Inches)
Connecting the NI USB-9421 to a Computer
Plug one end of the USB cable into the NI USB-9421 and the other end into
an available USB port on the computer. Refer to the NI-DAQmx for USB
Devices Getting Started Guide that shipped with your device, and is also
accessible from Start»All Programs»National Instruments»NI-DAQ,
for more information.
LED Indicator
The NI USB-9421 device has a green LED next to the USB connector. The
LED indicator indicates device status, as listed in Table 1. When the device
is connected to a USB port, the LED blinks steadily to indicate that the
device is initialized and is receiving power from the connection.
If the LED is not blinking, it may mean that the device is not initialized or
the computer is in standby mode. In order for the device to be recognized,
the device must be connected to a computer that has NI-DAQmx installed
on it. If your device is not blinking, make sure your computer has the latest
version of NI-DAQmx installed on it, and the computer is not in standby
mode.
Threaded Insert
M3x 0.5
8.5 mm (0.34 in.) Max Depth
72.2 mm
(2.84 in.)
85.7 mm
(3.37 in.)
76.1 mm
(3.00 in.)

NI USB-9421 User Guide and Specifications 10 ni.com
Wiring the NI USB-9421 Device
Caution A high voltage screw terminal backshell must be installed when using hazardous
voltages (>42.4 Vpk, 60 VDC).
Note Table 2 illustrates the accessories available from ni.com for use with the
NI USB-9421.
Table 1. LED State/Device Status
LED State Device Status
Not lit Device not connected or in suspend.
On, not blinking Device connected, but no module installed.
Single-blink Operating normally.
Double-blink Operating normally.
Quadruple-blink Device error. Refer to ni.com/support.
Table 2. Accessories
Device Accessory Accessory Description
USB-9421 with Screw Terminal NI 9932 10-terminal, detachable, high
voltage, screw terminal backshell1
USB-9421 with 25-pin D-SUB NI 9934 25-pin D-SUB connector
1 For more information about installing the backshell, refer to the Assembling the High Voltage Screw Terminal Backshell
section.

©National Instruments Corporation 11 NI USB-9421 User Guide and Specifications
Each channel of the NI USB-9421 has a terminal or pin, DI, to which you
can connect voltage or current signals. The NI USB-9421 also has a
common terminal or pin, COM, that is internally connected to the isolated
reference of the module. Each digital input channel on the NI USB-9421
has an LED that indicates the state of that channel. Refer to Table 3 for the
terminal assignments of the NI USB-9421 with screw terminal. Refer to
Figure 7 for the pin assignments of the NI USB-9421 with D-SUB.
Table 3. Terminal Assignments
Module Terminal Signal
0DI0
1DI1
2DI2
3DI3
4DI4
5DI5
6DI6
7DI7
8No connection
9Common (COM)
0
1
2
3
4
5
6
7
8
9
03
47

NI USB-9421 User Guide and Specifications 12 ni.com
Figure 7. Pin Assignments
Connecting Devices to the NI USB-9421
The NI USB-9421 has sinking inputs, meaning that when current goes
through or voltage is applied to the DI terminal or pin, DI provides a path
to ground for the current or voltage. The NI USB-9421 internally limits
current signals connected to DI. For more information about input current
protection, refer to the Specifications section.
You can connect 2-, 3-, and 4-wire sourcing-output devices to the
NI USB-9421. A sourcing-output device drives current or applies voltage
to DI. An example of a sourcing-output device is a PNP open collector.
Connect the output of the sourcing-output device to DI on the
NI USB-9421. Connect the common of the external device to the COM
terminal or pin. Figure 8 shows a possible configuration.
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
03
47

©National Instruments Corporation 13 NI USB-9421 User Guide and Specifications
Figure 8. Connecting a Device to the NI USB-9421 (3-Wire Device Shown)
The NI USB-9421 channel registers as ON when the sourcing-output
device applies a voltage or drives a current to DI that is in the input ON
range. The channel registers as OFF when the device applies a voltage or
drives a current to DI that is in the input OFF range. If no device is
connected to DI, the channel registers as OFF. The channel LED turns on
and off to indicate the state of the channel. Refer to the Specifications
section for more information about ON and OFF ranges.
Assembling the High Voltage Screw Terminal Backshell
The NI 9932 high voltage screw terminal backshell must be installed when
using hazardous voltages (>42.4 Vpk, 60 VDC). Refer to Figure 9 while
completing the following steps to assemble the backshell:
1. Connect the leads to the screw terminal and secure with the strain
relief.
2. Finish by snapping the backshell around the connector.
Figure 9. High Voltage Screw Terminal Backshell
1 Strain Relief
NI USB-9421
+
_
Sourcing-Output
Device
COM
DI
External
Power
Supply
1

NI USB-9421 User Guide and Specifications 14 ni.com
Figure 10. Assembled High Voltage Screw Terminal Backshell
Specifications
The following specifications are typical for the range 0 to 60 °C unless
otherwise noted. All voltages are relative to COM unless otherwise noted.
Input Characteristics
Number of channels................................8
Input type................................................Sinking
Digital logic levels
OFF state
Input voltage.............................≤5V
Input current .............................≤300 μA
ON state
Input voltage.............................11 to 30 V
Input current .............................≥3mA
I/O protection
Input voltage....................................40 V max
Reverse biased voltage ....................–30 V max
Input current ....................................7 mA max, internally limited
Input delay time ......................................100 μs max
Power Requirements
Power consumption from USB...............500 mA, max
Suspend mode..................................2.5 mA, max

©National Instruments Corporation 15 NI USB-9421 User Guide and Specifications
Bus Interface
USB specification .................................. USB 2.0 Hi-Speed
Physical Characteristics
Dimensions
With screw terminal........................ 14.0 cm × 8.8 cm × 2.5 cm
(5.52 in. × 3.47 in. × 1.00 in.)
With 25-pin D-SUB ........................ 12.6 cm × 8.8 cm × 2.5 cm
(4.95 in. × 3.47 in. × 1.00 in.)
Screw-terminal wiring............................ 12 to 24 AWG copper conductor
wire with 10 mm (0.39 in.) of
insulation stripped from the end
Torque for screw terminals .................... 0.5 – 0.6 N · m (4.4 – 5.3 lb · in.)
Weight
With screw terminal........................ Approx. 250 g (8.8 oz)
With D-SUB ................................... Approx. 245 g (8.6 oz)
Safety
If you need to clean the module, wipe it with a dry towel.
Safety Voltages
NI USB-9421 with Screw Terminal Safety Voltages
Connect only voltages that are within these limits.
Channel-to-COM ................................... 30 V max
Isolation
Channel-to-channel......................... No isolation between channels
Channel-to-earth ground
Withstand................................. 2,300 Vrms, verified by a 5 second
dielectric withstand test
Continuous............................... 250 Vrms,
Measurement Category II
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).

NI USB-9421 User Guide and Specifications 16 ni.com
NI USB-9421 with D-SUB Safety Voltages
Channel-to-COM ....................................30 V max
Isolation
Channel-to-channel..........................No isolation between channels
Channel-to-earth ground
Withstand .................................1,000 Vrms, verified by a 5 second
dielectric withstand test
Continuous ...............................60 VDC,
Measurement Category I
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 equipment, limited-energy parts of equipment,
circuits powered by regulated low-voltage sources, and electronics.
Safety Standards
The NI USB-9421 is designed to meet the requirements of the following
standards of safety for electrical equipment for measurement, control,
and laboratory use:
• IEC 61010-1, EN-61010-1
• UL 61010-1, CSA 61010-1
Note For UL and other safety certifications, refer to the product label or visit
ni.com/certification, search by model number or product line, and click the
appropriate link in the Certification column.
Hazardous Locations
The NI USB-9421 is not certified for use in hazardous locations.
Environmental
The NI USB-9421 is intended for indoor use only.
Operating temperature
(IEC60068-2-1, IEC 60068-2-2) ............0 to 60 °C
Storage temperature
(IEC60068-2-1, IEC 60068-2-2) ............–40 to 85 °C

©National Instruments Corporation 17 NI USB-9421 User Guide and Specifications
Operating humidity
(IEC 60068-2-56)................................... 10 to 90% RH, noncondensing
Storage humidity
(IEC 60068-2-56)................................... 5 to 95% RH, noncondensing
Maximum altitude .................................. 2,000 m
Pollution Degree (IEC 60664) ............... 2
Electromagnetic Compatibility
This product is designed to meet the requirements of the following
standards of EMC for electrical equipment for measurement, control,
and laboratory use:
• EN 61326 EMC requirements; Minimum Immunity
• EN 55011 Emissions; Group 1, Class A
• CE, C-Tick, ICES, and FCC Part 15 Emissions; Class A
Note For EMC compliance, operate this device with double-shielded cables.
CE Compliance
This product meets the essential requirements of applicable European
Directives, as amended for CE marking, as follows:
• 2006/95/EC; Low-Voltage Directive (safety)
• 2004/108/EC; Electromagnetic Compatibility Directive (EMC)
Note Refer to the Declaration of Conformity (DoC) for this product for any additional
regulatory compliance information. To obtain the DoC for this product, visit
ni.com/certification, search by model number or product line, and click the
appropriate link in the Certification column.
Environmental Management
National Instruments is committed to designing and manufacturing
products in an environmentally responsible manner. NI recognizes that
eliminating certain hazardous substances from our products is beneficial
not only to the environment but also to NI customers.
For additional environmental information, refer to the NI and the
Environment Web page at ni.com/environment. This page contains the
environmental regulations and directives with which NI complies, as well
as other environmental information not included in this document.

National Instruments, NI, ni.com, and LabVIEW are trademarks of National Instruments Corporation.
Refer to the Terms of Use section on ni.com/legal for more information about 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, refer to the
appropriate location: Help»Patents in your software, the patents.txt file on your CD, or
ni.com/patents.
© 2005–2007 National Instruments Corporation. All rights reserved. 371606D-01 Dec07
Waste Electrical and Electronic Equipment (WEEE)
EU Customers At the end of their life cycle, all products must be sent to a WEEE recycling
center. For more information about WEEE recycling centers and National Instruments
WEEE initiatives, visit ni.com/environment/weee.htm.
Where to Go for Support
The National Instruments Web site 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.
National Instruments corporate headquarters is located at
11500 North Mopac Expressway, Austin, Texas, 78759-3504.
National Instruments also has offices located around the world to help
address your support needs. For telephone support in the United States,
create your service request at ni.com/support and follow the calling
instructions or dial 512 795 8248. For telephone support outside the United
States, contact your local branch office:
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