NI 9421 8-Channel 24 V Logic, 100 µs, Sinking Digital Input Module

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  • 12 to 24 V logic, sinking digital inputs
  • D-Sub or screw-terminal connector options
  • Hot-swappable operation
  • Extreme industrial certifications/ratings
  • -40 to 70 °C operating range
  • 8-channel, 100 µs digital input
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The National Instruments NI 9421 is an 8-channel, 100 µs sinking digital input module for any NI CompactDAQ or CompactRIO chassis. Each channel is compatible with 12 to 24 V signals and features transient overvoltage protection of 2,300 Vrms between the input channels and earth ground. Each channel also has an LED that indicates the state of that channel. The NI 9421 works with industrial logic levels and signals for direct connection to a wide array of industrial switches, transducers, and devices.

There are two connector options for the NI 9421 - a 10-position screw-terminal connector and a 25-position D-Sub connector. This industry-standard 25-position D-Sub connector provides for low-cost cabling to a wide variety of accessories available from NI or other vendors. A number of vendors with custom D-Sub cable fabrication services can deliver cables with a pinout that matches your exact application needs.

NI recommends the NI 9932 strain-relief connector accessory for the NI 9421 for screw-terminal connectivity and the NI 9934 accessory for 25-position D-Sub connectivity.

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Specifications Documents

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Specifications Summary

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NI 9421 Packages

To use the NI 9421 , you need all items in the diagram below. Select Option 1 if you already own a C Series System, or Option 2 if you do not already own a chassis, controller, or software.

Roll over the icons below to learn why you need each item in the system

C Series System

1 Connectivity Accessories

NI 9421




NI 9421 and Accessories Only
NI 9421 Module
- 779002-01 Qty $ 99 each
- 779136-01 Qty $ 99 each
- 779136-02 Qty $ 262 each
Required Accessories
Connectivity Accessories -
Qty $ 30 each
Optional Accessories
Connector Block
Qty $ 53 each
Qty $ 63 each

Package Price: $ 129

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Select a Platform and Configure a System

Create a complete system with the NI 9421 and its accessories. However, the NI 9421 is compatible with multiple C Series Platforms, NI CompactDAQ and CompactRIO. Please review the comparison information below and select a platform to begin configuring your system.

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NI CompactDAQ NI CompactRIO
Mixed-Measurement Data Acquisition

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Time-Critical Control & Monitoring

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Features NI CompactDAQ NI CompactRIO
USB, Wi-Fi, Ethernet, Headless Operation Ethernet, Headless Operation
Up to -40 to 70 C
Up to 50 g shock and 5 grms operational vibration
Up to -40 to 70 C
Up to 50 g shock and 5 grms operational vibration
LabVIEW, LabVIEW Real-Time, C, C++, VB.NET, C#.NET LabVIEW, LabVIEW Real-Time, LabVIEW FPGA, C, C++
NI-DAQmx driver; configuration and troubleshooting tools; short time to first measurement NI-RIO driver; flexibility and customizabilty
PC-based data acquisition; embedded data-logging; portable and benchtop Single-point acquisition; closed-loop control; deterministic operation

System Assurance Programs

Reduce your setup time and total cost of ownership, and get a system you can use out of the box with National Instruments system assurance programs. System assurance programs include:

  • Installation and integration test of all individual hardware
  • Courtesy installation of system driver sets and application development environments
  • Extended warranty and calibration coverage for up to five years
  • Custom documentation plus a custom restore and startup utility

This service is only available for PXI, NI CompactRIO, and NI Compact FieldPoint systems.

Extended Warranties

National Instruments designs and manufactures all products to minimize failures, however unexpected failures can still occur. Extended warranties provide a fixed economical price at the time of system purchase, covering any repair costs for up to three years. In addition, they offer the following benefits:

  • Significant cost savings compared to individual repair incidents
  • Fault location, diagnostics, and repair by NI any time the system product fails
  • All parts and labor costs covered as well as any adjustments needed to restore the hardware to manufacturing specifications

For more information about your warranty options:


NI recognizes the need to maintain properly calibrated devices for high-accuracy measurements. NI provides manual calibration procedures, services to recalibrate your products, and automated calibration software to calibrate many NI measurement products.


NI training is the fastest, most certain route to productivity with NI tools and successful application development.

Repair Services

Return your registered product under warranty at no additional labor and parts cost. NI offers fault location, diagnostics, and repair any time the system fails as well as any adjustments needed to restore the hardware to manufacturing specifications.

Technical Support

Additional Product Information

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