NI 9421 24 V, Sinking Digital Input, 8 Ch Module

Starting at $ 99 (view pricing options)
The NI 9421 is an 8-channel, 100 µs sinking digital input module for any NI CompactDAQ or CompactRIO chassis. Each channel is compatible with 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 to directly connect to a wide array of industrial switches, transducers, and devices.

You can choose from 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 from NI or other vendors. Some vendors with custom D-SUB cable fabrication services can deliver cables with pinouts that match your exact application needs.

Recommended Accessories
-NI 9924 or other 25-pin D-SUB connector (for D-SUB variant)
-NI 9927 strain relief and operator protection (for screw-terminal variant)

Optional Accessories
-NI 9936 extra screw-terminal block (qty 10)
-NI 9980 extra spring-terminal block (qty 10)
Note: The NI 9980 is not compatible with the NI 9927 and must be used with low or nonhazardous voltages or installed in a properly rated enclosure.

Box Contents
-1 NI 9421 C Series module
-1 NI 9421 Operating Instructions and Specifications manual
-1 NI 9936 10-position connector (for screw-terminal variant)

Specifications Documents

  • View Data Sheet

Specifications Summary


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
- 779002-01 Qty $ 99 each
- 779136-01 Qty $ 99 each
- 779136-02 Qty $ 267 each
- 783734-01 Qty $ 99 each
Required Accessories
Connectivity Accessories -
Qty $ 30 each
Optional Accessories
Connector Block
Qty $ 53 each

Subtotal: $ 129

Add to Cart
Guarantee your price for 30 days (learn more) Request Quote

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.

Configure System Configure System

NI CompactDAQ NI CompactRIO
Mixed-Measurement Data Acquisition

Learn more

Time-Critical Control & Monitoring

Learn more

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

Service Programs for Hardware

At NI, we produce high-performance hardware and are committed to helping you maintain that performance for years to come. Our three- or five-year service programs for hardware and systems provide the coverage you need while ensuring lowest total cost of ownership over the life of your system:

  • Get up and running faster with system assembly and configuration services
  • Operate on a fixed budget with prepaid repair and calibration services
  • Maintain peak performance with a discounted calibration plan
  • Simply call us to schedule your service—no budget approval needed

To learn more about service programs for hardware and systems, see

Technical Support

With the knowledge, experience, and responsiveness of NI applications engineers in more than 30 languages and 40 countries, we have the technical support resources to ensure your success. Through our standard NI technical support program, we can help you:

  • Consult on how to use NI products
  • Overcome development challenges
  • Quickly resolve issues pre- or post-deployment

To access NI technical support services for your hardware, visit

Training and Certification

With extensive training options for new and experienced users, we can help you reduce development time and costs through faster learning and increased productivity with your NI hardware and systems. Gain the skills you need to design and develop high-quality applications:

  • Learn recommended techniques to reduce development time and improve application performance and scalability
  • Leverage more than 40 training courses taught by NI and industry experts
  • Attend training in a variety of formats, including online, virtual, and classroom settings

To find training courses for your hardware, visit

Consulting and Integration

NI and the extensive network of NI Alliance Partners provide a wide range of professional services so that together, we can assist you with the design, development, and deployment of even the most complex systems. Take advantage of the team’s in-depth knowledge of NI products and applications with the following services:

  • Prototyping and feasibility analysis
  • Startup, consulting, and development assistance
  • System integration
  • Migration and upgrade assistance

For more information on NI professional services and the Alliance Partner Network, see