National Instruments NI-9421 8-channel sinking digital input module

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National Instruments · CompactDAQ / CompactRIO

NI-9421

The NI-9421 is an 8-channel C Series sinking digital input module for industrial 24 V signals, with a maximum input delay of 100 µs. Connector and isolation specifications depend on the hardware variant.

ManufacturerNational Instruments

ModelNI-9421

Product Type8-channel sinking digital input module

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Digital inputs8 sinking input channels

Logic levels12 V and 24 V

Input delay100 µs maximum

PlatformNI C Series for CompactDAQ and CompactRIO

Channel indicationIndividual input-state LEDs

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Overview

Product overview

Key product information and technical features.

The NI-9421 connects industrial switches, transducers and other digital devices to a modular NI measurement system. Its channels are sinking inputs rather than digital outputs or bidirectional I/O.

NI offers screw-terminal, spring-terminal and D-Sub versions. Their continuous channel-to-earth isolation ratings differ, so the module label and connector must be checked before selecting wiring accessories or applying safety limits.

Eight input-only channels with sinking current direction.
Supports industrial 12 V and 24 V digital logic levels.
An LED on each channel indicates its input state.
Channel-to-earth isolation, with the rating determined by connector variant.

Verified specifications

Technical data

Verified product specifications.

Digital input channels	8 channels
Input type	Sinking
Maximum input delay	100 µs
OFF-state input voltage	≤5 V
ON-state input voltage	11 to 30 V
Channel-to-COM safety voltage	30 maximum V
Channel-to-channel isolation	None
Continuous channel-to-earth isolation by variant	D-Sub: 60 VDC, CAT I; screw/spring terminal: 250 Vrms, CAT II
Connector options	25-pin D-Sub; 10-position screw terminal; 10-position spring terminal

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Compatibility

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National Instruments

Manufacturer

CompactDAQ / CompactRIO

Host chassis platforms

NI C Series

Modular I/O family

NI-9421

Sinking digital input module

Confirm the module part number and connector before choosing accessories or applying the variant-specific isolation rating.

Manuals & software

Technical resources

Manuals, software and technical resources for this model.

NI-9421 Official Product PageProduct Page · ni.com

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NI 9421 DatasheetDatasheet · download.ni.com

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NI-9421 Dimensional DrawingsDimensional Drawings And CAD Models · ni.com

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C Series Hardware and LabVIEW CompatibilityTechnical resource

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FAQ

Product-specific questions

Product-specific answers based on available technical information.

Can the NI-9421 drive digital outputs?

No. It has eight digital input-only channels, with no digital output or bidirectional channels.

Is part number 779002-01 the D-Sub version?

No. NI identifies 779002-01 as the screw-terminal version. The non-conformal-coated D-Sub version is 779136-01. This catalog record has conflicting variant information, so its exact connector requires confirmation.

Are the digital inputs isolated from one another?

No. The datasheet specifies no channel-to-channel isolation. Channel-to-earth isolation is provided, with different continuous ratings for D-Sub and terminal versions.