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National Instruments PXI-6521 Isolated digital I/O module with mechanical relay outputs
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National Instruments · PXI

PXI-6521

The NI PXI-6521 is an industrial PXI digital I/O module combining eight isolated ±30 VDC inputs with eight non-latching mechanical relay outputs.

ManufacturerNational Instruments
ModelPXI-6521
Part Number779313-01
Product TypeIsolated digital I/O module with mechanical relay outputs
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Digital inputs8 bipolar, optically isolated channels
Input range−30 to +30 VDC differential
Relay outputs8: three Form C and five Form A
Signal connectionKeyed 37-pin male D-SUB
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Overview

Product overview

Key product information and technical features.

The PXI-6521 brings isolated industrial digital I/O to the PXI platform. Its inputs support sinking and sourcing signals at standard industrial 24 V logic levels.

Relay contacts switch externally powered circuits rather than supplying an output voltage. Form C channels provide normally open and normally closed contacts; Form A channels provide normally open contacts.

  • Channel-isolated inputs accommodate bipolar DC signals.
  • Programmable power-up states establish initial relay settings.
  • Digital filtering and change detection support input monitoring.
  • A configurable watchdog can move outputs to user-defined states following a communication timeout while board power remains present.
Verified specifications

Technical data

Verified product specifications.

Digital channel count16: 8 inputs and 8 relay outputs channels
Input differential voltage range−30 to +30 VDC
Input channel-to-channel isolation60 continuous VDC
Input channel-to-bus isolation150 continuous V
Relay configuration3 non-latching SPDT (Form C); 5 non-latching SPST (Form A)
Maximum relay switching voltage150 VAC or 150 VDC, Category II
Maximum relay current per channel2; subject to switching-power limit, external chassis ambient up to 55 °C A
Maximum relay switching power60 W / 60 VA
Signal connector37-pin keyed male D-SUB
Condition & included items

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Compatibility

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National Instruments

Manufacturer

PXI

Modular instrumentation platform

PXI-6521

Industrial isolated digital I/O and relay module

Connection requirement

Use the special keyed cables and accessories specified for NI 6521 devices.

Observe voltage, current, and switching-power limits together. Follow NI's hazardous-voltage wiring and PXI filler-panel requirements.
Manuals & software

Technical resources

Manuals, software and technical resources for this model.

NI PXI-6521 Product PageProduct Page · ni.com
Open →
NI 6521 SpecificationsSpecifications PDF · docs-be.ni.com
Open →
NI 6520/6521 User GuideUser Guide PDF · download.ni.com
Open →
NI 650x/651x/652x Cable and Accessory Compatibility GuideTechnical resource
Open →
Shipping, warranty & returns

Commercial terms

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Warranty
30-Day Warranty. Standard coverage applies.
Returns
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FAQ

Product-specific questions

Product-specific answers based on available technical information.

Does the PXI-6521 provide powered digital outputs?

Its outputs are electromechanical relay contacts that switch an external circuit. They do not supply the circuit's operating voltage.

Can it switch 150 V at 2 A?

Not simultaneously within the specified switching-power rating. The 150 V and 2 A maxima are constrained by the 60 W/60 VA switching-power limit.

Can an ordinary 37-pin D-SUB accessory be used?

Do not assume compatibility from pin count alone. NI requires special keyed cables and accessories for the PXI-6521.

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