PCI‑6251 | Product Introduction

The NI PCI‑6251 is a high-speed multi-function DAQ card (with 2 channels of AO, no isolation) from the M series of National Instruments (NI), based on PCI bus, half-length card, featuring:

16 channels of AI (16 bit/1.25 MS/s) + 2 channels of AO + 24 channels of DIO + 2 channels of countersNI

Suitable for high-speed acquisition in laboratories, small-scale closed-loop control, environments without strong interference, and test systems requiring analog output.

Part number: 779512‑01; discontinued (EOL), replacement model PCIe‑6351NI.

I. Basic Information

Model: PCI‑6251

Brand: National Instruments (NI)

Series: M-Series (high-speed, with AO, non-isolated)

Bus: PCI (3.3 V / 5 V compatible, half-length card)

Connector: 68-pin SCSI-II

Driver: NI-DAQmx

Operating Temperature: 0 ~ 55 °C

Isolation: No isolation (non-isolated type)

II. Analog Input AI (16 channels, high-speed)

Channels: 16 single-ended / 8 differential (software configurable) NI

Resolution: 16 bits, no bit loss guarantee NI

Maximum Sampling Rate: 1.25 MS/s (single channel); 1 MS/s (total of multiple channels) NI

Input Range (software selectable): ±0.1 V, ±0.2 V, ±0.5 V, ±1 V, ±2 V, ±5 V, ±10 V NI

Coupling: DC

Input Impedance: >10 GΩ || 100 pF

Maximum Working Voltage: ±11 V

CMRR: 95 dB @ DC~60 Hz

Input FIFO: 8,191 samples

III. Analog Output AO (2 channels)

Channels: 2 voltage output NI

Resolution: 16 bits NI

Maximum Update Rate: 2.8 MS/s (per channel) NI

Output Range: ±5 V, ±10 V (software selectable)

Drive Capacity: ±5 mA (per channel)

Setup Time: 10 µs (to ±0.5 LSB)

Load: Minimum 1 kΩ

IV. Digital I/O (DIO, 24 channels)

Channels: 24 bidirectional TTL (non-isolated) NI

Level: 5 V TTL/CMOS (compatible with 3.3 V)

Maximum Rate: 10 MHz

DO Drive: Maximum 10 mA/channel

Function: bidirectional input/output, event triggering, handshake signal

V. Counter / Timer

Channels: 2 32-bit general-purpose counters NI

Clock: 80 MHz internal base

Function: event counting, frequency / period measurement, pulse output, encoder, PWM

VI. Trigger and Synchronization

Trigger: AI analog trigger, PFI external digital trigger

Synchronization: RTSI multi-card synchronization

Data Transfer: DMA, interrupt, programmable I/O

VII. Installation and Usage Tips Installation

Power off and disconnect, insert into the standard PCI slot, secure the retaining screws; after powering on, MAX will recognize and self-check.

Cabling (68-pin SCSI-II)

AI: Single-ended AIn + GND; Differential AI+/AI−, common mode ≤ ±11 V, no isolation against ground loop.

AO: AO + AGND, load ≥ 1 kΩ,严禁 short circuit.

DIO： TTL common ground， avoid long-distance parallel lines； PFI used as trigger / clock.

Software configuration (NI-DAQmx)

Sampling： High-speed synchronous scanning

Range： Weak signal priority ±0.1 V / ±0.2 V

Trigger： Common edge trigger (rising / falling) Notes for Attention

No isolation, not suitable for strong industrial interference / high voltage.

AI input must not exceed ±11 V, AO must not be short-circuited.

VIII. Core Features

16 high-speed AI (1.25 MS/s/16 bit) + 2 AO + 24 DIO + 2 counters NI

PCI half-length card, NI-DAQmx driver stable

With analog output, suitable for closed-loop control and signal generation

Applicable: high-speed acquisition in the laboratory, small-scale control, test systems requiring AO