National Instruments USB-6251

The National Instruments USB-6251 is a USB-based multifunction data acquisition device delivering high-performance analog input, analog output, digital I/O, and counter/timer capabilities. This compact M Series DAQ integrates with laptops and portable computing platforms for laboratory automation, research, design verification, manufacturing test, and industrial automation. The device operates via NI-DAQmx driver software and National Instruments programming environments. Note: This device is obsolete but may be available from third-party suppliers.

– Technical Specifications

Analog Inputs
• 8 differential or 16 single-ended channels
• 16-bit resolution
• Sampling rate: 1.25 MS/s (single channel), 1.00 MS/s (aggregate)
• Input ranges: ±0.1 V to ±10 V (selectable)
• Maximum working voltage: ±11 V referenced to AI GND
• Input impedance: >10 GΩ || 100 pF (device on); 820 Ω (device off)
• CMRR (DC to 60 Hz): 100 dB
• Timing accuracy: 50 ppm; timing resolution: 50 ns
• Overvoltage protection: ±25 V (on, four pins), ±15 V (off, four pins)
• Input bias current: ±100 pA
• Crosstalk: –75 dB (adjacent channels), –95 dB (non-adjacent) at 100 kHz
• Small signal bandwidth (–3 dB): 1.7 MHz
• Input FIFO: 4,095 samples; scan list memory: 4,095 entries
• Absolute accuracy (10 V range): 1,920 µV

Analog Outputs
• 2 channels, 16-bit resolution
• Update rate: 2.86 MS/s (single channel), 2.00 MS/s per channel (dual)
• Output ranges: ±5 V, ±10 V
• Output current drive: ±5 mA

Digital I/O
• 24 programmable lines (inputs or outputs)
• 8 clocked lines

Counters/Timers
• 2 × 32-bit counters/timers with 80 MHz timebase
• 2 × 32-bit PWM outputs
• 2 quadrature encoder inputs (32-bit)

Electrical
• Warm-up time: 30 minutes
• Data transfer: DMA (scatter-gather), interrupts, programmed I/O

– Key Features

• High input impedance (>10 GΩ) minimizes loading effects
• Excellent CMRR (100 dB) for noise rejection
• Wide selectable input ranges support precision measurement and signal conditioning
• Dual PWM and quadrature encoder support enable motor control and position feedback
• 4,095-sample input FIFO reduces software overhead

– Typical Applications

• Laboratory instrumentation and automated test systems
• Research data acquisition and signal analysis
• Manufacturing process monitoring and verification
• Industrial automation and machine control
• Sensor interface and signal conditioning

– Compatibility & Integration

NI-DAQmx driver compatibility enables integration with LabVIEW, C/C++, .NET, and Python development environments. USB connectivity provides plug-and-play operation on standard computing platforms.