NI PCI-4451

Analog Input (AI)

• Channel Count: 2 true differential synchronous sampling channels
• ADC Resolution: 16-bit delta-sigma converter, 128x oversampling
• Sampling Rate Range: 5 kS/s to 204.8 kS/s, adjustable in 190.735 µS/s increments
• Input Voltage Ranges (Software Selectable Gain): ±42.4 V (-20 dB), ±31.6 V (-10 dB), ±10 V (0 dB), ±3.16 V (+10 dB), ±1 V (+20 dB)
• Anti-Aliasing Bandwidth: 45 kHz
• Inter-Channel Crosstalk: < -90 dB
• Dynamic Range: 114 dB

Analog Output (AO)

• Channel Count: 2 differential synchronous output channels
• DAC Resolution: 16-bit delta-sigma modulator with 8x interpolation oversampling
• Update Rate Range: 1.25 kS/s to 51.2 kS/s
• Programmable Output Attenuation: 0 dB, -20 dB, -40 dB
• Amplitude Flatness: ±0.2 dB from DC to 23 kHz
• Total Harmonic Distortion (THD): -90 dB at 1 kHz

Timing & Clock

• Internal Timebase Accuracy: ±100 ppm at 25 °C
• Multi-Board Synchronization: RTSI bus support for phase-locked multi-card acquisition

1.4 Functional Features

1. Simultaneous AI/AO operation for closed-loop frequency response testing
2. True differential input architecture eliminates common-mode industrial noise
3. Built-in analog + digital anti-imaging filters on output channels to suppress spurious harmonics
4. Software-selectable AC/DC input coupling for low-frequency static and high-frequency dynamic signals
5. Multi-level programmable gain to match microphones, IEPE accelerometers and voltage transducers
6. Self-calibration routine to correct offset and gain drift over temperature changes
7. Full NI-DAQmx driver support with LabVIEW, Python, C/C++ programming APIs

1.5 Application Scenarios

• Acoustic noise measurement for household appliances, automotive interiors
• Mechanical vibration testing of motors, bearings, gearboxes
• Frequency response analysis of speakers, sensors, structural components
• Audio equipment distortion and noise performance verification
• Small-scale wind tunnel dynamic pressure signal acquisition

1.6 Performance Parameters (Typical at 25°C)

• Input Noise Floor: < 1.2 µV RMS at maximum gain
• Settling Time: < 1 µs for full-scale voltage step
• Operating Temperature Range: 0 °C to 55 °C
• Storage Temperature: -40 °C to 85 °C
• Power Consumption: 18.2 W peak

1.7 Material & Construction Composition

• Main Substrate: FR-4 fire-retardant printed circuit board with copper trace shielding layers
• Signal Processing ICs: Multi-channel delta-sigma ADC/DAC chips, low-noise operational amplifiers, FPGA timing controller
• Front Panel Connector: Shielded D-SUB multi-pin metal connector with EMI gasket
• Mechanical Bracket: Cold-rolled steel PCI full-height retention bracket with corrosion-resistant zinc plating
• Passive Components: Low-temperature-drift metal film resistors, polypropylene low-noise signal capacitors

1.8 Structural Characteristics

• Form Factor: Standard full-length PCI bus board (32-bit PCI 33 MHz)
• Physical Dimensions: 10.6 cm width × 17.5 cm length
• Layout Design: Isolated analog and digital PCB zones separated by ground guard rings to minimize digital switching noise leakage to analog signal paths
• Thermal Layout: Copper thermal vias under high-power FPGA and ADC chips for passive heat dissipation
• EMI Suppression: Full perimeter copper ground shielding around all analog signal traces

1.9 Working Principle

1. Signal Input Stage: External transducer analog voltage enters true differential input buffer; software-controlled gain amplifies weak sensor signals, with AC/DC coupling capacitor network to block DC offset when required
2. Analog-to-Digital Conversion: Delta-sigma ADC samples analog input at oversampled high frequency, filters quantization noise to high-frequency bands, then decimates data to user-defined sampling rate for digital signal processing
3. Digital Timing & Synchronization: Onboard FPGA generates precise sample clock, trigger signals and RTSI synchronization pulses; FPGA buffers digitized waveform data before PCI bus data transfer to host PC memory
4. Digital-to-Analog Conversion: Host PC uploads arbitrary waveform data to onboard FIFO memory; delta-sigma DAC interpolates low-rate waveform data with digital filters, converts digital samples back to continuous analog voltage for stimulus output
5. Closed-Loop Measurement Logic: Synchronized input sampling and output waveform generation enable simultaneous stimulus injection and response capture for transfer function calculation

1.10 Installation Requirements

1. Host PC Slot: Unoccupied full-length 32-bit PCI expansion slot; PC chassis must support forced air cooling to maintain operating temperature limits
2. System Pre-Warm-Up: Power on host PC and allow 15 minutes of warm-up time before precision measurement to reach rated accuracy specifications
3. Mechanical Installation: Remove chassis slot blank plate; align PCI board edge connector with motherboard PCI slot; fully seat connector, fasten steel retention bracket screw to chassis frame
4. Wiring Installation: Use shielded twisted-pair cable for all analog signal connections; connect cable shield to front panel D-SUB metal shell to establish EMI ground reference
5. Software Installation: Install NI-DAQmx driver suite matching operating system; launch NI MAX configuration utility to detect PCI-4451 hardware and complete self-calibration

1.11 Operation Precautions

1. Voltage Input Protection: Do not apply input voltage exceeding ±42.4 V peak; overvoltage will permanently damage front-end amplifier circuits
2. ESD Handling: Wear grounded anti-static wristband before touching PCB or connectors; static discharge destroys sensitive ADC/DAC chips
3. Cooling Maintenance: Never operate the board with PC chassis side panel removed; insufficient airflow causes thermal drift and automatic measurement inaccuracy
4. Cable Management: Separate analog signal cables from power supply, motor drive and digital control wiring to avoid electromagnetic interference
5. Calibration Cycle: Execute self-calibration every 30 days of continuous operation; perform full external calibration annually with NI certified reference signal sources
6. Storage Rules: When not installed in host PC, store PCI board in original anti-static packaging at room temperature; avoid high-humidity and dusty storage environments