Description
1. Detailed Parameter Table
| Parameter Name | Parameter Value |
| Product Model | PXI-6251 |
| Manufacturer | National Instruments (NI) |
| Product Category | Multifunction Data Acquisition Module |
| Analog Input Channels | 16 single-ended / 8 differential |
| Analog Input Resolution | 16-bit |
| Analog Input Ranges | ±10 V, ±5 V, ±2.5 V, ±1 V, ±0.5 V, ±0.25 V, ±0.1 V, ±0.05 V |
| Maximum Sampling Rate | 1.25 MS/s (single channel), 1.25 MS/s (multichannel, with channel scanning) |
| Analog Output Channels | 2 |
| Analog Output Resolution | 16-bit |
| Analog Output Ranges | ±10 V |
| Analog Output Update Rate | 2.86 MS/s |
| Digital I/O Lines | 24 lines (configurable as input or output) |
| Counter/Timers | 24-bit, 80 MHz (2 counters) |
| Triggering | Analog and digital triggering; support for PXI trigger lines |
| DMA Channels | 3 |
| FIFO Buffer Size | 8 kS (analog input), 2 kS (analog output) |
| Connector Type | 68-pin VHDCI |
| Operating Temperature Range | 0 to 55 °C |
| Storage Temperature Range | -20 to 70 °C |
| Humidity Range | 5 to 95% non-condensing |
| Power Consumption | 4.5 W typical |
| Software Compatibility | LabVIEW, LabWindows/CVI, Measurement Studio, Visual Studio (C/C++, C#) |
NI PXI-6251
2. Product Introduction
The NI PXI-6251 is a high-performance multifunction data acquisition (DAQ) module designed for the PXI platform, offering a comprehensive set of features for analog input/output, digital I/O, and counter/timer operations. It is well-suited for a wide range of applications, from industrial monitoring and control to laboratory research and automated testing.
With 16 single-ended or 8 differential analog input channels, the PXI-6251 provides flexible connectivity to various sensors and signal sources. Its 16-bit resolution ensures accurate measurement of small signal variations, while the maximum sampling rate of 1.25 MS/s enables capture of fast-changing signals. The module also includes 2 analog output channels with 16-bit resolution and a 2.86 MS/s update rate, allowing for precise generation of control signals or waveforms.
The 24 digital I/O lines and 2 high-speed counter/timers add to the module’s versatility, making it capable of handling digital control tasks, event counting, and timing measurements. Integration with PXI trigger lines ensures seamless synchronization with other modules in a PXI system, enhancing its suitability for complex multi-module setups.
3. Core Advantages and Technical Highlights
High-Speed Sampling for Dynamic Signals
The PXI-6251’s 1.25 MS/s sampling rate (single channel) enables accurate capture of high-frequency signals, such as those encountered in vibration analysis or power electronics testing. For example, in monitoring the output of a switching power supply, the module can sample the voltage and current waveforms at a high rate to analyze transient behavior and ensure compliance with efficiency standards.
Versatile Analog Input Ranges
With 8 selectable input ranges (from ±0.05 V to ±10 V), the PXI-6251 can accommodate signals of varying amplitudes, eliminating the need for external signal conditioning in many cases. This flexibility is valuable in applications where sensor outputs vary widely, such as in environmental monitoring where temperature sensors may produce millivolt-level signals and pressure transducers generate volt-level signals.
Comprehensive I/O Capabilities
The combination of analog I/O, digital I/O, and counter/timers in a single module reduces the need for multiple specialized modules, saving space in the PXI chassis and simplifying system integration. In an automated test system, for instance, the PXI-6251 can handle analog measurements of device under test (DUT) outputs, generate analog stimuli via its output channels, control test fixtures using digital I/O, and count pulses from encoders to track DUT position—all in one compact module.
Robust Synchronization
Support for PXI trigger lines allows the PXI-6251 to synchronize with other PXI modules, such as signal generators or oscilloscopes, ensuring time-aligned data acquisition and control. In a multi-channel acoustic testing setup, this synchronization ensures that signals from multiple microphones are captured simultaneously, enabling accurate analysis of sound propagation and localization.
4. Typical Application Scenarios
Industrial Process Monitoring
In manufacturing plants, the PXI-6251 is used to monitor critical process parameters such as temperature, pressure, flow rate, and vibration. For example, in a chemical plant, it can continuously measure the temperature and pressure of reaction vessels via thermocouples and pressure transducers, providing real-time data to a control system that adjusts heating or cooling to maintain optimal conditions. The module’s digital I/O lines can also interface with relays to trigger alarms or shut down processes if parameters exceed safe limits.
Automated Test Equipment (ATE)
The PXI-6251 is a key component in ATE systems for electronics manufacturing, where it performs functional and parametric testing of components and assemblies. It can generate analog test signals (e.g., voltage ramps or sine waves) to stimulate DUTs, measure the DUT responses via its analog inputs, and use digital I/O to control test fixtures or read status indicators. In testing printed circuit boards (PCBs), the module can verify the functionality of analog circuits, such as amplifiers or filters, by measuring their gain, frequency response, and distortion.
Academic and Scientific Research
Research laboratories utilize the PXI-6251 for a wide range of experiments, from biomechanics to materials science. In a biomechanics lab, it can measure muscle activity (EMG signals) via surface electrodes and joint angles via potentiometers, providing data to study human movement. In materials testing, the module can monitor strain and stress in samples under load, helping researchers characterize material properties such as elasticity and strength.
Automotive Testing
In automotive engineering, the PXI-6251 is used to test vehicle components and systems. It can measure signals from sensors in engine control units (ECUs), such as throttle position and oxygen sensor outputs, to evaluate engine performance. The module’s counter/timers can track the rotation speed of shafts or wheels, while its analog outputs can simulate sensor signals to test ECU response. This makes it valuable for validating the functionality of automotive electronics during development.
NI PXI-6251
5. Related Model Recommendations
PXI Chassis
The PXI-6251 is designed to operate in PXI chassis such as the PXI-1042 (18-slot) or PXI-1031 (3-slot). These chassis provide power, cooling, and a high-speed backplane for communication with a PXI controller (e.g., PXI-8106). The PXI-1042 is suitable for large-scale test systems with multiple modules, while the PXI-1031 is ideal for compact setups or portable applications.
Signal Conditioning Modules
For applications requiring signal conditioning, pair the PXI-6251 with modules like the SCXI-1125 (isolated analog input conditioning) or SCXI-1102B (thermocouple conditioning). These modules amplify, filter, and isolate signals from sensors, ensuring compatibility with the PXI-6251’s input ranges and improving measurement accuracy in noisy environments.
Controllers
A PXI controller such as the PXI-8106 (embedded controller) or PXI-8360 (remote controller) is required to operate the PXI-6251. The controller runs software to configure the module, acquire data, and process results. For real-time applications, the PXI-8106 with LabVIEW Real-Time provides deterministic control and data processing.
Cables and Accessories
The PXI-6251 uses a 68-pin VHDCI connector, requiring cables like the NI SHC68-68-EPM (shielded cable) for connecting to sensors or signal conditioning modules. Terminal blocks such as the TB-2706 provide a convenient way to terminate field wires, simplifying wiring in industrial installations.
6. Installation, Commissioning and Maintenance Instructions
Installation Preparation
Power off the PXI chassis before installing the PXI-6251. Use an anti-static wristband to prevent electrostatic discharge (ESD) damage. Align the module with the guide rails in an available PXI slot and gently insert it until fully seated. Secure the module with front panel screws. Connect sensors or signal sources to the module using a compatible cable and terminal block, ensuring proper wiring of analog inputs, outputs, and digital lines.
Commissioning Steps
Power on the chassis and launch NI MAX to detect the PXI-6251. Install the latest NI-DAQmx driver software to ensure compatibility with programming environments. Configure the module’s channels (input ranges, single-ended/differential mode) via NI MAX or software. Calibrate the module using NI’s calibration utility to verify measurement accuracy—use a precision signal generator or DMM to apply known signals and confirm readings are within tolerance. Test the module with a sample application (e.g., a LabVIEW VI) to validate analog input/output, digital I/O, and counter functionality.
Maintenance Suggestions
Regularly inspect the module for loose connections, dust buildup, or physical damage. Clean the module’s connectors and vents with compressed air to prevent overheating. Check calibration annually using traceable standards to maintain measurement accuracy. If signal noise is detected, verify grounding and shielding of cables, and ensure sensor connections are secure. For persistent issues, refer to the user manual or contact NI technical support for troubleshooting assistance.
7. Service and Guarantee Commitment
NI provides a 3-year standard warranty for the PXI-6251, covering defects in materials and workmanship. During the warranty period, NI offers free repairs or replacements for qualifying issues. Technical support is available via online resources (knowledgebase, forums), email, and phone, with experts assisting in installation, configuration, and software integration. For out-of-warranty modules, NI offers repair and calibration services to extend operational life. With a focus on reliability, the PXI-6251 is backed by NI’s global service network, ensuring users receive timely support for their data acquisition needs.
