The National Instruments NI-9251 is a 2-channel Voltage Input Module designed for use with CompactRIO and CompactDAQ systems. Featuring mini XLR connectivity, this module facilitates low-distortion input that supports high dynamic range measurements necessary for testing and evaluating audio outputs. Unlike conventional sound-card based systems, the NI-9251 can be deployed rapidly, ensuring measurement repeatability and enhancing system efficiency. The module supports an update rate of up to 102.4 kS/s per channel, with a 3 Vrms input range and 24-bit resolution, making it ideal for precise audio analysis. Users can connect the NI-9251 to an NI-9260 through the mini XLR connector for a broader range of measurements typically associated with high-end audio analyzers. The differential input is established through AI+ and AI-, with its ground pin internally connected to chassis ground, allowing for connection of either ground differential or floating differential signals. Offering ±30 V overvoltage protection on both channels, the module features software-selectable AC/DC input coupling, maintaining maximum idle channel noise at approximately 8.5 μVrms. It operates with a single-ended input resistance of 2 MΩ and differential input resistance of 4 MΩ, alongside an input capacitance of 940 pF from the input pin to ground. The NI-9251 weighs 4.9 ounces and is backed by a comprehensive 2-3 year warranty, with user and maintenance manuals available for download. For pricing information, please consult a sales representative.