National Instruments NI-9251 C Series Voltage Input Module

The National Instruments NI-9251 (Part number: 783814-01) is a 2-Channel Voltage Input Module from the C Series. This model comes featured with mini XLR connectivity- a low-distortion input channel that offers high dynamic range measurements required in the testing and evaluation of modern audio outputs. Unlike other sound-card based systems, the National Instruments NI-9251 can be deployed quickly to ensure long-term measurement repeatability and improved test system uptime. For a better low-noise performance, the differential input in the NI 9251 is provided through a mini XLR connector.

This Voltage Input Module is designed for CompactRIO and CompactDAQ systems, offering up to 102.4 kS/s update rate, 3 Vrms input range, and 24-bit resolution. Coupling the NI-9251 with an NI-9260 through the mini XLR connector will allow users to perform a comprehensive range of measurements typically done through expensive, high-end audio analyzers. This module measures signals on AI+ with respect to AI- and its ground pin is internally connected to chassis ground. The AI+ and AI- come with a 2 MΩ resistor, also connected to chassis ground. Thus, users can connect either a ground differential signal or a floating differential signal to the input.

 The National Instruments NI-9251 module offers ±30 V overvoltage protection on both of its channels. This device offers software-selectable AC/DC input coupling and controls the maximum idle channel noise around 8.5 μVrms.  In addition, this module operates with 2 MΩ single ended and 4 MΩ differential input resistance and 940 pF input capacitance from the input pin to ground.