NI Strain Gauge Modules

NI strain gauge modules turn the small electrical changes produced by strained sensors into usable measurement data. A strain gauge changes resistance as a material stretches or compresses; a Wheatstone bridge converts that change into a voltage signal. National Instruments bridge input modules combine measurement circuitry with features such as excitation, amplification, filtering, and bridge completion. Applications include aircraft component testing, fatigue analysis, structural monitoring, load measurement, and machinery validation.

The NI C Series offers compact options for compatible CompactDAQ and CompactRIO systems. The NI-9235, part number 785995-01, provides eight simultaneous channels for 120-ohm quarter-bridge gauges. The NI-9236, available under part numbers including 785996-01 and 779994-02, targets 350-ohm quarter-bridge gauges. Both modules offer 24-bit conversion and sampling up to 10 kS/s per channel, helping engineers capture changing strain across multiple measurement locations without multiplexing between channels.

For more flexible bridge configurations, the NI-9237 provides four simultaneous channels with 24-bit resolution and sampling up to 50 kS/s per channel. It supports half-bridge and full-bridge sensors directly, making it useful for compatible load cells, torque sensors, and pressure transducers. Quarter-bridge measurements require external completion. Connector variants include the RJ50 version, part number 779521-01, and the D-SUB version, part number 780264-01. Accessories and wiring must match the specific variant.

On the RJ50 NI-9237, NI-9944 accessories provide 120-ohm quarter-bridge completion, while NI-9945 accessories provide 350-ohm completion. These accessories complete the electrical bridge; they do not replace the need to enter the correct sensor parameters or verify the complete measurement chain before recording test results.

NI SC Express modules serve systems built around PXI Express. The PXIe-4330, part number 781346-01, offers eight simultaneous channels at up to 25.6 kS/s per channel. The PXIe-4331, part number 781345-01, increases the maximum rate to 102.4 kS/s per channel. Both feature 24-bit conversion, quarter-, half-, and full-bridge configurations, programmable excitation per channel, remote sensing, and shunt calibration. Their integrated conditioning reduces the need for separate external conditioning equipment.

Selecting a module starts with the sensor rather than the channel count alone. Check nominal gauge resistance, bridge configuration, excitation requirements, signal range, and measurement bandwidth. Excessive excitation can heat the gauge and introduce measurement error. Cable resistance, grounding, and shielding also matter because bridge outputs are small. Configure gauge factor and scaling correctly, then perform offset nulling and appropriate shunt calibration before collecting test data.

Software compatibility is equally important when expanding an established installation. CompactDAQ and SC Express applications commonly use NI-DAQmx, while CompactRIO programming depends on the controller and supported operating mode. Verify the module, chassis, driver, and application versions together. For replacement hardware, provide Apex Waves with the model, complete part number, connector requirements, and calibration needs to help identify a suitable match for your existing strain measurement system.