Product Overview
The National Instruments NI 9235 is an 8 channel, 24 bit analog input module for CompactDAQ and CompactRIO systems. It is specifically designed for quarter bridge strain gauge measurements. The module includes built in bridge completion and excitation, which simplifies wiring and reduces the number of external components required for strain measurement.
The NI 9235 is part of the NI C Series platform, which provides modular signal conditioning for data acquisition and control systems. Each channel is optimized for low level bridge measurements, making the module suitable for structural test, fatigue analysis, stress measurement, and mechanical validation. The compact form factor allows many channels to be added to a single chassis.
Quarter Bridge Measurement
A quarter bridge configuration uses one active strain gauge and three fixed resistors to complete the bridge. The NI 9235 provides 120 ohm quarter bridge completion internally, which is a common resistance value for strain gauges. This internal completion reduces wiring complexity and helps maintain consistent bridge balance across channels.
The module supplies built in excitation for the bridge, so external excitation supplies are not required for basic strain measurements. This integrated signal conditioning approach is useful in dynamic test environments where many strain gauges must be connected quickly and reliably. The module is intended for quarter bridge sensors and should be paired with the appropriate gauge configuration for the measurement task.
Resolution and Sampling
The NI 9235 provides 24 bit analog input resolution, which supports fine measurement of small bridge output signals. Each channel can sample at up to 10 kS/s, allowing simultaneous capture of dynamic strain events across eight channels. The high resolution and per channel sampling rate make the module suitable for both static and dynamic strain measurements.
Low noise input circuitry and anti alias filtering help preserve signal quality in mechanical test setups. The module is designed to work with small millivolt level signals from strain gauges, so careful wiring and shielding are important for best results. TEDS support can help identify sensors and reduce setup errors when used with compatible strain gauges.
Isolation and Signal Integrity
The NI 9235 includes isolation between the input channels and the backplane, which helps protect the system from ground loops and common mode voltages present in industrial and mechanical test environments. Isolation is important when strain gauges are mounted on large structures, machines, or test articles that may have different ground potentials.
The module is built for reliable operation in CompactDAQ and CompactRIO chassis. It supports the timing and synchronization features of the C Series platform, allowing strain data to be correlated with other analog inputs, digital signals, and control outputs. This is useful in multi sensor tests where strain must be compared with load, displacement, acceleration, or temperature.
Software and System Integration
The NI 9235 is supported by NI-DAQmx driver software. It can be programmed with LabVIEW, LabWindows/CVI, Measurement Studio, and other development environments that support NI-DAQmx. Engineers can configure channels, set sampling rates, enable TEDS, and apply scaling for strain measurements through standard software tools.
The module can be used in CompactDAQ systems for portable or bench top data acquisition, and in CompactRIO systems for embedded monitoring and control. Because it is a C Series module, it can be mixed with other analog input, analog output, digital input and output, and counter modules in the same chassis. This modularity supports flexible system design and future expansion.
Typical Applications
Quarter bridge strain gauge measurement on metal and composite structures
Fatigue testing and durability test benches
Stress analysis in mechanical components and assemblies
Structural health monitoring and load frame instrumentation
Dynamic strain capture alongside acceleration, load, and displacement sensors
The NI 9235 provides a compact and integrated solution for eight channel quarter bridge strain measurement. Its 24 bit resolution, 10 kS/s per channel sampling, built in 120 ohm bridge completion, and C Series integration make it a practical module for mechanical test and measurement systems.
