National Instruments PXIe-4844 optical sensor interrogator

The NI PXIe-4844 optical sensor interrogator is a two-slot 3U PXI Express module for fibre Bragg grating (FBG) sensors. FBG sensors operate by reflecting a wavelength of light that corresponds to changes in physical phenomena such as strain and temperature.

The transmission medium is standard optic fibre instead of copper wire, making it possible to take measurements over distances of up to 10 km. FBG sensors can be used for the most common measurement types, including strain, temperature and pressure, and several sensors can be daisy chained along a single optic fibre to greatly reduce the size, weight and complexity of the measurement system.

The NI PXIe-4844 features four optical channels that are simultaneously scanned at 10 Hz. Each channel has an 80 nm wavelength range (1510 to 1590 nm), which can scan 20 or more FBG sensors per channel (more than 80 FBG sensors per module, depending on the sensor range).

The module also features an optical core that combines a high-power, low-noise swept wavelength laser with fibre Fabry-Perot tuneable filter technology. The module delivers a wavelength accuracy, repeatability and stability of 1 pm, which is equivalent to sensor accuracies of approximately 1.2 microstrain and 0.1°C for FBG strain and temperature sensors, respectively. Unlike most instruments, the interrogator does not require periodic external calibration as every scan is calibrated to an onboard NIST-traceable wavelength reference.

Applications that can benefit from the module include distributed measurements over long distances including bridges, dams and tunnels; energy, for monitoring wind turbine blades, pipelines, offshore platforms and power generators; and in transportation.