The aim of the MiniBRAGG project was to develop, test and manufacture a miniaturised acquisition unit for Fiber Bragg Grating (FBG) optical sensors to be remotely used for strain, pressure and temperature measurements in cabin and non-cabin areas. The development was based up-on FiberSensing’s proprietary tunable laser technology (BraggMETER) that enables multi-channel parallel acquisition over broadband tunability (100nm). This enables large sensor count to be addressed in a single compact instrument. The BraggMETER platform processing core was fully implemented in low-level electronics (microprocessors and FPGAs) that ensure high reliability, while reducing power consumption. The platform integrated an ultra-stable multi-line reference that ensures high accuracy over the full tuning range.
The BraggMETER platform relied on high speed analog to digital converters that restrict the maximum acquisition rate to 500S/s. Within the MiniBRAGG project the acquisition electronics were redesigned using high-speed comparators to increase the acquisition rate to 2000S/s, while maintaining the spectral resolution (±2pm) and reducing the power consumption. The driving electronics of the semiconductor optical amplifier that provides gain in the tunable laser cavity was redesigned to integrate three levels of overdriving protection to be complaint with ATEX.
- The envisaged instrument architecture integrated:
- the tunable laser module scanning 100nm at 2000S/s;
- the optoelectronic module that incorporates 8 independent photodetection blocks with digital gain control to ensure 20dB of dynamic range and;
- the processing module with digitalization based on multi-level high speed comparators, fast accurate spectral peak detection processing based on FPGAs and microprocessor for sensor calibration and interface through Ethernet.
All these features will be integrated into a compact equipment, that will be validated in-flight to achieve a TRL-6 at the end of the project.
Within the MiniBRAGG project a fully operational Fiber Bragg Grating (FBG) interrogation equipment has been designed, implemented and tested following the most demanding requirements for in-flight use in a large number of aircraft locations, both in-cabin and in non-cabin areas.
The equipment provides the following features:
- Simultaneous acquisition of 8 optical channels
- Wide bandwidth wavelength (100 nm)
- 2048 samples per second (user selectable from 1S/s to 2048S/s in powers of 2)
- High spatial resolution accuracy (2pm = picometer)
- Dimensions less than: 250mm x 120mm x 75mm
- Power consumption
- Use in A/C harsh environment and DO160 compliant
- ATEX compliant (EU guidelines for Atmosphere Explosibles)
- Operating Temperature: -35°C to 78°C
- Data output: Ethernet output . IENA communication (D, P and M type)
- Able to address up to 160 sensors of any magnitude, distributed over the 8 optical channels
- Data recording capacity, both on internal and external memories
- Digital filtering at different frequencies
- Sensor network configuration trough XML files
- Individual sensor conversion into engineering units using fourth order polynomials
- PTP synchronization
- Two different sensor timestamping modes
- Graphical User Interface for instrument communication
The equipment has been designed following Airbus requirements and has been tested following DO160 standards, The design is compatible with ATEX [Ex op is T3 Ga] IIA (formal certification currently in progress).
The MiniBRAGG equipment is a low consumption (<20W) equipment capable of simultaneously interrogating 160 sensors. Those 160 can be multiplexed over 8 fiber optic cables, greatly reducing cabling weight and thus contributing to the achievement of lightweight aircrafts. Furthermore, the employment of lightweight composite materials requires the improvement of monitoring systems to assess structural integrity of the parts, and thus the employment of FBG sensors interrogated by this compact and low consumption equipment will provide relevant environmental benefits while ensuring structural integrity of these new aircrafts.