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NEW OPTICAL SENSOR CONCEPT FOR AERONAUTICS

Objective

Development and demonstration of an optical system of sensors for aircraft, based on advanced optical fibre technology. Pressure and acceleration sensors will be investigated. A demonstrating network will be assembled and evaluated providing a set of preliminary results for follow-on work.
Three prototypes of angular encoders were tested. One of them was mounted on a compresser tested in a bench. ( by SNECMA ) The results obtained with this prototype were satisfactory. The 3rd prototype was designed to be linked with an optical harness before the optoelectronic unit for reason of versatility. The BERTIN laboratory tests have shown that this particular utilization has to be avoided. This sensor must be linked to the optoelectronic unit by its own harness without any other interface.



EMI tests (conducted emission, radiated emission, conducted susceptibility, radiated susceptability) were conducted by SNECMA on the angular encoder versus an electromagnetic sensor.



The tests on the pressure sensor ( by BERTIN and SEXTANT ) revealed its sensitivity to the fluid (air or oil) and a small operating temperature range which make it incompatible with aeronautical use.



An accurate fibre Bragg grating wavelength readout system was manufactured with a low cost spectometer by KING'S COLLEGE. A signal processing algorithm was necessary to achieve the high resolution. The tests were performed on 4 multiplexed gratings fabricated on -the same fibre, by KING'S COLLEGE, DEUTSCHE AEROSPACE AIRBUS.



The engine network was designed by BRITISH AEROSPACE, SNECMA and AEROSPATIALE to access the angular encoder and a set of multiplexed sensors (like the pressure sensor one). A multiplexer, using the tree multiplexing techniques, was manufactured for the tests. It was designed to be compatible with an engine core.



The components used in this network all resist high temperature withstanding : multimode graduated index fibre, 820 nm single mode fibre, multiway single and multimode connectors, couplers, delay lines, fused splices. The test results were stisfactory. The fading of the optical signal due to temperature change was under 3 dB. No incompatibily high temperature use was found on the selected components, but no ageing tests were performed. The results on the airframe network showed that FDDI could be sued for this application. The tests on individual components, intermediate assembly or protocol gave correct results on the whole.

The study covers the different aspects of a sensor network and uses new concepts of intrinsic optical fibre sensors. Sensors will be defined and designed by using advanced optical fibre technology, in association with a coherence multiplexing technique and an optical reading system of interferometric type. Two stages have been defined to implement a laboratory demonstrator. The first stage will be devoted to the realization of 2 compatible lines of sensors, one for optical fibre accelerometers and one for optical fibre pressure sensors. The same type of interferometer and data processing unit will be used for each sensor. The second stage will evaluate the complete system with both lines of optical fibre sensors arranged in the same network by using a common interferometer and data processing unit.

The programme of work consists of 8 tasks, defined as follows:
Study of requirements and definition of specifications.
Design of sensor heads, interferometer and processor units.
Development and assembly of sensors and measurements rig.
Study of aircraft system criteria for networking.
Test refinement and reports.
Assembly evaluation and review of system demonstrator.
Guidelines for programme continuation.
Studies for robotic applications.

This project is a pilot phase for the demonstration, through a laboratory rig, of the capability of such a network to be compatible with aircraft system criteria for future development. Parameters of interest such as measurement range and accuracy, environmental conditions (temperature, pressure, vibration, etc), and also number of sensors for multiplexing, network architecture (in terms of safety, redundancy, etc), will be taken into consideration for realistic operational applications. An extension of this sensor system will be studied for robotic applications.

Coordinator

Thomson-CSF
Address
Domaine De Corbeville
91404 Orsay
France

Participants (3)

INSTITUTO DE ENGENHARIA DE SISTEMAS E COMPUTADORES
Portugal
Address
Rua Alves Redol 9
1000 Lisboa
SMITHS AEROSPACE LTD.
United Kingdom
Address
Bishops Cleeve
GL52 4SF Cheltenham
TECHNICAL UNIVERSITY OF DENMARK
Denmark
Address
Anker Engelundsvej 1, Building 101
2800 Lyngby