Fiber optics can provide improved reliability, for control and monitoring of advanced aircraft but the technology must develop credibility in functional operation. Testing under realistic environmental conditions is necessary with information feedback provided to the component designers. A NASA / NAVY program, called FOCSI (Fiber Optic Control System Integration) is directed to these issues and is discussed in this paper.
The interconnection harness is a most basic and critical avionic system component that must support performance goals yet be easily installed, durable, maintainable and supportable. Decreased complexity and weight with increased signal bandwidth and multiplex capability are urgently needed. Fiber optics is proposed as a replacement for conventional wire harnesses. The Society of Automotive Engineers (SAE) document ARD50020 details various industry concerns with present fiber optic hardware and lists attributes of future needs.
Increasing levels of electromagnetic interference (EMI) coupled with the increasing use of composite materials on aircraft have created awareness and concern for susceptibility and weight of existing shielded electronics. Optical sensing techniques offer a solution due to their inherent immunity to EMI. Rosemount Inc.’s Aerospace Division has been developing an optical temperature sensor designed for aircraft and engine environments based on the fluorescent time rate of decay (TRD) principle.
In the past few years the industrial community has developed a number of fiber optic engineering sensors which appear to serve the needs of the Navy and are available for installation aboard the naval ships. To assess the validity of this claim, Commander, Naval Sea Systems Command (NAVSEA) tasked the Naval Research Laboratory (NRL) to purchase any fiber optic sensors offered commercially and evaluate them for naval use. Many sensors advertised needed years of development work before they would be ready for technical evaluation.
A fiber optic cable plant installed on the AEGIS cruiser USS Mobile Bay (CG 53) provides the opportunity to study the long term effects of the shipboard environment on passive fiber optic components. The current study consists of periodic inspections of the cable plant, including visual examination of connectors and OTDR measurements of the fibers. Measurements to date show no significant adverse impact to the performance characteristics of the fiber optic components from the shipboard environment.
This paper provides an overview of the major fiber optic developments within the Department of the Navy, concentrating on developments within the Naval Sea Systems Command (NAVSEA). Most of the fiber optic programs discussed were approved at the Chief Of Naval Operations (CNO) Executive Board (CEB) Meeting held in September 1990, and they include programs to develop standard fiber optic components and networks. These efforts are intended to capitalize on commercial industry products that use industry standards and open system architecture approaches such as FDDI, BISDN and FUTUREBUS+. Full military specifications will be imposed only when required, since both commercial and ruggedized equipments also will be installed on ships.
This paper highlights the efforts of the Naval Surface Warfare Center to develop a fiber optic pressure transducer. The initial application for this fiber optic sensor is to monitor the pressure in the sonar dome of a surface ship. This required a 0 - 100 pounds per square inch (gage) sensor. This sensor, developed by Luxtron, Incorporated, under a Small Business Innovative Research contract, utilizes a vibrating quartz crystal as the transduction mechanism. Changes in the resonant frequency of the quartz crystal as a result of force applied to the crystal is monitored using a simple fiber optic link. This paper discusses the principal of operation and design of the sensor, advantages and disadvantages of this type of sensor, development results to date, and future development plans.
Portions of this paper have been presented previously in a paper entitled “Fiberoptic pressure sensor based on vibrating quartz crystal technology” presented at the International Congress on Optical Science and Engineering, The Hague, Netherlands, March, 1990.
Use of fiberoptic technology in tethered undersea vehicle systems is reviewed with emphasis on communications and control. Examples are given for the Harbor Branch owned Remotely Operated Vehicle "SCOOP" (Scientific Collection and Observation Platform) which was recently outfitted with an improved telemetry system and fiberoptic umbilical.
Over the past decade, the demand from both government and private industry for small, lightweight, vehicle weight-in-motion (WIM) systems has grown substantially. During the 1980s, several techniques for weighing vehicles in motion were developed that include piezoelectric cables, capacitive mats, and hydraulic and bending-plate load cells. These different systems have advantages and disadvantages that trade off between accuracy, physical size, and system complexity. The smaller portable systems demonstrate medium to poor accuracy and repeatability while the larger more accurate systems are nonportable. A small, lightweight, and portable WIM system based on a fiber-optic pressure transducer has been developed by Oak Ridge National Laboratory (ORNL) to meet the demands of government and industry. The algorithm for extracting vehicle weight from the time-dependent sensor response is developed and presented in this report, along with data collected by the system for several classes of vehicles. These results show that the ORNL fiber-optic WIM system is a viable alternative to other commercial systems that are currently available.
Fibre optic systems present a very real hazard when used in the presence of combustible gases. A theoretical model of the ignition risks of fibre optic systems in such environments has been developed which compares well with experimentally determined minimum power levels for ignition. Whilst the strict theoretical model is complex, a simple method of determining the ignitions risks for arbitrary optical fibre parameters and wavelength is presented.
Coordinate measuring machines are as accurate as the probes used to trigger them for measurements. The errors which are introduced by probes into dimensional measurements are usually not known to everyday user. Here a comparison of results between a touch-trigger probe and an optoelectronic probe is presented.
Single-track absolute encoders have the advantage of mechanical simplicity although they require more complex electronics and software than conventional multi-track instruments. The presence of intelligence at the point of measurement means that diagnostics can be incorporated which are not possible in the conventional instrument.
The instruments described here use a track encoded with a pseudo-random-binary-sequence (PRBS) a small section of which is imaged onto a line-scan sensor. The digital word so imaged gives the coarse position while the exact location of edges in the image gives the fine position.
A temperature sensor system has been fabricated specifically for the harsh environment encountered in temperature measurement on gas turbine engines. Four components comprised the system: a thermally emissive source, a high temperature lightguide, a flexible optical cable and an electro-optic signal processor. The emissive source was located inside a sapphire rod so that the sapphire serves as both a lightguide and as a protective shroud. As the probe was heated, the thermal radiation from the emissive source increased with increasing temperature. The flexible optical cable was constructed with 200 micron core fiber and ruggedized for turbine engine applications. The electro-optic signal processor used the ratio of intensity in two wavelength intervals to determine a digital value of the temperature.
The probe tip was operated above 1900°C in a low velocity propane flame and above 1500°C at Mach .37. Probe housings, optical cables, and signal processors were constructed and environmentally tested for the temperature and vibration experienced by turbine engine sensors. This technology was used to build an optical exhaust gas sensor for a General Electric Aircraft Engines F404 turbine. The four optical probes and optical cable were a functional replacement for four thermocouple probes. The system was ground tested for 50 hours with an excess of 1000 thermal cycles. This optical temperature sensor system measured gas temperature up to the operational limit of the turbine engine.
With the advance of the application technology of optical fibers, the development of optical fiber connectors has been carried out extensively in recent years. Here one can single out optic rotary connectors which enable transfer of data signals from rotary objects. An optical rotary connector is expected to have higher reliability and durability than an electrical slip ring because of its ext- extremely stable contact.
Simple, rugged intensity type fiberoptic vibration sensors have been developed and pre-production prototypes presently are being evaluated. The transduction element consists of a pair of multimode optical fibers, one mounted on a cantilever reed, the second on a fixed anvil. At frequencies well below the reed's resonant frequency, light coupled from one fiber to the other is directly proportional to the acceleration. The basic operating characteristics of the sensors, detailed laboratory test results and preliminary field data are presented.
Since the inception of critical digital fly-by-wire systems the commercial and military aerospace industries have struggled with the issue of how to implement auxiliary flight control in the advent of computer and/or command transmission system faults or failures. One potential cause of these problems is the external electromagnetic environment (EME). An electrically isolated auxiliary flight control mode based on power-by-light technology could provide a cost effective, electromagnetic interference (EMI) resistant alternative to the electrical and mechanical backup systems in use today. This paper addresses the benefits and issues associated with power-by-light flight control and discusses the status of ongoing work to bring it to reality.
The first prototype using a silicon photodiode coupled with a pyroelectric sensor  has been modified to be set up on a car. Improvement has been achieved with the replacement of the IR PVDF material by a copolymer, which involves a new technology and a new poling procedure of the active device integrated on the Silicon chip. In addition, two other points are examined in this step : the design and the implementation of a 30 meter-range telemeter and the strategy of integration of the whole system.
Prior to 1970, when fiber optics was still in its infancy, an elaborate instrumentation system had already logged hundreds of hours of field operation using fiber optics for all command, control and data collection, as well as for some sensing. It seems highly improbable, when the best solid-state light sources of that period were not intended for communication purposes, fiber optic connectors were not commercially available, and the best fibers had losses measured in deciBels per meter (not kilometer). To totally eliminate all electrical wiring, the whole system was designed to run on nothing but compressed air, delivered by hoses composed only of dielectric material. This paper tells the unpublished story of some very early, very novel, fiber optic systems which were designed, built and operated by Boeing during the 1969 to 1974 time period to solve some extremely difficult instrumentation problems.
A brief review of the early history of fiber optics is included to help the reader better understand the problems of those early days, as well as appreciate the vast improvements which have been made during the past 20 years.