PMUX - The interface for engine data to AIDS

Abstract

The propulsion multiplexer (PMUX) unit, a new component of the Aircraft Integrated Data System, promises to improve the accuracy and reduce the weight of condition-mon itoring equipment in commercial engines. The new configuration will improve accuracy by packaging advanced technology pressure sensors within the elec- tronic unit and by using digital signal conditioning, made more practical by placing the microprocessor near the engine sensors. To reduce weight, the system will replace multiconductor cables with a serial digital data link. This paper discusses typical design requirements and describes the approach used in a unit designed for the 747- 300 aircraft. VER a decade ago, the interest in Aircraft Integrated Data Systems (AIDS) triggered a desire for gathering information useful in aircraft maintenance. At that time, the use of electronic computers was expanding, thus providing a means to conveniently store the details of individual airplane system performance on supporting ground-based equipment. Performance data from airborne operation could be re- corded, since it became practical to extract pertinent in- formation from existing avionic systems. Soon AIDS was used to record in-service engine performance. These data were obtained simply by monitoring cockpit instruments and in- corporating a few additional sensors on the engine. During the early planning of AIDS, engineers did not consider a signal summing box at the engine. In its absence, the task was to design an interface with existing engine in- struments and to add pressure and position sensors that would monitor the major engine parameters. The latter effort required installing electrical wiring between the actual sensor and the support electronics. The new equipment significantly increased aircraft weight and was vulnerable to the typical problems associated with a large bundle of electrical wires. When the AIDS concept was evolving, the viability of using electronic systems in the harsh engine environment had not been proven. Today, as AIDS and engine electronics have matured and the specific requirements for engine data are better defined, the propulsion multiplexer (PMUX) unit has gained acceptance as a better way to monitor engine parameters on both the 747-300 and the A310 aircraft. By changing from the original AIDS system to the new PMUX AIDS system, each 747 can be lighter in weight. The new system will feature a signal summing unit at each engine and serial digital communication to the AIDS data gathering box in the avionics bay. In progressing from the original AIDS configuration to that employing a PMUX, the on-engine pressure sensors were incorporated within the PMUX unit. Here, these critical sensors are in a more hospitable environment and can also allow the use of a design concept that takes advantage of the digital computer within this subsystem.