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Distributed system to control air giant's pressure
By Rick DeMeis, Senior Technical Editor -- Design News, September 9, 2002
Frankfurt, Germany — Controlling the interior environment of the world's largest airliner, the double-deck behemoth Airbus A380, could be an engineer's nightmare. Without bus systems, the resulting rat's nest of wiring, and its weight, could boost complexity and decrease payload. And the wrong bus could lead to hot and cold spots in the cabin.
Hamilton Sundstrand's (Windsor Locks, CT) Nord-Micro unit, supplier of the aircraft's cabin pressure and ventilation system, selected the Time Triggered Protocol (TTP®) bus from TTTech (Vienna, Austria) for the cabin pressure control system. According to Nord-Micro A380 Cabin Pressure Control System Project Manager Friedrich Scheerer, "TTP technology provides a standardized, cost-efficient (in terms of aircraft wiring and communications components), and advanced communications system needed for a distributed control architecture using synchronous components. Such an architecture optimizes both system availability and design of fault detection/confirmation algorithms for more reliable fault messages, while maintaining system operational performance."
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The voluminous double-deck interior of the Airbus A380 will require precise control of its environment. The TTP protocol was selected for reduction in aircraft wiring complexity and weight, as well as improved reliability. The A380 will make its maiden flight in late 2004 with airline service beginning in 2006. |
How it works. As opposed to event-triggering, TTP is based on a time-domain multiple access bus protocol where each module has a fixed time slot and agenda for communicating. Event triggered protocols are analogous to meetings where each person (unit) talks about whatever his or her area of expertise is and for as long as they want. The others must wait until the previous speaker stops—thus the more units in a system, the more unwieldy the communication between them becomes.
TTP, on the other hand, acts as a moderator. Each unit "voices" its contribution at a preassigned time for a fixed length of time (just a few microseconds) on fixed "topics" or data dumps. Communication is predictable and other units on the system know when to listen for the information they need. The system interface is very structured. With links precisely defined, subsystems can be developed and tested independently. An integrated architecture distributes functions across the network, resulting in a reduced number of electronic control units (ECUs) and sensors, cutting costs.
TTP integrated circuits have been available since 1998 and are also seeing growing interest for automotive data bus communications. Communication speeds up to 25 Mbit/sec (synchronous) are possible, and earlier this year prototypes reached 1 Gbit/sec. The TTP data frames carry upwards of 240 bytes of data. Networks can consist of 64 nodes, or 256 nodes with multiplexing. TTTech also provides an integrated software development environment, TTP-Tools, for distributed control system developers' use.
In other aerospace applications, under a five-year NASA program, Honeywell and SRI International are developing a digital aircraft engine controller using TTP technology. This could lead to other by-wire aircraft systems.
For more information on TTP control systems from TTTech, www.tttech.com. Enter 536
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