Aircraft landing gear system Essay Example | Topics and Well Written Essays - 1750 words

Aircraft landing gear system - Essay Example twisted, shielded pair with shield grounded at both ends Source (transmitter) must be able to handle 400 ? at the maximum. Receivers must have minimum effective input impedance of 8 ? Normally designed for range of less than 175 ft (or 50+ meters) A data â€Å"one† is created when the rising edge goes from 0 to 10+/- 1 positive volts; a data â€Å"zero† is created when the falling edge goes down from 0 to 10+/- 1 negative volts Error Checking ARINC 429 uses the odd parity bit to detect error and ensure that data that is being received is accurate. It is the last bit in a message transmission constantly changing with label and data change always resulting in â€Å"Odd Parity† always containing the number ‘1.’ Data Word Format An ARINC message is usually a single data word that is 32-bit long and includes five fields: Label; SDI; Data; SSM, and; Parity. Label identifies the kind of data that being transmitted and has a value of 8. SDI (or Source Destin ation Identifier), specifies the value of the intended receiver. In a system with multiple receivers, each receiver is assigned a value. Data, the actual message of the transmission, uses two kinds of format: the BCD (short for Binary Coded Decimal), uses four bits, and; the BNR (short for Binary encoding). Both define units, resolution, range, number of bits used and frequency of the label. SSM (or Status/Sign Matrix) assists in the interpretation of numeric values in the data field with values such as ‘north,’ ‘east,’ ‘plus,’ ‘minus,’ etc. Finally, P, for parity bit, is the last bit transmitted (Cook et al 462). c) Comparison of ARINC 429, ARINC 629 and MIL 1553B Databuses 1. Encoding Method ARINC 429 uses a bipolar return to 0 type of encoding; MIL 1553B uses the Manchester II biphase where a logic one (1) is transmitted as a bipolar coded signal I/O and a logic zero (0) as a bipolar coded signal I/O (TSCM 9-6.2). ARINC 629 also uses binary encoding. 2. Bus Coupling Method The ARINC 429 has integrated line transmitter/receivers that software can program to receive (Rx) or transmit (Tx) and operate at specific transmission rate independently of other channels. On the other hand, ARINC 629 incorporates bus controllers into every unit and coupling is made using current transformers without cutting off wires. Meanwhile, MIL 1553B uses the transformer and direct method of bus coupling. 3. Data Word Format ARINC 429 uses a 32-bit data format. Fig. 2 illustrates the allocation of bits in the fields. It also shows the numbering of bits from 1, or the LSB (Least Significant Bit), to 32, or the MSB (Most Significant Bit). In the order of transmission, the Label is transmitted first, with the MSB going out before the LSB, but in all other fields, the LSB is transmitted first. Fig. 2 shows the order of transmission by field (label, SDI, Data, SSM and P) within every field. MSB LSB Fig. 2 ARINC 429 32-bit Word Format ( AIM GmbH p. 15) Fig. 3 ARINC 429 Word Transfer Order (AIM GmbH p. 15) On the other hand, ARINC 629 uses a 20-bit date format, where the first three bits are allocated to word time synchronisation, the next 16 bits to data content and the last bit as parity bit. Fig. 4 illustrates the bit allocation in an ARINC 629 data bus system and shows that it has only three fields as opposed to the ARINC 429 that may have as