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Important Characteristics of MIL-STD-1553 Standard for Avionics and Aircraft

MIL-STD-1553 design was initially for control of military aircraft. Hence, the protocols and connections of gadgets and systems offered robust, reliable, and redundant solutions.

MIL-STD-1553 is a military standard that defines the characteristics of a serial data bus, and the US Department of Defense has published it. MIL-STD-1553 standard defines mechanical, electrical, and functional aspects of the serial data bus. The MIL-STD-1553 combines both physical and protocol standards, making it suitable for aerospace systems.

1.     Data Speed

MIL-STD-1553 uses a one megabit per sec data rate which is adequate for a large number of applications. However, other systems require higher speeds.

2.     Features of MIL-STD-1553

MIL-STD-1553 features include;

  • Multiple redundant balanced line physical layers
  • A network interface
  • Time-division multiplexing
  • Half-duplex command or response protocol

MIL-STD-1553 was a US air force standard; however, both military planes and civil aviation are currently using the standard.

3.     Physical Layer Standard

Allows a bus to have a single wire with an impedance of 70-85 ohms at a speed of 1MHz. In a circular connector, the center is the center pin becomes the bi-phase signal.  The transmitters and receivers transfer energy to the bus through isolation transformers.

4.     MIL-STD-1553 Advantages for Time-Triggered Networks

MIL-STD-1553 offers many advantages for time-triggered networks, which include;

  • Differential signaling offers defined idle time to prevent collisions between consecutive transmitters.
  • MIL-STD-1553 uses transformer isolation and optional transformer bus coupling, thus offering several advantages.
  • The MIL-STD-1553 is suitable in relatively harsh conditions. Hence, the serial data bus has to be fault-tolerant, making MIL_STD_1553 ideal for systems in commercial aircraft.

5.     Advantages of Transformer Bus Coupling in MIL-STD-1553

  • DC isolation
  • Common mode rejection
  • Lightning protection
  • Isolation resistors that are in series protect from short circuit faults.
  • Transformer bus coupling increases stub impedance for increased stub lengths.
  • The high transmit voltages of MIL-STD-1553 provide a robust data rate and cable length performance.

6.     MIL-STD-1553 Specifications

  • Overshoot
  • Ringing
  • Output noise
  • Transmitter zero-crossing distortion

7.     The MIL-STD-1553 Voltage States

MIL-STD-1553 sets differential signaling with three states, namely;

  • Idle state
  • Active high
  • Active low

Idle State of Voltage

  • The idle voltage enables receivers to determine the idle time, indicating its time to transmit to the next bus. Idle voltage helps prevent collision within the preceding nodes.
  • The signal encoding method for MIL-STD-1553 is Manchester bi-phase.

8.     Advantage of Differential Bus

The use of a differential bus instead of the single-end bus has the advantage of providing common-mode performance and lightning immunity. Hence a short circuit can’t bring down the whole system due to the protection MIL-STD-1553 offers by using a differential.

9.     Advantages of Transformer Isolation

  • Provides strength in DC isolation
  • Ability to survive lightning.
  • Common mode rejection

Note that common-mode rejection is essential in reducing noise along transmission lines.

10. MIL-STD-1553 Cable Specifications

  • The cable specifications for MIL-STD-1553 include;
  • Cable with twist and shield- 75% shield minimum
  • Cable with a characteristic impedance- 70-85 ohms at 1MHz
  • Cable-line with maximum attenuation-1.5 dB/100ft at 1MHz
  • Capacitance- 30pF/ft., maximum

11. MIL-STD-1553 Applications

  • Attack in fighter planes
  • Flight control
  • Mission computers
  • Weapon control for fighters
  • Transport aircraft

Conclusion

MIL-STD-1553 is a military standard that defines the electrical, functional, and mechanical characteristics of serial data buses used in avionics and aircraft. The physical layer that MIL-STD-1553 defines are suitable for time-triggered networking technologies. Idle voltages are vital in preventing collisions between two consecutive transmitters, thus enhancing effective communication and safety.

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