Avionic systems integration Flashcards
What does TDM (Time division multiplexing) enable
TDM enables the information from many signal channels to be transmitted through a single communication system
How much data can be transmitted through data highway
1 bit of information at a time
Why is a coupler unit used to connect sub-systems to the data highway
So that if one sub-system short circuits, all other systems will still function
Describe the MIL STD 1553 bus system
- developed in US military in 1970s
- adopted by NATO and given codification STANAG 3838
Data highway
- Bus controller
- remote terminal sub-system
- sub-system with RT capability
Bus if formed of a single twisted cable pair with a layer of shielding, with a maximum length of 100m
Data transmitted at 1 Mbits/s (slow)
Describe Manchester bi-phase
a change is made every bit time, even if same output. This is so it is easier to see faults in the system
List 3 types of words transferred
- command words
- data words
- status words
Describe command words
For a 5-bit terminal address, 2^5 -1 terminals can be connected to the bus.
(this is because 11111 is a broadcast address to all)
- T/R bit = 0, the terminal is to receive
- T/R bit = 1, the terminal is to transmit
- the sub-address/mode field is used to route data to and from a location in the RT (remote terminal)
Describe data words
16 bit data with 1 parity bit
Describe status word
- the status word is the first word by an RT to a BC command
- it provides a summary of the status/health of the RT
- The RT address field confirms the correct RT is responding
What is the response time of RT, when all data is recieved
14 microseconds
and inter-message gap is (2-5microseconds)
Describe STANAG 3910 (Europe)
- uses fibre optics
- bus controller
- sub systems in and out
- higher speed data
- 31 subsystems max
Describe Linear Token Passing Bus (USA)
- no specific bus controller, protocol is in each subsystem
- fibre optic star coupler
- 128 sub systems max
What is electromagnetic interference
When voltages or currents are present and affect the performance of the device
What is electromagnetic compatibility
The desired situation when a device or a system operates as intended within itself and its environments
An EMI problem can be designated as:
- intrasystem: problem comes from the system itself
- intersystem: problem comes from outside the system
An EMI problem arises because of the combination of 3 factors, these are:
- Source
- Transmission path
- Response
When does arc discharge occur
Arc discharge occurs when the electric field intensity between two conductors exceeds the breakdown strength of the dielectric separating them
What is the breakdown strength
A property of the dielectric, which could be a gas, a liquid or a solid :)
(Air: 30kV/mm)
What is the Schumann resonance
After lightning the interference spans across several Hz to 100MHz. But at 8 Hz its level is increased and this is the Schumann resonance
List three types of cosmic noise
- Galactic noise
- Thermal noise
- Anomalous solar noise
How is precipitation static caused
It is caused by aircraft in flight coming in contact with uncharged particles
- the positive element of the particle is reflected away from the aircraft and the negative particle adheres to the skin
- If aircraft does not have sufficient static dischargers, it may go into “CORONA”
List problems associated with p-static
- erratic instrument readouts
- erroneous magnetic compass readings
- complete loss of VHF communications
- weak transmissions and poor receptivity of radios
- VHF navigation system inoperative most of the time
- loss of all avionics in clouds
