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Module 5 Digital techniques > M5 > Flashcards

M5 Flashcards

1
Q

How is the instrument panel fixed?

A

This panel is normally sloped forward 15 degrees from the vertical to
minimize parallax errors.

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2
Q

What are the 6 flight instrument that creates a picture for the pilot?

A

These instruments are:
1. Airspeed Indicator
2. Gyro Horizon Indicator
3. Altimeter
4. Turn & Bank Indicator or Coordinator
5. Direction Indicator
6. Vertical Speed Indicator

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3
Q

What was the first attempt at instrument layout standardisation?

A

The basic six

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4
Q

What is known as the master instrument and where does it sit?

A

In this arrangement the “Gyro Horizon Indicator” (GHI) occupied the top centre position, and since it provides positive and direct indications of the aircraft attitude, it is utilized as the “Master Instrument”.

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5
Q

Where do the ASI and Altimeter sit in relation to the GHI?

A

As control of airspeed and altitude is directly related to attitude, the Air-Speed Indicator (ASI), Altimeter flank the GHI.

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6
Q

What sits below the GHI?

A

The HSI

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7
Q

What instruments are in the basic t?

A

There are now four key indicators:
1. Air Speed Indicator
2. Attitude Direction Indicator (ADI)
3. Altimeter
4. Horizontal Situation Indicator (HSI

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8
Q

What is an ADI known as in Boeing and Airbus EIS?

A

The ADI has evolved into an Electronic Attitude Director Indicator (EADI) on Boeing aircraft, (called a Primary Flight Display (PFD) on Airbus aircraft).

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9
Q

What is an HSI known as in Boeing and Airbus EIS?

A

The HSI has similarly become an Electronic Horizontal
Situation Indicator (EHSI) on Boeing or a Navigation Display (ND) on Airbus aircraft respectively

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10
Q

What are the benefits of EIS?

A

The advantages of using EIS are:
4. Variability and variety
5. Coloured displays
6. Important data is accentuated, temporarily unimportant data is suppressed
7. Fewer components are needed
8. All display units for EIS are the same type

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11
Q

How does information get transferred across screens from the CPUS?

A

via arinc 429 data busses.

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12
Q

What can a modern EADI show?

A

A modern EADI will display, or is capable of displaying:
* Pitch and roll information
* Ground speed
* Flight director information
* Glide slope and localiser deviation
* Numerous warning and status messages, including pitch and roll mode, navigation aid selected, radio altitude,
altitude alert and decision height

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13
Q

What can a modern EHSI show?

A

Items displayed include:
* Magnetic heading
* Radio steering commands for VOR/INS
* Way points, airports and navigation aids
* Distance to go
* ILS steering information

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14
Q

Advantages of LCDS over CRTS?

A

Advantages of LCDs are they are more robust than CRTs and have a lot lower and simpler power supply requirements. They also produce a lot less heat than CRTs.

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15
Q

What does a hexadecimal number represent?

A

A Hexadecimal number represents a 4 bit binary number

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16
Q

With analogue signals, what does bipolar mean?

A

AC (alternating current) analogue signals can be bipolar in that they have both positive and negative limits.

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17
Q

Explain DC unipolar

A

DC (direct current) analogue signals are unipolar in that they will have 0 volts as one limit with some level of either positive or negative voltage defining its other limit, but will never alternate between positive and negative voltages

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18
Q

How does a digital signal differ from an analogue one?

A

Digital signals are different from analogue signals in that there are only two (binary) levels of voltage: high for “ON” and low for “OFF”. These two different voltage levels are put into words to describe the value being transmitted. As stated in the previous Sub-Module, the binary number system is used in digital electronics because the two basic conditions of electricity, ON and OFF, can represent the two digits of the binary number system. When a switch is ON, it represents the digit 1, and when it is OFF, it represents the digit 0.

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19
Q

What is it possible to do with digital signals?

A

Unlike analogue signals, with digital signals it is possible to:
* Store values in computers or on disks
* Manipulate signals on a computer
* Compute new signals from digital values using a microprocessor
* Remove or reduce noise from signals

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20
Q

How is an analogue signal converted to a digital one?

A

Aircraft with digital instrumentation make use of pressure sensitive solid-state sensors that output digital
signals for collection and processing by aircraft computers. Others may retain their analogue sensors, but may
forward this information through an analogue-to-digital (A/D) converter for a computer to process and present
the digital information to cockpit displays.
An Analogue-to-Digital Converter (ADC) is a device that converts a continuous input voltage into a digital data
stream that represents the amplitude of the input analogue signal (image below). One would be used to convert
the analogue output from a microphone into digital signals for storage on a CD. The ADC performs conversions
periodically by sampling and quantizing the input signal over a very short period of time. The result is a
sequence of digital numbers that have been converted from continuous time and amplitude analogue signals to
discrete time and amplitude digital signals.

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21
Q

What are the the levels in an ADC?

A

The quantization levels.

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22
Q

What is resolution in an ADC?

A

Resolution refers to the number of quantization levels or bands that an ADC can sample or a DAC produce.

23
Q

What is the fastest type of ADC?

A

The fastest type of ADC is the direct comparison converter.

24
Q

How does a direct comparison converter work?

A

The fastest type of ADC is the direct comparison converter (Image below), in which each reference voltage used
in the comparison is assigned a digital value. The analogue voltage (Vin) to be sampled appears at the input of
all 7 high-gain differential operational amplifiers (op-amps). Each op-amp compares the analogue input voltage
with the fixed reference voltages (Vref) that are present at the remaining op-amp inputs. The resister ladder
network divides the reference voltage range into 7 different voltage levels for sampling and quantization. The
threshold detector in each op-amp drives the encoding logic to detect the highest reference that is exceeded.
The ADC encoder then uses this information to produce a 3-bit binary output. The direct comparison circuit may
be the fastest ADC; however, its circuitry becomes quite large for outputs of more than 3 or 4 bits.

25
Q

How does a ramp generation converter work?

A

A ramp generation A/D converter, sometimes called a counting A/D converter, compares the unknown input
voltage to a D/A connected as a ramp generator. As long as the unknown input is greater than the ramp signal,
the counter continues. As soon as the ramp exceeds the unknown voltage input, the counter stops and the
ramp is held at this fixed level. The count is then read by the computer.

26
Q

What is the disadvantage of a ramp generation converter?

A

The ramp generation A/D converter is really working as a peak detector. This can pose some problems if the
computer needs to sense variations of VI over short time periods. Therefore, the ramp generation A/D works
best in applications where the analogue signal level varies as a slow rate, such as a temperature sensor.

27
Q

Explain digital to analogue conversion

A

Digital-to-Analog Converters (DACs) are found in everyday use. For example, digital information stored on Digital
Video Discs (DVDs) uses a DAC to convert the digital data stream to analogue video signals. Digital-to-analogue
is the reverse of the above A/D conversion process with each binary number being converted back into nominal
levels by reconstructing the original waveform.
A DAC (DAC Symbol below) is a device that takes binary numbers, or combinations of binary numbers, and
changes them into their corresponding voltages, such that, for example, binary number 1 equals 1 volt, binary
number 2 equals 2 volts, binary number 3 equals 3 volts, and so on. A typical DAC converts a sequence of
binary digits (bits) into “impulses” that are then processed by a reconstruction filter to smooth out the step
response into continuous curves. These impulses are created by updating the analogue voltage output at
uniform sampling intervals, controlled by a clock timing signal (See DAC Output before Reconstruction below).
These are then interpolated by a low-pass reconstruction filter to fill in the gaps between the impulses creating
a continuously varied output. (See Reconstructed DAC Output) Other DAC methods produce a pulse-modulated
signal that can then be filtered in a similar way to produce a smoothly varying signal.

28
Q

What is a data transmitter known as?

A

A source

29
Q

What is a data receiver known as?

A

A sink

30
Q

Which arinc standard is a single source and multiple sinks?

A

Arinc 429

31
Q

Which arinc standard is multiple sources and multiple sinks?

A

Arinc 629

32
Q

Explain time division multiplexing

A

Time-Division Multiplexing (TDM) enabled different forms of information to be transmitted through a single
communication system. A multiplexer is used to sample input data sequentially and then stagger the different
data samples in time to form a composite digital pulse train for transmission. By knowing the clock time and
address of the various signals, a de-multiplexer at the receiving end decodes and distributes the individual
signals.

33
Q

What does arinc stand for?

A

ARINC is the acronym for Aeronautical Radio Incorporated, a corporation which was founded in 1929 in the
United States, in order to simplify radio communication and find common standards

34
Q

What are the basic capabilities of the a629 standard?

A

The newer A629 data bus, used in the Boeing 777, has a data rate of 2 Mbps, which is 20 times faster than A429,
and can handle 131 terminals instead of only 20.

35
Q

What is a simplex data exchange?

A

Simplex: One transmitter, one receiver, one way only. (Unidirectional).

36
Q

What is a half duplex data exchange?

A

one transmitter, one receiver, both directions, but only one at a time. (Bidirectional with limitations)

37
Q

What is a full duplex data exchange?

A

Full Duplex: One transmitter, one receiver, both directions at the same time. (Bidirectional) Data is also sent in either serial or parallel format.

38
Q

How does an a429 bus check for errors?

A

To detect errors, the specification prescribes the use of odd parity indication and optional error checking.

39
Q

Explain the transmission period interval?

A

The periodic interval of data transmission must be sufficient so that there is a minimal rate of change in the
data; such that if a data set is lost, the loss will be of little consequence

40
Q

How is an a429 bus constructed?

A

A twisted shielded pair of wires carries the ARINC 429 signal, with sets of information being transmitted at
periodic intervals.

41
Q

What is the a429 bus capabilities?

A

Each bus has only one transmitter and up to 20 receivers, however, a single LRU may have many transmitters or
receivers on different buses. A receiver is never allowed to respond on the same bus where a transmission has
occurred. However, since a LRU may have one or more transmitters and/or receivers (each on a separate bus),
an LRU may respond over another bus.

42
Q

With the a429 standard how is bi directional data transfer possible?

A

To obtain bi-directional data transfer between LRUs you must use at least two ARINC 429 buses.

43
Q

What are the advantages of serial transmission?

A

Advantages of serial transmission:
* Only a single line is required for transmission
* Only one set of digital circuitry is needed to process the data
* This is slower than parallel transmission but sufficient for ARINC 429
* Requirements

44
Q

Explain the make up of a429 wires?

A

ARlNC 429 serial transmission of information is via a uni- directional bus composed of a pair of 78 ohm twisted
shielded wires (See image of ARINC 429 Interconnection). One end of this twisted pair should terminate into
the data source and the other end should terminate into the data sink(s). The shields should be grounded at
both ends and at all production breaks in the cable.

45
Q

What are the two a429 bus speeds?

A

ARINC 429 defines two different transmission speeds:
- Low Speed (LS BUS) …… (12-14 kBit/ second)
- High Speed (HS BUS) …… (100 kBit/ second)
Low speed and high speed transmission may never occur on the same data bus, it is either a low speed or high speed bus.

46
Q

Explain a429 bus electrical characteristics

A

ARINC 429 uses a bipolar return to zero modulation with voltage levels of +5V. 0V, -5V on each conductor with
respect to ground. When one conductor is at +5V the other conductor will be at -5V and vice versa. One wire is
called A, + or HI; the other wire is called B, - or LO. The signals are kept to within +7.25 to +11V for HI; ±0.5V for
NULL and -7.25V to -11V for LO.
ARINC 429 words, consisting of a serial string of ‘1s’ and ‘0s’ are 32 bits long, with words separated by at least
four bit times of null (zero volts) which removes the need for a separate clock signal

47
Q

Explain information rates?

A

Important data is transmitted quite often, less important data is transmitted less often. This is what we call
Information Rate. As BCD-Data (Binary Coded Decimal) is used for displays only, it is transmitted every 500 ms
(average). BNR (Binary) is to be processed by other LRUs and therefore transmitted 6 to 20 times a second.

48
Q

What are the 5 parts of an a429 32 bit word?

A

A typical 32 bit word has 5 parts:
* 8 bit Label (Information Identifier)
* Source/destination identifier (SDI)
* Data area
* Sign/status matrix (SSM). The SSM is bits 30 and 31 for BCD data words, bits 29, 30 and 31 for BNR data words
* Odd parity bit
* Usage of the SDI and SSM is not mandatory

49
Q

Explain the a429 label

A

The Label identifies the type of information contained the word.
The MSB of the actual label is located in the LSB of the ARINC 429 word and is transmitted first out onto the bus.
Since the LSB of the ARINC word is transmitted first, this in effect, causes the label to be transmitted onto the
bus in reverse bit position order.
The label is part of every 32 bit ARINC 429 word and each word begins with a Label. A label is always transmitted
as the first 8 bits of the ARINC 429 word.

50
Q

Explain the a429 label/address

A

This label takes up the first 8 bits (1 to 8) of a word. It is octal coded (based 8 number system) the following
image gives some examples of application to illustrate the selected coding system.
Each word is identified by a label which defines its function: A word may represent aerodynamic information,
a radio frequency, or a series of binary data, each one of which controls the illumination of an inscription or
controls a function.
As nowadays the total amount of labels (256) available is no longer sufficient, they may be used for different
parameters. To determine the correct parameter the equipment identifier is also needed

51
Q

What is a source/destination identifier?

A

Source/Destination Identifier (SDI)
Bits 9 and 10 comprise the source/destination identifier, or SDl. The SDI function is used when it is necessary
to indicate the source of information, or when the information is directed to a specific location (which has a
minor function). For example, when specific words need to be directed to a specific system in a multi system
installation, or when the source system of a multi system installation needs to be recognisable from the word
content.

52
Q

What is Sign/Status Matrix (SSM)

A

Sign/Status Matrix (SSM) is Validity and complementary information accompanying the signal carried by the word: Each word includes
status or validity indicators. As far as validity information is concerned, there is no need for a separate wire to
carry the discrete validity, failure/warning or flag signal to the various receivers.
BNR Data have a SSM that consists of Bits 29 for Sign and 30 and 31 for Status.
In the case of a defect, a failure warning is transmitted.
BCD Data has a SSM consisting of Bits 30 and 31.
In the case of a failure, the data word is suppressed (not transmitted anymore).

53
Q

What is the a429 parity check?

A

By means of this parity bit, the receiver can check that the different bits forming the word have all been
completely and correctly transmitted. It is used to increase transmission security. After the rest of the word has
been assembled, the total number of ‘1’s’ is counted. If there are an even number of ‘1’s’ in bits 1 through 31
then bit 32 is set as a ‘1’ making the sum total of ‘1’s’ odd. If there are an odd number of ‘1’s’ in bits 1 through 31
then bit 32 is set as a ‘0’. Once again the total number of ‘1’s’ is odd. The 429 receiver (sink) input port checks for
odd parity to ensure transmission efficiency, whilst the source system may annunciate unreliable data words by
terminating transmission of the affected word on the data bus.

54
Q

page 41

A

page 41

Module 5 Digital techniques (1 decks)

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