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M5 > 5.3 Data conversion > Flashcards

5.3 Data conversion Flashcards

1
Q

Digital computers are being used in new areas such as

A

Thrust management and engine controls

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2
Q

The Use of digital systems means the flight crews workload is

A

Reduced

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3
Q

Important considerations in using digital computers are

A

Reducing system weight and size
Increasing data handling speed
Improved system reliability

This contributes to an increase in overall aircraft efficiency

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4
Q

Data is transmitted in analogue form
E.g hands on a clock or

digital form e.g numbers on a computer screen

A

.

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5
Q

Aircraft systems typically convert data from analogue to digital and vice versa

A

.

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6
Q

Analogue and digital signals CAN BOTH contain the same information

A

E.g analogue watch with arrows pointing to the numbers

Digital watch that just shows numbers

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7
Q

Digital data signals have two set signals in that

A

0 V represents OFF
5 V represents ON

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8
Q

Analogue signals vary continuously with time and have many different values.

A

..

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9
Q

Alternating current (AC) analogue signals can be bipolar

A

In that they have positive and negative limits

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10
Q

Direct current (DC) analogue signals are unipolar.

A

They fluctuate between 0 V AND either a positive or negative value but they never alternate between positive and negative voltages

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11
Q

By locating the transmitter of a synchro system remotely

A

An indicator can show fluid quantity or pressure, without the need to run tuning through the cockpit

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12
Q

Analogue signal can have an infinite number of possible values

A

As it varies from its minimum to its maximum extremes

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13
Q

digital data signals differ from analogue sinals why

A

they only have two (binary) levels of voltage: high for “ON” and low for “OFF”

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14
Q

a digital signal is a sequence of ones and zeros.

A

.

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15
Q

fibre optic cable transmits data transmits data with light pulses on or off 1 or 0

A

.

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16
Q

digital signal must be what in some way before its understandable

A

decoded

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17
Q

a binary digit is also called what

A

a bit

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18
Q

a bit or binary digit is what

A

smallest unit of information in a computer

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19
Q

analogue singals vary in magnitude uniformly. e.g.

A

a dimmer switch

20
Q

digital signals by contrast are simply on/off e..g.

A

a simple light switch without dimming

21
Q

digital computers processs information faster and more efficiently than analogue computers but what is their disadvantage

A

(digital) only process data in 1’s and 0’s

22
Q

temperature varies and has to be converted to a digital representation of temp for digital computers to process temp information.

A

.

23
Q

the circuits used to interface digital computers to analogue computers are called

A

digital to analogue (D/A) converters
analogue to digital (A/D) converters

24
Q

D/A converters change ….

A

the digital data words of a digital computer to an equivalent analogue signal as either a voltage or current source
many different types of D/A converters but each one has same basic description

25
Q

A/D converters change…

A

-the analogue signals received from sensors to digital data understood by the digital computer.
- Many types of A/D converters exist
- type depends on type of analogue signal and what digital computer needs to understand about the signal

26
Q

aircraft with digital instruments use

A

pressure-sensitive solid state sensors

output digi signals for collection and processing by aircraft computers

27
Q

An ADC converts a continous

A

imput voltage into a digital data stream

28
Q

ADC can be used to convert analogue output from a mic to digi signals for what

A

storage on a compact disc (CD)

29
Q

three types of ADC are

A
  • direct comparison converter
  • ramp generation A/D converter
  • successive approximation converter
30
Q

fastest type of ADC is what and is often called what

A

Direct comparison converter (DCC)
AKA Flash ADC

31
Q

DCC are fast and operate virtually without delay (latency) before a transfer of data beings following an instruction

A

.

32
Q

what is used when the highest possible sample rates are needed

A

DCC’s
- they convert analogue to digital.
-comparing with known reference values
more ref. known greater accuracy

33
Q

the greater resolution , the bigger and more power hungry the DCC becomes what happens to the sample rate

A

must be reduced

34
Q

optimal resolution for DCC is

A

8-bit

35
Q

applications for a DCC include

A
  • fastest digital oscilloscopes
  • microwave measurements
  • fibre optics
  • RADAR detection
  • Wideband radio
36
Q

Ramp generation ADC is AKA

A

counter- type ADC
-uses a binary counter to feed a digital to analog converter (DAC)
-uses a counter for conversion from analogue to digital.

37
Q

advantages of ramp generation (counter-type) ADC

A
  • simple and easy to use
  • very accurate and the precision can be increased by increasing the number of bits
  • fair balance of accurate output and cheap hardware costs
38
Q

disadvantages of ramp generation (counter-type) ADC

A

every time a new conversion starts, the counter is reset and has to start counting from all zeros
- hence the conversion time is significant
-it cannot sustain high-frequency input
- worst case when input V is equal to full scale output range of DAC

39
Q

successive approximation ADC is advanced version of the digital ramp type ADC

A

designed to reduce the conversion and increase speed of operation.

40
Q

successive aproximation ADC the normal counter is replaced with a

A

(SAR) successive approximation register.
- The SAR counts by changing the bits from MSB to LSB according to input

41
Q

Digital to analogue conversion is the reverse of the A/D process

A

with each binary number being converted back into nominal levels by reconstructing the original waveform

42
Q

there are four main DAC circuits

A
  • binary weighted resistor D/A converter circuit
  • binary ladder or R-2R ladder D/A converter circuit
  • Segmented DAC
  • Delta-sigma DAC
43
Q

binary weighted ladder DAC is one of the simplest DAC each bit..

A

of a binary input controls a solid -state switch.
the switch connects either a reference voltage or grounds to a corresponding binary weighted resistor

44
Q

advantages of R-2R ladder DAC

A
  • uses only two types of resistors
  • easily scalable to any number of bits
  • output impedance is always same despite the number of bits
45
Q

disadvantages of weighted resistor DAC

A
  • increasing the number of input bits requires large value resistors(increases exponentially)
  • the values of large resistors are not accurate
  • the error in resistor value causes the loss of accuracy of the DAC for large binary numbers
  • due to the difficulty of designing resistors, it is not practical to implement them
46
Q

reconstructing a signal from digital to analogue, or from analogue to digital can degrade the signal by

A

background noise and loss of signal

47
Q
A

M5 (12 decks)

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