5.3 Data conversion

Question 1

Digital computers are being used in new areas such as

Answer 1

Thrust management and engine controls

Question 2

The Use of digital systems means the flight crews workload is

Answer 2

Reduced

Question 3

Important considerations in using digital computers are

Answer 3

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

This contributes to an increase in overall aircraft efficiency

Question 4

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

digital form e.g numbers on a computer screen

Answer 4

.

Question 5

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

Answer 5

.

Question 6

Analogue and digital signals CAN BOTH contain the same information

Answer 6

E.g analogue watch with arrows pointing to the numbers

Digital watch that just shows numbers

Question 7

Digital data signals have two set signals in that

Answer 7

0 V represents OFF
5 V represents ON

Question 8

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

Answer 8

..

Question 9

Alternating current (AC) analogue signals can be bipolar

Answer 9

In that they have positive and negative limits

Question 10

Direct current (DC) analogue signals are unipolar.

Answer 10

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

Question 11

By locating the transmitter of a synchro system remotely

Answer 11

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

Question 12

Analogue signal can have an infinite number of possible values

Answer 12

As it varies from its minimum to its maximum extremes

Question 13

digital data signals differ from analogue sinals why

Answer 13

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

Question 14

a digital signal is a sequence of ones and zeros.

Answer 14

.

Question 15

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

Answer 15

.

Question 16

digital signal must be what in some way before its understandable

Answer 16

decoded

Question 17

a binary digit is also called what

Answer 17

a bit

Question 18

a bit or binary digit is what

Answer 18

smallest unit of information in a computer

Question 19

analogue singals vary in magnitude uniformly. e.g.

Answer 19

a dimmer switch

Question 20

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

Answer 20

a simple light switch without dimming

Question 21

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

Answer 21

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

Question 22

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

Answer 22

.

Question 23

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

Answer 23

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

Question 24

D/A converters change ….

Answer 24

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

Question 25

A/D converters change...

Answer 25

-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

Question 26

aircraft with digital instruments use

Answer 26

pressure-sensitive solid state sensors output digi signals for collection and processing by aircraft computers

Question 27

An ADC converts a continous

Answer 27

imput voltage into a digital data stream

Question 28

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

Answer 28

storage on a compact disc (CD)

Question 29

three types of ADC are

Answer 29

- direct comparison converter - ramp generation A/D converter - successive approximation converter

Question 30

fastest type of ADC is what and is often called what

Answer 30

Direct comparison converter (DCC) AKA Flash ADC

Question 31

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

Answer 31

.

Question 32

what is used when the highest possible sample rates are needed

Answer 32

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

Question 33

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

Answer 33

must be reduced

Question 34

optimal resolution for DCC is

Answer 34

8-bit

Question 35

applications for a DCC include

Answer 35

- fastest digital oscilloscopes - microwave measurements - fibre optics - RADAR detection - Wideband radio

Question 36

Ramp generation ADC is AKA

Answer 36

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

Question 37

advantages of ramp generation (counter-type) ADC

Answer 37

- 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

Question 38

disadvantages of ramp generation (counter-type) ADC

Answer 38

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

Question 39

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

Answer 39

designed to reduce the conversion and increase speed of operation.

Question 40

successive aproximation ADC the normal counter is replaced with a

Answer 40

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

Question 41

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

Answer 41

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

Question 42

there are four main DAC circuits

Answer 42

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

Question 43

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

Answer 43

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

Question 44

advantages of R-2R ladder DAC

Answer 44

- uses only two types of resistors - easily scalable to any number of bits - output impedance is always same despite the number of bits

Question 45

disadvantages of weighted resistor DAC

Answer 45

- 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

Question 46

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

Answer 46

background noise and loss of signal