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4 basic parts of an oscilloscope
- display system
- vertical system
- horizontal system
- trigger system
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Common controls for CRT scope
- beam finder
- focus
- intensity
- scale illumination
- trace rotation
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graticule of a scope
- i cm intervals
- 8 vertical x 10 horizontal
- 1/5 minor divisions
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vertical system
- controls amplitude & appearance
- adjusts vertical position
- input coupling (AC/DC)
- vertical sensitivity
- volts/div
- Ch.2 Inversion
- Chop and Alt modes
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horizontal system
- time aspect
- horizontal position
- sweep rate
- sec/div
- horizontal magnification
- delayed sweep
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trigger system
- trigger level and slope
- holdoff
- auto/normal trigger
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eye vs. camera
- band pass filter: 430 - 750 THz
- lens/focus ~ lens
- aperture ~ pupil/iris
- film(CCD) ~ retina
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retina
- rods - light sensor
- cones - colour sensor
- central part most sensitive
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angle of resolution
ability to distinguish b/w adjacent points of about 1/40th of 1 degree
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flicker & persistence of vision
- distinct flicker - 5 Hz
- noticeable flicker - 25 Hz
- imperceptible flicker - 30 Hz
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angle of view
clear perception of objects, 15o
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aspect ratio
- ratio b/w H and V dimensions
- NTSC (National Television System Committee) - 4:3
- HDTV - 16:9
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characteristics for a realistic representation of display
- shades of light and dark
- scene motion reproduced as picture motion
- natural colour
- 3D displacement required
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hue
brain's response to one or more wavelengths of light being sensed
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brightness
intensity of the light being observed
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saturation
purity of the colour being observed
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TV adjustment of hue, saturation, brightness
- hue: tint control
- saturation: colour control
- brightness: contrast & brightness controls
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Yellow is produced from:
saturated red + green
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magenta is produced from:
saturated red + blue
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cyan is produced from:
saturated green + blue
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white is produced from:
saturated red + green + blue
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black is produced from:
0% red + green + blue
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grey is produced from:
50% red + green + blue
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luminance level formula
Y = 0.299R + 0.587G + 0.144B
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Colours seen when objects are small:
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From RGB+B/W to Y+C signal transmission, the bandwidth requirement changed from ___ to ____:
17 MHz to 8 MHz
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Function of Balanced Modulators:
mix the R-Y and B-Y signals with a 3.58 MHz local oscillator to incerase the colour signal frequency so noise generated will be too high frequency to be noticed by the eye
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Sidebands
- by-product of increasing the frequency, humps below and above the carrier signal frequency on the frequency spectrum
- generally suppressed otherwise would "beat" with the sound carrier to produce visible interference at 920 kHz
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chrominance signal
phasor produced by the R-Y and B-Y colour signals, transmitted with the luminance level (Y)
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characteristic of the NTSC video signal
- luminance level (Y) + chrominance signal (C) transmitted
- 3.58 MHz phase shifted
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Angular displacement & amplitude of the phasor in the NTSC system correspond to:
- angular displacement: hue
- magnitude: degree of saturation
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In the phasor diagram of I/Q signals, what do I, -I, Q, -Q represent?
- I = orange
- -I = cyan
- Q = magenta
- -Q = green
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shadow mask
made of steel, placed b/w electron guns & phosphor coated inner surface of picture tube to make a higher accelerating voltage (20-30 kV)
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timing reference signals are
- w/in the horizontal blanking interval
- EAV (end of active video)
- SAC
- current line number
- 18-bit frame check sequence
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why does HDTV need data compression
signal is encoded as MPEG-2 in the studio
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computer video requires four parts:
- monitor
- memory
- graphics adapter
- application program
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multi-synch capability
can be used with a number of standards operating at different picture (vertical) frequencies
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resolution is determined by:
- # pixels/line
- # lines/frame
- speed the display technology can turn on/off the phosphor or LCD/plasma device
- scanning & retrace time of a line
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number of pixels per line is determined by
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dot pitch
distance between adjacent pixels, in mm
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DPI
dots per square inch, for printers
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graphics adapter / CRT controller
provide timing signals and refresh actions to constantly update the visual display device
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To ensure graphics adapter has access always to RAM:
- only allow CPU access during retrace
- use fast RAM
- use dual-port RAM
- CRT controller higher priority of access than CPU
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VGA
- video graphics adapter
- IC system developed by IBM
- display up to 256 colours on screen at a time
- analog system
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VGA interface to monitor via:
- new: 15 pin D connector
- old: 9 pin D connector
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DVI
- digital visual interface
- allows digital monitors to be used with PCs
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debug
- make use of machine code mnemonics or
- use direct numerical coding in hex or
- enter assembly language code
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normal text mode organized as ____ columns & ____ rows
80 columns 25 rows
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cosine correction
- correction when the light strikes the sensor at an angle
- reading = treading if the light strikes the sensor at a perpendicular angle x cosine of the angle of incidence
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Describe the light distribution of incandescent and fluorescent lightbulbs
- incandescent - brighter at sides than at base or the other end
- fluorescent - uniform radiation along the tube and no radiation from the ends
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means of categorizing artificial sources
- correlated colour temperature (CCT)
- colour rendering index (CRI)
- source efficacy
- lamp lumen depreciation
- rated average life
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correlated colour temperature
- chromaticity of the source
- <3000K - appear orange-white, "feels" warm
- >4000K - appears blue-white, "feels" cold
- >5000K - daylight
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colour rendering index
degree of resultant colour-shift objects undergo when illuminated by the light source as compared with the colour of those same objects when illuminated by a reference source of comparable colour temperature
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source efficacy
ratio of lumen/watt (light output per electrical power unit input)
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lamp lumen depreciation
- reduced light production due to aging
- caused by deterioration of phosphor, filament, cathode, or electrode
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average rated life
statistically determined estimate of average or median operational life
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shapes for incandescent lamps
- A - arbitrary
- G - globular
- ER - eliptical reflector
- PS - pear shaped
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fluorescent lamps
- uses ballast to provide proper starting voltage and operating current
- base conducts electricity to the cathode (filament) to heat it up
- filament produces electron cloud & its heat vapourizes the Hg vapour inside the bulb
- Hg energized to a higher state, release photon when drops back to shell
- photons collide with phosphor on inside of bulb
- light emitted
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advtanges of electronic ballasts (newer) over magnetic ballasts (older)
- better control of gas discharge process
- greater efficiency
- longer life
- operate at 25-60kHz (compared to powerline freq)
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run-length encoding
- form of data compression
- same data value occurs in many consecutive data elements are stored as a single data value and count
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relative encoding
transmitting the difference between each value and its predecessor, in place of the value itself
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quantizing error
error b/w the actual signal & the binary result
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DICOM
- Digital Imaging and Communications in Medicine
- 1024 levels (10 bits)
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TIFF
- Tagged Image File Format
- very large files, mostly uncompressed
- can produce compressed lossless files with LZW algorithm
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GIF
- Graphical Interchange Format
- 256 colours
- run-length encoding
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BMP
- Bit Map Picture
- invented by Microsoft
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JPEG
- Joint Photographic Experts Group
- stores images in a 24 bit format
- allows variable degrees of compression
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Huffman Coding
employs data structures of a binary tree to create smaller codes for common characters
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luminous intensity
- symbol: I
- unit: candela (cd)
- light intensity from a source in specific direction
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luminous flux
- symbol:
- unit: lumen (lm)
- intensity of light from a source
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illuminance
- symbol: E
- unit: lux (lx, lumen per square meter)
- density of luminous flux on a surface
- luminous flux/area
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luminous exitance
- symbol: M
- unit: lumen per square meter (lm/m2)
- flux density leaving a surface
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luminance
- symbol: L
- unit: candela per square meter (cd/m2)
- nrg reflected in a particular direction or passed through translucent material
- luminous intensity/(Acosa)
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quantity of light
- symbol: Q
- unit: lumen-second (lm.s)
- luminous nrg emitted or received during a period of time from a source whose luminous flux output varies with time
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4 ways of measuring light:
- photoemissive: release of electrons from photosensitive surface when light hits that surface
- photoconductive (junction): alteration of semiconductor material by radiation so its conductance is increased; fast response but low sensitivity
- photoconductive (bulk): higher sensitivity than junction, slower response
- photoelectric: radiation alters semiconductor material and generates a small voltage; Si - 0.5V, Ge - 0.1V
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