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Transcript
Data Presentation Elements
Muhajir Ab. Rahim
School of Mechatronics Engineering
Northern Malaysia College University of Engineering
Flashback….
input
True
value
Sensing
element
Signal
conditioning
element
Signal
processing
element
Data
output
presentation
Measured
element
value
Data presentation element is the final element in the measurement
system, its function is to present the measured value of the variable
to a human observer
Data
Presentation
Elements
Recorder/ Printer
Displays
Digital
Analogue
LED
CRT
LCD
Chart
Paperless
Laser
recorder
recorder
printer
EL
Pointerscale
indicator
Classification of Data Presentation Elements
Analogue Display
Eg; Pointer-scale indicator
Observer must interpolate if the pointer lies between two
scale marks, this may produce observation error due to :
i) Distance of the element from the observer
ii) Ambient lighting
iii) Eyesight, patience and skill of the observer
*this problem is avoided with digital display
Digital Display
 Digital display enables to show
i) character (aplhanumeric= alphabetical + numerical information)
ii) graphic (line diagrams, graphs, waveforms, bar charts, etc.,)
 Current, digital display technology
i) Light emitting diode, LED
ii) Cathode ray tube, CRT
iii) Liquid Crystal, LC
iv) Electro-luminescence, EL
Digital Display Principles
(Character displays)
 Common character format used
i) Seven-segment
ii) 7x5 dot-matrix
 Each character format has its own limitation
 Basically, character is formed by an array of
segment or dots, refers as (pixel= picture element)
 To display a character each pixel must be
separately switched ‘on’ and ‘off’ independently
of the other pixels.
Digital Display Principles
(Graphic displays)
 Consist large number of pixels arranged in rows
(along the y-axis) and columns (along the x-axis)
 To display a graphic, principle of pixel matrix
multiplexing, which is based on time division
multiplexing is used.
 Show example in the class, of 3x3 pixel matrix
(six electrical conductors for nine pixels)
1. Light Emitting Diode, LED
 Diode emits electromagnetic radiation over a
certain band of wavelength, when forward bias
 Essential materials to produce light in LED are
(GaAsP- emits red light) and (GaP- emits yellow
light)
 Intensity of emitting light is proportional to
forward bias current, IF
 High power consumption, only suitable for smallscale character display
2. Cathode Ray Tube, CRT
 Used to create large-scale display, referred as monitor
 Based on electron beam (electrons are emitted at the cathode
and accelerated towards the anode)
 Pixels are formed by phosphor dots (semiconductor
material) which emit visible radiation in response to the
impact of electrons.
 The electron beam is switched ‘on’ and ‘off’ to produce
required pattern for creating characters on screen. This
is done by applying high frequency pulse waveform to
the modulator electrode.
 High power consumption, and bulky but good for graphic
display
3. Liquid Crystal Displays (LCDs)
 Use light incident (polarization) on them to
create light and dark areas due to changes of
molecules orientation when electric field applied.
(please refer Figure 11.10 in text book)
 Pixel matrix multiplexing technique is used to
obtain a graphic display
 Lower operating voltage, lower power
consumption, good viewing angles (flat screen)
4. Electroluminescence Displays (EL)
 Light is emitted, due to (electroluminescence
effect) when a voltage is applied across
phospor material (zinc sulphide doped with
small amount of metal)
 Pixel matrix multiplexing technique is used to
obtain a graphic display
 Higher operating voltage and greater power
consumption than LCD. But good contrast ratio
(brighter) and viewing angle.
Recorder/ Printer
To provide a continuous record, on paper
or on archive memory, of the time variation
of measured variables.
Eg; chart recorder, paperless recorder,
laser printer