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 Chart Pointerscale indicator LED CRT LCD Paperless Laser recorder Analogue recorder printer EL Classification of Data Presentation Elements
Analogue Display l 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 l Digital display enables to show i) character (aplhanumeric= alphabetical + numerical information) ii) graphic (line diagrams, graphs, waveforms, bar charts, etc. , ) l 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) l Common character format used i) Seven-segment ii) 7 x 5 dot-matrix Each character format has its own limitation l Basically, character is formed by an array of segment or dots, refers as (pixel= picture element) l To display a character each pixel must be separately switched ‘on’ and ‘off’ independently of the other pixels. l
Digital Display Principles (Graphic displays) Consist large number of pixels arranged in rows (along the y-axis) and columns (along the x-axis) l To display a graphic, principle of pixel matrix multiplexing, which is based on time division multiplexing is used. l Show example in the class, of 3 x 3 pixel matrix (six electrical conductors for nine pixels) l
1. Light Emitting Diode, LED Diode emits electromagnetic radiation over a certain band of wavelength, when forward bias l Essential materials to produce light in LED are (Ga. As. P- emits red light) and (Ga. P- emits yellow light) l Intensity of emitting light is proportional to forward bias current, IF l High power consumption, only suitable for smallscale character display l
2. Cathode Ray Tube, CRT Used to create large-scale display, referred as monitor l Based on electron beam (electrons are emitted at the cathode l and accelerated towards the anode) Pixels are formed by phosphor dots (semiconductor material) which emit visible radiation in response to the impact of electrons. l 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. l High power consumption, and bulky but good for graphic display l
3. Liquid Crystal Displays (LCDs) l 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 l Lower operating voltage, lower power consumption, good viewing angles (flat screen) l
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) l Pixel matrix multiplexing technique is used to obtain a graphic display l Higher operating voltage and greater power consumption than LCD. But good contrast ratio (brighter) and viewing angle. l
Recorder/ Printer l To provide a continuous record, on paper or on archive memory, of the time variation of measured variables. l Eg; chart recorder, paperless recorder, laser printer
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