display systems in process industries
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Display Systems in
Process Industries
Presented By:
Mohammad Umar RehmanElectrical Engg. Department
Aligarh Muslim University
Aligarh
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Introduction to Display Systems
Performance Criteria Commonly Used Techniques & Basic
Mechanisms
Indicative & Illuminative Displays
Some More Displays Conclusion
Presentation Outline
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Introduction
Display devices provide instantaneous but non-permanent communication of information betweena process or system and a human observer.
The basic purpose of all displays is the same to deliver visual information to the user.
But the means through which this is accomplished
varies significantly among the various types and
technologies of display devices.
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Introduction (Contd)
Being more Specific a Display System performs thefollowing functions:
Quantitative Readings: reading the state of a machineor process in numerical terms
Qualitative Readings: quality of machine state suchas temperature & pressure
Checking whether the process variables are withinpermissible limits
To make adjustments: modifying set point on control
information
Monitoring status of the process: high pressure,emergency shutdown etc.
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Performance Criteria
Fundamental Criterion:
Information should be presented to the observer
in as clear and unambiguous a way as possible.
Other important Criteria : Accuracy
Sensitivity
Speed of response
Ergonomic factors involving the visibility,
legibility
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Commonly Used Techniques
1. Indicating Devices
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Display Technique Mechanism Configurations
Moving Pointer
Electromechanicalmovement of apointer over a fixed
scale
Horizontal/vertical, straight,arc circular, or segmentscales with edgewise strip,
hairline, or arrow shapedpointers
Moving ScaleMovement; indicationby position of scalew.r.t. fixed pointer
Moving Dial or moving drumanalog indicators, digitaldrum indicators
Bar Graph
Indication byheight/length of avertical/horizontalcolumn
Moving Column provided bymechanically driven ribbonor LED/LCD elements
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Contd
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2. Illuminative Displays
Display Technique Mechanism Configurations
LEDs
Light output provided byrecombination & electro-luminescence in a F.B. diode
Red, yellow, green displaysconfigured as lamps, bargraphs,7-&16-segmentalphanumeric displays, dotmatrix displays
LCDs
The modulation of intensity oftransmitted-reflected light by theapplication of an electric field to aLC cell
Reflective/transmissivedisplays, bar graph, 7-segment, dot matrix,alphanumeric panels
Plasma Displays Cathode glow of a neon gasdischarge
Nixie Tubes, 7-segmentdisplays, Plasma Displays
CRT Displays
Energy of scanning electron beamby phosphor is converted to light
Monochrome & ColorTubes, storage tubes,configured as analog,storage, sampling ordigitizing oscilloscopes,
VDUs
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Indicative Devices
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Moving-pointer and moving-scale
indicators
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Simple & Rugged but erroneous due toparallax
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Bar-graph indicator (for detecting
trends of the process)
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Illuminative Displays
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The Familiar CRT
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Schematic DiagramCRT Monitor
Offers Robustness, Adaptability, but lacks focus and linearity
Moreover, they pose serious health hazards. Thus nearly obsolete
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LED/Matrix Display
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Offer High efficiency, response
time, flexibility, Cost has been
decreasing continuously
But have lower life & cant be
used in hazardous environments
LED display is rightly said to be
the display of the future
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Liquid Crystal Display (LCD)
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Energy Efficient, attractive
choice in power-critical
portable applications like PDAs,
Laptops.
But
Quality Control is difficult &
require external lighting
mechanism to be easily visible
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Plasma Displays
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Wide viewing angle
capability, does not needback lighting, and is flicker
free.
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The Human Machine Interface
(combines both Monitoring & Control)
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Some More Displays
Group Displays
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Show operating parametersof the control loops,emphasizing set-point (SP),process variable(PV), andOutput signal (OP).Operator can select a loop,control mode and canchange SP & OP
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Overview Displays
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SP shown as a reference line, deviations shown by vertical barsQuick detection of unstable of control loop
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Detail Display
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Specific to a single control loop
Similar to graphic display butincludes additional info about thevariables
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Graphic Displays (as in SCADA)
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Allows the operator to see a pictorial representation of the whole processIt is interactive, dynamically changing as real-time information changes
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Trend Displays
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Similar to chart recorders. Show the profile of a process variable as itchanges over a fixed time period. Useful for observing patternof operating history. Trends can be stored for further use.
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Conclusion
The display field is vast. Newer display technologies
continue to evolve, in synchronism with modern-day
convergence devices and systems. However, the
general awareness and knowledge about display
systems are on a lower level, compared to the hype
of related developments in the convergence arena.
In order to capitalize on displays that match modern
devices and incorporate control strategies, a
concerted effort is needed by the diverse fields todevelop effective, efficient, and economical display
systems.
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References
1. Attwood, Dennis A. et. al.Ergonomic Solutions for theProcess Industries Elsevier Press,2008.
2. Boyes, W. ed. Instrumentation Reference Book FourthEdition, Butterworth-Heinemann,2010.
3. McMillan, G. K. Process/Industrial Instruments & ControlsHandbook Fifth Edition, McGraw Hill, 2005.
4. Myers, Robert L., Display Interfaces - Fundamentals andStandards, John Wiley & Sons, New York,2002.
5. Patranabis, D. Principles of Industrial Instrumentation,Second Edition, TMH, New Delhi, 2004.
6. Singh, S.K., Computer Based Process Control, 3/e, PHI,New Delhi, 2005.
7. Electronics for You , January 2001.
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Thank You!!
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Queries
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