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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