Human Interface

8/3/2019 Human Interface

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HUMAN INTERFACE

To promote error free operation Safe and effective control functions

Group of interacting plant personals

Instrumentation and control system engineers Initial setting Regular monitoring Plant operators Monitoring Supervising Running the process in different stages (startup, operation, and shutdown)

Classification

Low-Level Human Interface (LLHI) High-Level Human Interface (HLHI)

Low-Level Human Interface

Panel board Instruments (indicators, recorders) Located close to LCU or DI/OU(100-200 feet)


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High-Level Human Interface

High level display devices (CRT, Printers and magnetic storage devices) Located anywhere in the plant

Configurations

Stand-alone Control Configuration Geographically centralized configuration Geographically distributed configuration

Stand-alone Control Configuration

Small and simple Applicable to a small process/digital control system with conventional controllers.

Geographically centralized configuration

Functionally distributed however geographically centralized Low-level as backup of High-level interfaces.

Advantage

Monitoring without disturbing plant operation


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Geographically distributed configuration

LLHI- plant area

HLHI- control roomAdvantages

Reduction in control room size Reduction in field wiring cost

Operator Interface Requirements

Process Monitoring Process control Process Diagnostics Process record keeping

Process Monitoring


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Normal Functions

Instantaneous value of process variables Continuous (flow, temp and pressure) Discrete variables (pump and switch positions) Status of any sensors

Tag should be included Process variables with Engg units Derived variables

Abnormal status

Alarm status of individual variable Display alarm limit Distinct alarm condition for different status Multiple alarm condition with priority status Combination of several variables at abnormal condition.

Trended Variables

Group of trended variables With engg units, time increments, and absolute time of day. With additional informations set point, allowed range and allowed rate etc.

Process control

Rapid access to continues control loop and logic sequences Facility to change

Control modes Set point Result of changes

Operator to perform logical operations with interlocking signal monitoring Information about new step initiation and halting any operations in order to perform new

logical sequences.


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Facility to manipulate control outputs to avoid single point failure.

Process Diagnosis

Information about hazardous condition

Test sensor and analyzers of process variables Test components and modules, controllers, communication elements, computing devices

and human interface itself.

Automatic detection of process faults

First-out alarm function Priority alarming functions More advanced diagnosis based on combination of alarming functions, mode of failure

Process Record Keeping

Record of short-term trending information Manual input of process data Recording of alarms : tag name of PV, time of alarm, type of alarm Periodic records of PV information Long-term storage and retrieval of information Recording of operator control actions

LLOI

Connected directly to LCU Controlling and monitoring LCU Dedicated to single LCU

Applications

conjunction with HLOI In place of HLOI Only during emergency and failure conditions


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Advantages

Suitable for operators trained to use panel-board instruments Less expensive for small applications Manual backup HLOI and control equipment

Typical LLOI instruments are

Control station Indicator station Alarm annunciators Trend recorders Smart instrumentation

Smart Continuous control station

Bar graph- Sp and PV Control output as % Digital display with units High and Low alarms Mode of operation

(slow and fast mode)

Ramp button for SP and PV Operational status alarm


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Manual Loader station

Low cost alternative of Continuous control station Back up purpose

Indicator station

To monitor process variables not associated with control loop Similar to control station with no control

push button

Optional alarming facilityLogic (sequential) station

push button and indicating lights Used for turn on/offpumps, start

automatic sequence, feed i/ps to logic

systems

Simple and low cost LLOI

Smart announciators

Alarm prioritization Annunciation and acknowledgement mode options


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First-out annunciation Alarm cutout

Chart recorders

Analog and Digital recorders Round chart , bar chart. P based recorders

Display with memory Impact or heat mechanism for plotting Axis with scale plain papers can be used Automatic labeling, range selection using alpha-numeric key Distinguish plots with colors and symbolsSmart announciators

Alarm prioritization Annunciation and acknowledgement mode options First-out annunciation Alarm cutout

Chart recorders

Analog and Digital recorders Round chart , bar chart. P based recorders

Display with memory Impact or heat mechanism for plotting Axis with scale plain papers can be used Automatic labeling, range selection using alpha-numeric key Distinguish plots with colors and symbols


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LLOI requirements

Display and push buttons sealed against the atmosphere Display with high visibility in the expected ambient light condition Push button with tactile feedback to the operatorsHLOI

Shared interface not dedicated to any LCU Control over any or all LCUs CRT and advanced display techniques (VDUs) Information shared thro shared communication facilitiesAdvantages

Saving floor space and equipment expensesArchitecture configurations

Centralized HLOI Decentralized HLOI

Overlap type Fixed HLOI Modular HLOI

Single central processing unit CRT can access to any of the control loop More no of CRT can be used as backups Peripherals are shared not dedicated

to any CRT.

Disadvantages

Complex peripheral switching andMemory-sharing implementation

Limited to less number of loops and


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Data points

More display response time Too expensive for small ones

Sharing of data among HLOI The loss of any single HLOI does not affect the system. More expensive method No extra back up units necessary


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Fixed HLOI configuration

Optional additional hardware

Secondary CRTS Keyboards Printers Mass Storage units Trend recorders voice alarm system Interface port to special communication systems Backups for all important units

Advantages

Flexibility in configuration

Modular HLOI configuration


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Modular HLOI configuration in detail

Elements used as HLOI

Microprocessor and memory components

Winchester disk magnetic disk Read/write optical disk

Removable mass memory

Floppy disk Magnetic tape Read only optical disks

Printers and plotters

Black and white dot matrix printer Pen plotter ink-jet printer Thermal transfer printers

Modular packaging Approach

Additional units

CRT module Alarm panel module


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Panel board instrumentationmodule

Work space moduleDesired characteristics on modules

Good anthropometic design Elimination of glare Easy accessibility of peripherals Simple interconnection of modules

Operator Display

Plant level Display : Information about entire unit, single are many Area level display : portion of plant (related to each other) information. Group level Display : single process information Loop level : individual control loop information


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Plant level display

Plant level information summary

Area- level display

Selected plant area displayTypes

Deviation overview display Absolute value display Panel board type display

Deviation overview display

Bar graph of deviation in process variable from set point Normalized deviation to total span Clustered plot representing no of groups in each area Exceed predetermined level deviation alarm initiated graph colour changes (green-band

concept).


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Absolute value display

Absolute PV indication Additional information: set

Value and high/low alarm limit

Panel board type display

Tag number of loops and PV PV is not in alarm low-key colour PV in alarm statuschanges color

With flashing

Underlining also possible colourblind operator

Addition to tag no, absolute valuealso displayed


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Other area level display

Area graphic display piping and Instrumentation diagram Alarm summary display list of current alarm, outstanding alarm, tag number, description of

alarm, alarm time, type of alarm, alarm status (returned to normal, acknowledgement etc)


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Group level display

Mimics panel board display: SP, control output, PV, manual, automatic, cascade mode, highlow alarm level,

Logical station, trend records

Advantages

Without additional hardware, additional stations and recorders can be added. Duplications of stations and recorders are also possible.

Other types of Display (as area display)

Batch control displays :Permits to start, top, continue, diagnose

problems in logic sequence.

Operator guides :Information about problem diagnosed by

Automatic system, emergency alternatives


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Loop-level displays : single loop information

One PV as a function of another PV Tuning display - with following facilities

Fast trend plotting manual,/auto station List of tuning parameters


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Graphic display features

Static fields background of dynamic display, includes labels, symbols and other necessaryitems

Data fields PV numerical values with units Dynamic display elements size , color , shape flexibility Zooming facility

Design considerations for displays

Simple with necessary information , freedom to change include more information Over flashy and light-colored back-ground not suitable Top 2 lines common information, bottom two line communication between operator and

HLOI

Color consistency Addition to color change during alarm state blinking , underlining should be provided.

Engineering Interface

LLEI- low level, minimum functional devices

inexpensive

HLEI full-function devices, more powerful, expensive.

Functions

System configuration : define hardware configuration, interconnections, control logic andcomputational algorithm

Operator interface configuration : define operator interacting system System documentation System failure diagnosis

Requirements

General requirements

Access security : security mech to protect unauthorized user Erconomic design : prompt-and response sequence facility, data formats understandable to

process instrumentation Engg, interconnection between engineering interfaces


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Data reasonableness and consistency : self checking of data entered by the engineers forconsistency and reasonableness.

User convenience: easy to interface EI without shutdown of the system Cost effectiveness

Requirements

System configuration requirements

Define the address of input output points based on their location in the sharedcommunication in an informative way.

Provision to define tag names and associated descriptions Define signal conditioning need to perform (such as linearization, zero and span adjustment,

unit conversion)

Provision to select ,configure and tune the control algorithms Define the communication among various units included in the control function (shared

communication address)

Documents

Human Interface