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Operator Graphical Displays for Process Control System

This article is about Operator Graphical Displays used in petrochemical plants for process control systems and technical specification required. This article is referenced from engineering standard SAES-Z-001 and international codes and standards.

Operator Graphical Displays: Best Practices for Design and Navigation

In the industrial process control systems (PCS) world, operator graphical displays are the primary means of obtaining information and controlling the system. These displays are crucial for informing operators of the process status and enabling them to make decisions on how to control the system. As such, it is important to ensure that the design and navigation of operator graphical displays are optimized for maximum effectiveness. This article will explain the best practices for designing and navigating operator graphical displays.

General Operator Graphics Requirements

In order to ensure that operator graphical displays are effective, certain requirements need to be taken into consideration. Firstly, all graphics should include a title, date and time, and display name. Secondly, a consistent approach should be taken to the appearance and functionality of the graphics. Bright colours should be used to convey key information, and subdued colours should be used for process vessels, process lines and equipment labels. Furthermore, process lines should either be drawn horizontally or vertically, and crossovers should be minimized.

Design Philosophy

When designing operator graphics, a standardized approach should be taken for the entire process plant. This includes the layout, data representation, colour choices, display access and navigation, control strategies, control modes and data validity. Wherever possible, library elements should be used when assigning elements to a graphic, as this ensures consistency between elements on graphics.

For example, if the background colour of a process value indication in a controller element is specified to be flashing red for unacknowledged alarm condition, solid red for acknowledged alarm condition, and flashing background colour for unacknowledged return-to-normal alarms, this behaviour should be specified in a display convention file and the element linked to the display convention.

Display Navigation

Operators should be able to easily access specific displays and graphics by pressing dedicated function keys, selecting from a list of displays in directories and menus, or by typing display or graphic names. Display navigation should be configured such that it is possible to move between related displays and graphics of different detail levels or of the same detail level with a maximum of two operator actions. Any graphic display should be accessible via no more than three operator actions, and all process graphics should include a “Previous Display” button or capability which will call-up the previous process graphic when selected.

Control Strategies

Control strategy information should be shown on primary process graphic displays and should be dynamic, reflecting the actual current state of the strategy. Process data associated with control strategies should be updated at least once every two seconds. The operator should be able to perform all the basic monitoring and control functions from graphic display or control faceplates called from the primary process graphic display.

These functions include, but are not limited to, monitoring process variables, manipulating setpoints, switching control modes, and manually driving outputs. Control strategy information should be displayed on process graphics in such a way that the operator can determine what is being controlled, the control mode for individual controllers, and which are constrained or limited in some way. Where alternate control paths exist for advanced process controls, the graphical interconnecting line representation should change colour to indicate the active control path.

Control Faceplate Displays

Control faceplates should show dynamic process and status information about a function block or tag and should permit an operator to change required parameter values associated with the function block.

This includes the tag ID, tag descriptor, process input, setpoint, and output values displayed numerically with engineering units, process input, setpoint, and output in bar or graphical representation, control mode (auto/manual) and setpoint status (remote/local), visual indication of setpoint and output high and low limits, symbolic and alphanumeric indication of discrete states, for signal selectors all available process inputs with visual indication of which input is selected and the selection method, and visual indication for alarm status, acknowledgeable on a point-by-point basis.

The following actions should be possible from each faceplate as applicable: change control block mode, change setpoint and other operator settable parameters, issue commands to multi-state devices, and adjust outputs in manual mode. Faceplates should be constructed from templates, with the layout and operational characteristics of the individual faceplates inherited from the template such that each faceplate constructed from the template will have the same look and operational characteristics as the template.

Plant Safety Displays (PSD)

Plant Safety Displays (PSD) should be provided and configured with the PCS. The PSD should consist of a collection of displays whose purpose is to provide status information for the various safety devices located throughout the plant. The PSDs should be configured in a hierarchy allowing the operator to easily view the overall status of all plant safety equipment on a single display while enabling the operator to obtain more detailed information by drilling down to selected process areas.

The top-level PSD should be an aerial view of the plant showing the major equipment as it is arranged in the facility. It should indicate the status of the H2S / LEL gas detectors in their physical location throughout the plant, contain a wind speed and wind direction indication dial, if available, to enable the viewer to quickly determine the down-wind direction for any alarm, contain an indicator showing the ESD bypass status for each plant area, contain an indicator showing the gas detector bypass status for each plant area, contain a single symbol to indicate the fire alarm status for the plant, and contain a single symbol to indicate the PCS cabinet alarm status for the plant.

In process facilities which are made up of multiple plant or process areas, the top-level PSD should be configured to call-up a more detailed PSD display for each process or plant area by selecting the physical location of the plant on the top level display. The process / plant area PSDs should display an aerial view of the particular process area. The status of all H2S / LEL gas detectors should be shown on these displays, in their specific locations.

Gas detector indicators on the process / plant area PSDs should be configured to bring up a removable overlay which displays the detector measurement by selecting the detector graphic symbol. Furthermore, the ESD bypass indicators and Gas Detector bypass indicators related to the plant area should be displayed on the process / plant area PSD, while the online / offline status of major equipment should be indicated on the process / plant area PSDs.

H2S / LEL Gas Detector Indicators for Plant Safety Displays

The status of all H2S / gas detectors should be superimposed on the PSD displays using a small circle to indicate each device. Indicators should be placed onto the plant layout display at the location in which they exists in the field. When no alarm is present, the symbol should be shown in green colour. Gas detector symbols should be configured to change colour when in alarm condition based on the type of detector which is in alarm. H2S alarms should cause the symbol to change to a blue colour and LEL detector alarms should be indicated with a red colour.

Gas detector symbols should be configured to change to a different colour based on the alarm level. High alarms should be indicated using a light blue or red colour based on the type of detector in alarm. High-High alarms should be indicated using a dark blue or red colour. Gas detector indicators should be configured to show acknowledge / unacknowledged status for each alarm using a non-flashing / flashing symbol (respectively) similar to process alarms. Gas detector indicators should also be configured to show the detector fault for each detector using a separate colour.

Conclusion

Operator graphical displays are a vital part of industrial process control systems, as they provide operators with the necessary information to control the system. It is therefore important to ensure that the design and navigation of operator graphical displays are optimized for maximum effectiveness. This article has outlined the best practices for designing and navigating operator graphical displays, including general operator graphics requirements, design philosophy, display navigation, control strategies, and control faceplate displays. Furthermore, it has outlined the requirements for plant safety displays and H2S / LEL gas detector indicators. When adhering to these best practices, operators will be able to more effectively control the system and ensure the safety of the plant.

  1. International Codes and Standards Used in Process Control System.
  2. Process Control System Segregation in Terms of Risk Areas.
  3. Spare and Expansion Capabilities of Process Control System.
  4. Process Control and Equipment Protection.
  5. Control Console Technical Specification for Industrial Control Projects.
  6. Guidelines for Process Alarm Systems: Alarm System Management.
  7. Distributed Control System (DCS) Historization and Trending.
  8. Process Control System Access and Security.
  9. Process Control System Integration and Interface with other Disciplines.
  10. Technical Requirements for System, Network and Server Cabinets – PCS.
  11. Electrical Wiring and Power Distribution for Distributed Control Systems.
  12. Process Control Network Cabling Requirements | PDFBAG

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