Recommended Practice for Pipeline SCADA DisplaysAPI RECOMMENDED PRACTICE 1165 FIRST EDITION, JANUARY 2007 REAFFIRMED, JULY 2012 Copyright American Petroleum Institute... If a controller
Purpose
This Recommended Practice (RP) provides essential guidelines for the design and implementation of displays in pipeline Supervisory Control and Data Acquisition Systems (SCADA) Its main objective is to document industry standards that assist pipeline companies or operators in selecting a new SCADA system or updating and expanding their existing systems.
This RP provides guidance for pipeline companies and SCADA system developers on best practices for creating effective human machine interfaces (HMI) Key design elements covered include hardware, navigation, color schemes, font choices, symbols, data entry methods, and control/selection techniques.
Scope Limitations
This RP was developed by a task force from the API Cybernetics Subcommittee, drawing on industry standards for liquid pipeline SCADA systems The majority of the participants are involved in the operation of crude, product, chemical, and natural gas pipeline systems.
It is recognized that each pipeline company has unique operating philosophies and SCADA systems; therefore, not all elements of this recommended practice may be applicable
• Some pipeline control centers are a combination of several different SCADA systems
• Some of these SCADA systems may not have the developer tools necessary to implement the recommended practices
• Some operators may have existing display techniques that bridge over into unique operating philosophies
This RP focuses on best practices and examples for display techniques, rather than dictating operational control philosophy or the overall functionality of SCADA systems It is essential for readers to possess a solid understanding of pipeline operations and display techniques, and they may need to consult additional publications for further background or information.
This RP serves as a supplementary resource to existing procedures and effective display techniques in software development and implementation, without replacing them It does not cover regulatory or individual company standards.
1 ASM Consortium Guidelines—Effective Operator Display Design Version 2.01, July 28, 2000.
2 Galitz, W O (1993) User-interface screen design New York, NY: John Wiley & Sons: Amazon.com.
3 Gilmore, W.E., Gertman, D.I., & Blackman, H.S (1989) User-computer interface in process control a human factors engi- neering handbook San Diego, CA: Academic Press.
4 Jacko, J., A., & Salvendy, G (1996) “Hierarchical menu design: breadth, depth, and task complexity.” Perceptual and
5 Kiger, J I (1984) “The depth and breath trade-off in the design of menu-driven user interfaces.” International Journal of man-machine studies, 20, 201-213
6 O’Hara, J., Brown, W., Lewis, P & Perensky, J (2002) Human-system design review guidelines (NUREG-0700, rev 2) Washington DC: U.S Nuclear Regulatory Commission
7 Paap, K R (1988) Design of Menus In M Helander (ed.) Handbook of Human-Computer Interaction (pp 205-235) North Holland: Elsevier Science Publishers B.V.
8 Perlman, G (1984) Making the right choices with menus Proceedings of INTERACT (pp 291-295).
9 Roske-Hofstrand, R J & Paap, K R (1986) “Cognitive networks as a guide to menu organization: An application in the automated cockpit.” Ergonomics, 29(11), 1301-1311.
10 Savage, R E & Habinek, J K (1984) “A multilevel menu-driven user interface: Design and evaluation through simula- tion.” In J C Thomas & M L Schneider (Eds.) Human factors in computer systems, (pp 165-186) Norwood, N.J.: Ablex.
11 Smith, S., & Mosier, J (1986) Guidelines for designing user interface software (ESD-TR-86-278) Hanscom Air Force Base, Massachusetts: Electronic Systems Division, AFSC.
12 Snowberry, K Parkinson, S R., & Sisson, N (1985) “Effects of help fields on navigating through hierarchical menu structures.” International Journal of Man-Machine Studies, 22, 479-491.
The American Petroleum Institute (API) is the leading trade association for the oil and natural gas industry, representing over 400 members engaged in various sectors of the industry By leveraging the knowledge and expertise of its members and staff, API aims to promote a robust and sustainable oil and natural gas sector.
The API Cybernetics Subcommittee oversees the science of communication and control processes, offering educational resources and best practices to the pipeline industry for effective remote monitoring and operation of pipelines.
3.3 Button Bars: Button Bars are used to place fixed links between a series of displays or to provide links to submenus.
Client-server architecture distributes computing tasks across multiple client computers within a network, allowing them to access information from central servers This contrasts with a centralized system where a powerful mainframe handles all processing, while less capable terminals merely send requests and display the processed results.
3.5 control center: Physical location where controllers monitor and control the pipeline systems A control center typically consists of one or more controller consoles which are manned 24 hours a day, 365 days a year.
3.6 controllers: Personnel who are responsible for monitoring and controlling the pipeline system
3.7 dialog box: An interactive message box A temporary window on the screen that contains a set of choices whenever the executing program needs to collect information from the user.
3.8 display(s): The visual presentation of text and objects on a monitor.
Gestalt principles of perception, originating from German psychologists in the 1920s, emphasize the concept of "unified whole." These theories explore how individuals naturally organize visual elements into cohesive groups when specific principles are applied.
3.10 hidden text: Information that is not visible (in background) to the Controller until a specific event occurs, at which time the text becomes visible (in foreground)
A 3.11 hot spot refers to a specific area, symbol, or text on a display that, when selected, enables navigation to a predefined display, executes a command, or opens a new window This term is synonymous with navigation buttons, poke points, and poke boxes.
Human Factors Engineering (HFE) focuses on creating systems that prioritize safety, comfort, effectiveness, and usability The primary objective is to design these systems in a way that minimizes user frustration, reduces errors, and enhances productivity.
3.13 Human Machine Interface (HMI): A computer workstation normally associated with a graphics workstation that allows interaction between people and end devices
3.14 invalid: An indication of a point state that is undefined, out of range, or otherwise unknown.
Liquid Crystal Display (LCD) technology consists of two sheets of polarizing material with a liquid crystal solution sandwiched between them When an electric current is applied, the liquid crystals align in a way that either permits or blocks light, functioning like individual shutters This mechanism enables precise control over light transmission, making LCDs a popular choice for various display applications.
3.16 monitor: The term monitor refers to the hardware used to present SCADA displays to the controller
3.17 navigation button: An image of a button on a computer screen which simulates being “pushed” when clicked by the mouse
3.18 offscan: A term used to describe a point that has been deactivated from the active polling sequence (not scanned or refreshed by SCADA system).
3.19 operator: A term used for a company that monitors and controls a pipeline system
3.20 poke point: The control that is placed on top of an object that causes an action to occur when clicked.
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3.21 pop-up: A sub display, that temporarily overlays the viewing area, used to provide additional details related to the current display.
3.22 remote: A field device, such as a Remote Terminal Unit (RTU), Programmable Logic Controller (PLC) or Flow Com- puter, that communicates data and field information to and from the SCADA host
3.23 SCADA Controllable: A device or point that is controllable from the control center through the SCADA system.
The term "should" in this standard signifies commonly accepted practices, while allowing operators the flexibility to identify alternative methods that may be equally or more effective.
3.25 Supervisory Control and Data Acquisition (SCADA): A system which is a combination of computer hardware and software used to send commands and acquire data for the purpose of monitoring and controlling.
3.26 static: A term used to describe a point or object that does not change state.
3.27 tag: 1 A text string attached to a database point that indicates some relevant detail about the point
2 A type of data attribute associated with a database point
4 Human Factors Engineering Considerations in Display Design
Display design involves the arrangement and presentation of information on a monitor, which can vary significantly based on the display's intended function Consequently, the requirements for display design are often unique to each display, tailored to its primary purpose.
Effective display design is crucial for optimal information transfer to users Information must be presented clearly and consistently, organized logically, and located in expected areas Displays should maintain a clean and orderly appearance, facilitate easy navigation, and provide clear indications of interrelationships.
Display design should be guided by the following Gestalt principles, a psychology term which refers to theories of visual perception:
• Proximity—The human perception system tries to organize objects into groups if they are near each other in space.
• Similarity—Objects are perceived as a group or set if they visually share common properties, such as size, color, orientation in space, or brightness.
• Closure—The human visual perception system tries to complete figures and establish meaningful wholes Incomplete objects or symbols can then be perceived as complete or whole.
Humans naturally favor stability in their visual surroundings, making materials presented at right angles and organized in vertical or horizontal groupings more visually appealing than those with curved or angled designs.
In addition, display design should incorporate the general principles of Human Factors Engineering (HFE) discussed in the next sections.
Short-term Memory
An essential principle in display design is the limitation of human short-term memory (STM), where conscious information processing occurs Research indicates that STM can handle approximately seven blocks of information, plus or minus two, with a block defined as any meaningful cluster, such as a word, phrase, or number For new information to be added to STM, the existing data must be processed and transferred to long-term memory; otherwise, it risks being forgotten as new information takes its place.
The limitation of Short-Term Memory (STM) does not imply that a display should contain only seven, plus or minus two, points or symbols Instead, representation techniques can help the controller perceive multiple points as a single block Grouping related information, using visual demarcations like boxes, and employing closure by enclosing values within figures can enhance processing efficiency It is essential to group related information while breaking larger groups into subgroups based on user tasks and perceptions Additionally, varying the spacing of items rather than maintaining equal distances aids in the grouping process Presenting information in numeric, alphabetic, or chronological order further assists in mentally associating related groups STM also influences the number of displays needed; for instance, if a controller must compare data across different displays, STM considerations become crucial.
`,,```,,,,````-`-`,,`,,`,`,,` - ments are higher than if the same information were on a single display STM limitations pose strong arguments for a minimal number of displays with well-grouped data.
Signal-to-Noise Ratio
Communicating in a crowded room is challenging due to the overwhelming background noise that obscures words, making it hard to distinguish conversations This phenomenon mirrors the difficulty in locating a target on a display as more items are added, where anything that isn't the target becomes noise, complicating the search Therefore, when designing a display, it's crucial to evaluate each element's impact on user behavior, as even low-use items can hinder the identification of important information.
Effective display design emphasizes the importance of including only purposeful elements Each display should convey as much useful information as possible while avoiding the inclusion of unnecessary items.
Eye Scan Pattern
The placement and size of objects on a display significantly influence their perceived importance Research indicates that larger items and those positioned at the top and center attract more attention Initial eye scan patterns typically focus on specific areas, with crucial information ideally located in the upper left and lower right corners However, this does not imply that data in other areas will be overlooked, as controllers will examine the entire display after the initial scan.
Figure 1—Initial Eye Scan Pattern on a Display i
Initial Eye Scan Pattern on a Display
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Consistency
Consistency in display design is crucial, particularly for controllers using multiple monitors Early documentation of interface standards, including the placement, shape, color, and presentation of both static and dynamic elements, ensures uniformity This consistency enables quicker responses from controllers by guiding them on where to find relevant data and how it will be presented.
Consistent text presentation is crucial for readability; excessive changes in font size, style, color, capitalization, shading, or underlining can create confusion and hinder comprehension.
On-screen language should closely resemble natural conversation, steering clear of local jargon unless it is industry-specific and aids in the quick comprehension of all system users.
Coding
Coding assigns meaning to visual cues, such as using color to distinguish between normal and abnormal conditions or employing shapes to represent device symbols like pumps, valves, and meters.
Coding enhances information delivery by using visual cues, such as color, to convey messages succinctly For instance, employing red exclusively for emergencies allows alarms to change color instead of displaying the word "emergency." Additionally, coding helps overcome short-term memory (STM) limitations, as color is processed before conscious awareness, enabling effective information transfer even when STM is overwhelmed.
Before starting to build displays, it is crucial to establish a coding scheme A comprehensive list of attributes requiring codes should be outlined prior to selecting coding options This principle is applicable to the four primary coding methods.
1 Layout and Position (See Section 6).
4 Alpha-numeric or Text (See Section 8.5).
Exercise caution not to overuse coding, as it can then lose its effectiveness The following traits should be kept in mind:
• Detectable—The controller should be able to detect the stimulus Blink rates beyond human thresholds for detection do not make good codes.
The controller must effectively distinguish the code from its background and other codes Utilizing alternating colors, such as blue-yellow-blue for one meaning and yellow-blue-yellow for another, is not an effective coding technique.
• Compatible—The code should have natural associations where possible, such as associating red/green with stop/go and danger/safe
Code should only be implemented if it significantly influences the behavior of the controller; otherwise, it is unnecessary Aesthetic coding or variations without functional purpose do not justify the inclusion of code.
Consistency in coding is crucial for effective system development, as it fosters a reliable stimulus-response mechanism Developers must maintain uniform coding practices throughout the system and avoid altering coding characteristics mid-display to ensure coherence and functionality.
To enhance understanding, it is essential to utilize multiple coding techniques, as demonstrated by a stop sign, which incorporates various elements such as color (red), shape (octagonal), alphanumeric text (“stop”), and its position (right side of the road).
General Considerations
Modern SCADA systems utilize computers and workstations connected via local networks for their primary human-machine interface This approach is not only cost-effective but also scalable and easily upgradable to adapt to changing requirements.
Display Devices
Controllers receive information through video monitors that utilize various technologies, including cathode ray tubes (CRT), liquid crystal displays (LCD), projection, and plasma It is standard practice to use large monitors capable of displaying high-resolution images.
5.2.2 Number of Monitors per Controller Console
Controller consoles and workstations are generally designed with multiple monitors of the same technology, with the number determined by the expected workload and the need for concurrent display viewing The clarity of information presented on each monitor is crucial, and the display sub-system software's capability to manage multiple displays on a single monitor can also affect monitor size and quantity Typically, these consoles are arranged horizontally in front of or around the controller, with stacking of two or more rows of horizontally oriented monitors being a common setup.
5.2.3 External or Remote Display Devices
Control rooms can benefit from various display devices beyond standard monitors at workstations, including large projection systems and portable computers It is essential that remote data presentations closely mirror the information shown in the main control center for consistency and clarity.
Display projection systems enable large audiences to view the same data simultaneously In control rooms, overhead projectors are commonly used to display images on wall-mounted monitors, controlled by console computers Additionally, large-screen rear-projection systems serve a similar purpose.
A handheld terminal, which includes mobile PCs, PDAs, Pocket PCs, tablet PCs, and laptop PCs, utilizes application software to connect with SCADA process control systems through wireless networking technology.
Ensuring safety, integrity, and security is crucial for remote or handheld SCADA device interfaces, particularly when enabling remote access through wireless technology For comprehensive information on SCADA security, refer to API 1164 Pipeline SCADA.
Display Response
The response time of a display sub-system is influenced by hardware performance and software design In contemporary SCADA systems utilizing client-server architecture, both the server and the client HMI computer play a crucial role in determining the initial display call-up time and the data refresh rate It is essential to periodically review display response times after installation.
Display call-up time refers to the duration from when a display is requested to when it is fully rendered In SCADA system design, it is essential to anticipate reasonable display call-up times Typically, under normal processing loads, display call-up times should be one second or less.
Display refresh rates determine how often data updates on a screen, with software design playing a crucial role in whether all data fields are refreshed simultaneously or individually The refresh rate can vary based on the type of data being displayed, such as status or analog values, and the speed at which data is acquired from remote devices It is often essential to refresh the display as quickly as possible after the SCADA host computer processes the incoming data.
Controller Input Devices
A controller input device is any peripheral that connects to a main computer, allowing users to enter information Common examples include keyboards, mice, trackballs, touch-sensitive screens, control grips, joysticks, graphics tablets, and voice recognition devices.
The standard input devices for SCADA systems are the computer keyboard and mouse or trackball Keyboards allow users to input instructions and data through various key layouts and labels, with options for additional numeric and special-purpose function keys defined by software Meanwhile, a mouse or trackball serves as a hand-guided device that maneuvers the cursor on the screen, typically featuring at least two multifunctional buttons.
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In larger control centers, it is uncommon to have a dedicated input device for each monitor Instead, console workstations are generally equipped with a keyboard and a mouse or trackball, allowing operators to manage input across multiple monitors efficiently.
General Considerations
When designing a display, developers must determine the information to present based on the display's purpose and the tasks it supports Engaging with the controllers who will use the display is crucial for this decision-making process Displays that accurately model real-world processes are more intuitive for controllers, enabling them to respond effectively to both normal and abnormal situations However, overly detailed representations, such as including every component of field piping and equipment, can lead to visual clutter Therefore, graphics should be simplified while still accurately reflecting the actual conditions in the field.
Pipeline information can be presented in graphical or tabular formats Graphical displays are ideal for showcasing physical pipeline configurations, while tabular formats are more effective for summarizing text or numeric data, including event logs, alarm summaries, ticket details, and proving reports Additionally, tabular displays are useful for aggregating numbers from various locations, regardless of their geographical proximity.
In graphical or tabular displays, information typically flows from left to right and top to bottom, without the use of geographical orientation However, overview graphics, such as pipeline overlays on topographic maps, often represent information flow in a geographical context To enhance bidirectional station displays, dynamic directional indicators can be incorporated.
Display Hierarchy
SCADA systems are designed with a hierarchical structure that includes various levels of operational displays, each providing increasing detail This organization reduces the number of displays a controller must manage and logically groups information for easy access An example of a well-structured four-level system is presented in Table 1.
Table 1—Four Level Display Hierarchy
This display is a qualitative overview of all the pipelines operated, assuming more than one pipeline is being monitored by the same Controller Console
The overview, often represented as a pipeline systems map, serves as the top level in the hierarchy, showcasing the fundamental geographic arrangement of all pipelines This visual representation can be enhanced with navigation buttons, allowing users to easily access detailed displays of individual pipelines.
Operation of controllable field devices is normally not allowed from this display.
Operational Overview Displays or Primary Displays
This graphical or tabular display presents a single pipeline system This display could be designed with navigation buttons for access to individual station displays
Operation of controllable field devices is sometimes allowed from this display.
3 Station Displays or Secondary Displays
This display visually represents a specific station or a group of locations, emphasizing intricate details in station piping and field devices It showcases the functionality of the station, including equipment status and analog data Additionally, the design may incorporate navigation buttons for easy access to detailed displays.
Operation of controllable field devices is typically allowed from this display.
This display presents greater equipment detail and additional operational or point information, etc Examples could include control displays and informational displays
Control displays are typically pop-up type parent/child in nature and contain in-depth information for a specific data point including ranges, alarm limits, remote name, current value, etc
Informational displays include summaries for database information, event logs, trends, etc.
Window Management Issues
Effective window management is crucial in HMI design, addressing key factors such as the maximum number of open windows, their sizing and locations, the behavior of new windows in relation to existing ones, and the methods for closing, minimizing, or resizing windows.
To effectively manage open windows, it is essential to limit the maximum number of windows per monitor, irrespective of the display type Only pop-up control windows, layers, and overlays associated with a parent window should remain open until either they or the parent window is closed Child windows must be designed to move above the parent window, while secondary windows can overlay the main window but must include a close button to facilitate a return to the main interface.
The technique offers several advantages, such as reducing memory usage, streamlining the controller interface with the computer system, and ensuring connectivity between open main windows and related windows However, it may also restrict controller flexibility and necessitate the use of multiple monitors to ensure an adequate display of visible windows.
One effective technique for managing open windows is to impose no limit on their maximum number This approach enhances the controller's ability to interact with the computer system, offering nearly limitless monitor space and functionality However, it also poses risks, such as overloading the computer's resources, which can lead to system instability, and increasing the likelihood of losing track of important windows obscured by others, thereby disrupting the connection between the current visible window and its associated windows.
Window size can be either fixed or variable, influenced by the data displayed and user preferences It's crucial to ensure that important information, such as alarm names, timestamps, and messages, remains visible without the need for scrolling, especially when resizing the window To avoid data clipping or truncation, implementing window scaling is recommended.
Consistent window locations are essential for similar display types, ensuring that pop-up windows are always rendered in the same area of the main window These windows should be designed to minimize interference with the parent display data and configured to move above the parent display when necessary.
New windows can be designed to replace existing ones or be layered on top It's essential for the controller to have easy access to the main map or menu for starting over Additionally, alarm windows must remain visible and not be minimized, ensuring they stay on top of any layered windows.
SCADA system display capabilities vary depending on the chosen operating system, software, and hardware Some SCADA HMIs operate with multiple monitors as a single workspace, while others work independently Both configurations are valid; however, using a single workspace across multiple monitors allows for greater detail on complex displays, although it may reduce portability to single monitor HMIs.
Screen savers are discouraged on 24/7 active controller workstations located in secure areas However, for SCADA workstations in unsecured locations, it is advisable to implement screen savers that require passwords for added security.
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General Considerations
Effective navigation design is essential for the successful operation of SCADA systems by controllers It necessitates thorough planning that aligns with the software's capabilities and the pipeline system's operational needs Engaging with SCADA developers and controllers for input is crucial A preliminary step may involve vendor-provided training to familiarize users with the software's features and navigation techniques Understanding windowing, layering, and menu functionalities is vital before commencing the design process.
Navigation Techniques
Navigation techniques in SCADA systems refer to the various methods a controller can use to interact with displays Effective navigation design should offer multiple access methods to any display, including menus, button bars, hot spots, and navigation buttons Additionally, mouse buttons and keyboard keys can perform different functions depending on the navigation technique employed.
The controller must enable access to essential displays with minimal keystrokes or mouse clicks, allowing navigation through displays using a single input device For instance, a single action, such as a mouse click, should allow users to move to another level in hierarchical displays or toggle between the last two displays effortlessly.
Menus serve as a navigation tool for accessing different displays and should maintain consistency in terminology and structure To enhance user experience, menus must be logically organized to reduce scanning and search time Common sorting methods include arranging items by frequency of use, related display types, and geographic areas.
The number of menu options directly affects the required menu levels When multiple levels are necessary, logical grouping is essential for the controller Additionally, if numerous levels are involved, incorporating a help field or a preview feature that anticipates next-level options can enhance user experience.
Menus serve as essential navigation tools within pipeline systems, facilitating movement between various pipeline stations and SCADA applications Common types of menus include pull-downs, pop-ups, button bars, and dedicated display menus.
Pull-down menus, often referred to as "drop-down menus" or "pop-down menus," are the most prevalent type of menu utilized in graphical user interfaces (GUIs) When a user clicks on the menu title, the menu expands downward, revealing its options Users can select items by highlighting the desired line in the menu and either clicking on it or releasing the mouse button.
Pop-up menus are interactive elements that appear when a user clicks or presses a selected option within a dialog box, revealing additional menu choices.
Button Bars can be used to place fixed links between a series of displays or to provide links to submenus.
7.2.2 Hot Spots and Navigation Buttons
Hot spots and navigation buttons are interactive elements on a display that enable users to navigate to predefined screens While hot spots may lack visible indicators, it is essential for users to be informed about their functionality In contrast, navigation buttons are represented as images on the screen, mimicking the appearance of physical buttons.
“pushed” when clicked by the mouse and provides navigation to some pre-defined display
In long pipelines featuring multiple stations, individual station displays can be equipped with navigation buttons, allowing controllers to easily move between stations sequentially Additionally, hot spots on a pipeline system overview map can facilitate navigation to specific station displays by using the station names as clickable links.
The primary method of navigation involves using the mouse to position the cursor over hot spots and buttons While the mouse has a limited number of buttons, its functionality can enhance navigation options For instance, a left click may open a specific station display, whereas a right click can lead to the display linked to the most recent alarm.
Historically, dedicated keyboard keys were used to navigate displays However, keyboard sequences are not intuitive, and can be confusing Therefore, keyboard navigation alone is not commonly used.
Zoom, Pan, and Overlays
When designing graphic displays, it's crucial to consider the density of information to ensure that controllers can easily interpret the data High display density may necessitate the use of zoom, pan, layering, and overlay techniques, particularly for complex displays like maps and trends These features enable controllers to adjust the level of detail according to their specific needs Typically, zoom and pan functions are controlled via mouse buttons, while layers and overlays are activated through dedicated buttons Trend displays exemplify the advantages of zooming, as it allows for a reduction in the number of data points, thereby improving the clarity and interpretability of trends.
General Considerations
SCADA displays utilize various objects, including symbols and text, to convey information to the controller Each object possesses attributes such as color, size, shape, and fill, which enhance the information presented Effective design and planning of SCADA displays require a balanced combination of these diverse object types to ensure clarity and functionality.
There should be a distinct difference between controllable and non-controllable objects This may be done with color, borders, fonts, highlights, symbols, etc.
Color
Utilizing color significantly enhances a controller's ability to gather and process information, greatly improving search and identification tasks when implemented effectively Color serves as a powerful tool for emphasizing related data spread across a display.
The following are some guidelines to consider when choosing color.
To ensure clarity in SCADA displays, it is essential to limit the number of colors to a maximum of eleven, as research suggests However, exceptions may apply for specific applications such as batch tracking screens and commodity labeling.
Effective use of color in control room operations is crucial, as excessive application can lead to confusion and distraction While color can enhance functionality, its overuse or inconsistent application may hinder performance As the frequency and variety of colors increase, the impact of each color diminishes, reducing their attention-getting value.
When selecting colors, it is essential to ensure that each color is distinctly recognizable from the others The best contrast is achieved by using the three additive primary colors (red, green, blue) and the three additive secondary colors (yellow, cyan, magenta), along with white Avoid low contrast combinations, such as yellow on white, yellow on green, and cyan on green Colors should be chosen to provide strong contrast with each other and the background, with the most effective contrast being a light foreground against a dark background.
The apparent color of an object on display can be affected by the ambient lighting in the surrounding area Therefore, it is essential to assess colors under various lighting conditions to ensure accurate representation.
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To effectively capture a controller's attention, dynamic and high-priority information should utilize vibrant colors, while static information can be represented with less intense shades like gray for background objects Flashing colors should be reserved for critical events, such as unacknowledged alarms, to ensure they stand out However, using flashing colors for static operating conditions is discouraged, as it may distract from other important operational data.
Understanding color meanings can be simplified by using straightforward colors and leveraging their common applications in daily life Complicated or poorly designed color schemes can detract from controller performance instead of improving it.
Colors carry specific meanings in our society, as exemplified by traffic lights: red signifies stop and danger, yellow warns of potential hazards, and green indicates safety and permission to proceed.
Colors with multiple meanings can diminish their ability to attract attention and may cause confusion or errors, particularly in stressful situations To avoid this, it is essential to maintain consistency in color usage across all displays.
Color serves as a key indicator for conveying information, but it should be complemented by additional cues like symbols or text A best practice involves using a combination of colors, symbols, and text coding For instance, alongside a pump symbol, a text string can indicate the pump's status, enhancing the information provided by the color alone.
Symbols and Shapes
Utilizing symbols enhances understanding and recognition compared to plain text Establishing a consistent set of symbols is crucial for effective and clear display design It is important to employ standard symbol libraries in the creation of displays across all systems.
Symbols play a crucial role in representing equipment components and product flow, as they should clearly convey their meanings These symbols must be designed to visually resemble the objects, processes, or operations they depict Additionally, maintaining a consistent size for symbols across all designs is essential for clarity and coherence.
`,,```,,,,````-`-`,,`,,`,`,,` - plays and images chosen should be identifiable from the maximum viewing distance and under minimal ambient lighting condi- tions
Symbols should be designed as solid forms and kept simple to minimize distortion Utilizing fills and patterns can enhance detail, such as using proportional area fills in a tank symbol to represent tank volume accurately.
Appendix A1 contains examples of the more commonly used pipeline symbols.
Animation
Animation in SCADA displays involves the dynamic alteration of an object's size, shape, orientation, and movement, which is linked to variables within the SCADA system, including both analog and status values.
Animation can sometimes be distracting for controllers, leading to its limited use However, simple animations can be beneficial in specific scenarios, such as using variable size bars to represent analog readings of tank levels and for batch tracking purposes.
Text
Text legibility and comprehension are significantly influenced by two key factors: content and textual format Content refers to the information being conveyed, while format pertains to the optimal presentation style of the text.
Choosing the right font type, size, and spacing is essential for effectively presenting information on a graphical display The selection of fonts is influenced by the display technology, whether pixel or vector-based Key considerations for text formatting include the distance from the controller to the screen, monitor size, display resolution, and the spacing between characters and lines It's important to maintain a consistent case—uppercase, lowercase, or proper case—throughout the text Consistent application of formatting techniques across all displays enhances clarity and readability.
Simple sans serif fonts such as Arial, Helvetica, and Verdana provide greater clarity due to their straight lines and clear definitions, making them preferable over highly stylized fonts like Times New Roman Additionally, scripted and special effect font styles, including italicized or bolded variations, are typically avoided for better readability.
The selected font should be scaleable without deterioration in the quality of the displayed characters The chosen font should also have easily distinguishable ‘similar’ characters such as o & 0, 9 & q, X & K, S & 5, etc
Proper spacing around and within text is essential for readability, especially for controllers Fixed text spacing is ideal for tabular displays, while variable spacing suits other formats better In cases where large amounts of text are presented in a table, using a monotype or non-proportional font like Courier New ensures that each character occupies the same width, allowing for proper alignment of numbers and text.
In addition, the font weight should be heavy enough to stand out from the background; however if the font is too bold, adjacent characters may appear to run together
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Formatting techniques are applicable to all text displayed, including numeric values for dynamic data and character strings representing dynamic states Static labels identify symbols or dynamic values, while messages provide detailed information or feedback to the controller Additionally, abbreviations are utilized to present common terms in a concise manner.
Labels are essential for providing the fundamental information needed to identify, activate, or manipulate items They can be in the form of text, numbers, alphanumeric characters, or a combination of these Common types of labels include display labels, such as display titles, symbol labels like pump names, and data field labels, for instance, BBLS.
Labels must be clear, easy to read, and informative Use straightforward language or intuitive abbreviations to communicate meaning concisely It is important to avoid using similar names for different functions to prevent confusion.
Labels identifying symbols or text should be positioned close to the corresponding object for clarity Consistent placement relative to the symbol or text is essential, ensuring sufficient separation from surrounding elements for easy recognition For instance, all valve labels should maintain the same relative location to their respective valve symbols.
In data tables, every row or column must have a unique and descriptive label For repeated data fields, labels should be positioned either to the left of the rows or above the columns to enhance data grouping.
Messages can be categorized as prompts, diagnostic messages, or informational/status updates To enhance clarity, it's advisable to position key information at the beginning or end of the message, while less critical details can be included in the middle.
Messages must be clear, factual, and informative, using an affirmative and active voice They should consist of short, meaningful, and common words, ensuring simplicity Ideally, messages should require no transformation, computation, interpolation, or reference searching.
Using abbreviations effectively enables developers to present content clearly and concisely on various displays It is essential that these abbreviations maintain a consistent form—being short, meaningful, distinct, and free of punctuation Only standard and widely recognized abbreviations that the audience is familiar with should be utilized.
A standardized list of abbreviations and acronyms should be developed for online user reference, encompassing those used in point descriptors, graphic text descriptors, and engineering units Utilizing one to three character abbreviations can help reduce display clutter.
General Considerations
Object dynamics refers to changes in an object’s characteristics associated with changes in the database point(s) tied to that object
Database point changes typically involve modifications in value or state, as well as alterations in data attributes Key object characteristics that can be adjusted include color, shape, texture, area, line fill, and text In the industry, color and text are primarily used to represent object dynamics, although other attributes like line fill can also be utilized to indicate levels, such as in a tank.
Data Values
Every database point possesses a specific state or value, with some points, such as statuses, having multiple discrete states, while others, like analogs, accumulators, and tanks, are represented by numerical values It is crucial for the current or last known state or value of a database point to be clearly displayed and recognizable by the controller Additionally, for points utilizing multiple object characteristics to indicate states or values, at least one characteristic should remain consistent when data attributes are applied.
When displaying discrete data states, it's important to utilize multiple object characteristics A notable presentation technique involves pairing a character or a combination of characters with a colored symbol For instance, an open valve is represented by a green valve symbol accompanied by the green text "OPN" on a black background.
Appendix A1 provides examples of how color and text characteristics change for pump and valve states, utilizing a red and green color scheme inspired by stoplight familiarity This color coding is applicable to various pipeline devices with discrete states, and the examples include text abbreviations in parentheses It is essential to consistently apply these discrete states across all displays for clarity and uniformity.
Indicating the flow state in a pipe symbol using color is an effective practice For instance, a red pipe symbol can represent no flow conditions, while a green pipe symbol signifies detected flow.
Text objects can exhibit dynamic effects through hidden or visible text Hidden text displays an alarm message while the normal state matches the background color, rendering it effectively invisible When the normal state has abnormal data attributes, it becomes visible This approach minimizes display clutter, as most devices are usually not in an alarm state.
The visible text object type employs distinct colors to represent various point states, with text content often changing accordingly For instance, a fire alarm displays "FIRE ALARM" during an alarm and "FIRE CLEAR" when the situation is resolved An example of this can be found in Appendix A2.
It is common practice to display numeric values with foreground colors based on the state of the database point An example of this is demonstrated in Appendix A5-4.
Data Attributes
In a SCADA system, each database point possesses various data attributes that extend beyond its actual value These attributes represent specific qualities or characteristics of the point It is crucial for controllers to have easy access to both the data value and its attributes on a display, particularly those that signal the unreliability of the point's value or state.
The list of available data states is generally specific to the SCADA system in use The following states are not an all inclusive list
In some cases, the terminology is different between SCADA systems.
A database point can possess multiple data attributes simultaneously, regardless of whether the data is sourced from a field device or generated internally within the SCADA system.
A remote can operate in two modes: on-scan and off-scan In the on-scan mode, the remote's data is updated regularly, while in the off-scan mode, the SCADA system stops polling or processing the remote, resulting in no data updates.
Each database point can enter a manual override condition, allowing for manual adjustments by the controller without updating to reflect the actual field value This mode is particularly useful during instrument failures, as erroneous real-time values can lead to confusion or miscalculations In contrast, in real-time mode, the database point continuously updates to align with changes in the field value.
Status, analog, meter, and tank database points can generate alarms based on specific conditions and user-defined parameters Alarm states for analog, meter, and tank points may include high-high, low-low, rate-of-change, and deviation Status points can also have one or more defined alarm states Additionally, some systems can categorize alarms by severity, providing a visual indication of the alarm's severity level.
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When communication is lost to a remote, the SCADA system is no longer receiving updated data from the remote
A database point can be alarm inhibited to prevent alarms from being generated, while updated data for the point is still processed.
When an alarm is generated for a point, the point can be in either an unacknowledged or acknowledged state
Users can add informational tags to database points to convey important details, such as whether a point is reserved, unavailable, not commandable, or associated with a warning message This attribute signifies the presence of a tag.
9.3.2 Data Attribute Hierarchy and Display Techniques
A consistent method for presenting data attributes is essential, ensuring that the same technique is applied across all attributes whenever possible Since displaying every data attribute for each data point is impractical, it is crucial to establish a hierarchy of attributes, allowing controllers to focus on the most significant ones.
Key data attributes for symbol and text displays include off-scan, manual, communication failure, and alarm inhibit, arranged in a specific order of precedence For instance, if a point is both off-scan and in manual mode, only the off-scan data attribute will be displayed.
Having displays for documentation and training that illustrate data attribute hierarchies and display techniques can be beneficial Controllers can refer to these displays when they are unsure about a particular display technique.
It is common to utilize multiple techniques to represent data attributes, such as combining characters with color schemes For instance, a point in manual override may display a black "M" on a yellow background, while an off-scan point might show a white "O" on a blue background Text strings can also effectively indicate data attributes, with further examples provided in Appendix A1.
Object Selection
A "poke point" refers to the control positioned atop an object that triggers an action upon being clicked It is essential for the selection area of poke points to be adequately sized to ensure accurate selection of objects or buttons If a poke point is too small, it can cause user frustration during selection Additionally, overlapping poke points should be avoided, as they can result in unpredictable outcomes.
It is essential to distinguish between controllable and non-controllable objects Industry techniques for this differentiation include using color-coded labels—one color for controllable objects and another for non-controllable ones—altering the mouse pointer shape when hovering over objects, or adding borders to them For instance, as shown in Appendix A1-2 and A1-3, non-controllable devices are labeled in white, while controllable devices are marked with cyan labels.
Choosing a poke point for an object typically leads to a pop-up display that shows the available commands for the associated device It is crucial to ensure that the correct device has been selected and verified.
A device can be controlled from multiple displays, such as starting a pump from a piping, overview, or hydraulic gradient display It is essential to assess the status of related devices to decide whether the primary device should be operable from a display that lacks those associated devices.
Command Execution
To enhance the control of pipeline devices, it is essential to implement a two-step action process before sending commands to field devices This approach minimizes the risk of accidental operations due to misplaced mouse clicks A widely used method is the select-before-operate technique, where users first select a device from a display and then must click a separate button to execute the command For instance, a user would first select a valve and then click an open button to issue the command to open the valve.
In many systems, executing a command typically involves two mouse clicks on a control pop-up display For instance, once a valve is selected, users must first choose either the open or close button, followed by clicking the execute button to complete the action.
Certain commands necessitate data input, such as setting an analog setpoint Typically, multiple actions are needed before the setpoint is transmitted to the field A widely used method involves selecting the analog value, inputting the new value via a pop-up, and then clicking the execute button.
Effective feedback is essential to signal the success or failure of a controller command A command failure can be communicated through an alarm message, a device symbol blinking in a distinct color, or accompanying text next to the device symbol Conversely, a successful command is indicated by a change in the device symbol and the state text reflecting the new status.
Error Management
Effective display design techniques must incorporate error management to minimize invalid entries A well-designed interface should facilitate the management of errors and mistakes that users may encounter during functional tasks It is essential for the interface to enable easy correction and recovery, while also safeguarding the application against severe user errors.
Error messages are alphanumeric notifications that appear when an invalid value is entered or an incorrect selection is made For instance, if a controller inputs a discharge setpoint that falls outside the acceptable operating range, an error message will indicate that the value is out of range and request a new setpoint Ideally, this message should also display the valid input range for clarity.
Effective display design must accommodate both informational and warning messages, which are often triggered by executed commands For instance, when a command is sent, a warning may indicate a violation of operating procedures This allows the controller to either cancel the command before it reaches the field device or to continue with the execution of the command.
Consistency within a Company
Each pipeline company may adopt a unique approach to implementing SCADA systems, meaning that not all aspects of this recommended practice will be relevant A key factor to consider is ensuring that the operator interface maintains a high level of consistency in both functionality and appearance.
Documentation
To ensure clarity and consistency, it is essential to document the operator interface standards for SCADA systems, given their extensive and detailed nature Regular reviews and updates of this documentation are necessary to maintain its accuracy.
Consistency between Control Centers and Remote Locations
To improve communication and reduce confusion between control center and field personnel, it is essential to maintain consistency in displays, control panels, and indicators across both locations This consistency should encompass colors, symbols, text, and labels Additionally, standardizing naming conventions for equipment tags, station names, and other identifiers is crucial for alignment between the control center and remote sites.
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MOC (Management of Change)
All display changes should follow a Management of Change (MOC) process OPS Advisory Bulletin ADB-03-09 highlights some of the concerns with improper control of SCADA system changes
Documented procedures should exist and be followed for modifying SCADA displays
It is good practice for owners and operators of pipeline systems to periodically review their SCADA displays for accuracy
Companies should consider using off-line, backup, or development workstations/servers to help ensure that impending display changes are tested before moving the changes into production
After testing and verification, the display can be installed in the production system, ensuring to archive previous versions of SCADA system displays The installation should be coordinated with pipeline controllers to minimize disruption Additionally, when new display functionalities are introduced, it is essential to provide proper notification and training for the controllers.
Appendix A presents a variety of display samples for designing SCADA interfaces, incorporating information from this document and showcasing industry-accepted techniques for the liquids pipeline sector The choice of display types depends on the SCADA system's intended use, the complexity of pipeline operations, and the operating philosophy of the company.
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This article presents examples of object dynamics for common states and data attributes associated with the primary symbols and text used in SCADA displays The same principles can be applied to other symbols and text as needed.
Each page provides symbol recommendations by displaying the symbol in all valid orientations at the top It also indicates the text state location, data attribute location, and device label Below, a grid illustrates the device in typical valid states and common data attribute combinations, where multiple data attributes adhere to the documented hierarchy, excluding tag attributes.
Non SCADA Controlled Field ID - >
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Appendix A1-2: Non SCADA Controllable Valves
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Non SCADA Controlled Field ID - >
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In this example, hidden text is represented by red text on a black background for alarm states, while normal states appear as black text on a black background, effectively concealing the information unless abnormal data attributes are present When a device is in a normal state but has abnormal data attributes, the text is displayed in green on a black background This approach minimizes display clutter, as most devices are not usually in an alarm state The actual text displayed corresponds to the specific device, such as pressure relief or high tank, and remains unchanged despite fluctuations in value.
In this example, the text object utilizes a red/green color scheme to indicate danger levels, with red representing a more hazardous state The displayed text varies according to the current status; for instance, a discrete point shows "LOCAL" in red on a black background during an alarm and "AUTO" in green on a black background when the system is clear.
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This example of an analog point display is applicable to various numeric value database types, including analogs, accumulators, and tanks The page showcases several techniques for displaying analog data, along with potential color and text options for different data attribute combinations.
High-High Alarm High Alarm Normal Low Alarm Low-Low Alarm Deviation - Plus Deviation -
123.4HR 123.4HR 123.4HR 123.4HR 123.4HR 123.4HR 123.4 HR T
123.4 LR 123.4 LR 123.4LR 123.4LR 123.4 LR 123.4LR 123.4 LR T
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This example piping display integrates both static and dynamic symbols, text, navigation buttons, and numeric data from previous examples It serves to illustrate how these individual elements can be interconnected effectively.
To Station BCD To Station DEF
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Summary displays are an effective method for presenting information about multiple data points, organized in rows with relevant information in columns Common types of summary displays include databases, alarms, events, and communications Initially, these displays often feature a default filter for the data, with additional filtering options available based on the summary type, such as filtering by date, pipeline system, remote location, or point name.
Display hierarchy design enables users to access detailed displays by selecting a row in the summary Navigation can vary, as multiple detailed displays may be available depending on the selected column within a specific row To enhance data evaluation and pinpoint specific information, filtering and sorting options are often included Additionally, paging or scrolling features are typically implemented to accommodate summary displays that may span multiple pages.
Alarms serve as crucial indicators of abnormal conditions within a system, alerting controllers through an alarm management system Examples of alarms include un-commanded device changes, limit violations, and abnormal communication statuses Alarms can be categorized by severity levels, each with distinct visual and auditory signals, such as Critical (Red), Medium (Yellow), Low (Cyan), Informational (White), and Normal (Green) Additionally, unacknowledged alarms typically flash, while acknowledged alarms remain steady, ensuring clear differentiation between the two states.
In the Alarm Summary example, each alarm message includes an event timestamp, the name of the alarm point, a description of the alarm, and its severity level Selecting an alarm allows users to quickly access a detailed station display for further analysis of the related data.
Various types of tabular alarm displays are available, including an unacknowledged alarm summary that shows the latest unacknowledged alarms sorted by severity Additionally, a system alarm summary presents all outstanding alarms arranged by severity, while a chronological alarm summary lists all outstanding alarms in chronological order, regardless of their severity.
Filtering and sorting options are available for various parameters, including timestamp, pipeline system, remote, point name, point description, and message text However, to reduce the likelihood of overlooking an alarm, filtering is generally not enabled on the unacknowledged alarm display.
Time / Date System Station Remote Description Condition State/Value Point Name
13:21:20 25-Apr-05 PL 02 Station A Remote A Discharge Pressure HI HI 1430.0 PSI REMOTE_A_PL02_DSC
13:25:43 25-Apr-05 PL 01 Station A Remote B Batch Interface ALARM I/F IN REMOTE_B_PL01_INTFACE
13:32:54 25-Apr-05 PL 04 Station A Remote A Sampler Pump ALARM ON REMOTE_A_PL04_SAMPPMP
14:22:03 25-Apr-05 PL 02 Station A Remote B Receipt Pressure NORMAL 133.0 PSI REMOTE_B_PL02_RECPTPR
14:33:26 25-Apr-05 PL 02 Station A Remote B Cntrl Building Door INFO OPEN REMOTE_A_PL02_BLDGDOOR
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SCADA systems record all alarms, commands, and system messages as events, allowing controllers to review past activities Access to these events is typically facilitated through an event summary display, where each event is presented as a row.