SCADA Display Design Philosophy

The design of operator displays plays a critical role in the effective monitoring of process conditions. An effective display should provide operators with the necessary information in an intuitive and accessible format. This article will outline the design philosophy for operator displays, including the layout, data representation, color choices, display access and navigation, and how control strategies are commissioned and de-commissioned.

Layout

When designing operator displays, a consistent approach should be used for the appearance (look-and-feel) and functionality. Highly animated objects that may inadvertently divert the operator from important process information should be avoided. The layout should include standard line sizes, equipment representation, orientation, fonts, titles, etc.

Data Representation

Data representation should include process values and alarms. The operator should be able to easily access specific displays and graphics by selecting from a list of displays in directories or menus, or by typing display or graphic names. A link should be provided to move between related displays and graphics with different detail levels or of the same detail level. Invalid values should be highlighted with a different color.

Color Choices

The color choices should include process lines, control lines, process equipment, titles, etc.

Display Access and Navigation

The operator interface should utilize a windowing graphical user interface (GUI) environment such as Microsoft Windows, making extensive use of mouse point-click-drag functions, pull-down menus and interactive dialog boxes. The displays should contain static graphical information, as well as dynamic elements that reflect the information contained in the host computer’s database. Database point values displayed by such dynamic elements may be either telemetered from RTUs or calculated by the host server.

Control Strategies

Control strategies should be commissioned and de-commissioned in a consistent manner. The operator should be able to use elements on the display as pushbuttons to initiate pre-defined actions. These should include, as a minimum, the ability to bring up pop-up notes, trend graphs, other displays, Microsoft Excel or Access based reports, run command sequences, and access records in other databases.

Alarm Zone

Each display or graphic should have a dedicated alarm zone which should display, as a minimum, the three most recent alarms. Graphics design should maximize the use of single display with several layers, such that the layers disappear/reappear (declutter/clutter) automatically depending on the level of magnification.

Creating User-Friendly and Accessible Operator Displays for the Industrial Process

As industrial operations become increasingly automated, it is essential to ensure that their operator displays are both user-friendly and accessible. This article outlines specific requirements for creating operator displays that meet these two criteria, such as providing graphic titles and limiting the number of operator actions, as well as providing features such as faceplates, trends, and diagnostic displays.

Navigating Through Displays

In order to create displays that are easy for operators to navigate and use, there should be a limit of no more than three operator actions required to access any graphic display. Additionally, when a graphic display has an associated primary control display, such as a group display, it should have a target that immediately calls up the associated control display, and this target should be located in the same spot on every graphic that uses this feature. Furthermore, consideration should be given to preventing operators from opening too many windows and potentially masking important process information.

General Operator Graphics Requirements

The following requirements should be met when creating operator graphics: graphics titles, date and time, and graphics descriptions should all be located in standard areas; process and control line crossovers should be minimized; main process lines should be bold with secondary lines being of finer width; and process lines should either be drawn horizontally or vertically.

Faceplates

Faceplates should show dynamic process and status information about process elements such as a single control loop, pump, MOV, etc. They should be provided as separate displays or as graphic elements, and should be accessible for any tag on a graphic display with a maximum of two operator actions. Faceplates should include the tag ID, tag descriptor, process input, setpoint, output values displayed numerically with engineering units and in bar graph representation, auto/manual mode and remote/local setpoint status, visual indication for alarm status (including alarm inhibited or disabled), and symbolic and alphanumeric indication of discrete states both for two state devices and multi-state devices.

Operator Graphics

All control, monitoring, and status attributes of any tag should be displayable on graphics. For analog points, this includes measurement, setpoint, span, alarm limits, and output. For digital points, this includes input and output status. Status information includes alarm status, control mode, and control status. The format of numeric data should have the capabilities to display numeric data in formats ranging from a single digit to 8 digits (not including the sign or decimal place), and from 0 to 5 decimal places, and the numeric formatting should be configurable on an individual basis. Each state of a multi-state device should be indicated by a unique foreground/background color combination.

Trend Displays

Operator workstations should be capable of displaying trends, which should be available in adjustable window sizes. Text accompanying the trend should show the tag ID, minimum scale value, maximum scale value, engineering units, and current value. The time periods and process value scales available for trend displays should be selectable. Real time trends should be updated every two seconds with actual process data, and an option should be provided to initiate historical trend displays for any process tag or calculated variable that has been stored in either the on-line history or off-line history media. Scale and time span adjustment should also be provided on trend displays.

Diagnostic Displays

A dynamic communications overview display should be provided to show the status of the communication system and its components, and diagnostic displays should be provided to show the operational status and error conditions for all system components. On-line and off-line diagnostics should be provided to assist in system maintenance and troubleshooting, with diagnostics being provided for every major system component and peripheral. Communications diagnostic displays should show errors for each of the redundant paths, and system displays should be provided for cabinet temperature alarms and system power faults.

Data Quality

The system should display data quality indications for analog value and status point indication, including telemetry failed, manually set, calculated from manually set data, alarm blocked for analog points with alarm settings, digital and analog output marked interlocked.

Marked Tag Management

When a controlled device or a line fed by a controlled device requires maintenance, the system should provide a facility for limiting control of the device. The system should allow operators to inhibit control of devices by means of a secure, multi-level marking feature. Each point should be able to be provided with a visual attribute showing that the point has one or more tags on each display where that point is shown, and the system should permit no means of bypassing the control inhibit caused by a mark. A group mark function should also be provided that allows an operator to define a marked point, select multiple points, and apply the same marking to all selected points.

Control Functions

The operator should be able to perform all basic monitoring and control functions from graphic displays, such as changing process variables, alarm logs, set-points, switching control modes, manually driving outputs, or initiating maintenance bypasses for input points.

Reports

Out-of-range and unknown status inputs and associated calculated blocks should be flagged by a special character such as a question mark or other reserved symbol. The default location for the report printouts should be the operator console from which the report was requested. Reports should be configured to be activated on demand (operator request), scheduled (shift, daily, and monthly), and/or on event. The system should also include dedicate printers for reports only.