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IEC 62744:2014 – Representation of States of Objects by Graphical Symbols
💡 Key Insight: Traditional graphical symbols in IEC 60617 and IEC 60417 depict objects in a single static state (typically de-energized). This standard bridges the gap between static symbols and the dynamic operational states that operators actually need to monitor and control in real-world systems.
1. Scope and Purpose
IEC 62744 provides generic rules for the representation of operational states of objects by graphical symbols standardized in IEC 60617, ISO 14617, IEC 60417, and similar standards. It addresses a fundamental limitation of existing graphical symbol standards: they present symbols in a single static form, typically representing the “de-energized” or “off” state, but do not provide guidance on how to represent objects in their various operational states occurring during the active life cycle.
As a horizontal standard, its purpose is to ensure coherence across the corpus of standardization documents, avoid duplication of work, and prevent contradictory requirements. It provides guidance for developers and designers of graphical symbols as well as for designers of human-machine interface (HMI) systems used in supervisory environments.
✅ Why This Matters: Modern HMI systems in power plants, manufacturing lines, and building automation display hundreds of equipment states simultaneously. Standardized dynamic graphical symbols reduce operator cognitive load, minimize misinterpretation, and improve situational awareness.
2. Principles of Dynamic State Representation
2.1 Presentation Sets
The standard introduces the concept of a “presentation set” — a family of discrete presentation forms of a graphical symbol derived from a basic static symbol, where each form represents a defined operational state. For example, a motor symbol might have presentation forms for stopped (gray), running (green), faulted (red flashing), and maintenance (blue outline). Each symbol in the set maintains visual continuity with the base symbol while clearly differentiating states.
2.2 Operational States Classification
The standard identifies generic operational states that typically occur during the active operation period of an object — from commissioning through decommissioning. These include: not energized (default), energized/standby, in operation, fault, out of service, and maintenance mode. Each state has recommended visual coding principles that balance clarity, accessibility, and industrial convention.
| Operational State | Recommended Visual Coding | Typical Application |
|---|---|---|
| Not energized / OFF | Base symbol, neutral color (gray) | Equipment available but inactive |
| Energized / Standby | Base symbol, subdued color (blue/dim) | Equipment ready but not actively processing |
| In operation / ON | Base symbol, active color (green) | Equipment performing its function |
| Fault / Alarm | Base symbol, warning color, flashing (red/yellow) | Equipment requires attention |
| Out of service | Base symbol with cross or strikethrough | Equipment intentionally taken offline |
| Maintenance mode | Base symbol with tool/wrench indicator | Equipment under maintenance |
2.3 Reasons for State Changes
The standard identifies four primary triggers for state changes that need graphical representation: changes in the supervised process (e.g., a pump starting due to level change), operator commands (manual start/stop), time-controlled activities (scheduled operations), and sporadic changes (unexpected fault conditions). Each trigger type may warrant different visual emphasis — for instance, operator-initiated changes typically use standard transitions, while fault-initiated changes should use salient alarms.
⚠️ Engineering Note: The standard recommends limiting the number of distinct states per symbol to 5-7 to avoid operator confusion. More complex state machines should be represented through additional information fields (text labels, tooltips) rather than symbol complexity.
3. Application Rules and Design Guidelines
3.1 Basic Shape Meanings
To ensure cross-cultural intuitiveness, the standard establishes general principles for basic shape meanings: circles typically represent rotating machinery (pumps, fans, motors), squares represent electrical equipment (transformers, switchgear), triangles represent valves and directional elements, and diamonds represent measurement/indication points. These conventions align with existing IEC 60617 and ISO 14617 usage while extending them to dynamic states.
3.2 Color and Animation Guidelines
The standard provides guidance on using color, brightness, and animation for state indication. Green indicates normal operation, yellow/amber indicates caution or standby, red indicates fault or alarm, blue indicates special conditions, and gray/white indicates inactive. Flashing should be used sparingly for alarm conditions only, with a recommendation of 1-3 Hz flash rate for critical alarms and steady indication for non-critical states. The standard notes that approximately 8% of male operators have some form of color vision deficiency, so color should never be the sole differentiator.
| Indication Attribute | Recommended Use | Restrictions |
|---|---|---|
| Color | Primary state differentiation | Must be supplemented by shape/text |
| Flashing | Alarm/urgent conditions only | Limited to 2-3 flash rates max |
| Brightness | Subdued vs. active states | Ensure minimum contrast ratio 3:1 |
| Shape modification | Out-of-service/blocked states | Maintain base symbol recognizability |
3.3 Information Placement
Recommended information placement follows a consistent format: the graphical symbol occupies the primary position, with status text above/below, measured values to the right, and unit/tag information to the left. This standardization reduces searching time when operators scan large HMI displays.
4. Engineering Design Insights
💡 Practical Takeaways for Engineers:
- Apply the “glance test”: An operator should be able to determine the state of any equipment item within 2 seconds of looking at the display. If your symbols require reading text to distinguish states, the visual coding needs improvement.
- Consistency across standards: Coordinate with IEC 61082 (electrical diagrams) and ISO 81714 for symbol design. Your organization may need a symbol style guide that references all applicable standards to ensure consistency across engineering disciplines.
- Consider accessibility: With 8% of operators having color vision deficiencies, use redundant coding (shape + color + text). High-contrast modes and symbol customization should be supported for operators with visual impairments.
- Dynamic behavior documentation: Each presentation set should be documented with a state transition diagram showing allowed transitions, triggering events, and timing behavior. This is essential for both HMI software development and operator training.
- Lifecycle management: As plant equipment is modified or replaced, the graphical symbol presentation sets must be updated. Include symbol documentation in your configuration management processes.
5. Frequently Asked Questions
Q1: Does this standard apply to all graphical symbols or only those in IEC/ISO standards?
The standard provides rules that can be applied to any graphical symbols used for representing operational states of objects, but it focuses on symbols from IEC 60617, ISO 14617, and IEC 60417. Organizations can extend the rules to their own custom symbols following the same principles.
Q2: How does this standard relate to alarm management standards (e.g., IEC 62682)?
The standard explicitly excludes alarm state classification and management — that is covered by dedicated alarm management standards. IEC 62744 focuses on the graphical representation of operational states, while alarm standards address alarm philosophy, prioritization, and operator response. The two should be coordinated in HMI design: alarm states use the standard’s flashing/prominent visual coding, but alarm management follows separate standards.
Q3: What if my system requires more than 6-7 operational states?
For objects with many operational states (e.g., a complex gas turbine with 20+ operating modes), the standard recommends using a layered approach: the primary symbol shows a high-level state (running/stopped/fault), with detailed state information available through tooltips, secondary detail panes, or hierarchical navigation.
Q4: How should I handle transient states (e.g., “starting up” or “shutting down”)?
Transient states such as start-up, shutdown, or transition between operational modes should be represented as distinct states in the presentation set. The standard recommends using animation (e.g., slow pulsing or color cycling) to indicate that a state change is in progress, distinguishing it from steady-state conditions.
