Skill Display Construction - HMI Symbol Choice

Choosing the right symbol for every equipment family on a Canvas display — Solution first, then HPG, HMI, Wizard, and only primitives as a last resort.

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Purpose

This page is the canonical reference for picking the right symbol when authoring a Canvas display. It expands Skill Display Construction - Canvas §4.5 (Choosing a symbol source) into a per-equipment-class lookup with sizing tables and the SymbolLabels keys each family exposes.

Load this skill when:

• The display you are building shows physical equipment — vessels, pumps, motors, valves, blowers, instruments, heat exchangers, conveyors.
• You are about to compose a piece of equipment from Rectangle, Ellipse, Polygon, or Path primitives. Stop. Read this page first. Primitives are the last resort, not the first move.
• You inherited a solution and want to keep new displays visually consistent with what is already there.

The cost of choosing the wrong source: a display that visually disagrees with the rest of the plant's screens, drifts under theme switches, or composes a vessel that is read as a sketch instead of as standard equipment. The cost of choosing the right source: usually one Symbol element with two SymbolLabels.

Section 1 — The symbol source order

Before composing any equipment from primitives, look for an existing symbol. The search order is fixed:

1. Solution symbols. list_elements('Solution') shows what the plant has already standardized on. If a Solution/Tanks/Tank_Vertical exists, use it — other displays in this solution already do. Mixing Solution symbols with Library symbols or Wizards for the same equipment type produces a screen set that visually disagrees with itself.
2. HPG Library (High Performance Graphics). list_elements('Library/HPG'). Flat, theme-aware symbols that respond to the standard state convention (0=Off/Stopped/Closed, 1=On/Running/Open, 2=Disabled/Out-of-Service) via the HPOffFill/HPOnFill/HPDisableFill theme brushes. This is the right default for operator control screens.
3. HMI Library for detailed/realistic symbols. list_elements('Library/HMI'). Traditional detailed symbols with shading and depth — right for training material, technical diagrams, and mechanical documentation. Wrong for live operator screens (too much visual noise competes with state communication).
4. Wizard symbols for fast-path canonical equipment. Five pre-wired Wizards (BLOWER, MOTOR, PUMP, TANK, VALVE) cover the most common cases — state and rotation dynamics are already wired internally.
5. Compose from primitives (ShapeGroup of Rectangle / Ellipse / Path) only when none of the above fits. This is the slowest path and the one most likely to drift across displays. Use the ShapeGroup recipe in Canvas §5 (Recipe 1 — Vessel with jacket).

Rule: when writing to an existing solution, run list_elements('Solution') before reaching for a Library symbol or a Wizard. Match what is already there.

Section 2 — Per-equipment-class recommended path

For each equipment family the operator is likely to name, this table maps to the recommended SymbolName path. Always confirm the actual symbol exists in the current release with list_elements(<parent path>) before referencing it — library content evolves between releases.

If list_elements() on the detailed-alternative path returns nothing matching the family, walk through the path one level higher (list_elements('Library/HMI')) and scan the subfolder names. The HMI library is ~1600 symbols deep — entries beyond what this table names exist for many narrow industries (pharma, oil & gas, water, food & bev, electrical, building automation).

Section 3 — Sizing per equipment family

All symbols scale to any proportional size. Maintain aspect ratio — never stretch asymmetrically. The base "recommended" sizes below are calibrated for a standard 1600×900 control-room Canvas; scale up proportionally on 1920×1080 or 4K-scaled canvases.

When in doubt, use Standard. The Compact column is for dense equipment grids (a 4×3 motor wall, a row of identical valves). Hero is for single-equipment focus displays (one reactor at the center of a process-area overview, one pump on a maintenance-detail screen).

Minimum sizes are hard floors: below them the symbol's internal labels and state indicators degrade past readable. If the layout pressures you below the minimum, redesign the layout — do not shrink the symbol.

Section 4 — SymbolLabels keys per family

SymbolLabels is the only way to push data into a symbol. Key matches a slot the symbol declares internally (case-sensitive). LabelValue is the binding (typically @Tag.<path>). FieldType: "Expression" is the default.

The keys exposed by the five Wizards (confirmed against Designer):

Library/HPG and Library/HMI symbol keys vary by symbol. Call list_elements('Library/HPG/<subpath>/<SymbolName>') to discover the keys a specific symbol exposes. Common conventions:

• State-based symbols expose State as the primary boolean / enum.
• Level-based symbols (tanks, drums, hoppers) expose Level and often HighAlarm / LowAlarm.
• Flow-based symbols (pumps, blowers, valves) may expose Flow or FlowRate in addition to State.
• Instrument-bubble symbols (Library/HMI/Instruments) expose a Tag key for the ISA tag name shown in the bubble.

SymbolLabels rules — from Skill Display Construction - Basics §7:

• Key must match a label key defined inside the symbol (case-sensitive).
• LabelValue uses @Tag.X / @Client.Context.X / @Now / composite strings.
• Never use @Label.X in display-element SymbolLabels — @Label. is a symbol-definition internal only.
• Never bind via direct properties on the Symbol element itself — SymbolLabels is the only data path into a symbol.

Section 5 — Discovery tools

The runtime catalogues are the authoritative source — this page's tables are guidance, not a contract. Always discover before placing:

list_elements('Solution')              -- symbols already in this solution
list_elements('Library/HPG')           -- HPG library top level
list_elements('Library/HPG/Pumps')     -- HPG pumps subfolder
list_elements('Library/HMI')           -- HMI library top level (large, may truncate)
list_elements('Library/HMI/Valves')    -- specific HMI subfolder
list_elements('Wizard')                -- the 5 Wizard symbols

Truncation: list_elements() returns at most 50 entries per call. When the result includes truncated: true, drill into specific subfolders to see complete listings.

Section 6 — Common pitfalls

Section 7 — Related skills

• Skill Display Construction - Basics — required prerequisite. Covers theme-first thinking, the build loop, binding syntax, and the global minimum-size table.
• Skill Display Construction - Canvas — the paradigm context for this skill. §4.5 (Choosing a symbol source) is the seed this page expands; §5 (Equipment cookbook) is where Recipe 1 (vessel) and Recipe 2 (Wizard) live.
• High Performance HMI Compliance — the philosophy behind the HPG library and the state-convention conventions used here.
• ISA-101 HMI Compliance — ISA-101 instrument-bubble conventions and the HMI symbol library's alignment to them.

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