diffuser/wiki/Reference-Contracts.md

Reference — Contracts

Note

Pending full node review (2026-05). Topic contract, output shape and configuration schema for diffuser. Sources of truth: src/commands/index.js, src/specificClass.js getOutput(), and generalFunctions/src/configs/diffuser.json.

For an intuitive overview, return to the Home.

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Topic contract

The registry lives in src/commands/index.js. Each descriptor maps a canonical msg.topic to its handler in src/commands/handlers.js; aliases emit a one-time deprecation warning the first time they fire.

Canonical topic	Aliases	Payload	Unit	Effect
data.flow	air_flow	number	volumeFlowRate (default m3/h)	Push the measured air flow into the diffuser model. Clamps to ≥ 0 and recomputes OTR.
set.density	density	number	bottom-coverage %	Update the diffuser bottom-coverage % used as the OTR curve family key.
set.water-height	height_water	number	m	Update the water column height above the diffusers. Clamps to ≥ 0 and recomputes static head + total pressure.
set.header-pressure	header_pressure	number	mbar (gauge)	Update the header (supply) pressure above atmospheric. Feeds air-density correction.
set.elements	elements	number	integer > 0	Update the count of active diffuser elements. Drives per-element flow and total membrane area.
set.alfa-factor	alfaFactor	number	dimensionless (typically 0–1)	Update the alpha correction used in the kg O₂/h calculation.

There are no query topics today (no query.curves / query.cog analogue). The full state is on Port 0 every time a setter fires.

There are no mode / source allow-lists — the diffuser has no operational modes (auto / virtualControl / fysicalControl). Every input topic is accepted from every source.

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Data model — getOutput() shape

Composed in Diffuser.getOutput() then delta-compressed by outputUtils.formatMsg('process'). Consumers see only the keys that changed since the last emit.

Scalar keys

Key	Type	Unit	Source	Notes
iPressure	number	mbar (gauge)	this.i_pressure	Echo of last set.header-pressure.
iMWater	number	m	this.i_m_water	Echo of last set.water-height.
iFlow	number	Nm³/h (config-defaulted)	this.i_flow	Echo of last data.flow.
nFlow	number	Nm³/h	derived	Normalised air flow at standard conditions (T=20 °C, p=1.01325 bar, RH=0). Rounded 2 dp.
oOtr	number	g O₂ / Nm³	curve interpolation	Oxygen transfer rate at current density + flux. Rounded 2 dp.
oPLoss	number	mbar	o_p_water + o_p_flow	Total head loss: static head from water column + diffuser ΔP. Rounded 2 dp.
oKgo2H	number	kg O₂ / h	derived	Mass-rate of oxygen transfer. Uses α-factor and water height.
oFlowElement	number	Nm³/h per element	nFlow / elements	Per-element air flow. Rounded 2 dp.
oFluxPerM2	number	Nm³ / (h · m² membrane)	nFlow / totalMembraneArea	Canonical curve x-axis. Rounded 2 dp.
efficiency	number	% (0–100)	_combineEff	Combined OTR / ΔP score: high OTR + low ΔP → high score. Rounded 2 dp.
slope	number	g O₂/Nm³ per Nm³/(h·m²)	curve segment	Local OTR-vs-flux slope at the operating point. Rounded 3 dp.
oZoneOtr	number	kg O₂ / m³ / day	getReactorOtr(zoneVolume)	Reactor-zone OTR. Zero when diffuser.zoneVolume is unset or non-positive.
idle	boolean	—	this.i_flow ≤ 0	Derived predicate, not an FSM state.
warning	array of strings	—	this.warning.text	Flow-per-element band excursions at ± 2 % hysteresis.
alarm	array of strings	—	this.alarm.text	Flow-per-element band excursions at ± 10 % hysteresis.

Per-measurement keys

Note

The diffuser does not emit typed MeasurementContainer keys. There is no <type>.<variant>.<position>.<childId> shape on this node. Parents that want OTR / ΔP via the standard ChildRouter handshake have to wait for the future phase that promotes oOtr / oZoneOtr to typed series — tracked in Limitations.

Status badge

getStatusBadge() in specificClass.js:

Condition	Symbol	Fill	Text
alarm.state	(error compose)	red	first entry of alarm.text
warning.state	⚠	yellow	first entry of warning.text
idle (no alarm/warn)	(idle compose)	grey	<oKgo2H> kg o2 / h
active (no alarm/warn)	🟢	green (default)	<oKgo2H> kg o2 / h

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Configuration schema — editor form to config keys

Source of truth: generalFunctions/src/configs/diffuser.json + src/nodeClass.js buildDomainConfig.

General (config.general)

Form field	Config key	Default	Notes
Name	general.name	"Diffuser"	Human-readable label.
(auto-assigned)	general.id	null	Node-RED node id.
Default unit	general.unit	"Nm3/h"	Default airflow unit.
Enable logging	general.logging.enabled	true	Master switch.
Log level	general.logging.logLevel	info	debug / info / warn / error.

Asset (config.asset)

Form field	Config key	Default	Notes
Asset model	asset.model	"gva-elastox-r"	Curve registry id. Resolved via loadCurve(model). Falls back to the default on miss.
Asset tag number	asset.assetTagNumber	""	External asset registry tag (Bedrijfsmiddelenregister).

Functionality (config.functionality)

Form field	Config key	Default	Notes
Software type	functionality.softwareType	"diffuser"	Constant. Used in the parent-register handshake.
Role	functionality.role	"Aeration diffuser"	Free-text role label.
Position vs parent	functionality.positionVsParent	"atEquipment"	One of upstream / atEquipment / downstream. Carried on the child.register Port-2 message to the reactor.

Diffuser (config.diffuser)

Form field	Config key	Default	Range	Notes
Zone number	diffuser.number	1	int ≥ 1	Sequential zone number; used in the node label.
Element count	diffuser.elements	1	int ≥ 1	Number of active diffuser elements.
Membrane area / element	diffuser.membraneAreaPerElement	null	m² > 0	Overrides curve _meta.membraneArea_m2_per_element. Final fallback is 0.18 m² (Jäger TD-65 / GVA).
Diffuser density (bottom coverage)	diffuser.density	15	% > 0, typical 10–25	Curve-family key. Multi-coverage curves are interpolated; single-coverage curves are clamped. Replaces the legacy "elements per m²" semantics — an earlier refactor mislabelled this column.
Water height	diffuser.waterHeight	0	m ≥ 0	Static head + kg O₂/h factor.
Alpha factor	diffuser.alfaFactor	0.7	typically 0–1	Oxygen-transfer correction.
Header pressure	diffuser.headerPressure	0	mbar ≥ 0 (gauge)	Above atmospheric. Feeds air-density correction.
Local atmospheric pressure	diffuser.localAtmPressure	1013.25	mbar > 0	Density baseline (hidden by default).
Water density	diffuser.waterDensity	997	kg/m³ > 0	Static head calculation (hidden by default).
Zone volume	diffuser.zoneVolume	0	m³ ≥ 0	Aeration zone volume. When > 0, populates oZoneOtr (kg O₂ / m³ / day).

Unit policy

The diffuser uses a non-canonical, supplier-curve-friendly unit policy — airflow lives in Nm³/h (not m³/s) on the wire, and pressure stays in mbar (not Pa) at every boundary. Internal arithmetic converts mbar ↔ Pa where needed (_heightToPressureMbar, _calcAirDensityMbar).

Quantity	Boundary unit	Internal	Notes
Air flow	Nm3/h	Nm3/h	Normalised internally; curves are in this unit.
Header pressure	mbar (gauge)	Pa (intermediate)	Converted in _calcAirDensityMbar.
Atmospheric pressure	mbar	Pa (intermediate)	Same.
Water height	m	m	Converted to mbar head via _heightToPressureMbar.
Membrane area	m² / element	m² / element	Curve metadata or config override.
Temperature	hardcoded 20 °C	K (internal in _calcAirDensityMbar)	No temperature input topic today.

This deliberately diverges from rotatingMachine's canonical-Pa/m³·s⁻¹/W/K policy because the supplier curves and operator-facing dashboards are all in Nm³/h + mbar. The cost is reduced reuse with MeasurementContainer (see Limitations).

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Child registration

The diffuser is a leaf node — it accepts no children. Itself, it registers with the upstream parent (typically a reactor) at startup via the Port-2 handshake.

flowchart LR
    diff[diffuser]:::equip -->|child.register<br/>payload = node.id<br/>positionVsParent = atEquipment<br/>distance| reactor[reactor / parent]:::unit
    classDef equip fill:#86bbdd,color:#000
    classDef unit fill:#50a8d9,color:#000

Direction	Counterparty	Side-effect
outbound at startup	upstream reactor (Port 2)	sends child.register with positionVsParent default atEquipment and the configured distance
inbound	—	none accepted

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Events emitted

Emitter	Event	When
source.emitter	'output-changed'	At the end of every _recalculate() — i.e. on every input setter. BaseNodeAdapter listens and pushes delta-compressed Port 0 + Port 1 messages.
source.measurements.emitter	(none)	The diffuser does not currently publish typed MeasurementContainer series. Future phase.

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Related pages

Page	Why
Home	Intuitive overview
Reference — Architecture	Code map, OTR / ΔP pipeline, output ports
Reference — Examples	Shipped flows + debug recipes
Reference — Limitations	Known issues and open questions
EVOLV — Topic Conventions	Platform-wide topic rules
EVOLV — Telemetry	Port 0 / 1 / 2 InfluxDB layout