The `measurement` node is the sensor-side of every EVOLV flow. It takes raw signal data, applies offset / scaling / smoothing / outlier rejection, and publishes a conditioned value into the shared `MeasurementContainer`. A parent equipment node (rotatingMachine, pumpingStation, reactor, ...) subscribes automatically via the child-registration handshake on port 2.
## At a glance
| Item | Value |
|---|---|
| Node category | EVOLV |
| Inputs | 1 (message-driven) |
| Outputs | 3 — `process` / `dbase` / `parent` |
| Tick period | 1 s |
| Input modes | `analog` (default) — one scalar per msg. `digital` — object payload with many keys. |
### Analog — one scalar per message (PLC / 4-20 mA)
The classic pattern — what the node did before v1.1. `msg.payload` is a single number. The node runs one offset → scaling → smoothing → outlier pipeline and emits exactly one MeasurementContainer slot keyed by the asset's type + position.
```json
{ "topic": "measurement", "payload": 12.34 }
```
Use when one Node-RED `measurement` node represents one physical sensor.
### Digital — object payload, many channels (MQTT / IoT / JSON)
Use when one Node-RED `measurement` node represents one physical **device** that publishes multiple readings. Common shapes:
`scaling` / `smoothing` / `outlierDetection` are optional — missing sections inherit the top-level analog-mode fields. `key` is the JSON field name inside `msg.payload`; `type` is the MeasurementContainer axis — any string works, not just the physical-unit-backed defaults.
## Input topics
| Topic | Payload | Effect |
|---|---|---|
| `measurement` | number (analog) / object (digital) | drives the pipeline |
| `calibrate` | — | set the offset so the current output matches `Source Min` (scaling on) or `Process Min` (scaling off). Requires a stable window — aborts if the signal is fluctuating. |
`{ topic: "registerChild", payload: <nodeId>, positionVsParent, distance }` — emitted once ~200 ms after deploy so the parent equipment node registers this sensor.
3.**Scaling** (if enabled) — linear interpolation from `[inputMin, inputMax]` to `[absMin, absMax]` with boundary clamping.
4.**Smoothing** — current value pushed into the rolling window; the configured method produces the smoothed output.
5.**Min/Max tracking** — both raw (pre-smoothing) and smoothed min/max tracked for display.
6.**Constrain** — smoothed value clamped to `[absMin, absMax]`.
7.**Emit** — `MeasurementContainer.type(...).variant('measured').position(...).distance(...).value(out, ts, unit)` triggers the event `<type>.measured.<position>` (lowercase) that the parent equipment subscribes to.
In digital mode, each channel runs this pipeline independently.
## Smoothing methods — quick reference
| Method | Use case |
|---|---|
| `none` | pass raw value through — useful for testing |
| `mean` | simple arithmetic average over window |
| `min` / `max` | worst-case / peak reporting |
| `sd` | outputs standard deviation (noise indicator) |
| `median` | outlier-resistant central tendency |
| `weightedMovingAverage` | later samples weighted higher |
| `lowPass` | EMA-style attenuation of high-frequency noise |
| `kalman` | recursive noise filter, converges to steady value |
| `savitzkyGolay` | polynomial smoothing over 5-point window |
## Outlier methods — quick reference
| Method | Best when |
|---|---|
| `zScore` | signal is approximately normal; threshold = # of SDs |
| `iqr` | signal is non-normal; robust to skewed distributions |
| `modifiedZScore` | small samples; uses median / MAD instead of mean / SD |
> **Historical bug fixed 2026-04-13:** The dispatcher compared against camelCase keys (`lowPass`, `zScore`, ...) but the validator lowercases enum values. Result: 4 smoothing methods and 2 outlier methods were silently no-ops when chosen from the editor — they fell through to the "unknown" branch and emitted the raw last value. Review any flow deployed before 2026-04-13 that relied on these methods.
## Unit policy
Unknown measurement types (anything not in the container's built-in `measureMap`: `pressure`, `flow`, `power`, `temperature`, `volume`, `length`, `mass`, `energy`) are accepted without unit compatibility checks. This lets digital channels use `humidity` (`%`), `co2` (`ppm`), arbitrary IoT units. Known types still validate strictly.
71 tests — coverage includes every smoothing method, every outlier strategy, scaling, interpolation, constrain, calibration, stability, simulation, per-channel pipelines, digital-mode dispatch, malformed-channel handling, event emits.
End-to-end benchmark scripts live in the superproject at `/tmp/m_e2e_baseline.py` (analog) and `/tmp/m_digital_e2e.py` (digital). Run against a Dockerized Node-RED stack (`docker compose up -d nodered`).
## Production status
Trial-ready as of 2026-04-13 after the session that fixed the silent dispatcher bug and added digital mode. See [session 2026-04-13](../../sessions/2026-04-13-measurement-digital-mode.md) and the memory file `node_measurement.md`.
