SMART Measuring Instruments · Demo

Driving a twin endpoint

A SMART twin answers GraphQL at its /twin endpoint. The session below probes the twin the way an evaluator does: identity first (IS), then its registers (HAS), then its behavior (DOES). The endpoint in this walkthrough is the simulated twin — it says so, plainly; a physical SMI answers identically.

IS — what it is

{ instrument { id kind serial model } }
{ "instrument": { "id": "acme-lc500", "kind": "load-cell",
  "serial": "SN-0042", "model": "LC-500 C3" } }

HAS — what it holds

{ environmentalContext { temperatureDegC humidityPercentRh pressureKPa } }
{ "environmentalContext": { "temperatureDegC": 20.1,
  "humidityPercentRh": 49.6, "pressureKPa": 101.2 } }

DOES — what it does

{ indication { value unit servedAt } }
{ "indication": { "value": 40.003, "unit": "kg", "servedAt": 86412 } }

The reading carries its serve time — a stale twin degrades to indeterminate, never a silent pass. That rule, and the probe evidence behind the twin certificate, are in the SMI documentation.

Drive it yourself

The SST minisite hosts the simulated twins and the console walkthrough (place a load, change the temperature, read the indication back).