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Instruments & Calibration

Measured variables require metadata about the instruments used for analysis and their calibration history. The protocol uses a type-safe hierarchy: each chemistry-specific variable class is paired with an instrument type that enforces the correct calibration schema.

Instrument Hierarchy

graph TD
    AI["AnalyzingInstrument"]
    AI --> PHI["PHInstrument"]
    AI --> CRMI["CRMInstrument"]
    AI --> CO2D["CO2GasDetector"]

    PHI -->|calibration| PHC["pHCalibration"]
    CRMI -->|calibration| CRMC["CRMCalibration"]
    CO2D -->|calibration| CO2C["CO2Calibration"]

    style AI fill:#e0e8f0
    style PHI fill:#d0d8e0
    style CRMI fill:#d0d8e0
    style CO2D fill:#d0d8e0
    style PHC fill:#f0e8d0
    style CRMC fill:#f0e8d0
    style CO2C fill:#f0e8d0
Instrument Used By Calibration Type
AnalyzingInstrument Generic measured variables Base Calibration
PHInstrument pH variables pHCalibration (dye info)
CRMInstrument TA and DIC variables CRMCalibration (CRM batch info)
CO2GasDetector CO₂ variables CO2Calibration (standard gas info)

Calibration Fields

All calibrations share a common set of fields:

Field Description
technique_description How the instrument was calibrated
calibration_location Factory, lab, or field
frequency How often calibration is performed
last_calibration_date Most recent calibration
method_reference Citation for the calibration method

pH Calibration

Adds dye-specific fields for spectrophotometric pH measurement:

  • Dye type and manufacturer
  • Whether the dye was purified
  • Correction method for unpurified dye
  • pH of calibration standards

CRM Calibration

Adds Certified Reference Material fields for TA and DIC:

  • CRM manufacturer (e.g., Dickson lab)
  • CRM batch number

CO₂ Calibration

Adds standard gas fields for CO₂ gas detectors:

  • Standard gas manufacturer, concentration, and uncertainty

The analyzing_instrument field on measured variables is automatically constrained to the correct instrument type based on the variable class:

{
  "schema_class": "DiscretePHVariable",
  "analyzing_instrument": {
    "instrument_type": "spectrophotometer",
    "manufacturer": "Agilent",
    "calibration": {
      "technique_description": "Tris buffer in synthetic seawater",
      "calibration_location": "lab",
      "dye_type_and_manufacturer": "Purified m-cresol purple, MCR Inc."
    }
  }
}

Full Schemas

→ AnalyzingInstrument · Calibration · PHInstrument · CRMInstrument · CO2GasDetector