Equipment · Controlled Procedure
VC-SOP-0502 — PhytoSense Mesh Calibration
The procedure for verifying and calibrating the PhytoSense Mesh — the distributed sensor network measuring sap flow, turgor, VOC, and chlorophyll fluorescence — so that every downstream control loop and alarm acts on trustworthy data.
Uncalibrated data drives bad control. Climate, irrigation, and containment alarms all consume PhytoSense readings. A drifted node can mask a real hazard or trigger false response. A node past its calibration window is flagged suspect and excluded from auto-control until verified.
1. Purpose
To define the controlled method for routine verification, calibration, and drift management of PhytoSense Mesh nodes so that measurement accuracy stays within tolerance, suspect nodes are isolated from control loops, and the calibration state of the network is fully traceable.
2. Scope
Applies to all PhytoSense Mesh node types across the facility: sap-flow, turgor-pressure, VOC, and fluorescence sensors, plus their MDF gateways. The data these feed governs VC-SOP-0102 (climate), VC-SOP-0118 (dosing), and VC-SOP-0402 (pressure cross-checks). Excludes the Spectral Canopy Array imaging chain (VC-SOP-0124).
3. Definitions
| Term | Definition |
|---|---|
| Node | A single PhytoSense sensor unit reporting to an MDF gateway. |
| Reference Standard | A traceable calibration source (gas mix, pressure standard, fluorescence target) of known value. |
| Drift | Slow divergence of a node's reading from true value between calibrations. |
| Suspect Node | A node out of tolerance or past its window; excluded from auto-control pending action. |
| Calibration Window | The maximum interval between calibrations for a given node type. |
| As-Found / As-Left | The node reading before and after calibration; the pair documents drift. |
4. Responsibilities
| Role | Responsibility |
|---|---|
| Instrumentation Engineer (Owner) | Owns the calibration program; approves tolerances and standards; signs out-of-tolerance dispositions; owns this SOP. |
| Calibration Technician | Performs verification and calibration; records as-found/as-left. |
| Watch Commander | Authorizes removing a node from auto-control during calibration. |
| CHLORA | Tracks calibration windows; flags suspect nodes; excludes them from control; logs results. |
5. Equipment & Standards
- Traceable reference standards: certified VOC gas mix, pressure standard, fluorescence reference target
- Calibration standards within their own certification date
- Field calibration kit and MDF diagnostic tablet
- Node access permissions and any required PPE for the zone
- CHLORA calibration register open for as-found/as-left entry
6. Calibration Windows & Tolerances
| Node Type | Window | Tolerance | As-Found Fail Action |
|---|---|---|---|
| Sap-flow | 90 days | ±3 % of reading | Recalibrate; review affected dosing logs |
| Turgor-pressure | 90 days | ±0.02 MPa | Recalibrate; flag stress-alarm history |
| VOC | 60 days | ±5 % or ±2 ppb | Recalibrate; cross-check neighbor nodes |
| Fluorescence | 120 days | ±2 % Fv/Fm | Recalibrate; re-baseline zone canopy |
| MDF gateway clock | 30 days | ±50 ms | Resync; audit timestamp continuity |
7. Procedure
7.1 Scheduling & Suspect Isolation
- CHLORA lists nodes due within the next 7 days; the Technician sequences work to minimize control-loop gaps.
- Before touching a node, the Watch Commander authorizes its removal from auto-control; CHLORA substitutes the nearest healthy node or holds the loop at last-good.
- Any node already flagged suspect is prioritized.
7.2 As-Found Verification
- Present the reference standard to the node without adjustment; record the as-found reading.
- Compare against tolerance (Section 6). If within tolerance, log as-found = as-left and proceed to release.
- If out of tolerance, record the deviation and notify the Instrumentation Engineer for disposition — including review of any control action taken on bad data.
7.3 Adjustment & As-Left
- Adjust the node against the reference standard across its operating range (minimum 3-point: low, mid, high).
- Record the as-left reading at each point; confirm all within tolerance.
- A node that cannot be brought into tolerance is tagged out-of-service and scheduled for replacement; CHLORA keeps it excluded.
7.4 Cross-Validation & Release
- Cross-check the calibrated node against at least one neighbor reading the same zone; agreement must be within combined tolerance.
- Verify the gateway timestamp is synced within ±50 ms before re-enabling control input.
- Watch Commander authorizes return to auto-control; CHLORA restores the node and stamps the new window.
7.5 Quality Checkpoints
- Reference standards within their own certification date
- As-found and as-left recorded for every node (drift traceable)
- Out-of-tolerance findings dispositioned with control-history review
- Neighbor cross-validation within combined tolerance before release
- No node returned to auto-control without Watch Commander authorization
8. Anomaly Responses
| Finding | Indication | Immediate Action |
|---|---|---|
| Window Lapsed | Node past calibration window | CHLORA flags suspect and excludes from control; schedule within 48 h. |
| Out of Tolerance | As-found exceeds tolerance | Disposition with engineer; review control actions on the bad data window. |
| Neighbor Disagreement | Calibrated node still disagrees with neighbors | Hold release; investigate sensor or local plant condition before trusting either node. |
| Gateway Time Skew | Timestamp drift > 50 ms | Resync; audit affected records for ordering errors; notify monitoring. |
9. Records
- As-found / as-left calibration records per node (retained 5 years)
- Out-of-tolerance dispositions and control-history reviews
- Out-of-service tags and replacement records
- Calibration register with current windows (CHLORA), feeding metrics and monitoring
10. References
- VC-SOP-0124 — Spectral Canopy Array Calibration & Imaging
- VC-SOP-0102 — Greenhouse Climate & Lighting Control
- VC-SOP-0118 — Hydro-Loop Nutrient Dosing & pH Balance
- VC-SOP-0402 — Hydro-Loop Overpressure Response
- Operational Metrics · Monitoring Systems
11. Revision History
| Rev | Date | Author | Summary |
|---|---|---|---|
| A–C | 2087–2089 | Instrumentation Engineer | Initial issue; per-type windows and tolerances established. |
| D | 2090-09-17 | Instrumentation Engineer | Suspect-node auto-exclusion and as-found/as-left record added. |
| E | 2091-05-08 | Instrumentation Engineer | Neighbor cross-validation gate and gateway clock sync formalized. CBO approval. |