Hartwell Controls

Hartwell’s six-cell assembly line is a hostile place for radios and a worse place for ambiguous faults. Four variable-frequency drives sit within twenty metres of Cell 4. The previous gateway forwarded edge transitions to the cloud, where retries and VFD noise produced an average of seventeen false stops a week.

“The useful change was not another dashboard. It was proving why the line stopped, in order, while the evidence was still warm.”
— Luis Ortega, Controls Engineering Lead, Hartwell Controls

Deployment

Eight WB-1 nodes carry 84 active channels: 4–20 mA pressure loops, dry contacts, vibration summaries, and guarded E-stop state. Each cell owns its local decision path. A LoRa relay carries low-rate fleet state across the concrete bay; no safety decision waits for that relay.

Before and after

Measure	Before	After	Window
False VFD-correlated trips	17 / week	1 / week	eight production weeks
E-stop state fanout	96 ms	7.1 ms worst case	5,000 injected events
Product changeover	38 min	9 min	twelve changeovers
Offline rule uptime	91.6%	99.98%	90-day isolated run

The remaining false trip was a real loose shield. The audit record placed the noise burst before the contact edge and made the physical fix obvious.

Production rule

rule: cell4-estop-hold
priority: 100
when:
  any:
    - input: cell.4.estop_a
      equals: open
    - input: cell.4.estop_b
      equals: open
then:
  - output: cell.4.drive_enable
    set: false
  - output: cell.4.air_dump
    set: true
  - hold_until: safety.cell4.manual_reset
  - emit: audit.safety_hold

This rule never auto-resets. The M7 path resolves the outputs locally; the ESP32 publishes the evidence afterward. That boundary is explained in the architecture and the industrial use case.

What changed operationally

Controls engineers now deploy reviewed rule data instead of site-specific firmware. Changeover recipes carry a version, a priority band, and a rollback record. Maintenance can export the NDJSON evidence before power-cycling a cabinet, which ended the old argument over whether a stop was “network” or “machine.”