Barometric Pressure (zone)

Definition

Barometric Pressure is the absolute air pressure within a cultivation zone, in hectopascals. It is sensed directly by MEMS absolute-pressure transducers on the PhytoSense Mesh, one per zone plus a facility outdoor reference. While it tracks ambient weather, in a pressure-controlled facility it is also actively managed: cultivation cells are held at a small differential to neighbouring spaces, so the zone-to-reference pressure delta is itself a monitored quantity that reveals fan balance and seal condition.

Why it matters

Barometric pressure plays two roles. First, it is the reference baseline that makes other metrics honest: ppm gas readings (CO₂, VC-MET-103) and dissolved-oxygen saturation both depend on absolute pressure, so an uncorrected drift biases the whole gas panel. Second, the zone-to-corridor pressure differential is a containment signal — sustained loss of the intended negative or positive offset means a door is ajar, a fan has failed, or a seal has degraded, which links this metric directly to Containment Integrity (VC-MET-401).

Formula

A directly measured signal. Reported zone pressure is the transducer reading after factory and thermal compensation, with the controlled differential derived alongside:

P_zone = P_raw + c_T(T) + c_cal

  P_raw   MEMS transducer reading (hPa)
  c_T(T)  thermal-compensation term
  c_cal   span/offset from annual barometric reference

Containment differential (advisory, links to VC-MET-201):
  ΔP = P_zone − P_corridor
  target ΔP held per zone classification (GCL-1..GCL-4);
  loss of intended ΔP sign or magnitude raises a seal alert.

Gas-correction export:
  k_P = P_zone / 1013.25  → supplied to CO₂ & DO sheets.

Inputs

Units & Scale

Reported in hectopascals to whole-hPa precision. Pressure is intensive and not summed; the zone figure stands alone, with the zone-to-corridor differential (ΔP, in pascals) reported alongside as the containment-relevant quantity. Confidence degrades to DEGRADED when the zone barometer disagrees with the outdoor reference by more than weather can explain (a drifting transducer) or when the controlled ΔP cannot be held despite a healthy fan command.

Sampling & Source

• Sampled every 1 minute from the PhytoSense Mesh zone, corridor, and outdoor-reference barometers.
• Thermally compensated; the gas-correction factor k_P is exported to the CO₂ and DO sheets.
• Stale handling: a barometer silent > 3 min is dropped; loss of the zone unit falls back to the outdoor reference plus modelled offset with a DEGRADED flag.
• Calibration: annual check against the facility barometric standard; drift > 0.5 hPa raises a metrology work order.

Thresholds

Recent Trend

Zone-A barometric pressure, last 14 sampling roll-ups (hPa):

Interpretation Guidance

Related Metrics

Related SOPs

• SOP Library — pressure-differential & containment procedures.
• Containment-differential loss response on CRIT — see Containment SOP set in the SOP Library.
• Pressurization-fan interlock & alarm escalation — Monitoring Systems.