packing — environment (humidity-rh)
Physics
Section titled “Physics”A capacitive relative-humidity (RH) sensor’s polymer dielectric absorbs ambient water vapor, changing its capacitance in proportion to %RH; a transmitter converts that capacitance to a 0-100% RH scalar. In a packing/warehouse zone, sustained high humidity softens corrugate board (reducing box compression strength and stacking integrity), degrades hot-melt or pressure-sensitive adhesive tack, and can promote condensation on cold product entering a warm zone, all of which lower package and product shelf stability. This recipe reuses the generic high/high-high plus rate-of-rise threshold detector (rw_analytics.thermal.ThermalParams) for this non-temperature scalar: the field names high_c/high_high_c/rise_c_per_min are historically named for Celsius, but that is purely cosmetic here — the underlying math (an absolute warn threshold, a higher alarm threshold, and a rate-of-rise check) is unit-agnostic and applies identically to %RH as to deg C, because the registry has no dedicated environment detector; this is a deliberate, documented simplification given the current detector registry, not a physics error. Warehouse/packing-zone humidity changes on a minutes-to-hours scale (a dock door cycling, an HVAC setpoint change), so sampling at 0.1 Hz (once every 10 s) gives ample Nyquist margin over the fastest realistic RH change rate (on the order of 1%RH/min from a dock door opening in humid weather) while keeping data volume low for a slowly-varying scalar.
Sensor
Section titled “Sensor”- Spec: capacitive relative-humidity transmitter, 0-100% RH, analog or digital output
- Signal: scalar (%), range n/a
Example parts
Section titled “Example parts”- Vaisala HMP60 humidity and temperature transmitter (0-100% RH, 4-20 mA / Modbus output)
- Sensirion SHT35-DIS humidity/temperature sensor module (industrial I2C, 0-100% RH) with an industrial transmitter enclosure — pair with a DIN-rail signal conditioner for a 4-20 mA or Modbus output if the edge DAQ has no native I2C input
- E+E Elektronik EE210 humidity/temperature transmitter (0-100% RH, 4-20 mA output)
Mounting
Section titled “Mounting”Mount the transmitter’s sensing head at operator-height (1.5-2 m) on a column or wall in the packing/case-sealing zone, away from direct dock-door airflow and away from any shrink-wrap or steam-tunnel equipment’s direct exhaust, so the reading represents general zone conditions rather than a local equipment plume. Use a perforated protective cap if dust or cardboard fiber is present.
Wiring
Section titled “Wiring”4-20 mA or Modbus RTU output (per the chosen transmitter) goes to an analog input channel or RS-485 port on the edge box’s DAQ module; use a shielded twisted pair and ground the shield at the DAQ end only to avoid a ground loop with nearby conveyor or sealer drive electronics.
Validation
Section titled “Validation”use a calibrated reference hygrometer to log ambient %RH at the sensor’s location for 30 minutes while opening an adjacent dock door in humid outdoor conditions to create a known RH swing, and compare the recipe’s logged %RH trace against the reference
Expected: recipe-reported %RH tracks the reference hygrometer within +/-3% RH over the full excursion, and the warn/alarm events fire within one sample interval of the reference crossing the configured thresholds
Safety notes
Section titled “Safety notes”- de-energize and lock out (LOTO) any conveyor or sealer circuit the transmitter’s power or signal wiring passes near before routing cable through shared cable trays or junction boxes
- mount the transmitter and its cable run clear of forklift traffic lanes and conveyor pinch points in the packing area
- secure the cable run so it cannot be snagged by a case, pallet, or powered conveyor section passing beneath the mounting location
180–650 USD, difficulty 1/5, ~15 min install downtime.