cnc_mill — environment (dust-concentration)

Physics

An optical/laser particulate sensor passes a sample air stream through a laser beam and measures light scattering off suspended particles to estimate mass concentration (mg/m3), commonly reported as PM-class bins. Dry machining (chip dust) or wet machining (coolant mist aerosolized by the spindle) both elevate local particulate concentration near the enclosure or mist-collection exhaust; a rising trend signals a filter loading up or an extraction fan degrading, both a housekeeping/health hazard and a precursor to visible haze on guarding and optics. 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 mg/m3 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. Particulate concentration near an exhaust duct changes on a sub-minute to minutes scale, so sampling at 1 Hz gives ample margin over the fastest realistic concentration change rate while resolving transient spikes from a cutting pass.

Sensor

Spec: optical/laser particulate concentration sensor, mass concentration output, PM1/PM2.5/PM10 bins
Signal: scalar (ug/m3), range n/a

Example parts

Sensirion SPS30 particulate matter sensor module (laser scattering, PM1/2.5/4/10 mass concentration output via I2C/UART) — pair with an industrial DIN-rail enclosure and a signal conditioner for a 4-20 mA or Modbus output if the edge DAQ has no native I2C/UART input
TSI DustTrak II 8530 aerosol monitor (real-time mg/m3 mass concentration, analog output)
Palas Fidas Fine industrial particulate monitor (continuous mg/m3 output)

Mounting

Mount the sensor’s inlet in the mist-collection exhaust ductwork (downstream of the enclosure, upstream of the filter bank) or just inside the CNC enclosure near the extraction take-off point, oriented per the sensor’s datasheet airflow requirement. Position it so it does not obstruct the duct’s cross-section or restrict exhaust airflow; use a saddle-tap fitting rather than a full-bore intrusion into the duct.

Wiring

Sensor output (I2C/UART, or a 4-20 mA / Modbus signal from the conditioner) goes to a digital or analog input channel on the edge box’s DAQ module; route the cable along the duct support away from the spindle drive’s power cabling and ground the shield at the DAQ end only.

Validation

run the mill on a known dry-machining job while blocking the extraction fan intake partially (simulating filter loading) and compare the recipe’s logged mg/m3 trace against a reference particulate monitor placed alongside the installed sensor

Expected: recipe-reported mg/m3 tracks the reference monitor within +/-15% over the test, and the warn/alarm events fire within one sample interval of the reference crossing the configured thresholds

Safety notes

de-energize and lock out (LOTO) the extraction fan and any machine circuit the sensor’s wiring passes near before cutting into or tapping the duct
do not install the sensor or its mounting hardware in a way that obstructs or restricts exhaust ductwork airflow; a blocked or narrowed duct reduces extraction effectiveness and increases operator exposure to airborne particulate
wear appropriate respiratory protection when accessing the duct or enclosure interior for installation, per the site’s existing dust-exposure procedure

Cost

150–900 USD, difficulty 3/5, ~60 min install downtime.