Why it matters
It is the most defensible mechanism in a safety system because it can be explained after the fact by pointing at a number and a constant. That property matters enormously when an incident is being investigated.
Monitoring & detection
Threshold detection
Threshold detection classifies a reading by comparing it against one or more fixed limits, producing a discrete state such as safe, warning, danger or critical.
How it works
Each channel carries a set of ordered limits. A reading is compared against them in order and assigned the highest state it satisfies. Inverted channels, where a lower value means more hazard, need their comparison reversed.
Example
A channel with warn at 300 and critical at 700 classifies a reading of 450 as WARN.
In Alfa HazardX
Per-sensor thresholds run on the node and again server-side. The flame channel is inverted - a brighter flame pulls the analog value down - so its check is reversed throughout.
Read further
Related terms
- Hazard detectionHazard detection is the act of determining that a hazardous condition exists now, usually by comparing a sensor reading against a defined limit.
- Risk classificationRisk classification reduces multiple sensor readings to a single ordered state - such as SAFE, MODERATE or CRITICAL - that expresses how dangerous the current situation is.
- Sensor driftSensor drift is the gradual change in a sensor's output over time for an unchanged input, caused by ageing, contamination or environmental exposure.