The three ways a BAS sensor silently goes wrong — and why commissioning-day accuracy doesn't last forever.
A sensor that was verified accurate at commissioning does not stay that way indefinitely, even if nothing ever visibly fails. No fault alarm fires. No wire comes loose. The sensor just gradually starts telling the control loop something slightly different from the truth. Understanding why requires separating three distinct ideas that get lumped together under "the sensor is off": offset error, span error, and drift — which is really just offset and/or span error changing slowly over time.