ConstA reading is changing faster than its safe rate.
A condition a policy of the program's own raised, named by code.
A reading that is not a finite number, such as the NaN a failed probe produces. It changes nothing: a setpoint's output holds, and a level or a surge carries on from the last good reading.
A controlled reading drifted outside its safe band.
A falling level will reach empty within a few more samples.
Which threshold a reading crossed.