DSC Scanning Time

Why not ask the "Honeywell TPS DCS" manufacturer?

If you have to program the alarm scanning than it cn be relatively quite long, ask yourself how soon you need to know when there's an overtemperature, a high level, or any alarm condition. Certainly where the correction is manual then 1 or 2 seconds makes little difference to the operators reaction. If the alarm initiates and emergency shutdown procedure (ESD) which can take several minutes or even hours, then scanning times of a few seconds are OK.

The only time I've experiences millisecond scanning is in electronic systems, tripping a supply, stopping a robot, but in most process control reactions are slow. Ask yourself how soon do you need to know something is going wrong, and take action.

A DCS will not scan for alarms. The controller scan time is based on the requirements for your process control philosophy usually dictated by the process/engineering technology provider (the people who own the process chemistry and designed the plant). Measurement inputs are scanned at a pre-set interval or scan time and the system data updated, if an alarm or abnormal condition exists it will be identified when the measurement input is scanned by the system and an alarm will be generated (if configured). Typical inputs for control and interlock loops have much shorter scan times than those for indication loops.