Instrumentation and SCADA · Signals and Basic Control
What Are Setpoints and Deadbands?
A setpoint is a target or action point, and a deadband prevents rapid switching near that point.
Equipment that starts and stops at exactly one value may chatter when the reading moves slightly. A deadband separates the start and stop points. Operators use facility settings and do not invent new values.
A fan may start at a high temperature and stop only after the room cools below a lower point. This keeps it from switching every few seconds.
Setpoints should come from approved operating needs, not from trial and error during an alarm. Moving a setpoint may affect several pieces of equipment and may change alarm time. Before an authorized change, note the old value and the reason. Watch the process long enough to see the result. A deadband should be wide enough to prevent rapid cycling but still protect the process. Repeated starts can heat motors and wear starters, valves, and pumps. NEMA MG 1 says a standard (Design A or B) motor is built for two starts in a row from cold, or one start when it is already at running temperature, unless the motor maker allows more.
Record the old setting before any authorized setpoint or deadband change.
Key point: A deadband separates the start and stop points so equipment does not switch rapidly near one value.
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Wastewater Instrumentation, SCADA, and Process Control Fundamentals
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