What Is a Closed Control Loop?

In a closed loop, a measured value returns to a controller. The controller changes an output to move the process toward a target. In an open loop, the output stays where a person or schedule puts it.

A level controller may speed up a pump as a wet well rises. In manual mode, the pump speed stays at the operator setting until someone changes it.

A closed loop depends on a trustworthy measurement. If the level signal fails low, an automatic pump may slow or stop at the wrong time. Open-loop operation removes that feedback, so a person must watch the result. Neither mode is always better. The correct mode depends on equipment condition and the written response. When control changes from automatic to manual, define who will watch the process and how often it will be checked.

Manual control requires a named person and a clear checking schedule.

Key point: A closed loop adjusts the output from feedback; an open loop holds the output where a person or schedule puts it.