Proportional-plus-integral control is the recommended control action for most applications. Often called PI control, it combines proportional action and integral action in one controller. The…

Integral (reset) action is the result of an integration of controller error with time. With integral action, controller output is proportional to both the size…

(Controller output can go directly to a valve or to the setpoint of another controller. In the following discussions, it is assumed that controllers send…

Controllers can be adjusted to function correctly in many different applications. Each controller usually has three adjustment modes: • Proportional. Controller output changes by an…

Differential gap control is a refinement of on/off control. Instead of changing output from on (100%) to off (0%) at a single setpoint, differential gap…

On/off control is the simplest mode of automatic control. It has only two outputs—on (100%) or off (0%)—and only responds to the sign of the…

In open loop control, the controller adjusts the final control element without measuring the process. An example of open loop control is a cycle timer…

Control loops can be either manual or automatic. A manual control loop requires a human being to observe the value of the controlled variable. If…

When used in the early design phase, hazard assessment review techniques uncover necessary changes that can be made at minimum cost. Later, errors may be…

This is employed, particularly in larger, more complex facilities, to confirm that good design practices have been used. It is best conducted using finished P&IDs.…