A device that has an output that varies to regulate a controlled variable in a certain way. A controller can be either analog or digital instruments independently, or may equivalent instruments such as the joint-control system. An automatic controller varies its output automatically in response to input directly or indirectly from measured process variables. A manual loading station manual controller, and the output is not depending on the measured process variables but can be varied only by manual adjustment. A controller may be integral with other functional elements of a control loop.
