Elements of a system

Most systems need to be controlled, and this is usually done by means of a feedback loop which checks the outputs and feeds the results back into the system. A system with a feedback loop is called a closed-loop system.

Digital control systems use a programme or series of commands to control the system's functioning.

All systems have three main elements:

• Input(s)
• Process(es)
• Output(s)

The most basic type of system is called an open-loop system. In this type of system, the input triggers the process and the process controls the output. The diagram shows an open-loop system in manufacturing.

A more complex type of system is a closed-loop system. Like an open-loop they have inputs, processes and outputs, but they also have another element called feedback. Feedback is information from the output of a system which is 'fed back' into the input to control the way the system works.

The following diagram for a manufacturing process shows feedback from customer and employee satisfaction surveys being used to control the process, by adjusting inputs and thereby modifying outputs.