Input & Output Interfaces

Input/output or I/O interface is the interaction between a central processing device, such as a PLC, and input and output devices. Inputs are the signals or data received by the processing system from a digital input device, such as a switch, relay or contactor, and analog inputs from various sensors indicating the status of physical parameters, such as temperature, pressure etc. Outputs are the signals or data sent from the processing system to digital output devices, such as an indicator, lamp, alarm, relay or contactor and analog output devices, such as motors, valves and Proportional Controllers etc.

Switch and Indicator Switches

A switch is an electrical component that can "make" or "break" an electrical circuit, interrupting the current or diverting it from one conductor to another. The mechanism of a switch removes or restores the conducting path in a circuit when it is operated. It may be operated manually, for example, a light switch or a keyboard button, may be operated by a moving object such as a door, or may be operated by some sensing element for pressure, temperature or flow.

Relays

A relay is an electrically operated switch. Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state relays. Relays are used where it is necessary to control a circuit by a separate low-power signal, or where several circuits must be controlled by one signal.

Indicators (LED, lamps, beacon/emergency/stop lamps)

Emergency lamp, signal tower lights, indicator lights, andon lights, warning lights, industrial signal lights, tower lights, beacon and light towers are commonly used on equipment in industrial manufacturing and process control environments to provide visual indicators of a machine state or process event to machine operators, technicians, production managers and factory personnel.

Contactors

A contactor is an electrically controlled switch used for switching an electrical power circuit, similar to a relay except with higher current ratings and a few other differences. A contactor is typically controlled by a circuit which has a much lower power level than the switched circuit, such as a 24-volt coil electromagnet controlling a 220-volt motor switch.