Input Devices, Output Devices, and Operator Interface
A wide variety of sensors, switches, and other Input devices are available to detect movement, light, temperature, color, pressure, and many other variables. There are two broad categories of Input Devices. Discrete, or digital, input devices simply provide on/off information. Analog devices detect a value within a range.
Contactors, motor starters, valves, and other Output devices are used to turn on/off motors, lights, heating elements, and other equipment that affects the system in some way. Like Input devices, both Discrete and Analog Output devices are available.
With Analog I/O, Signal Conditioners are often required to convert from one signal level to another, so that the Controller's Inputs and Outputs are compatible with the Input Devices and Output Devices they are connected.
An Operator Interface, or Human Machine Interface (HMI), device is a special type of Input/Output (I/O) device that either allows a human operator to control the system (e.g., turn a machine on or off), or gives the operator information about the system (e.g., how many parts were made today). HMI devices often provide both input and output capabilities in a single product.