What is a human-machine interface? What is an operator interface?

Human-machine interface (HMI) and operator interface (OI) devices help humans monitor and change industrial or facility processes or factory automation. They began as control panels with mechanical devices, then incorporated electrical elements, microprocessors, and often have been replaced in form and function by computers or thin-clients, often referred to as a user interfaces (UI), OI, or HMI with a touch screen or touch panels (computers with a screen that actuate on contact), keyboard, mouse or keypad, or voice actuation. HMIs connect via communications or networking protocols connect modern control panels to sensors that provide information, actuators that change the process, and logic devices (sometimes embedded in the HMI) that make decisions. Augmented reality functionality and digital twin simulation capabilities are enhancing the next generation of HMIs.