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Operator Interface (O/I), Human Machine Interface (HMI), and Man Machine Interface (MMI) are all terms used to describe equipment that allows an operator or system user to manipulate or control a machine or process. You will find all these terms are used regularly to describe such systems. Well, except for MMI – that’s not politically correct these days… We will settle on O/I or Operator Interface as our term of choice for our initial discussion.
If you have operated an ATM or used a computer Kiosk you are already familiar with a form of Operator Interface. In the industrial world, Operator Interfaces range from very simple keypads with text displays to complex graphical interfaces (meaning you can draw pictures for visualization purposes) that are fully configurable to allow control and monitoring of a large number of devices. They are usually attached to some type of controller, such as a PLC, through a communication link.