Terms used by us in controls engineering


The following definitions are collected from different sources, including Australian Standards (IEC 61131-3 Programmable controllers – Programming languages; ISA-88.01 Batch Control Part 1: Models and Terminology). Some definitions were slightly modified for local use.

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PLC - A programmable logic controller is an industrial digital computer which has been ruggedised and adapted for the control of manufacturing processes, such as assembly lines, or robotic devices, or any activity that requires high reliability control and ease of programming and process fault diagnosis.

HMI - A Human Machine Interface is a software application that presents information to an operator or user about the state of a process, and to accept and implement the operators control instructions. Typically information is displayed in a graphic format (Graphical User Interface or GUI). An HMI is often a part of a SCADA (Supervisory Control and Data Acquisition) system.

SCADA - Supervisory control and data acquisition is a control system architecture comprising computers networked data communications and graphical user interfaces (GUI) for high-level process supervisory management, while also comprising other peripheral devices like programmable logic controller (PLC) and discrete Proportional Integral Differentiator (PID) controllers to interface with process plant or machinery. The use of SCADA has been considered also for management and operations of project-driven-process in construction.

Remote I/O hardware is an I/O device without a computing unit. Generally, it is physically located in different areas to process I/O signals and exchange data with the CPU unit of a PLC via an industrial bus.

Remote IO (remote I/O) panel - similarly to distributed I/O panel, field I/O panel, DX panel are interchangeable terms and refer to an enclosure which hosts remote I/O hardware, amongst other things, to provide an interface point for sensors, buttons, valves, lights and other devices. The remote I/O then provides input to a central system such as a PLC or takes outputs from the central system to devices.

Modes of Operation

Auto Mode - The equipment is completely controlled through automatic systems. Other than activating safety interlocks or changing the mode, the operator has no direct control over the operation of the equipment.

Manual Mode - The equipment is completely controlled by the operator through the HMI. The equipment will not respond to automatic system commands. It is up to the operator to decide when to operate the equipment.

Local Mode - The equipment is completely controlled by personnel in the field from local control stations. The equipment will not respond to commands from automatic systems nor from the HMI.

Out of Service (OOS) Mode - The equipment is de-selected from operation and will not operate under any circumstances.

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