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The input/output arrangements may be built into a simple PLC, or the PLC may have external I/O modules attached to a fieldbus or computer network that plugs into the PLC. The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control , distributed control systems , and networking .
In 1978, Opto 22 developed the first computer-based plug-in I/O modules, and created the Yellow-Black-White-Red color scheme used to identify digital AC input, digital AC output, digital DC input, and digital DC output modules respectively. In 1982, the company created Optomux, a serial-based I/O system using the ASCII protocol.
Power-line communication (PLC) is the carrying of data on a conductor that is also used simultaneously for AC electric power transmission or electric power distribution to consumers. The line that does so is known as a power-line carrier. In the past, power lines were solely used for transmitting electricity. However, with the introduction of ...
The Sercos (serial real-time communication system) interface is a globally standardized open digital interface for the communication between industrial controls, motion devices (drives) and input output devices (I/O). Sercos I and II are standardized in IEC 61491 and EN 61491.
IEC 61131-3 is the third part (of 10) of the international standard IEC 61131 for programmable logic controllers.It was first published in December 1993 [1] by the IEC; the current (third) edition was published in February 2013.
The HomePlug Powerline Alliance is a trade association of electronics manufacturers, service providers, and retailers that establishes standards for, and tests members' devices for compliance to, the various HomePlug power line communication technologies.
The processors receive information from input modules, process the information and decide control actions to be signalled by the output modules. The field inputs and outputs can be analog signals e.g. 4–20 mA DC current loop or two-state signals that switch either "on" or "off", such as relay contacts or a semiconductor switch.
A remote terminal unit (RTU) is a microprocessor-controlled electronic device that interfaces objects in the physical world to a distributed control system or SCADA (supervisory control and data acquisition) system by transmitting telemetry data to a master system, and by using messages from the master supervisory system to control connected objects. [1]