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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 .
Actuator Sensor Interface (AS-Interface or ASi) is an industrial networking solution (Physical Layer, Data access Method and Protocol) used in PLC, DCS and PC-based automation systems. It is designed for connecting simple field I/O devices (e.g. binary ON/OFF devices such as actuators, sensors, rotary encoders, analog inputs and outputs, push ...
The input modules receive information from sensing instruments in the process (or field) and the output modules transmit instructions to the final control elements, such as control valves. The field inputs and outputs can either be continuously changing analog signals e.g. current loop or 2 state signals that switch either on or off , such as ...
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.
This allows SCADA system engineers to perform both the design and implementation of a program to be executed on an RTU or PLC. A programmable automation controller (PAC) is a compact controller that combines the features and capabilities of a PC-based control system with that of a typical PLC. PACs are deployed in SCADA systems to provide RTU ...
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 ...
Ladder logic was originally a written method to document the design and construction of relay racks as used in manufacturing and process control. [1] Each device in the relay rack would be represented by a symbol on the ladder diagram with connections between those devices shown.
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.