What is a PLC?
A programmable logic controller (PLC), also known as a programmable controller, is a resilient and durable digital computer that is used in the control of industrial manufacturing processes. Common uses are on assemble lines, monitoring and controlling robotic devices, and any industrial activity requiring a high degree of reliability. PLCs are usually relatively easy to program and can assist in the diagnosis of process errors.
Industrial automation processes employ PLCs as one of their basic components. One use of a PLC is to control an industrial machine as a stand-alone computer. Often PLCs are network connected and controlled remotely by a server architecture that is part of a SCADA system. In this case they are under the control of the SCADA and HMI software packages being run on the servers.
A Human-Machine Interface (HMI) is a program that enables human operators to interact with PLCs. The HMI is used to monitor, control, and configure the PLCs. Another important function of the HMI is alarm reporting based on input from the PLCs. A simple HMI may just be a system of lights and buttons indicating various functions that the human operator can perform. Complex HMIs make use of PLCs that are network connected to a computer that is running programming and monitoring software.
An industrial automation system has a basic control structure that involves sensing, logical control and actuation of devices, and operator interfaces. Sensors are used to monitor a physical property, such as pressure, and translate the information into electrical signals. Logical control dispatches these signals and device actuation may occur in response to them. Operator interfaces are where humans interact with the equipment and can monitor or in some cases override the automation process in response to certain conditions. This basic structure employing sensors, actuators, logic, and human interfaces is the standard model for control systems in any scenario.
Remote PLC access
Most PLC models have a communications port built-in and use the RS-232, RS-422, RS-485, or Ethernet protocols.
Typically you configure a PLC by way of its serial and USB port. These are present by default in the majority of PLCs and most of them have at least one additional ethernet port. The ethernet port is used to connect the PLC to a network hub. From here, PLC access is gained by the servers that are controlling and monitoring the processes, as well as any network connected machines.
To achieve remote PLC access, your connections need to be virtualized.