Soft PLC
A Soft-PLC or SoftPLC ( programmable logic controller in software) consists of a PC - usually an industrial PC , embedded PC or box PC - a PLC software and the I / O modules or fieldbus extensions such as B. Bus Terminals . Features:
- PLC is dependent on the PC's operating system, often Windows with real-time expansion, meanwhile also Linux with / without real-time expansion.
- possible failure in the event of a system crash
- The PC-CPU cannot be fully used for the PLC functionality.
- The soft PLC needs a real-time - kernel - the operating system for the control of computing time that the computer operating system (eg. Windows releases) to the PLC.
- Access to I / Os is via plug-in cards with integrated I / Os or fieldbus connection, or via Ethernet-based fieldbus systems with real-time Ethernet .
operation area
The soft PLC runs under a host operating system such as B. under Windows, Linux or Unix and can therefore be operated like a computer. The soft PLC has a wide range of uses, especially in industry. Often special small computers are built on which a touch screen is mounted. With their help, you can monitor processes at any time using the appropriate software and intervene as quickly as possible. You also have the option of designing the circuits differently at any time.
A possible advantage over a normal PLC is that you do not need an additional PC or programming device to change the programmed circuits, since the programming software and the control software can be on one PC (mostly only under Windows). In addition, maintenance is often considerably simplified thanks to integrated remote maintenance software . In addition, the available resources (CPU performance, main memory / RAM, permanent storage / Flash or HD) are usually higher or significantly more cost-effective compared to dedicated PLC systems. Due to the nature of the system, however, such a system harbors the risk that the entire control system may fail if any additional program fails. Therefore, these systems are not used in safety-critical systems. Nevertheless, they are used in many different areas of industrial automation technology such as B. production systems, but also often used in training courses.
The processes are programmed similarly to a conventional PLC , mostly according to IEC 61131-3 . With manufacturer-independent tools such as B. CODESYS , soft PLCs and conventional PLCs can be programmed in the same way and thus a common code base can be built up.
construction
A conventional PLC is built with elements (= assemblies) that are usually programmed with a computer or a special programming device. In operation, however, these controls run without this computer. An additional PC must also be used to implement process diagrams ( visualization ) that always show the current system status. With the Soft-PLC, however, all these components are combined on one computer. You then simply control a machine with this PC. So you can program very complicated circuits and only need very little space. Program changes can therefore also be carried out quickly without much effort.