A PLC device essentially consists of a base station with some inputs and outputs. The basic version features a processor in the central assembly, signal inputs and outputs, the interface, and an operating system.
Depending on the model’s complexity, controllers may have a different number of analogue or digital inputs and outputs. These are linked to the system or machine via sensors and actuators. For instance, at the inputs, sensors such as temperature, level, or pressure sensors monitor the machine functions. The operating system will then evaluate the collected information and compare it with programmed user-defined parameters before sending the corresponding control signals to the outputs.
The actuators that regulate the functions can also vary. They can be:
- Electric valves - used with hydraulics and compressed air
- Contactors - used for switching electric motors
- Drive control modules
As well as this, one of the greatest advantages of PLCs is their cross-system networking capabilities with other computers and devices. Even older models can be connected to new devices using the appropriate cables, plugs, and adapters.
Most controllers can be connected to a computer using a serial cable. Serial device servers are suitable for this, and conventional serial components can also be connected via LAN. Ethernet media converters are also used to ensure compatibility and connect different transmission media. Common interfaces are RS-232 and RS-485 with DB-9 and DB-25 connectors.
A programmable logic controller will become more efficient with the right additional equipment and can be expanded with devices via the interface. It is also possible to include additional add-on modules with extra I/O if needed. Further PLC hardware components include:
- HMIs (human-machine interfaces)
- Touch panels (for visualisation, operation, and diagnosis of machines and systems)
- Communication modules (such as MODBUS)
- DIN rails (for optimal assembly)
- Displays and monitors (for directly displaying operating data)
- Smart gateway (intelligent IIoT networking)