The Barth Elektronik STG-500 is considered to be the smallest industrial PLC is now available in RS Components.
It comes with a fully integrated circuit board with no peripheral components at all - this is how it can become small size - as a result, it also caters for high fault tolerance, stability and ease of maintenance.
It provides 10 I/Os and operating voltage range of 7V to 32V, making them ideal for use in 12V or 24V battery-powered applications. Built-in protection for all I/Os, high shock and vibration resistance, and IP20 sealing, ensure reliability in harsh environments.
It caters graphical programming interface via the freeware miCon-L Software Suite.
PLC can be deployed for building automation - for instance, to serve as the controller to intercept rain drops as input and to close the window for the output.