gosh this is so simple. the arduino reads the sensor.
the arduino outputs an analogue signal to the input of the PLC.
use the arduino for scaling.
of course you can just use any of the many digital inputs and read the sensor directly.
here is what I found on their site:
Controller with integrated PROFINET IO controller interface for communication between SIMATIC controllers, HMI, programming device or other automation components
Communication module with PROFIBUS DP master interface
Communication module PROFIBUS DP slave interface
Integrated digital and analog inputs/outputs
Communication modules for expansion of controllers with additional communications interfaces
Different digital and analog signal modules.
Communication modules (RS232/RS485) for communication via point-to-point connection.
Ethernet switch with 4 ports for implementation of many different network topologies