With SIL3 Safe HMI versions, whenever a driver operates a touchscreen, two touch layers, situated one behind the other, are activated, feeding a comparative signal to a safety unit on the Safe HMI. The safety unit evaluates the touch event and translates it into a safety value, which is safely transferred to ABB’s safety PLC using PROFINET/PROFIsafe communication.
By transferring the PROFINET/PROFIsafe values to ABB’s safety CPU, the state of selection can be saved using the AC500-S safety CPU’s flash memory, ensuring that all events have persistent status. The flexibility of Structured Text and the ability to implement complex logic to handle and store all these selection states on the Safe HMI, are critical to the solution’s success. Furthermore, the ability to distribute Safe HMI information to more than one controller using not only PROFINET/PROFIsafe IO Controller but also PROFINET/PROFIsafe IO Device functionality is critical to the selection.