What it is – a software function block for S5 and S7 heating control
The Siemens 6ES7171-2YA00-0AA0 is a function block (FB) for heating control, designed to work with the ZA724 function blocks library on SIMATIC S5 and S7 platforms. It handles the heating logic – no current or voltage measurement on this firmware part.
Lifecycle and sourcing – still current, easy to get
This block carries a lifecycle stage of 'current', meaning Siemens still delivers it. No sign of nearing phase-out. For a legacy S5 or S7 system that needs this exact heating logic, it's the straight path – no substitute needed, still on the active list.