Which 1500T PLC is the cheapest for running SIMATIC Rotary Knife?

And what is the difference between running the application on a 1515T and a 1511T?

Rotary Knife lib: https://support.industry.siemens.com/cs/ww/en/view/109757260

Thanks!

The smaller the number (1511, 1513, etc.), the cheaper it is.

But also: the smaller the number, the slower and less memory the PLC has.

Just check the technical data of the PLCs here in SIOS, you'll see the difference right away. Also take care about the amount of technology objects the PLC can handle regarding memory, this can be seen almost at the end of the technical data.

You might also consider to check TIA Selection Tool.

Regards,
daviso