I would like to select Siemens PlC CPU (S7-300 or S7-400) for a typical project with 256 Digital I/O, 8 Analog Ouput and 8 Analog Input. I have 8 Closed Loops in my Project. Please let me know, How can I Select CPU for this Project? At all, What is criteria for selecting CPU when I have Analog Output (closed loop)? Is it Criteria to compare Digital I/O with Analog I/O?

 

I think that S7-300 will be perfect, using cpu315 or higher, you can use PID modules for closed loop also , you can use analog input and output module to accomplish it using soft PID.

 

Hi Mahoor,

you should consider the S7-300 CPU's of the recently released C versions.
They have significantly faster program execution times than the older types.

But you should also consider S7-400 with the smallest CPU type 412-1. Such a solution would only be slightly more expensive than an S7-300 solution. Especially as you will have to use IFMs in the S7-300 rack to expand to several racks.
In the S7-400 you can keep everything in one rack.
Only limitation is that the CPU 412-1 only has 1 MPI/DP port.

Best regards,
Jesper M. Pedersen