PLC preformance Q ?

Hello..

I am right now comparing two Siemens PLC CPU´s. (s5 and S7 CPU)
But just to be sure I wonder what data is the most crucial information of importance when i want to know the CPU´s performance ?

When im comparing two systems I look on Execution times and so on..

Examplewise : I have an S5 944CPU that i want to replace and the result i get from my reasearch for 300 and 400 is S7 317-2DP CPU and my reslut on a S7 400 is a 414-2 CPU.. Can this be correct ? im very unsure..

With boolean operations 317 and 414 are comparable. But when it comes to arithmetic 414 is much faster.

Don't forget that you need to consider the size of the program and the I/O space as well.

That is an interesting question.
How "big" an S7 CPU does one need in order to replace an S5 CPU ?

I just checked the instruction times for a S5-944, an S7-315, an S7-317 and an S7-414. I checked only the execution times for a boolean "AND", Load and transfer of a dataword, and addition of an integer.

 

CPU    944    315       317         414

A      0.8    0.1..0.3  0.05..0.06  0.06

L DW   1.7    1.8       0.24        0.12

T DW   1.4    1.6       0.30        0.075

+ I    0.8    0.6       0.2         0.06

It looks like the 315 is the closest one to the 944 !
The others are much faster.

I didnt check or consider floating point math, as you are upgrading from a S5-944.

I also did not check how much i/o each CPU can handle, or how much memory there is.
But I am sure that the 512kB on the 317 will be more than enough to replace the program in the 944.

Ok Thank you all for the answers and help..

This is very intressting 315-2DP is the closest... But im abit unsure about if it can handle my kommunikation. I have 2 modbus cards for 2 HMIs, 1 FMS card to 4 Other Controllers and a DP card to 13 I/O nodes.
I dont know exact how many bytes each connection are processing..

You didn't seem to get the point...

The 315 is the closest to the 944 only in that it is nearly as slow as the 944.