Tomb Rule for estimation of memory occupation in SIMATIC PLC.

Halo colleagues

Customers and sellers frequently ask about a tomb rule to memory estimation of SIMATIC PLC.

I know three tools to do it:

• Simatic configuration tool (in CA01 CD).

• Protime Excel table (for PCS7 - also in CA01, see FAQ http://support.automation.siemens.com/WW/view/en/11909215 )

• FAQ in Intranet: Calculator for estimating the memory requirements of typical automation tasks in an S7-CPU (V4.0) http://support.automation.siemens.com/WW/view/en/21626533

Unhappily, however, these tools require precisions knowledge about the installation (how many positioning tasks, PID, S7-Graph steps, etc.). Some times, the installation is too simple, (just belts or pumps) or detailed information is not always available, for example because it is only a budget.

I know that is impossible to have precision in the memory calculation without all information: it is possible to be too conservative (and not economically competitive) or too aggressive (with the risk of start up problems). But I fell is that sometimes is necessary have a statistical tool that gives some like that: “with assertively of X %, for Y1 digital signals and Y2 analogic signals, a memory requirements stay between Z1 and Z2 Kbytes”.

One time I start to work around the topic and come to the tomb rule (for big installations):

Memory [bytes] = 22.000 + 100*(digital points) + 200*(analogical points), but I don’t have more time to work around it, and it will needs certainly a practical validation.

I open this discussion place with a hope that we can sum experiences and ideas, and with that, we mount a clear picture of the theme.

New question published by AutoGen_782819 is split to a separate thread with the subject How many DI and Modbus data I can add?.

Best regards
Min_Moderator