Read the spindle speed in a SIEMENS PLC s7 300 with python snap7

Question

I would like to read the spindle speed of a Siemens PLC 317-2DP with NCU 720.2.

To do that, I use the python snap 7 library. I managed the connexion to the PLC, but I would like to read the spindle speed with the function read_area(area: Areas, dbnumber: int, start: int, size: int). I am unable to find the parameters dbNumber, start and size for my case.

Does someone can help me please? I read that it depends of the configuration of the PLC, but where I can find this configuration?

Thanks for your help

I read the documentation from Siemens "SINUMERIK 840D sl NC variables and interface signals" but I didn't find what I needed...

Answer 1

In general in order to access to a variable in the plc you need to have a db block as I previously mentioned in one of my comments, but one important thing is to marked this block as not optimized:

if you have created this db an you recently added new variables a compile is needed to recalculate the offset in the variables. If you perform these steps successfully you will be able to see the offsets like in the following image:

I post this information as an answer for people that need that information in the future.

Regards

Miguel

Answer 2

Just to add more information to the answer, in the case of the S300 they are not able to mark the optimized block access (At least in my case a S313-2 DP)