PID on Siemens


Thread Starter


I have faced the following problem. I'm not an expert of PID tuning but i have programmed both allen bradley slc500 and siemens S7. the FB47 seems to work only in the OB35. When i used the FB 47 in an FB or FC it doesn't work or at least react as a proportional controller. I have tried hundreds of configuration (changing P,I,D) but the only parameters which change the response is the Proportional. (i have enable the I and D components). The situation change completely when i use the OB35 where all the components have effects on the response.
thanks a lot for any help
By changing the OB you change the time base - not important for the P part which is dependant on error (SP-PV) but very important for the I and D parts. I can't remember off hand, but there must be an input to the FB to specify the time base. Otherwise you must compensate with the tuning parameters.

Hope this helps,
Peter Kosin