cascade control using siemens fb41_C

[tajammal]

dear friends!
i want to use output of one controller (PID siemens FB41_c)as setpoint of second controller.(cascade control?). how can i scale 1st. controller output to setpoint range of second controller.
thanks

[KalleOlsen]

With LMN_HLM / LMN_LLM.

Try also to select FB41 and push the magical F1 button.

With your Step7 installation you will also find the CTRL-manual (pdf).

K

[Jeff23spl]

i try to use 0-100% (0.0000 to 1.0000) as all input and output of my pid and the rescale it to engeneer units...i feel it easier this way.

I did few analog cascade to on-off reverse controling to save analog card for motorised valves....A first pid determine the output needed to get the sp asked and than another pid control output pulses to open or close the valve according to position setpoint

be aware of your scan time VS where you put the subroutine....The doc and help file about it is very good for pid controler