Controlling 2 different outputs on 1 PID loop

Hi All

Step 7 in ladder again folks!
I have a PID loop already configured, now I now wish to have a Profibus configured VFD to be controlled off the same output. Ie. The VFD (Control Word) and my PID Output (REAL) are to be directly proportional.

How would I achieve this by means of converting the REAL(MD) PID Control Variable to my PROFIBUS CNTROL WORD (MW)?

Thanks

Darren

Hi Darren,

I have done this before by scaling the output of the PID into a 16 bit address 0-100% = 0-65536 then using this integer to drive the analogue output.

Lance.

iN STEP7 IF U USED CONT_C LOOP FOR ANALOG, OUTPUT WE CAN OBTAIN IN BOTH. I.E. IN WORD ASWELL AS IN REAL. IF U DONT FIND, THEN USE UNSCALE FB TO UNSCALE REAL TO WORD AND OUTPUT OF UNSCALE CAN BE USED FOR VFD CONTROL.

Hi
Thanks for the feedback, FC106 did not accept the method you said as there were type conflicts? It was looking for and INTEGER, when I wanted to use a WORD on the output. However, I have addressed it from the LMN_PER on the CONT_C PID block? Maybe this will be acceptable?

Darren

Use themove command, move integer to word.
Isn´t max analog value 24648 !!
Also check the VFD control value how big the value can be eg. siemens max value is Hmm? was it 14xxx something.

Darren, in my experience, the VFD will have a 16 bit control word (for stop/start direction etc) and a 16 bit speed setpoint, normally referenced as an integer (assuming you are controlling it via Profibus). If you set the PQW address for the speed setpoint to type integer in the symbol table, you can use FC106 to convert your real demand from the PID block to an integer for an analogue output. However, the Siemens VFDs I have used have 100% speed demand=16384 which is not the same as an analogue output hence FC106 is not suitable here.