Siemens FB41 PID

Hi all.

I have problem starting up a mixing plant.
There is 4 PID loops in the control system.

PID for: Flow Working range 0-30000 kg/h by a gear pump
Flow Working range 0-12000 kg/h by a gear pump
level Working range 0-100 %
Temp. Working range 0-250 C.

All the loops are very simpel i can control them i man. mode
but in auto mode only the Level loop can be controlled and even this loop is sometime not working. It is stable but 10 % from its setpoint.
I can adjust PID from a SCADA system.
I have the PLC program and can see the loops in the PLC (S315)

All the loops are scanned every scan and not i OB35.
The company that have make the program claims that it works in all there other installations.

My question is can i copy the FB where the PID FB is included
into OB 35 when the FB also controlling som start and stop.

Banker

From the Siemens help on FB41 (highlight the block and press F1):

If you can control them in manual mode and not in automatic, that means either gains are not set correctly, or something is connected wrong or scaled wrong.
FB41 must be in cyclic OB such as OB35 otherwise integral and derivative time constants don't have any sense.

Firt thing you need to do is to place PID controllers in OB35.
Second, you need to make sure you used correct units when using FB 41 inputs.

Good luck

P.S. Of course, if you have four loops you'll have four PID FBs and also four instance DBs