S7-300 Pid

Dear All
I am using CPU 313 for payoff tension control.There is AC servo drives to payoff.The speed referance to the drive is from PID of S7-300 .Tension feedback is from load cel(0-10VDC).Tension set point to PID is from OPerator panel.
I have tried FB41 but stability in the tension not proper
Is there any other method to use the PID from S7-300
Please anyone has please send me.Also suggest some good examples with manuals
Warm Regards
Nehe

how are you doing this?
In other words do you have a block diagram?
Are you summing the output with the line speed?
Using a diameter calculator?

Paoff Is Mobile Unit

Hii
Payoff is running witout line speed referance
Warm Regards
Nehe

It is generally not a good idea to run a motor driven velocity based loadcell controlled unwind without a linespeed reference. And you are seeing why. In order to get the PI loop to provide the whole speed reference the loop gains need to be very high. This usually results in instability.

Ideally you would have a speed reference indicating the speed of the machine pulling web off the unwind as well as some method of calculating product roll diameter. Then you can use the speed reference to provide the majority of the required unwind speed and run with much lower PI loop gains.

Also, you don't want to use differential correction if this is a drive based or PLC based tension loop. The tension changes too fast for the loop scan rate and you can't calculate a meaningful differential.

Keith

Besic

Please provoide me some PID base examples using S7-300 i think it will solve my problem
I have used same concept without line speed and working fine from last four year witout problem.In S7-300 i have not much knowledge of PID block how to use it?
Warm Regards
Nehe

Pid Fb41

Hi bhimaji,

I'll try to say what I do when I implement a PID block in S7-300/400:

1) Make the call from OB35 to get it called every i.e. 50ms
2) Set this block imputs to 0:
MAN_ON (if you aren't using manual or doing it outside block)
PV_PER (as you are not using analog inputs and not converting
then inside PID block)
3) Set the following to what you need:
P_SEL proportional part
I_SEL integral part
D_SEL derivative part
GAIN proportional gain
TI integral time in T#1m2s5ms format
TD derivative time in T#1m2s5ms format
LMN_HLM upper output limit
LMN_LLM lower output limit
4) Connect this ones
PV_IN Process value in REAL format
SP_INT Setpoint in REAL format
LMN Output between (LMN_HLM and LMN_LLM)

I hope this helps,
Kelkoon

Thanks a lot

warm regards
Nehe