PID_Temp can not control temperature stable

Dear all 

I am under commissioning an extruder with 6 zones. Each zone uses one SSR for heating and one Solenoid for cooling. The control system is 1513 CPU and using PWM for the controlling method. PID writes in OB30 with interrupt time 100ms. The cooling water comes from a chiller and the temperature of the water about 14 -22 degrees.  

The problem is I can not maintain the temperature one degree around the setpoint. I had changed many times of Gain, Ti, Td but also still unstable. I want to make the output of cooling or heating sooner as attach capture but impossible. 

At the end, I have to accept the setpoint as zone 2 (See the capture) with big Gain = 10 and Ti=0, Td = 25 (s). It's still unstable because of big gain but if I set less gain, the system also big fluctuation. 

Do you have any advice for my case? 

Could you share your experience of PID temp tuning?

I have some question about PID_Temp, 

Why the heating out can on only the cooling already of (=0%)?

Why the Cooling out can on only the heating already of (=0%)

Thanks in advance 

Best regards

Sie-Auto

 Hello CaOd

Thanks for the idea, now the problem was solved, it's depending on the zone but the final value is Ti=0 for heat and cool, Gain of heat = 0.8 t0 1 depending the zone and Td also depending on the zone from 50s to 100s. Gain of cooling also depending zone and from 16 to 22

CaOd

Hello,

in myopinion is your problem that you have a too high gain, too low Ti and too high value.
That's the reason that your output is "switching between 0 and 100 %.

Please start with a lower gain e.g. 2 and a Ti with e.g. 10 s and a TD e.g. 2 s.

Then should you record the temperature and output data.

I don't know so much about your system.
Your extruder have not a high heat capacity.
That's the reason to start with a low gain.

How do you configure your PWM-output, min/max

Please give us a few more information and we will help you so good as we can.

regards
CaOd