Hi all,
I am looking at a problem with an S7-200 CN (controlling a filling and sealing machine) which has a PID Loop that controls a heating element on a sealing blade. The problem is that when the PLC's capacitor is fully discharged, after not having used the machine for over a week, then it takes over a day for the temperature of the sealing blade to stabilize around the set point. Once the temperature has finally stabilized then on the next test (perhaps a day later) the temperature stabilizes very quickly (within about 15 minutes).
Why does it take so long to stabilize the temperature after the PLC's capacitor has been discharged? Does the PLC store any other tuning parameters besides the base PID values in some form of volatile memory?
Some information about the process:
Any help would be greatly appreciated! Thanks.
I am looking at a problem with an S7-200 CN (controlling a filling and sealing machine) which has a PID Loop that controls a heating element on a sealing blade. The problem is that when the PLC's capacitor is fully discharged, after not having used the machine for over a week, then it takes over a day for the temperature of the sealing blade to stabilize around the set point. Once the temperature has finally stabilized then on the next test (perhaps a day later) the temperature stabilizes very quickly (within about 15 minutes).
Why does it take so long to stabilize the temperature after the PLC's capacitor has been discharged? Does the PLC store any other tuning parameters besides the base PID values in some form of volatile memory?
Some information about the process:
- Set point: 180 degrees celcius
- Process Variable Range: 0-4000 (divided by 10 to scale to degrees)
- Sample Time: 1.0s
- Gain: 3.0
- Integral: 4.0
- Derivative: 4.0
- Output Value Range: 0.00 - 1.00
Any help would be greatly appreciated! Thanks.
