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Problems with 3step PID control- long time autotunning

Created by: tell at: 6/7/2013 10:04 PM (2 Replies)

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6/7/2013 10:04 PM	Rate (0)
tell Posts: 4 Rating: (0)	I have a Siemens S7-1212C and start auto-tuning, but the process is not completed. Remains around 40%, and standing there for hours and hours With analog sensor I measure the water level in the canal, the actuators can open / close water outlet. The water level must be constant. So I get the controller analog input signal 0-10V, Actuator I control with a digital output, beside this, the limit switches detect the start and end position of the actuator. Setpoint has the value 80, the input value 85 actuator is closed-a low level. Then start pretuning and input value begins to fall, it is placed output_UP and actuator opens until it is completely open-high level. Input after 10 minutes dropped to 50 and then this value is not changed. Pretunning be implemented, but it never ends. What's wrong with AUTOTUNING that it not take place until the end? Thanks in advance for the help Attachment PID.zip (48 Downloads)
tell Posts: 4 Rating: (0)	Last edited by: tell at: 6/7/2013 10:50 PM Last edited by: tell at: 6/7/2013 10:08 PM
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6/11/2013 12:09 PM	Rate (0)
Denilson Pegaia Platinum Expert Joined: 9/23/2005 Last visit: 3/24/2023 Posts: 4180 Rating: (1332)	Hi, Autotunning algorithms, e.g. working thinking that the field work in same way. Based on this, it creates math calculation to find the tunning solution. Sometimes, however, the Autotunnings fault because the field doesn’t react as spected.Other times, the sampling time is to distant of the real model that the autotuning doesn’t could identify some “response curves” characteristics. Either when the field reacts too fast, or to slow. Try to change the OB cicle time for something near to reaction speed of your field. If it doesn’t works, maybe you should configure the pid parameters by himself.
	Last edited by: Pegaia at: 6/11/2013 12:10 PM Denilson Pegaia Siemens Industry Sector Technical Support
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6/11/2013 1:25 PM	Rate (0)
Marcjan Platinum Member Joined: 4/22/2010 Last visit: 12/15/2022 Posts: 5697 Rating: (702)	Hello, What i always do before starting autotune is bring the PV close to the SV with PID on manual. Then start autotune. This may help the autotune algorithm to find the settings before it hangs itself. Regards, Marcjan
	Problem solved? Please let us know! Please no technical questions by PM, use the forum sections for your questions.
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