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S71200 PID Loop Inactive After Running

Created by: jon_masheen at: 6/23/2010 10:05 AM (6 Replies)

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6/23/2010 10:05 AM	Rate (0)
jon_masheen Regular Member Joined: 6/24/2008 Last visit: 8/11/2022 Posts: 13 Rating: (0)	I have configured & tuned a singlePID loop on a CPU 1214C DC/DC/DC and runs in automatic. I have configured the HMI to display the PID Output, PID Error & PID Status. Under normal conditions these display:- PID Output = 0-27678 PID Error = 0 PID Status = 3 Infrequently these all display 0. Which makes think the PID loop has been made inactive with no error code? From the forum, this could be the sample time being exceeded & will make the PID loop inactive. The PIDblockis in a cylicblock that is called every 100mS. I have added the sample code to my PLC s/w. Is there anything else that could cause the PID loop to be made inactive? I there a log that can be checked?

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6/24/2010 9:27 AM	Rate (0)
wax Advanced Member Joined: 6/1/2010 Last visit: 11/6/2024 Posts: 36 Rating: (4)	hello are you sure that the EN of PID_compact FB is always set to 1 ? If not the PID_compact FB don't restart in automatic mode. for restarting in automatic mode the PID_compact_FB you can set to 3 "Pid_compact_DB".sRet.i_Mode. (and set to 0 for stopping, it's the state output)

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6/24/2010 12:50 PM	Rate (0)
Denilson Pegaia Platinum Expert Joined: 9/23/2005 Last visit: 11/14/2024 Posts: 4352 Rating: (1452)	Hi, ihear that if a input (setpoint or process value)rearches the alarms values, the PID becomes inactive too. In this case, I suggest try to use a LIMIT before these inputs.
	Denilson Pegaia Siemens Industry Sector Technical Support
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6/25/2010 10:06 AM	Rate (0)
jon_masheen Regular Member Joined: 6/24/2008 Last visit: 8/11/2022 Posts: 13 Rating: (0)	I have the PID block enabled permanently. I have scaled my process input & clamped so that it is within the limits set in the PID block. Used the raw value intially & this faulted the PID block with an error code 1. Have checked FAQ & if the sample time is exceeded then the PID block isforced into an inactive state, status =0. Set up the sample monitoring, with the cyclic OB scan time set to 100mSec. This output value has not increased. Currently the sample monitoring has been disabled, to ascertain whether this will stop the problem. Any other ideas, are welcome.

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7/24/2010 4:28 PM	Rate (0)
kbouwman Experienced Member Joined: 4/21/2007 Last visit: 1/10/2024 Posts: 39 Rating: (0)	I am having this same problem. I have my program setup the same as you describe. Have you discovered anything new?

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7/26/2010 1:19 PM	Rate (0)
Denilson Pegaia Platinum Expert Joined: 9/23/2005 Last visit: 11/14/2024 Posts: 4352 Rating: (1452)	Hi, I let some PID typs on /tf/WW/en/Posts/33957#163489 Please check it. While we don't found the real cause, I suggest to use a PID lean: /tf/WW/en/Posts/33957#163489
	Denilson Pegaia Siemens Industry Sector Technical Support
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8/5/2010 11:56 AM	Rate (0)
jon_masheen Regular Member Joined: 6/24/2008 Last visit: 8/11/2022 Posts: 13 Rating: (0)	Was given a work around by Siemens Tech Support UK. Was to check theIW used as the Process value was between 32767 & -32768before moving to a MW that was tagged to the PID block. Prior to this I used a scaling block for the IW & used the scaled value into the PID block. The Scaling FC was also called from the Cyclic OB200. The PID block was also enabled when required. The system has been up& running without the PID block failing & becoming inactive.

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