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PID, gradually changing setpoint

4/19/2012 1:29 PM	Rate (0)
Nenad Posts: 14 Rating: (0)	Hi, If anybody has idea how to solve this: I need to use PID controller but not with constant setpoint, but with gradually changing setpoint. For example, I need to change water temperature output from 100 degC to 50 degC in 50 minutes, slowly by changing temperature 1 degC in minute. Not faster. Slower is allowed but not too much. Output controls the mixing valve. Additional problem is that piping is very long and changes takes time to affect output (integral is big) I dont know if I was clear. If you have questions I will try to clarify. Thanks in advance. Nenad
Nenad Posts: 14 Rating: (0)
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4/19/2012 6:47 PM	Rate (0)
marwanco62 Posts: 53 Rating: (2)	What about substarcting 1 degree from setpoint evey 1 minute? Then play with P,I,D parameters, regards
marwanco62 Posts: 53 Rating: (2)
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4/19/2012 7:21 PM	Rate (0)
hdhosseini Diamond Member Joined: 1/28/2009 Last visit: 1/22/2026 Posts: 6892 Rating: (1368)	Nenad Hi, If anybody has idea how to solve this: I need to use PID controller but not with constant setpoint, but with gradually changing setpoint. For example, I need to change water temperature output from 100 degC to 50 degC in 50 minutes, slowly by changing temperature 1 degC in minute. Not faster. Slower is allowed but not too much. Nenad Hello , You need a function in attachment in STEP7(S7300 and 400). A kind of set point generation.For microwin, you can search the title (setpoint generator) in the forum or internet for S7200 version. check if this function can be utilized for your purpose: How can you limit the pitch of jumps with S7-200? Best regards, Hamid Hosseini Attachment ramp_soak.pdf (380 Downloads)
	Demo Channel on Youtube
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4/19/2012 9:23 PM	Rate (0)
Nenad Posts: 14 Rating: (0)	Hi, Changing setpoint or setpoint generator was my idea also, but as I mentioned response is very slow, so I need to wait until temperature stabilize before changing to next setpoint. Othervise I will change setpoint too much and when feedback comes on it will be too late to slow down the change. Thanks for the link. It will help for smooth change. Still, if anyone has any more ideas please share with me. Best regards Nenad
Nenad Posts: 14 Rating: (0)
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4/19/2012 10:01 PM	Rate (0)
marwanco62 Posts: 53 Rating: (2)	What about FIXING setpoint at 50degree, and controling the time by trying different smaller P , then fine tune with small I. Regards
marwanco62 Posts: 53 Rating: (2)
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4/20/2012 11:20 AM	Rate (0)
Nenad Posts: 14 Rating: (0)	Thank you both for your efforth. Seems like lot of testing will get me there. Best regards Nenad
Nenad Posts: 14 Rating: (0)
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1/23/2026 1:20 PM	Rate (0)
B_agil Joined: 2/14/2025 Last visit: 1/23/2026 Posts: 6 Rating: (0)	Have you already pretunning your PID during the commisioning?

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