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MAN (manual value) in Continous PID block

Created by: madnesssm at: 10/23/2012 3:05 PM (7 Replies)

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10/23/2012 3:05 PM	Rate (0)
madnesssm Advanced Member Joined: 6/11/2012 Last visit: 3/11/2023 Posts: 30 Rating: (0)	Hi all, i am confused about MAN (manual value) in Continous PID block. Can somebody explain me, for what used that parameter actually? I have find manual about PID, and there is written " THE MANUAL VALUE INPUT IS USED TO SET A MANUAL VALUE USING THE OPERATOR INTERFACE FUNCTION". But i don't understand it..... Please help. TNX. MADNESSSM

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10/23/2012 3:25 PM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 5/26/2023 Posts: 6802 Rating: (1345)	madnesssm Hi all, i am confused about MAN (manual value) in Continous PID block. Can somebody explain me, for what used that parameter actually? I have find manual about PID, and there is written " THE MANUAL VALUE INPUT IS USED TO SET A MANUAL VALUE USING THE OPERATOR INTERFACE FUNCTION". But i don't understand it..... Please help. TNX. MADNESSSM Hello, What kind of PID function do you use? Just to translate that part of manual to undestandable English, I can say : Each PID controller has at leat 3 operatin modes.When it is in restart mode(1), every thing is set to zero(or safe position for value on actuator).When it is in manual(2), a fixed value is sent to output on the actuator.For this normally a bit (Man_on) is activated and "MAN" is effective as LMN output. And finally auto mode(3) which both restart and manual bits are de activated and PID controller governs the output based on error. Hope this helps Best regards, Hamid Hosseini
	Demo Channel on Youtube
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10/23/2012 3:25 PM	Rate (0)
billwest Posts: 510 Rating: (117)	In AUTO, the PID block calculates the output. Inmanual, the PID block is not calculating the output. The output is the reult of an operator or program value input at MAN. In starting up a process the PID block is normally in manual mode with an output of 0.0 or some value that maintains a static state. When the process is ready to begin, levels, temperatures, pressures, ....., have reached the proper values, the PID block isswitched to AUTO either by logic or operator input. When the PID block is in manual mode, if a value of 0 is entered for MAN the output of the PID is 0%. If a value of 100 is entered at MAN, the output is 100% I hope this is clear. Good Luck billwest
billwest Posts: 510 Rating: (117)
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10/23/2012 3:35 PM	Rate (0)
dchartier Grandmaster Joined: 9/27/2006 Last visit: 5/30/2023 Posts: 12026 Rating: (2594)	Hello madnesssm; There are various descriptions of the PID function blocks available from different manuals, but in this case the simplest explanation can be seen rom the following FAQ: What should you watch out for when calling and assigning parameters to the controller functions in function blocks (S)FB41, (S)FB42 and (S)FB43? When using these blocks, please watch out for the following points. 1. *FB 41 "CONT_C"* To guarantee a constant scanning frequency, the controller should be called in a cyclic interrupt OB without call-up conditions (e.g. OB35). The "CYCLE" parameter corresponds to the scan time. The time between block calls must be configured here (e.g. time base of the OB35). The default controller setting is manual mode (MAN_ON=true). The control loop is interrupted. In this mode the variable matches the MAN manual value. In order to ensure a smooth switchover from manual to automatic mode, at least two block cycles must be conducted in manual mode. When the CPU is restarted, a block cycle should be conducted with "COM_RST" = true. The "COM_RST" parameter can be used to block the controller. ... From the text above you can see that the MANvariable containsthe manual setpoint which the controller will apply when the Boolean tag MAN_ON is active (=True). So if you configure your OP to change the value of MAN_ON in your CONT_C block (by accessing the DB address of the tag) then you can switch the PID from Manual operation to Auto, and vice-versa. In Manual mode the value written to the MAN variable is the value the controller will output to the actuator of your loop. Hope this helps, Daniel Chartier

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10/23/2012 3:52 PM	Rate (0)
madnesssm Advanced Member Joined: 6/11/2012 Last visit: 3/11/2023 Posts: 30 Rating: (0)	Ok guys, i got it. Thanks. I thought it also. But i have problem, and that is why i'm confused. When i set MAN_ON on false PID calculates output, but problem is when i set MAN_ON on true, then PID output is still last calculated value, not MAN value. I attached a picture to see what happens. And don't to be confusion, i am calling PID in OB35. Attachment PICTURE.jpg (179 Downloads)

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10/23/2012 4:22 PM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 5/26/2023 Posts: 6802 Rating: (1345)	madnesssm Ok guys, i got it. Thanks. I thought it also. But i have problem, and that is why i'm confused. When i set MAN_ON on false PID calculates output, but problem is when i set MAN_ON on true, then PID output is still last calculated value, not MAN value. I attached a picture to see what happens. And don't to be confusion, i am calling PID in OB35. Hello, Normally this happen when you have setpoint=0 and process value =0. When you work in a dynamic process, auto-->manual switchover is with bump! But note, manual to automatic switchover is guranteed bumpless internally.Please check the following link: FB58,Bumpless manual to automatic switchover This is a nice trick(DISV=0): in manual mode, we have this: LMN_I= LMN-LMN_P in automaticmode,we have: LMN=LMNP+LMN_I=LMNP + (LMN-LMN_P) =LMN BUMPLESS PID FB41 MANUAL Manual Value It is possible to switch over between a manual and an automatic mode. In the manual mode, the manipulated variable is corrected to a manually selected value. The integrator (INT) is set internally to LMN - LMN_P - DISV and the derivative unit (DIF) to 0 and matched internally. This means that a switchover to the automatic mode does not cause any sudden change in the manipulated value. Best regards, Hamid Hosseini
	Last edited by: hdhosseini at: 10/23/2012 5:56 PM Last edited by: hdhosseini at: 10/23/2012 4:28 PM Demo Channel on Youtube
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10/23/2012 9:26 PM	Rate (0)
madnesssm Advanced Member Joined: 6/11/2012 Last visit: 3/11/2023 Posts: 30 Rating: (0)	I solve mine problem. Tnx for help. BR!

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6/22/2020 6:58 AM	Rate (0)
Jen_Moderator Moderator Joined: 6/19/2017 Last visit: 5/30/2023 Posts: 6924 Rating: (137)	New question published by Kaviaaaaaaaan is split to a separate thread with the subject Can't equalize the manual and automatic values in the ID. Best regards Jen_Moderator
	My Forum is the place to personalize your profile, track your topics, and maintain content that interests you. Best regards Jen_Moderator
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